ASTM E384-22
(Test Method)Standard Test Method for Microindentation Hardness of Materials
Standard Test Method for Microindentation Hardness of Materials
SIGNIFICANCE AND USE
5.1 Hardness tests have been found to be very useful for materials evaluation, quality control of manufacturing processes and research and development efforts. Hardness, although empirical in nature, can be correlated to tensile strength for many metals and alloys, and is also an indicator of machinability, wear resistance, toughness and ductility.
5.2 Microindentation tests are utilized to evaluate and quantify hardness variations that occur over a small distance. These variations may be intentional, such as produced by localized surface hardening, for example, from shot blasting, cold drawing, flame hardening, induction hardening, etc., or from processes such as carburization, nitriding, carbonitriding, etc.; or, they may be unintentional variations due to problems, such as decarburization, localized softening in service, or from compositional/microstructural segregation problems. Low test forces also extend hardness testing to materials too thin or too small for macroindentation tests. Microindentation tests permit hardness testing of specific phases or constituents and regions or gradients too small for evaluation by macroindentation tests.
5.3 Because microindentation hardness tests will reveal hardness variations that commonly exist within most materials, a single test value may not be representative of the bulk hardness. Vickers tests at 1000 gf can be utilized for determination of the bulk hardness, but, as for any hardness test, it is recommended that a number of indents are made and the average and standard deviation are calculated, as needed or as required.
5.4 Microindentation hardness testing is generally performed to quantify variations in hardness that occur over small distances. To determine these differences requires a very small physical indentation. Testers that create indents at very low test forces must be carefully constructed to accurately apply the test forces exactly at the desired location and must have a high-quality optical syste...
SCOPE
1.1 This test method covers determination of the microindentation hardness of materials.
1.2 This test method covers microindentation tests made with Knoop and Vickers indenters under test forces in the range from 9.8 × 10-3 to 9.8 N (1 to 1000 gf).
1.3 This test method includes an analysis of the possible sources of errors that can occur during microindentation testing and how these factors affect the precision, bias, repeatability, and reproducibility of test results.
1.4 Information pertaining to the requirements for direct verification and calibration of the testing machine and the requirements for the manufacture and calibration of Vickers and Knoop reference hardness test blocks are in Test Method E92.
Note 1: While Committee E04 is primarily concerned with metals, the test procedures described are applicable to other materials.
1.5 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 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.
1.7 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
Relations
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: E384 − 22
Standard Test Method for
Microindentation Hardness of Materials
This standard is issued under the fixed designation E384; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 2. Referenced Documents
1.1 This test method covers determination of the microin-
2.1 ASTM Standards:
dentation hardness of materials.
C1326Test Method for Knoop Indentation Hardness of
Advanced Ceramics
1.2 This test method covers microindentation tests made
withKnoopandVickersindentersundertestforcesintherange C1327Test Method for Vickers Indentation Hardness of
-3
from 9.8 × 10 to 9.8 N (1 to 1000 gf). Advanced Ceramics
E3Guide for Preparation of Metallographic Specimens
1.3 This test method includes an analysis of the possible
E7Terminology Relating to Metallography
sourcesoferrorsthatcanoccurduringmicroindentationtesting
E92Test Methods for Vickers Hardness and Knoop Hard-
and how these factors affect the precision, bias, repeatability,
ness of Metallic Materials
and reproducibility of test results.
E140Hardness Conversion Tables for Metals Relationship
1.4 Information pertaining to the requirements for direct
Among Brinell Hardness, Vickers Hardness, Rockwell
verification and calibration of the testing machine and the
Hardness, Superficial Hardness, Knoop Hardness, Sclero-
requirements for the manufacture and calibration of Vickers
scope Hardness, and Leeb Hardness
and Knoop reference hardness test blocks are in Test Method
E175Terminology of Microscopy (Withdrawn 2019)
E92.
E177Practice for Use of the Terms Precision and Bias in
NOTE1—WhileCommitteeE04isprimarilyconcernedwithmetals,the
ASTM Test Methods
test procedures described are applicable to other materials.
E691Practice for Conducting an Interlaboratory Study to
1.5 Units—The values stated in SI units are to be regarded
Determine the Precision of a Test Method
asstandard.Nootherunitsofmeasurementareincludedinthis
E766Practice for Calibrating the Magnification of a Scan-
standard.
ning Electron Microscope
1.6 This standard does not purport to address all of the
E1268Practice for Assessing the Degree of Banding or
safety concerns, if any, associated with its use. It is the
Orientation of Microstructures
responsibility of the user of this standard to establish appro-
E2554Practice for Estimating and Monitoring the Uncer-
priate safety, health, and environmental practices and deter-
tainty of Test Results of a Test Method Using Control
mine the applicability of regulatory limitations prior to use.
