Enhanced corrosion resistance of laser powder bed fusion 316L stainless steel by modifying the microstructure through heat treatment

This study aims to investigate the microstructural evolution of laser powder bed fusion (LPBF) 316L stainless steel during heat treatment and its effect on corrosion resistance through microstructural characterization and corrosion testing. The results show that the as-built LPBF samples featured melt pool boundaries, cellular structures, a few nano-sized manganese silicate particles and irregular grains with strong fiber texture <101>, which are retained after heat treatment at 450 °C. With temperature increase to 850 °C, a σ phase rich in Cr, Mo, and S elements was formed. Subsequently, after heat treatment at 1100 °C, melt boundary disappears and large square grains similar to the cast counterparts appear. Electrochemical tests demonstrate that the corrosion resistance of LPBF samples surpasses the cast samples heat treated at 1100 °C. In addition, annealing at or below 1100 °C will reduce the corrosion resistance of LPBF samples due to the formation of hazardous precipitates. However, after heat treatment at 1300 °C, the best corrosion resistance was obtained due to the diffusion of Cr, Mo and S elements into the matrix and homogeneous microstructure. This study provides a method for effectively improving the corrosion resistance of LPBF 316L stainless steel and understanding the corresponding corrosion mechanism.