Effect Of Microstructure Heterogeneity On Mechanical Properties Of C-Mn Weld Metal

Carbon-Manganese(C-Mn)weld metal is mainly composed of grain boundary ferrite(GF)and acicular ferrite(AF).As the mechanical properties of GF is different from that of AF,the weld metal is heterogeneous in micro scale and the heterogeneity will influence the mechanical properties of weld metal.In this paper,the tensile tests combined with scanning electron microscope(SEM)observation were performed to study the effect of microstructure heterogeneity on the deformation and failure behavior,instrumented indentation tests were performed to determine the mechanical properties of GF and AF,and the microstructure-based finite element simulation was adopted to investigate the microscopic stress/strain distribution and stress triaxiality buildup during tension process,the strain localization bands were used to predict the failure behavior of weld metal.In the end,the effect of microstructure heterogeneity on the mechanical properties of heat-treated weld metal was investigated.The main results were listed as follow:(1)The yield strength and work hardening exponent of acicular ferrite is higher than that of grain boundary ferrite,thus,the mechanical properties of weld metal is heterogeneous in micro scale;(2)Microstructure heterogeneity significantly influences the deformation behavior and failure modes of weld metal,the failure mode of longitudinal specimen is spilt failure and that of transverse specimen is a mixed spilt failure and shear failure mode;the microstructure heterogeneity of weld metal causes heterogeneous microscopic deformation,the stress is higher in AF,and GF bears higher plastic strain during tension process,strain localization bands in GF can be used to predict the failure behavior of weld metal;(3)The microstructure heterogeneity results in stress triaxiality buildup in weld metal,and the stress triaxiality varies during tension,the variation can be divided into three processes before necking: initial stage,transition stage and stable stage;(4)PWHT significantly influences the mechanical properties of individual microstructure in weld metal,hence,it influences the mechanical properties of weld metal;flow stress of GF decreases after PWHT,that of AF decreases after heat treating at 400 ? and 700 ? while increases slightly after heat treating at 600 ?;the level of plastic strain localization in weld metal increases after heat treating at 400 ? and 600 ?,which leads to the reduction of fracture strain of weld metal.