ASTM E92-23

Standard Test Methods for Vickers Hardness and Knoop Hardness of Metallic Materials

SIGNIFICANCE AND USE
4.1 Vickers and Knoop hardness tests have been found to be very useful for materials evaluation, quality control of manufacturing processes and research and development efforts. Hardness, although empirical in nature, can be correlated to tensile strength for many metals, and is an indicator of wear resistance and ductility.  
4.2 Microindentation hardness tests extend testing to materials that are too thin or too small for macroindentation hardness tests. Microindentation hardness tests also allow specific phases or constituents and regions or gradients too small for macroindentation hardness testing to be evaluated. Recommendations for microindentation testing can be found in Test Method E384.  
4.3 Because the Vickers and Knoop hardness will reveal hardness variations that may exist within a material, a single test value may not be representative of the bulk hardness.  
4.4 The Vickers indenter usually produces essentially the same hardness number at all test forces when testing homogeneous material, except for tests using very low forces (below 25 gf) or for indentations with diagonals smaller than about 25 µm (see Test Method E384). For isotropic materials, the two diagonals of a Vickers indentation are equal in length.  
4.5 The Knoop indenter usually produces similar hardness numbers over a wide range of test forces, but the numbers tend to rise as the test force is decreased. This rise in hardness number with lower test forces is often more significant when testing higher hardness materials, and is increasingly more significant when using test forces below 50 gf (see Test Method E384).  
4.6 The elongated four-sided rhombohedral shape of the Knoop indenter, where the length of the long diagonal is 7.114 times greater than the short diagonal, produces narrower and shallower indentations than the square-based pyramid Vickers indenter under identical test conditions. Hence, the Knoop hardness test is very useful for evaluating hardness gradients since Knoo...
SCOPE
1.1 These test methods cover the determination of the Vickers hardness and Knoop hardness of metallic materials by the Vickers and Knoop indentation hardness principles. This standard provides the requirements for Vickers and Knoop hardness machines and the procedures for performing Vickers and Knoop hardness tests.  
1.2 This standard includes additional requirements in annexes:    
Verification of Vickers and Knoop Hardness Testing Machines  
Annex A1  
Vickers and Knoop Hardness Standardizing Machines  
Annex A2  
Standardization of Vickers and Knoop Indenters  
Annex A3  
Standardization of Vickers and Knoop Hardness Test Blocks  
Annex A4  
Correction Factors for Vickers Hardness Tests Made on Spherical and Cylindrical Surfaces  
Annex A5  
1.3 This standard includes nonmandatory information in an appendix which relates to the Vickers and Knoop hardness tests:    
Examples of Procedures for Determining Vickers and Knoop Hardness Uncertainty  
Appendix X1  
1.4 This test method covers Vickers hardness tests made utilizing test forces ranging from 9.807 × 10-3 N to 1176.80 N (1 gf to 120 kgf), and Knoop hardness tests made utilizing test forces from 9.807 × 10-3 N to 19.613 N (1 gf to 2 kgf).  
1.5 Additional information on the procedures and guidance when testing in the microindentation force range (forces ≤ 1 kgf) may be found in Test Method E384, Test Method for Microindentation Hardness of Materials.  
1.6 Units—When the Vickers and Knoop hardness tests were developed, the force levels were specified in units of grams-force (gf) and kilograms-force (kgf). This standard specifies the units of force and length in the International System of Units (SI); that is, force in Newtons (N) and length in mm or µm. However, because of the historical precedent and continued common usage, force values in gf and kgf units are provided for information and much of the discussion in this standard as well as the...

General Information

• Status: Published
• Publication Date: 30-Jun-2023
• ICS: 77.040.10 - Mechanical testing of metals
• Technical Committee: E28 - Mechanical Testing
• Drafting Committee: E28.06 - Indentation Hardness Testing

Relations

• Refers: ASTM C1327-15(2019) - Standard Test Method for Vickers Indentation Hardness of Advanced Ceramics
• Effective Date: 01-Jul-2019
• Refers: ASTM E7-15 - Standard Terminology Relating to Metallography
• Effective Date: 01-Jun-2015
• Refers: ASTM C1327-15 - Standard Test Method for Vickers Indentation Hardness of Advanced Ceramics
• Effective Date: 01-Jan-2015
• Refers: ASTM E7-14 - Standard Terminology Relating to Metallography
• Effective Date: 01-Nov-2014
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM C1326-13 - Standard Test Method for Knoop Indentation Hardness of Advanced Ceramics
• Effective Date: 01-Aug-2013
• Refers: ASTM E177-13 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2013
• Refers: ASTM E74-13a - Standard Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines
• Effective Date: 01-May-2013
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM E74-13 - Standard Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines
• Effective Date: 01-Mar-2013
• Refers: ASTM E74-12 - Standard Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines
• Effective Date: 01-Dec-2012
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011
• Refers: ASTM E177-10 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Oct-2010
• Refers: ASTM E175-82(2010) - Standard Terminology of Microscopy (Withdrawn 2019)
• Effective Date: 01-Jul-2010
• Refers: ASTM E384-10 - Standard Test Method for Microindentation Hardness of Materials
• Effective Date: 01-Feb-2010

Overview

ASTM E92-23, Standard Test Methods for Vickers Hardness and Knoop Hardness of Metallic Materials, establishes procedures for determining the hardness of metallic materials using the Vickers and Knoop indentation methods. These test methods are essential for materials evaluation, quality control during manufacturing, and research and development. The standard covers requirements for testing machines, indenters, procedures for conducting tests, and guidance for both microindentation and macroindentation hardness assessments. The Vickers and Knoop hardness tests are widely recognized for their reliability and applicability to a range of metallic materials, especially those that are thin, small, or require phase-specific evaluation.

Key Topics

• Vickers and Knoop Hardness Overview:

  • Vickers test uses a square-based pyramidal diamond indenter.
  • Knoop test uses a rhombohedral (elongated) diamond indenter.
  • Both methods evaluate indentation hardness under static load, calculating hardness from measured indentations.

• Test Methods and Machines:

  • Detailed requirements for machine verification and calibration.
  • Guidance on selection, handling, and care of indenters.
  • Annexes cover standardization and correction factors for non-flat surfaces.

• Microindentation and Macroindentation:

  • Microindentation (≤1 kgf force) is suitable for small, thin samples and specific regions or constituents.
  • Macroindentation covers higher forces (up to 120 kgf for Vickers).
  • Test Method E384 provides additional microindentation procedures.

• Data Reporting and Accuracy:

  • Hardness values must specify test forces used (e.g., 400 HK 0.5).
  • Surface preparation and specimen alignment are critical for test accuracy.
  • Annexes and appendices provide procedures for estimating measurement uncertainty and correcting for curvature effects.

Applications

The Vickers and Knoop hardness tests described in ASTM E92-23 find practical use in various industries and scenarios:

• Materials Evaluation:

  • Assessment of mechanical properties such as hardness, ductility, tensile strength, and wear resistance.
  • Examination of microstructural gradients and localized phases within alloys and engineered materials.

• Quality Control:

  • Routine hardness testing for product assurance during manufacturing of metallic components.
  • Verification of heat treatment, surface finishing, and coating integrity.

• Research & Development:

  • Baseline characterization of new metal formulations and production processes.
  • Detailed analysis for failure investigations.

• Thin Layers and Gradients:

  • Measurement of surface coatings, claddings, and thin films where traditional macrohardness tests are not feasible.
  • Evaluation of hardness profiles across welds, diffusion zones, or heat-affected regions.

• Precision Components:

  • Determination of hardness in minute or delicate items such as wires, foils, and micro-mechanical parts.

Related Standards

ASTM E92-23 references and aligns with several other key standards in hardness testing and materials evaluation:

• ASTM E384: Test Method for Microindentation Hardness of Materials (detailed microhardness test guidance).
• ASTM E140: Hardness Conversion Tables for Metals (conversion among Vickers, Knoop, Rockwell, Brinell, and others).
• ASTM C1326 / C1327: Test Methods for Knoop and Vickers Hardness for advanced ceramics.
• ISO 6507-1: Metallic Materials - Vickers Hardness Test - Part 1.
• ISO/IEC 17025: General Requirements for Laboratories.
• ASTM E3: Guide for Preparation of Metallographic Specimens.

Practical Value

Implementing ASTM E92-23 ensures:

• Consistent and reliable hardness measurements for metallic materials.
• Accurate quality control data for process validation and certification.
• Improved product performance by validation of mechanical properties.
• Enhanced research rigor through standardized test procedures.

