ASTM B933-20

Standard Test Method for Microindentation Hardness of Powder Metallurgy (PM) Materials

SIGNIFICANCE AND USE
5.1 Microindentation hardness testing provides a measure of the hardness of the microstructural constituents of a porous material. It indicates the hardness the material would have if there were no pores present and the material was tested using macroindentation hardness methods. Loads are limited to a maximum of 200 gf to reduce the likelihood of interference from the porosity.  
5.2 Microindentation hardness tests allow the evaluation of specific phases, microstructural constituents, and regions or gradients too small for macroindentation hardness testing.
SCOPE
1.1 This test method covers the determination of the microindentation hardness of powder metallurgy (PM) materials. The test method differs from the approach used for pore-free materials in terms of the precautions required to deal with the porosity.  
1.2 This procedure covers tests made with the Knoop or Vickers indenters under loads in the range from 1 to 200 gf.  
1.3 Automated testing is not generally suitable for use with porous PM materials, because acceptable indentations require avoiding placing indentations in the immediate vicinity of a pore, a condition not guaranteed with automated placement of the indentations. Any automated testing shall allow for review of indentations post-test to reject any distorted or unusually large indentations in accordance with 9.4.  
1.4 A method for converting the directly measured indentation lengths to other hardness scales, for example, HRC is described in Appendix X1.  
1.5 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.  
1.6 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.

General Information

• Status: Published
• Publication Date: 30-Sep-2020
• ICS: 77.160 - Powder metallurgy
• Technical Committee: B09 - Metal Powders and Metal Powder Products
• Drafting Committee: B09.05 - Structural Parts

Relations

• Refers: ASTM B243-18 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Oct-2018
• Refers: ASTM B243-16 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Jul-2016
• Refers: ASTM B243-13 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Nov-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 B243-12 - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Jul-2012
• Refers: ASTM B243-11 - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Nov-2011
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011
• Refers: ASTM E384-10 - Standard Test Method for Microindentation Hardness of Materials
• Effective Date: 01-Feb-2010
• Refers: ASTM E384-10e1 - Standard Test Method for Knoop and Vickers Hardness of Materials
• Effective Date: 01-Feb-2010
• Refers: ASTM B243-10 - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Jan-2010
• Refers: ASTM B243-09a - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Dec-2009
• Refers: ASTM E384-09 - Standard Test Method for Microindentation Hardness of Materials
• Effective Date: 01-May-2009
• Refers: ASTM B243-09 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Jan-2009
• Refers: ASTM E691-08 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Oct-2008
• Refers: ASTM B243-08a - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Mar-2008

Overview

ASTM B933-20: Standard Test Method for Microindentation Hardness of Powder Metallurgy (PM) Materials establishes procedures for determining the microindentation hardness of powder metallurgy materials using either Knoop or Vickers indenters. Specifically developed for PM materials, this method addresses the impact of porosity on hardness measurements by applying controlled loads up to 200 gf, minimizing interference from pores. This standard offers critical guidance for manufacturers, researchers, and quality control professionals seeking accurate measurement of microstructural hardness in PM components.

Key Topics

• Microindentation Testing: Utilizes loads between 1 and 200 gf with Knoop or Vickers diamond indenters to measure hardness at the microstructural level.
• Porosity Considerations: Procedures differ from those used for pore-free materials, with specific precautions to account for the inherent porosity of PM specimens.
• Sample Preparation: Detailed recommendations ensure correct sample mounting, grinding, polishing, and etching to reliably reveal porosity and microstructural features, allowing for accurate hardness measurements.
• Manual vs. Automated Testing: Automated indentation is generally unsuitable for porous PM materials due to difficulty avoiding pores; when used, automated systems must allow manual review and rejection of questionable indentations.
• Test Reporting: The standard specifies required reporting elements, including sample identification, indenter type, load, magnification, measured phase or constituent, etchant details, and the average result of at least five valid indentations.
• Conversion to Other Scales: Guidance is provided for approximate conversion of microindentation results to other hardness scales, such as HRC.

