1、Designation: E1077 14Standard Test Methods forEstimating the Depth of Decarburization of SteelSpecimens1This standard is issued under the fixed designation E1077; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last rev
2、ision. A number in parentheses indicates the year of last reapproval. Asuperscript 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.INTRODUCTIONThese test methods may be used to estima
3、te the average or greatest depth of decarburization inhardened or non-hardened steel products. The test methods described range from simple screeningtests to more statistically rigorous test methods depending upon the needs of the investigation.1. Scope1.1 These test methods cover procedures for est
4、imating thedepth of decarburization of steels irrespective of thecomposition, matrix microstructure, or section shape. Thefollowing 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
5、a dispute, the rigorous quantitative or linealanalysis method (see 7.3.5 and 7.3.6) shall be the refereemethod. These methods can be employed with any cross-sectional shape. The chemical analytical methods generallyreveal a greater depth of decarburization than the microscopi-cal methods but are lim
6、ited to certain simple shapes and byavailability of equipment. These techniques are generallyreserved for research studies. The microindentation hardnessmethod is suitable for accurate measurements of hardenedstructures with relatively homogeneous microstructures.1.3 The values stated in SI units ar
7、e to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices
8、 and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A941 Terminology Relating to Steel, Stainless Steel, RelatedAlloys, and FerroalloysE3 Guide for Preparation of Metallographic SpecimensE7 Terminology Relating to MetallographyE340 Test
9、 Method for Macroetching Metals and AlloysE350 Test Methods for Chemical Analysis of Carbon Steel,Low-Alloy Steel, Silicon Electrical Steel, Ingot Iron, andWrought IronE384 Test Method for Knoop and Vickers Hardness ofMaterialsE407 Practice for Microetching Metals and AlloysE415 Test Method for Atom
10、ic Emission Vacuum Spectro-metric Analysis of Carbon and Low-Alloy SteelE1951 Guide for Calibrating Reticles and Light MicroscopeMagnifications3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in these test methods, seeTerminology E7 and Terminology A941.3.2 Definitions of Terms Spec
11、ific to This Standard:3.2.1 average depth of decarburizationthe mean value offive or more measurements of the total depth of decarburiza-tion.3.2.2 average free-ferrite depththe mean value of five ormore measurements of the depth of complete decarburization.1These test methods are under the jurisdic
12、tion of ASTM Committee E04 onMetallography and are the direct responsibility of Subcommittee E04.14 onQuantitative Metallography.Current edition approved Jan. 1, 2014. Published March 2014. Originallyapproved in 1985. Last previous edition approved in 2005 as E1077 01(2005).DOI: 10.1520/E1077-14.2Fo
13、r referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700
14、, West Conshohocken, PA 19428-2959. United States13.2.3 complete decarburizationloss of carbon content atthe surface of a steel specimen to a level below the solubilitylimit of carbon in ferrite so that only ferrite is present.3.2.4 free-ferrite depththe perpendicular distance from thesurface of the
15、 specimen to that location where the structure isno longer fully ferritic, that is, other transformation productsare observed.NOTE 1The term free ferrite has also been used to describe globular,isolated grains of proeutectoid ferrite in the microstructure of medium-carbon hypoeutectoid steels.3.2.5
16、maximum depth of decarburizationthe largest mea-sured value of the total depth of decarburization.3.2.6 partial decarburizationloss of carbon content at thesurface of a steel specimen to a level less than the bulk carboncontent of the unaffected interior but greater than the roomtemperature solubili
17、ty limit of carbon in ferrite.3.2.7 total depth of decarburizationthe perpendicular dis-tance from the specimen surface to that location in the interiorwhere the bulk carbon content is reached; that is, the sum of thedepths of complete and partial decarburization.4. Summary of Test Method4.1 These t
18、est methods are designed to detect changes in themicrostructure, hardness, or carbon content at the surface ofsteel sections due to decarburization. The depth of decarbur-ization is determined as the depth where a uniformmicrostructure, hardness, or carbon content, typical of theinterior of the spec
19、imen, is observed.5. Significance and Use5.1 These test methods are used to detect surface losses incarbon content due to heating at elevated temperatures, as inhot working or heat treatment.5.2 Results of such tests may be used to qualify material forshipment according to agreed upon guidelines bet
