1、Designation: E 975 03Standard Practice forX-Ray Determination of Retained Austenite in Steel withNear Random Crystallographic Orientation1This standard is issued under the fixed designation E 975; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、 of revision, 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.INTRODUCTIONThe volume percent of retained austenite (face-centered cubic phase) in steel is determined
3、 bycomparing the integrated chromium or molybdenum X-ray diffraction intensity of ferrite (bodycen-tered cubic phase) and austenite phases with theoretical intensities. This method should be applied tosteels with near random crystallographic orientations of ferrite and austenite phases because prefe
4、rredcrystallographic orientations can drastically change these measured intensities from theoretical values.Chromium radiation was chosen to obtain the best resolution of X-ray diffraction peaks for othercrystalline phases in steel such as carbides. No distinction has been made between ferrite andma
5、rtensite phases because the theoretical X-ray diffraction intensities are nearly the same. Hereafter,the term ferrite can also apply to martensite. This practice has been designed for unmodifiedcommercial X-ray diffractometers or diffraction lines on film read with a densitometer.Other types of X-ra
6、diations 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 problemsassociated with the use of cobalt or co
7、pper radiation, these radiations are not considered in thispractice.1. Scope1.1 This practice covers the determination of retained aus-tenite phase in steel using integrated intensities (area underpeak above background) of X-ray diffraction peaks usingchromium Kaor molybdenum KaX-radiation.1.2 The m
8、ethod applies to carbon and alloy steels with nearrandom crystallographic orientations of both ferrite and auste-nite phases.1.3 This practice is valid for retained austenite contentsfrom 1 % by volume and above.1.4 If possible, X-ray diffraction peak interference fromother crystalline phases such a
9、s carbides should be eliminatedfrom the ferrite and austenite peak intensities.1.5 Substantial alloy contents in steel cause some change inpeak intensities which have not been considered in thismethod. Application of this method to steels with total alloycontents exceeding 15 weight % should be done
10、 with care. Ifnecessary, the users can calculate the theoretical correctionfactors to account for changes in volume of the unit cells foraustenite and ferrite resulting from variations in chemicalcomposition.1.6 This standard does not purport to address all of thesafety concerns, if any, associated
11、with its use. 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.2. Significance and Use2.1 SignificanceRetained austenite with a near randomcrystallographic orientation is
12、 found in the microstructure ofheat-treated low-alloy, high-strength steels that have medium(0.40 weight %) or higher carbon contents. Although thepresence of retained austenite may not be evident in themicrostructure, and may not affect the bulk mechanical prop-erties such as hardness of the steel,
13、 the transformation ofretained austenite to martensite during service can affect theperformance of the steel.2.2 UseThe measurement of retained austenite can beincluded in low-alloy steel development programs to determineits effect on mechanical properties. Retained austenite can bemeasured on a com
14、panion sample or test section that is1This practice is under the jurisdiction of ASTM Committee E04 on Metallog-raphy and is the direct responsibility of Subcommittee E04.11 on X-Ray andElectron Metallography.Current edition approved Nov. 1, 2003. Published December 2003. Originallyapproved in 1984.
15、 Last previous edition approved in 2000 as E 975 00.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.included in a heat-treated lot of steel as part of a quality controlpractice. The measurement of retained austenite in steels fromser
16、vice can be included in studies of material performance.3. Principles for Retained Austenite Measurement byX-Ray Diffraction3.1 A detailed description of a retained austenite measure-ment using X-ray diffraction is presented by the SocietyofAutomotive Engineers.2Since steel contains crystallinephase
17、s such as ferrite or martensite and austenite, a uniqueX-ray diffraction pattern for each crystalline phase is producedwhen the steel sample is irradiated with X-irradiation. Carbidephases in the steel will also produce X-ray diffraction patterns.3.2 For a randomly oriented sample, quantitative meas
18、ure-ments of the relative volume fraction of ferrite and austenitecan be made from X-ray diffraction patterns because the totalintegrated intensity of all diffraction peaks for each phase isproportional to the volume fraction of that phase. If thecrystalline phase or grains of each phase are randoml
