ASTM E1077-91(1997)
(Test Method)Standard Test Methods for Estimating the Depth of Decarburization of Steel Specimens
Standard Test Methods for Estimating the Depth of Decarburization of Steel Specimens
SCOPE
1.1 These test methods cover procedures for estimating the depth of decarburization of steels irrespective of the composition, matrix microstructure, or section shape. The following basic procedures may be used:
1.1.1 Screening methods.
1.1.2 Microscopical methods.
1.1.3 Microindentation hardness methods.
1.1.4 Chemical analysis methods.
1.2 In case of a dispute, the rigorous quantitative or lineal analysis method (see 7.3.5 and 7.3.6) shall be the referee method. These methods can be employed with any cross-sectional shape. The chemical analytical methods generally reveal a greater depth of decarburization than the microscopical methods but are limited to certain simple shapes and by availability of equipment. These techniques are generally reserved for research studies. The microindentation hardness method is suitable for accurate measurements of hardened structures with relatively homogeneous microstructures.
1.3 The values stated in SI units are to be regarded as standard. The inch-pound equivalents are in parentheses and may be approximate.
1.4 This standard does not purport to address all of the safety problems, 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:E1077–91(Reapproved 1997)
Standard Test Methods for
Estimating the Depth of Decarburization of Steel
Specimens
This standard is issued under the fixed designation E 1077; 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 (ε) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
INTRODUCTION
These test methods may be used to estimate the average or greatest depth of decarburization in
hardened or non-hardened steel products. The test methods described range from simple screening
tests to more statistically rigorous test methods depending upon the needs of the investigation.
1. Scope 2. Referenced Documents
1.1 These test methods cover procedures for estimating the 2.1 ASTM Standards:
depth of decarburization of steels irrespective of the composi- A 919 Terminology Relating to Heat Treatment of Metals
tion, matrix microstructure, or section shape. The following E 3 Practice for Preparation of Metallographic Specimens
basic procedures may be used: E 7 Terminology Relating to Metallography
1.1.1 Screening methods. E 340 Test Method for Macroetching Metals and Alloys
1.1.2 Microscopical methods. E 350 Test Methods for ChemicalAnalysis of Carbon Steel,
1.1.3 Microindentation hardness methods. Low-Alloy Steel, Silicon Electrical Steel, Ingot Iron, and
1.1.4 Chemical analysis methods. Wrought Iron
1.2 In case of a dispute, the rigorous quantitative or lineal E 384 Test Method for Microhardness of Materials
analysis method (see 7.3.5 and 7.3.6) shall be the referee E 407 Practice for Microetching Metals and Alloys
method. These methods can be employed with any cross- E 415 Test Method for Optical Emission Vacuum Spectro-
sectional shape. The chemical analytical methods generally metric Analysis of Carbon and Low-Alloy Steel
reveal a greater depth of decarburization than the microscopi-
3. Terminology
cal methods but are limited to certain simple shapes and by
3.1 Definitions:
availability of equipment. These techniques are generally
3.1.1 Fordefinitionsoftermsusedinthesetestmethods,see
reserved for research studies. The microindentation hardness
Terminology E 7 and Definitions E 44.
method is suitable for accurate measurements of hardened
3.2 Definitions of Terms Specific to This Standard:
structures with relatively homogeneous microstructures.
3.2.1 average depth of decarburization—the mean value of
1.3 The values stated in SI units are to be regarded as
five or more measurements of the total depth of decarburiza-
standard. The inch-pound equivalents are in parentheses and
tion.
may be approximate.
3.2.2 average free-ferrite depth—the mean value of five or
1.4 This standard does not purport to address all of the
more measurements of the depth of complete decarburization.
safety concerns, if any, associated with its use. It is the
3.2.3 complete decarburization—loss of carbon content at
responsibility of the user of this standard to establish appro-
the surface of a steel specimen to a level below the solubility
priate safety and health practices and determine the applica-
limit of carbon in ferrite so that only ferrite is present.
bility of regulatory limitations prior to use.
These test methods are under the jurisdiction of ASTM Committee E-4 on
Metallography and are the direct responsibility of Subcommittee E04.14 on Annual Book of ASTM Standards, Vol 01.02.
Quantitative Metallography. Annual Book of ASTM Standards, Vol 03.01.
Current edition approved Aug. 15, 1991. Published October 1991. Originally Annual Book of ASTM Standards, Vol 03.05.
