ASTM B294-92(2006)e1
(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.
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 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 B294; 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.
´ NOTE—Added research report footnote to Section 8 editorially in June 2009.
1. Scope 2.2 ISO Standard:
ISO 3738-2 Hardmetals—Rockwell hardness test (Scale
1.1 This test method covers the hardness testing of ce-
A)—Part 2, Preparation and calibration of standard test
mented carbides by use of the Rockwell hardness tester with
blocks
the Rockwell A scale (diamond indenter and 588.4 N (60 kgf)
load) in the range of Rockwell A80 and above. Also covered
3. Significance and Use
are the procedures for the testing and selection of diamond
3.1 Rockwell hardness is one of the more important prop-
indenters,themanagementandtraceabilityofthefourlevelsof
erties used to evaluate cemented carbides. For compositional
standard test blocks, the acquisition of secondary standard test
groups of cemented carbides, hardness is an indication of wear
blocks,andthemakingandcalibrationofworkingstandardtest
resistance and toughness. Lower hardness grades usually
blocks.
indicate less wear resistance but greater toughness. For a
1.2 The Rockwell hardness tester is a convenient and
specificgradeofcementedcarbide,hardnessisanindicationof
reliable means of measuring the hardness of cemented car-
the metallurgical quality of the material. In no case is hardness
bides. A hardness value is obtained easily, but it is subject to
the only property to be considered in evaluating cemented
considerable error unless certain precautions are observed.
carbides.
1.3 Test Methods E18 shall be followed except where
otherwise indicated in this test method.
4. Apparatus
1.4 The values stated in SI units are to be regarded as
4.1 Scale—All hardness tests shall be made on the regular
standard. The values given in parentheses are for information
(asopposedtosuperficial)Rockwelltester,usinga588.4N(60
only.
kgf) load (Rockwell A scale).
1.5 This standard does not purport to address all of the
4.2 Effect of Vibration—The Rockwell hardness tester
safety concerns, if any, associated with its use. It is the
should be located in a vibration-free area in order to avoid
responsibility of the user of this standard to establish appro-
erroneous results. If this is not possible, the tester shall be
priate safety and health practices and determine the applica-
mounted so as to minimize vibrations, since vibrations tend to
bility of regulatory limitations prior to use.
cause erratic readings.
2. Referenced Documents 4.3 Indenter—The standard indenter shall be selected, in
2 accordance with the Annex to this test method, from diamond
2.1 ASTM Standards:
cone indenters specified for Rockwell A scale use and in
E18 Test Methods for Rockwell Hardness of Metallic Ma-
conformance with Test Methods E18.
terials
4.3.1 The indenter, and an indentation made with it, in
E29 Practice for Using Significant Digits in Test Data to
hardened steel or cemented carbide should be examined
Determine Conformance with Specifications
optically at approximately 50-diameter magnification for de-
fects, conformance to shape, and mounting of the diamond.
Examination should be made when selecting an indenter,
This test method is under the jurisdiction of ASTM Committee B09 on Metal
occasionally during use, and whenever some event may be
Powders and Metal Powder Products and is the direct responsibility of Subcom-
suspected of having damaged the diamond or its mounting.
mittee B09.06 on Cemented Carbides.
Current edition approved April 1, 2006. Published April 2006. Originally
4.4 Anvils—Select an anvil suitable for the specimen to be
approved in 1954. Last previous edition approved in 2001 as B294 – 92 (2001).
tested. The shoulder of the screw and the mating surface of the
DOI: 10.1520/B0294-92R06E01.
2 anvil should be clean. Seat the anvil securely. For the best
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B294–92 (2006)
accuracy, flat test pieces should be tested on a flat anvil of 6.2 Disregard the first two readings after an indenter has
approximately 6-mm ( ⁄4-in.) diameter. The bearing surface of been newly mounted.
this anvil, with a Rockwell C hardness of at least 60, shall be
6.3 Limit the speed of applying the major load so that the
polished smooth and be free of pits and heavy scratches. The
movement of the weights is completed in 4 to 6 s, with no test
test piece should be supported suitably, with the test surface
piece on the testing equipment and with the machine set to
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
9 1
15mm( ⁄16in.).Ifless,thenaflatsurfaceatleast3-mm( ⁄8-in.) specimens.
wide shall be prepared on which to conduct the test, and there 6.8.4 Determine the Rockwell A hardness of the test speci-
shall be an opposite flat surface such that the specimen
men, with determinations at three or more locations chosen at
conforms to the requirements of 5.2 and 5.3. If the test surface random, or as dictated by the purpose of the test.
is curved or the opposite surface must be supported in a
6.8.5 Calculate the arithmetic mean of the hardness deter-
V-anvil, the repeatability and reproducibility limits of 8.2 and
minations. Apply the correction determined as in 6.8.3, giving
8.3 may not apply.
due regard to the algebraic sign.
