ASTM E3246-22

Standard Test Methods for Differential Indentation Depth Hardness of Metallic Materials

SIGNIFICANCE AND USE
4.1 The Differential Indentation Depth hardness test is an empirical indentation hardness test that can provide useful information about metallic materials. This information can correlate to tensile strength, wear resistance, ductility, and other physical characteristics of metallic materials, and can be useful in quality control and selection of materials.  
4.2 Differential Indentation Depth hardness tests are considered satisfactory for acceptance testing of commercial shipments, and have been used in industry for this purpose.  
4.3 Differential Indentation Depth hardness testing at a specific location on a part might not represent the physical characteristics of the whole part or end product. Machines that comply with this Standard are used when machines that comply with the regular hardness standards such as Test Methods E10, E18, E92, and E384 cannot be used. Test results obtained with these machines are comparable BUT NOT EQUIVALENT to those obtained with machines that comply with the above mentioned standards.  
4.4 Differential Indentation Depth hardness testing machines covered by this standard do not comply with Test Methods E10, E18, E92, or E110.
SCOPE
1.1 This test method covers the determination of the Differential Indentation Depth hardness of metallic materials by the Differential Indentation Depth hardness principle. This standard provides the requirements for Differential Indentation Depth hardness testing machines and the procedures for performing Differential Indentation Depth hardness tests.  
1.2 This standard includes additional requirements in annexes:    
Verification of Differential Indentation Depth Hardness Testing Machines  
Annex A1  
Guidelines for Determining the Minimum Thickness of a Test Piece  
Annex A2  
1.3 This standard includes non-mandatory information in appendixes which relates to the Differential Indentation Depth hardness test.    
List of ASTM Standards Giving Hardness Numbers Corresponding to Tensile Strength  
Appendix X1  
Examples of Procedures for Determining Differential Indentation Depth Hardness Uncertainty  
Appendix X2  
Examples of Indenters Used in Differential Indentation Depth Machines  
Appendix X3  
1.4 Units—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 micrometers (µm). However, because of continued common usage, values are provided in other units of measure for information.  
1.5 The test principles, testing procedures, and verification procedures are essentially identical for all the Differential Indentation Depth hardness testing instruments. The testing instruments may use different test forces and indenter shapes. The type and size of the indenters are matched to the design of the instrument by the manufacturer. Accordingly, the indenters, probes and other instrument components are generally not interchangeable among manufacturers.  
1.6 The hardness number reported by these instruments are based on direct correlations to existing hardness scales as determined by each manufacturer for each instrument and hardness scale. Unless otherwise noted on the instrument or in the operating manual for the instrument, the hardness numbers reported by the instrument are only applicable to non-austenitic steels. See 5.6.1 for additional information.  
1.7 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.8 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 Organizati...

General Information

• Status: Published
• Publication Date: 31-Mar-2022
• ICS: 77.040.10 - Mechanical testing of metals
• Technical Committee: E28 - Mechanical Testing
• Drafting Committee: E28.06 - Indentation Hardness Testing

Relations

• Refers: ASTM A370-24 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Mar-2024
• Refers: ASTM A370-19 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Jul-2019
• Refers: ASTM E18-18 - Standard Test Methods for Rockwell Hardness of Metallic Materials
• Effective Date: 01-Jul-2018
• Refers: ASTM A370-17a - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-Nov-2017
• Refers: ASTM E18-17 - Standard Test Methods for Rockwell Hardness of Metallic Materials
• Effective Date: 01-Jul-2017
• Refers: ASTM A370-17 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Jan-2017
• Refers: ASTM A370-15 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Nov-2015
• Refers: ASTM A370-14 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-May-2014
• Refers: ASTM E10-14 - Standard Test Method for Brinell Hardness of Metallic Materials
• Effective Date: 01-May-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 A370-13 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-Nov-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 E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM E18-12 - Standard Test Methods for Rockwell Hardness of Metallic Materials
• Effective Date: 01-Dec-2012
• Refers: ASTM A370-12a - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-Oct-2012

Overview

ASTM E3246-22: Standard Test Methods for Differential Indentation Depth Hardness of Metallic Materials defines empirical test methods for determining the Differential Indentation Depth (DID) hardness of metallic materials. This standard specifies requirements for DID hardness testing machines and outlines procedures for performing and verifying these tests, offering valuable data correlated to key mechanical properties like tensile strength, wear resistance, and ductility. The DID method is particularly relevant when conventional indentation hardness tests (such as Brinell, Rockwell, or Vickers) cannot be applied.

Key Topics

• Purpose and Scope

  • Covers the determination of hardness in metallic materials using the DID principle.
  • Defines equipment requirements and operating procedures.
  • Sets guidelines for machine verification and specifies supporting annexes and appendices for specialized needs.

• Test Principle

  • Utilizes a verified machine to apply a specified sequence of forces to an indenter, measuring the difference in indentation depth between two force steps.
  • The DID hardness number is derived from this depth difference, calibrated to existing recognized hardness scales.

• Applicability

  • Suitable for acceptance testing in commercial shipment and industrial quality control.
  • Used when standard methods (ASTM E10, E18, E92, E384) are not feasible.
  • Results are comparable but not equivalent to standard hardness test outcomes.

• Reporting and Verification

  • Results must indicate the DID method and specific scale used.
  • Routine and periodic machine verification are required to ensure test reliability.
  • Test data must be reported in accordance with ASTM guidelines, including ambient testing conditions, equipment used, and operator identification.

• Limitations

  • Recommended for non-austenitic steels unless otherwise specified.
  • Individual test locations may not represent overall part properties.
  • DID test machine components are typically manufacturer-specific and incompatible between brands.

Applications

The Differential Indentation Depth hardness method is valuable in situations such as:

• Material Selection: Rapidly comparing mechanical properties of metal samples for selection or development.
• Quality Control: Efficient screening of batches to verify hardness consistency and compliance.
• Acceptance Testing: Assessing product shipments where standard hardness methods cannot be applied due to sample geometry or size.
• Field Testing: Utilizing portable hardness testers for in-situ measurements on-site, particularly when a non-destructive and quick hardness check is necessary.
• Testing Non-Standard Shapes: Evaluating components with unconventional shapes, surface conditions, or thin sections, provided machine-specific guidelines are followed.

Related Standards

Testing according to ASTM E3246-22 is closely linked to several international and industry standards, including:

• ASTM E10: Brinell Hardness of Metallic Materials
• ASTM E18: Rockwell Hardness of Metallic Materials
• ASTM E92: Vickers Hardness of Metallic Materials
• ASTM E384: Microindentation Hardness
• ASTM E140: Hardness Conversion Tables for Metals
• ISO 18265: Conversion of Hardness Values
• SAE J417: Hardness Tests and Hardness Number Conversions
• ISO/IEC 17025: General Requirements for Competence of Testing Laboratories

Practical Value

ASTM E3246-22 provides a robust empirical method for hardness testing when conventional approaches are impractical, ensuring manufacturers and quality control personnel can reliably assess critical material properties. Its procedures ensure standardized, repeatable results, making it a key tool for supporting material certification, process control, and regulatory compliance in modern manufacturing and metalworking environments.

Keywords

Differential Indentation Depth, hardness testing, metallic materials, ASTM E3246-22, quality control, mechanical properties, verification, portable hardness tester, non-destructive testing, standards compliance