Chart Techniques
1.7 This international standard was developed in accor-
E2587Practice for Use of Control Charts in Statistical
dance with internationally recognized principles on standard-
Process Control
ization established in the Decision on Principles for the
2.2 ISO Standard:
Development of International Standards, Guides and Recom-
ISO/IEC 17025 General Requirements for the Competence
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. of Testing and Calibration Laboratories
1 2
This test method is under the jurisdiction of ASTM Committee E04 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Metallography and is the direct responsibility of Subcommittee E04.05 on Micro- contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
indentation Hardness Testing. With this revision the test method was expanded to Standards volume information, refer to the standard’s Document Summary page on
include the requirements previously defined in E28.92, Standard Test Method for the ASTM website.
Vickers Hardness Testing of Metallic Material that was under the jurisdiction of The last approved version of this historical standard is referenced on
E28.06 www.astm.org.
Current edition approved Oct. 1, 2022. Published November 2022. Originally Available from International Organization for Standardization (ISO), 1, ch. de
approved in 1969. Last previous edition approved in 2017 as E384–17. DOI: la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http://
10.1520/E0384-22 www.iso.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
E384 − 22
3. Terminology 3.3 Formulae—The formulae presented in 3.3.1 – 3.3.4 for
calculating microindentation hardness are based upon an ideal
3.1 Definitions—For definitions of terms used in this test
tester and conditions. The measured value of the microinden-
method, see Terminology E7.
tation hardness of a material is subjected to several sources of
3.2 Definitions of Terms Specific to This Standard:
errors. Based on Eq 1-9, variations in the applied force,
3.2.1 calibrating, v—determining the values of the signifi-
geometrical variations between diamond indenters, and human
cant parameters by comparison with values indicated by a
errorsinmeasuringindentationlengthswillaffecttheprecision
reference instrument or by a set of reference standards.
ofthecalculatedmaterialhardness.Themagnitudeoftheerror
3.2.2 Knoop hardness number, HK, n—an expression of that variations of each of these parameters have on the
hardness obtained by dividing the force applied to the Knoop
calculated value of a microindentation measurement is dis-
indenter by the projected area of the permanent impression cussed in Section 10.
made by the indenter.
3.3.1 For Knoop hardness tests, in practice, test loads are in
grams-forceandindentationdiagonalsareinmicrometers.The
3.2.3 Knoop indenter, n—a rhombic-based pyramidal-
Knoop hardness number is calculated using the following:
shaped diamond indenter with edge angles of/ A = 172° 30'
3 3 2
and/ B = 130° 0' (see Fig. 1).
HK 51.000 310 3 P/A 51.000 310 3 P/ c 3 d (1)
~ ! ~ !
p p
3.2.4 microindentation hardness test, n—a hardness test
or
using a calibrated machine to force a diamond indenter of
HK 514229 3 P/d (2)
specific geometry into the surface of the material being
evaluated,inwhichthetestforcesrangefrom1to1000gf(9.8 /B
tan
-3
×10 to9.8N),andtheindentationdiagonal,ordiagonals,are 2
c 5 (3)
p
measured with a light microscope after load removal; for any
/A
2tan
microindentation hardness test, it is assumed that the indenta- 2
tion does not undergo elastic recovery after force removal.
where:
NOTE 2—Use of the term microhardness should be avoided because it
P = force, gf,
implies that the hardness, rather than the force or the indentation size, is
d = length of long diagonal, µm,
very low.
A = projected area of indentation, µm
p
3.2.5 verifying, v—checking or testing the instrument to
/A = included longitudinal edge angle, 172° 30’
assure conformance with the specification.
/B = included transverse edge angle, 130° 0’ (see Fig. 1
and,
3.2.6 Vickers hardness number, HV, n—an expression of
c = indenter constant relating projected area of the inden-
hardness obtained by dividing the force applied to a Vickers p
tation to the square of the length of the long diagonal,
indenterbythesurfaceareaofthepermanentimpressionmade
ideally 0.07028.
by the indenter.