19、y ori-ented, the integrated intensity from any single diffraction peak( hkl) crystalline plane is also proportional to the volumefraction of that phase:Iahkl5 KRahklVa/2where:K 5 Ioe4/m2c4! 3 l3A/32pr!andRahkl51/F/2pLPe22M!v2where:Iahkl= integrated intensity per angular diffraction peak(hkl)inthea-p
20、hase,Io= intensity of the incident beam, = linear absorption coefficient for the steel,e,m = charge and mass of the electron,r = radius of the diffractometer,c = velocity of light,l = wavelength of incident radiation,A = cross sectional area of the incident beam,v = volume of the unit cell,/F/2= str
21、ucture factor times its complex conjugate,p = multiplicity factor of the (hkl) reflection,u = Bragg angle,LP = Lorentz Polarization factor which is equal to(1 + cos22u)/sin2u cos u fornormaldiffractomet-ric analysis but becomes (1 + cosu22a cos22u)/(sin2u cos u) (1 + cos22a) when a mono-chromator is
22、 used in which diffraction by mono-chromator and sample take place in the sameplane; 2a is the diffraction angle of the mono-chromator crystal. If diffraction by the mono-chromator occurs in a plane perpendicular to theplane of sample diffraction, then LP = (cos22a + cos22u)/sin2ucos (1 + cos22a),e2
23、 M= Debye-Waller or temperature factor which is afunction of u where M=B(sin2u)/l2, B =8p2(s)2, where s2is the mean square displacementof the atoms from their mean position, in adirection perpendicular to the diffracting plane,andVa= volume fraction of thea -plane.K is a constant which is dependent
24、upon the selection ofinstrumentation geometry and radiation but independent of thenature of the sample. The parameter, R, is proportional to thetheoretical integrated intensity. The parameter, R, dependsupon interplanar spacing (hkl), the Bragg angle, u, crystalstructure, and composition of the phas
25、e being measured. R canbe calculated from basic principles.3.3 For steel containing only ferrite (a) and austenite (g)and no carbides, the integrated intensity from the ( hkl) planesof the ferrite phase is expressed as:Iahkl5 KRahklVa/23.3.1 A similar equation applies to austenite. We can thenwrite
26、for any pair of austenite and ferrite hkl peaks:Iahkl/Ighkl5 Rahkl/Rghkl!Va/Vg!#3.3.2 The above ratio holds if ferrite or martensite andaustenite are the only two phases present in a steel and bothphases are randomly oriented. Then:Va1 Vg5 13.3.3 The volume fraction of austenite ( Vg) for the ratio
27、ofmeasured integrated intensities of ferrite and austenite peak toR-value is:Vg5 Ig/Rg/Ia/Ra! 1 Ig/Rg!# (1)2Retained Austenite and Its Measurement by X-ray Diffraction, SAE SpecialPublication 453, SAE, Warrendale, PA 15096.TABLE 1 Calculated Theoretical Intensities Using Chromium KaRadiationAhkl Sin
28、u/lu f Df8 Df9 /F/2LP P TBN2R(a 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 0.001803B101.5C200 0.34887 53.06 15.218 1.6 0.9 745.0 2.805 6 0.9172 0.001803B20.73C211 0.42728 78.20 13.133 1.6 0.8 534.6 9.388 24 0.8784 0.001803B190.8
29、C(g iron, face-centered cubic, unit-cell dimension ao= 3.60):111 0.24056 33.44 18.687 1.6 0.9 4684.4 4.554 8 0.9597 0.0004594B75.24C200 0.27778 39.52 17.422 1.6 0.9 4018.3 3.317 6 0.9467 0.0004594B34.78C220 0.39284 64.15 14.004 1.6 0.8 2472.0 3.920 12 0.8962 0.0004594B47.88CAData from “International
30、 Tables for X-Ray Crystallography,” Physical and Chemical Tables, Vol III, Kynoch Press, Birmingham, England, 1962, pp. 60, 61, 210, 213;Weighted Ka1and Ka2value used (l = 2.29092).BTemperature factor (T =e2M) where M=B(sin2u)/l2and 2B = 0.71. Also N is the reciprocal of the unit-cell volume.CCalcul
31、ated intensity includes the variables listed that change with X-ray diffraction peak position.E9750323.3.4 For numerous ferrite and austenite peaks each ratio ofmeasured integrated intensity to R-value can be summed:Vg5FS1q(j 5 1qIgjRgjD/S1P(i 5 1PIai/RaiD1S1q(j 5 1qIgj/RgjDG(2)3.3.5 If carbides are
32、 present:Va1 Vg1 Vc5 13.3.6 Then the volume fraction of austenite ( Va) for theratio of measured ferrite and austenite integrated intensity toR-value is:Vg5 1 2 Vc!Ig/Rg!/Ia/Ra! 1 Ig/Rg!# (3)3.3.7 For numerous ferrite and austenite peaks the ratio ofmeasured integrated intensity to R-values can be s
33、ummed:Vg5 1 2 Vc!1/q(j 5 1qIgj/Rgj! /1/P(i 5 1pIai/Rai!1 1/q(j 5 1qIgj/Rgj!# (4)3.4 The volume fraction of carbide, Vc, should be deter-mined by chemical extraction or metallographic methods.Adequate X-ray diffraction peak resolution for the identifica-tion of carbide peaks is required to avoid incl
34、uding carbidepeaks in the retained austenite measurement.4. Procedure4.1 Sample Preparation:4.1.1 Samples for the X-ray diffractometer must be cut witha minimum amount of heat effect. Since most steels containingretained austenite are relatively hard, abrasive cutoff wheelsare frequently used. If ad
