Monte Carlo simulation of grain growth in heat-affected zone of 12 wt.% Cr ferritic stainless steel hybrid welds

The grain structure in the heat-affected zone (HAZ) of 12 wt.% Cr ferritic stainless steel under laser + pulsed gas metal arc welding (laser + GMAW-P) hybrid welding was studied experimentally and theoretically. First, an adaptive combined volumetric heat source model was used to calculate the temperature field in laser + GMAW-P hybrid welding. Then a three dimensional Monte Carlo method using the computed thermal cycles was applied to simulate the evolution of grain structure in the hybrid welding HAZ of the ferritic stainless steel. The predicted fusion zone geometry and the mean grain size agree with the measured results for different welding conditions in laser + GMAW-P hybrid welding of ferritic stainless steel. The simulate results showed that in hybrid welding the width of coarse grain heat-affected zone and the grain structure varied dramatically along the fusion line direction, the maximum mean grain size near the top surface was much larger than that close to the weld root.