3.2.7 Vickers indenter, n—a square-based pyramidal-shaped 3.3.2 The Knoop hardness, kgf/mm is determined as fol-
diamond indenter with face angles of 136° (see Fig. 2). lows:
FIG. 1 Knoop Indenter
E384 − 22
FIG. 2 Vickers Indenter
HK 514.229 3 P /d (4) where:
1 1
P = force, N, and
where:
d = mean diagonal length of the indentations, mm.
P = force, kgf, and
d = length of long diagonal, mm.
3.4 Equations for calculating % Error and Repeatability for
periodic verification is determined as follows:
3.3.3 The Knoop hardness reported with units of GPa is
determined as follows:
¯
d 2 d
? ref?
2 E 5100S D (10)
HK 50.014229 3 P /d (5)
2 2 d
ref
where:
where:
P = force, N, and
2 E = % error in performance of the periodic verification,
d = length of the long diagonal of the indentation, mm. ¯
d = the measured mean diagonal length in µm, and
d = the reported certified mean diagonal length, µm.
ref
3.3.4 FortheVickershardnesstest,inpractice,testloadsare
in grams-force and indentation diagonals are in micrometers.
d 2 d
max min
R 5100 (11)
The Vickers hardness number is calculated as follows:
S D
¯
d
3 3 2
HV 51.000 310 3 P/A 52.000 310 3 Psin α/2 /d (6)
~ !
s
where:
or
R = repeatability in performance of the periodic
HV 51854.4 3 P/d (7)
verification,
d = the longest diagonal length measurement on the
max
where:
standardized test block, µm,
P = force, gf,
d = the shortest diagonal length measurement on the
2 min
A = surface area of the indentation, µm ,
s
standardized test block, µm, and
d = mean diagonal length of the indentation, µm, and
¯
d = the measured mean diagonal length in µm.
α = face angle of the indenter, 136° 0’ (see Fig. 2).
3.3.5 The Vickers hardness, kgf/mm is determined as
4. Summary of Test Method
follows:
4.1 In this test method, a hardness number is determined
HV 51.8544 3 P /d (8)
1 1
based on the formation of a very small indentation by appli-
where:
cation of a relatively low force, in comparison to traditional
bulk indentation hardness tests.
P = force, kgf, and
d = mean diagonal length of the indentations, mm.
4.2 A Knoop or Vickers indenter, made from diamond of
3.3.6 The Vickers hardness reported with units of GPa is
specific geometry, is pressed into the test specimen surface
determined as follows:
under an applied force in the range of 1 to 1000 gf using a test
HV 50.0018544 3 P /d (9) machine specifically designed for such work.
2 2
E384 − 22
4.3 The size of the indentation is measured using a light metrically identical as a function of depth and there will be
microscope equipped with a filar type eyepiece, or other type variations in Knoop hardness, particularly at test forces <200
of measuring device (see Terminology E175). gf, over the force range defined in 1.2 (and above this range);
consequently, Knoop hardness is not normally used to define
4.4 The Knoop hardness number is based upon the force
bulk hardness, except at 500 gf where E140 gives conversions
divided by the projected area of the indentation. The Vickers
toothertestscales,andKnooptestsshouldnotbeperformedat
hardnessnumberisbasedupontheforcedividedbythesurface
test forces above 1000 gf. The majority of Knoop tests of case
area of the indentation.
hardness variations are conducted at forces from 100gf to 500
4.5 It is assumed that elastic recovery does not occur when
gf. If the test is being conducted to meet a specified bulk
the indenter is removed after the loading cycle, that is, it is
hardness value, such as HRC, then most such tests will be
assumed that the indentation retains the shape of the indenter
conducted with Knoop at a 500 gf load. Because of the large
aftertheforceisremoved,butthisisnotalwaystrue.InKnoop
difference between the long and short Knoop diagonals, the
testing, it is assumed that the ratio of the long diagonal to the
Knoopindenterisoftenbettersuitedfordeterminingvariations
shortdiagonaloftheimpressionisthesameasfortheindenter,
of hardness over very small distances compared to the Vickers
7.114, but this is not always true due to elastic recovery.
indenter. Vickers and Knoop tests at forces ≤25 gf are
susceptible to imprecision due to the difficulty in measuring
5. Significance and Use
extremely small indents (<20 µm) by light microscopy with
5.1 Hardness tests have been found to be very useful for
high precision and reproducibility.Tests made at forces≤25 gf
materials evaluation, quality control of manufacturing pro-
should be considered to be qualitative in nature. Likewise, test
cesses and research and development efforts. Hardness, al-
forces that create indents <20 µm in length should be avoided
thoughempiricalinnature,canbecorrelatedtotensilestrength
whenever possible and should be considered to be qualitative
for many metals and alloys, and is also an indicator of
innature.Thesuccessofthespecimenpreparationprocedurein
machinability, wear resistance, toughness and ductility.