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: E3246 − 22
Standard Test Methods for
Differential Indentation Depth Hardness of Metallic
Materials
This standard is issued under the fixed designation E3246; 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.
1. Scope* 1.6 The hardness number reported by these instruments are
based on direct correlations to existing hardness scales as
1.1 This test method covers the determination of the Differ-
determined by each manufacturer for each instrument and
ential Indentation Depth hardness of metallic materials by the
hardness scale. Unless otherwise noted on the instrument or in
Differential Indentation Depth hardness principle. This stan-
the operating manual for the instrument, the hardness numbers
dard provides the requirements for Differential Indentation
reported by the instrument are only applicable to non-austenitic
Depth hardness testing machines and the procedures for
steels. See 5.6.1 for additional information.
performing Differential Indentation Depth hardness tests.
1.7 This standard does not purport to address all of the
1.2 This standard includes additional requirements in an-
safety concerns, if any, associated with its use. It is the
nexes:
responsibility of the user of this standard to establish appro-
Verification of Differential Indentation Depth Annex A1
priate safety, health, and environmental practices and deter-
Hardness Testing Machines
mine the applicability of regulatory limitations prior to use.
Guidelines for Determining the Minimum Thickness Annex A2
of a Test Piece
1.8 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.3 This standard includes non-mandatory information in
ization established in the Decision on Principles for the
appendixes which relates to the Differential Indentation Depth
Development of International Standards, Guides and Recom-
hardness test.
mendations issued by the World Trade Organization Technical
List of ASTM Standards Giving Hardness Numbers Appendix X1
Barriers to Trade (TBT) Committee.
Corresponding to Tensile Strength
Examples of Procedures for Determining Appendix X2
Differential Indentation Depth Hardness
2. Referenced Documents
Uncertainty
Examples of Indenters Used in Differential Appendix X3
2.1 ASTM Standards:
Indentation Depth Machines
A370 Test Methods and Definitions for Mechanical Testing
1.4 Units—This standard specifies the units of force and
of Steel Products
length in the International System of Units (SI); that is, force in
E6 Terminology Relating to Methods of Mechanical Testing
Newtons (N) and length in micrometers (μm). However,
E10 Test Method for Brinell Hardness of Metallic Materials
because of continued common usage, values are provided in
E18 Test Methods for Rockwell Hardness of Metallic Ma-
other units of measure for information.
terials
E29 Practice for Using Significant Digits in Test Data to
1.5 The test principles, testing procedures, and verification
Determine Conformance with Specifications
procedures are essentially identical for all the Differential
E92 Test Methods for Vickers Hardness and Knoop Hard-
Indentation Depth hardness testing instruments. The testing
ness of Metallic Materials
instruments may use different test forces and indenter shapes.
E110 Test Method for Rockwell and Brinell Hardness of
The type and size of the indenters are matched to the design of
Metallic Materials by Portable Hardness Testers
the instrument by the manufacturer. Accordingly, the indenters,
E140 Hardness Conversion Tables for Metals Relationship
probes and other instrument components are generally not
Among Brinell Hardness, Vickers Hardness, Rockwell
interchangeable among manufacturers.
Hardness, Superficial Hardness, Knoop Hardness, Sclero-
scope Hardness, and Leeb Hardness
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 April 1, 2022. Published May 2022. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2021 as E3246–21. Last previous edition approved in 2021 as Standards volume information, refer to the standard’s Document Summary page on
E3246–21. DOI: 10.1520/E3246–22 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
E3246 − 22
E177 Practice for Use of the Terms Precision and Bias in 3.2.2 The error, E, in the performance of a Differential
ASTM Test Methods Indentation Depth hardness testing machine at each hardness
E384 Test Method for Microindentation Hardness of Mate- level, relative to a standardized scale, is determined as:
rials
¯
E 5 H 2 H (2)
STD
E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method where:
2.2 ISO Standards:
¯
H = average of n hardness measurements H , H , …, H
1 2 n
ISO 18265 Metallic Materials—Conversion of Hardness
made on a reference standard as part of a perfor-
Values
mance verification, and
ISO/IEC 17011 Conformity Assessment—General Require-
H = certified average hardness number of the reference
STD
ments for Accreditation Bodies Accrediting Conformity
standard.
Assessment Bodies
3.2.3 The range, R, in the performance of a Differential
ISO/IEC 17025 General Requirements for the Competence
Indentation Depth hardness testing machine at each hardness
of Testing and Calibration Laboratories
level, under the particular verification conditions, is estimated
2.3 Society of Automotive Engineers (SAE) Standard:
by the range of n hardness measurements made on a reference
SAE J417 Hardness Tests and Hardness Number Conver-
standard as part of a performance verification, defined as:
sions
R 5 H 2 H (3)
max min
3. Terminology and Equations
where:
3.1 Definitions:
H = highest hardness number, and
max
3.1.1 differential indentation depth hardness test, n—an
H = lowest hardness number.
min
indentation hardness test using a verified hardness testing
3.2.4 The repeatability, r, in the performance of a Differen-
machine to force a truncated diamond cone indenter, diamond
tial Indentation Depth hardness testing machine at each hard-
spheroconical indenter or tungsten carbide ball indenter, under
ness level, under the particular verification conditions, is
specified conditions, into the surface of the material under test,
estimated by the range of n hardness measurements made on a
and to measure the difference in depth of the indentation as the
reference standard as part of a performance verification divided
force on the indenter is increased from a specified preliminary
by the mean of the measurements, defined as:
test force to a specified total test force and then returned to the
preliminary test force.
H 2 H
max min
r 5 × 100 where r is in % (4)
S D
¯
3.1.2 differential indentation depth hardness number, n—a
H
number derived from the net increase in the depth of indenta-
3.2.5 The relative error, E , in the performance of a
R
tion as the force on an indenter is increased from a specified
Differential Indentation Depth hardness testing machine at
preliminary test force to a specified total test force and then
each hardness level, relative to a standardized reference value,
returned to the preliminary test force.
is calculated as an absolute percent relative error determined
3.1.3 differential indentation depth hardness testing
as:
machine, n—a machine capable of performing a Differential
H 2 H
STD
Indentation Depth hardness test and displaying the resulting
E 5 100 × (5)
U S DU
R
H
STD
hardness number.
4. Significance and Use
3.1.4 The definitions of Brinell hardness scale, Brinell
hardness number, calibration, direct verification, expanded
4.1 The Differential Indentation Depth hardness test is an
uncertainty, ductility, force, hardness, indentation hardness,
empirical indentation hardness test that can provide useful
indirect verification, load, reference standard, resolution, Rock-
information about metallic materials. This information can
well hardness number, standardization, stress, tensile strength,
correlate to tensile strength, wear resistance, ductility, and
testing machine, and verification are used as defined in
other physical characteristics of metallic materials, and can be
Terminology E6.
useful in quality control and selection of materials.
3.2 Equations—The Differential Indentation Depth hardness
4.2 Differential Indentation Depth hardness tests are consid-
number is a calculated number, which, by method of
ered satisfactory for acceptance testing of commercial
calculation, correlates to the hardness in the scale that it is
shipments, and have been used in industry for this purpose.
being converted to.
¯
4.3 Differential Indentation Depth hardness testing at a
3.2.1 The average, H, of a set of n hardness measurements
H , H , …, H is calculated as: specific location on a part might not represent the physical
1 2 n
characteristics of the whole part or end product. Machines that
H 1H 1…1H
1 2 n
¯
H 5 (1)
comply with this Standard are used when machines that
n
comply with the regular hardness standards such as Test
Methods E10, E18, E92, and E384 cannot be used. Test results
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
obtained with these machines are comparable BUT NOT
4th Floor, New York, NY 10036, http://www.ansi.org.
EQUIVALENT to those obtained with machines that comply
Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale,
PA 15096, http://www.sae.org. with the above mentioned standards.
E3246 − 22
4.4 Differential Indentation Depth hardness testing ma- 5.1.3 Indenters for the Differential Indentation Depth hard-
chines covered by this standard do not comply with Test ness test include a truncated diamond cone indenter, diamond
Methods E10, E18, E92, or E110. spheroconical indenter, and tungsten carbide ball indenter of
specified diameter.
5. Principles of Test and Apparatus
5.2 Calculation of the Differential Indentation Depth Hard-
5.1 Differential Indentation Depth Hardness Test
ness Number—During a Differential Indentation Depth hard-
Principle—The general principle of the Differential Indentation
ness test, the force on the indenter is increased from a
Depth hardness test is illustrated in Fig. 1. The test is divided
preliminary test force to a total test force, and then returned to
into three steps of force application and removal.
the preliminary test force. The difference in the two indentation
Step 1—The indenter is brought into contact with the test
depth measurements, while under the preliminary test force, is
specimen, and the preliminary test force is applied. The
measured as h (see Fig. 1).
baseline depth measurement (baseline depth of indentation) at
5.2.1 The unit measurement for h is μm. From the value of
the point where the preliminary test force, F , is achieved is
h, the differential hardness number is derived. The reported
noted as the zero set point for depth measurement.
hardness number is calculated by the instrument from the
Step 2—The force on the indenter is increased by the
differential indentation depth hardness number according to
