1、Designation: E975 03 (Reapproved 2008)E975 13Standard Practice forX-Ray Determination of Retained Austenite in Steel withNear Random Crystallographic Orientation1This standard is issued under the fixed designation E975; the number immediately following the designation indicates the year oforiginal a
2、doption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONThe volume percent of retained austenite (face-centered cubic phase)
3、in steel is determined bycomparing the integrated chromium or molybdenum X-ray diffraction intensity of ferrite(bodycentered(body-centered cubic phase) and austenite phases with theoretical intensities. Thismethod should be applied to steels with near random crystallographic orientations of ferrite
4、andaustenite phases because preferred crystallographic orientations can drastically change these measuredintensities from theoretical values. Chromium radiation was chosen to obtain the best resolution ofX-ray diffraction peaks for other crystalline phases in steel such as carbides. No distinction h
5、as beenmade between ferrite and martensite phases because the theoretical X-ray diffraction intensities arenearly the same. Hereafter, the term ferrite can also apply to martensite. This practice has beendesigned for unmodified commercial X-ray diffractometers or diffraction lines on film read with
6、adensitometer.Other types of X-radiations such as cobalt or copper can be used, but most laboratories examiningferrous materials use chromium radiation for improved X-ray diffraction peak resolution ormolybdenum radiation to produce numerous X-ray diffraction peaks. Because of special problemsassoci
7、ated with the use of cobalt or copper radiation, these radiations are not considered in thispractice.1. Scope1.1 This practice covers the determination of retained austenite phase in steel using integrated intensities (area under peak abovebackground) of X-ray diffraction peaks using chromium K or m
8、olybdenum K X-radiation.1.2 The method applies to carbon and alloy steels with near random crystallographic orientations of both ferrite and austenitephases.1.3 This practice is valid for retained austenite contents from 1 % by volume and above.1.4 If possible, X-ray diffraction peak interference fr
9、om other crystalline phases such as carbides should be eliminated from theferrite and austenite peak intensities.1.5 Substantial alloy contents in steel cause some change in peak intensities which have not been considered in this method.Application of this method to steels with total alloy contents
10、exceeding 15 weight % should be done with care. If necessary, theusers can calculate the theoretical correction factors to account for changes in volume of the unit cells for austenite and ferriteresulting from variations in chemical composition.1.6 UnitsThe values stated in inch-pound units are to
11、be regarded as standard. No other units of measurement are includedin this The values given in parentheses are mathematical conversions to SI units that are provided for information only and arenot considered standard.1.7 This standard does not purport to address all of the safety concerns, if any,
12、associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.1 This practice is under the jurisdiction of ASTM Committee E04 on Metallography and is the direct
13、responsibility of Subcommittee E04.11 on X-Ray and ElectronMetallography.Current edition approved June 1, 2008Feb. 15, 2013. Published September 2008February 2013. Originally approved in 1984. Last previous edition approved in 20032008as E975 03.E975 03(2008). DOI: 10.1520/E0975-03R08.10.1520/E0975-
14、13.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. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior
15、editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States12. Significance and Use2.1 SignificanceRetain
16、ed austenite with a near random crystallographic orientation is found in the microstructure ofheat-treated low-alloy, high-strength steels that have medium (0.40 weight %) or higher carbon contents. Although the presenceof retained austenite may not be evident in the microstructure, and may not affe
17、ct the bulk mechanical properties such as hardnessof the steel, the transformation of retained austenite to martensite during service can affect the performance of the steel.2.2 UseThe measurement of retained austenite can be included in low-alloy steel development programs to determine itseffect on
18、 mechanical properties. Retained austenite can be measured on a companion sample or test section that is included in aheat-treated lot of steel as part of a quality control practice. The measurement of retained austenite in steels from service can beincluded in studies of material performance.3. Pri