removing preparation-induced damage can, and will, influence
testresults;thisproblembecomesmorecriticalasthetestforce
5.2 Microindentationtestsareutilizedtoevaluateandquan-
decreases.
tify hardness variations that occur over a small distance.These
variations may be intentional, such as produced by localized
6. Apparatus
surface hardening, for example, from shot blasting, cold
drawing, flame hardening, induction hardening, etc., or from
6.1 Test Machine—The test machine must support the test
processes such as carburization, nitriding, carbonitriding, etc.;
specimen and control the movement of the indenter into the
or, they may be unintentional variations due to problems, such
specimenunderapreselectedtestforce,andshouldhavealight
as decarburization, localized softening in service, or from
optical microscope to select the desired test locations and to
compositional/microstructural segregation problems. Low test
measure the size of the indentations produced by the test. The
forces also extend hardness testing to materials too thin or too
planeofthesurfaceofthetestspecimenmustbeperpendicular
smallformacroindentationtests.Microindentationtestspermit
to the axis of the indenter and the direction of the force
hardness testing of specific phases or constituents and regions
application.Theplaneofthetestspecimensurfacemustbeflat,
orgradientstoosmallforevaluationbymacroindentationtests.
and free of surface relief, in order to obtain valid, usable test
data. The hardness test machine must meet the verification
5.3 Because microindentation hardness tests will reveal
requirements defined in Test Method E92.
hardnessvariationsthatcommonlyexistwithinmostmaterials,
6.1.1 Force Application—The test machine shall be capable
a single test value may not be representative of the bulk
of applying the test forces according to the following:
hardness. Vickers tests at 1000 gf can be utilized for determi-
6.1.1.1 The time from the initial application of the force
nation of the bulk hardness, but, as for any hardness test, it is
recommended that a number of indents are made and the until the full test force is reached shall not exceed 10 s.
6.1.1.2 Theindentershallc
...
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: E384 − 17 E384 − 22
Standard Test Method for
Microindentation Hardness of Materials
This standard is issued under the fixed designation E384; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This test method covers determination of the microindentation hardness of materials.
1.2 This test method covers microindentation tests made with Knoop and Vickers indenters under test forces in the range from
-3
9.8 × 10 to 9.8 N (1 to 1000 gf).
1.3 This test method includes an analysis of the possible sources of errors that can occur during microindentation testing and how
these factors affect the precision, bias, repeatability, and reproducibility of test results.
1.4 Information pertaining to the requirements for direct verification and calibration of the testing machine and the requirements
for the manufacture and calibration of Vickers and Knoop reference hardness test blocks are in Test Method E92.
NOTE 1—While Committee E04 is primarily concerned with metals, the test procedures described are applicable to other materials.
1.5 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard.
1.6 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.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C1326 Test Method for Knoop Indentation Hardness of Advanced Ceramics
C1327 Test Method for Vickers Indentation Hardness of Advanced Ceramics
E3 Guide for Preparation of Metallographic Specimens
This test method is under the jurisdiction of ASTM Committee E04 on Metallography and is the direct responsibility of Subcommittee E04.05 on Microindentation
Hardness Testing. With this revision the test method was expanded to include the requirements previously defined in E28.92, Standard Test Method for Vickers Hardness
Testing of Metallic Material that was under the jurisdiction of E28.06
Current edition approved June 1, 2017Oct. 1, 2022. Published August 2017November 2022. Originally approved in 1969. Last previous edition approved in 20162017
as E384 – 16.E384 – 17. DOI: 10.1520/E0384-1710.1520/E0384-22
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on 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
E384 − 22
E7 Terminology Relating to Metallography
E92 Test Methods for Vickers Hardness and Knoop Hardness of Metallic Materials
E140 Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness,
Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb Hardness
E175 Terminology of Microscopy (Withdrawn 2019)
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E766 Practice for Calibrating the Magnification of a Scanning Electron Microscope
E1268 Practice for Assessing the Degree of Banding or Orientation of Microstructures
E2554 Practice for Estimating and Monitoring the Uncertainty of Test Results of a Test Method Using Control Chart Techniques
E2587 Practice for Use of Control Charts in Statistical Process Control
2.2 ISO Standard:
ISO/IEC 17025 General Requirements for the Competence of Testing and Calibration Laboratories
3. Terminology
3.1 Definitions—For definitions of terms used in this test method, see Terminology E7.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 calibrating, v—determining the values of the significant parameters by comparison with values indicated by a reference
instrument or by a set of reference standards.
