Thermal simulation of heat affected zone performance by QP980 quenching-partitioning steel laser welding

In this study, the Gleeble-3500 thermal simulation system was used to simulate the different sub-regions of the heat affected zone (HAZ) of QP980 quenching-partitioning steel laser welding. The microstructure and properties of each sub-region were studied and compared with the same region of the HAZ of the welded joint. The results show that the microstructure of each sub-region of the HAZ during welding obtained by thermal simulation is consistent with that of the same region of the laser welded joints. The mechanical properties analysis shows that the tensile strength and hardness of the sub-critical HAZ (SCHAZ) are the lowest in the thermal simulation samples, and the elongation after fracture is the largest in the whole HAZ during welding. In the tensile test, obvious elongation also occurs in SCHAZ, indicating that its ductility is the best. The hardness analysis of the cross-section of the welded joint shows that the hardness of the inter-critical HAZ (ICHAZ) of the welded joint is lower than that of the base metal (BM), which is the softening zone of the welded joint. The tensile properties and cross-sectional hardness distribution of the welded joint reveal that the weak area of the welded joint is located in the ICHAZ, which is consistent with the performance of the simulated HAZ during welding. Through the analysis of the microstructure of the SCHAZ, compared with the BM, the geometrically necessary dislocation (GND) is reduced; the average grain size is increased, and the low-angle boundary grain content is decreased.