Effect of heat input on the microstructure and mechanical properties of the simulated coarse-grained heat-affected zone (CGHAZ) of novel twining-induced plasticity(TWIP) steel

The study of strengthening mechanisms associated with the HAZ is of significant interest for improving the mechanical properties. In this study, the effect of different heat inputs (6.21, 13.89, 19.64, 27.78, and 36.75 KJ.cm(-1)) on the microstructure, carbide precipitation, and mechanical properties of CGHAZ in a novel FeCMnSi TWIP steel was explored by using welding thermal simulations. The results showed that the CGHAZ organization did not experience phase transformation after different welding thermal cycles. As the heat input increased, and the grain size was 95.87, 107.03, 109.65, 98.68, and 136.95 mu m, respectively. The factor of grain size variation with heat input is the dissolution of AlN particles and the generation of carbides at grain boundaries. The dramatic deterioration of CGHAZ toughness at a heat input of 27.78 KJ.cm(-1) is mainly attributed to the enrichment of carbon and silicon elements at the grain boundaries in the CGHAZ, which leads to cracks along the grain boundaries. At this time, the fracture mode of CGHAZ shifts from ductility to intergranular brittleness. It is proposed that fine grain strengthening is the main factors in improving strength, and carbide precipitation is responsible for the significant decrease in toughness in the novel FeCMnSi TWIP steel. It provides an effective guide for the application of FeCMnSi TWIP steels.