Effect of Mn on Microstructure and Corrosion Resistance of Duplex Stainless Steel Surfacing Layer

CrNiMoMn duplex stainless steel surfacing layers with Mn content of 1, 2, 3 and 4% were prepared on Q235 substrate by TIG welding powder surfacing. The effects of Mn on the microstructure, hardness and corrosion resistance of CrNiMoMn duplex stainless steel were studied by microstructure observation, hardness test, immersion corrosion and electrochemical test. The results showed that with the increase in Mn content, the proportion of austenite phase increased, and (Cr, Mn) oxides, (Mn, Si, Cr) oxysulfides and other inclusions were generated. Mn element was dissolved in the matrix to form solid solution strengthening, which will increase the hardness of the material. Mn element could promote the redistribution of alloy elements in the two phases, thereby changing the corrosion resistance of the material. When the Mn content was 2%, the minimum pitting equivalent difference between ferrite and austenite phases was 3.420. The maximum thickness of passivation film was 0.380 nm, and the dispersion effect index of passivation film was closest to 1, which was 0.912, indicating that its corrosion resistance was the best.