Effect of alloy elements on the mechanical properties and pitting corrosion resistance of 316LN austenitic stainless steel

The effect of four alloying elements, N, Cr, Mo and Ni, on the grain size, mechanical properties and pitting corrosion resistance of 316LN austenitic stainless steel for primary coolant pipes in nuclear power plants were investigated. When the nitrogen concentration increases in the stainless steel, the grain size and growth trend dramatically decrease. Increasing the nitrogen concentra-tion can improve the mechanical properties and particularly, the pitting corrosion resistance goes up before the nitrogen concentration reaches 0.20%. Grain refinement achieved by the addition of nitrogen is propitious to the mechanical properties of the stainless steel, but this is not the main mechanism for the increase in mechanical properties. Cr and Ni elements have no obvious impact on the grain size and mechanical properties, but Cr can improve the pitting corrosion resistance slightly while the passive film loses its stability as the Ni concentration increases. When the Mo concentration increases, the strength and pitting corrosion resistance increase, but the grain size and elongation decrease.