THERMO-METALLURGICAL SIMULATION OF LASER WELDING ND: YAG THROUGH BI-PHASE MODEL APPLIED FOR DUAL PHASE STEELS

摘要

The objectives of this study are to simulate the evolution in fraction of solid state phase transformation of dual phase steel DP600 in laser welding Nd:YAG by transparent mode with thickness of 1.25mm and 0.1mm gap and to evaluate the properties of the welded joint such as the mean hardness and tensile properties. Two models, thermal and metallurgical model, are coded in the subroutines DFLUX and UMAT of Abaqus, the resolutions are done separately between them. Conical heat source model with Gaussian distribution is used in thermal problem. Waeckel and Koistinen-Marburger model are used for modeling the austenitization and the cooling cycle during phase transformation of welding. The volume fraction of the ferrite, austenite and martensite are used to calculate the hardness and tensile properties of the welded joint and base metal. The simulation revealed that the final phase under influent of high speed welding gives higher volume fraction of martensite in FZ with participation of other volume fractions of austenite and ferrite that can be overlooked. Because of the thin HAZ, the fine mesh in HAZ is needed for accurate results. Finally the mean hardness in Vickers and tensile strength in different areas are identified.