Applications

Implementing ASTM B933-20 in laboratory and industrial settings supports:

• Quality Control in PM Manufacturing: Verifies the consistency and suitability of microstructural constituents, crucial for performance-critical parts in automotive, aerospace, and engineering applications.
• Research and Development: Enables detailed microhardness profiling of specific phases or gradients in novel PM alloys, facilitating material optimization.
• Failure Analysis: Allows investigation of localized hardness in microstructural regions, helping identify causes of unexpected mechanical performance.
• Educational Use: Serves as an authoritative reference in academic and training environments for students learning about powder metallurgy characterization.

The method is especially valuable for evaluating features too small for traditional macrohardness testing and for characterizing local variations resulting from processing or thermal treatment.

Related Standards

For comprehensive understanding and complementary procedures, reference the following standards:

• ASTM E384 – Test Method for Microindentation Hardness of Materials: General method for microindentation hardness applicable to a wide range of materials, referenced for equipment and baseline procedures.
• ASTM B243 – Terminology of Powder Metallurgy: Provides standardized PM terminology essential for interpreting this standard.
• MPIF Standard Guides 70, 71, and 72: Practical guides for preparing ferrous, copper-based, and aluminum PM materials for metallographic evaluation.
• ASTM E691 – Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method: Informs on precision and reproducibility requirements when implementing ASTM B933-20.

Practical Value

Adherence to ASTM B933-20 ensures consistent, reliable microindentation hardness testing of powder metallurgy materials. By addressing the unique challenges presented by porosity and providing robust procedures for sample preparation and measurement, this standard helps manufacturers and laboratories maintain high quality and traceability in PM production. Utilizing these guidelines enhances confidence in microhardness data, supporting the adoption and innovation of powder metallurgy components across diverse industries.

