6533b823fe1ef96bd127fccd

RESEARCH PRODUCT

Numerical simulation of heat transfer, fluid flow and elements diffusion during laser welding of dissimilar steels

subject

description

The design of new steel grades offering equivalent mechanical performances for lower thicknesses and the added value with the possibility to join two different steel grades, require development and control of joining processes. Thanks to high precision and good flexibility, the laser welding became one of the most used processes for joining of dissimilar welded blanks. The prediction of local chemical composition in the weld formed between dissimilar steels in function of the welding parameters is essential because the dilution rate and the distribution of alloying elements in the melted zone determine the final tensile strength of the weld. The goal of the present study is to create and to validate a multiphysical numerical model studying the mixing of dissimilar steels in laser weld pool. For a better understanding of materials mixing based on convection-diffusion process in the melted pool in case of full penetrated laser welding, a 3D simulation developed within COMSOL Multiphysics®, including heat transfer, fluid flow and transport of species has been performed to provide the weld geometry and quantitative mapping of elements distributions in the melted zone. In order to reduce computation time, the model has been developed basing on the following hypothesis: a steady keyhole approximation and solved in quasi-stationary form. Turbulent flow model was used to calculate velocity field. Fick law for diluted species was integrated to simulate the transport of alloying elements in the weld pool. In parallel, to validate the model, a number of experiments using pure Ni foils as tracers have been performed to obtain mapping post-mortem of Ni distribution in the melted zone. The results of simulations have been found in good agreement with experimental data. Afterwards the model was applied to laser welding between Dual Phase steel (DP) and high Mn steel (TWIP) and finally it was adapted to the study of coating dissolution in laser weld pool.