19、nciples for Retained Austenite Measurement by X-Ray Diffraction3.1 Adetailed description of a retained austenite measurement using X-ray diffraction is presented by the Society ofAutomotiveEngineers.2 Since steel contains crystalline phases such as ferrite or martensite and austenite, a unique X-ray
20、 diffraction patternfor each crystalline phase is produced when the steel sample is irradiated with X-irradiation. Carbide phases in the steel will alsoproduce X-ray diffraction patterns.3.2 For a randomly oriented sample, quantitative measurements of the relative volume fraction of ferrite and aust
21、enite can bemade from X-ray diffraction patterns because the total integrated intensity of all diffraction peaks for each phase is proportionalto the volume fraction of that phase. If the crystalline phase or grains of each phase are randomly oriented, the integrated intensityfrom any single diffrac
22、tion peak (hkl) crystalline plane is also proportional to the volume fraction of that phase:I hkl 5KR hkl V /2where:K 5I o e4 /m 2 c4!3 3 A /32pir!andR hkl 51/F/2 pLPe22M!v 2where:I hkl = integrated intensity per angular diffraction peak (hkl) in the -phase,Io = intensity of the incident beam, = lin
23、ear absorption coefficient for the steel,e,m = charge and mass of the electron,r = radius of the diffractometer,c = velocity of light, = wavelength of incident radiation,A = cross sectional area of the incident beam,v = volume of the unit cell,/ F /2 = structure factor times its complex conjugate,p
24、= multiplicity factor of the (hkl) reflection, = Bragg angle,2 Retained Austenite and Its Measurement by X-ray Diffraction , SAE Special Publication 453, Society of Automotive Engineers (SAE), 400 Commonwealth Dr.,Warrendale, PA 15096-0001, http:/www.sae.org.TABLE 1 Calculated Theoretical Intensitie
25、s Using Chromium K RadiationAhkl Sin/ f f f9 /F/2 LP P TB N2 R( iron, body-centered cubic, unit-cell dimension ao = 2.8664):110 0.24669 34.41 18.474 1.6 0.9 1142.2 4.290 12 0.9577 0.001803B 101.5C200 0.34887 53.06 15.218 1.6 0.9 745.0 2.805 6 0.9172 0.001803B 20.73C211 0.42728 78.20 13.133 1.6 0.8 5
26、34.6 9.388 24 0.8784 0.001803B 190.8C( iron, face-centered cubic, unit-cell dimension a o = 3.60):111 0.24056 33.44 18.687 1.6 0.9 4684.4 4.554 8 0.9597 0.0004594B 75.24C200 0.27778 39.52 17.422 1.6 0.9 4018.3 3.317 6 0.9467 0.0004594B 34.78C220 0.39284 64.15 14.004 1.6 0.8 2472.0 3.920 12 0.8962 0.
27、0004594B 47.88CA Data from “International Tables for X-Ray Crystallography,” Physical and Chemical Tables, Vol III, Kynoch Press, Birmingham, England, 1962, pp. 60, 61, 210, 213;Weighted K1 and K2 value used ( = 2.29092).B Temperature factor (T = e2M) where M = B(sin 2 )/2 and 2B = 0.71. Also N is t
28、he reciprocal of the unit-cell volume.C Calculated intensity includes the variables listed that change with X-ray diffraction peak position.E975 132LP = Lorentz Polarization factor which is equal to (1 + cos2 2)/sin2 cos for normal diffractometric analysis but becomes(1 + cos 2 2 cos2 2)/(sin2 cos )
29、 (1 + cos2 2) when a monochromator is used in which diffraction bymonochromator and sample take place in the same plane; 2 is the diffraction angle of the monochromator crystal. Ifdiffraction by the monochromator occurs in a plane perpendicular to the plane of sample diffraction, then LP = (cos22 +
30、cos 2 2)/sin2 cos (1 + cos2 2),e2 M = Debye-Waller or temperature factor which is a function of where M = B( sin2 )/2, B = 8pi 2 (s)2, where s2 is themean square displacement of the atoms from their mean position, in a direction perpendicular to the diffracting plane,andV = volume fraction of the -p
31、lane.K is a constant which is dependent upon the selection of instrumentation geometry and radiation but independent of the natureof the sample. The parameter, R, is proportional to the theoretical integrated intensity. The parameter, R, depends upon interplanarspacing (hkl), the Bragg angle, , crys
32、tal structure, and composition of the phase being measured. R can be calculated from basicprinciples.3.3 For steel containing only ferrite () and austenite () and no carbides, the integrated intensity from the ( hkl) planes of theferrite phase is expressed as:I hkl 5KR hkl V /23.3.1 A similar equati
33、on applies to austenite. We can then write for any pair of austenite and ferrite hkl peaks:I hkl /I hkl 5R hkl /R hkl!V /V!#3.3.2 The above ratio holds if ferrite or martensite and austenite are the only two phases present in a steel and both phases arerandomly oriented. Then:V 1V 513.3.3 The volume
34、 fraction of austenite ( V) for the ratio of measured integrated intensities of ferrite and austenite peak toR-value is:V 5I /R /I /R!1I /R!# (1)V 5(I /R )/I /R!1I /R!# (1)3.3.4 For numerous ferrite and austenite peaks each ratio of measured integrated intensity to R-value can be summed:V 5FS 1q (j5
