ASTM B294-92(2006)
(Test Method)Standard Test Method for Hardness Testing of Cemented Carbides
Standard Test Method for Hardness Testing of Cemented Carbides
SIGNIFICANCE AND USE
Rockwell hardness is one of the more important properties used to evaluate cemented carbides. For compositional groups of cemented carbides, hardness is an indication of wear resistance and toughness. Lower hardness grades usually indicate less wear resistance but greater toughness. For a specific grade of cemented carbide, hardness is an indication of the metallurgical quality of the material. In no case is hardness the only property to be considered in evaluating cemented carbides.
SCOPE
1.1 This test method covers the hardness testing of cemented carbides by use of the Rockwell hardness tester with the Rockwell A scale (diamond indenter and 588.4 N (60 kgf) load) in the range of Rockwell A80 and above. Also covered are the procedures for the testing and selection of diamond indenters, the management and traceability of the four levels of standard test blocks, the acquisition of secondary standard test blocks, and the making and calibration of working standard test blocks.
1.2 The Rockwell hardness tester is a convenient and reliable means of measuring the hardness of cemented carbides. A hardness value is obtained easily, but it is subject to considerable error unless certain precautions are observed.
1.3 Test Methods E 18 shall be followed except where otherwise indicated in this test method.
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:B294–92(Reapproved 2006)
Standard Test Method for
Hardness Testing of Cemented Carbides
This standard is issued under the fixed designation B 294; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope ISO 3738-2 Hardmetals—Rockwell hardness test (Scale
A)—Part 2, Preparation and calibration of standard test
1.1 This test method covers the hardness testing of ce-
blocks
mented carbides by use of the Rockwell hardness tester with
the Rockwell A scale (diamond indenter and 588.4 N (60 kgf)
3. Significance and Use
load) in the range of Rockwell A80 and above. Also covered
3.1 Rockwell hardness is one of the more important prop-
are the procedures for the testing and selection of diamond
erties used to evaluate cemented carbides. For compositional
indenters,themanagementandtraceabilityofthefourlevelsof
groups of cemented carbides, hardness is an indication of wear
standard test blocks, the acquisition of secondary standard test
resistance and toughness. Lower hardness grades usually
blocks,andthemakingandcalibrationofworkingstandardtest
indicate less wear resistance but greater toughness. For a
blocks.
specificgradeofcementedcarbide,hardnessisanindicationof
1.2 The Rockwell hardness tester is a convenient and
the metallurgical quality of the material. In no case is hardness
reliable means of measuring the hardness of cemented car-
the only property to be considered in evaluating cemented
bides. A hardness value is obtained easily, but it is subject to
carbides.
considerable error unless certain precautions are observed.
1.3 Test Methods E18 shall be followed except where
4. Apparatus
otherwise indicated in this test method.
4.1 Scale—All hardness tests shall be made on the regular
1.4 The values stated in SI units are to be regarded as
(asopposedtosuperficial)Rockwelltester,usinga588.4N(60
standard. The values given in parentheses are for information
kgf) load (Rockwell A scale).
only.
4.2 Effect of Vibration—The Rockwell hardness tester
1.5 This standard does not purport to address all of the
should be located in a vibration-free area in order to avoid
safety concerns, if any, associated with its use. It is the
erroneous results. If this is not possible, the tester shall be
responsibility of the user of this standard to establish appro-
mounted so as to minimize vibrations, since vibrations tend to
priate safety and health practices and determine the applica-
cause erratic readings.
bility of regulatory limitations prior to use.
4.3 Indenter—The standard indenter shall be selected, in
2. Referenced Documents accordance with the Annex to this test method, from diamond
2 cone indenters specified for Rockwell A scale use and in
2.1 ASTM Standards:
conformance with Test MethodsE18.
E18 Test Methods for Rockwell Hardness and Rockwell
4.3.1 The indenter, and an indentation made with it, in
Superficial Hardness of Metallic Materials
hardened steel or cemented carbide should be examined
E29 Practice for Using Significant Digits in Test Data to
optically at approximately 50-diameter magnification for de-
Determine Conformance with Specifications
3 fects, conformance to shape, and mounting of the diamond.
2.2 ISO Standard:
Examination should be made when selecting an indenter,
occasionally during use, and whenever some event may be
suspected of having damaged the diamond or its mounting.
This test method is under the jurisdiction of ASTM Committee B09 on Metal
Powders and Metal Powder Products and is the direct responsibility of Subcom-
4.4 Anvils—Select an anvil suitable for the specimen to be
mittee B09.06 on Cemented Carbides.
tested. The shoulder of the screw and the mating surface of the
Current edition approved April 1, 2006. Published April 2006. Originally
anvil should be clean. Seat the anvil securely. For the best
approved in 1954. Last previous edition approved in 2001 as B 294 – 92 (2001).
accuracy, flat test pieces should be tested on a flat anvil of
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
approximately 6-mm ( ⁄4-in.) diameter. The bearing surface of
Standards volume information, refer to the standard’s Document Summary page on
this anvil, with a Rockwell C hardness of at least 60, shall be
the ASTM website.