additional test force, F , to achieve the total test force, F. The
calibration curves specific to the machine as designed by the
total test force is held for a specified dwell time. The hardness
manufacturer.
testing machine limits the total test force to the device-specific
5.2.2 The Differential Indentation Depth hardness number is
value.
an arbitrary number, which, by method of calculation, results in
Step 3—The additional test force is removed, returning to the
a higher number for harder material. The Differential Indenta-
preliminary test force. At the point where the preliminary test
tion Depth hardness number is converted to a hardness number
force, F , is achieved, the final depth of indentation is
from commonly used hardness scales.
measured. The Differential Indentation Depth hardness number
5.2.3 Differential Indentation Depth hardness numbers shall
is derived from the difference, h, in the final and baseline
not be designated by a number alone because it is necessary to
indentation depths while under the preliminary test force. The
indicate which scale is displayed by the instrument.
preliminary test force is removed and the indenter is removed
5.2.3.1 Examples:
from the test specimen.
64 HRC(DID) = Rockwell hardness number of 64 on Rockwell C scale
5.1.1 There are several designs of the Differential Indenta-
332 HBW(DID) = Brinell hardness number of 332
72 HRBW(DID) = Rockwell hardness number of 72 on the Rockwell B scale
tion Depth hardness testing machine. Indenters and probes are
generally not interchangeable between machines of different 5.2.4 A reported Differential Indentation Depth hardness
number or the average value of Differential Indentation Depth
design.
5.1.2 For the Differential Indentation Depth hardness test, hardness measurements shall be rounded in accordance with
Practice E29 with a resolution no greater than the resolution of
the preliminary test forces range between 10N and 100N and
the total test forces range between 50N and 1000N and are the hardness number display of the testing machine.
specified by the manufacturers. The preliminary force used is 5.2.4.1 When the Differential Indentation Depth hardness
approximately 20 % of the value of the total test force used. test is used for the acceptance testing of commercial products
FIG. 1 Differential Indentation Depth Hardness Test Method (Schematic Diagram)
E3246 − 22
and materials, the user should take into account the potential reported hardness number on the specific material to be tested.
measurement differences between hardness testing machines Verification should be performed according to A1.4.
(see Section 10, Precision and Bias).
5.7 Reference Standards—Reference standards meeting the
requirements of Test Methods E10, E18, or E92, or combina-
NOTE 1—Because of the allowable ranges in the tolerances for the range
and error of a hardness testing machine, as specified in the verification tions thereof shall be used to verify the testing machine.
requirements of Annex A1, it is possible for one hardness testing machine
NOTE 3—Reference standards certified to revision Test Methods E18-07
to have a test result that is one or more hardness points different than
or later meet the requirements of this standard.
another hardness testing machine, yet both hardness testing machines can
NOTE 4—Appropriate reference standards are not available for all
be within verification tolerances (see Table A1.3). Commonly, for accep-
geometric shapes, or materials, or both.
tance testing, hardness numbers are rounded to whole numbers following
Practice E29. Users are encouraged to address rounding practices with
6. Test Piece
regards to acceptance testing within their quality management system, and
make any special requirements known during contract review.
6.1 For best results, both surfaces of the test piece should be
5.3 Differential Indentation Depth Testing Machine—The smooth, even and free from oxide scale, foreign matter, and
Differential Indentation Depth testing machine shall make lubricants. An exception is made for certain materials such as
hardness determinations by applying the test forces and mea- reactive metals that might adhere to the indenter. In such
suring the depth of indentation in accordance with the Differ- situations, a suitable lubricant such as kerosene may be used.
The use of a lubricant shall be defined on the test report.
ential Indentation Depth hardness test principle.
5.3.1 See the Equipment Manufacturer’s Instruction Manual
6.2 Preparation shall be carried out in such a way that any
for a description of the machine’s characteristics, limitations,
alteration of the surface hardness of the test surface (for
and respective operating procedures.
example, due to heat or cold-working) is minimized.
5.3.2 The Differential Indentation Depth testing machine
6.3 The thickness of the test piece or of the layer under test
shall automatically convert the depth measurements to a
should be as defined in tables in Annex A2. These tables were
hardness number and indicate the hardness number and scale
determined from studies conducted by the manufacturers and
by an electronic device or by a mechanical indicator.
have proven to give reliable results. For all other materials, the
5.4 Indenters—The standard Differential Indentation Depth
thickness of the test piece should exceed 10 times the depth of
indenters are diamond spheroconical indenters, truncated dia-
indentation. In general, no deformation should be visible on the
mond cone indenters or tungsten carbide balls. Indenter char-
back of the test piece after the test, although not all such
acteristics are specified by the manufacturers.
marking is indicative of a bad test.
5.4.1 Dust, dirt, or other foreign materials shall not be 6.3.1 Special consideration should be made when testing
allowed to accumulate on the indenter, as this will affect the
parts that exhibit hardness gradients; for example, parts that
test results. were case-hardened by processes such as carburizing,
carbonitriding, nitriding, induction, etc. The minimum thick-
5.5 Specimen Support—A specimen support shall be used
ness guidelines given in Annex A2 only apply to materials of
when necessary for supporting the specimen to be tested. It is
uniform hardness, and should not be used to determine the
necessary to support the specimen when the specimen stiffness
appropriate use for measuring parts with hardness gradients.
is such that the specimen will flex under the test loads.
The selection of an appropriate instrument for parts with
5.5.1 Flat pieces should be tested on a flat support that has
hardness gradients should be made by special agreement.
a smooth, flat bearing surface whose plane is perpendicular to
6.4 When testing on convex cylindrical and spherical
the axis of the indenter.
surfaces, the result might not accurately indicate the true
5.5.2 Small diameter cylindrical pieces shall be tested with
hardness; therefore, the corrections given for the instrument by
a hard V-grooved support with the axis of the V-groove directly
the manufacturer shall be applied.
under the indenter, or on hard, parallel, twin cylinders properly
6.4.1 Concave surfaces may be able to be tested with the
positioned and clamped in their base. These types of specimen
Differential Indentation Depth method if the machine manu-
supports shall support the specimen with the apex of the
facturer specifies suitability of the specific Differential Depth
cylinder directly under the indenter.
hardness testing machine to test conditions. Do not test on
5.5.3 Special supports or fixtures, including clamping
concave surfaces if the manufacturer does not specify suitabil-
fixtures, may be used for testing pieces or parts that cannot be
ity of the Differential Indentation Depth hardness testing
supported by standard supports.
machine for testing on concave surfaces.
NOTE 2—Not all reference standards will have parallel surfaces that are
6.5 When testing small diameter specimens, the accuracy of
supported by standard supports. Reference standards with non-parallel or
the test will be seriously affected by alignment between the
non-flat surfaces are examples of reference standards that can require a
special support or fixture.
indenter and the test piece, by surface finish, and, if the
specimen is cylindrical, by the straightness of the cylinder.
5.6 Verification—Differential Indentation Depth hardness
testing machines shall be verified periodically in accordance
7. Test Procedure
with Annex A1.
5.6.1 Because the reported values are correlations to exist- 7.1 Perform a daily verification of the Differential Indenta-
ing hardness scales, the user should verify the accuracy of the tion Depth hardness testing machine in accordance with A1.4
E3246 − 22
prior to making hardness tests. Hardness measurements shall 7.5.5 Maintain the total force, F, for the total force dwell
be made only on the calibrated surface of the reference time specified by the manufacturer.
standard.
7.5.6 Remove the additional test force, F , and allow the
instrument to cycle through the preliminary test force, F , then
7.2 Differential Indentation Depth hardness tests should be
carried out at ambient temperature within the limits of 10 °C to measure the depth of penetration. This is the final depth
35 °C (50 °F to 95 °F). Users of the Differential Indentation measurement.
Depth hardness test are cautioned that the temperature of the
7.5.7 The testing machine shall calculate the difference
test material and the temperature of the hardness tester can
between the final and baseline depth measurements and indi-
affect test results. Consequently, users should ensure that the
cate the resulting hardness number. The hardness number is
test temperature does not adversely affect the hardness mea-
derived from the differential increase in depth of indentation.
surement.
7.6 Throughout the test, protect the apparatus from shock or
7.3 Support the test piece rigidly so that displacement of the
vibration that could affect the hardness measurement result.
test surface is minimized (see 5.5).
7.7 After each removal and replacement of the indenter, the
7.4 Test Cycle—Use the manufacturer’s procedure to control
operation of the machine should be checked in accordance with
the test cycle. The test cycle to be used with the hardness
the daily verification method specified in Annex A1.
testing machine should match, as closely as possible, the test
cycle used for the indirect verification of the hardness testing
7.8 Maintain a distance of at least three times the diameter,
machine.
d, of the indentation (see Fig. 2) between the centers of two
NOTE 5—Varying the values of the testing cycle parameters can produce
adjacent indentations.
different hardness results.
7.8.1 The distance from the center of any indentation to an
7.5 Test Procedure—There are many designs of Differential
