ASTM A255-10(2014)
(Test Method)Standard Test Methods for Determining Hardenability of Steel
Standard Test Methods for Determining Hardenability of Steel
SIGNIFICANCE AND USE
3.1 This test method covers the procedure for determining the hardenability of steel by the end-quench or Jominy test. The test consists of water quenching one end of a cylindrical test specimen 1.0 in. in diameter and measuring the hardening response as a function of the distance from the quenched end.
SCOPE
1.1 These test methods cover the identification and description of test methods for determining the hardenability of steels. The two test methods include the quantitative end-quench or Jominy Test and a method for calculating the hardenability of steel from the chemical composition based on the original work by M. A. Grossman.
1.2 The selection of the test method to be used for determining the hardenability of a given steel shall be agreed upon between the supplier and user. The Certified Material Test Report shall state the method of hardenability determination.
1.3 The calculation method described in these test methods is applicable only to the range of chemical compositions that follow:
Element
Range, %
Carbon
0.10–0.70
Manganese
0.50–1.65
Silicon
0.15–0.60
Nickel
1.50 max
Chromium
1.35 max
Molybdenum
0.55 max
Copper
0.35 max
Vanadium
0.20 max
1.4 Hardenability is a measure of the depth to which steel will harden when quenched from its austenitizing temperature (Table 1). It is measured quantitatively, usually by noting the extent or depth of hardening of a standard size and shape of test specimen in a standardized quench. In the end-quench test the depth of hardening is the distance along the specimen from the quenched end which correlates to a given hardness level. (A) A variation of ±10°F (6°C) from the temperatures in this table is permissible.(B) Normalizing and austenitizing temperatures are 50°F (30°C) higher for the 6100 series.
1.5 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: A255 − 10 (Reapproved 2014)
Standard Test Methods for
Determining Hardenability of Steel
This standard is issued under the fixed designation A255; 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 responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 These test methods cover the identification and descrip-
bility of regulatory limitations prior to use.
tionoftestmethodsfordeterminingthehardenabilityofsteels.
The two test methods include the quantitative end-quench or
2. Referenced Documents
Jominy Test and a method for calculating the hardenability of
steelfromthechemicalcompositionbasedontheoriginalwork 2.1 ASTM Standards:
E18Test Methods for Rockwell Hardness of Metallic Ma-
by M. A. Grossman.
terials
1.2 The selection of the test method to be used for deter-
E112Test Methods for Determining Average Grain Size
mining the hardenability of a given steel shall be agreed upon
2.2 ASTM Adjuncts:
between the supplier and user. The Certified Material Test
ASTM Hardenability Chart
Report shall state the method of hardenability determination.
1.3 The calculation method described in these test methods
is applicable only to the range of chemical compositions that END-QUENCH OR JOMINY TEST
follow:
3. Description
Element Range, %
3.1 This test method covers the procedure for determining
Carbon 0.10–0.70
Manganese 0.50–1.65 thehardenabilityofsteelbytheend-quenchorJominytest.The
Silicon 0.15–0.60
test consists of water quenching one end of a cylindrical test
Nickel 1.50 max
specimen 1.0 in. in diameter and measuring the hardening
Chromium 1.35 max
response as a function of the distance from the quenched end.
Molybdenum 0.55 max
Copper 0.35 max
Vanadium 0.20 max
4. Apparatus
1.4 Hardenability is a measure of the depth to which steel
4.1 Support for Test Specimen—Afixture for supporting the
will harden when quenched from its austenitizing temperature
test specimen vertically so that the lower end of the specimen
(Table 1). It is measured quantitatively, usually by noting the
is a distance of 0.5 in. (12.7 mm) above the orifice of the
extentordepthofhardeningofastandardsizeandshapeoftest
water-quenching device.Asatisfactory type of support for the
specimen in a standardized quench. In the end-quench test the
standard 1.0-in. (25.4-mm) specimen is shown in Fig. 1.
depthofhardeningisthedistancealongthespecimenfromthe
quenched end which correlates to a given hardness level. NOTE 1—Asuitable support for other sizes and shapes of specimens is
shown in Fig. X1.1.