5.5 Preparation of Mounted Carbides—Remove mounted
6.8.6 Report the corrected arithmetic mean of the hardness
carbides from the steel body by heating or some other
determinations, rounded in accordance with Practice E29 to
convenient method. All braze metal or other bond material
the nearest 0.1 HRA.
shall be removed from both the test surface and the opposite
face.The specimen should then be prepared as described in 5.1
through 5.4.
When the second decimal place is less than 0.05, leave the first decimal place
unchanged. When the second decimal place is more than 0.05, increase the first
6. Procedure
decimal place by 0.1. When the second decimal place is exactly 5 and the first
6.1 Procedures that are not described in this test method
decimal place is odd, increase the first decimal by 0.1. If the first decimal place is
shall conform to those of Test Methods E18. even, leave it unchanged.
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B294–92 (2006)
7. Report 8.2 The repeatability limit (r) is 0.3 HRA. On the basis of
test error alone, the difference in absolute value of two test
7.1 Report the following information:
results obtained in the same laboratory on the same test
7.1.1 All details necessary for identification of the test
specimen will be expected to exceed 0.3 HRA only approxi-
specimen,
mately 5 % of the time. The repeatability standard deviation
7.1.2 The corrected mean hardness,
(S ) is 0.1 HRA.
r
7.1.3 The range of hardness determinations,
8.3 The reproducibility limit (R) between or among labora-
7.1.4 The number of hardness determinations,
tories is 0.4 HRA when each has calibrated its machine,
7.1.5 The smallest division of readout or graduation of the
indenter, and operator system with a standard test block that
hardness test machine and whether it is digital or analog,
has itself been calibrated to the same superior test block used
7.1.6 The identification and original source of calibration
to calibrate the test blocks of the other laboratories. On the
for the standard test blocks used,
basis of test error alone, the difference in absolute value of the
7.1.7 A reference to this test method, and
test results obtained in different laboratories on the same test
7.1.8 Details of any deviations from this test method, of
specimen will be expected to exceed 0.4 HRA only approxi-
optional procedures used, and of any conditions and occur-
mately 5 % of the time. The reproducibility standard deviation
rences that may have affected the results.
(S ) is 0.14 HRA.
R
8. Precision and Bias
8.4 Neither the data of the interlaboratory study nor theo-
retical considerations suggest a bias in this test procedure.
8.1 Thefollowingstatementsregardingtherepeatabilityand
8.5 If the test specimens are of a hardness substantially
reproducibility of hardness (HRA) measurements of cemented
outside the hardness ranges of the standard test blocks on
carbide test specimens shall apply only within the hardness
which the indenter has been performance tested, and if inter-
range established for the indenter in accordance withA1.8.2 or
laboratory reproducibility is critical, the same indenter and
A1.8.3. See Table A1.1.
standard test blocks should be used by each laboratory.
The statements of repeatability and reproducibility in this section are based on
9. Keywords
aninterlaboratorystudyconductedbytheCementedCarbideProducersAssociation.
6 9.1 cemented carbides; hardness; indenters; Rockwell hard-
Supporting data have been filed at ASTM International Headquarters and may
be obtained by requesting Research Report B09-1016. 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 Master Standard Test Blocks:
fies the control of master, primary, secondary, and working
A1.3.1 Of three sets of five master standard test blocks, Set
standard test blocks. It specifies the preparation and calibration
1 is retained by the CCPA. Set 2 has been released by the
of primary, secondary, and working standard test blocks. It also
CCPA to Wilson Instruments, so that Wilson Instruments may
specifies the procedure for selecting indenters having the
serve as the calibrating agency for secondary standard test
required precision from standard Scale A indenters. Both test
blocks traceable through primary standard test blocks to the set
blocks and indenters complying with this Annex are required
of master standard test blocks. Set 3 is retained by the
for Rockwell hardness testing of cemented carbides by the
Secretariat of ISO/TC 119.
procedures of this test method.
A1.3.2 The sets of master standard test blocks retained by
the CCPA and ISO/TC 119 shall be kept a
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