ARP_1820B-2007

__________________________________________________________________________________________________________________________________________SAETechnicalStandardsBoardRulesprovidethat:“ThisreportispublishedbySAEtoadvancethestateoftechnicalandengineeringsciences.Theuseofthisreportisentirelyvoluntary,anditsapplicabilityandsuitabilityforanyparticularuse,includinganypatentinfringementarisingtherefrom,isthesoleresponsibilityoftheuser.”SAEreviewseachtechnicalreportatleasteveryfiveyearsatwhichtimeitmaybereaffirmed,revised,orcancelled.SAEinvitesyourwrittencommentsandsuggestions.Copyright©2007SAEInternationalAllrightsreserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystemortransmitted,inanyformorbyanymeans,electronic,mechanical,photocopying,recording,orotherwise,withoutthepriorwrittenpermissionofSAE.TOPLACEADOCUMENTORDER:Tel:[phone](insideUSAandCanada)Tel:[phone](outsideUSA)Fax:[phone]Email:[e-mail]:(0.012mm)oftheintersection,andthusallowsevaluationoftheseverityofcarburizationanddecarburizationatadepthof0.00015in(0.0038mm)ormore.Themagnificationalsofacilitatesdetectionandmeasurementofthinlayersoftotaldecarburizationandintergranularoxidation.1.SCOPEThispracticeprovidesamethodofevaluatingmicrohardnessandmicrostructureveryclosetothesurfaceofadiskspecimen.Itisusefulforprocesscontrolinheattreatmentofsteelpartstodetectnitridingandcarburizationaswellasdecarburizationandexcessiveintergranularoxidation.Italsomaybevaluableforotherevaluations,e.g.,platedcoatingsandothermaterials.2.REFERENCESTherearenoreferencedpublicationsspecifiedherein.3.PROCESSCONTROLFORHEATTREATMENTOFSTEELPARTS3.1Fabricatediscordisc-sectorspecimens1/8to1/4in(3to6mm)thick,witha1/4to1/2in(6to12mm)radius,smallcentralholepermissible,ofthesamealloyasthepartswithtextureofcircumferentialsurfaceapproximately32µin(0.8µm)(see4.4).3.2Heattreatspecimenswithpartsbutdonottemperspecimensmadefromcarbon,low-alloy,andmartensiticcorrosion-resistantsteels.EXCEPTION:Temperspecimensmadefromsteelsexhibitingsecondaryhardeningcharacteristics,e.g.,H-11.CopyrightSAEInternationalProvidedbyIHSunderlicensewithSAENotforResaleNoreproductionornetworkingpermittedwithoutlicensefromIHS--`,,```,,,,````-`-`,,`,,`,`,,`---SAEARP1820B-2-3.3Metallographicallymountspecimenssothatcircumferentialsurfaceisreadyforgrindingandpolishing.3.4Grindandpolishspecimenstoproduceamagnificationof3to5Xneartheintersections(I)ofthechordalandcircumferentialsurfaces(seeFigure1).ThemagnificationisD/c,where“D”isthediscdiameterand“c”isthelengthofthechordalsurface.3.5DetermineKnoopmicrohardness,using500gload,onatraversefromanintersection(I)atthemidthicknessofthedisk.Makethefirstimpression0.0005in(0.012mm),andthesecond0.0005in(0.012mm)furtherfromtheintersection.Makesubsequentimpressionssoastoproduceasmoothcurvewhendepthversushardnessisplotted.3.5.1Continuetestingmicrohardnessatincreasingdepthsapproximately0.001in(0.025mm)apartuntilcorehardnessisdetermined,i.e.,untilthereisnosignificantdifferenceinmicrohardnessatadjacentlocations.Convertmicrohardnessat0.0003in(0.008mm)depthandatcoremicrohardnessfromKnooptoHRC(see3.7.2).3.5.1.1Inabilitytoobtaincorehardness,i.e.,consistentmicrohardness,maybeduetosmalldiscdiameterorshortchordlength.Insuchacase,grindthespecimenfurthertolengthenthechord.3.6Determinedepth(d)beneathsurfaceusingEquation1,theapproximateformulaofEquation2,ornomographssimilartoFigure2(formeasurementsininches)andFigure3(formeasurementsinmillimeters).(Eq.2)where:r=radiusofdiscΔ=distancefromintersectionc=lengthofchordalsurface3.7PlotHardnessVersusDepthCurve3.7.1DepthofPartialDecarburizationThedepthofpartialdecarburizationisthedepth,d,inthousandthsofaninchormultiplesof0.025mm,determinedasin3.5and3.6,atthelocationwheretheKnoophardnessiswithin20pointsofthecoreKnoophardness.3.7.2SeverityofPartialDecarburizationTheseverityofpartialdecarburizationisthedifferencebetweentheHRChardness(convertedfromKnoop)at0.0003in(0.008mm)depthandthatofthecore.3.7.3CarburizationandNitridingThepresenceisindicatedbyKnoophardnessat0.0005in(0.0127mm)depth,oranyotherlocation,inexcessofKnoophardnessofcore.(Eq.1)(Eq.2)CopyrightSAEInternationalProvidedbyIHSunderlicensewithSAENotforResaleNoreproductionornetworkingpermittedwithoutlicen