1.5 Thevaluesstatedininch-poundunitsaretoberegarded
4.2 Water-QuenchingDevice—Awater-quenchingdeviceof
as standard. The values given in parentheses are mathematical
suitable capacity to provide a vertical stream of water that can
conversions to SI units that are provided for information only
be controlled to a height of 2.5 in. (63.5 mm) when passing
and are not considered standard.
through an orifice 0.5 in. (12.7 mm) in diameter. A tank of
1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
These test methods are under the jurisdiction of ASTM Committee A01 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Steel, Stainless Steel and Related Alloys and are the direct responsibility of Standards volume information, refer to the standard’s Document Summary page on
Subcommittee A01.15 on Bars. the ASTM website.
Current edition approved Oct. 1, 2014. Published October 2014. Originally Standard ASTM Hardenability Charts (8 ⁄2 by 11 in. pads of 50 charts) are
approved in 1942. Last previous edition approved in 2010 as A255–10. DOI: available from ASTM International Headquarters. Order Adjunct No. ADJA0255.
10.1520/A0255-10R14. Original adjunct produced in 1945.
*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
A255 − 10 (2014)
A
TABLE 1 Normalizing and Austenitizing Temperatures
hardening characteristics. The sample shall be held at the
Ordered
temperature listed in Table 1 for 1 h and cooled in air.
Normalizing Austenitizing
Carbon
Steel Series Temperature, Temperature, Tempering of the normalized sample to improve machinability
Content,
°F (°C) °F (°C)
is permitted.
max, %
1000, 1300, 1500, 0.25 and under 1700 (925) 1700 (925)
6.2 Heating—Place the specimen in a furnace that is at the
3100, 4000, 4100
specified austenitizing temperature (Table 1) and hold at this
4300, 4400, 4500, 0.26 to 0.36, 1650 (900) 1600 (870)
temperature for 30 min. In production testing slightly longer
4600, 4700, 5000, incl
B
5100, 6100,
times up to 35 min may be used without appreciably affecting
8100, 8600, 8700,
8800, 9400, 9700, results. It is important to heat the specimen in such an
atmosphere that practically no scaling and a minimum of
0.37 and over 1600 (870) 1550 (845)
decarburization takes place. This may be accomplished by
2300, 2500, 3300, 0.25 and under 1700 (925) 1550 (845)
4800, 9300
heating the specimen in a vertical position in a container with
0.26 to 0.36, 1650 (900) 1500 (815)
an easily removable cover containing a layer of cast-iron chips
incl
0.37 and over 1600 (870) 1475 (800) with the bottom face of the specimen resting on the chips.
9200 0.50 and over 1650 (900) 1600 (870)
6.2.1 Other methods consist of placing the specimen in an
A
A variation of ±10°F (6°C) from the temperatures in this table is permissible.
appropriately sized hole in a graphite block or placing the
B
Normalizing and austenitizing temperatures are 50°F (30°C) higher for the 6100
specimen in an upright tube attached to a flat base, both of a
series.
heat-resistant metal, with the collar projecting for a tong hold.
Place a disk of graphite or carbon, or a layer of carbonaceous
material such as charcoal, in the bottom of the tube to prevent
sufficient capacity to maintain the water temperature require-
scaling.
ments of 6.3 with a small pump and control valves will be
6.2.2 Foraparticularfixtureandfurnace,determinethetime
foundsatisfactory.Thewater-supplylineshallalsobeprovided
required to heat the specimen to the austenitizing temperature
with a quick opening valve.
byinsertingathermocoupleintoaholedrilledaxiallyinthetop
of the specimen. Repeat this procedure periodically, for ex-
5. Test Specimens
ample once a month, for each combination of fixture and
5.1 Wrought Specimens—End-quench specimens shall be
furnace.
