Numerical simulation and process optimization of laser surface treatment on duplex stainless steel

Abstract

Duplex stainless steel (DSS) has excellent mechanical properties and corrosion resistance. The excellent performance is due to an approximately equal ratio of ferrite and austenite, 50:50. Influenced by the welding thermal cycle, the ratio of ferrite and austenite shows an imbalance in DSS welded joints, resulting in the loss of performance. Laser surface treatment (LST) has marvelous advantages of high flexibility and efficiency to restore corrosion resistance of DSS welded joints. The effect of LST is dependent on laser scanning parameters, material composition, specimen geometry, and so on. The resulting phase ratio is very sensitive to those parameters. In this paper, three different types of DSS, 2304, 2205, and 2507, were used as test pieces. The temperature field under different LST parameters was calculated by finite element analysis, which helped to optimize the LST processing window. The phase transformation of DSS was divided into three steps: austenite to ferrite and ferrite grain growth in the heating stage, ferrite to austenite in the cooling stage. The effect of thermal history on the ratio of ferrite and austenite was investigated by thermal simulation experiment and numerical calculation. The calculation results were in good agreement with metallographic measurement. It was concluded that the established numerical simulation is capable of optimizing LST processing parameters and predicting the phase ratio of DSS after certain thermal cycle considering different material conditions and thermal conditions.