edge of the test piece shall be at least two and a half times the
Indentation Depth hardness testing machines, requiring various
diameter of the indentation (see Fig. 2).
levels of operator control. Some hardness testing machines can
perform the Differential Indentation Depth hardness test pro-
NOTE 6—Indentation Spacing—The hardness of the material immedi-
cedure automatically with almost no operator influence, while
ately surrounding a previously made indentation will usually increase due
other machines require the operator to control most of the test
to the induced residual stress and work-hardening caused by the indenta-
tion process. If a new indentation is made in this affected material, the
procedure.
measured hardness number will likely be higher than the true hardness of
7.5.1 Bring the indenter into contact with the test surface in
the material as a whole. Also, if an indentation is made too close to the
a direction perpendicular to the surface and, if possible, at a
edge of the material or very close to a previously made indentation, there
velocity within the maximum contact velocity as recommended
might be insufficient material to constrain the deformation zone surround-
by the instrument manufacturer.
ing the indentation. This can result in an apparent lowering of the hardness
7.5.2 Apply the preliminary test force, F . number. Both of these circumstances can be avoided by allowing
appropriate spacing between indentations and from the edge of the
7.5.3 Maintain the preliminary force for the preliminary
material.
force dwell time specified by the manufacturer, then measure
the depth of penetration. This is the baseline depth measure-
7.9 Number of Measurements—One measurement shall con-
ment.
stitute a test.
7.5.4 Increase the force by the value of the additional test
NOTE 7—While one measurement constitutes a test, the average of
force, F , needed to obtain the required total test force, F. The
1 multiple measurements can provide the user with a more accurate
additional force, F , shall be applied in a controlled manner. indication of the hardness of the test location.
FIG. 2 Schematic of Minimum Indentation Spacing
E3246 − 22
8. Conversion to Other Hardness Scales or Tensile 10. Precision and Bias
Strength Values
10.1 The precision of this test method is based on an
8.1 The design of the Differential Indentation Depth hard- intralaboratory study of ASTM E3246 – Standard Test Method
ness testing machine is such that the hardness number is for Differential Indentation Depth Hardness of Metallic
directly calculated from the measured differential indentation Materials, conducted in 2018. A single laboratory participated
depth for one or more hardness scales. These direct calcula- in this study, testing a single standardized Rockwell reference
tions are based upon empirical comparison tests conducted by standard. Every “test result” represents an individual measure-
the manufacturer and verified by indirect verification using ment. The laboratory reported 50 replicate test results. Except
reference standards that were measured according to Test for the use of only one laboratory, Practice E691 was followed
Methods E10, E18, or E92, or combinations thereof. for the design and analysis of the data; the details are given in
ASTM RR:E28-2000.
8.2 There is no general method of accurately converting the
10.1.1 Repeatability limit, rL—The difference between re-
Differential Indentation Depth hardness numbers on one scale
petitive results obtained by the same operator in a given
to Differential Indentation Depth hardness numbers on another
laboratory applying the same test method with the same
scale, or to other types of hardness numbers, or to tensile
apparatus under constant operating conditions on identical test
strength values. Such conversions are, at best, approximations
material within short intervals of time would in the long run, in
and, therefore, should be avoided except for special cases
the normal and correct operation of the test method, exceed the
where a reliable basis for the approximate conversion has been
following values only in one case in 20.
obtained by comparison tests.
10.1.1.1 Repeatability can be interpreted as maximum dif-
NOTE 8—The Standard Hardness Conversion Tables for Metals, E140,
ference between two results, obtained under repeatability
give approximate conversion values for specific materials such as steel,
austenitic stainless steel, nickel and high-nickel alloys, cartridge brass,
conditions, that is accepted as plausible due to random causes
copper alloys, and alloyed white cast irons. The Rockwell hardness data in
under normal and correct operation of the test method.
the conversion tables of E140 was determined using steel ball indenters.
10.1.1.2 Repeatability limits are listed in Table 1.
NOTE 9—ASTM standards giving approximate hardness-tensile
10.1.2 Reproducibility limit, R—The difference between two
strength relationships are listed in Appendix X1.
single and independent results obtained by different operators
NOTE 10—Other international standards for conversion, for example,
ISO 18265 or SAE J417, can provide conversion values that differ from applying the same test method in different laboratories using
other conversion standards.
different apparatus on identical test material would, in the long
run, in the normal and correct operation of the test method,
9. Report
exceed the following values only in one case in 20.
10.1.2.1 Reproducibility can be interpreted as maximum
9.1 The test report shall include the following information:
difference between two results, obtained under reproducibility
9.1.1 The hardness number. All reports of hardness numbers
conditions, that is accepted as plausible due to random causes
shall indicate the scale used. The reported number shall be
under normal and correct operation of the test method.
rounded in accordance with Practice E29 (see 5.2.4).
10.1.2.2 Reproducibility limits cannot be calculated from a
9.1.1.1 When hardness numbers obtained by Differential
single laboratory’s results.
Indentation Depth measurement are reported, the test method
10.1.3 The above terms (repeatability limit and reproduc-
shall be noted in parenthesis after the number and hardness
ibility limit) are used as specified in Practice E177.
scale, for example 35 HRC(DID), where HRC(DID) is for
10.1.4 Any judgment in accordance with statement X1.1
Hardness Differential Indentation Depth Rockwell C, HV-
would normally have an approximate 95 % probability of
(DID) is for Hardness Differential Indentation Depth Vickers,
being correct, however the precision statistics obtained in this
and HBW(DID) is for Hardness Differential Indentation Depth
ILS must not be treated as exact mathematical quantities that
Brinell.
are applicable to all circumstances and uses. The limited
9.1.2 The ambient temperature at the time of test, if outside
number of laboratories reporting replicate results essentially
the limits of 10 °C to 35 °C (50 °F to 95 °F), unless it has been
guarantees that there will be times when differences greater
shown not to affect the measurement result.
than predicted by the ILS results will arise, sometimes with
9.1.3 Identification of the equipment used to obtain the
considerably greater or smaller frequency than the 95 %
hardness number.
probability limit would imply. Consider the repeatability limit
9.1.4 Identification of the equipment operator.
as a general guide, and the associated probability of 95 % as
9.1.5 The test date.
only a rough indicator of what can be expected.
10.2 Bias—Reference material tested: Certified Rockwell
reference standard, SN 15R2117 from Westport, mean hard-
TABLE 1 Hardness (HRC) ness 44.30 HRC, expanded uncertainty 0.40 HRC, standard
base uncertainty 0.197. The mean reported test measurement
Repeatability Preliminary
Average Standard Repeatability
was 44.7. The maximum reported test measurement was 45.9.
Material Tested
Deviation Limit
x¯ s r
r L
Supporting data have been filed at ASTM International Headquarters and may
Rockwell reference
44.71 0.60 1.67
standard be obtained by requesting Research Report RR:E28-2000. Contact ASTM Customer
Service at [e-mail].
E3246 − 22
The minimum reported test measurement was 43.6. The Manual. A full precision and bias statement will be generated
standard deviation of the reported test measurements was 0.59. within 5 years of first approval of this standard as required.
10.3 The precision statement was determined through sta-
11. Keywords
tistical examination of 50 individual test results, from a single
laboratory, on a single certified Rockwell reference standard.
11.1 hardness; indentation depth; mechanical test; metals;
portable
10.4 This is a preliminary precision and bias statement in
accordance with section A21.5.1 of the ASTM Form and Style
ANNEXES
(Mandatory Information)
A1. VERIFICATION OF DIFFERENTIAL INDENTATION DEPTH HARDNESS TESTING MACHINES
A1.1 Scope A1.2.3 All instruments used to make measurements re-
quired by this Annex shall be calibrated metrologically trace-
A1.1.1 Annex A1 specifies two types of procedures for
able to the SI when a system of traceability exists, except as
verifying Differential Indentation Depth hardness testing ma-
noted otherwise.
chines: indirect verification, and daily verification.
A1.2.4 Indirect verification of the testing machine shall be
A1.1.2 Indirect verification is a process for periodically
performed at the place of manufacture, rebuild or repair, or at
verifying the performance of the testing machine by means of
the location where it will be used.
reference standards and indenters.
NOTE A1.1—It is recommended that the calibration agency that is used
A1.1.3 The daily verification is a process for monitoring the
to conduct the verifications of Differential Indentation Depth hardness
performance of the testing machine between indirect verifica-
testing machines be accredited to the requirements of ISO 17025 (or an
equivalent) by an accrediting body recognized by the International
tions by means of reference standards.
Laboratory Accreditation Cooperation (ILAC) as operating to the require-
A1.1.4 Adherence to this standard and annex provides
ments of ISO/IEC 17011.
metrological traceability to the SI, except as stated otherwise.
A1.3 Indirect Verification
A1.2 General Requirements
A1.3.1 An indirect verification of the testing machine shall
A1.2.1 The testing machine shall be verified at specific
be performed, at a minimum, in accordance with the schedule
instances and at periodic intervals as specified in Table A1.1,
given in Table A1.1. The frequency of indirect verifications
and when circumstances occur that might affect the perfor-
should be based on the usage of the testing machine.
mance of the testing machine.
A1.3.2 The testing machine shall be verified for each
A1.2.2 The temperature at the verification site shall be
