Effect of microstructure heterogeneity on microscopic stress triaxiality of a C-Mn weld metal

Strain incompatibility between soft grain boundary ferrite and hard acicular ferrite in C-Mn weld metal during tensile gives rise to stress triaxiality accumulation in microscale. Effect of microstructure heterogeneity on microscopic stress triaxiality were investigated in the study by conducting microstructure-based finite element analysis. It is found that stress triaxiality buildup in microscale is attributed to the microstructure heterogeneity of weld metal (the microstructure contrast and the local microstructure distribution); the stress triaxiality in grain boundary ferrite approaches to the plane strain state in longitudinal specimens, whereas it spreads from pure shear to plane strain states in transverse specimens; the local constraint of grain boundary ferrite has pronounced effects on the stress triaxiality of acicular ferrite. At final, the tension process is divided into three characteristic stages: initial stage, transition stage and stable stage according to the evolution of the stress triaxiality, which is consistent with the macroscopic observation. As a results, the triaxiality can be used as an indicator to measure the heterogeneity of the microstructure, correlating well with the macroscale deformation.