ASTM A255-10(2018)
(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.
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.7 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.
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Designation: A255 − 10 (Reapproved 2018)
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, health, and environmental practices and deter-
1.1 These test methods cover the identification and descrip-
mine the applicability of regulatory limitations prior to use.
tionoftestmethodsfordeterminingthehardenabilityofsteels.
1.7 This international standard was developed in accor-
The two test methods include the quantitative end-quench or
dance with internationally recognized principles on standard-
Jominy Test and a method for calculating the hardenability of
ization established in the Decision on Principles for the
steelfromthechemicalcompositionbasedontheoriginalwork
Development of International Standards, Guides and Recom-
by M. A. Grossman.
mendations issued by the World Trade Organization Technical
1.2 The selection of the test method to be used for deter-
Barriers to Trade (TBT) Committee.
mining the hardenability of a given steel shall be agreed upon
between the supplier and user. The Certified Material Test 2. Referenced Documents
Report shall state the method of hardenability determination.
2.1 ASTM Standards:
1.3 The calculation method described in these test methods E18Test Methods for Rockwell Hardness of Metallic Ma-
is applicable only to the range of chemical compositions that terials
follow: E112Test Methods for Determining Average Grain Size
2.2 ASTM Adjuncts:
Element Range, %
ASTM Hardenability Chart
Carbon 0.10–0.70
Manganese 0.50–1.65
Silicon 0.15–0.60
END-QUENCH OR JOMINY TEST
Nickel 1.50 max
Chromium 1.35 max
3. Description
Molybdenum 0.55 max
Copper 0.35 max
3.1 This test method covers the procedure for determining
Vanadium 0.20 max
thehardenabilityofsteelbytheend-quenchorJominytest.The
1.4 Hardenability is a measure of the depth to which steel
test consists of water quenching one end of a cylindrical test
will harden when quenched from its austenitizing temperature
specimen 1.0 in. in diameter and measuring the hardening
(Table 1). It is measured quantitatively, usually by noting the
response as a function of the distance from the quenched end.
extentordepthofhardeningofastandardsizeandshapeoftest
specimen in a standardized quench. In the end-quench test the
4. Apparatus
depthofhardeningisthedistancealongthespecimenfromthe
4.1 Support for Test Specimen—Afixture for supporting the
quenched end which correlates to a given hardness level.
test specimen vertically so that the lower end of the specimen
1.5 Thevaluesstatedininch-poundunitsaretoberegarded
is a distance of 0.5 in. (12.7 mm) above the orifice of the
as standard. The values given in parentheses are mathematical
water-quenching device.Asatisfactory type of support for the
conversions to SI units that are provided for information only
standard 1.0-in. (25.4-mm) specimen is shown in Fig. 1.
and are not considered standard.
NOTE 1—Asuitable support for other sizes and shapes of specimens is
1.6 This standard does not purport to address all of the
shown in Fig. X1.1.
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 Sept. 1, 2018. Published September 2018. Originally Standard ASTM Hardenability Charts (8 ⁄2 by 11 in. pads of 50 charts) are
approvedin1942.Lastpreviouseditionapprovedin2014asA255–10(2014).DOI: available from ASTM International Headquarters. Order Adjunct No. ADJA0255.
10.1520/A0255–10R18. 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 (2018)
A
TABLE 1 Normalizing and Austenitizing Temperatures NOTE 2—Other sizes and shapes of test specimens are described in
Appendix X1.
Ordered
Normalizing Austenitizing
Carbon
Steel Series Temperature, Temperature,
Content,
°F (°C) °F (°C) 6. Procedure
max, %
1000, 1300, 1500, 0.25 and under 1700 (925) 1700 (925)
6.1 Normalizing—The wrought product from which the
3100, 4000, 4100
specimenistobepreparedshallbenormalizedtoensureproper
4300, 4400, 4500, 0.26 to 0.36, 1650 (900) 1600 (870)
4600, 4700, 5000, incl hardening characteristics. The sample shall be held at the
B
5100, 6100,
temperature listed in Table 1 for 1 h and cooled in air.
8100, 8600, 8700,
8800, 9400, 9700,
Tempering of the normalized sample to improve machinability
is permitted.
0.37 and over 1600 (870) 1550 (845)
2300, 2500, 3300, 0.25 and under 1700 (925) 1550 (845)
6.2 Heating—Place the specimen in a furnace that is at the
4800, 9300
0.26 to 0.36, 1650 (900) 1500 (815)
specified austenitizing temperature (Table 1) and hold at this
incl
temperature for 30 min. In production testing slightly longer
0.37 and over 1600 (870) 1475 (800)
times up to 35 min may be used without appreciably affecting
9200 0.50 and over 1650 (900) 1600 (870)
A results. It is important to heat the specimen in such an
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
atmosphere that practically no scaling and a minimum of
series.
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
4.2 Water-QuenchingDevice—Awater-quenchingdeviceof
with the bottom face of the specimen resting on the chips.
suitable capacity to provide a vertical stream of water that can
6.2.1 Other methods consist of placing the specimen in an
be controlled to a height of 2.5 in. (63.5 mm) when passing
appropriately sized hole in a graphite block or placing the
through an orifice 0.5 in. (12.7 mm) in diameter. A tank of
specimen in an upright tube attached to a flat base, both of a
sufficient capacity to maintain the water temperature require-
heat-resistant metal, with the collar projecting for a tong hold.
ments of 6.3 with a small pump and control valves will be
Place a disk of graphite or carbon, or a layer of carbonaceous
foundsatisfactory.Thewater-supplylineshallalsobeprovided
material such as charcoal, in the bottom of the tube to prevent
with a quick opening valve.
scaling.