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: B933 − 20
Standard Test Method for
Microindentation Hardness of Powder Metallurgy (PM)
Materials
This standard is issued under the fixed designation B933; 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* 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the determination of the micro-
B243 Terminology of Powder Metallurgy
indentation hardness of powder metallurgy (PM) materials.
E384 Test Method for Microindentation Hardness of Mate-
The test method differs from the approach used for pore-free
rials
materials in terms of the precautions required to deal with the
E691 Practice for Conducting an Interlaboratory Study to
porosity.
Determine the Precision of a Test Method
1.2 This procedure covers tests made with the Knoop or
2.2 MPIF Standards:
Vickers indenters under loads in the range from 1 to 200 gf.
Standard70 GuidetoSamplePreparationofFerrousPowder
Metallurgy (PM) Materials for Cross-Sectional Metallo-
1.3 Automated testing is not generally suitable for use with
graphic Evaluation
porous PM materials, because acceptable indentations require
Standard 71 Guide to Sample Preparation of Copper-Based
avoiding placing indentations in the immediate vicinity of a
Powder Metallurgy (PM) Materials for Cross-Sectional
pore, a condition not guaranteed with automated placement of
Metallographic Evaluation
the indentations.Any automated testing shall allow for review
Standard 72 Guide to Sample Preparation of Aluminum
of indentations post-test to reject any distorted or unusually
Powder Metallurgy (PM) Materials for Cross-Sectional
large indentations in accordance with 9.4.
Metallographic Evaluation
1.4 Amethod for converting the directly measured indenta-
3. Terminology
tion lengths to other hardness scales, for example, HRC is
3.1 Definitions of powder metallurgy (PM) terms can be
described in Appendix X1.
found in Terminology B243. Additional descriptive informa-
1.5 This standard does not purport to address all of the
tion is available under General Information on PM on the
safety concerns, if any, associated with its use. It is the
ASTM B09 web page.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter- 4. Summary of Test Method
mine the applicability of regulatory limitations prior to use.
4.1 Microindentation hardness testing uses a calibrated
1.6 This international standard was developed in accor-
machine to force a pyramidal-pointed diamond indenter into
dance with internationally recognized principles on standard-
the surface of the test material under a known test load. The
ization established in the Decision on Principles for the
microindentation hardness value is calculated from the indent-
Development of International Standards, Guides and Recom-
ing force divided by the projected area of the resulting
mendations issued by the World Trade Organization Technical indentation.
Barriers to Trade (TBT) Committee. NOTE 1—This test method is designed specifically for use on porous
PM materials. It is intended to be a companion to Test Method E384.
There are specific differences that are intentional, such as restricting the
applied load to a maximum of 200 gf; otherwise, the details on equipment
and procedures in Test Method E384 shall be adhered to. The specific
differences relate to the presence of porosity in the PM materials. Special
1 2
This test method is under the jurisdiction of ASTM Committee B09 on Metal For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Powders and Metal Powder Products and is the direct responsibility of Subcom- contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
mittee B09.05 on Structural Parts. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Oct. 1, 2020. Published October 2020. Originally the ASTM website.
approved in 2004. Last previous edition approved in 2016 as B933 – 16. DOI: Available from Metal Powder Industries Federation (MPIF), 105 College Rd.
10.1520/B0933-20. East, Princeton, NJ 08540, http://www.mpif.org.
*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
B933 − 20
precautions are required during sample preparation to reveal pores and
feature to be tested. Magnification ranges for various indenta-
heterogeneous microstructural features so that appropriate test locations
tion lengths are as follows:
may be selected.
Indentation Length Magnification
(µm) Max Min
5. Significance and Use
<76 . . . 400
76 to 125 800 300
5.1 Microindentationhardnesstestingprovidesameasureof
>125 600 200
the hardness of the microstructural constituents of a porous
9.3 Apply the test load.
material. It indicates the hardness the material would have if
there were no pores present and the material was tested using
9.4 Examine the indentation for possible sources of error
macroindentation hardness methods. Loads are limited to a such as distorted or unusually large indentations. The two
maximum of 200 gf to reduce the likelihood of interference
sections of each diagonal should agree within 20 % of each
from the porosity. other. Discard any distorted or unusually large indentations.
Unusually large indentations sometimes occur due to the
5.2 Microindentation hardness tests allow the evaluation of
presence of pores directly under the indentation.
specific phases, microstructural constituents, and regions or
gradients too small for macroindentation hardness testing.
9.5 Measure the length of the diagonals of the indentation,
taking care to avoid backlash by moving only in one direction.
6. Apparatus
For Knoop microindentation hardness, read the length of the
larger diagonal to 0.1 µm. For Vickers microindentation
6.1 MicroindentationHardnessTestingMachine, capable of
hardness, measure both diagonals to the nearest 0.1 µm and
applying the required load, equipped with a Knoop or Vickers
calculate the average.
indenter, and provision for measuring the length of the diago-
nals of the indentation.
9.6 Make additional indentations. Space the indentations, so
that adjacent tests do not interfere with each other. The
6.2 Apparatus requirements are summarized in method Test
minimum spacing between tests is illustrated in Fig. 1.
Method E384.
10. Calculation or Interpretation of Results
7. Reagents and Materials
10.1 TheKnooporVickersmicroindentationhardnessnum-
7.1 MetallographicEtchants, suitable for the material being
bers may be calculated using the following formulae or by
tested.
using tables in Test Method E384.
10.1.1 Knoop—Using the units of force and length com-
8. Test Specimen
monly employed, that is, for force P in gf, and a long diagonal
8.1 Specimen Mounting:
d in micrometres, the Knoop hardness is calculated:
8.1.1 Sample mounting is recommended for convenience in
HK 5 14 229P/d
surface preparation, edge retention, and ease of testing. The
sample should be supported adequately in the mounting
10.1.2 Vickers—Using the units of force and length com-
medium.
monly employed, that is, for force P in gf, and the mean of the
two diagonals d in micrometres, the Vickers hardness is
8.2 Specimen Preparation:
calculated:
8.2.1 Guidelines for grinding and polishing specimens are
provided in MPIF Standard Guides 70, 71, and 72.
HV 5 1854.4P/d
8.2.2 Care should be taken to ensure that the true area
10.1.3 For indentation diagonals measured in millimetres,
fraction of porosity is revealed throughout the entire cross
tablesofHKandHVvaluesaretabulatedinTestMethodE384.
section of the specimen. It is essential in surface prepa
...