Routine compliance with ASTM E92-23 supports manufacturers, laboratories, and researchers in achieving internationally recognized results, facilitating global trade and technological advancement in materials science.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E92 − 23
Standard Test Methods for
Vickers Hardness and Knoop Hardness of Metallic
Materials
This standard is issued under the fixed designation E92; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* continued common usage, force values in gf and kgf units are
provided for information and much of the discussion in this
1.1 These test methods cover the determination of the
standard as well as the method of reporting the test results
Vickers hardness and Knoop hardness of metallic materials by
refers to these units.
the Vickers and Knoop indentation hardness principles. This
NOTE 1—The Vickers and Knoop hardness numbers were originally
standard provides the requirements for Vickers and Knoop
defined in terms of the test force in kilogram-force (kgf) and the surface
hardness machines and the procedures for performing Vickers
area or projected area in millimetres squared (mm ). Today, the hardness
and Knoop hardness tests. numbers are internationally defined in terms of SI units, that is, the test
force in Newtons (N). However, in practice, the most commonly used
1.2 This standard includes additional requirements in an-
force units are kilogram-force (kgf) and gram-force (gf). When Newton
nexes:
units of force are used, the force must be divided by the conversion factor
9.80665 N/kgf.
Verification of Vickers and Knoop Hardness Testing Machines Annex A1
Vickers and Knoop Hardness Standardizing Machines Annex A2
1.7 The test principles, testing procedures, and verification
Standardization of Vickers and Knoop Indenters Annex A3
procedures are essentially identical for both the Vickers and
Standardization of Vickers and Knoop Hardness Test Blocks Annex A4
Correction Factors for Vickers Hardness Tests Made on Annex A5
Knoop hardness tests. The significant differences between the
Spherical and Cylindrical Surfaces
two tests are the geometries of the respective indenters, the
1.3 This standard includes nonmandatory information in an
method of calculation of the hardness numbers, and that
appendix which relates to the Vickers and Knoop hardness
Vickers hardness may be used at higher force levels than
tests:
Knoop hardness.
NOTE 2—While Committee E28 is primarily concerned with metallic
Examples of Procedures for Determining Vickers and Appendix X1
Knoop Hardness Uncertainty materials, the test procedures described are applicable to other materials.
Other materials may require special considerations, for example see
1.4 This test method covers Vickers hardness tests made
C1326 and C1327 for ceramic testing.
-3
utilizing test forces ranging from 9.807 × 10 N to 1176.80 N
1.8 This standard does not purport to address all of the
(1 gf to 120 kgf), and Knoop hardness tests made utilizing test
-3 safety concerns, if any, associated with its use. It is the
forces from 9.807 × 10 N to 19.613 N (1 gf to 2 kgf).
responsibility of the user of this standard to establish appro-
1.5 Additional information on the procedures and guidance
priate safety, health, and environmental practices and deter-
when testing in the microindentation force range (forces ≤ 1
mine the applicability of regulatory limitations prior to use.
kgf) may be found in Test Method E384, Test Method for
1.9 This international standard was developed in accor-
Microindentation Hardness of Materials.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
1.6 Units—When the Vickers and Knoop hardness tests
Development of International Standards, Guides and Recom-
were developed, the force levels were specified in units of
mendations issued by the World Trade Organization Technical
grams-force (gf) and kilograms-force (kgf). This standard
specifies the units of force and length in the International Barriers to Trade (TBT) Committee.
System of Units (SI); that is, force in Newtons (N) and length
in mm or μm. However, because of the historical precedent and 2. Referenced Documents
2.1 ASTM Standards:
These test methods are under the jurisdiction of ASTM Committee E28 on
Mechanical Testing and is the direct responsibility of Subcommittee E28.06 on
Indentation Hardness Testing. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved July 1, 2023. Published August 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1952. Last previous edition approved in 2017 as E92–17. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E0092-23. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E92 − 23
C1326 Test Method for Knoop Indentation Hardness of force, the length of the long diagonal of the projected area of
Advanced Ceramics the indentation is measured to calculate the Knoop hardness
C1327 Test Method for Vickers Indentation Hardness of number.
Advanced Ceramics
3.1.4 Vickers hardness number, HV, n—the calculated result
E3 Guide for Preparation of Metallographic Specimens
from a Vickers hardness test, which is proportional to the test
E6 Terminology Relating to Methods of Mechanical Testing
force applied to the Vickers indenter divided by the surface
E7 Terminology Relating to Metallography
area of the permanent indentation made by the indenter after
E29 Practice for Using Significant Digits in Test Data to
removal of the test force.
Determine Conformance with Specifications
3.1.4.1 Discussion—The surface area of the permanent in-
E74 Practices for Calibration and Verification for Force-
dentation made by the Vickers indenter is calculated based
Measuring Instruments
partly on the measured mean length of the two diagonals of the
E140 Hardness Conversion Tables for Metals Relationship
projected area of the indentation.
Among Brinell Hardness, Vickers Hardness, Rockwell
3.1.5 Vickers hardness test, n—an indentation test in which
Hardness, Superficial Hardness, Knoop Hardness, Sclero-
a Vickers square-based pyramidal diamond indenter having
scope Hardness, and Leeb Hardness
3 specified face angles is forced under specified conditions into
E175 Terminology of Microscopy (Withdrawn 2019)
the surface of the test material, and, after removal of the test
E177 Practice for Use of the Terms Precision and Bias in
force, the lengths of the two diagonals of the projected area of
ASTM Test Methods
the indentation are measured to calculate the Vickers hardness
E384 Test Method for Microindentation Hardness of Mate-
number.
rials
E691 Practice for Conducting an Interlaboratory Study to 3.2 Definitions of Terms Specific to This Standard:
Determine the Precision of a Test Method
3.2.1 standardization, n—to bring in conformance to a
known standard through verification or calibration.
2.2 ISO Standards:
ISO 6507-1 Metallic Materials—Vickers hardness Test— 3.2.2 microindentation hardness test, n—a hardness test,
Part 1: Test Method
normally in the Vickers or Knoop scales, using test forces in
-3
ISO/IEC 17011 Conformity Assessment—General Require- the range of 9.807 × 10 to 9.807 N (1 to 1000 gf).
ments for Accreditation Bodies Accrediting Conformity
3.2.3 macroindention hardness test, n—a hardness test using
Assessment Bodies
test forces normally higher than 9.807 N (1 kgf). Macroinden-
ISO/IEC 17025 General Requirements for the Competence
tation tests include Vickers, Rockwell and Brinell.
of Testing and Calibration Laboratories
NOTE 3—Use of the term microhardness should be avoided because it
implies that the hardness, rather than the force or the indentation size, is
3. Terminology and Equations
very low.
3.1 Definitions of Terms—For the standard definitions of
3.2.4 scale, n—a specific combination of indenter (Knoop or
terms used in this test method, see Terminology E6 and
Vickers) and the test force (kgf).
Terminology E7.
3.2.4.1 Discussion—For example, HV 10 is a scale defined
3.1.1 indentation hardness, n—the hardness as evaluated
as using a Vickers indenter and a 10 kgf test force and HK 0.1
from measurements of area or depth of the indentation made by
is a scale defined as using a Knoop indenter and a 100 gf test
forcing a specified indenter into the surface of a material under
force. See 5.10 for the proper reporting of the hardness level
specified static loading conditions.
and scale.
3.1.2 Knoop hardness number, HK, n—the calculated result
3.2.5 as-found condition, n—the state of the hardness ma-
from a Knoop hardness test, which is proportional to the test
chine as reflected by the initial verification measurements made
force applied to the Knoop indenter divided by the projected
prior to performing any cleaning, maintenance, adjustments or
area of the permanent indentation made by the indenter after
repairs associated with an indirect verification.
removal of the test force.
3.2.6 hardness machine, n—a machine capable of perform-
3.1.2.1 Discussion—The projected area of the permanent
ing a Vickers or Knoop hardness test.
indentation made by the Knoop indenter is calculated based
partly on the measured length of the long diagonal of the
3.2.7 hardness testing machine, n—a Vickers or Knoop
projected area of the indentation.
hardness machine used for general testing purposes.
3.1.3 Knoop hardness test, n—an indentation test in which a
3.2.8 hardness standardizing machine, n—a Vickers or
Knoop rhombic-based pyramidal diamond indenter having
Knoop hardness machine used for the standardization of
specified edge angles, is forced under specified conditions into
Vickers or Knoop hardness test blocks.
the surface of the test material, and, after removal of the test
3.2.8.1 Discussion—A hardness standardizing machine dif-
fers from a hardness testing machine by having tighter toler-
ances on certain parameters.
The last approved version of this historical standard is referenced on
3.3 Equations:
www.astm.org.
¯
3.3.1 The average d of a set of n diagonal length measure-
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. ments d , d , …, d is calculated as:
1 2 n
E92 − 23
d 1d 1…1d 4.4 The Vickers indenter usually produces essentially the
1 2 n
¯
d 5 (1)
n same hardness number at all test forces when testing homoge-
neous material, except for tests using very low forces (below
where each of the individual diagonal measurements d , d ,
1 2
25 gf) or for indentations with diagonals smaller than about 25
…, d is the mean of the two diagonal length measurements in
n
μm (see Test Method E384). For isotropic materials, the two
the case of a Vickers indentation, or is the long diagonal length
diagonals of a Vickers indentation are equal in length.
measurement in the case of a Knoop indentation.
4.5 The Knoop indenter usually produces similar hardness
3.3.2 The repeatability R in the performance of a Vickers or
numbers over a wide range of test forces, but the numbers tend
Knoop hardness machine at each hardness level, under the
to rise as the test force is decreased. This rise in hardness
particular verification conditions, is determined from n diago-
number with lower test forces is often more significant when
nal measurements made on a standardized test block as part of
testing higher hardness materials, and is increasingly more
a performance verification. The repeatability is estimated as the
significant when using test forces below 50 gf (see Test Method
percent range of n diagonal measurements with respect to the
E384).
measured average hardness value as:
4.6 The elongated four-sided rhombohedral shape of the
d 2 d
max min
R 5 100 × (2)
Knoop indenter, where the length of the long diagonal is 7.114
S D
¯
d
times greater than the short diagonal, produces narrower and
where: shallower indentations than the square-based pyramid Vickers
indenter under identical test conditions. Hence, the Knoop
d = the longest diagonal length measurement made on the
max
hardness test is very useful for evaluating hardness gradients
standardized test block,
since Knoop indentations can be made closer together than
d = the shortest diagonal length measurement made on
min
Vickers indentations by orienting the Knoop indentations with
the standardized test block, and
¯
the short diagonals in the direction of the hardness gradient.
d = the average (see 3.3.1) of the n diagonal length
measurements made on the standardized test block.