hardness scale where a direct calculation of hardness number
measured with an instrument having an accuracy of at least
from the measured indentation depth is performed.
62.0 °C (63.6 °F). It is recommended that the temperature be
NOTE A1.2—The manufacturer of the device provides the information
monitored throughout the verification period, and significant
of what scales are calculated directly from the indentation depth. Consult
with the manufacturer of the device if this information is not found in the
temperature variations be recorded and reported. Temperature
operating instructions or other documentation.
measurement may not be measured at the verification site for a
daily verification or when qualifying additional user’s indent-
A1.3.3 Reference standards meeting the requirements of
ers in accordance with A1.3.9.
Test Methods E10, E18, or E92, or combinations thereof where
appropriate as in accordance with A1.3.2 shall be used in the
appropriate hardness ranges for each scale to be verified. These
TABLE A1.1 Verification Schedule for a Differential Indentation
Depth Hardness Testing Machine
ranges are given in Table A1.2 and Table A1.3. Hardness
Verification measurements shall be made only on the calibrated surface of
Schedule
Procedure
the reference standard.
Indirect verification Recommended every 12 months, or more often
if needed. A1.3.4 The testing cycle to be used for the indirect verifi-
Shall be no longer than every 18 months.
cation shall be the same as is typically used by the user.
To qualify an indenter that was not verified in
the last indirect verification, only a partial
A1.3.5 Prior to performing the indirect verification, ensure
indirect verification is performed, (see A1.4).
that the testing machine is working freely, and that the indenter
Daily verification Required each day that hardness tests are to and support are seated adequately. Make at least two hardness
be made.
measurements on a suitable test piece to seat the indenter and
Recommended whenever the indenter is
support. The results of these measurements need not be
changed.
recorded.
E3246 − 22
TABLE A1.2 Maximum Allowable Range and Error of Testing
repeatability, r, and relative error, E , should be within the
R
Machines for Ranges of Reference Standards in the Rockwell C
tolerances of Table A1.3 for the Vickers and Brinell scales. If
and Rockwell B Scales
the calculated values of error, E, range, R, repeatability, r, or
Range of
relative error, E , fall outside of the specified tolerances, this is
R
Standardized Maximum Maximum Maximum
an indication that the hardness tests made since the last indirect
Reference Range, R Error, E Repeatability, r
A
Standards
verification might be suspect.
HRBW < 60 3.0 ± 3.0 # 0.03 % or
A1.3.7 Cleaning and Maintenance—Perform cleaning and
$ 60 and < 80 2.5 ± 2.5 1.0 HRBW,
$ 80 2.0 ± 2.0 whichever is routine maintenance of the testing machine (when required) in
larger
accordance with the manufacturer’s specifications and instruc-
tions.
HRC < 35 4.0 ± 2.0 # 0.03 % or
$ 35 and < 60 3.5 ± 1.5 1.0 HRC,
A1.3.8 Indirect Verification Procedure—The indirect verifi-
$ 60 3.0 ± 1.5 whichever is
cation procedure requires that the testing machine be verified
larger
A
using one or more of the user’s indenters.
The user might find that high, medium and low range reference standards are
unavailable commercially for some scales. In these cases one or two reference
A1.3.8.1 One reference standard shall be tested from each
standards where available can be used. It is recommended that all high range
of the hardness ranges (usually three ranges) for each hardness
reference standards for Rockwell scales using a ball indenter should be less than
100 HR units. scale to be verified, as given in Table A1.2 and Table A1.3. The
difference in hardness between any of the reference standards
shall be at least 5 hardness points for each Rockwell scale, and
TABLE A1.3 Maximum Allowable Range and Error of Testing
50 points for Vickers and Brinell. The user might find that high,
Machines for Ranges of Reference Standards in the Vickers and
medium and low range reference standards are unavailable
Brinell Hardness Scales
commercially for some scales. In these cases, reference stan-
Range of Standardized Maximum Relative Maximum
dards from two ranges may be used. The testing machine shall
A
Reference Standards Error, E Repeatability, r
R
be verified using the reference standards from the two available
HV < 300 4 % # 4.0 %
ranges. In this case, the testing machine is considered verified
$ 300 and < 700 3 % # 3.0 %
$ 700 2.5 % # 2.0 %
for only the part of a scale bracketed by the levels of the
reference standards.
HBW < 125 4 %
A1.3.8.2 On each reference standard, make five measure-
$ 125 and < 225 3 % 4 %
$ 225 2.5 %
ments distributed uniformly over the test surface. Determine
A
The user might find that high, medium and low range reference standards are
the error, E, range, R, and repeatability, r, in the performance
unavailable commercially for some scales. In these cases one or two reference
of the testing machine using Eq 2, Eq 3 and Eq 4 for each
standards where available can be used. It is recommended that all high range
hardness level of each Rockwell hardness scale to be verified
reference standards for Rockwell scales using a ball indenter should be less than
100 HR units.
or repeatability, r, and relative error, E , for each hardness
R
level of each Vickers or Brinell hardness scale to be verified.
A1.3.8.3 The error, E, range, R, and repeatability, r, shall be
A1.3.6 As-found Condition:
within the tolerances of Table A1.2 when using the Rockwell
A1.3.6.1 It is recommended that the as-found condition of scales and the repeatability, r, and relative error, E , should be
R
the testing machine be assessed as part of an indirect verifica-
within the tolerances of Table A1.3 when using the Vickers and
tion. This is important for documenting the historical perfor- Brinell scales. The indirect verification shall be approved only
mance of the machine in the scales used since the last indirect
when the testing machine measurements of range, repeatability,
verification. This procedure should be conducted prior to any error and relative error meet the specified tolerances using at
cleaning, maintenance, adjustments, or repairs. least one of the user’s indenters.
A1.3.6.2 When the as-found condition of the testing ma-
A1.3.8.4 In the case that the testing machine cannot pass the
chine is assessed, it shall be determined with the user’s
range, repeatability, error or relative error verifications with the
indenter(s) that are normally used with the testing machine. At
user’s indenter, a number of corrective actions may be at-
least two reference standards, each from a different hardness
tempted to bring the testing machine within tolerances. These
range as defined in Table A1.2 or Table A1.3, should be tested
actions are limited to cleaning, maintenance, using another of
for each hardness scale that will undergo indirect verification.
the user’s indenters, or combinations thereof. The indirect
The difference in hardness between any of the reference
verification procedures shall be repeated after making the
standards shall be at least 5 hardness points for each Rockwell
allowed corrective actions.
scale, and 50 points for Vickers and Brinell.
NOTE A1.3—When a testing machine fails indirect verification, the
A1.3.6.3 On each reference standard, make at least two
testing machine can be verified again using a Reference indenter (indenter
measurements distributed uniformly over the test surface.
that has already passed indirect verification) for those hardness levels that
A1.3.6.4 Determine the error, E, and the range, R, (Eq 2 and failed the indirect verification with the user’s indenter. If the testing
machine passes the range, error, repeatability and relative error tests with
Eq 3) when using the Rockwell scales, or repeatability, r, and
a Reference indenter, it is an indication that the user’s indenter is out of
relative error, E , (Eq 4 and Eq 5) in the performance of the
R
tolerance. A new indenter can be acquired by the user as a corrective
testing machine for each reference standard that is measured.
action (see A1.3.9) and repeating the indirect verification procedures. If
A1.3.6.5 The error, E, and the range, R, should be within the
the testing machine continues to fail the range, error, repeatability or
tolerances of Table A1.2 for the Rockwell scales. The relative error tests of an indirect verification with the Reference indenter,
E3246 − 22
it is an indication that there is a problem with the machine and not the
A1.4.3.3 Before performing the daily verification tests,
user’s indenter.
ensure that the testing machine is working freely, and that the
indenter is seated adequately. Make at least two hardness
A1.3.8.5 If the testing machine continues to fail the range,
measurements on a suitable test piece. The results of these
repeatability, error or relative error tests following corrective
measurements need not be recorded.
actions, the testing machine shall undergo adjustment and/or
A1.4.3.4 Make at least two hardness measurements on each
repair followed by an indirect verification.
of the daily verification reference standards, uniformly distrib-
A1.3.9 Qualifying Additional User’s Indenters—In cases
uted over the surface of the reference standards.
where the testing machine passes indirect verification using
A1.4.3.5 For each reference standard, calculate the error, E,
only one of the user’s indenters, only that one indenter is
(see Eq 2) and the range, R, (see Eq 3) when using the
considered verified for use with the specific testing machine.
Rockwell scales, or calculate the repeatability, r, (see Eq 4) and
Before any other indenter may be used, it shall be verified for
the relative error, E , (see Eq 5) from the measured hardness
R
use with the specific verified testing machine. This requirement
numbers. The testing machine with the indenter is regarded as
does not apply to changing an indenter ball. The indenter
performing satisfactorily if both E and R or if both r and E for
R
verifications may be made at any time after the indirect
all reference standards are within the maximum tolerances
verification, and may be performed by the user as follows.
given in Table A1.2 and Table A1.3. Note that if the differences
A1.3.9.1 The testing machine and indenter shall be verified
between the individual hardness numbers and the certified
together using the indirect verification procedures of A1.3.8
value for a reference standard are all within the maximum
with the following exception. The verification shall be per-
error, E, tolerances given in Table A1.2 or the relative error, E ,
R
formed on at least two reference standards (high and low
tolerances given in Table A1.3, the above
...