5. Test Specimens
6.2.2 Foraparticularfixtureandfurnace,determinethetime
required to heat the specimen to the austenitizing temperature
5.1 Wrought Specimens—End-quench specimens shall be
byinsertingathermocoupleintoaholedrilledaxiallyinthetop
preparedfromrolledorforgedstockandshallrepresentthefull
crosssectionoftheproduct.Ifnegotiatedbetweenthesupplier of the specimen. Repeat this procedure periodically, for ex-
ample once a month, for each combination of fixture and
and the user, the end-quench specimen may be prepared from
a given location in a forged or rolled product or from a furnace.
continuous cast billet. The test specimen shall be 1.0 in. (25.4
6.3 Quenching—Adjust the water-quenching device so that
mm) in diameter by 4.0 in. (101.6 mm) in length, with means
the stream of water rises to a free height of 2.5 in. (63.5 mm)
for hanging it in a vertical position for end quenching.
above the 0.5-in. (12.7-mm) orifice, without the specimen in
Dimensions of the preferred specimen and of an optional
position. The support for the specimen shall be dry at the
specimen (Note 2) are given in Figs. 2 and 3. The specimen
beginning of each test. Then place the heated specimen in the
shall be machined from a bar previously normalized in
support so that its bottom face is 0.5 in. above the orifice, and
accordance with 6.1 and of such size as to permit the removal
turn on the water by means of the quick-opening valve. The
ofalldecarburizationinmachiningto1.0in.round.Theendof
time between removal of the specimen from the furnace and
the specimen to be water cooled shall have a reasonably
thebeginningofthequenchshouldnotbemorethan5s.Direct
smooth finish, preferably produced by grinding. Normalizing
the stream of water, at a temperature of 40 to 85°F (5 to
may be waived by agreement between the supplier and the
30°C), against the bottom face of the specimen for not less
user.The previous thermal history of the specimen tested shall
than 10 min. Maintain a condition of still air around the
always be recorded.
specimen during cooling. If the specimen is not cold when
5.2 Cast Specimens—A separately cast end-quench speci-
removed from the fixture, immediately quench it in water.
men may be used for non-boron steels. Cast specimens are not
6.4 Hardness Measurement—Two flats 180° apart shall be
suitable for boron steel grades due to erratic results.Agraphite
ormetalmoldmaybeusedtoformanoverlengthspecimen1.0 ground to a minimum depth of 0.015 in. (0.38 mm) along the
entire length of the bar and Rockwell C hardness measure-
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. ments made along the length of the bar. Shallower ground
depthscanaffectreproducibilityofresults,andcorrelationwith
(31.8-mm) diameter specimen which shall be machined to the
final specimen size. Cast tests need not be normalized. cooling rates in quenched bars.
A255 − 10 (2018)
FIG. 1 Test Specimen in Support for Water Quenching
FIG. 2 Preferred Test Specimen
FIG. 3 Optional Test Specimen
6.4.1 The preparation of the two flats must be carried out cooling and a coarse, soft-grinding wheel are recommended to
with considerable care. They should be mutually parallel and avoidheatingthespecimen.Inordertodetecttemperingdueto
the grinding done in such a manner that no change of the grinding, the flat may be etched with one of the following
quenched structure takes place. Very light cuts with water etchant solutions:
A255 − 10 (2018)
NOTE 3—5% nitric acid (concentrated) and 95% water by volume.
6.4.4.2 For reporting purposes, hardness readings should be
NOTE 4—50% hydrochloric acid (concentrated) and 50% water by
recorded to the nearest integer, with 0.5 HRC values rounded
volume.
to the next higher integer.
Wash the sample in hot water. Etch in solution No. 1 until
7. Plotting Test Results
black.Washinhotwater.ImmerseinsolutionNo.2for3sand
wash in hot water. Dry in air blast. 7.1 Test results should be plotted on a standard hardenabil-
ity chart prepared for this purpose, in which the ordinates
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
10. Introduction
important to position the indenter accurately when testing
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 s
...
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 (Reapproved 2014) A255 − 10 (Reapproved 2018)
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 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.7 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:
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 Oct. 1, 2014Sept. 1, 2018. Published October 2014September 2018. Originally approved in 1942. Last previous edition approved in 20102014
as A255 – 10.A255–10 (2014). DOI: 10.1520/A0255-10R14.10.1520/A0255–10R18.
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’sstandard’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 (2018)
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)±10 °F (6 °C) from the temperatures in this table is
permissible.
B
Normalizing and austenitizing temperatures are 50°F (30°C)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.
FIG. 1 Test Specimen in Support for Water Quenching
A255 − 10 (2018)
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.
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°F85 °F (5 to 30°C),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.
FIG. 2 Preferred Test Specimen
A255 − 10 (2018)
FIG. 3 Optional Test Specimen
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.
A255 − 10 (2018)
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
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