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: B933 − 16 B933 − 20
Standard Test Method for
Microindentation Hardness of Powder Metallurgy (PM)
Materials
This standard is issued under the fixed designation B933; 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*
1.1 This test method covers the determination of the microindentation hardness of powder metallurgy (PM) materials. The test
method differs from the approach used for pore-free materials in terms of the precautions required to deal with the porosity.
1.2 This procedure covers tests made with the Knoop or Vickers indenters under loads in the range from 1 to 200 gf.
1.3 Automated testing is not generally suitable for use with porous PM materials, because acceptable indentations require avoiding
placing indentations in the immediate vicinity of a pore, a condition not guaranteed with automated placement of the indentations.
Any automated testing shall allow for review of indentations post-test to reject any distorted or unusually large indentations in
accordance with 9.4.
1.4 A method for converting the directly measured indentation lengths to other hardness scales, for example, HRC is described
in Appendix X1.
1.5 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.6 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:
B243 Terminology of Powder Metallurgy
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 MPIF Standards:
Standard 70 Guide to Sample Preparation of Ferrous Powder Metallurgy (PM) Materials for Cross-Sectional Metallographic
Evaluation
This test method is under the jurisdiction of ASTM Committee B09 on Metal Powders and Metal Powder Products and is the direct responsibility of Subcommittee B09.05
on Structural Parts.
Current edition approved April 1, 2016Oct. 1, 2020. Published April 2016October 2020. Originally approved in 2004. Last previous edition approved in 20142016 as B933
– 14.16. DOI: 10.1520/B0933-16.10.1520/B0933-20.
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 Metal Powder Industries Federation (MPIF), 105 College Rd. East, Princeton, NJ 08540, http://www.mpif.org.
*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
B933 − 20
Standard 71 Guide to Sample Preparation of Copper-Based Powder Metallurgy (PM) Materials for Cross-Sectional Metallo-
graphic Evaluation
Standard 72 Guide to Sample Preparation of Aluminum Powder Metallurgy (PM) Materials for Cross-Sectional Metallographic
Evaluation
3. Terminology
3.1 Definitions of powder metallurgy (PM) terms can be found in Terminology B243. Additional descriptive information is
available inunder the Related Materials sectionGeneral Information on PM of Vol 02.05 of theon the ASTM B09 web Annual Book
of ASTM Standards.page.
4. Summary of Test Method
4.1 Microindentation hardness testing uses a calibrated machine to force a pyramidal-pointed diamond indenter into the surface
of the test material under a known test load. The microindentation hardness value is calculated from the indenting force divided
by the projected area of the resulting indentation.
NOTE 1—This test method is designed specifically for use on porous PM materials. It is intended to be a companion to Test Method E384. There are
specific differences that are intentional, such as restricting the applied load to a maximum of 200 gf; otherwise, the details on equipment and procedures
in Test Method E384 shall be adhered to. The specific differences relate to the presence of porosity in the PM materials. Special precautions are required
during sample preparation to reveal pores and heterogeneous microstructural features so that appropriate test locations may be selected.
5. Significance and Use
5.1 Microindentation hardness testing provides a measure of the hardness of the microstructural constituents of a porous material.
It indicates the hardness the material would have if there were no pores present and the material was tested using macroindentation
hardness methods. Loads are limited to a maximum of 200 gf to reduce the likelihood of interference from the porosity.
5.2 Microindentation hardness tests allow the evaluation of specific phases, microstructural constituents, and regions or gradients
too small for macroindentation hardness testing.
6. Apparatus
6.1 Microindentation Hardness Testing Machine, capable of applying the required load, equipped with a Knoop or Vickers