35、1q IjRj D/S1P (i51PIi/RiD1S1q (j51qIj/RjDG (2)V 5S 1q (j51qIjRj D/FS1P (i51PIi/RiD1S 1q(j51qIj/RjDG (2)3.3.5 If carbides are present:V 1V 1V c 513.3.6 Then the volume fraction of austenite ( V) for the ratio of measured ferrite and austenite integrated intensity to R-valueis:V 512V c!I /R!/I /R !1I
36、/R!# (3)V 512V c!(I /R)/I /R !1(I /R)# (3)3.3.7 For numerous ferrite and austenite peaks the ratio of measured integrated intensity to R-values can be summed:V 5312Vc!S1/q (j51qIj/Rj!D/1/P(i51pIa i/Ra i!11/q (j51qI j/R j! 4V5(12Vc) (4)FS1q (j51qIj/Rj!DG/F1P(i51pIa i/Ra i!11q (j51q(Ir i/Rr i)G3.4 The
37、 volume fraction of carbide, Vc, should be determined by chemical extraction or metallographic methods. AdequateX-ray diffraction peak resolution for the identification of carbide peaks is required to avoid including carbide peaks in the retainedaustenite measurement.E975 1334. Procedure4.1 Sample P
38、reparation:4.1.1 Samples for the X-ray diffractometer mustshall be cut with a minimum amount of heat effect. Since most steels containingretained austenite are relatively hard, abrasive cutoff wheels are frequently used. If adequate cooling is not used, heat effects fromabrasive cutoff wheels can be
39、 substantial and, in some cases, can transform retained austenite. Saw cutting rather than abrasivewheel cutting is recommended for sample removal whenever it is practical.4.1.2 Rough grinding using a milling tool or high-pressure coarse grinding can deform the surface and transform some of theretai
40、ned austenite to a depth that is greater than the surface depth analyzed. Final milling or rough grinding cuts limited to a depthof 0.010-in. 0.010-in (0.254 mm). or less should reduce the depth of deformation.4.1.3 Standard metallographic wet-grinding and polishing methods shall be used to prepare
41、samples for X-ray analysis. Gritreductions of 80, 120, 240, 320, 400, and 600 silicon carbide or alumina abrasives may be used but other valid grit combinationsmay also be used.Afinal surface polish of 6-m 2.36 10-4in. (6-m) diamond or an equivalent abrasive polish is required. Sampleetching, observ
42、ation for heat effects, and repolishing is a recommended safeguard.4.1.4 Since deformation caused by dull papers or over-polishing can transform some of the retained austenite, electrolyticpolishing or chemical polishing of initial samples of each grade and condition should be used to verify proper
43、metallographicsample preparation. Standard chromic-acetic acid for electropolishing 0.005-in. (0.127 mm) from samples ground to 600 grit orspecific chemical polishing solutions for a particular grade of steel polished to a 6-m 2.36 10-4in. (6-m) finish can be used toverify the metallographic polish.
44、 Hot-acid etching is not recommended because of selective etching of one phase or along apreferred crystallographic direction.4.1.5 If retained austenite content on the surface of a sample is desired and the sample can be mounted in the diffraction system,no preparation is needed.4.1.6 Sample size m
45、ustshall be large enough to contain the Xray beam at all angles of 2 required for the X-ray diffractionanalysis to prevent errors in the analysis. In most cases, a 1- an area of 1 in.2 square area(645.16 mm2) is sufficient, but samplesize depends upon the dimensions of the incident X-ray diffraction
46、. When using molybdenum radiation, select peaks in the rangefrom 28 to 40 2 for best results.4.2 X-Ray Equipment:4.2.1 Astandard X-ray diffractometer with a pulse height selector circuit is preferred for the measurement, but an X-ray cameraplus densitometer readings of the film may be used. X-ray fi
47、lm and adequate photographic development techniques are requiredto assure a linear response of the film to the X-ray intensity.Any diffraction system may be used that consists of an x-ray source,an angular measurement capability, and an x-ray detection system. The system must be capable of obtaining
48、 the entire diffractionpeak along with adjacent background levels, capable of detecting at least two separate austenite reflections and a ferrite reflection,and capable of normalizing any equipment-specific intensity biases not accounted for by R-factors.4.2.2 A chromium X-ray source with a vanadium
49、 metal or compound filter to reduce the K radiation is recommended.Chromium radiation produces a minimum of Xray fluorescence of iron. Chromium radiation provides for the needed X-raydiffraction peak resolution and allows for the separation of carbide peaks from austenite and ferrite peaks.4.2.3 Other radiation such as copper, cobalt, or molybde-nummolybdenum can be used, but none of these provide th