5. Principle of Test and Apparatus
3.3.3 The error E in the performance of a Vickers or Knoop
5.1 Vickers and Knoop Hardness Test Principle—The gen-
hardness machine at each hardness level, relative to a standard-
eral principle of the Vickers and Knoop indentation hardness
ized reference value, is calculated as a percent error determined
test consists of two steps.
as:
5.1.1 Step 1—The applicable specified indenter is brought
¯
d 2 d
? ref?
into contact with the test specimen in a direction normal to the
E 5 100 × (3)
S D
d
ref
surface, and the test force F is applied. The test force is held for
a specified dwell time and then removed.
where:
5.1.2 Step 2—For the Vickers hardness test, the lengths of
¯
d = the average (see 3.3.1) of n diagonal length mea-
the two diagonals are measured and the mean diagonal length
surements made on a standardized test block as
is calculated, which is used to derive the Vickers hardness
part of a performance verification, and
value. For the Knoop hardness test, the length of the long
d = the certified diagonal length reported for the stan-
ref
diagonal is measured, which is used to derive the Knoop
dardized test block.
hardness value.
¯
= absolute value (non-negative value without regard
|d2d |
ref
¯ 5.1.3 Most materials will exhibit some elastic recovery
to its sign) of the difference between d and d .
ref
when the indenter is removed after the loading cycle. However,
for the purposes of calculating the hardness results from the
4. Significance and Use
indentation diagonal lengths, it is assumed that the indentation
4.1 Vickers and Knoop hardness tests have been found to be
retains the shape of the indenter after the force is removed. In
very useful for materials evaluation, quality control of manu-
Knoop testing, it is assumed that the ratio of the long diagonal
facturing processes and research and development efforts.
to the short diagonal of the indentation is the same as for the
Hardness, although empirical in nature, can be correlated to
indenter.
tensile strength for many metals, and is an indicator of wear
5.2 Testing Machine—The testing machine shall support the
resistance and ductility.
test specimen and control the movement of the indenter into the
4.2 Microindentation hardness tests extend testing to mate-
specimen under a preselected test force, and should have a light
rials that are too thin or too small for macroindentation
optical microscope to select the desired test location and to
hardness tests. Microindentation hardness tests also allow
measure the size of the indentation produced by the test. The
specific phases or constituents and regions or gradients too
plane of the surface of the test specimen should be perpendicu-
small for macroindentation hardness testing to be evaluated. lar to the axis of the indenter which is the direction of the force
Recommendations for microindentation testing can be found in
application.
Test Method E384.
5.2.1 See the equipment manufacturer’s instruction manual
for a description of the machine’s characteristics, limitations,
4.3 Because the Vickers and Knoop hardness will reveal
and respective operating procedures.
hardness variations that may exist within a material, a single
test value may not be representative of the bulk hardness. 5.3 Indenters:
E92 − 23
TABLE 1 Standard Hardness Scales and Test Forces
5.3.1 Indenters for general Vickers or Knoop hardness
testing shall comply with the requirements of a Class B Approximate Approximate
Vickers Knoop Test force
Test force Test force
A
indenter or better in accordance with Annex A3.
scale scale (N)
(kgf) (gf)
5.3.2 Vickers Indenter—The ideal Vickers indenter (see Fig.
HV 0.001 HK 0.001 0.009807 0.001 1
A3.1) is a highly polished, pointed, square-based pyramidal HV 0.01 HK 0.01 0.09807 0.01 10
HV 0.015 HK 0.015 0.1471 0.015 15
diamond with face angles of 136° 0’.
HV 0.02 HK 0.02 0.1961 0.02 20
5.3.3 Knoop Indenter—The ideal Knoop indenter (see Fig. HV 0.025 HK 0.025 0.2451 0.025 25
HV 0.05 HK 0.05 0.4903 0.05 50
A3.2) is a highly polished, pointed, rhombic-based, pyramidal
HV 0.1 HK 0.1 0.9807 0.1 100
diamond. The included longitudinal edge angles are 172° 30’
HV 0.2 HK 0.2 1.961 0.2 200
HV 0.3 HK 0.3 2.942 0.3 300
and 130° 0’.
HV 0.5 HK 0.5 4.903 0.5 500
HV 1 HK 1 9.807 1 1000
NOTE 4—The user should consult with the manufacturer before apply-
HV 2 HK 2 19.61 2 2000
ing macroindentation test forces (over 1 kgf) with diamond indenters
HV 3 29.41 3
previously used for microindentation testing. The diamond mount may not
HV 5 49.03 5
be strong enough to support the higher test forces and the diamond may
HV 10 98.07 10
not be large enough to produce the larger indentation sizes.
HV 20 196.1 20
HV 30 294.1 30
5.4 Measurement Device—The diagonals of the indentation
HV 50 490.3 50
HV 100 980.7 100
are measured (see 7.9.2) using a light microscope equipped
HV 120 1177 120
with a filar type eyepiece (see Terminology E175), or other
A
The user should consult with the manufacturer before applying macroindentation
type of measuring device. Additional guidance on measuring
test forces (over 1 kgf) for Knoop hardness testing. The diamond may not be large
devices may be found in Test Method E384.
enough to produce the larger indentation sizes (see Note 4).
5.4.1 The testing machine’s measuring device shall be
capable of reporting the diagonal lengths to within the require-
ments of 7.9.2.
5.4.2 The measuring device may be an integral part of the where:
tester or a stand-alone instrument, such as a high quality
α = face angle of the diamond indenter = 136°, and
measuring microscope or measuring system. To obtain the
d = mean Vickers indentation diagonal length (mm).
V
highest quality image for measuring the indentation diagonal,
Other units of force and length may be used; however, the
the measuring microscope should have adjustable illumination
reported Vickers hardness number shall be converted to the
intensity, adjustable alignment, aperture, and field diaphragms.
units of kgf and mm, as follows and given in Table 2.
5.4.3 Magnifications should be provided so that the diago-
5.8.1 Microindentation Vickers hardness is typically deter-
nal can be enlarged to greater than 25 % but less than 75 % of
mined using indentation test forces in grams-force (gf) and
the field width. The device may be built with single or multiple
indentation diagonals measured in micrometres (μm). The
magnifying objectives.
Vickers hardness number, in terms of gf and μm, is calculated
as follows:
5.5 Verifications—All testing machines, indentation measur-
F F
ing devices and indenters used to perform Vickers and Knoop
~gf! ~gf!
HV 5 1000 × 1.8544 × 5 1854.4 × (6)
2 2
hardness tests shall be verified periodically in accordance with d d
V ~µm! V ~µm!
Annex A1 prior to performing hardness tests.
5.8.2 Macroindentation Vickers hardness is typically deter-
5.6 Test Blocks—Test blocks meeting the requirements of mined using indentation test forces in kilograms-force (kgf)
Annex A4 shall be used to verify the testing machine in and indentation diagonals measured in millimetres (mm). The
Vickers hardness number, in terms of kgf and mm, is calculated
accordance with Annex A1.
as follows:
5.7 Test Forces—The standard hardness test forces are given
F
~kgf!
in Table 1. Other non-standard test forces may be used by
HV 5 1.8544 × (7)
d
special agreement. V ~mm!
5.8 Calculation of the Vickers Hardness Number—The
Vickers hardness number is based on the indentation test force
TABLE 2 Vickers and Knoop Formulae
F in kgf divided by the surface area A of the indentation in
S
mm .
Vickers hardness number
Force (F) unit Diagonal (d) unit Formula
F 2
Test force
~kgf! kgf mm HV = 1.8544 × F/d
HV 5 5 (4)
gf μm HV = 1854.4 × F/d
Surface Area A 2
S mm
~ !
N mm HV = 0.1891 × F/d
Knoop hardness number
The surface area (A ) of the indentation is calculated as:
S
Force (F) unit Diagonal (d) unit Formula
2 2 kgf mm HK = 14.229 × F/d
d d
V V
gf μm HK = 14229 × F/d
A 5 5 (5)
S
α 1.8544 2
N mm HK = 1.451 × F/d
2sin
E92 − 23
5.8.3 The Vickers hardness number, in terms of indentation 5.10.1 For nonstandard dwell times, other than 10 s to 15 s,
test forces in Newtons (N) and indentation diagonals measured the hardness shall be supplemented with the actual total force
in millimetres (mm), is calculated as follows: dwell time used in seconds separated by a “/”.
5.10.2 The reported Vickers and Knoop hardness number
F F
1.8544
~N! ~N!
HV 5 × 5 0.1891 × (8) shall be reported rounded to three significant digits in accor-
2 2
9.80665 d d
V mm V mm
~ ! ~ !
dance with Practice E29.
5.9 Calculation of the Knoop Hardness Number—The
5.10.3 Examples:
Knoop hardness number is based on the indentation test force
400 HK 0.5 = Knoop hardness of 400 determined with a 500 gf (0.5 kgf)
(kgf) divided by the projected area A of the indentation indentation test force.
P
99.2 HV 0.1 = Vickers hardness of 99.2 determined with a 100 gf (0.1 kgf)
(mm ).
indentation test force.
725 HV 10 = Vickers hardness of 725 determined with a 10 kgf indentation
F
Test force
kgf
~ !
HK 5 5 (9) test force.
Projected Area A 2
P ~mm !
400 HK 0.1 /22. = Knoop hardness of 400 determined with a 100 gf (0.1 kgf)
indentation test force and a 22 s total force dwell time.
The projected area (A ) of the indentation is calculated as:
P
6. Test Piece
A 5 d × c (10)
P K P
6.1 There is no standard shape or size for a Vickers or
where:
Knoop test specimen. The specimen on which the indentation
d = Knoop indentation long diagonal length (mm), and
K
is made should conform to the following:
c = indenter constant relating the projected area of the
P
indentation to the square of the length of the long
6.2 Preparation—For optimum accuracy of measurement,
diagonal, ideally 0.07028, where: the test should be performed on a flat specimen with a polished
or otherwise suitably prepared surface. The quality of the
/B
required surface finish can vary with the forces and magnifi-
tan
c 5 5 0.07028 (11) cations used. The lower the test force and the smaller the
P
/A
indentation size, the more critical is the surface preparation. In
2tan
all tests, the preparation should be such that the indentation
where: perimeter and the indentation tips in particular, can be clearly
defined when observed by the measuring system. Surface
/A = the included longitudinal edge angle, 172° 30’, and
preparation recommendations for low-force microindentation
/B = included transverse edge angle, 130° 0’.
testing can be found in Test Method E384.
Other units of force and length may be used, however, the
6.2.1 The test surface shall be free of any defects that could
Knoop hardness number shall be converted to the units of kgf
affect the indentation or the subsequent measurement of the
and mm, as follows and as given in Table 2.
diagonals. It is well known that improper grinding and polish-
5.9.1 Knoop hardness is typically determined using inden-
ing methods can alter test results either due to excessive
tation test forces in grams-force (gf) and indentation long
heating or cold work. Some materials are more sensitive to
diagonal measured in micrometres (μm). The Knoop hardness
preparation-induced damage than others; therefore, special
number, in terms of gf and μm, is calculated as follows:
precautions shall be taken during specimen preparation. Re-
F F
move any damage introduced during specimen preparation.
~gf! ~gf!
HK 5 1000 × 14.229 × 5 14229 × (12)
2 2
d d 6.2.2 The specimen surface should not be etched before
K µm K µm
~ ! ~ !
making an indentation. Etched surfaces can obscure the edge of
5.9.2 The Knoop hardness number, in terms of indentation
the indentation, making an accurate measurement of the size of
test forces in kgf and the indentation long diagonal measured in
the indentation difficult. There may be microindentation testing
mm, is calculated as follows:
applications where a light etch may be appropriate (see Test
F Method E384).
~kgf!
HK 5 14.229 × (13)
d
K ~mm!
6.3 Alignment—To obtain usable information from the test,
the specimen should be prepared or mounted so that the test
5.9.3 The Knoop hardness number, in terms of indentation
surface is perpendicular to the axis of the indenter. This can
test forces in Newtons (N) and the indentation long diagonal
readily be accomplished by surface grinding (or otherwise