indenter, and provision for measuring the length of the diagonals of the indentation.
6.2 Apparatus requirements are summarized in method Test Method E384.
7. Reagents and Materials
7.1 Metallographic Etchants, suitable for the material being tested.
8. Test Specimen
8.1 Specimen Mounting:
8.1.1 Sample mounting is recommended for convenience in surface preparation, edge retention, and ease of testing. The sample
should be supported adequately in the mounting medium.
8.2 Specimen Preparation:
8.2.1 Guidelines for grinding and polishing specimens are provided in Appendix X2.MPIF Standard Guides 70, 71, and 72.
8.2.2 Care should be taken to ensure that the true area fraction of porosity is revealed throughout the entire cross section of the
specimen. It is essential in surface preparation to remove all smeared metal and to identify pores clearly so that they may be
avoided during testing.
8.2.3 The specimen should be lightly etched prior to microindentation hardness testing. Careful etching is necessary as heavy
etching obscures features and interferes with the measurement of the diagonals of the indentation.
B933 − 20
8.2.4 For heat treated steels, swabbing with, or immersion in, 2 % nital for 4 to 7 s gives an appropriate structure.
9. Procedure
9.1 Support the specimen so that its surface is perpendicular to the axis of the indenter.
9.2 Select a suitable location for testing and an appropriate load and magnification for the test. A 100 gf load is recommended for
hardened materials. Lower loads may be used for softer materials or when small regions need to be tested. For the best precision,
use the highest load compatible with the feature to be tested. Magnification ranges for various indentation lengths are as follows:
Indentation Length Magnification
(μm) Max Min
<76 . . . 400
76 to 125 800 300
>125 600 200
9.3 Apply the test load.
9.4 Examine the indentation for possible sources of error such as distorted or unusually large indentations. The two sections of
each diagonal should agree within 20 % of each other. Discard any distorted or unusually large indentations. Unusually large
indentations sometimes occur due to the presence of pores directly under the indentation.
9.5 Measure the length of the diagonals of the indentation, taking care to avoid backlash by moving only in one direction. For
Knoop microindentation hardness, read the length of the larger diagonal to 0.1 μm. For Vickers microindentation hardness, measure
both diagonals to the nearest 0.1 μm and calculate the average.
9.6 Make additional indentations. Space the indentations, so that adjacent tests do not interfere with each other. The minimum
spacing between tests is illustrated in Fig. 1.
10. Calculation or Interpretation of Results
10.1 The Knoop or Vickers microindentation hardness numbers may be calculated using the following formulae or by using tables
in Test Method E384.
FIG. 1 Minimum Spacing Between Indentations
B933 − 20
10.1.1 Knoop—Using the units of force and length commonly employed, that is, for force P in gf, and a long diagonal d in
micrometres, the Knoop hardness is calculated:
HK 5 14229 P/d
HK 5 14 229 P/d
10.1.2 Vickers—Using the units of force and length commonly employed, that is, for force P in gf, and the mean of the two
diagonals d in micrometres, the Vickers hardness is calculated:
HV 5 1854.4 P/d
10.1.3 For indentation diagonals measured in millimetres, tables of HK and HV values are tabulated in Test Method E384.
11. Report
11.1 Report the following information:
11.1.1 The identification of the sample and the location at which the microindentation hardness was measured,
11.1.2 The type of indenter, Knoop or Vickers, and the load used,
11.1.3 The magnification used,
11.1.4 The identity, or description of the phase or microstructural constituent measured,
11.1.5 The type of etchant used, the duration, and method of etching, and
11.1.6 The average of at least five acceptable measurements shall be reported as the microindentation hardness of the material,
microstructural constituent, or other feature measured.
11.1.7 Knoop (HK) or Vickers (HV) microindentation hardness shall be reported along with the test load used, for example, 400
HK 100 gf or 400 HV 100 gf. This is the preferred method. However, an alternative method expressing the load in kilograms force