20、ween pur-chaser and manufacturer, for guidance as to machiningallowances, or to assess the influence of processing upondecarburization tendency.5.3 Screening tests are simple, fast, low-cost tests designedto separate non-decarburized samples from those with appre-ciable decarburization. Based on the
21、 results of such tests, theother procedures may be utilized as applicable.5.4 Microscopical tests require a metallographically pol-ished cross section to permit reasonably accurate determinationof the depth and nature of the decarburization present. Severalmethods may be employed for estimation of t
22、he depth ofdecarburization.The statistical accuracy of each varies with theamount of effort expended.5.5 Microindentation hardness methods are employed onpolished cross sections and are most suitable for hardenedspecimens with reasonably uniform microstructures. This pro-cedure can be used to define
23、 the depth to a specific minimumhardness or the depth to a uniform hardness.5.6 Chemical analytical methods are limited to specimenswith simple, uniform shapes and are based on analysis ofincremental turnings or after milling at fixed increments.5.7 Microscopical tests are generally satisfactory for
24、 deter-mining the suitability of material for intended use, specificationacceptance, manufacturing control, development, or research.6. Sampling6.1 Samples should be taken at locations that are represen-tative of the bulk specimen. The location and number ofsamples taken depends on the nature of the
25、 material to be testedand will be defined upon agreements between manufacturerand purchaser.6.2 Specimens for screening tests using bulk hardness tests,such as the Rockwell test, should be small enough so that theycan be properly supported on the anvil of the tester. Thespecimen surface should not b
26、e altered except for scaleremoval (if present) using a method that will not alter thesubsurface metal.6.3 Specimens for the microscopical methods or for micro-indentation hardness tests or for macroscopic screening meth-ods should be cut from the bulk specimen perpendicular to thelongitudinal axis o
27、f the product so that measurements are madeon a transverse plane. This procedure permits determination ofthe variation of decarburization around the periphery of thespecimen.6.3.1 For specimens up to about 2.5-cm diameter, the entirecross section is polished and examined. For larger crosssections, o
28、ne or more specimens shall be prepared to assessvariations in surface decarburization. Figs. 1-3 show examplesof typical sampling schemes that may be used for largersections; the sampling scheme for large sections should bedetermined upon mutual agreement between manufacturer andpurchaser.6.4 Specim
29、ens for chemical analytical methods must be ofsufficient length so that the weight of incremental turnings isadequate for chemical analysis or the size of milled surfaces islarge enough for sparking yet small enough to fit in thespecimen holder.7. Procedure7.1 Screening Methods:7.1.1 Bulk Surface Ha
30、rdnessFor hardened specimens, par-ticularly those in the as-quenched condition, a short section ofthe material to be heat treated is cut and heat treated in thesame manner, or along with, the material of interest. The testspecimen, however is not tempered.Any scale on the test pieceis removed by wir
31、e brushing, glass-bead blasting, etc., andhardness tested, usually with the Rockwell C scale. Thepresence of decarburization is indicated by the differencebetween the surface hardness and the theoretical maximumhardness for the carbon content of the steel. This method ismost suitable for those steel
32、s with bulk carbon contents belowabout 0.55 % carbon but will detect gross decarburization insteels with higher bulk carbon contents. The method is notsuitable for steels that cannot be quench-hardened, forexample, low-carbon steels.7.1.2 Macroscopical Etch AppearanceThe presence ofdecarburization i
33、s indicated by a difference in etching contrastbetween the surface and the interior of the specimen. Atransverse section can be ground and macroetched or polishedE1077 142and microetched. The method is suitable for as-rolled, as-forged, annealed, normalized, or heat-treated specimens. Thedecarburize
34、d surface layer, if present, usually exhibits a light-etching appearance. Suitable macroetchants are listed in TestMethod E340.7.2 Microscopical Methods:7.2.1 Microscopical methods are most suitable for measur-ing the depth of decarburization of as-hot rolled, as-forged,annealed, or normalized speci