3.2.2 Knoop hardness number, HK, n—an expression of hardness obtained by dividing the force applied to the Knoop indenter by
the projected area of the permanent impression made by the indenter.
3.2.3 Knoop indenter, n—a rhombic-based pyramidal-shaped diamond indenter with edge angles of / A = 172° 30' and / B =
130° 0' (see Fig. 1).
3.2.4 microindentation hardness test, n—a hardness test using a calibrated machine to force a diamond indenter of specific
-3
geometry into the surface of the material being evaluated, in which the test forces range from 1 to 1000 gf (9.8 × 10 to 9.8 N),
and the indentation diagonal, or diagonals, are measured with a light microscope after load removal; for any microindentation
hardness test, it is assumed that the indentation does not undergo elastic recovery after force removal.
FIG. 1 Knoop Indenter
The last approved version of this historical standard is referenced on www.astm.org.
Available from International Organization for Standardization (ISO), 1, ch. de la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http://www.iso.org.
E384 − 22
FIG. 2 Vickers Indenter
NOTE 2—Use of the term microhardness should be avoided because it implies that the hardness, rather than the force or the indentation size, is very low.
3.2.5 verifying, v—checking or testing the instrument to assure conformance with the specification.
3.2.6 Vickers hardness number, HV, n—an expression of hardness obtained by dividing the force applied to a Vickers indenter by
the surface area of the permanent impression made by the indenter.
3.2.7 Vickers indenter, n—a square-based pyramidal-shaped diamond indenter with face angles of 136° (see Fig. 2).
3.3 Formulae—The formulae presented in 3.3.1 – 3.3.4 for calculating microindentation hardness are based upon an ideal tester
and conditions. The measured value of the microindentation hardness of a material is subjected to several sources of errors. Based
on Eq 1-9, variations in the applied force, geometrical variations between diamond indenters, and human errors in measuring
indentation lengths will affect the precision of the calculated material hardness. The magnitude of the error that variations of each
of these parameters have on the calculated value of a microindentation measurement is discussed in Section 10.
3.3.1 For Knoop hardness tests, in practice, test loads are in grams-force and indentation diagonals are in micrometers. The Knoop
hardness number is calculated using the following:
3 3 2
HK 5 1.000 310 3~P/A ! 5 1.000 310 3P/~c 3d ! (1)
p p
or
HK 5 14229 3P/d (2)
/B
tan
c 5 (3)
p
/A
2tan
where:
P = force, gf,
d = length of long diagonal, μm,
A = projected area of indentation, μm
p
/A = included longitudinal edge angle, 172° 30’
/B = included transverse edge angle, 130° 0’ (see Fig. 1 and,
E384 − 22
c = indenter constant relating projected area of the indentation to the square of the length of the long diagonal, ideally
p
0.07028.
3.3.2 The Knoop hardness, kgf/mm is determined as follows:
HK 5 14.229 3P /d (4)
1 1
where:
P = force, kgf, and
d = length of long diagonal, mm.
3.3.3 The Knoop hardness reported with units of GPa is determined as follows:
HK 5 0.014229 3P /d (5)
2 2
where:
P = force, N, and
d = length of the long diagonal of the indentation, mm.
3.3.4 For the Vickers hardness test, in practice, test loads are in grams-force and indentation diagonals are in micrometers. The
Vickers hardness number is calculated as follows:
3 3 2
HV 5 1.000 310 3P/A 5 2.000 310 3Psin~α/2!/d (6)
s
or
HV 5 1854.4 3P/d (7)
where:
P = force, gf,
A = surface area of the indentation, μm ,
s
d = mean diagonal length of the indentation, μm, and
α = face angle of the indenter, 136° 0’ (see Fig. 2).
3.3.5 The Vickers hardness, kgf/mm is determined as follows:
HV 5 1.8544 3P /d (8)
1 1
where:
P = force, kgf, and
d = mean diagonal length of the indentations, mm.
3.3.6 The Vickers hardness reported with units of GPa is determined as follows:
HV 5 0.0018544 3P /d (9)
2 2
where:
P = force, N, and
d = mean diagonal length of the indentations, mm.
