ASTM A956/A956M-22

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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: A956/A956M − 17a A956/A956M − 22
Standard Test Method for
Leeb Hardness Testing of Steel Products
This standard is issued under the fixed designation A956/A956M; 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 Leeb hardness of steel, cast steel, and cast iron (Part A), including the
methods for the verification of Leeb hardness testing instruments (Part B), and the calibration of standardized test blocks (Part C).
NOTE 1—The original title of this standard was “Standard Test Method for Equotip Hardness Testing of Steel Products.”
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used
independently of the other, and values from the two systems shall not be combined.
1.3 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.
1.4 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:
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
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions:
3.1.1 calibration—determination of the values of the significant operating parameters of the instrument by comparison with values
indicated by a reference instrument or by a set of reference standards.
This test method is under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee A01.13
on Mechanical and Chemical Testing and Processing Methods of Steel Products and Processes.
Current edition approved Nov. 1, 2017Sept. 1, 2022. Published December 2017September 2022. Originally approved in 1996. Last previous edition approved in 2017 as
A956/A956M – 17.A956/A956M – 17A.
Leeb and Equotip are registered trademarks used with permission of Proceq SA. DOI: 10.1520/A0956_A0956M-17A.10.1520/A0956_A0956M-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 pageon 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
A956/A956M − 22
3.1.2 Leeb hardness number—a number equal to the ratio of the rebound velocity to the impact velocity of a 0.118 in. [3 mm] or
0.197 in. [5 mm] (based on the type of impact device) diameter spherically shaped tungsten carbide, silicon nitride, or diamond
tipped impact body, multiplied by 1000.
Rebound Velocity
L 5 31000
Impact Velocity
The Leeb hardness number is followed by the symbol HL with one or more suffix characters representing the type of impact
device.
3.1.3 Leeb hardness test—a dynamic hardness test method using a calibrated instrument that impacts a spherically shaped tungsten
carbide, silicon nitride, or diamond tipped body with a fixed velocity (generated by a spring force) onto a surface of the material
under test. The ratio of the rebound velocity to the impact velocity of the impact body is a measure of the hardness of the material
under test.
3.1.4 surface finish—all references to surface finish in this test method are defined as surface roughness (that is, Ra = average
roughness value, AA = arithmetic average).
3.1.5 verification—checking or testing the instrument to ensure conformance with this test method.
4. Summary of Test Method
4.1 During a hardness test, an impact body with a spherically shaped tungsten carbide, silicon nitride, or diamond tip impacts, after
being propelled to the specified velocity, the test surface from which it rebounds. The impact and rebound velocities are measured
when the impact body is approximately 0.039 in. [1 mm] from the test surface. This is accomplished by means of a permanent
magnet mounted in the impact body which, during the test, moves through a coil in the impact device and induces an electric
voltage on both the impact and rebound movements. These induced voltages are proportional to the respective impact and rebound
velocities. The quotient of these measured voltage values derived from the impact and rebound velocities, multiplied by the factor
1000 produces a number which constitutes the Leeb hardness value.
5. Significance and Use
5.1 Hardness of a material is a poorly defined term that may have many meanings depending on the type of test performed and
the expectations of the person involved. The Leeb hardness test is of the dynamic or rebound type, which primarily depends both
on the plastic and on the elastic properties of the material being tested. The results obtained are indicative of the strength and
dependent on the heat treatment of the material tested.
5.2 The Leeb hardness test is a superficial determination only measuring the condition of the surface contacted. The results
generated at that location do not represent the part at any other surface location and yield no information about the material at
subsurface locations.
A. GENERAL DESCRIPTION OF INSTRUMENTS AND TEST PROCEDURE FOR LEEB HARDNESS TEST
6. Apparatus
6.1 The instrument used for Leeb hardness testing consists of (1) an impact device that is equipped with a spherically shaped
tungsten carbide, silicon nitride, or synthetic diamond tipped impact body, an induction coil velocity measuring assembly, and a
support ring, and (2) an electronic digital display hardness indicating device.
6.2 Impact Devices—There are eight types of impact devices used in Leeb hardness testing. These are the D, DC, D+15, DL,G,
C, S, and the E impact units. Brief descriptions of the types of devices and their common applications are given in Appendix X1.
