1、Designation: E 975 03 (Reapproved 2008)Standard 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 adopti
2、on 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) in st
3、eel is determined 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 pha
4、ses because preferredcrystallographic 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 betw
5、een ferrite andmartensite 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.Ot
6、her 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 problemsassociated with the us
7、e of cobalt or copper 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-ra
8、diation.1.2 The method 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 crystall
9、ine phases such as 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
10、 % should be done 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 UnitsThe values stated in inch-pound units are to beregarded as standar
11、d. No other units of measurement areincluded in this standard.1.7 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 and determine the applica
12、-bility of regulatory limitations prior to use.2. Significance and Use2.1 SignificanceRetained austenite with a near randomcrystallographic orientation is found in the microstructure ofheat-treated low-alloy, high-strength steels that have medium(0.40 weight %) or higher carbon contents. Although th
13、e1This 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 June 1, 2008. Published September 2008. Originallyapproved in 1984. Last previous edition approved in
14、2003 as E 975 03.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.presence of retained austenite may not be evident in themicrostructure, and may not affect the bulk mechanical prop-erties such as hardness of the steel, the transforma
15、tion 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 companion sample o
16、r test section that isincluded in a heat-treated lot of steel as part of a quality controlpractice. The measurement of retained austenite in steels fromservice can be included in studies of material performance.3. Principles for Retained Austenite Measurement byX-Ray Diffraction3.1 A detailed descri
17、ption of a retained austenite measure-ment using X-ray diffraction is presented by the SocietyofAutomotive Engineers.2Since steel contains crystallinephases such as ferrite or martensite and austenite, a uniqueX-ray diffraction pattern for each crystalline phase is producedwhen the steel sample is i
18、rradiated with X-irradiation. Carbidephases in the steel will also produce X-ray diffraction patterns.3.2 For a randomly oriented sample, quantitative measure-ments of the relative volume fraction of ferrite and austenitecan be made from X-ray diffraction patterns because the totalintegrated intensi
19、ty of all diffraction peaks for each phase isproportional to the volume fraction of that phase. If thecrystalline phase or grains of each phase are randomly ori-ented, the integrated intensity from any single diffraction peak( hkl) crystalline plane is also proportional to the volumefraction of that
20、 phase:Iahkl5 KRahklVa/2where:K 5 Ioe4/m2c4! 3 l3A/32pr!andRahkl51/F/2pLPe22M!v2where:Iahkl= integrated intensity per angular diffraction peak(hkl)inthea-phase,Io= intensity of the incident beam, = linear absorption coefficient for the steel,e,m = charge and mass of the electron,r = radius of the di
21、ffractometer,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= structure factor times its complex conjugate,p = multiplicity factor of the (hkl) reflection,u = Bragg angle,LP = Lorentz Polarization factor which
22、is equal to(1 + cos22u)/sin2u cos u for normal diffractomet-ric analysis but becomes (1 + cosu22a cos22u)/(sin2u cos u) (1 + cos22a) when a mono-chromator is used in which diffraction by mono-chromator and sample take place in the sameplane; 2a is the diffraction angle of the mono-chromator crystal.
23、 If diffraction by the mono-chromator occurs in a plane perpendicular to theplane of sample diffraction, then LP = (cos22a + cos22u)/sin2ucos (1 + cos22a),e2 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 a
24、toms from their mean position, in adirection perpendicular to the diffracting plane,andVa= volume fraction of thea -plane.K is a constant which is dependent upon the selection ofinstrumentation geometry and radiation but independent of thenature of the sample. The parameter, R, is proportional to th
25、etheoretical integrated intensity. The parameter, R, dependsupon interplanar spacing (hkl), the Bragg angle, u, crystalstructure, and composition of the phase being measured. R canbe calculated from basic principles.3.3 For steel containing only ferrite (a) and austenite (g)and no carbides, the inte
26、grated 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 for any pair of austenite and ferrite hkl peaks:Iahkl/Ighkl5 Rahkl/Rghkl!Va/Vg!#2Retained Austenite and Its Measurement by X-ray Diffraction ,
27、SAE SpecialPublication 453, Society of Automotive Engineers (SAE), 400 Commonwealth Dr.,Warrendale, PA 15096-0001, http:/www.sae.org.TABLE 1 Calculated Theoretical Intensities Using Chromium KaRadiationAhkl Sinu/lu f Df8 Df9 /F/2LP P TBN2R(a iron, body-centered cubic, unit-cell dimension ao= 2.8664)
28、: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 0.001803B190.8C(g iron, face-centered cubic, unit-cell dimension ao= 3.60):111 0.24056 33.44 18.687 1.6
29、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 Tables for X-Ray Crystallography,” Physical and Chemical Tables, Vol III, Kynoch Press, B
30、irmingham, 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.CCalculated intensity includes the variables listed that change with X-ray diffraction peak posit
31、ion.E 975 03 (2008)23.3.2 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 ofmeasured integrated intensities of ferrite and austenite p
32、eak toR-value is:Vg5 Ig/Rg/Ia/Ra! 1 Ig/Rg!# (1)3.3.4 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 present:Va1 Vg1 Vc5 13.3.6 Then the volume fraction o
33、f 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 summed:Vg5 1 2 Vc!1/q(j 5 1qIgj/Rgj! /1/P(i 5 1pIai/Rai
34、!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 including carbidepeaks in the retained austenite measureme
35、nt.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 adequate cooling is not used, heat effectsfrom abrasive
36、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-pressurecoarse grinding can deform the surface and transform
37、 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 and polishingmethods shall be used to prepare samples
38、 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 required. Sampleetching, observation for heat effects, an
39、d 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 should be used to verify propermetallographic sample prepa
40、ration. 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-acid etching is not recom-mended because of selective
41、 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 1- in.square area is sufficient, but sample size depe
42、nds 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 preferred for the measurement, but an X-raycamera plus
43、 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 filter to reduce the Kbradiation is recommended.Chromium
44、 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 copper, cobalt, or molybde-num can be used, but none of
45、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 filter is usedto produce a large number of X-ray diffract
46、ion 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 thismethod.4.3.1 Entire diffraction peaks minus background u
47、nder 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 thepeak for one-half of the total peak counting time. Total
48、background 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 peaks for austenite contents of less than 5 %.4.3.2 Wh
49、ere 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, softwareE 975 03 (2008)3supplied with 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
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