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: E3246 − 21 E3246 − 22
Standard Test Methods for
Differential Indentation Depth Hardness of Metallic
Materials
This standard is issued under the fixed designation E3246; 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.
1. Scope Scope*
1.1 This test method covers the determination of the Differential Indentation Depth hardness of metallic materials by the
Differential Indentation Depth hardness principle. This standard provides the requirements for Differential Indentation Depth
hardness testing machines and the procedures for performing Differential Indentation Depth hardness tests.
1.2 This standard includes additional requirements in annexes:
Verification of Differential Indentation Depth Annex A1
Hardness Testing Machines
Guidelines for Determining the Minimum Thickness Annex A2
of a Test Piece
1.3 This standard includes non-mandatory information in appendixes which relates to the Differential Indentation Depth hardness
test.
List of ASTM Standards Giving Hardness Numbers Appendix X1
Corresponding to Tensile Strength
Examples of Procedures for Determining Appendix X2
Differential Indentation Depth Hardness
Uncertainty
Examples of Indenters Used in Differential Appendix X3
Indentation Depth Machines
1.4 Units—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 micrometers (μm). However, because of continued common usage, values are provided in other units of measure
for information.
1.5 The test principles, testing procedures, and verification procedures are essentially identical for all the Differential Indentation
Depth hardness testing instruments. The testing instruments may use different test forces and indenter shapes. The type and size
of the indenters are matched to the design of the instrument by the manufacturer. Accordingly, the indenters, probes and other
instrument components are generally not interchangeable among manufacturers.
1.6 The hardness number reported by these instruments are based on direct correlations to existing hardness scales as determined
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 Jan. 1, 2021April 1, 2022. Published March 2021May 2022. Originally approved in 2021 as E3246–21. Last previous edition approved in 2021
as E3246–21. DOI: 10.1520/E3246–2110.1520/E3246–22
*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
E3246 − 22
by each manufacturer for each instrument and hardness scale. Unless otherwise noted on the instrument or in the operating manual
for the instrument, the hardness numbers reported by the instrument are only applicable to non-austenitic steels. See 5.6.1 for
additional information.
1.7 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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.8 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:
A370 Test Methods and Definitions for Mechanical Testing of Steel Products
B19 Specification for Cartridge Brass Sheet, Strip, Plate, Bar, and Disks
B36/B36M Specification for Brass Plate, Sheet, Strip, And Rolled Bar
B96/B96M Specification for Copper-Silicon Alloy Plate, Sheet, Strip, and Rolled Bar for General Purposes and Pressure Vessels
B103/B103M Specification for Phosphor Bronze Plate, Sheet, Strip, and Rolled Bar
B121/B121M Specification for Leaded Brass Plate, Sheet, Strip, and Rolled Bar
B122/B122M Specification for Copper-Nickel-Tin Alloy, Copper-Nickel-Zinc Alloy (Nickel Silver), and Copper-Nickel Alloy
Plate, Sheet, Strip, and Rolled Bar
B130 Specification for Commercial Bronze Strip for Bullet Jackets
B134/B134M Specification for Brass Wire
B152/B152M Specification for Copper Sheet, Strip, Plate, and Rolled Bar
B370 Specification for Copper Sheet and Strip for Building Construction
E6 Terminology Relating to Methods of Mechanical Testing
E10 Test Method for Brinell Hardness of Metallic Materials
E18 Test Methods for Rockwell Hardness of Metallic Materials
E29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
E92 Test Methods for Vickers Hardness and Knoop Hardness of Metallic Materials
E110 Test Method for Rockwell and Brinell Hardness of Metallic Materials by Portable Hardness Testers
E140 Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness,
Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb Hardness
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 American Bearings Manufacturer Association Standard:
ABMA 10-1989 Metal Balls
2.2 ISO Standards:
ISO 18265 Metallic Materials—Conversion of Hardness Values
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
2.3 Society of Automotive Engineers (SAE) Standard:
SAE J417 Hardness Tests and Hardness Number Conversions
3. Terminology and Equations
3.1 Definitions:
3.1.1 differential indentation depth hardness test, n—an indentation hardness test using a verified hardness testing machine to force
a truncated diamond cone indenter, diamond spheroconical indenter or tungsten carbide ball indenter, under specified conditions,
into the surface of the material under test, and to measure the difference in depth of the indentation as the force on the indenter
is increased from a specified preliminary test force to a specified total test force and then returned to the preliminary test force.
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.
Available from American Bearing Manufacturers Association (ABMA), 2025 M Street, NW, Suite 800, Washington, DC 20036.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale, PA 15096, http://www.sae.org.
E3246 − 22
3.1.2 differential indentation depth hardness number, n—a number derived from the net increase in the depth of indentation as the
force on an indenter is increased from a specified preliminary test force to a specified total test force and then returned to the
preliminary test force.
3.1.3 differential indentation depth hardness testing machine, n—a machine capable of performing a Differential Indentation
Depth hardness test and displaying the resulting hardness number.
3.1.4 The definitions of Brinell hardness scale, Brinell hardness number, calibration, direct verification, expanded uncertainty,
ductility, force, hardness, indentation hardness, indirect verification, load, reference standard, resolution, Rockwell hardness
number, standardization, stress, tensile strength, testing machine, and verification are used as defined in Terminology E6.
3.2 Equations—The Differential Indentation Depth hardness number is a calculated number, which, by method of calculation,
correlates to the hardness in the scale that it is being converted to.
3.2.1 The average,H¯, of a set of n hardness measurements H , H , …, H is calculated as:
1 2 n
H 1H 1…1H
1 2 n
¯
H 5 (1)
n
3.2.2 The error,E, in the performance of a Differential Indentation Depth hardness testing machine at each hardness level, relative
to a standardized scale, is determined as:
¯
E 5 H 2 H (2)
STD
where:
H¯ = average of n hardness measurements H ,H , …, H made on a reference standard as part of a performance verification,
1 2 n
and
H = certified average hardness number of the reference standard.
STD
3.2.3 The range,R, in the performance of a Differential Indentation Depth hardness testing machine at each hardness level, under
the particular verification conditions, is estimated by the range of n hardness measurements made on a reference standard as part
of a performance verification, defined as:
R 5 H 2 H (3)
max min
where:
H = highest hardness number, and
max
H = lowest hardness number.
min
3.2.4 The repeatability,r, in the performance of a Differential Indentation Depth hardness testing machine at each hardness level,
under the particular verification conditions, is estimated by the range of n hardness measurements made on a reference standard
as part of a performance verification divided by the mean of the measurements, defined as:
H 2 H
max min
r 5 3100 where r is in % (4)
S D
¯
H
3.2.5 The relative error,E , in the performance of a Differential Indentation Depth hardness testing machine at each hardness
R
level, relative to a standardized reference value, is calculated as an absolute percent relative error determined as:
H 2 H
STD
E 5 100 3 (5)
U S DU
R
H
STD
4. Significance and Use
4.1 The Differential Indentation Depth hardness test is an empirical indentation hardness test that can provide useful information
about metallic materials. This information can correlate to tensile strength, wear resistance, ductility, and other physical
characteristics of metallic materials, and can be useful in quality control and selection of materials.
E3246 − 22
4.2 Differential Indentation Depth hardness tests are considered satisfactory for acceptance testing of commercial shipments, and
have been used in industry for this purpose.
4.3 Differential Indentation Depth hardness testing at a specific location on a part might not represent the physical characteristics
of the whole part or end product. Machines that comply with this Standard are used when machines that comply with the regular
hardness standards such as Test Methods E10, E18, E92, and E384 cannot be used. Test results obtained with these machines are
comparable BUT NOT EQUIVALENT to those obtained with machines that comply with the above mentioned standards.
4.4 Differential Indentation Depth hardness testing machines covered by this standard do not comply with Test Methods E10, E18,
E92, or E110.
5. Principles of Test and Apparatus
5.1 Differential Indentation Depth Hardness Test Principle—The general principle of the Differential Indentation Depth hardness
test is illustrated in Fig. 1. The test is divided into three steps of force application and removal.
Step 1—The indenter is brought into contact with the test specimen, and the preliminary test force is applied. The baseline depth
measurement (baseline depth of indentation) at the point where the preliminary test force, F , is achieved is noted as the zero set
point for depth measurement.
Step 2—The force on the indenter is increased by the additional test force, F , to achieve the total test force, F. The total test
force is held for a specified dwell time. The hardness testing machine limits the total test force to the device-specific value.
Step 3—The additional test force is removed, returning to the preliminary test force. At the point where the preliminary test force,
F , is achieved, the final depth of indentation is measured. The Differential Indentation Depth hardness number is derived from
the difference, h, in the final and baseline indentation depths while under the preliminary test force. The preliminary test force is
removed and the indenter is removed from the test specimen.
5.1.1 There are several designs of the Differential Indentation Depth hardness testing machine. Indenters and probes are generally
not interchangeable between machines of different design.
5.1.2 For the Differential Indentation Depth hardness test, the preliminary test forces range between 10N and 100N and the total
test forces range between 50N and 1000N and are specified by the manufacturers. The preliminary force used is approximately
20 % of the value of the total test force used.
5.1.3 Indenters for the Differential Indentation Depth hardness test include a truncated diamond cone indenter, diamond
spheroconical indenter, and tungsten carbide ball indenter of specified diameter.
FIG. 1 Differential Indentation Depth Hardness Test Method (Schematic Diagram)
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5.2 Calculation of the Differential Indentation Depth Hardness Number—During a Differential Indentation Depth hardness test,
the force on the indenter is increased from a preliminary test force to a total test force, and then returned to the preliminary test
force. The difference in the two indentation depth measurements, while under the preliminary test force, is measured as h (see Fig.
1).
5.2.1 The unit measurement for h is μm. From the value of h, the differential hardness number is derived. The reported hardness
number is calculated by the instrument from the differential indentation depth hardness number according to calibration curves
specific to the machine as designed by the manufacturer.
5.2.2 The Differential Indentation Depth hardness number is an arbitrary number, which, by method of calculation, results in a
higher number for harder material. The Differential Indentation Depth hardness number is converted to a hardness number from
commonly used hardness scales.
5.2.3 Differential Indentation Depth hardness numbers shall not be designated by a number alone because it is necessary to
indicate which scale is displayed by the instrument.
5.2.3.1 Examples:
64 HRC(DID) = Rockwell hardness number of 64 on Rockwell C scale
332 HBW(DID) = Brinell hardness number of 332
72 HRBW(DID) = Rockwell hardness number of 72 on the Rockwell B scale
5.2.4 A reported Differential Indentation Depth hardness number or the average value of Differential Indentation Depth hardness
measurements shall be rounded in accordance with Practice E29 with a resolution no greater than the resolution of the hardness
number display of the testing machine.
5.2.4.1 When the Differential Indentation Depth hardness test is used for the acceptance testing of commercial products and
materials, the user should take into account the potential measurement differences between hardness testing machines (see Section
10, Precision and Bias).
NOTE 1—Because of the allowable ranges in the tolerances for the range and error of a hardness testing machine, as specified in the verification
requirements of Annex A1, it is possible for one hardness testing machine to have a test result that is one or more hardness points different than another
hardness testing machine, yet both hardness testing machines can be within verification tolerances (see Table A1.3). Commonly, for acceptance testing,
hardness numbers are rounded to whole numbers following Practice E29. Users are encouraged to address rounding practices with regards to acceptance
