Thermo-Metallurgical Simulation of Laser Welding Nd: YAG Through the Bi-Phase Model Applied for Dual Phase Steels

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 in 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. Austenization and cooling phase of bi-phase metal, ferrite-pearlite(FP) and martensite(M) follow metallurgical model, Waeckel model and  Koistinen-Marburger model. The volume fraction of the ferrite-pealite, 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 the influence of high speed welding gives a higher volume fraction of martensite in FZ with participation of the other volume fractions of the austenitic and ferrite- pearlite. 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.

Keywords—  Laser Weld, phase transformation, ABAQUS user subroutine DFLUX & UMAT.