ε1 5
published as E 1077 – 85. Last previous edition E 1077 – 85. Annual Book of ASTM Standards, Vol 03.06.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1077–91 (1997)
3.2.4 free-ferrite depth—the perpendicular distance from 6. Sampling
the surface of the specimen to that location where the structure
6.1 Samples should be taken at locations that are represen-
is no longer fully ferritic, that is, other transformation products
tative of the bulk specimen. The location and number of
are observed.
samplestakendependsonthenatureofthematerialtobetested
and will be defined upon agreements between manufacturer
NOTE 1—The term free ferrite has also been used to describe globular,
isolated grains of proeutectoid ferrite in the microstructure of medium-
and purchaser.
carbon hypoeutectoid steels.
6.2 Specimens for screening tests using bulk hardness tests,
such as the Rockwell test, should be small enough so that they
3.2.5 maximum depth of decarburization—the largest mea-
sured value of the total depth of decarburization. can be properly supported on the anvil of the tester. The
specimen surface should not be altered except for scale
3.2.6 partial decarburization—loss of carbon content at the
removal (if present) using a method that will not alter the
surface of a steel specimen to a level less than the bulk carbon
subsurface metal.
content of the unaffected interior but greater than the room
temperature solubility limit of carbon in ferrite. 6.3 Specimens for the microscopical methods or for micro-
indentation hardness tests or for macroscopic screening meth-
3.2.7 total depth of decarburization—the perpendicular dis-
tance from the specimen surface to that location in the interior ods should be cut from the bulk specimen perpendicular to the
longitudinal axis of the product so that measurements are made
wherethebulkcarboncontentisreached;thatis,thesumofthe
depths of complete and partial decarburization. on a transverse plane. This procedure permits determination of
the variation of decarburization around the periphery of the
specimen.
4. Summary of Test Method
6.3.1 For specimens up to about 2.5-cm (1-in.) diameter, the
4.1 These test methods are designed to detect changes in the
entire cross section is polished and examined. For larger cross
microstructure, hardness, or carbon content at the surface of
sections, one or more specimens shall be prepared to assess
steel sections due to decarburization. The depth of decarbur-
variations in surface decarburization. Figs. 1-3 show examples
ization is determined as the depth where a uniform microstruc-
of typical sampling schemes that may be used for larger
ture, hardness, or carbon content, typical of the interior of the
sections; the sampling scheme for large sections should be
specimen, is observed.
determined upon mutual agreement between manufacturer and
purchaser.
5. Significance and Use
6.4 Specimens for chemical analytical methods must be of
5.1 These test methods are used to detect surface losses in
sufficient length so that the weight of incremental turnings is
carbon content due to heating at elevated temperatures, as in
adequate for chemical analysis or the size of milled surfaces is
hot working or heat treatment.
large enough for sparking yet small enough to fit in the
5.2 Results of such tests may be used to qualify material for
specimen holder.
shipment according to agreed upon guidelines between pur-
chaser and manufacturer, for guidance as to machining allow-
7. Procedure
ances, or to assess the influence of processing upon decarbur-
ization tendency. 7.1 Screening Methods:
5.3 Screening tests are simple, fast, low-cost tests designed
7.1.1 Bulk Surface Hardness—For hardened specimens,
to separate non-decarburized samples from those with appre-
particularly those in the as-quenched condition, a short section
ciable decarburization. Based on the results of such tests, the
of the material to be heat treated is cut and heat treated in the
other procedures may be utilized as applicable.
same manner, or along with, the material of interest. The test
5.4 Microscopical tests require a metallographically pol-
specimen, however is not tempered.Any scale on the test piece
ished cross section to permit reasonably accurate determina- is removed by wire brushing, glass-bead blasting, etc., and
tion of the depth and nature of the decarburization present.
hardness tested, usually with the Rockwell C scale. The
Several methods may be employed for estimation of the depth
presence of decarburization is indicated by the difference
of decarburization. The statistical accuracy of each varies with
between the surface hardness and the theoretical maximum
the amount of effort expended.
hardness for the carbon content of the steel. This method is
5.5 Microindentation hardness methods are employed on most suitable for those steels with bulk carbon contents below
polished cross sections and are most suitable for hardened about 0.55 % carbon but will detect gross decarburization in
specimens with reasonably uniform microstructures. This pro- steels with higher bulk carbon contents. The method is not
cedure can be used to define the depth to a specific minimum
suitable for steels that cannot be quench-hardened, for ex-
hardness or the depth to a uniform hardness. ample, low-carbon steels.