testing within their quality management system, and make any special requirements known during contract review.
5.3 Differential Indentation Depth Testing Machine—The Differential Indentation Depth testing machine shall make hardness
determinations by applying the test forces and measuring the depth of indentation in accordance with the Differential Indentation
Depth hardness test principle.
5.3.1 See the Equipment Manufacturer’s Instruction Manual for a description of the machine’s characteristics, limitations, and
respective operating procedures.
5.3.2 The Differential Indentation Depth testing machine shall automatically convert the depth measurements to a hardness
number and indicate the hardness number and scale by an electronic device or by a mechanical indicator.
5.4 Indenters—The standard Differential Indentation Depth indenters are diamond spheroconical indenters, truncated diamond
cone indenters or tungsten carbide balls. Indenter characteristics are specified by the manufacturers.
5.4.1 Dust, dirt, or other foreign materials shall not be allowed to accumulate on the indenter, as this will affect the test results.
5.5 Specimen Support—A specimen support shall be used when necessary for supporting the specimen to be tested. It is necessary
to support the specimen when the specimen stiffness is such that the specimen will flex under the test loads.
5.5.1 Flat pieces should be tested on a flat support that has a smooth, flat bearing surface whose plane is perpendicular to the axis
of the indenter.
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5.5.2 Small diameter cylindrical pieces shall be tested with a hard V-grooved support with the axis of the V-groove directly under
the indenter, or on hard, parallel, twin cylinders properly positioned and clamped in their base. These types of specimen supports
shall support the specimen with the apex of the cylinder directly under the indenter.
5.5.3 Special supports or fixtures, including clamping fixtures, may be used for testing pieces or parts that cannot be supported
by standard supports.
NOTE 2—Not all reference standards will have parallel surfaces that are supported by standard supports. Reference standards with non-parallel or non-flat
surfaces are examples of reference standards that can require a special support or fixture.
5.6 Verification—Differential Indentation Depth hardness testing machines shall be verified periodically in accordance with Annex
A1.
5.6.1 Because the reported values are correlations to existing hardness scales, the user should verify the accuracy of the reported
hardness number on the specific material to be tested. Verification should be performed according to A1.4.
5.7 Reference Standards—Reference standards meeting the requirements of Test Methods E10, E18, or E92, or combinations
thereof shall be used to verify the testing machine.
NOTE 3—Reference standards certified to revision Test Methods E18-07 or later meet the requirements of this standard.
NOTE 4—Appropriate reference standards are not available for all geometric shapes, or materials, or both.
6. Test Piece
6.1 For best results, both surfaces of the test piece should be smooth, even and free from oxide scale, foreign matter, and
lubricants. An exception is made for certain materials such as reactive metals that might adhere to the indenter. In such situations,
a suitable lubricant such as kerosene may be used. The use of a lubricant shall be defined on the test report.
6.2 Preparation shall be carried out in such a way that any alteration of the surface hardness of the test surface (for example, due
to heat or cold-working) is minimized.
6.3 The thickness of the test piece or of the layer under test should be as defined in tables in Annex A2. These tables were
determined from studies conducted by the manufacturers and have proven to give reliable results. For all other materials, the
thickness of the test piece should exceed 10 times the depth of indentation. In general, no deformation should be visible on the
back of the test piece after the test, although not all such marking is indicative of a bad test.
6.3.1 Special consideration should be made when testing parts that exhibit hardness gradients; for example, parts that were
case-hardened by processes such as carburizing, carbonitriding, nitriding, induction, etc. The minimum thickness guidelines given
in Annex A2 only apply to materials of uniform hardness, and should not be used to determine the appropriate use for measuring
parts with hardness gradients. The selection of an appropriate instrument for parts with hardness gradients should be made by
special agreement.
6.4 When testing on convex cylindrical and spherical surfaces, the result might not accurately indicate the true hardness; therefore,
the corrections given for the instrument by the manufacturer shall be applied.
6.4.1 Concave surfaces may be able to be tested with the Differential Indentation Depth method if the machine manufacturer
specifies suitability of the specific Differential Depth hardness testing machine to test conditions. Do not test on concave surfaces
if the manufacturer does not specify suitability of the Differential Indentation Depth hardness testing machine for testing on
concave surfaces.
6.5 When testing small diameter specimens, the accuracy of the test will be seriously affected by alignment between the indenter
and the test piece, by surface finish, and, if the specimen is cylindrical, by the straightness of the cylinder.
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7. Test Procedure
7.1 Perform a daily verification of the Differential Indentation Depth hardness testing machine in accordance with A1.4 prior to
making hardness tests. Hardness measurements shall be made only on the calibrated surface of the reference standard.
7.2 Differential Indentation Depth hardness tests should be carried out at ambient temperature within the limits of 10 °C to 35 °C
(50 °F to 95 °F). Users of the Differential Indentation Depth hardness test are cautioned that the temperature of the test material
and the temperature of the hardness tester can affect test results. Consequently, users should ensure that the test temperature does
not adversely affect the hardness measurement.
7.3 Support the test piece rigidly so that displacement of the test surface is minimized (see 5.5).
7.4 Test Cycle—Use the manufacturer’s procedure to control the test cycle. The test cycle to be used with the hardness testing
machine should match, as closely as possible, the test cycle used for the indirect verification of the hardness testing machine.
NOTE 5—Varying the values of the testing cycle parameters can produce different hardness results.
7.5 Test Procedure—There are many designs of Differential Indentation Depth hardness testing machines, requiring various levels
of operator control. Some hardness testing machines can perform the Differential Indentation Depth hardness test procedure
automatically with almost no operator influence, while other machines require the operator to control most of the test procedure.
7.5.1 Bring the indenter into contact with the test surface in a direction perpendicular to the surface and, if possible, at a velocity
within the maximum contact velocity as recommended by the instrument manufacturer.
7.5.2 Apply the preliminary test force, F .
7.5.3 Maintain the preliminary force for the preliminary force dwell time specified by the manufacturer, then measure the depth
of penetration. This is the baseline depth measurement.
7.5.4 Increase the force by the value of the additional test force, F , needed to obtain the required total test force, F. The additional
force, F , shall be applied in a controlled manner.
7.5.5 Maintain the total force, F, for the total force dwell time specified by the manufacturer.
7.5.6 Remove the additional test force, F , and allow the instrument to cycle through the preliminary test force, F , then measure
1 0
the depth of penetration. This is the final depth measurement.
7.5.7 The testing machine shall calculate the difference between the final and baseline depth measurements and indicate the
resulting hardness number. The hardness number is derived from the differential increase in depth of indentation.
7.6 Throughout the test, protect the apparatus from shock or vibration that could affect the hardness measurement result.
7.7 After each removal and replacement of the indenter, the operation of the machine should be checked in accordance with the
daily verification method specified in Annex A1.
7.8 Maintain a distance of at least three times the diameter, d, of the indentation (see Fig. 2) between the centers of two adjacent
indentations.
7.8.1 The distance from the center of any indentation to an edge of the test piece shall be at least two and a half times the diameter
of the indentation (see Fig. 2).
NOTE 6—Indentation Spacing—The hardness of the material immediately surrounding a previously made indentation will usually increase due to the
induced residual stress and work-hardening caused by the indentation process. If a new indentation is made in this affected material, the measured
hardness number will likely be higher than the true hardness of the material as a whole. Also, if an indentation is made too close to the edge of the material
or very close to a previously made indentation, there might be insufficient material to constrain the deformation zone surrounding the indentation. This
E3246 − 22
FIG. 2 Schematic of Minimum Indentation Spacing
can result in an apparent lowering of the hardness number. Both of these circumstances can be avoided by allowing appropriate spacing between
indentations and from the edge of the material.
7.9 Number of Measurements—One measurement shall constitute a test.
NOTE 7—While one measurement constitutes a test, the average of multiple measurements can provide the user with a more accurate indication of the
hardness of the test location.
8. Conversion to Other Hardness Scales or Tensile Strength Values
8.1 The design of the Differential Indentation Depth hardness testing machine is such that the hardness number is directly
calculated from the measured differential indentation depth for one or more hardness scales. These direct calculations are based
upon empirical comparison tests conducted by the manufacturer and verified by indirect verification using reference standards that
were measured according to Test Methods E10, E18, or E92, or combinations thereof.
8.2 There is no general method of accurately converting the Differential Indentation Depth hardness numbers on one scale to
Differential Indentation Depth hardness numbers on another scale, 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.
NOTE 8—The Standard Hardness Conversion Tables for Metals, E140, give approximate conversion values for specific materials such as steel, austenitic
stainless steel, nickel and high-nickel alloys, cartridge brass, copper alloys, and alloyed white cast irons. The Rockwell hardness data in the conversion
tables of E140 was determined using steel ball indenters.
NOTE 9—ASTM standards giving approximate hardness-tensile strength relationships are listed in Appendix X1.
NOTE 10—Other international standards for conversion, for example, ISO 18265 or SAE J417, can provide conversion values that differ from other
conversion standards.
9. Report
9.1 The test report shall include the following information:
9.1.1 The hardness number. All reports of hardness numbers shall indicate the scale used. The reported number shall be rounded
in accordance with Practice E29 (see 5.2.4).
9.1.1.1 When hardness numbers obtained by Differential Indentation Depth measurement are reported, the test method shall be
noted in parenthesis after the number and hardness scale, for example 35 HRC(DID), where HRC(DID) is for Hardness Differential
Indentation Depth Rockwell C, HV(DID) is for Hardness Differential Indentation Depth Vickers, and HBW(DID) is for Hardness
Differential Indentation Depth Brinell.
E3246 − 22
TABLE 1 Hardness (HRC)
Repeatability Preliminary
Average Standard Repeatability
Material Tested
Deviation Limit
x¯ s r
r L
Rockwell reference
44.71 0.60 1.67
standard
9.1.2 The ambient temperature at the time of test, if outside the limits of 10 °C to 35 °C (50 °F to 95 °F), unless it has been shown
not to affect the measurement result.
9.1.3 Identification of the equipment used to obtain the hardness number.
9.1.4 Identification of the equipment operator.
9.1.5 The test date.
10. Precision and Bias
10.1 The precision of this test method is based on an intralaboratory study of ASTM E3246 – Standard Test Method for
Differential Indentation Depth Hardness of Metallic Materials, conducted in 2018. A single laboratory participated in this study,
testing a single standardized Rockwell reference standard. Every “test result” represents an individual measurement. The
laboratory reported 50 replicate test results. Except for the use of only one laboratory, Practice E691 was followed for the design
and analysis of the data; the details are given in ASTM RR:E28-2000.
10.1.1 Repeatability limit, rL—The difference between repetitive results obtained by the same operator in a given laboratory
applying the same test method with the same apparatus under constant operating conditions on identical test material within short
intervals of time would in the long run, in the normal and correct operation of the test method, exceed the following values only
in one case in 20.
10.1.1.1 Repeatability can be interpreted as maximum difference between two results, obtained under repeatability conditions, that
is accepted as plausible due to random causes under normal and correct operation of the test method.
10.1.1.2 Repeatability limits are listed in Table 1.
10.1.2 Reproducibility limit, R—The difference between two single and independent results obtained by different operators
