Standard Test Method for Hardness Testing of 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 E18 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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Historical
Publication Date
14-Jan-1992
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ASTM B294-92(1997) - Standard Test Method for Hardness Testing of Cemented Carbides
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NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: B 294 – 92 (Reapproved 1997)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
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 3. Significance and Use
1.1 This test method covers the hardness testing of ce- 3.1 Rockwell hardness is one of the more important prop-
mented carbides by use of the Rockwell hardness tester with erties used to evaluate cemented carbides. For compositional
the Rockwell A scale (diamond indenter and 588.4 N (60 kgf) groups of cemented carbides, hardness is an indication of wear
load) in the range of Rockwell A80 and above. Also covered resistance and toughness. Lower hardness grades usually
are the procedures for the testing and selection of diamond indicate less wear resistance but greater toughness. For a
indenters, the management and traceability of the four levels of specific grade of cemented carbide, hardness is an indication of
standard test blocks, the acquisition of secondary standard test the metallurgical quality of the material. In no case is hardness
blocks, and the making and calibration of working standard test the only property to be considered in evaluating cemented
blocks. carbides.
1.2 The Rockwell hardness tester is a convenient and
4. Apparatus
reliable means of measuring the hardness of cemented car-
4.1 Scale—All hardness tests shall be made on the regular
bides. A hardness value is obtained easily, but it is subject to
considerable error unless certain precautions are observed. (as opposed to superficial) Rockwell tester, using a 588.4 N (60
kgf) load (Rockwell A scale).
1.3 Test Methods E 18 shall be followed except where
otherwise indicated in this test method. 4.2 Effect of Vibration—The Rockwell hardness tester
should be located in a vibration-free area in order to avoid
1.4 The values stated in SI units are to be regarded as
standard. The values given in parentheses are for information erroneous results. If this is not possible, the tester shall be
mounted so as to minimize vibrations, since vibrations tend to
only.
1.5 This standard does not purport to address all of the cause erratic readings.
4.3 Indenter—The standard indenter shall be selected, in
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- accordance with the Annex to this test method, from diamond
cone indenters specified for Rockwell A scale use and in
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. conformance with Test Methods E 18.
4.3.1 The indenter, and an indentation made with it, in
2. Referenced Documents
hardened steel or cemented carbide should be examined
2.1 ASTM Standards: optically at approximately 50-diameter magnification for de-
E 18 Test Methods for Rockwell Hardness and Rockwell fects, conformance to shape, and mounting of the diamond.
Superficial Hardness of Metallic Materials Examination should be made when selecting an indenter,
E 29 Practice for Using Significant Digits in Test Data to occasionally during use, and whenever some event may be
Determine Conformance with Specifications suspected of having damaged the diamond or its mounting.
2.2 ISO Standard: 4.4 Anvils—Select an anvil suitable for the specimen to be
3738-2 Hardmetals—Rockwell hardness test (Scale A)— tested. The shoulder of the screw and the mating surface of the
Part 2, Preparation and calibration of standard test blocks anvil should be clean. Seat the anvil securely. For the best
accuracy, flat test pieces should be tested on a flat anvil of
approximately 6-mm ( ⁄4-in.) diameter. The bearing surface of
this anvil, with a Rockwell C hardness of at least 60, shall be
polished smooth and be free of pits and heavy scratches. The
This test method is under the jurisdiction of ASTM Committee B-9 on Metal
Powders and Metal Powder Productsand is the direct responsibility of Subcommit-
test piece should be supported suitably, with the test surface
tee B09.06 on Cemented Carbides.
perpendicular to the line of travel of the indenter. Dust, dirt,
Current edition approved Jan. 15, 1992. Published March 1992. Originally
grease, or scale should not be allowed to accumulate on any
published as B 294 – 54 T. Last previous edition B 294 – 86.
part of the apparatus, as this will affect the results.
Annual Book of ASTM Standards, Vol 03.01.
Annual Book of ASTM Standards, Vol 14.02.
4.5 Test Blocks—Secondary standard test blocks or working
Available from American National Standards Institute, 11 W. 42nd St., 13th
standard test blocks that have been prepared and calibrated in
floor, New York, NY 10036.