3 polished smooth and be free of pits and heavy scratches. The
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036. test piece should be supported suitably, with the test surface
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B294–92 (2006)
perpendicular to the line of travel of the indenter. Dust, dirt, apply a major load of 60 Kg. Verification should be by direct
grease, or scale should not be allowed to accumulate on any observation of the weight motion, if visible.
part of the apparatus, as this will affect the results. 6.4 Do not permit the time of maintaining the major load
4.5 Test Blocks—Secondary standard test blocks or working after the motion of the needle or the changing of the digital
standard test blocks that have been prepared and calibrated in readout has ceased to exceed 2 s. Removal of the major load
accordance with the Annex to this test method shall be used. should be gradual by operating lever in manual machines or by
motor in automatic machines, and should not exceed two
5. Test Specimens
additional seconds. On manual machines, abrupt actuation of
5.1 Size of Specimens—A minimum thickness of 1.6 mm
the major load trip lever may affect the hardness value
( ⁄16 in.) is recommended. With thinner specimens, breakage
obtained.Abruptactuationofthemajorloadremovalleverwill
may occur, resulting in damage to the anvil, the indenter, or
significantly affect the hardness value obtained.
both. Specimens that have enough overhang to cause imbal-
6.5 The Rockwell A hardness value is read after the major
ance shall be supported properly. The 6-mm ( ⁄4-in.) anvil will
load has been removed and while the minor load is still
support flat test specimens up to approximately 113 g ( ⁄4 lb)
applied.
and will also support the standard test blocks recommended
6.6 The distance between the centers of any two adjacent
previously. indentations, and the distance between the center of any
5.2 Preparation of Test Specimens—The finish of the test
indentationandtheedgeofatestspecimen,shallbeatleast1.5
surface is of major importance. The surface to be tested should mm (0.06 in.).
be prepared to obtain a roughness of Ra#0.2 µm (8 µin.) A
6.7 Hardness should be read or estimated to the nearest 0.1
coarser finish will provide a wider range of readings. Prepara- HRA. Calculations should be carried to two decimal places.
tion shall be conducted in such a way that alteration of the
6.8 Make two trial determinations of the hardness of the test
surface due to heat or cold-working is minimized. A 220-grit specimen. This action also reassures that the indenter is seated
medium hardness resinoid bond diamond wheel, downfed 0.01
properly.
mm(0.0005in.)perpasswithabundantflowofcoolant,should
6.8.1 Select the standard test block having a value closest to
providethedesiredsurface.Thethicknessofthelayerremoved
thetrialhardnessofthetestspecimen.DeterminetheRockwell
from an as-sintered surface to be tested shall be not less than
A hardness at three points on the block.
0.2 mm (0.008 in.).
6.8.2 If the arithmetic mean of the three determinations
5.3 The surfaces of the test specimen shall be flat and
differs from the certified hardness value of the standard test
parallel within one part per hundred parts in general practice,
block by more than 60.5 HRA, check the diamond indenter
but within one part per thousand parts when critical compari-
and the testing equipment, and eliminate the cause of the error.
sonsarebeingmade.Thesurfaceincontactwiththeanvilshall
Repeat the determinations.
be free of any irregularity (for example, a previous hardness
6.8.3 If the arithmetic mean of the three determinations
indentation). Taper that results in the test surface not being
differs from the certified hardness value of the standard test
normal to the axis of the indenter, or irregularity that causes
block by 60.5 HRA or less, record the difference, giving due
instability during the test, will result in error. regard to the algebraic sign. This difference will be used to
5.4 When determining the hardness of a test specimen with
correct the arithmetic mean of the hardness of the test
a curved surface, the radius of curvature shall not be less than specimens.
9 1
15mm( ⁄16in.).Ifless,thenaflatsurfaceatleast3-mm( ⁄8-in.)
6.8.4 Determine the Rockwell A hardness of the test speci-
wide shall be prepared on which to conduct the test, and there men, with determinations at three or more locations chosen at
shall be an opposite flat surface such that the specimen
random, or as dictated by the purpose of the test.
conforms to the requirements of 5.2 and 5.3. If the test surface 6.8.5 Calculate the arithmetic mean of the hardness deter-
is curved or the opposite surface must be supported in a
minations. Apply the correction determined as in 6.8.3, giving
V-anvil, the repeatability and reproducibility limits of 8.2 and
due regard to the algebraic sign.