may be used in accordance with ISO, for example, 400 HK 0.1 or 400 HV 0.1. Report HK and HV values to the nearest whole
number.
12. Precision and Bias
12.1 The repeatability, r, and reproducibility, R, of measurements were determined in accordance with Practice E691. Members
of the Powder Metallurgy Parts Association of the Metal Powder Industries Federation conducted the interlaboratory test program.
The test sample was prepared from heat treated FL-4605. One Knoop and one Vickers microindentation hardness indent was made
in the surface of the test sample, and these indentations were measured by 12 participating laboratories.
12.2 The mean Knoop microindentation hardness value was 701 HK 100 gf with a repeatability of 22 and a reproducibility of 76.
Duplicate microindentation hardness results from one laboratory should not be considered suspect at the 95 % confidence level
unless they differ by more than 22. For the same test specimen, Knoop microindentation hardness results from two different
laboratories should not be considered suspect at the 95 % confidence level unless they differ by more than 76.
12.3 The mean Vickers microindentation hardness value was 716 HV 100 gf with a repeatability of 43 and a reproducibility of
178. Duplicate microindentation hardness results from one laboratory should not be considered suspect at the 95 % confidence
level unless they differ by more than 43. For the same test specimen, Vickers microindentation hardness results from two different
laboratories should not be considered suspect at the 95 % confidence level unless they differ by more than 178.
13. Keywords
13.1 Knoop microindentation hardness; microindentation hardness; PM; powder metallurgy; Vickers microindentation hardness
B933 − 20
APPENDIXESAPPENDIX
(Nonmandatory Information)
X1. CONVERSION TO OTHER HARDNESS SCALES
X1.1 It is sometimes desired to express microindentation hardness values in terms of equivalents to other hardness scales, for
example, HRC. There is no direct conversion from microindentation hardness to HRC. Approximate values can be obtained
through the procedure described in this appendix.
X1.1.1 The following procedure describes a method for conversion to HRC.
X1.1.2 Obtain four or five standard HRC test blocks that span the range from the low 20’s HRC to the 60’s HRC.
X1.1.3 Remove a small portion from each standard test block, being careful to avoid any procedure that might affect the hardness
of the test block material, and make a metallographic mount with the standardized face of the test block at the surface of the mount.
X1.1.4 Polish the specimens using standard procedures (see Appendix X2).MPIF Standard Guides 70, 71, and 72).
X1.1.5 Using either a Knoop or a Vickers indenter and a
100 gf test load (other loads might be used for a conversion to hardness scales such as HRB or HRF), make five indentations at
various points in each of the standard specimens.
X1.1.6 Measure the length of the diagonals of the indentations.
X1.1.7 Prepare a graph with the filar units, micrometres, or Knoop/Vickers microindentation hardness number on the y-axis
(ordinate) and HRC on the x-axis (abscissa). Plot all measured diagonals and, using regression analysis (regression of y on x),
construct a best-fit curve to the data points.
X1.1.8 In future tests, take any diagonal reading and use the graph to convert to HRC.
NOTE X1.1—The graph that is constructed applies to the specific instrument used for the microindentation hardness test, the test load used, and the person
performing the test. A separate graph needs to be plotted for each operator, each test instrument, and for each load used for microindentation hardness
testing.
X1.1.9 Precision of the Graphical Conversion:
X1.1.9.1 Seven laboratories participated in an interlaboratory study. Each laboratory developed a regression line for their own
instrument. The regression line was plotted based on the results (six-reading averages) of measurements on five HRC standard test
blocks with hardness ranging from 25.4 HRC 25.4 HRC to 63.2 HRC. The seven laboratories found the hardness of a circulated
unknown sample to average 56.5 HRC.
X1.1.9.2 With this test method, 95 % of any future readings would be expected to repeat in a laboratory within 4.0 HRC points
B933 − 20
at this level; for six-reading averages within 1.6 HRC points. For a laboratory to duplicate an
...