A number in parentheses indicates the year of last reapproval. This standard has been approved for use by agencies of the U. Department of Defense. The test methods described range from simple screeningtests to more statistically rigorous test methods depending upon the needs of the investigation. Thefollowing basic procedures may be used
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A number in parentheses indicates the year of last reapproval. This standard has been approved for use by agencies of the U. Department of Defense. The test methods described range from simple screeningtests to more statistically rigorous test methods depending upon the needs of the investigation.
Thefollowing basic procedures may be used 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 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.
No other units of measurement are included in thisstandard. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.
Referenced Documents2. Current edition approved Jan. Published March Originallyapproved in Last previous edition approved in as E — 01 DOI: United States NOTE 1—The term free ferrite has also been used to describe globular,isolated grains of proeutectoid ferrite in the microstructure of medium-carbon hypoeutectoid steels. Summary of Test Method4. The depth of decarbur-ization is determined as the depth where a uniformmicrostructure, hardness, or carbon content, typical of theinterior of the specimen, is observed.
Significance and Use5. Based on the results of such tests, theother procedures may be utilized as applicable. Severalmethods may be employed for estimation of the depth ofdecarburization.
The statistical accuracy of each varies with theamount of effort expended. This pro-cedure can be used to define the depth to a specific minimumhardness or the depth to a uniform hardness. The location and number ofsamples taken depends on the nature of the material to be testedand will be defined upon agreements between manufacturerand purchaser.
Thespecimen surface should not be altered except for scaleremoval if present using a method that will not alter thesubsurface metal.
This procedure permits determination ofthe variation of decarburization around the periphery of thespecimen. For larger crosssections, one or more specimens shall be prepared to assessvariations in surface decarburization. The testspecimen, however is not tempered. Any scale on the test pieceis removed by wire brushing, glass-bead blasting, etc. 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 steels with bulk carbon contents belowabout 0. The method is notsuitable for steels that cannot be quench-hardened, forexample, low-carbon steels. The method is suitable for as-rolled, as-forged, annealed, normalized, or heat-treated specimens.
Thedecarburized surface layer, if present, usually exhibits a light-etching appearance. Suitable macroetchants are listed in TestMethod E 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-worked or fully annealed structures.
The depth of completedecarburization is easiest to assess due to the excellent 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 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 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 decarburization.
Ex-amples of decarburization for as-rolled, heat treated, andspheroidize-annealed steels are shown in Figs. Unmounted, unprotectedspecimens can be satisfactorily prepared using certain auto-matic polishing devices.
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 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 electroless plating providesFIG. Polishing must be practiced using techniques that produce atrue representation of the surface microstructure, as describedin Guide E3. Specialetchants can be used if dictated by the situation encountered.
Insuch cases, agreement should be obtained between manufac-turer and purchaser. Etching with nital or picral will reveal thepearlite. 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 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 in Guide E It may be helpful toscan the specimen at low magnification for the measurement.
ASTM E1077 - 14
Based on the results of such tests, the other procedures may be utilized as applicable. Several methods may be employed for estimation of the depth of decarburization. The statistical accuracy of each varies with the amount of effort expended. This procedure can be used to define the depth to a specific minimum hardness or the depth to a uniform hardness.