preparedfromrolledorforgedstockandshallrepresentthefull
6.3 Quenching—Adjust the water-quenching device so that
crosssectionoftheproduct.Ifnegotiatedbetweenthesupplier
the stream of water rises to a free height of 2.5 in. (63.5 mm)
and the user, the end-quench specimen may be prepared from
above the 0.5-in. (12.7-mm) orifice, without the specimen in
a given location in a forged or rolled product or from a
position. The support for the specimen shall be dry at the
continuous cast billet. The test specimen shall be 1.0 in. (25.4
beginning of each test. Then place the heated specimen in the
mm) in diameter by 4.0 in. (101.6 mm) in length, with means
support so that its bottom face is 0.5 in. above the orifice, and
for hanging it in a vertical position for end quenching.
turn on the water by means of the quick-opening valve. The
Dimensions of the preferred specimen and of an optional
time between removal of the specimen from the furnace and
specimen (Note 2) are given in Figs. 2 and 3. The specimen
thebeginningofthequenchshouldnotbemorethan5s.Direct
shall be machined from a bar previously normalized in
thestreamofwater,atatemperatureof40to85°F(5to30°C),
accordance with 6.1 and of such size as to permit the removal
against the bottom face of the specimen for not less than 10
ofalldecarburizationinmachiningto1.0in.round.Theendof
min. Maintain a condition of still air around the specimen
the specimen to be water cooled shall have a reasonably
duringcooling.Ifthespecimenisnotcoldwhenremovedfrom
smooth finish, preferably produced by grinding. Normalizing
the fixture, immediately quench it in water.
may be waived by agreement between the supplier and the
6.4 Hardness Measurement—Two flats 180° apart shall be
user.The previous thermal history of the specimen tested shall
ground to a minimum depth of 0.015 in. (0.38 mm) along the
always be recorded.
entire length of the bar and Rockwell C hardness measure-
5.2 Cast Specimens—A separately cast end-quench speci-
ments made along the length of the bar. Shallower ground
men may be used for non-boron steels. Cast specimens are not
depthscanaffectreproducibilityofresults,andcorrelationwith
suitable for boron steel grades due to erratic results.Agraphite
cooling rates in quenched bars.
ormetalmoldmaybeusedtoformanoverlengthspecimen1.0
6.4.1 The preparation of the two flats must be carried out
in. (25.4 mm) in diameter which shall be cut to the standard
with considerable care. They should be mutually parallel and
specimen size. The mold may also be used to form a 1.25-in.
the grinding done in such a manner that no change of the
(31.8-mm) diameter specimen which shall be machined to the
quenched structure takes place. Very light cuts with water
final specimen size. Cast tests need not be normalized.
cooling and a coarse, soft-grinding wheel are recommended to
avoidheatingthespecimen.Inordertodetecttemperingdueto
NOTE 2—Other sizes and shapes of test specimens are described in
Appendix X1. grinding, the flat may be etched with one of the following
etchant solutions:
6. Procedure
NOTE 3—5% nitric acid (concentrated) and 95% water by volume.
6.1 Normalizing—The wrought product from which the
NOTE 4—50% hydrochloric acid (concentrated) and 50% water by
specimenistobepreparedshallbenormalizedtoensureproper volume.
A255 − 10 (2014)
FIG. 1 Test Specimen in Support for Water Quenching
FIG. 2 Preferred Test Specimen
FIG. 3 Optional Test Specimen
Wash the sample in hot water. Etch in solution No. 1 until
black.Washinhotwater.ImmerseinsolutionNo.2for3sand
wash in hot water. Dry in air blast.