B 294
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. Abrupt actuation of the major load removal lever will
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
indentation and the edge of a test specimen, shall be at least 1.5
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 (0.0005 in.) per pass with abundant flow of coolant, should
6.8.1 Select the standard test block having a value closest to
provide the desired surface. The thickness of the layer removed the trial hardness of the test specimen. Determine the Rockwell
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 than6 0.5 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.
sons are being made. The surface in contact with the anvil shall 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
15 mm ( ⁄16 in.). If less, then a flat surface at least 3-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 Practice E 29 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 Methods E 18.
7.1.4 The number of hardness determinations,
6.2 Disregard the first two readings after an indenter has
7.1.5 The smallest division of readout or graduation of the
been newly mounted.
hardness test machine and whether it is digital or analog,
6.3 Limit the speed of applying the major load so that the
7.1.6 The identification and original source of calibration
movement of the weights is completed in 4 to 6 s, with no test
for the standard test blocks used,
piece on the testing equipment and with the machine set to
apply a major load of 60 Kg. Verification should be by direct
When the second decimal place is less than 0.05, leave the first decimal place
observation of the weight motion, if visible.
unchanged. When the second decimal place is more than 0.05, increase the first
6.4 Do not permit the time of maintaining the major load
decimal place by 0.1. When the second decimal place is exactly 5 and the first
after the motion of the needle or the changing of the digital
decimal place is odd, increase the first decimal by 0.1. If the first decimal place is
readout has ceased to exceed 2 s. Removal of the major load even, leave it unchanged.
B 294
7.1.7 A reference to this test method, and 8.3 The reproducibility limit (R) between or among labora-
7.1.8 Details of any deviations from this test method, of tories is 0.4 HRA when each has calibrated its machine,
optional procedures used, and of any conditions and occur- indenter, and operator system with a standard test block that
rences that may have affected the results. has itself been calibrated to the same superior test block used
to calibrate the test blocks of the other laboratories. On the
8. Precision and Bias
basis of test error alone, the difference in absolute value of the
test results obtained in different laboratories on the same test
8.1 The following statements regarding the repeatability and
specimen will be expected to exceed 0.4 HRA only approxi-
reproducibility of hardness (HRA) measurements of cemented
mately 5 % of the time. The reproducibility standard deviation
carbide test specimens shall apply only within the hardness
(S ) is 0.14 HRA.
range established for the indenter in accordance with A1.8.2 or
R
8.4 Neither the data of the interlaboratory study nor theo-
A1.8.3. See Table A1.1.
retical considerations suggest a bias in this test procedure.
8.2 The repeatability limit (r) is 0.3 HRA. On the basis of
8.5 If the test specimens are of a hardness substantially
test error alone, the difference in absolute value of two test
outside the hardness ranges of the standard test blocks on
results obtained in the same laboratory on the same test
which the indenter has been performance tested, and if inter-
specimen will be expected to exceed 0.3 HRA only approxi-
laboratory reproducibility is critical, the same indenter and
mately 5 % of the time. The repeatability standard deviation
standard test blocks should be used by each laboratory.
(S ) is 0.1 HRA.
r
9. Keywords
9.1 cemented carbides; hardness; indenters; Rockwell hard-
The statements of repeatability and reproducibility in this section are based on
an interlaboratory study conducted by the Cemented Carbide Producers Association. 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- master standard test blocks. Set 3 is retained by the Secretariat
fies the control of master, primary, secondary, and working of ISO/TC 119.
standard test blocks. It specifies the preparation and calibration A1.3.2 The sets of master standard test blocks retained by
of primary, secondary, and working standard test blocks. It also the CCPA and ISO/TC 119 shall be kept as permanent
specifies the procedure for selecting indenters having the standards and shall be used only when calibration of a new
required precision from standard Scale A indenters. Both test master standard is required.
blocks and indenters complying with this Annex are required A1.3.3 Blocks retained by ISO/TC 119 shall be retained as
for Rockwell hardness testing of cemented carbides by the unused international standards. Only in the event of destruction
procedures of this test method. of some or all of Set 1 retained by the CCPA, and then only by
majority vote of the members of ISO/TC 119/SC4, shall they
A1.2 Hierarchy and Availability of Standard Test Blocks:
be released to be used for the calibration of new master
A1.2.1 Secondary standard test blocks, and the calibration
standard test blocks. They shall then be returned to ISO
...

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