measured in millimetres (mm), is calculated as follows:
machining) the opposite side of the specimen parallel with the
F F
14.229
N N
~ ! ~ ! side to be tested. Non-parallel test specimens can be tested
HK 5 × 5 1.451 × (14)
2 2
9.80665 d d
using clamping and leveling fixtures designed to align the test
K ~mm! K ~mm!
surface properly to the indenter.
5.10 Hardness Number—Vickers and Knoop hardness val-
ues are not designated by a number alone because it is 6.4 Mounted Test Specimens—In many instances, especially
necessary to indicate which force has been employed in in microindentation testing, it is necessary to mount the
making the test. The hardness numbers shall be followed by the specimen for convenience in preparation and to maintain a
symbol HV for Vickers hardness, or HK for Knoop hardness, sharp edge when surface gradient tests are to be performed on
and be supplemented by a value representing the test force in the test specimen. When mounting is required, the specimen
kgf. shall be adequately supported by the mounting medium so that
E92 − 23
the specimen does not move during force application, that is, 7.4.1 After each change of a test force, it is recommended
avoid the use of polymeric mounting compounds that creep that the operation of the machine be checked by performing a
under the indenter force (see Test Method E384). periodic verification as specified in A1.5, particularly for
machines where the weights that create test forces are changed
6.5 Thickness—The thickness of the specimen tested shall
manually or there is a chance of jamming occurring when
be such that no bulge or other marking showing the effect of
weights are changed.
the test force appears on the side of the piece opposite the
indentation. The thickness of the material under test should be 7.5 Positioning the Test Specimen—Place the test specimen
at least ten times the depth of the indentation (see Note 5).
in the appropriate fixture or on the tester stage so that the test
Similarly, when testing a coating on a material, the minimum surface is perpendicular to the indenter axis.
thickness of the coating should be at least ten times the depth
7.6 Locate the Test Point—Focus the measuring microscope
of the indentation.
with a low power objective so that the specimen surface can be
NOTE 5—The Vickers indentation depth h is approximately
V
observed. Adjust the light intensity and adjust the diaphragms
h 5 0.143 × d (15) for optimum resolution and contrast. Adjust the position of the
V V
or approximately 1/7 of the mean diagonal length d . The Knoop in-
test specimen so that the indentation will be made in the
V
dentation depth h is approximately
K
desired location on the test surface. Before applying the force,
h 5 0.033 × d (16) make a final focus using the measuring objective (see 7.9 and
K K
or approximately 1/30 of the long diagonal length d .
K Table 3).
6.6 Radius of Curvature—Due caution should be used in 7.7 Force Application—Apply the selected test force as
interpreting or accepting the results of tests made on spherical
follows in a manner and in an environment that prevents shock
or cylindrical surfaces, particularly when using low test forces. or vibration during the indenting process.
Results will be affected even in the case of the Knoop test
7.7.1 For microindentation testing, the indenter shall contact
where the radius of curvature is in the direction of the short the specimen at a velocity between 15 μm/s and 70 μm/s. For
diagonal. Annex A5 provides correction factors that shall be
macroindentation testing, the contact velocity should not ex-
applied to Vickers hardness values obtained when tests are ceed 0.2 mm/s.
made on spherical or cylindrical surfaces. Additional require-
7.7.2 The time from the initial application of the force until
ments are specified in 9.3 and 9.4 when reporting corrected the full test force is reached shall not be more than 10 s.
hardness values.
7.7.3 The full test force shall be applied for 10 s to 15 s
unless otherwise specified.
7. Test Procedure
7.7.4 For some applications it may be necessary to apply the
7.1 Verification—A periodic verification procedure shall be
test force for longer times. In these instances the tolerance for
performed in accordance with A1.5 within one week prior to
the time of the applied force shall be 6 2 s. The application
making hardness tests. The periodic verification should be
time shall be defined in the report.
performed on a daily basis.
7.7.5 Remove the test force without shock or vibration.
7.7.6 During the entire test cycle of force application and
7.2 Test Temperature—Vickers and Knoop hardness tests
removal, the test machine should be protected from shock or
should be carried out at a temperature within the limits of
vibration. To minimize vibrations, the operator should avoid
10 °C to 35°C (50 °F to 95 °F). Because variations within this
contacting the machine in any manner during the entire test
temperature range may affect results, users may choose to
cycle.
control temperature within a tighter range.
7.8 Test Location—After the force is removed, switch to the
7.3 Indenter—Select the indenter, either Knoop or Vickers,
to suit the desired test to be performed. Refer to the manufac- measuring mode, and select the proper objective lens. Focus
the image, adjust the light intensity if necessary, and adjust the
turer’s instruction manual for the proper procedure if it is
necessary to change indenters. diaphragms for maximum resolution and contrast.
7.8.1 Examine the indentation for its position relative to the
7.3.1 After each change, or removal and replacement, of the
indenter, it is recommended that a periodic verification be desired location and for its symmetry.
7.8.2 If the indentation did not occur at the desired spot, the
performed as specified in A1.5.
7.3.2 Occasionally clean the indenter with a cotton swab tester is out of alignment. Consult the manufacturer’s instruc-
tion manual for the proper procedure to produce alignment.
and alcohol. Avoid creating static charges during cleaning.
Indenting a piece of paper placed on top of the test specimen Make another indentation and recheck the indentation location.
Readjust and repeat as necessary.
will often remove oil from the indenter. Do not touch the
diamond tip with fingers.
7.9 Indentation Measurement—Measure both diagonals of a
7.3.3 Indenters should be examined periodically and re-
Vickers indentation or the long diagonal of a Knoop indenta-
placed if they become worn, dulled, chipped, cracked or
tion by operating the measuring device in accordance with the
separated from the mounting material. Checks of the indenter
manufacturer’s instruction manual.
by the user may be performed by visual inspection of the
7.9.1 When the indentation measuring device is a light
resulting indentations performed on test blocks.
microscope that requires the full indentation to be seen and
7.4 Magnitude of Test Force—Set the desired test force on measured in the field of view, the highest magnification that
the tester by following the manufacturer’s instructions. can image the full indentation shall be used. To stay within the
E92 − 23
flat field of the objective, the indentation length should not nonsymmetrical aspect of the indentations has rotated 90°, then
exceed 75 % of the field width. The objective selected to the specimen surface may not be perpendicular to the indenter
measure the indentation should have an objective resolution axis and may yield incorrect hardness results. If the nonsym-
(r ) that is ≤ 2 % of the diagonal length to be measured. metrical nature of the indentation remains in the same
obj
Objective resolution (r ) is a function of the numerical orientation, check the indenter for damage or misalignment as
obj
aperture (NA) of the objective, see Note 6. The minimum described in 7.10.4.
recommended diagonal lengths to be measured by typical
7.10.4 The alignment of the indenter may be checked using
objectives are shown in Table 3. a test specimen, such as a standardized test block, known to
produce uniformly shaped indentations. Confirm that the test
NOTE 6—The objective’s resolution (r ) is defined as:
obj
block surface is perpendicular to the indenter axis as described
r 5 λ ⁄ 2 × NA (17)
~ !
obj in 7.10.3. Make an indentation. If the indentation is not
symmetrical, the indenter is misaligned, and the tester shall not
where:
be used until it meets the requirements of sections 7.10.1 or
λ = the wave length of the light in μm (approx. 0.55 μm for green
light), and 7.10.2.
NA = the numerical aperture of the objective as defined by the
7.10.5 Some materials may have nonsymmetrical indenta-
manufacturer. (The NA is frequently marked on the side of each
tions even if the indenter and the specimen surface are
objective.) Example: For a 50× objective with a NA of 0.65
perfectly aligned. Tests on single crystals or on textured
using green light, r = 0.55 μm / (2 × 0.65) = 0.42 μm.
obj
materials may produce such results. When tests on these types
7.9.2 Determine the length of the diagonals to within 0.5 μm
of materials produce nonsymmetrical indents exceeding the
or less. For indentations less than 40 μm, determine the length
limits of 7.10.1 or 7.10.2, it should be noted on the test report.
of the diagonals to within 0.25 μm or less. For indentations less
7.10.6 Brittle materials such as ceramics may crack as a
than 20 μm, the length of the diagonals should be determined
result of being indented. Specific details for testing ceramics
to within 0.1 μm or less. In all cases, smaller measurement
are contained in Test Methods C1326 and C1327.
increments may be reported if the equipment is capable of
7.11 Spacing of Indentations—Generally more than one
displaying smaller measurement increments.
indentation is made on a test specimen. It is necessary to ensure
7.10 Indentation Examination:
that the spacing between indentations is large enough so that
7.10.1 Vickers—For a Vickers indentation, if one half of
adjacent tests do not interfere with each other.
either diagonal is more than 5 % longer than the other half of
7.11.1 For most testing purposes, the minimum recom-
that diagonal, or if the four corners of the indentation are not in
mended spacing between separate tests, and minimum distance
sharp focus, the test surface may not be perpendicular to the
between an indentation and the edge of the specimen are
indenter axis. Check the specimen alignment as described in
illustrated in Fig. 1.
7.10.3.
7.11.2 For some applications, closer spacing of indentations
7.10.2 Knoop—For a Knoop indentation, if one half of the
than those shown in Fig. 1 may be desired. If closer indentation
long diagonal is greater than 10 % longer than the other, or if
spacing is used, it shall be the responsibility of the testing
both ends of the indentation are not in sharp focus, the test
laboratory to verify the accuracy of the testing procedure.
specimen surface may not be perpendicular to the indenter
axis. Check the specimen alignment as given in 7.10.3.
8. Conversion to Other Hardness Scales or Tensile
7.10.3 If the diagonal legs are unequal by an amount greater
Strength Values
than the limits defined in 7.10.1 or 7.10.2, rotate the specimen
8.1 There is no general method of accurately converting the
90° and make another indentation in an untested region. If the
Vickers or Knoop hardness numbers using one test force to
hardness numbers using a different test force, or to other types
TABLE 3 Recommended Indentation Diagonal Lengths for
of hardness numbers, or to tensile strength values. Such
Commonly used Objectives and NA
conversions are, at best, approximations and, therefore, should
Commonly used Typical NA Objective Recommended
be avoided except for special cases where a reliable basis for
Objective (will vary by Resolution Diagonal
the approximate conversion has been obtained by comparison
A
Magnifications objective type) (r ) μm Lengths μm
obj
tests. For homogeneous materials and test forces ≥ 100 gf,
2.5× 0.07 3.93 196.5 or longer
5× 0.10 2.75 137.5 or longer microindentation Vickers hardness numbers are in reasonable
10× 0.25 1.10 55 or longer
agreement with macroindentation Vickers hardness numbers.
20× 0.40 0.69 34.5 or longer
Refer to E140 for hardness conversion tables for metals.