35、equate cooling is not used, heat effectsfrom abrasive cutoff wheels can be substantial and, in somecases, can transform retained austenite. Saw cutting rather thanabrasive wheel cutting is recommended for sample removalwhenever it is practical.4.1.2 Rough grinding using a milling tool or high-pressu
36、recoarse grinding can deform the surface and transform some ofthe retained austenite to a depth that is greater than the surfacedepth analyzed. Final milling or rough grinding cuts limited toa depth of 0.010-in. or less should reduce the depth ofdeformation.4.1.3 Standard metallographic wet-grinding
37、 and polishingmethods shall be used to prepare samples for X-ray analysis.Grit reductions of 80, 120, 240, 320, 400, and 600 siliconcarbide or alumina abrasives may be used but other valid gritcombinations may also be used. A final surface polish of 6-mdiamond or an equivalent abrasive polish is req
38、uired. Sampleetching, observation for heat effects, and repolishing is arecommended safeguard.4.1.4 Since deformation caused by dull papers or over-polishing can transform some of the retained austenite, elec-trolytic polishing or chemical polishing of initial samples ofeach grade and condition shou
39、ld be used to verify propermetallographic sample preparation. Standard chromic-aceticacid for electropolishing 0.005-in. from samples ground to 600grit or specific chemical polishing solutions for a particulargrade of steel polished to a 6-m finish can be used to verifythe metallographic polish. Hot
40、-acid etching is not recom-mended because of selective etching of one phase or along apreferred crystallographic direction.4.1.5 Sample size must be large enough to contain the Xraybeam at all angles of 2u required for the X-ray diffractionanalysis to prevent errors in the analysis. In most cases, a
41、 1- in.square area is sufficient, but sample size depends upon thedimensions of the incident X-ray diffraction. When usingmolybdenum radiation, select peaks in the range from 28 to 402u for best results.4.2 X-Ray Equipment:4.2.1 A standard X-ray diffractometer with a pulse heightselector circuit is
42、preferred for the measurement, but an X-raycamera plus densitometer readings of the film may be used.X-ray film and adequate photographic development techniquesare required to assure a linear response of the film to the X-rayintensity.4.2.2 A chromium X-ray source with a vanadium metal orcompound fi
43、lter to reduce the Kbradiation is recommended.Chromium radiation produces a minimum of Xray fluorescenceof iron. Chromium radiation provides for the needed X-raydiffraction peak resolution and allows for the separation ofcarbide peaks from austenite and ferrite peaks.4.2.3 Other radiation such as co
44、pper, cobalt, or molybde-num can be used, but none of these provide the resolution ofchromium radiation. Copper radiation is practical only when adiffracted-beam monochromator is employed, because ironX-ray fluorescence will obscure the diffracted peaks.4.2.4 A molybdenum source with a zirconium fil
45、ter is usedto produce a large number of X-ray diffraction peaks.4.3 X-Ray MethodX-ray diffraction peaks from othercrystalline phases such as carbides must be separated fromaustenite and ferrite peaks. The linearity of the chart recorderor photographic film shall be verified prior to utilizing thisme
46、thod.4.3.1 Entire diffraction peaks minus background under thepeaks shall be recorded to obtain integrated peak intensities.Peaks without carbide or second phase interference can bescanned, and the total peak plus background recorded. Back-ground counts are obtained by counting on each side of thepe
47、ak for one-half of the total peak counting time. Totalbackground is subtracted from peak plus background to obtainthe integrated intensity. Alternatively, software supplied withthe diffractometer can be used. In general, a diffractometerscanning rate of 0.52u/min or less is recommended to definethe
48、peaks for austenite contents of less than 5 %.4.3.2 Where carbide or other phase X-ray diffraction peakinterference exists, planimeter measurements of area under theaustenite and ferrite peaks on X-ray diffraction charts can beused to obtain integrated intensity. Alternatively, softwaresupplied with
49、 the diffractometer can be used. Carbide interfer-ence with austenite and ferrite peaks of the more commoncarbides is shown in Fig. 1.4.3.3 Another method of determining integrated intensityinvolves cutting peak areas from the charts and weighing themwith an analytical balance.4.3.4 Assuming a 10 % variation in each peak intensity,chromium peak ratios of integrated intensities (areas under thepeaks minus background) for the (220) austenite peak relativeE975033to (200) austenite peak shall range from 1.1 to 1.7 to satisfy therequirement of thi