8.3 may not apply.
6.8.6 Report the corrected arithmetic mean of the hardness
5.5 Preparation of Mounted Carbides—Remove mounted
determinations, rounded in accordance with PracticeE29 to
carbides from the steel body by heating or some other
the nearest 0.1 HRA.
convenient method. All braze metal or other bond material
7. Report
shall be removed from both the test surface and the opposite
face.The specimen should then be prepared as described in 5.1
7.1 Report the following information:
through 5.4. 7.1.1 All details necessary for identification of the test
specimen,
6. Procedure
7.1.2 The corrected mean hardness,
6.1 Procedures that are not described in this test method
7.1.3 The range of hardness determinations,
shall conform to those of Test MethodsE18.
6.2 Disregard the first two readings after an indenter has
When the second decimal place is less than 0.05, leave the first decimal place
been newly mounted.
unchanged. When the second decimal place is more than 0.05, increase the first
6.3 Limit the speed of applying the major load so that the
decimal place by 0.1. When the second decimal place is exactly 5 and the first
movement of the weights is completed in 4 to 6 s, with no test
decimal place is odd, increase the first decimal by 0.1. If the first decimal place is
piece on the testing equipment and with the machine set to even, leave it unchanged.
B294–92 (2006)
7.1.4 The number of hardness determinations, specimen will be expected to exceed 0.3 HRA only approxi-
7.1.5 The smallest division of readout or graduation of the mately 5 % of the time. The repeatability standard deviation
hardness test machine and whether it is digital or analog, (S ) is 0.1 HRA.
r
7.1.6 The identification and original source of calibration 8.3 The reproducibility limit (R) between or among labora-
for the standard test blocks used, tories is 0.4 HRA when each has calibrated its machine,
7.1.7 A reference to this test method, and indenter, and operator system with a standard test block that
7.1.8 Details of any deviations from this test method, of has itself been calibrated to the same superior test block used
optional procedures used, and of any conditions and occur- to calibrate the test blocks of the other laboratories. On the
rences that may have affected the results. basis of test error alone, the difference in absolute value of the
test results obtained in different laboratories on the same test
8. Precision and Bias specimen will be expected to exceed 0.4 HRA only approxi-
mately 5 % of the time. The reproducibility standard deviation
8.1 Thefollowingstatementsregardingtherepeatabilityand
(S ) is 0.14 HRA.
R
reproducibility of hardness (HRA) measurements of cemented
8.4 Neither the data of the interlaboratory study nor theo-
carbide test specimens shall apply only within the hardness
retical considerations suggest a bias in this test procedure.
range established for the indenter in accordance withA1.8.2 or
8.5 If the test specimens are of a hardness substantially
A1.8.3. See Table A1.1.
outside the hardness ranges of the standard test blocks on
8.2 The repeatability limit (r) is 0.3 HRA. On the basis of
which the indenter has been performance tested, and if inter-
test error alone, the difference in absolute value of two test
laboratory reproducibility is critical, the same indenter and
results obtained in the same laboratory on the same test
standard test blocks should be used by each laboratory.
9. Keywords
9.1 cemented carbides; hardness; indenters; Rockwell hard-
The statements of repeatability and reproducibility in this section are based on
aninterlaboratorystudyconductedbytheCementedCarbideProducersAssociation. ness test; Scale A; test blocks
ANNEX
(Mandatory Information)
A1. PREPARATION, CALIBRATION, AND CONTROL OF STANDARD TEST BLOCKS AND SELECTION OF SCALE A
INDENTERS USED IN THE PERFORMANCE OF THE PROCEDURES OF THIS TEST METHOD
A1.1 Scope and Field of Application—This Annex speci- A1.3.1 Of three sets of five master standard test blocks, Set
fies the control of master, primary, secondary, and working 1 is retained by the CCPA. Set 2 has been released by the
standard test blocks. It specifies the preparation and calibration
CCPA to Wilson Instruments, so that Wilson Instruments may
of primary, secondary, and working standard test blocks. It also
serve as the calibrating agency for secondary standard test
specifies the procedure for selecting indenters having the
blocks traceable through primary standard test blocks to the set
required precision from standard Scale A indenters. Both test
of master standard test blocks. Set 3 is retained by the
blocks and indenters complying with this Annex are required
Secretariat of ISO/TC 119.
for Rockwell hardness testing of cemented carbides by the
A1.3.2 The sets of master standard test blocks retained by
procedures of this test method.
the CCPA and ISO/TC 119 shall be kept as permanent
standards and shall be used only when calibration of a new
A1.2 Hierarchy and Availability of Standard Test Blocks:
master standard is required.
A1.2.1 Secondary standard test blocks, and the calibration
A1.3.3 Blocks retained by ISO/TC 119
...
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