20× 0.45 0.61 30.5 or longer
40× 0.55 0.50 25 or longer Additional requirements are specified in 9.2 and 9.4 when
40x 0.65 0.42 21 or longer
reporting converted hardness values.
50× 0.65 0.42 21 or longer
NOTE 7—E140 gives approximate hardness conversion values for
60× 0.70 0.39 19.5 or longer
specific materials such as steel, nickel and high-nickel alloys, cartridge
100× 0.80 0.34 17 or longer
brass, copper alloys, alloyed white cast irons, and wrought aluminum
100× 0.95 0.29 14.5 or longer
products.
A
This is the magnification of the objective and may not be the total magnification
of the system. Many systems have a 10× eyepiece that increases the total
magnification by a factor of 10 at the operator’s eye. This additional magnification
9. Report
does not change the optical resolution (r ) or the recommended diagonal lengths.
obj
9.1 Report the following information:
E92 − 23
FIG. 1 Minimum Recommended Spacing for Vickers and Knoop Indentations
9.1.1 The results (see 5.10), the number of tests, and, where 10. Precision and Bias
appropriate, the mean and standard deviation of the results,
10.1 Four separate interlaboratory studies have been con-
9.1.2 Test force,
ducted in accordance with Practice E691 to determine the
9.1.3 The total force application time if outside the limits of
precision, repeatability, and reproducibility of this test method.
10 s to 15 s as defined in 7.7.3,
The four studies are defined as follows:
9.1.4 Any unusual conditions encountered during the test,
(1) Vickers and Knoop tests, six test forces in the micro-
and
indentation range, twelve laboratories, manual measurements,
9.1.5 The test temperature, when outside the recommended
seven different hardness level test specimens. See Test Method
allowable range of 10 °C to 35 °C (50 °F to 95 °F).
E384.
(2) Vickers and Knoop tests, two test forces in the micro-
9.2 Reporting Converted Hardness Values—When reporting
indentation range, seven laboratories, image-analysis and
hardness values that have been converted from one type of
manual measurements, four different hardness level test speci-
hardness test or hardness scale to another type of hardness test
mens. See Test Method E384.
or hardness scale, the original measurement number and test
(3) Vickers and Knoop tests, six test forces in the micro
scale shall also be reported (see E140).
range, twenty-five laboratories, manual measurements, six
9.2.1 A common historical practice is to report the con-
different hardness level test specimens. See Test Method E384.
verted hardness value followed by the measured hardness value
(4) Vickers tests, four test forces in the macro range, seven
given in parentheses. For example: 353 HBW (372 HV), where
laboratories, manual measurements, three different hardness
353 HBW is the converted hardness value and 372 HV is the
level test specimens. See 10.3.
original measurement value.
9.2.2 Other formats for reporting converted hardness values,
10.2 Studies 1 through 3—The results and discussion of
such as data tables, may be used, however, the original
Studies 1 through 3 are given in Test Method E384.
measurement number and test scale shall also be reported and
10.3 Study 4—The macroindentation Vickers precision
clearly identified.
statement is based on an interlaboratory study of Test Methods
9.3 Reporting Curvature Corrected Hardness Values—
E92, Standard Test Method for Vickers Hardness of Metallic
When reporting Vickers or Knoop hardness test values that
Materials, conducted in 2001. Seven laboratories tested three
have been corrected for testing on cylindrical or spherical
different standard hardness test blocks using macro range test
surfaces (see 6.6), the following information shall be indicated
forces of 1, 5, 10, and 20 kgf. Only four laboratories were also
in the test report or documented in the test lab/customer
able to provide results at 50 kgf test force. Every “test result”
contract or agreement:
represents an individual determination of the Vickers hardness
–the test values are corrected due to testing on a curved
of the material. Each laboratory was asked to report triplicate
surface,
test results in order to permit the estimation of intralaboratory
–the source of correction value, if other than the correction
precision. Practice E691 was followed for the design and
tables given in Annex A5 for convex cylindrical surfaces.
analysis of the data; the details are given in ASTM Research
9.4 Since all converted or curvature-corrected hardness Report No. RR: E04-1007.
values are considered approximate, the reported hardness
values shall be rounded in accordance with the Rounding
Method of Practice E29 and should have no more significant
Supporting data have been filed at ASTM International Headquarters and may
digits than is given for the data in the applicable conversion or
be obtained by requesting Research Report RR:E04-1007. Contact ASTM Customer
correction table. Service at [e-mail].
E92 − 23
10.3.1 The precision statement was determined through 10.3.3 The above terms (repeatability limit and reproduc-
statistical examination of 288 results, from seven laboratories, ibility limit) are used as specified in Practice E177.
on three test blocks. The materials were described as the
10.4 Bias—There is no recognized standard by which to
following:
estimate the bias of this test method.
Material 1: 200 HV
Material 2: 400 HV
11. Keywords
Material 3: 800 HV
10.3.2 Repeatability and reproducibility limits are listed in 11.1 hardness; indentation; Knoop; macroindentation; mi-
Tables 4-8. croindentation; Vickers
TABLE 4 Vickers Hardness at 1 kgf Test Force (HV 1)
Repeatability Reproducibility
Test Block
Average Standard Deviation Standard Deviation Repeatability Limit Reproducibility Limit
Nominal Hardness
(HV) Bias (HV) (HV) (HV) (HV)
(HV)
¯
X % s s r R
r R
200 209.2 N/A 4.1 7.1 11.5 19.9
400 413.8 N/A 8.1 15.6 22.8 43.7
800 812.9 N/A 21.8 21.8 61.1 61.1
E92 − 23
TABLE 5 Vickers Hardness at 5 kgf Test Force (HV 5)
Repeatability Reproducibility
Test Block
Average Standard Deviation Standard Deviation Repeatability Limit Reproducibility Limit
Nominal Hardness
(HV) Bias (HV) (HV) (HV) (HV)
(HV)
¯
X % s s r R
r R
200 199.0 N/A 1.7 5.2 4.7 14.5
400 421.8 N/A 4.8 7.3 13.3 20.5
800 828.0 N/A 8.9 19.5 25.0 54.6
TABLE 6 Vickers Hardness at 10 kgf Test Force (HV 10)
Repeatability Reproducibility
Test Block
Average Standard Deviation Standard Deviation Repeatability Limit Reproducibility Limit
Nominal Hardness
(HV) Bias (HV) (HV) (HV) (HV)
(HV)
¯
X % s s r R
r R
200 198.1 N/A 2.1 3.0 6.0 8.5
400 398.5 N/A 2.9 9.1 8.2 25.4
800 800.2 N/A 2.3 11.7 6.6 32.7
TABLE 7 Vickers Hardness at 20 kgf Test Force (HV 20)
Repeatability Rep
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E92 − 17 E92 − 23
Standard Test Methods for
Vickers Hardness and Knoop Hardness of Metallic
Materials
This standard is issued under the fixed designation E92; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 These test methods cover the determination of the Vickers hardness and Knoop hardness of metallic materials by the Vickers
and Knoop indentation hardness principles. This standard provides the requirements for Vickers and Knoop hardness machines and
the procedures for performing Vickers and Knoop hardness tests.
1.2 This standard includes additional requirements in annexes:
Verification of Vickers and Knoop Hardness Testing Machines Annex A1
Vickers and Knoop Hardness Standardizing Machines Annex A2
Standardization of Vickers and Knoop Indenters Annex A3
Standardization of Vickers and Knoop Hardness Test Blocks Annex A4
Correction Factors for Vickers Hardness Tests Made on Annex A5
Spherical and Cylindrical Surfaces
1.3 This standard includes nonmandatory information in an appendix which relates to the Vickers and Knoop hardness tests:
Examples of Procedures for Determining Vickers and Appendix X1
Knoop Hardness Uncertainty
-3
1.4 This test method covers Vickers hardness tests made utilizing test forces ranging from 9.807 × 10 N to 1176.80 N (1 gf to
-3
120 kgf), and Knoop hardness tests made utilizing test forces from 9.807 × 10 N to 19.613 N (1 gf to 2 kgf).
1.5 Additional information on the procedures and guidance when testing in the microindentation force range (forces ≤ 1 kgf) may
be found in Test Method E384, Test Method for Microindentation Hardness of Materials.
1.6 Units—When the Vickers and Knoop hardness tests were developed, the force levels were specified in units of grams-force
(gf) and kilograms-force (kgf). This standard specifies the units of force and length in the International System of Units (SI); that
is, force in Newtons (N) and length in mm or μm. However, because of the historical precedent and continued common usage, force
values in gf and kgf units are provided for information and much of the discussion in this standard as well as the method of
reporting the test results refers to these units.
These test methods are under the jurisdiction of ASTM Committee E28 on Mechanical Testing and is the direct responsibility of Subcommittee E28.06 on Indentation
Hardness Testing.
Current edition approved April 1, 2017July 1, 2023. Published May 2017August 2023. Originally approved in 1952. Last previous edition approved in 20162017 as
E92–16. DOI: 10.1520/E0092-17.–17. DOI: 10.1520/E0092-23.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E92 − 23
NOTE 1—The Vickers and Knoop hardness numbers were originally defined in terms of the test force in kilogram-force (kgf) and the surface area or
projected area in millimetres squared (mm ). Today, the hardness numbers are internationally defined in terms of SI units, that is, the test force in Newtons
(N). However, in practice, the most commonly used force units are kilogram-force (kgf) and gram-force (gf). When Newton units of force are used, the
force must be divided by the conversion factor 9.80665 N/kgf.
1.7 The test principles, testing procedures, and verification procedures are essentially identical for both the Vickers and Knoop
hardness tests. The significant differences between the two tests are the geometries of the respective indenters, the method of
calculation of the hardness numbers, and that Vickers hardness may be used at higher force levels than Knoop hardness.
NOTE 2—While Committee E28 is primarily concerned with metallic materials, the test procedures described are applicable to other materials. Other
materials may require special considerations, for example see C1326 and C1327 for ceramic testing.
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
1.9 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C1326 Test Method for Knoop Indentation Hardness of Advanced Ceramics
C1327 Test Method for Vickers Indentation Hardness of Advanced Ceramics
E3 Guide for Preparation of Metallographic Specimens
E6 Terminology Relating to Methods of Mechanical Testing
E7 Terminology Relating to Metallography
E29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
E74 Practices for Calibration and Verification for Force-Measuring Instruments
E140 Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness,
Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb Hardness
E175 Terminology of Microscopy (Withdrawn 2019)
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E384 Test Method for Microindentation Hardness of Materials
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
2.2 ISO Standards:
ISO 6507-1 Metallic Materials—Vickers hardness Test—Part 1: Test Method
ISO/IEC 17011 Conformity Assessment—General Requirements for Accreditation Bodies Accrediting Conformity Assessment
Bodies
ISO/IEC 17025 General Requirements for the Competence of Testing and Calibration Laboratories
3. Terminology and Equations
3.1 Definitions of Terms—For the standard definitions of terms used in this test method, see Terminology E6 and Terminology
E7.
3.1.1 indentation hardness, n—the hardness as evaluated from measurements of area or depth of the indentation made by forcing
a specified indenter into the surface of a material under specified static loading conditions.
3.1.2 Knoop hardness number, HK,n—the calculated result from a Knoop hardness test, which is proportional to the test force
applied to the Knoop indenter divided by the projected area of the permanent indentation made by the indenter after removal of
