Computational prediction of mechanical properties of a C-Mn weld metal based on the microstructures and micromechanical properties

The effects of the mechanical properties and microstructure of grain boundary ferrite (GF) and acicular ferrite (AF) on the tensile properties of C-Mn steel weld metal were investigated using a micromechanics-based finite element method. Considering indentation size effect, the uniaxial elastic-plastic properties for the constituent phases were determined by the instrumented nano-indentation test. Actual microstructures of the weld deposited metal obtained by optical microscopy were used as the representative volume elements (RVEs) in the modelling. Periodic boundary condition was used in the simulation to quantitatively evaluate the strain distribution due to the microstructure-level heterogeneity in terms of the mechanical properties and the distribution of the individual grain boundary ferrite and acicular ferrite. The macroscopic mechanical properties of the weld metal obtained from the tensile test were predicted well by the numerical results. It is found that the incompatible deformation between the harder acicular ferrite and the softer grain boundary ferrite tends to localize along grain boundary ferrite where failure usually initiate in the form of localized plastic strain as observed in the experiment.