Thisstudyaimstoinvestigatetheeffectofthe1-stepquenchingandpartitioning(Q&P)processonthemicrostructureandtheresultingVicker’shardnessof0.3C-1.5Si-1.5Mnsteelbyusingin-situdilatometry,opticalmicroscopy(OM),scanningelectronmicroscopy(SEM),X-raydiffractometry(XRD),andVicker’shardnessmeasurement.Systematicanalysesindicatethatthemicrostructureofthespecimensquenchedandpartitionedat150℃,200℃,250℃,and300℃mainlycompriseslathmartensiteandretainedaustenite.Thedilatometrycurveofthespecimenpartitionedat150℃ispresumablyascribedtotheformationofisothermalmartensite.Intheearlystagesofpartitioningat200℃,thenearlyunchangeddilatationcurveiscloselyrelatedtothesynergisticeffectofisothermalmartensiteformationandtransitionalepsiloncarbideprecipitation.Inthelaterstagesofpartitioningat200℃,theslightincreaseinthedilatationcurveisduetothecontinuousisothermalmartensiteformation.Withfurtherincreaseinpartitioningtemperatureto250℃,thedilatationincreasesgraduallyupto3600s,whichisrelatedtocarbonpartitioningandlowerbainiteformation.Partitioningatahighertemperatureof300℃causesarapidincreaseinthedilatationcurveduringtheinitialstages,whichsubsequentlylevelsoffuponprolongingthepartitioningtime.Thisismainlyattributedtotherapiddiffusionofcarbonfromathermalmartensitetoretainedausteniteandcontinuousformationoflowerbainite.