the test force.
3.1.2.1 Discussion—
The projected area of the permanent indentation made by the Knoop indenter is calculated based partly on the measured length
of the long diagonal of the projected area of the indentation.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
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3.1.3 Knoop hardness test, n—an indentation test in which a Knoop rhombic-based pyramidal diamond indenter having specified
edge angles, is forced under specified conditions into the surface of the test material, and, after removal of the test force, the length
of the long diagonal of the projected area of the indentation is measured to calculate the Knoop hardness number.
3.1.4 Vickers hardness number, HV,n—the calculated result from a Vickers hardness test, which is proportional to the test force
applied to the Vickers indenter divided by the surface area of the permanent indentation made by the indenter after removal of the
test force.
3.1.4.1 Discussion—
The surface area of the permanent indentation made by the Vickers indenter is calculated based partly on the measured mean length
of the two diagonals of the projected area of the indentation.
3.1.5 Vickers hardness test, n—an indentation test in which a Vickers square-based pyramidal diamond indenter having specified
face angles is forced under specified conditions into the surface of the test material, and, after removal of the test force, the lengths
of the two diagonals of the projected area of the indentation are measured to calculate the Vickers hardness number.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 standardization, n—to bring in conformance to a known standard through verification or calibration.
3.2.2 microindentation hardness test, n—a hardness test, normally in the Vickers or Knoop scales, using test forces in the range
-3
of 9.807 × 10 to 9.807 N (1 to 1000 gf).
3.2.3 macroindention hardness test, n—a hardness test using test forces normally higher than 9.807 N (1 kgf). Macroindentation
tests include Vickers, Rockwell and Brinell.
NOTE 3—Use of the term microhardness should be avoided because it implies that the hardness, rather than the force or the indentation size, is very low.
3.2.4 scale, n—a specific combination of indenter (Knoop or Vickers) and the test force (kgf).
3.2.4.1 Discussion—
For example, HV 10 is a scale defined as using a Vickers indenter and a 10 kgf test force and HK 0.1 is a scale defined as using
a Knoop indenter and a 100 gf test force. See 5.10 for the proper reporting of the hardness level and scale.
3.2.5 as-found condition, n—the state of the hardness machine as reflected by the initial verification measurements made prior to
performing any cleaning, maintenance, adjustments or repairs associated with an indirect verification.
3.2.6 hardness machine, n—a machine capable of performing a Vickers or Knoop hardness test.
3.2.7 hardness testing machine, n—a Vickers or Knoop hardness machine used for general testing purposes.
3.2.8 hardness standardizing machine, n—a Vickers or Knoop hardness machine used for the standardization of Vickers or Knoop
hardness test blocks.
3.2.8.1 Discussion—
A hardness standardizing machine differs from a hardness testing machine by having tighter tolerances on certain parameters.
3.3 Equations:
3.3.1 The average d¯ of a set of n diagonal length measurements d , d , …, d is calculated as:
1 2 n
d 1d 1…1d
1 2 n
¯
d 5 (1)
n
where each of the individual diagonal measurements d , d , …, d is the mean of the two diagonal length measurements in the
1 2 n
case of a Vickers indentation, or is the long diagonal length measurement in the case of a Knoop indentation.
3.3.2 The repeatability R in the performance of a Vickers or Knoop hardness machine at each hardness level, under the particular
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verification conditions, is determined from n diagonal measurements made on a standardized test block as part of a performance
verification. The repeatability is estimated as the percent range of n diagonal measurements with respect to the measured average
hardness value as:
d 2 d
max min
R 5 100 × (2)
S D
¯
d
where:
d = the longest diagonal length measurement made on the standardized test block,
max
d = the shortest diagonal length measurement made on the standardized test block, and
min
d¯ = the average (see 3.3.1) of the n diagonal length measurements made on the standardized test block.
3.3.3 The error E in the performance of a Vickers or Knoop hardness machine at each hardness level, relative to a standardized
reference value, is calculated as a percent error determined as:
¯
d 2 d
? ref?
E 5 100 ×S D (3)
d
ref
where:
d¯ = the average (see 3.3.1) of n diagonal length measurements made on a standardized test block as part of a performance
verification, and
d = the certified diagonal length reported for the standardized test block.
ref
¯ ¯
=
|d2d | absolute value (non-negative value without regard to its sign) of the difference between d and d .
ref ref
4. Significance and Use
4.1 Vickers and Knoop hardness tests have been found to be very useful for materials evaluation, quality control of manufacturing
processes and research and development efforts. Hardness, although empirical in nature, can be correlated to tensile strength for
many metals, and is an indicator of wear resistance and ductility.
4.2 Microindentation hardness tests extend testing to materials that are too thin or too small for macroindentation hardness tests.
Microindentation hardness tests also allow specific phases or constituents and regions or gradients too small for macroindentation
hardness testing to be evaluated. Recommendations for microindentation testing can be found in Test Method E384.
4.3 Because the Vickers and Knoop hardness will reveal hardness variations that may exist within a material, a single test value
may not be representative of the bulk hardness.
4.4 The Vickers indenter usually produces essentially the same hardness number at all test forces when testing homogeneous
material, except for tests using very low forces (below 25 gf) or for indentations with diagonals smaller than about 25 μm (see Test
Method E384). For isotropic materials, the two diagonals of a Vickers indentation are equal in length.
4.5 The Knoop indenter usually produces similar hardness numbers over a wide range of test forces, but the numbers tend to rise
as the test force is decreased. This rise in hardness number with lower test forces is often more significant when testing higher
hardness materials, and is increasingly more significant when using test forces below 50 gf (see Test Method E384).
4.6 The elongated four-sided rhombohedral shape of the Knoop indenter, where the length of the long diagonal is 7.114 times
greater than the short diagonal, produces narrower and shallower indentations than the square-based pyramid Vickers indenter
under identical test conditions. Hence, the Knoop hardness test is very useful for evaluating hardness gradients since Knoop
indentations can be made closer together than Vickers indentations by orienting the Knoop indentations with the short diagonals
in the direction of the hardness gradient.
5. Principle of Test and Apparatus
5.1 Vickers and Knoop Hardness Test Principle—The general principle of the Vickers and Knoop indentation hardness test consists
of two steps.
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5.1.1 Step 1—The applicable specified indenter is brought into contact with the test specimen in a direction normal to the surface,
and the test force F is applied. The test force is held for a specified dwell time and then removed.
5.1.2 Step 2—For the Vickers hardness test, the lengths of the two diagonals are measured and the mean diagonal length is
calculated, which is used to derive the Vickers hardness value. For the Knoop hardness test, the length of the long diagonal is
measured, which is used to derive the Knoop hardness value.
5.1.3 Most materials will exhibit some elastic recovery when the indenter is removed after the loading cycle. However, for the
purposes of calculating the hardness results from the indentation diagonal lengths, it is assumed that the indentation retains the
shape of the indenter after the force is removed. In Knoop testing, it is assumed that the ratio of the long diagonal to the short
diagonal of the indentation is the same as for the indenter.
5.2 Testing Machine—The testing machine shall support the test specimen and control the movement of the indenter into the
specimen under a preselected test force, and should have a light optical microscope to select the desired test location and to
measure the size of the indentation produced by the test. The plane of the surface of the test specimen should be perpendicular
to the axis of the indenter which is the direction of the force application.
5.2.1 See the equipment manufacturer’s instruction manual for a description of the machine’s characteristics, limitations, and
respective operating procedures.
5.3 Indenters:
5.3.1 Indenters for general Vickers or Knoop hardness testing shall comply with the requirements of a Class B indenter or better
in accordance with Annex A3.
5.3.2 Vickers Indenter—The ideal Vickers indenter (see Fig. A3.1) is a highly polished, pointed, square-based pyramidal diamond
with face angles of 136° 0’.
5.3.3 Knoop Indenter—The ideal Knoop indenter (see Fig. A3.2) is a highly polished, pointed, rhombic-based, pyramidal
diamond. The included longitudinal edge angles are 172° 30’ and 130° 0’.
NOTE 4—The user should consult with the manufacturer before applying macroindentation test forces (over 1 kgf) with diamond indenters previously used
for microindentation testing. The diamond mount may not be strong enough to support the higher test forces and the diamond may not be large enough
to produce the larger indentation sizes.
5.4 Measurement Device—The diagonals of the indentation are measured (see 7.9.2) using a light microscope equipped with a filar
type eyepiece (see Terminology E175), or other type of measuring device. Additional guidance on measuring devices may be found
in Test Method E384.
5.4.1 The testing machine’s measuring device shall be capable of reporting the diagonal lengths to within the requirements of
7.9.2.
5.4.2 The measuring device may be an integral part of the tester or a stand-alone instrument, such as a high quality measuring
microscope or measuring system. To obtain the highest quality image for measuring the indentation diagonal, the measuring
microscope should have adjustable illumination intensity, adjustable alignment, aperture, and field diaphragms.
5.4.3 Magnifications should be provided so that the diagonal can be enlarged to greater than 25 % but less than 75 % of the field
width. The device may be built with single or multiple magnifying objectives.
5.5 Verifications—All testing machines, indentation measuring devices and indenters used to perform Vickers and Knoop hardness
tests shall be verified periodically in accordance with Annex A1 prior to performing hardness tests.
5.6 Test Blocks—Test blocks meeting the requirements of Annex A4 shall be used to verify the testing machine in accordance with
Annex A1.
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5.7 Test Forces—The standard hardness test forces are given in Table 1. Other non-standard test forces may be used by special
agreement.
5.8 Calculation of the Vickers Hardness Number—The Vickers hardness number is based on the indentation test force F in kgf
divided by the surface area A of the indentation in mm .
S
F
Testforce
kgf
~ !
HV 5 5 (4)
SurfaceArea A 2
S~mm !
The surface area (A ) of the indentation is calculated as:
S
2 2
d d
V V
A 5 5 (5)
S
α 1.8544
2sin
where:
α = face angle of the diamond indenter = 136°, and
d = mean Vickers indentation diagonal length (mm).
V
Other units of force and length may be used; however, the reported Vickers hardness number shall be converted to the units of
kgf and mm, as follows and given in Table 2.
5.8.1 Microindentation Vickers hardness is typically determined using indentation test forces in grams-force (gf) and indentation
diagonals measured in micrometres (μm). The Vickers hardness number, in terms of gf and μm, is calculated as follows:
F F
gf gf
~ ! ~ !
HV 5 1000 ×1.8544 × 5 1854.4 × (6)
2 2
d d
V µm V µm
~ ! ~ !
5.8.2 Macroindentation Vickers hardness is typically determined using indentation test forces in kilograms-force (kgf) and
indentation diagonals measured in millimetres (mm). The Vickers hardness number, in terms of kgf and mm, is calculated as
follows:
F
kgf
~ !
HV 5 1.8544 × (7)
d
V~mm!
TABLE 1 Standard Hardness Scales and Test Forces
Approximate Approximate
Vickers Knoop Test force
Test force Test force
A
scale scale (N)
(kgf) (gf)
HV 0.001 HK 0.001 0.009807 0.001 1
HV 0.01 HK 0.01 0.09807 0.01 10
HV 0.015 HK 0.015 0.1471 0.015 15
HV 0.02 HK 0.02 0.1961 0.02 20
HV 0.025 HK 0.025 0.2451 0.025 25
HV 0.05 HK 0.05 0.4903 0.05 50
HV 0.1 HK 0.1 0.9807 0.1 100
HV 0.2 HK 0.2 1.961 0.2 200
HV 0.3 HK 0.3 2.942 0.3 300
HV 0.5 HK 0.5 4.903 0.5 500
HV 1 HK 1 9.807 1 1000
HV 2 HK 2 19.61 2 2000
HV 3 29.41 3
HV 5 49.03 5
HV 10 98.07 10
HV 20 196.1 20
HV 30 294.1 30
HV 50 490.3 50
HV 100 980.7 100
HV 120 1177 120
A
The user should consult with the manufacturer before applying macroindentation
test forces (over 1 kgf) for Knoop hardness testing. The diamond may not be large
enough to produce the larger indentation sizes (see Note 4).
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TABLE 2 Vickers and Knoop Formulae
Vickers hardness number
Force (F) unit Diagonal (d) unit Formula
kgf mm HV = 1.8544 × F/d
gf μm HV = 1854.4 × F/d
N mm HV = 0.1891 × F/d
Knoop hardness number
Force (F) unit Diagonal (d) unit Formula
kgf mm HK = 14.229 × F/d
gf μm HK = 14229 × F/d
N mm HK = 1.451 × F/d
5.8.3 The Vickers hardness number, in terms of indentation test forces in Newtons (N) and indentation diagonals measured in
millimetres (mm), is calculated as follows:
F F
1.8544
~N! ~N!
HV 5 × 5 0.1891 × (8)
2 2
9.80665 d d
V~mm! V~mm!
5.9 Calculation of the Knoop Hardness Number—The Knoop hardness number is based on the indentation test force (kgf) divided
by the projected area A of the indentation (mm ).
P
F
Testforce
~kgf!
HK 5 5 (9)
ProjectedArea A 2
P~mm !
The projected area (A ) of the indentation is calculated as:
P
A 5 d ×c (10)
P K P
where:
d = Knoop indentation long diagonal length (mm), and
K
c = indenter constant relating the projected area of the indentation to the square of the length of the long diagonal, ideally
P
0.07028, where:
/B
tan
c 5 5 0.07028 (11)
P
/A
2tan
where:
/A = the included longitudinal edge angle, 172° 30’, and
/B = included transverse edge angle, 130° 0’.
Other units of force and length may be used, however, the Knoop hardness number shall be converted to the units of kgf and
mm, as follows and as given in Table 2.
5.9.1 Knoop hardness is typically determined using indentation test forces in grams-force (gf) and indentation long diagonal
measured in micrometres (μm). The Knoop hardness number, in terms of gf and μm, is calculated as follows:
F F
~gf! ~gf!
HK 5 1000 ×14.229 × 5 14229 × (12)
2 2
d d
K µm K µm
~ ! ~ !
5.9.2 The Knoop hardness number, in terms of indentation test forces in kgf and the indentation long diagonal measured in mm,
is calculated as follows:
F
~kgf!
HK 5 14.229 × (13)
d
K mm
~ !
5.9.3 The Knoop hardness number, in terms of indentation test forces in Newtons (N) and the indentation long diagonal measured
in millimetres (mm), is calculated as follows:
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F F
14.229
N N
~ ! ~ !
HK 5 × 5 1.451 × (14)
2 2
9.80665 d d
K mm K mm
~ ! ~ !
5.10 Hardness Number—Vickers and Knoop hardness values are not designated by a number alone because it is necessary to
indicate which force has been employed in making the test. The hardness numbers shall be followed by the symbol HV for Vickers
hardness, or HK for Knoop hardness, and be supplemented by a value representing the test force in kgf.
5.10.1 For nonstandard dwell times, other than 1010 s to 15 s, the hardness shall be supplemented with the actual total force dwell
time used in seconds separated by a “/”.
5.10.2 The reported Vickers and Knoop hardness number shall be reported rounded to three significant digits in accordance with
Practice E29.
5.10.3 Examples:
400 HK 0.5 = Knoop hardness of 400 determined with a 500 gf (0.5 kgf)
indentation test force.
99.2 HV 0.1 = Vickers hardness of 99.2 determined with a 100 gf (0.1 kgf)
indentation test force.
725 HV 10 = Vickers hardness of 725 determined with a 10 kgf indentation
test force.
400 HK 0.1 /22. = Knoop hardness of 400 determined with a 100 gf (0.1 kgf)
indentation test force and a 22 s total force dwell time.
6. Test Piece
6.1 There is no standard shape or size for a Vickers or Knoop test specimen. The specimen on which the indentation is made
should conform to the following:
6.2 Preparation—For optimum accuracy of measurement, the test should be performed on a flat specimen with a polished or
otherwise suitably prepared surface. The quality of the required surface finish can vary with the forces and magnifications used.
The lower the test force and the smaller the indentation size, the more critical is the surface preparation. In all tests, the preparation
should be such that the indentation perimeter and the indentation tips in particular, can be clearly defined when observed by the
measuring system. Surface preparation recommendations for low-force microindentation testing can be found in Test Method
E384.
6.2.1 The test surface shall be free of any defects that could affect the indentation or the subsequent measurement of the diagonals.
It is well known that improper grinding and polishing methods can alter test results either due to excessive heating or cold work.
Some materials are more sensitive to preparation-induced damage than others; therefore, special precautions shall be taken during
specimen preparation. Remove any damage introduced during specimen preparation.
6.2.2 The specimen surface should not be etched before making an indentation. Etched surfaces can obscure the edge of the
indentation, making an accurate measurement of the size of the indentation difficult. There may be microindentation testing
applications where a light etch may be appropriate (see Test Method E384).
6.3 Alignment—To obtain usable information from the test, the specimen should be prepared or mounted so that the test surface
is perpendicular to the axis of the indenter. This can readily be accomplished by surface grinding (or otherwise machining) the
opposite side of the specimen parallel with the side to be tested. Non-parallel test specimens can be tested using clamping and
leveling fixtures designed to align the test surface properly to the indenter.
6.4 Mounted Test Specimens—In many instances, especially in microindentation testing, it is necessary to mount the specimen for
convenience in preparation and to maintain a sharp edge when surface gradient tests are to be performed on the test specimen.
When mounting is required, the specimen shall be adequately supported by the mounting medium so that the specimen does not
move during force application, that is, avoid the use of polymeric mounting compounds that creep under the indenter force (see
Test Method E384).
6.5 Thickness—The thickness of the specimen tested shall be such that no bulge or other marking showing the effect of the test
force appears on the side of the piece opposite the indentation. The thickness of the material under test should be at least ten times
E92 − 23
the depth of the indentation (see Note 5). Similarly, when testing a coating on a material, the minimum thickness of the coating
should be at least ten times the depth of the indentation.
NOTE 5—The Vickers indentation depth h is approximately
V
h 5 0.143 ×d (15)
V V
or approximately 1/7 of the mean diagonal length d . The Knoop indentation depth h is approximately
V K
h 5 0.033 ×d (16)
K K
or approximately 1/30 of the long diagonal length d .
K
6.6 Radius of Curvature—Due caution should be used in interpreting or accepting the results of tests made on spherical or
cylindrical surfaces, particularly when using low test forces. Results will be affected even in the case of the Knoop test where the
radius of curvature is in the direction of the short diagonal. Annex A5 provides correction factors that shall be applied to Vickers
hardness values obtained when tests are made on spherical or cylindrical surfaces. Additional requirements are specified in 9.3 and
9.4 when reporting corrected hardness values.
7. Test Procedure
7.1 Verification—A periodic verification procedure shall be performed in accordance with A1.5 within one week prior to making
hardness tests. The periodic verification should be performed on a daily basis.
7.2 Test Temperature—Vickers and Knoop hardness tests should be carried out at a temperature within the limits of 1010 °C to
35°C (50 to 95°F).(50 °F to 95 °F). Because variations within this temperature range may affect results, users may choose to
control temperature within a tighter range.
7.3 Indenter—Select the indenter, either Knoop or Vickers, to suit the desired test to be performed. Refer to the manufacturer’s
instruction manual for the proper procedure if it is necessary to change indenters.
7.3.1 After each change, or removal and replacement, of the indenter, it is recommended that a periodic verification be performed
as specified in A1.5.
7.3.2 Occasionally clean the indenter with a cotton swab and alcohol. Avoid creating static charges during cleaning. Indenting a
piece of paper placed on top of the test specimen will often remove oil from the indenter. Do not touch the diamond tip with fingers.
7.3.3 Indenters should be examined periodically and replaced if they become worn, dulled, chipped, cracked or separated from
the mounting material. Checks of the indenter by the user may be performed by visual inspection of the resulting indentations
performed on test blocks.
7.4 Magnitude of Test Force—Set the desired test force on the tester by following the manufacturer’s instructions.
7.4.1 After each change of a test force, it is recommended that the operation of the machine be checked by performing a periodic
verification as specified in A1.5, particularly for machines where the weights that create test forces are changed manually or there
is a chance of jamming occurring when weights are changed.
7.5 Positioning the Test Specimen—Place the test specimen in the appropriate fixture or on the tester stage so that the test surface
is perpendicular to the indenter axis.
7.6 Locate the Test Point—Focus the measuring microscope with a low power objective so that the specimen surface can be
observed. Adjust the light intensity and adjust the diaphragms for optimum resolution and contrast. Adjust the position of the test
specimen so that the indentation will be made in the desired location on the test surface. Before applying the force, make a final
focus using the measuring objective (see 7.9 and Table 3).
7.7 Force Application—Apply the selected test force as follows in a manner and in an environment that prevents shock or vibration
during the indenting process.
7.7.1 For microindentation testing, the indenter shall contact the specimen at a velocity between 15 μm/s and 70 μm/s. For
macroindentation testing, the contact velocity should not exceed 0.2 mm/s.
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7.7.2 The time from the initial application of the force until the full test force is reached shall not be more than 10 s.
7.7.3 The full test force shall be applied for 1010 s to 15 s unless otherwise specified.
7.7.4 For some applications it may be necessary to apply the test force for longer times. In these instances the tolerance for the
time of the applied force shall be 6 2 s. The application time shall be defined in the report.
7.7.5 Remove the test force without shock or vibration.
7.7.6 During the entire test cycle of force application and removal, the test machine should be protected from shock or vibration.
To minimize vibrations, the operator should avoid contacting the machine in any manner during the entire test cycle.
7.8 Test Location—After the force is removed, switch to the measuring mode, and select the proper objective lens. Focus the
image, adjust the light intensity if necessary, and adjust the diaphragms for maximum resolution and contrast.
