Use of EBSD technique to examine microstructure and cracking in a bainitic steel

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1、ScriptaMaterialia,Vol.39,No.3,pp.295±300,1998ElsevierScienceLtdPergamonCopyright©1998ActaMetallurgicaInc.PrintedintheUSA.Allrightsreserved.1359-6462/98$19.001.00PIIS1359-6462(98)00170-5USEOFEBSDTECHNIQUETOEXAMINEMICROSTRUCTUREANDCRACKINGINABAINITICSTEEL³²

2、E.Bouyne,H.M.Flower*,T.C.Lindley*andA.Pineau*DepartmentofMaterials,ImperialCollege,LondonSW72BP,UK²CentredesMateÂriauxÐEcoledesMinesdeParis,BP87,91003Evry(France)(ReceivedFebruary16,1998)IntroductionDynamiccrackpropagationandcrackarrestisanimportantissuei

3、nthefieldofstructuralintegrity.Focusisusuallyplacedontheinitiationstep(KIc)toavoidcatastrophicfailuresofstructures.Nevertheless,itisoftenrequiredinsafetyanalysistoconsiderthatacrackmightinitiate(forexampleinlocalbrittlezones)andleadtothepropagationathighs

4、peedofacleavagecrack.Itisimportanttoknowwhetherornotthematerialwillbeabletoarrestthatcrackbeforeitgoesthroughtheentirestructure.Toanswerthatquestionitisessentialtounderstandcleavagemicromechanismsduringcrackpropagationinordertoassesstheenergydissipatedahe

5、adofthecracktip.Inapreviousstudy[1]thesemicro-mechanismswereinvestigatedinalowalloysteelwithabainiticmicrostructure.Itwasshownthatacrackpropagatingathighvelocity(aÇ'500m/s)isformedbyanetworkofmicrocracksinterconnectedtoeachothersurroundingislandsofunbroke

6、nligamentsleftbehindthecrackfront.Theseligamentswhichneedtobedeformedplasticallybeforefinalfracturelargelycontributetothedissipatedenergyduringcrackpropagationandatcrackarrest.TheseobservationsaresimilartothoseofHoaglandetal.[2]madeonothersteels.Togofurth

7、er,itisnowimportanttounderstandthelinkbetweenthematerialmicrostructureandthisnetworkofcleavagemicro-cracks,specificallytoidentifytherelevantmicrostructuralfeaturesleadingtoasinglemicro-crack(unitcrackpath)andthecrystallographicnatureofcleavagefracture.The

8、preliminaryresultspresentedinthispaperwereobtainedusingtheElectronBack-ScatterDiffractiontechnique(EBSD).Thismethodenablescrystallographicinformationstobeobtainedfromsmallsurfaceregionsofbulksamples(;1mmdiameterand3