Table 1 provides the specifications for the Leeb scales according to impact device type.
6.3 See 8.1.1 when using replacement machine components.
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TABLE 1 Specifications of Standard Leeb Hardness Testing Devices
Property Symbol Unit D/DC S E D+15 DL C G
A
Impact velocity V ft/s [m/s] 6.73 [2.05] 6.73 [2.05] 6.73 [2.05] 5.58 [1.7] 5.97 [1.82] 4.56 [1.39] 9.78 [2.98]
A
± 5 % ± 5 % ± 5 % ± 5 % ± 5 % ± 5 % ± 5 %
Impact body, mass M oz [g] 0.192 ± 0.002 0.190 ± 0.002 0.192 ± 0.002 0.273 ± 0.002 0.256 ± 0.002 0.109 ± 0.002 0.705 ± 0.002
[5.45 ± 0.05] [5.40 ± 0.05] [5.45 ± 0.05] [7.75 ± 0.05] [7.25 ± 0.05] [3.1 ± 0.05] [20.00 ± 0.05]
Indenter, radius R in. [mm] 0.059 [1.5] 0.059 [1.5] 0.059 [1.5] 0.059 [1.5] 0.055 [1.39] 0.059 [1.5] 0.098 [2.5]
B C
material TC Si N PCD TC TC TC TC
3 4
D
hardness h HV2 1600 ± 100 1600 ± 100 $4500 1600 ± 100 1600 ± 100 1600 ± 100 1600 ± 100
Maximum distance of H in. [mm] 0.079 [2.0] 0.079 [2.0] 0.079 [2.0] 0.079 [2.0] 0.079 [2.0] 0.079 [2.0] 0.118 [3.0]
ball indenter from the
test piece surface when
measuring velocity
A
Impact direction: vertical down, in the direction of gravity.
B
TC = tungsten carbide.
C
PCD = polycrystaline diamond.
D
The hardness of the impact body E indenter is informational, not required to be verified.
7. Test Piece
7.1 Form—The Leeb hardness test is acceptable for steel, cast steel, and cast iron with varying shapes and sizes.
7.2 Thickness and Weight—The thickness and weight of the test piece shall be considered when selecting the impact device to be
employed. The following guidelines are offered as minimum weights and sizes of test pieces for selecting the proper test
equipment. Test pieces of weights less than the minimum or pieces of any weight with sections less than the minimum thickness
require rigid support and coupling to a thick, heavier non-yielding surface to resist the impact of the device. Failure to provide
adequate support and coupling will produce test results lower than the true hardness value.
Minimum Mass Minimum Mass Minimum Minimum
Impact
without with Thickness Thickness
Device
Rigid Support Rigid Support (Uncoupled) (Coupled)
D, DC, D+15, 0.984 in. 0.118 in.
11.0 lb [5 kg] 4.4 lb [2 kg]
DL,S, E [25 mm] [3 mm]
2.756 in. 0.394 in.
G 33.1 lb [15 kg] 11.0 lb [5 kg]
[70 mm] [10 mm]
0.394 in. 0.039 in.
C 3.3 lb [1.5 kg] 0.3 lb [0.5 kg]
[10 mm] [1 mm]
7.3 Curvature—Test pieces with curved surfaces may be tested on either the convex or concave surfaces providing that this radius
of curvature of the specimens is matched to the size of the support ring and is not less than 1.969 in. [50 mm] for the G impact
device or 1.181 in. [30 mm] for other impact devices.
7.4 Surface Finish/Preparation—The test surface shall be carefully prepared to avoid any alterations in hardness caused by heating
during grinding or by work hardening during machining. Any paint, scale, pits, or other surface coatings shall be completely
removed. The surfaces to be tested shall be smooth. Failure to provide adequate surface finish will produce questionable test
results. Coarse finishes will tend to lower the measured value. It is recommended that the test surface be machined or ground and
polished to the following finishes. (The grinding wheel grit size shown for each finish is offered for guidance in achieving the finish
noted.)
Surface Finish—Ra Grit Size
Impact Device
(max) (Approx.)
