ASTM E1077-2001(2005) Standard Test Methods for Estimating the Depth of Decarburization of Steel Specimens《钢试样的脱碳深度估计的标准试验方法》.pdf

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1、Designation: E 1077 01 (Reapproved 2005)Standard Test Methods forEstimating the Depth of Decarburization of SteelSpecimens1This standard is issued under the fixed designation E 1077; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,

2、the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.INTRODUCTIONThese test methods may b

3、e used to estimate 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 pr

4、ocedures for estimating thedepth of decarburization of steels irrespective of the composi-tion, matrix microstructure, or section shape. The followingbasic 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 metho

5、ds.1.2 In case of 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 m

6、ethods but are limited 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 sta

7、ted in SI units are to be regarded asstandard. The inch-pound equivalents are in parentheses andmay be approximate.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

8、safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A 941 Terminology Relating to Steel, Stainless Steel, Re-lated Alloys and FerroalloysE3 Guide for Preparation of Metallographic SpecimensE7 Terminology Relat

9、ing to MetallographyE 340 Test Method for Macroetching Metals and AlloysE 350 Test Methods for ChemicalAnalysis of Carbon Steel,Low-Alloy Steel, Silicon Electrical Steel, Ingot Iron, andWrought IronE 384 Test Method for Microindentation Hardness of Ma-terialsE 407 Practice for Microetching Metals an

10、d AlloysE 415 Test Method for Optical Emission Vacuum Spectro-metric Analysis of Carbon and Low-Alloy SteelE 1951 Guide for Calibrating Reticals and Light Micro-scope Magnifications3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in these test methods, seeTerminology E7and Terminolo

11、gy A 941.3.2 Definitions of Terms Specific 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.1The

12、se test methods are under the jurisdiction of ASTM Committee E04 onMetallography and are the direct responsibility of Subcommittee E04.14 onQuantitative Metallography.Current edition approved May 1, 2005. Published May 2005. Originallyapproved in 1985. Last previous edition approved in 2001 as E 107

13、7 01e1.2For 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.1Copyright ASTM International, 100 Barr Harbor Drive,

14、PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.3 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 fromthe sur

15、face of the specimen to that location where the structureis no 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 st

16、eels.3.2.5 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 roomtemperatu

17、re solubility 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 Method

18、4.1 These test 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 uniform microstruc-ture, hardness, or carbon content, typical of the interi

19、or of thespecimen, 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 g

20、uidelines between pur-chaser and manufacturer, for guidance as to machining allow-ances, or to assess the influence of processing upon decarbur-ization tendency.5.3 Screening tests are simple, fast, low-cost tests designedto separate non-decarburized samples from those with appre-ciable decarburizat

21、ion. Based on the 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 determina-tion of the depth and nature of the decarburization present.Several methods may be employed

22、for estimation of the depthof decarburization. The statistical accuracy of each varies withthe amount 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 c

23、an be used to define 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 genera

24、lly satisfactory for 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

25、on the nature of the 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

26、surface should not be 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 th

27、elongitudinal axis of 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 (1-in.) diameter, theentire cross section is polished and examined.

28、 For larger crosssections, one 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 manufact

29、urer andpurchaser.6.4 Specimens 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 M

30、ethods:7.1.1 Bulk Surface HardnessFor hardened specimens,particularly those in the as-quenched condition, a short sectionof the 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 t

31、est pieceis removed by wire 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 ismos

32、t suitable for those steels 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, for ex-ample, low-carbon steels.7.1.2 Macroscopical Etch AppearanceThe

33、presence ofdecarburization is indicated by a difference in etching contrastbetween the surface and the interior of the specimen. Atransverse section can be ground and macroetched or polishedE 1077 01 (2005)2and microetched. The method is suitable for as-rolled, as-forged, annealed, normalized, or he

34、at-treated specimens. Thedecarburized surface layer, if present, usually exhibits a light-etching appearance. Suitable macroetchants are listed in TestMethod E 340.7.2 Microscopical Methods:7.2.1 Microscopical methods are most suitable for measur-ing the depth of decarburization of as-hot rolled, as

35、-forged,annealed, or normalized specimens. 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 decarburiza

36、tion is moredifficult than with hot-worked 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 e

37、xcellent contrastbetween the free-ferrite 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

38、 used to assess thetotal depth of decarburization. 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

39、certain highalloyspheroidize-annealed 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 decarb

40、urization. Ex-amples of decarburization 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 ce

41、rtain auto-matic polishing devices. Low-nap cloths should be employed;polishing with abrasives finer than 1-m diamond is oftenunnecessary. When such devices are not available, or whenFIG. 1 Typical Sampling Schemes for Round Bars of Different SizeE 1077 01 (2005)3specimens are small or of an inconve

42、nient shape for suchdevices, specimens should be mounted in clamps or in variousplastic 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 electrol

43、ess plating providesoptimum edge retention and 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 E 407) suc

44、h as nital or picral, based on theexperience of 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,epsil

45、on martensite will be present in the surface region 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

46、 beaged at about 560C (1040F) for1htoprecipitate pearlite atthe grain boundaries in the core region where the carboncontent is above 1.16 %. Etching with nital or picral will revealthe pearlite.3, 4Figs. 10 and 11 illustrates these conditions.7.3 Measurement:7.3.1 The depth of complete or partial de

47、carburization, orboth, can be assessed in a variety of ways depending on thedesired accuracy. Measurements can be made using an ocularmicrometer reticle, a screw (Filar) micrometer ocular, or witha scale placed against a ground-glass projection screen. Mea-surements can be made on the image or on ph

48、otographs.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 in Guide E 1951.7.3.2 The optimum magnification for measurement must bechosen based on

49、 the observed structure. It may be helpful toscan the specimen at low magnification for the measurement.The magnification used should be high enough to permit3Sedriks,A. J., and Mulhearn, T. O., “Austenitic Manganese Steel: Structure andProperties of Decarburized Layer,” Journal of the Iron and Steel Institute, Vol 202,November 1964, pp. 907911.4Sedriks, 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. 2 Typical Sampling Schemes for Square Bars