telyC,andtransferredtoafurnaceheldatC,wheretheyremainformintoallowtemperaturestabilization.ThepartsarethenaustemperedinamoltensaltbathheldatC,formin.Arelativelyhighaustemperingtemperatureisusedtoobtainahighamountofretainedausteniteaftertreatment.AftertheDAAStreatment,thematrixmicrostructureshowsafinemixtureofferriteneedlesandretainedaustenite.AschematicofthethermalcycleisshowninFig.a.TheDAAStreatmentiscertainlylaboriousandcannotbeusedunderusualmoldingcircumstances.Nevertheless,itistheonlymethodcapableofrevealinglowalloyductilecastironmacrostructures,tothebestoftheauthor’sknowledge.Afterthisprocedure,theretainedaustenitekeepsthecrystallineorientationdefinedduringsolidification.Therefore,etchingwithPicral()revealsthegrainstructureofthesolidificationaustenite.Itmustbeemphasizedthatsuchmacrostructu有被鉴别出来。
这也表明层片状石墨可以在