7.8.1 Examine the indentation for its position relative to the desired location and for its symmetry.
7.8.2 If the indentation did not occur at the desired spot, the tester is out of alignment. Consult the manufacturer’s instruction
manual for the proper procedure to produce alignment. Make another indentation and recheck the indentation location. Readjust
and repeat as necessary.
7.9 Indentation Measurement—Measure both diagonals of a Vickers indentation or the long diagonal of a Knoop indentation by
operating the measuring device in accordance with the manufacturer’s instruction manual.
7.9.1 When the indentation measuring device is a light microscope that requires the full indentation to be seen and measured in
the field of view, the highest magnification that can image the full indentation shall be used. To stay within the flat field of the
objective, the indentation length should not exceed 75%75 % of the field width. The objective selected to measure the indentation
should have an objective resolution (r ) that is ≤ 2%2 % of the diagonal length to be measured. Objective resolution (r ) is a
obj obj
function of the numerical aperture (NA) of the objective, see Note 6. The minimum recommended diagonal lengths to be measured
by typical objectives are shown in Table 3.
NOTE 6—The objective’s resolution (r ) is defined as:
obj
r 5 λ⁄ 2 × NA (17)
~ !
obj
where:
λ = the wave length of the light in μm (approx. 0.55 μm for green light), and
NA = the numerical aperture of the objective as defined by the manufacturer. (The NA is frequently marked on the side of each objective.) Example:
For a 50× objective with a NA of 0.65 using green light, r = 0.55 μm / (2 × 0.65) = 0.42 μm.
obj
TABLE 3 Recommended Indentation Diagonal Lengths for
Commonly used Objectives and NA
Commonly used Typical NA Objective Recommended
Objective (will vary by Resolution Diagonal
A
Magnifications objective type) (r ) μm Lengths μm
obj
2.5× 0.07 3.93 196.5 or longer
5× 0.10 2.75 137.5 or longer
10× 0.25 1.10 55 or longer
20× 0.40 0.69 34.5 or longer
20× 0.45 0.61 30.5 or longer
40× 0.55 0.50 25 or longer
40x 0.65 0.42 21 or longer
50× 0.65 0.42 21 or longer
60× 0.70 0.39 19.5 or longer
100× 0.80 0.34 17 or longer
100× 0.95 0.29 14.5 or longer
A
This is the magnification of the objective and may not be the total magnification
of the system. Many systems have a 10× eyepiece that increases the total
magnification by a factor of 10 at the operator’s eye. This additional magnification
does not change the optical resolution (r ) or the recommended diagonal lengths.
obj
E92 − 23
7.9.2 Determine the length of the diagonals to within 0.5 μm or less. For indentations less than 40 μm, determine the length of
the diagonals to within 0.25 μm or less. For indentations less than 20 μm, the length of the diagonals should be determined to within
0.1 μm or less. In all cases, smaller measurement increments may be reported if the equipment is capable of displaying smaller
measurement increments.
7.10 Indentation Examination:
7.10.1 Vickers—For a Vickers indentation, if one half of either diagonal is more than 5 % longer than the other half of that
diagonal, or if the four corners of the indentation are not in sharp focus, the test surface may not be perpendicular to the indenter
axis. Check the specimen alignment as described in 7.10.3.
7.10.2 Knoop—For a Knoop indentation, if one half of the long diagonal is greater than 10 % longer than the other, or if both ends
of the indentation are not in sharp focus, the test specimen surface may not be perpendicular to the indenter axis. Check the
specimen alignment as given in 7.10.3.
7.10.3 If the diagonal legs are unequal by an amount greater than the limits defined in 7.10.1 or 7.10.2, rotate the specimen 90°
and make another indentation in an untested region. If the nonsymmetrical aspect of the indentations has rotated 90°, then the
specimen surface may not be perpendicular to the indenter axis and may yield incorrect hardness results. If the nonsymmetrical
nature of the indentation remains in the same orientation, check the indenter for damage or misalignment as described in 7.10.4.
7.10.4 The alignment of the indenter may be checked using a test specimen, such as a standardized test block, known to produce
uniformly shaped indentations. Confirm that the test block surface is perpendicular to the indenter axis as described in 7.10.3. Make
an indentation. If the indentation is not symmetrical, the indenter is misaligned, and the tester shall not be used until it meets the
requirements of sections 7.10.1 or 7.10.2.
7.10.5 Some materials may have nonsymmetrical indentations even if the indenter and the specimen surface are perfectly aligned.
Tests on single crystals or on textured materials may produce such results. When tests on these types of materials produce
nonsymmetrical indents exceeding the limits of 7.10.1 or 7.10.2, it should be noted on the test report.
7.10.6 Brittle materials such as ceramics may crack as a result of being indented. Specific details for testing ceramics are contained
in Test Methods C1326 and C1327.
7.11 Spacing of Indentations—Generally more than one indentation is made on a test specimen. It is necessary to ensure that the
spacing between indentations is large enough so that adjacent tests do not interfere with each other.
7.11.1 For most testing purposes, the minimum recommended spacing between separate tests, and minimum distance between an
indentation and the edge of the specimen are illustrated in Fig. 1.
7.11.2 For some applications, closer spacing of indentations than those shown in Fig. 1 may be desired. If closer indentation
spacing is used, it shall be the responsibility of the testing laboratory to verify the accuracy of the testing procedure.
FIG. 1 Minimum Recommended Spacing for Vickers and Knoop Indentations
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8. Conversion to Other Hardness Scales or Tensile Strength Values
8.1 There is no general method of accurately converting the Vickers or Knoop hardness numbers using one test force to hardness
numbers using a different test force, or to other types of hardness numbers, or to tensile strength values. Such conversions are, at
best, approximations and, therefore, should be avoided except for special cases where a reliable basis for the approximate
conversion has been obtained by comparison tests. For homogeneous materials and test forces ≥ 100 gf, microindentation Vickers
hardness numbers are in reasonable agreement with macroindentation Vickers hardness numbers. Refer to E140 for hardness
conversion tables for metals. Additional requirements are specified in 9.2 and 9.4 when reporting converted hardness values.
NOTE 7—E140 gives approximate hardness conversion values for specific materials such as steel, nickel and high-nickel alloys, cartridge brass, copper
alloys, alloyed white cast irons, and wrought aluminum products.
9. Report
9.1 Report the following information:
9.1.1 The results (see 5.10), the number of tests, and, where appropriate, the mean and standard deviation of the results,
9.1.2 Test force,
9.1.3 The total force application time if outside the limits of 1010 s to 15 s as defined in 7.7.3,
9.1.4 Any unusual conditions encountered during the test, and
9.1.5 The test temperature, when outside the recommended allowable range of 10°C to 35°C (50°F to 95°F).10 °C to 35 °C (50 °F
to 95 °F).
9.2 Reporting Converted Hardness Values—When reporting hardness values that have been converted from one type of hardness
test or hardness scale to another type of hardness test or hardness scale, the original measurement number and test scale shall also
be reported (see E140).
9.2.1 A common historical practice is to report the converted hardness value followed by the measured hardness value given in
parentheses. For example: 353 HBW (372 HV), where 353 HBW is the converted hardness value and 372 HV is the original
measurement value.
9.2.2 Other formats for reporting converted hardness values, such as data tables, may be used, however, the original measurement
number and test scale shall also be reported and clearly identified.
9.3 Reporting Curvature Corrected Hardness Values—When reporting Vickers or Knoop hardness test values that have been
corrected for testing on cylindrical or spherical surfaces (see 6.6), the following information shall be indicated in the test report
or documented in the test lab/customer contract or agreement:
–the test values are corrected due to testing on a curved surface,
–the source of correction value, if other than the correction tables given in Annex A5 for convex cylindrical surfaces.
9.4 Since all converted or curvature-corrected hardness values are considered approximate, the reported hardness values shall be
rounded in accordance with the Rounding Method of Practice E29 and should have no more significant digits than is given for the
data in the applicable conversion or correction table.
10. Precision and Bias
10.1 Four separate interlaboratory studies have been conducted in accordance with Practice E691 to determine the precision,
repeatability, and reproducibility of this test method. The four studies are defined as follows:
(1) Vickers and Knoop tests, six test forces in the microindentation range, twelve laboratories, manual measurements, seven
different hardness level test specimens. See Test Method E384.
(2) Vickers and Knoop tests, two test forces in the microindentation range, seven laboratories, image-analysis and manual
measurements, four different hardness level test specimens. See Test Method E384.
(3) Vickers and Knoop tests, six test forces in the micro range, twenty-five laboratories, manual measurements, six different
hardness level test specimens. See Test Method E384.
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(4) Vickers tests, four test forces in the macro range, seven laboratories, manual measurements, three different hardness level
test specimens. See 10.3.
10.2 Studies 1 through 3—The results and discussion of Studies 1 through 3 are given in Test Method E384.
10.3 Study 4—The macroindentation Vickers precision statement is based on an interlaboratory study of Test Methods E92,
Standard Test Method for Vickers Hardness of Metallic Materials, conducted in 2001. Seven laboratories tested three different
standard hardness test blocks using macro range test forces of 1, 5, 10, and 20 kgf. Only four laboratories were also able to provide
results at 50 kgf test force. Every “test result” represents an individual determination of the Vickers hardness of the material. Each
laboratory was asked to report triplicate test results in order to permit the estimation of intralaboratory precision. Practice E691
was followed for the design and analysis of the data; the details are given in ASTM Research Report No. RR: E04-1007.
10.3.1 The precision statement was determined through statistical examination of 288 results, from seven laboratories, on three
test blocks. The materials were described as the following:
Material 1: 200 HV
Material 2: 400 HV
Material 3: 800 HV
10.3.2 Repeatability and reproducibility limits are listed in Tables 4-8.
10.3.3 The above terms (repeatability limit and reproducibility limit) are used as specified in Practice E177.
10.4 Bias—There is no recognized standard by which to estimate the bias of this test method.
11. Keywords
11.1 hardness; indentation; Knoop; macroindentation; microindentation; Vickers
TABLE 4 Vickers Hardness at 1 kgf Test Force (HV 1)
Repeatability Reproducibility
Test Block
Average Standard Deviation Standard Deviation Repeatability Limit Reproducibility Limit
Nominal Hardness
(HV) Bias (HV) (HV) (HV) (HV)
(HV)
X¯ % s s r R
r R
200 209.2 N/A 4.1 7.1 11.5 19.9
400 413.8 N/A 8.1 15.6 22.8 43.7
800 812.9 N/A 21.8 21.8 61.1 61.1
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:E04-1007. Contact ASTM Customer
Service at [e-mail].
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TABLE 5 Vickers Hardness at 5 kgf Test Force (HV 5)
Repeatability Reproducibility
Test Block
Average Standard Deviation Standard Deviation Repeatability Limit Reproducibility Limit
Nominal Hardness
(HV) Bias (HV) (HV) (HV) (HV)
(HV)
X¯ % s s r R
r R
200 199.0 N/A 1.7 5.2 4.7 14.5
400 421.8 N/A 4.8 7.3 13.3 20.5
800 828.0 N/A 8.9 19.5 25.0 54.
...