A255 − 10 (2014)
6.4.1.1 Thepresenceoflighterordarkerareasindicatesthat represent HRC values and the abscissae represent the distance
hardness and structure have been altered in grinding. If such from the quenched end of the specimen at which the hardness
changes caused by grinding are indicated, new flats may be determinations were made. When hardness readings are taken
prepared. on two or more flats, the values at the same distance should be
6.4.2 When hardness tests are made, the test specimen rests averaged and that value used for plotting. A facsimile of the
on one of its flats on an anvil firmly attached to the hardness standard ASTM hardenability chart on which typical harden-
machine. It is important that no vertical movement be allowed ability curves have been plotted is shown in Fig. 4.
when the major load is applied. The anvil must be constructed
to move the test specimen past the penetrator in accurate steps 8. Index of Hardenability
of ⁄16 in. (1.5 mm). Resting the specimen in a V-block is not
8.1 The hardenability of a steel can be designated by a
permitted.
specific HRC hardness value or HRC hardness value range at
6.4.2.1 The Rockwell tester should periodically be checked
a given Jominy (“J”) distance. Examples of this method are
againststandardtestblocks.Itisrecommendedthatatestblock
4 7
J ⁄16 in. (6.4 mm) = 47 HRC min, J ⁄16 in. (11.1 mm) = 50
be interposed between the specimen and the indenter to check
HRC max, and J ⁄16 in. (7.9 mm) = 38–49 HRC.
the seating of the indenter and the specimen simultaneously.
For general statements regarding the use of test blocks and
9. Report
surface conditions, reference should be made to 4.7 and 5.2,
9.1 Report the following information that may be recorded
respectively, of Test Methods E18.
on the ASTM hardenability chart:
6.4.3 Exercisecareinregisteringthepointoftheindenterin
9.1.1 Previous thermal history of the specimen tested, in-
relationship to the quenched end of the specimen as well as
cluding the temperature of normalizing and austenitizing,
providing for accurate spacing between indentations. A low-
9.1.2 Chemical Composition,
powermeasuringmicroscopeissuitableforuseindetermining
9.1.3 ASTM grain size (McQuaid-Ehn) as determined by
the distance from the quenched end to the center of the first
Test Methods E112, unless otherwise indicated, and
impression and in checking the distance from center to center
9.1.4 A prominent notation on the standard hardenability
of the succeeding impressions. It has been found that with
chart if any of the test specimens listed in Appendix X1 are
reasonableoperatingcareandawell-builtfixture,itispractical
used.
to locate the center of the first impression 0.0625 6 0.004 in.
(1.5 6 0.10 mm) from the quenched end. The variations
CALCULATION OF HARDENABILITY
betweenspacingsshouldbeevensmaller.Obviously,itismore
important to position the indenter accurately when testing
10. Introduction
low-hardenability steels than when testing high-hardenability
10.1 This method of Jominy Hardenability calculation from
steels. The positioning of the indenter should be checked with
the chemical ideal diameter (DI) on a steel is based on the
sufficientfrequencytoprovideassurancethataccuracyrequire-
original work of M. A. Grossman and provides increased
ments are being met. In cases of lack of reproducibility or of
accuracy by refinement of the carbon multiplying factors and
differences between laboratories, indenter spacing should be
the correlation of a boron factor (B.F.) with carbon and alloy
measured immediately.
1 content. These refinements were based on analysis of thou-
6.4.4 Readingsshallbetakeninstepsof ⁄16in.(1.6mm)for
sands of heats of boron and non-boron 1500, 4100, 5000, and
the first 16 sixteenths (25.4 mm), then 18, 20, 22, 24, 28, and
8600 series steels encompassing a range of compositions as
32 sixteenths of an inch. Values below 20 HRC are not
follows and a range of DI as contained in Tables 2-5. The
recorded because such values are not accurate. When a flat on
accuracyofthistestmethodandthetechniquesusedtodevelop
which readings have been made is used as
...
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: A255 − 10 A255 − 10 (Reapproved 2014)
Standard Test Methods for
Determining Hardenability of Steel
This standard is issued under the fixed designation A255; 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 These test methods cover the identification and description of test methods for determining the hardenability of steels. The
two test methods include the quantitative end-quench or Jominy Test and a method for calculating the hardenability of steel from
the chemical composition based on the original work by M. A. Grossman.