D, DC, D+15, DL,S, E 78.7 μin. [2 μm] 200
G 275.6 μin. [7 μm] 65
C 15.7 μin. [0.4 μm] 500
7.5 Magnetic Fields—Performance of the Leeb hardness test on parts with a residual magnetic field may affect the results. It is
recommended that any residual magnetic field be less than 4 G.
7.6 Vibration—Vibration of the test specimen may affect the results of the Leeb hardness test. It is recommended that this test be
performed with the test piece at rest.
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7.7 Temperature—The temperature of the test piece may affect the results of the test. In addition, this effect may be different for
different materials. Testing to this procedure shall be performed with the temperature of the test piece between 39 °F [4 °C] and
100 °F [38 °C]. At temperatures outside this range, the user shall develop a temperature correction for the specific material being
tested.
8. Verification of Apparatus
8.1 Verification Method—Prior to each shift, work period, or use, and following a period of extended continuous use (1000
impacts), the instrument shall be verified as specified in Part B. Any instrument not meeting the requirements of Part B shall not
be employed for the acceptance testing of product.
8.1.1 Cautionary note: When replacement parts are used in a Leeb hardness tester it is important that they be fully compatible with
the original equipment, otherwise incorrect hardness readings may be obtained. Calibration using a single standard test block may
indicate acceptable results, but additional calibration tests using blocks of differing hardness may yield unacceptable results. If
replacement, non-original equipment parts are used, multiple block calibration verification is strongly advised. Specifically, one
calibration block of a hardness equal to or lower than the minimum expected hardness of the material being tested, one calibration
block of a hardness equal to or greater than the maximum expected hardness of the material being tested, and one calibration block
near the middle of the range should be used.
9. Procedure
9.1 To perform a hardness test, the impact device is connected to the user interface device and powered on.
9.1.1 The impact device is readied for impact.
9.1.1.1 Mechanically Charged Device—Some impact devices are charged mechanically by pulling the impact body against a
spring or other mechanism that propels the impact body at the prescribed velocity. The impact device, while not in contact with
the test piece, is held firmly with one hand while the charging mechanism is activated with the other hand. Once the impact body
is in the charged position the charging mechanism is allowed to slowly return to its resting position.
9.1.1.2 Otherwise Charged Device—Devices that are not charged mechanically may use gravity or other force application method
to propel the impact body at the prescribed velocity. Charging of these devices should be conducted according to manufacturer’s
instructions.
9.1.2 After placing the readied (loaded) impact device on the test surface, trigger the impact by actuating the release mechanism
according to manufacturer’s instructions.
9.1.3 The Leeb hardness value is displayed or otherwise used by a user interface device after the impact.
NOTE 2—The user interface device may take the form of a computer or PLC that does not display the hardness value directly to the user. Such a user
interface device may use the hardness value to operate an automatic sorting machine or simply log the value in a database.
9.2 Alignment—To prevent errors resulting from misalignment, the base support ring of the impact device shall be held snugly and
perpendicular to the surface of the test piece.
9.3 Impact Direction—The impact device is calibrated for the down vertical impact direction (perpendicular to a horizontal
surface). For other impact directions such as 45° from the horizontal plane or from underneath, the measured hardness values will
require adjustment (see 10.2). Some newer models automatically compensate for test direction.
9.4 Spacing Indentations—The distance between any two impact points shall not be less than two diameters edge-to-edge. The
distance between the impact point and a specimen edge shall not be less than three diameters edge-to-edge. No point shall be
impacted more than once.
9.5 Reading the Leeb Instrument—Hardness values in Leeb units are read directly on the electronic display of the indicator device.
The indicated value is automatically replaced with the next test impact result.
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2 2
9.6 Number of Impacts—Five impacts in an area of approximately 1 in. [645 mm ] shall constitute a test. If the material being
tested is considered to be nonhomogeneous (for example, cast iron) ten impacts in an area shall be made to constitute a test.
10. Calculation of Hardness Result
10.1 The hardness test result shall be the arithmetic average of the five individual impact readings in the measuring area.
10.2 Compensation for Test Direction—When using a Leeb instrument without automatic compensation for test direction, the
compensation value for direction of test impact is to be subtracted from the average value determined for the measuring area. This
compensation value can be determined in accordance with Tables 2-9.
