Study On Mechanical Properties And Microstructures Of Dual-phase Steels Tailor-welded Blanks Based On Temperature

Owning to the advantages such as reducing body weight,enhancing vehicle safety and cutting down the fabricating cost,dual-phase steels laser tailor welded blanks (TWBs) technique has become the mainstream measure to fabricate lightweight vehicle. However,with the enhancement of the steel strength,its formability is worsened dramatically.So,failure and fracture are always occurred in stamping.As a new production technology,warm plastic forming can help to solve these problems.Thus,it is very important for the forming technologies to research on warm deforming behavior and microstructures changing rule of the dual-phase steels TWBs.Taking the dual-phase steels B340/590DP and TWBs as the research object, through the tensile experiment,and the analysis of microstructures,this artical discusses the mechanical properties and microstructure changing rule of base metal and TWBs synthetically.Main contents of this paper are given below.Firstly,through the normal temperature tensile test,the mechanics performance of base metal and TWBs with longitudinal weld were investigated.The warm tensile experiments of base metal and TWBs with longitudinal weld were conducted in different temperatures and different strain rates.Meanwhile,effect of deforming temperature,deforming strain rate on mechanical properties was discussed.Based on analyzing the effect of warm tensile process parameters on the flow stress, Deformation activation energy was functioned as a contingency.The flow stress constitutive equation of base metal and TWBs was established on the basis of Z parameter.The stress-strain curves obtained by this model are in good agreement with experimental results,which confirmed that the developed models are accurate and valid. The flow stress constitutive equation containing softening factor was improved. Functional relation between softening factor and temperature was established.The flow stress of based metal and TWBs were predicted by the proposed models,which were used to comparing with the equation based on Z parameter.Optical microscope(OM) and scanning electron microscopy(SEM) observations were carried out to investigate the microstructure and tensile fracture surfaces of based metal and TWBs tested by warm tensile tests.The mechanical properties and microstructure changing rule were discussed under different deformation conditions.