1.2 The selection of the test method to be used for determining the hardenability of a given steel shall be agreed upon between
the supplier and user. The Certified Material Test Report shall state the method of hardenability determination.
1.3 The calculation method described in these test methods is applicable only to the range of chemical compositions that follow:
Element Range, %
Carbon 0.10–0.70
Manganese 0.50–1.65
Silicon 0.15–0.60
Nickel 1.50 max
Chromium 1.35 max
Molybdenum 0.55 max
Copper 0.35 max
Vanadium 0.20 max
1.4 Hardenability is a measure of the depth to which steel will harden when quenched from its austenitizing temperature (Table
1). It is measured quantitatively, usually by noting the extent or depth of hardening of a standard size and shape of test specimen
in a standardized quench. In the end-quench test the depth of hardening is the distance along the specimen from the quenched end
which correlates to a given hardness level.
1.5 The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are for information
only.mathematical conversions to SI units that are provided for information only and are not considered 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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
E18 Test Methods for Rockwell Hardness of Metallic Materials
E112 Test Methods for Determining Average Grain Size
2.2 ASTM Adjuncts:
ASTM Hardenability Chart
These test methods are under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel and Related Alloys and are the direct responsibility of Subcommittee
A01.15 on Bars.
Current edition approved May 1, 2010Oct. 1, 2014. Published June 2010October 2014. Originally approved in 1942. Last previous edition approved in 20072010 as
ε1
A255 – 07A255 – 10. . DOI: 10.1520/A0255-10.10.1520/A0255-10R14.
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.
3 1
Standard ASTM Hardenability Charts (8 ⁄2 by 11 in. pads of 50 charts) are available from ASTM International Headquarters. Order Adjunct No. ADJA0255. Original
adjunct produced in 1945.
*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
A255 − 10 (2014)
A
TABLE 1 Normalizing and Austenitizing Temperatures
Ordered
Normalizing Austenitizing
Carbon
Steel Series Temperature, Temperature,
Content,
°F (°C) °F (°C)
max, %
1000, 1300, 1500, 0.25 and under 1700 (925) 1700 (925)
3100, 4000, 4100
4300, 4400, 4500, 0.26 to 0.36, 1650 (900) 1600 (870)
4600, 4700, 5000, incl
B
5100, 6100,
8100, 8600, 8700,
8800, 9400, 9700,
0.37 and over 1600 (870) 1550 (845)
2300, 2500, 3300, 0.25 and under 1700 (925) 1550 (845)
4800, 9300
0.26 to 0.36, 1650 (900) 1500 (815)
incl
0.37 and over 1600 (870) 1475 (800)
9200 0.50 and over 1650 (900) 1600 (870)
A
A variation of ±10°F (6°C) from the temperatures in this table is permissible.
B
Normalizing and austenitizing temperatures are 50°F (30°C) higher for the 6100
series.
END-QUENCH OR JOMINY TEST
3. Description
3.1 This test method covers the procedure for determining the hardenability of steel by the end-quench or Jominy test. The test
consists of water quenching one end of a cylindrical test specimen 1.0 in. in diameter and measuring the hardening response as
a function of the distance from the quenched end.
4. Apparatus
4.1 Support for Test Specimen—A fixture for supporting the test specimen vertically so that the lower end of the specimen is
a distance of 0.5 in. (12.7 mm) above the orifice of the water-quenching device. A satisfactory type of support for the standard
1.0-in. (25.4-mm) specimen is shown in Fig. 1.
NOTE 1—A suitable support for other sizes and shapes of specimens is shown in Fig. X1.1.
4.2 Water-Quenching Device—A water-quenching device of suitable capacity to provide a vertical stream of water that can be
controlled to a height of 2.5 in. (63.5 mm) when passing through an orifice 0.5 in. (12.7 mm) in diameter. A tank of sufficient
capacity to maintain the water temperature requirements of 6.3 with a small pump and control valves will be found satisfactory.