11. Conversion to Other Hardness Scales or Tensile Strength Values
11.1 There is no direct correlation between the Leeb hardness test principle and other hardness methods or a tensile strength test.
All such conversions are, at best, approximations and therefore conversions should be avoided except for special cases where a
reliable basis for the approximate conversion and the accuracy of the conversion has been obtained by comparison testing. No
conversions shall be employed without specific agreement between the party specifying this test method and the party performing
the hardness test.
12. Report
12.1 Report the following information:
12.1.1 The average Leeb hardness number for each test area with the impact device indicated (for example, xxx HLD or xxx
HLD+15).
12.1.2 When hardness values converted from the Leeb number are reported, the instrument used shall be reported in parentheses,
for example, HB (HLG).
TABLE 2 Compensation Values for Other Impact Directions:
Device D
L
D
-6 -12 -20 -29
-6 -12 -19 -27
-5 -11 -18 -25
-5 -10 -17 -24
-5 -10 -16 -22
-4 -9 -15 -20
-4 -8 -14 -19
-4 -8 -13 -18
-3 -7 -12 -17
-3 -6 -11 -16
-3 -6 -10 -15
-2 -5 -9 -14
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TABLE 3 Compensation Values for Other Impact Directions:
Device D + 15
L
D + 15
-7 -14 -26 -38
-7 -13 -25 -36
-6 -12 -23 -34
-6 -12 -22 -32
-6 -11 -21 -30
-6 -11 -20 -28
-5 -10 -19 -27
-5 -10 -18 -25
-5 -9 -17 -24
-4 -9 -16 -22
-4 -8 -15 -21
-4 -8 -14 -20
TABLE 4 Compensation Values for Other Impact Directions:
Device E
L
E
-5 -9 -18 -26
-4 -9 -17 -24
-4 -9 -16 -22
-4 -8 -15 -21
-4 -8 -14 -20
-4 -8 -13 -18
-3 -7 -12 -17
-3 -7 -12 -16
-3 -6 -11 -15
-3 -6 -10 -14
-3 -5 -9 -13
-2 -5 -8 -12
13. Precision and Bias
13.1 The precision of this test method is based on an interlaboratory study of E140, Standard Hardness Conversion Tables for
Metals Relationship Among Brinell Hardenss, Vickers Hardenss, Rockwell Hardness, Superficial Hardness, Knoop Hardness,
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:E28-1044. Contact ASTM Customer
Service at service@astm.org.
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TABLE 5 Compensation Values for Other Impact Directions:
Device C
L
C
A A
-7 -15
-7 -14
-7 -13
-6 -13
-6 -12
-6 -11
-5 -10
-5 -10
-4 -9
-4 -8
-4 -7
-3 -6
A
Not permitted.
TABLE 6 Compensation Values for Other Impact Directions:
Device G (Steel)
L
G
. . . . . . -12 -18
. . . . . . -11 -17
. . . . . . -11 -16
-2 -5 -10 -15
. . . . . . -9 -14
. . . . . . -9 -13
. . . . . . -8 -12
. . . . . . -8 -11
. . . . . . -7 -10
Scleroscope Hardness, and Leeb Hardness, conducted in 2006. Six laboratories tested five unique blocks at varying hardness levels.
Every “test result” represents an individual determination and nine replicate test results were reported by each lab for each level.
Practice E691 was followed for the design and analysis of the data; the details are given in ASTM Research Report RR:E28-1044.
13.1.1 Repeatability (r)—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 1 case
in 20.
13.1.1.1 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.
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TABLE 7 Compensation Values for Other Impact Directions:
Device G (Grey Cast Iron)
L
G
. . . . . . -11 -17
. . . . . . -11 -16
-2 -5 -10 -15
. . . . . . -9 -14
. . . . . . -9 -13
TABLE 8 Compensation Values for Other Impact Directions:
Device DL
L
DL
-3 -6 -11 -16
-3 -5 -9 -14
-2 -5 -8 -13
-2 -4 -7 -11
-2 -3 -6 -10
-1 -3 -5 -9
-1 -2 -4 -7
-1 -2 -3 -6
13.1.1.2 Repeatability limits are listed in Table 10.
13.1.2 Reproducibility (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 1 case in 20.
13.1.2.1 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.