35、mens. These methods can also beapplied to heat-treated specimens, although with less certaintyin determining the maximum affected depth. Spheroidize-annealed or cold-worked specimens can also be evaluated; but,detection of structural variations due to decarburization is moredifficult than with hot-w
36、orked or fully annealed structures.7.2.2 Measurement of the depth of decarburization is basedon evaluation of the variation in microstructure at the surfacedue to the change in carbon content. The depth of completedecarburization is easiest to assess due to the excellent contrastbetween the free-fer
37、rite layer, when present, and the interiorstructure. The depth of partial decarburization can best beassessed when this zone contains ferrite and pearlite. If thespecimen has been spheroidized, the variation in carbidecontent in the partially decarburized zone is used to assess thetotal depth of dec
38、arburization. For heat-treated specimens, thepresence of non-martensitic structures in the partially decar-burized zone is used to estimate the total depth of decarbur-ization. Such measurements will generally underestimate thetotal depth of decarburization. For certain highalloyspheroidize-annealed
39、 tool steels, the depth of decarburizationcan be estimated by changes in the etch color. For austeniticmanganese steels in the solution-annealed condition, depthscorresponding to certain carbon contents can be defined bychanges in the microstructure due to decarburization. Ex-amples of decarburizati
40、on for as-rolled, heat treated, andspheroidize-annealed steels are shown in Figs. 4-9, respec-tively.7.2.3 Specimen polishing must be conducted in a mannerthat does not produce edge rounding. Unmounted, unprotectedspecimens can be satisfactorily prepared using certain auto-matic polishing devices. L
41、ow-nap cloths should be employed;polishing with abrasives finer than 1-m diamond is oftenunnecessary. When such devices are not available, or whenspecimens are small or of an inconvenient shape for suchdevices, specimens should be mounted in clamps or in variousFIG. 1 Typical Sampling Schemes for Ro
42、und Bars of Different SizeE1077 143plastic media. With some mounting media, edge preservationmay be inadequate. The compression mounting epoxy materi-als generally provide the best edge retention of the commonlyavailable plastics. Electrolytic or electroless plating providesoptimum edge retention an
43、d is recommended for critical work.Polishing must be practiced using techniques that produce atrue representation of the surface microstructure, as describedin Guide E3.7.2.4 Etching should be conducted using standard etchants,(see Test Methods E407) such as nital or picral, based on theexperience o
44、f the rater with the material being tested. Specialetchants can be used if dictated by the situation encountered. Insuch cases, agreement should be obtained between manufac-turer and purchaser.7.2.5 For solution-annealed austenitic manganese steels,epsilon martensite will be present in the surface r
45、egion wherethe carbon content is below about 0.5 % carbon. This structureis best revealed by etching first with 2 % nital for 5 s and thenwith 20 % aqueous sodium metabisulphite for about 20 s.Aftermeasurement of the depth of this layer, the specimen can beaged at about 560C for1htoprecipitate pearl
46、ite at the grainboundaries in the core region where the carbon content isabove 1.16 %. Etching with nital or picral will reveal thepearlite.3,4Figs. 10 and 11 illustrates these conditions.3Sedriks,A. J., and Mulhearn, T. O., “Austenitic Manganese Steel: Structure andProperties of Decarburized Layer,
47、” Journal of the Iron and Steel Institute, Vol 202,November 1964, pp. 907911.FIG. 2 Typical Sampling Schemes for Square Bars of Different SizeE1077 1447.3 Measurement: 7.3.1 The depth of complete or partial decarburization, orboth, can be assessed in a variety of ways depending on thedesired accurac
48、y. Measurements can be made using an ocularmicrometer reticle, a screw (Filar) micrometer ocular, or with4Sedriks, A. J., “Austenitic Manganese Steel: A Technique for Measuring theExtent of Decarburization,” Journal of the Iron and Steel Institute, Vol 204,February 1966, pp. 142145.FIG. 3 Typical Sa
49、mpling Schemes for Flat and Rectangular Bars of Different SizeFIG. 4 Example of an As-Rolled, Fully Pearlitic Alloy Steel Microstructure With No Apparent Decarburization. Dark Layer at Surface IsIron Oxide (Mill Scale) (200, 2 % Nital Etch)E1077 145a scale placed against a ground-glass projection screen. Mea-surements can be made on the image or on photographs.Measurements can also be made using image analysis tech-niques. The accuracy of the measurement device should beestablished using a stage micrometer. Light microscope cali-bration procedures can be found i
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