The water-supply line shall also be provided with a quick opening valve.
FIG. 1 Test Specimen in Support for Water Quenching
A255 − 10 (2014)
5. Test Specimens
5.1 Wrought Specimens—End-quench specimens shall be prepared from rolled or forged stock and shall represent the full cross
section of the product. If negotiated between the supplier and the user, the end-quench specimen may be prepared from a given
location in a forged or rolled product or from a continuous cast billet. The test specimen shall be 1.0 in. (25.4 mm) in diameter
by 4.0 in. (101.6 mm) in length, with means for hanging it in a vertical position for end quenching. Dimensions of the preferred
specimen and of an optional specimen (Note 2) are given in Figs. 2 and 3. The specimen shall be machined from a bar previously
normalized in accordance with 6.1 and of such size as to permit the removal of all decarburization in machining to 1.0 in. round.
The end of the specimen to be water cooled shall have a reasonably smooth finish, preferably produced by grinding. Normalizing
may be waived by agreement between the supplier and the user. The previous thermal history of the specimen tested shall always
be recorded.
5.2 Cast Specimens—A separately cast end-quench specimen may be used for non-boron steels. Cast specimens are not suitable
for boron steel grades due to erratic results. A graphite or metal mold may be used to form an overlength specimen 1.0 in. (25.4
mm) in diameter which shall be cut to the standard specimen size. The mold may also be used to form a 1.25-in. (31.8-mm)
diameter specimen which shall be machined to the final specimen size. Cast tests need not be normalized.
NOTE 2—Other sizes and shapes of test specimens are described in Appendix X1.
6. Procedure
6.1 Normalizing—The wrought product from which the specimen is to be prepared shall be normalized to ensure proper
hardening characteristics. The sample shall be held at the temperature listed in Table 1 for 1 h and cooled in air. Tempering of the
normalized sample to improve machinability is permitted.
6.2 Heating—Place the specimen in a furnace that is at the specified austenitizing temperature (Table 1) and hold at this
temperature for 30 min. In production testing slightly longer times up to 35 min may be used without appreciably affecting results.
It is important to heat the specimen in such an atmosphere that practically no scaling and a minimum of decarburization takes place.
This may be accomplished by heating the specimen in a vertical position in a container with an easily removable cover containing
a layer of cast-iron chips with the bottom face of the specimen resting on the chips.
6.2.1 Other methods consist of placing the specimen in an appropriately sized hole in a graphite block or placing the specimen
in an upright tube attached to a flat base, both of a heat-resistant metal, with the collar projecting for a tong hold. Place a disk of
graphite or carbon, or a layer of carbonaceous material such as charcoal, in the bottom of the tube to prevent scaling.
6.2.2 For a particular fixture and furnace, determine the time required to heat the specimen to the austenitizing temperature by
inserting a thermocouple into a hole drilled axially in the top of the specimen. Repeat this procedure periodically, for example once
a month, for each combination of fixture and furnace.
6.3 Quenching—Adjust the water-quenching device so that the stream of water rises to a free height of 2.5 in. (63.5 mm) above
the 0.5-in. (12.7-mm) orifice, without the specimen in position. The support for the specimen shall be dry at the beginning of each
test. Then place the heated specimen in the support so that its bottom face is 0.5 in. above the orifice, and turn on the water by
means of the quick-opening valve. The time between removal of the specimen from the furnace and the beginning of the quench
should not be more than 5 s. Direct the stream of water, at a temperature of 40 to 85°F (5 to 30°C), against the bottom face of
the specimen for not less than 10 min. Maintain a condition of still air around the specimen during cooling. If the specimen is not
cold when removed from the fixture, immediately quench it in water.