13.1.2.2 Reproducibility limits are listed in Table 10.
13.1.3 The above terms (repeatability limit and reproducibility limit) are used as specified in Practice E177.
13.1.4 Any judgment in accordance with statements 13.1.1 and 13.1.2 would have an approximate 95 % probability of being
correct.
13.2 Bias—At the time of the study, there was no accepted reference material suitable for determining the bias for this test method,
therefore no statement on bias is being made.
13.3 The precision statement was determined through statistical examination of 252 results, from 6 laboratories, on blocks
representing 5 levels of hardness. These five levels have been described as the following:
Level 1: 800 HLD
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TABLE 9 Compensation Values for Other Impact Directions:
Device S
L
S
-4 -9 -16 -23
-4 -8 -15 -22
-4 -8 -14 -21
-4 -7 -13 -19
-3 -7 -12 -18
-3 -7 -12 -16
-3 -6 -11 -15
-3 -6 -10 -14
-3 -5 -9 -12
-2 -5 -8 -11
-2 -5 -7 -10
Level 2: 720 HLD
Level 3: 670 HLD
Level 4: 600 HLD
Level 5: 520 HLD
13.3.1 To judge the equivalency of two test results, it is recommended to choose the level closest in characteristics to the test level.
B. VERIFICATION OF LEEB HARDNESS INSTRUMENTS
14. Scope
14.1 Part B covers the procedure for verification of Leeb hardness instruments by a standardized block method.
15. General Requirements
15.1 Before a Leeb hardness instrument is verified, the instrument shall be examined to ensure that:
15.1.1 The batteries in the indicating device are not discharged, and faulty batteries are replaced as required.
15.1.2 The impact device is clean, and the spherical tip of the impact body is free from all foreign matter (for example, dust, dirt,
grease, scale, etc.).
15.1.3 The tip of the impact body is free from cracks or deformed areas.
15.1.4 The test block is placed on a clean, level, firmly supported base.
16. Verification by Standardized Test Blocks
16.1 Check the Leeb hardness instrument by making two impacts on a five impacts uniformly distributed across a calibrated test
surface of a standardized test block.
16.2 The Leeb hardness instrument shall be considered verified if the individual arithmetic average of the five individual impact
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TABLE 10 Hardness
Repeatability Reproducibility
A
Average Repeatability Limit Reproducibility Limit
Standard Deviation Standard Deviation
Material
S S r R
x¯ r R
Blocks 0521, 0520, and 0519 – 795.7 3.4 6.5 9.5 18.1
Level 1 hardness
Blocks 0518, 0517, and 0516 – 728.9 4.1 5.9 11.6 16.6
A
Level 2 hardness
Blocks 0515, 0514, and 0513 – 674.7 2.7 4.4 7.5 12.4
Level 3 hardness
Blocks 0512, 0511, and 0510 – 595.9 2.4 5.1 6.8 14.4
Level 4 hardness
Blocks 059, 058, and 057 – 512.8 3.0 8.0 8.5 22.5
A
Level 5 hardness
A
Data from only five laboratories used.
readings fall within 66 HL units of the reference value. value of the calibrated surface. Any instrument not verified shall not be
used for testing without repair and re-verification.
C. CALIBRATION OF STANDARDIZED HARDNESS TEST BLOCKS FOR LEEB HARDNESS INSTRUMENTS
17. Scope
17.1 Part C covers the calibration of standardized hardness test blocks used for the verification of Leeb hardness instruments.
18. Manufacture
18.1 Each test block shall be made of steel with dimensions not less than 3.543 in. [90 mm] in diameter by 2.126 in. [54 mm] thick
for impact devices D, DC, D+15, DL,C,S, and E and 4.724 in. [120 mm] in diameter by 2.756 in. [70 mm] thick for impact device
G. The two opposite end plane surfaces shall be parallel.
18.2 Each block shall be specifically prepared and heat treated to give a specific hardness and the necessary homogeneity and
stability of structure.
18.3 Each steel b
...