简介：ThemicrostructureandhardnessoftheHAZina800MPagradeultra-low-carbonmicroalloyedsteelwerestudied.Theresultsindicatethattheheataffectedzone(HAZ)oftheRPC(Relaxation-Precipitation-Controlling)steelpossessesacontinuousgradientstructure,andcanbeclassifiedintothreezones,i.e.CGHAZ(coarse-grainHAZ),FGHAZ(fine-grainHAZ)andICHAZ(intercriticaltemperatureHAZ).ThemicrostructuresintheHAZareallcomposedofbainite-likestructure.ThemicrostructareintheCGHAZmainlyconsistsoflath-likebainiteandgranularbainite.Theinfluencesofheatinputandt8/5onthehardnessintheHAZofRPCsteelarenotable.Withtheincreaseofheatinputandt8/5,thesofteningtendencyofHAZbecomesobvious.ThehardeningphenomenonthatnormallyoccursintheCGHAZdoesnottakeplacewiththissteelintherangeofexperimentalconditions.ThesofteningintheICHAZisboundtooccur.Henceappropriateweldingtechnologiesneedtobeselected.