3.4 Equations for calculating % Error and Repeatability for periodic verification is determined as follows:
¯
d 2 d
ref
E 5 100S D (10)
d
ref
¯
d 2 d
? ref?
E 5 100S D (10)
d
ref
E384 − 22
where:
E = % error in performance of the periodic verification,
d¯ = the measured mean diagonal length in μm, and
d = the reported certified mean diagonal length, μm.
ref
d 2 d
max min
R 5 100 (11)
S D
¯
d
where:
R = repeatability in performance of the periodic verification,
d = the longest diagonal length measurement on the standardized test block, μm,
max
d = the shortest diagonal length measurement on the standardized test block, μm, and
min
d¯ = the measured mean diagonal length in μm.
4. Summary of Test Method
4.1 In this test method, a hardness number is determined based on the formation of a very small indentation by application of a
relatively low force, in comparison to traditional bulk indentation hardness tests.
4.2 A Knoop or Vickers indenter, made from diamond of specific geometry, is pressed into the test specimen surface under an
applied force in the range of 1 to 1000 gf using a test machine specifically designed for such work.
4.3 The size of the indentation is measured using a light microscope equipped with a filar type eyepiece, or other type of measuring
device (see Terminology E175).
4.4 The Knoop hardness number is based upon the force divided by the projected area of the indentation. The Vickers hardness
number is based upon the force divided by the surface area of the indentation.
4.5 It is assumed that elastic recovery does not occur when the indenter is removed after the loading cycle, that is, it is assumed
that the indentation retains the shape of the indenter after the force is removed, but this is not always true. In Knoop testing, it is
assumed that the ratio of the long diagonal to the short diagonal of the impression is the same as for the indenter, 7.114, but this
is not always true due to elastic recovery.
5. Significance and Use
5.1 Hardness tests have been found to be very useful for materials evaluation, quality control of manufacturing processes and
research and development efforts. Hardness, although empirical in nature, can be correlated to tensile strength for many metals and
alloys, and is also an indicator of machinability, wear resistance, toughness and ductility.
5.2 Microindentation tests are utilized to evaluate and quantify hardness variations that occur over a small distance. These
variations may be intentional, such as produced by localized surface hardening, for example, from shot blasting, cold drawing,
flame hardening, induction hardening, etc., or from processes such as carburization, nitriding, carbonitriding, etc.; or, they may be
unintentional variations due to problems, such as decarburization, localized softening in service, or from compositional/
microstructural segregation problems. Low test forces also extend hardness testing to materials too thin or too small for
macroindentation tests. Microindentation tests permit hardness testing of specific phases or constituents and regions or gradients
too small for evaluation by macroindentation tests.
5.3 Because microindentation hardness tests will reveal hardness variations that commonly exist within most materials, a single
test value may not be representative of the bulk hardness. Vickers tests at 1000 gf can be utilized for determination of the bulk
hardness, but, as for any hardness test, it is recommended that a number of indents are made and the average and standard deviation
are calculated, as needed or as required.
5.4 Microindentation hardness testing is generally performed to quantify variations in hardness that occur over small distances.
To determine these differences requires a very small physical indentation. Testers that create indents at very low test forces must
be carefully constructed to accurately apply the test forces exactly at the desired location and must have a high-quality optical
system to precisely measure the diagonal (or diagonals) of the small indents. Test forces in the upper range of the force range
E384 − 22
defined in 1.2 may be used to evaluate bulk hardness. In general, the Vickers indenter is better suited for determining bulk (average)
properties as Vickers hardness is not altered by the choice of the test force, from 2525 gf to 1000 gf, because the indent geometry
is constant as a function of indent depth. The Knoop indentation, however, is not geometrically identical as a function of depth
and there will be variations in Knoop hardness, particularly at test forces <200 gf, over the force range defined in 1.2 (and above
this range); consequently, Knoop hardness is not normally used to define bulk hardness, except at 500 gf where E140 gives
conversions to other test scales, and Knoop tests should not be performed at test forces above 1000 gf. The majority of Knoop tests
of case hardness variations are conducted at forces from 100100 gf to 500 gf. If the test is being conducted to meet a specified bulk
hardness value, such as HRC, then most such tests will be conducted with Knoop at a 500 gf load. Because of the large difference
between the long and short Knoop diagonals, the Knoop indenter is often better suited for determining variations of hardness over
very small distances compared to the Vickers indenter. Vickers and Knoop te
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.