5.6 Chemical analytical methods are limited to specimens
7.1.2 Macroscopical Etch Appearance—The presence of
with simple, uniform shapes and are based on analysis of
decarburization is indicated by a difference in etching contrast
incremental turnings or after milling at fixed increments.
between the surface and the interior of the specimen. A
5.7 Microscopical tests are generally satisfactory for deter- transverse section can be ground and macroetched or polished
miningthesuitabilityofmaterialforintendeduse,specification and microetched. The method is suitable for as-rolled, as-
acceptance, manufacturing control, development, or research. forged, annealed, normalized, or heat-treated specimens. The
E1077–91 (1997)
FIG. 1 Typical Sampling Schemes for Round Bars of Different Size
decarburized surface layer, if present, usually exhibits a light- total depth of decarburization. For heat-treated specimens, the
etching appearance. Suitable macroetchants are listed in Test presence of non-martensitic structures in the partially decar-
Method E 340. burized zone is used to estimate the total depth of decarbur-
7.2 Microscopical Methods: ization. Such measurements will generally underestimate the
7.2.1 Microscopical methods are most suitable for measur- total depth of decarburization. For certain highalloy
ing the depth of decarburization of as-hot rolled, as-forged, spheroidize-annealed tool steels, the depth of decarburization
annealed, or normalized specimens.These methods can also be can be estimated by changes in the etch color. For austenitic
applied to heat-treated specimens, although with less certainty manganese steels in the solution-annealed condition, depths
in determining the maximum affected depth. Spheroidize- corresponding to certain carbon contents can be defined by
annealed or cold-worked specimens can also be evaluated; but, changes in the microstructure due to decarburization. Ex-
detectionofstructuralvariationsduetodecarburizationismore amples of decarburization for as-rolled, heat treated, and
difficult than with hot-worked or fully annealed structures. spheroidize-annealed steels are shown in Figs. 4-9, respec-
7.2.2 Measurement of the depth of decarburization is based tively.
on evaluation of the variation in microstructure at the surface 7.2.3 Specimen polishing must be conducted in a manner
due to the change in carbon content. The depth of complete that does not produce edge rounding. Unmounted, unprotected
decarburization is easiest to assess due to the excellent contrast specimens can be satisfactorily prepared using certain auto-
between the free-ferrite layer, when present, and the interior matic polishing devices. Low-nap cloths should be employed;
structure. The depth of partial decarburization can best be polishing with abrasives finer than 1-µm diamond is often
assessed when this zone contains ferrite and pearlite. If the unnecessary. When such devices are not available, or when
specimen has been spheroidized, the variation in carbide specimens are small or of an inconvenient shape for such
content in the partially decarburized zone is used to assess the devices, specimens should be mounted in clamps or in various
E1077–91 (1997)
FIG. 2 Typical Sampling Schemes for Square Bars of Different Size
plastic media. With some mounting media, edge preservation contentisabove1.16 %.Etchingwithnitalorpicralwillreveal
,
6 7
the pearlite. Figs. 10 and 11 illustrates these conditions.
may be inadequate. The compression mounting epoxy materi-
als generally provide the best edge retention of the commonly 7.3 Measurement:
available plastics. Electrolytic or electroless plating provides
7.3.1 The depth of complete or partial decarburization, or
optimum edge retention and is recommended for critical work.
both, can be assessed in a variety of ways depending on the
Polishing must be practiced using techniques that produce a
desired accuracy. Measurements can be made using an ocular
true representation of the surface microstructure, as described
micrometer reticle, a screw (Filar) micrometer ocular, or with
in Practice E 3. a scale placed against a ground-glass projection screen. Mea-
surements can be made on the image or on photographs. The
7.2.4 Etching should be conducted using standard etch-ants,
accuracy of the measurement device should be established
(see Test Methods E 407) such as nital or picral, based on the
using a stage micrometer.
experience of the rater with the material being tested. Special
7.3.2 The optimum magnification for measurement must be
etchantscanbeusedifdictatedbythesituationencountered.In
chosen based on the observed structure. It may be helpful to
such cases, agreement should be obtained between manufac-
scan the specimen at low magnification for the measurement.
turer and purchaser.
The magnification used should be high enough to permit
7.2.5 For solution-annealed austenitic manganese steels,
epsilon martensite will be present in the surface region where
the carbon content is below about 0.5 % carbon. This structure
is best revealed by etching first with 2 % nital for 5 s and then
Sedriks,A.J.,andMulhearn,T.O.,“AusteniticManganeseSteel:Structureand
Properties of Decarburized Layer,” Journal of the Iron and Steel Institute, Vol 202,
with 20 % aqueous sodium metabisulphite for about 20 s.After
November 1964, pp. 907–911.
measurement of the depth of this layer, the specimen can be
Sedriks, A. J., “Austenitic Manganese Steel: A Technique f
...
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