6.4 Hardness Measurement—Two flats 180° apart shall be ground to a minimum depth of 0.015 in. (0.38 mm) along the entire
length of the bar and Rockwell C hardness measurements made along the length of the bar. Shallower ground depths can affect
reproducibility of results, and correlation with cooling rates in quenched bars.
FIG. 2 Preferred Test Specimen
A255 − 10 (2014)
FIG. 3 Optional Test Specimen
6.4.1 The preparation of the two flats must be carried out with considerable care. They should be mutually parallel and the
grinding done in such a manner that no change of the quenched structure takes place. Very light cuts with water cooling and a
coarse, soft-grinding wheel are recommended to avoid heating the specimen. In order to detect tempering due to grinding, the flat
may be etched with one of the following etchant solutions:
NOTE 3—5 % nitric acid (concentrated) and 95 % water by volume.
NOTE 4—50 % hydrochloric acid (concentrated) and 50 % water by volume.
Wash the sample in hot water. Etch in solution No. 1 until black. Wash in hot water. Immerse in solution No. 2 for 3 s and wash
in hot water. Dry in air blast.
6.4.1.1 The presence of lighter or darker areas indicates that hardness and structure have been altered in grinding. If such
changes caused by grinding are indicated, new flats may be prepared.
6.4.2 When hardness tests are made, the test specimen rests on one of its flats on an anvil firmly attached to the hardness
machine. It is important that no vertical movement be allowed when the major load is applied. The anvil must be constructed to
move the test specimen past the penetrator in accurate steps of ⁄16 in. (1.5 mm). Resting the specimen in a V-block is not permitted.
6.4.2.1 The Rockwell tester should periodically be checked against standard test blocks. It is recommended that a test block be
interposed between the specimen and the indenter to check the seating of the indenter and the specimen simultaneously. For general
statements regarding the use of test blocks and surface conditions, reference should be made to 4.7 and 5.2, respectively, of Test
Methods E18.
6.4.3 Exercise care in registering the point of the indenter in relationship to the quenched end of the specimen as well as
providing for accurate spacing between indentations. A low-power measuring microscope is suitable for use in determining the
distance from the quenched end to the center of the first impression and in checking the distance from center to center of the
succeeding impressions. It has been found that with reasonable operating care and a well-built fixture, it is practical to locate the
center of the first impression 0.0625 6 0.004 in. (1.5 6 0.10 mm) from the quenched end. The variations between spacings should
be even smaller. Obviously, it is more important to position the indenter accurately when testing low-hardenability steels than when
testing high-hardenability steels. The positioning of the indenter should be checked with sufficient frequency to provide assurance
that accuracy requirements are being met. In cases of lack of reproducibility or of differences between laboratories, indenter
spacing should be measured immediately.
6.4.4 Readings shall be taken in steps of ⁄16 in. (1.6 mm) for the first 16 sixteenths (25.4 mm), then 18, 20, 22, 24, 28, and 32
sixteenths of an inch. Values below 20 HRC are not recorded because such values are not accurate. When a flat on which readings
have been made is used as a base, the burrs around the indentation shall be removed by grinding unless a fixture is used which
has been relieved to accommodate the irregularities due to the indentations.
6.4.4.1 Hardness readings should preferably be made on two flats 180° apart. Testing on two flats will assist in the detection
of errors in specimen preparation and hardness measurement. If the two probes on opposite sides differ by more than 4 HRC points
at any one position, the test should be repeated on new flats, 90° from the first two flats. If the retest also has greater than 4 HRC
points spread, a new specimen should be tested.
6.4.4.2 For reporting purposes, hardness readings should be recorded to the nearest integer, with 0.5 HRC values rounded to
the next higher integer.
7. Plotting Test Results
7.1 Test results should be plotted on a standard hardenability chart prepared for this purpose, in which the ordinates represent
HRC values and the abscissae represent the distance from the quenched end of the specimen at which the hardness determinations
A255 − 10 (2014)
were made. When hardness readings are taken on two or more flats, the val
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