Effects Of Heat Treatment On Miscrost-Ructure And Mechanical Property Of D406A Steel Welded Joint

The effect of different heat treatment （Quenching and Temperingtreatment、Quenching and Partitioning treatmeat、Full annealing treatment）onmicrostructure and mechanical properrites of D406A steel weld joints specimenwas studied in this paper．The model on microstructure change of TIG weldjoint in D406A was theorized for microstructure of joints．The results shows that the miscrostructure of weld metal zone and heataffected zone are barren martensite，the misrostrcture of base metal zone wasgranular pearlites after TIG weld by an optical microscope(OM) observed．Theresidual stress of weld metal zone is the tensive stress and after heat treament theresidual stress have chengeg from435MPA to-94MPa．By comparing the effect of different heat treatment of D406A weld jointsspecimen， we kown that the highest hardness value zone was heat-affectzone(HAZ)and the fracture appears in substrate near welding zone for all heatreatmeat．The results show that the microstrucrue of D406A welding joints after Q&Pheat treatmeat consists of retained austenite and martensite， the residualaustenite content was about7%from the measurement of specimens after heattreatment of the residual austenite content；the volume fraction and the carboncontent of martensite plays an important role in tensile strength，the plasticityand toughness depends primarily on the retained austenite．So D406A has abetter combination of high strength and plasticity after this treatmeat．From theOrthogonal experiment wo known partition time，quenching temperature andpartition temperature had differents effect of mechanical property for Q&Ptreatment．After heat treatment to weld metal zone we know that the microstructurehad improved and its impact energy was the highest of all specimen．1.5mm cold-rolled sheet of D406A was obtained from3.5mm sheet throughcold rolling process(10%pass-8passes Single direction cold rolling)．It can befound banded structure in cold-rolled sheet of D406A steel after cold-rolled．Because of different TIG welding parameter with3.5mm sheet，the fracture appears in heat-affect zone for all heat treatmeat．...