Understanding heterogeneous nucleation and predicting grain size in wire and arc additive manufacturing of steels with inoculation

Inoculation has become a common practice to achieve grain refinement in metal additive manufacturing, and its application in steels has been extensively investigated in recent years. However, the nucleation behavior of equiaxed grains under high temperature gradient and fast cooling rate solidification conditions in additive manufacturing is still not well understood. And grain size prediction models for additive manufacturing of steel is lacking. In this work, a numerical microstructure simulation model is developed to simulate the growth and nucleation behaviors of grains in additive manufacturing, and to predict the grain size of inoculated steels with equiaxed grain structure. Here a wire and arc additive manufacturing (WAAM) of duplex stainless steel is selected for case study. The simulation results are in a good agreement with the experimental results.