applying the same test method in different laboratories using different apparatus on identical test material would, in the long run,
in the normal and correct operation of the test method, exceed the following values only in one case in 20.
10.1.2.1 Reproducibility can be interpreted as maximum difference between two results, obtained under reproducibility conditions,
that is accepted as plausible due to random causes under normal and correct operation of the test method.
10.1.2.2 Reproducibility limits cannot be calculated from a single laboratory’s results.
10.1.3 The above terms (repeatability limit and reproducibility limit) are used as specified in Practice E177.
10.1.4 Any judgment in accordance with statement X1.1 would normally have an approximate 95 % probability of being correct,
however the precision statistics obtained in this ILS must not be treated as exact mathematical quantities that are applicable to all
circumstances and uses. The limited number of laboratories reporting replicate results essentially guarantees that there will be times
when differences greater than predicted by the ILS results will arise, sometimes with considerably greater or smaller frequency than
the 95 % probability limit would imply. Consider the repeatability limit as a general guide, and the associated probability of 95 %
as only a rough indicator of what can be expected.
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:E28-2000. Contact ASTM Customer
Service at [e-mail].
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10.2 Bias—Reference material tested: Certified Rockwell reference standard, SN 15R2117 from Westport, mean hardness 44.30
HRC, expanded uncertainty 0.40 HRC, standard base uncertainty 0.197. The mean reported test measurement was 44.7. The
maximum reported test measurement was 45.9. The minimum reported test measurement was 43.6. The standard deviation of the
reported test measurements was 0.59.
10.3 The precision statement was determined through statistical examination of 50 individual test results, from a single laboratory,
on a single certified Rockwell reference standard.
10.4 This is a preliminary precision and bias statement in accordance with section A21.5.1 of the ASTM Form and Style Manual.
A full precision and bias statement will be generated within 5 years of first approval of this standard as required.
11. Keywords
11.1 hardness; indentation depth; mechanical test; metals; portable
ANNEXES
(Mandatory Information)
A1. VERIFICATION OF DIFFERENTIAL INDENTATION DEPTH HARDNESS TESTING MACHINES
A1.1 Scope
A1.1.1 Annex A1 specifies two types of procedures for verifying Differential Indentation Depth hardness testing machines:
indirect verification, and daily verification.
A1.1.2 Indirect verification is a process for periodically verifying the performance of the testing machine by means of reference
standards and indenters.
A1.1.3 The daily verification is a process for monitoring the performance of the testing machine between indirect verifications by
means of reference standards.
A1.1.4 Adherence to this standard and annex provides metrological traceability to the SI, except as stated otherwise.
A1.2 General Requirements
A1.2.1 The testing machine shall be verified at specific instances and at periodic intervals as specified in Table A1.1, and when
circumstances occur that might affect the performance of the testing machine.
A1.2.2 The temperature at the verification site shall be measured with an instrument having an accuracy of at least 62.0 °C
(63.6 °F). It is recommended that the temperature be monitored throughout the verification period, and significant temperature
variations be recorded and reported. Temperature measurement may not be measured at the verification site for a daily verification
or when qualifying additional user’s indenters in accordance with A1.3.9.
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TABLE A1.1 Verification Schedule for a Differential Indentation
Depth Hardness Testing Machine
Verification
Schedule
Procedure
Indirect verification Recommended every 12 months, or more often
if needed.
Shall be no longer than every 18 months.
To qualify an indenter that was not verified in
the last indirect verification, only a partial
indirect verification is performed, (see A1.4).
Daily verification Required each day that hardness tests are to
be made.
Recommended whenever the indenter is
changed.
A1.2.3 All instruments used to make measurements required by this Annex shall be calibrated metrologically traceable to the SI
when a system of traceability exists, except as noted otherwise.
A1.2.4 Indirect verification of the testing machine shall be performed at the place of manufacture, rebuild or repair, or at the
location where it will be used.
NOTE A1.1—It is recommended that the calibration agency that is used to conduct the verifications of Differential Indentation Depth hardness testing
machines be accredited to the requirements of ISO 17025 (or an equivalent) by an accrediting body recognized by the International Laboratory
Accreditation Cooperation (ILAC) as operating to the requirements of ISO/IEC 17011.
A1.3 Indirect Verification
A1.3.1 An indirect verification of the testing machine shall be performed, at a minimum, in accordance with the schedule given
in Table A1.1. The frequency of indirect verifications should be based on the usage of the testing machine.
A1.3.2 The testing machine shall be verified for each hardness scale where a direct calculation of hardness number from the
measured indentation depth is performed.
NOTE A1.2—The manufacturer of the device provides the information of what scales are calculated directly from the indentation depth. Consult with the
manufacturer of the device if this information is not found in the operating instructions or other documentation.
A1.3.3 Reference standards meeting the requirements of Test Methods E10, E18, or E92, or combinations thereof where
appropriate as in accordance with A1.3.2 shall be used in the appropriate hardness ranges for each scale to be verified. These ranges
are given in Table A1.2 and Table A1.3. Hardness measurements shall be made only on the calibrated surface of the reference
standard.
A1.3.4 The testing cycle to be used for the indirect verification shall be the same as is typically used by the user.
A1.3.5 Prior to performing the indirect verification, ensure that the testing machine is working freely, and that the indenter and
support are seated adequately. Make at least two hardness measurements on a suitable test piece to seat the indenter and support.
The results of these measurements need not be recorded.
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TABLE A1.2 Maximum Allowable Range and Error of Testing
Machines for Ranges of Reference Standards in the Rockwell C
and Rockwell B Scales
Range of
Standardized Maximum Maximum Maximum
Reference Range, R Error, E Repeatability, r
A
Standards
HRBW < 60 3.0 ± 3.0 # 0.03 % or
$ 60 and < 80 2.5 ± 2.5 1.0 HRBW,
$ 80 2.0 ± 2.0 whichever is
larger
HRC < 35 4.0 ± 2.0 # 0.03 % or
$ 35 and < 60 3.5 ± 1.5 1.0 HRC,
whichever is
$ 60 3.0 ± 1.5
larger
A
The user might find that high, medium and low range reference standards are
unavailable commercially for some scales. In these cases one or two reference
standards where available can be used. It is recommended that all high range
reference standards for Rockwell scales using a ball indenter should be less than
100 HR units.
TABLE A1.3 Maximum Allowable Range and Error of Testing
Machines for Ranges of Reference Standards in the Vickers and
Brinell Hardness Scales
Range of Standardized Maximum Relative Maximum
A
Reference Standards Error, E Repeatability, r
R
HV < 300 4 % # 4.0 %
$ 300 and < 700 3 % # 3.0 %
$ 700 2.5 % # 2.0 %
HBW < 125 4 %
$ 125 and < 225 3 % 4 %
$ 225 2.5 %
A
The user might find that high, medium and low range reference standards are
unavailable commercially for some scales. In these cases one or two reference
standards where available can be used. It is recommended that all high range
reference standards for Rockwell scales using a ball indenter should be less than
100 HR units.
A1.3.6 As-found Condition:
A1.3.6.1 It is recommended that the as-found condition of the testing machine be assessed as part of an indirect verification. This
is important for documenting the historical performance of the machine in the scales used since the last indirect verification. This
procedure should be conducted prior to any cleaning, maintenance, adjustments, or repairs.
A1.3.6.2 When the as-found condition of the testing machine is assessed, it shall be determined with the user’s indenter(s) that
are normally used with the testing machine. At least two reference standards, each from a different hardness range as defined in
Table A1.2 or Table A1.3, should be tested for each hardness scale that will undergo indirect verification. The difference in hardness
between any of the reference standards shall be at least 5 hardness points for each Rockwell scale, and 50 points for Vickers and
Brinell.
A1.3.6.3 On each reference standard, make at least two measurements distributed uniformly over the test surface.
A1.3.6.4 Determine the error, E, and the range, R, (Eq 2 and Eq 3) when using the Rockwell scales, or repeatability, r, and relative
error, E , (Eq 4 and Eq 5) in the performance of the testing machine for each reference standard that is measured.
R
E3246 − 22
A1.3.6.5 The error, E, and the range, R, should be within the tolerances of Table A1.2 for the Rockwell scales. The repeatability,
r, and relative error, E , should be within the tolerances of Table A1.3 for the Vickers and Brinell scales. If the calculated values
R
of error, E, range, R, repeatability, r, or relative error, E , fall outside of the specified tolerances, this is an indication that the
R
hardness tests made since the last indirect verification might be suspect.
A1.3.7 Cleaning and Maintenance—Perform cleaning and routine maintenance of the testing machine (when required) in
accordance with the manufacturer’s specifications and instructions.
A1.3.8 Indirect Verification Procedure—The indirect verification procedure requires that the testing machine be verified using one
or more of the user’s indenters.
A1.3.8.1 One reference standard shall be tested from each of the hardness ranges (usually three ranges) for each hardness scale
to be verified, as given in Table A1.2 and Table A1.3. The difference in hardness between any of the reference standards shall be
at least 5 hardness points for each Rockwell scale, and 50 points for Vickers and Brinell. The user might find that high, medium
and low range reference standards are unavailable commercially for some scales. In these cases, reference standards from two
ranges may be used. The testing machine shall be verified using the reference standards from the two available ranges. In this case,
the testing machine is considered verified for only the part of a scale bracketed by the levels of the reference standards.
A1.3.8.2 On each reference standard, make five measurements distributed uniformly over the test surface. Determine the error, E,
range, R, and repeatability, r, in the performance of the testing machine using Eq 2, Eq 3 and Eq 4 for each hardness level of each
Rockwell hardness scale to be verified or repeatability, r, and relative error, E , for each hardness level of each Vickers or Brinell
R
hardness scale to be verified.
A1.3.8.3 The error, E, range, R, and repeatability, r, shall be within the tolerances of Table A1.2 when using the Rockwell scales
and the repeatability, r, and relative error, E , should be within the tolerances of Table A1.3 when using the Vickers and Brinell
R
scales. The indirect verification shall be approved only when the testing machine measurements of range, repeatability, error and
relative error meet the specified tolerances using at least one of the user’s indenters.
A1.3.8.4 In the case that the testing machine cannot pass the range, repeatability, error or relative error verifications with the user’s
indenter, a number of corrective actions may be attempted to bring the testing machine within tolerances. These actions are limited
to cleaning, maintenance, using another of the user’s indenters, or combinations thereof. The indirect verification procedures shall
be repeated after making the allowed corrective actions.
NOTE A1.3—When a testing machine fails indirect verification, the testing machine can be verified again using a Reference indenter (indenter that has
already passed indirect verification) for those hardness levels that failed the indirect verification with the user’s indenter. If the testing machine passes
the range, error, repeatability and relative error tests with a Reference indenter, it is an indication that the user’s indenter is out of tolerance. A new indenter
can be acquired by the user as a corrective action (see A1.3.9) and repeating the indirect verification procedures. If the testing machine continues to fail
the range, error, repeatability or relative error tests of an indirect verification with the Reference indenter, it is an indication that there is a problem with
the machine and not the user’s indenter.
A1.3.8.5 If the testing machine continues to fail the range, repeatability, error or relative error tests following corrective actions,
the testing machine shall undergo adjustment and/or repair followed by an indirect verification.
A1.3.9 Qualifying Additional User’s Indenters—In cases where the testing machine passes indirect verification using only one of
the user’s indenters, only that one indenter is considered verified for use with the specific testing machine. Before any other
E3246 − 22
indenter may be used, it shall be verified for use with the specific verified testing machine. This requirement does not apply to
changing an indenter ball. The indenter verifications may be made at any time after the indirect verification, and may be performed
by the user a
...