Effect of C and N content on the microstructure and performance of 316H austenitic stainless steel used in sodium-cooled fast reactor heat exchanger

316H austenitic stainless steel is used as the main structural material of the Chinese fourth-generation advanced sodium-cooled fast reactor heat exchanger. The premise of realizing domestic production is to obtain the reasonable control limit of the key trace-elements such as C and N. However, the ASTM standard shows a wide range of control of C element in 316H alloy, which makes it difficult to balance the intergranular corrosion resistance and welding performance of the alloy, especially for large-size tube sheet, flange and other parts where C element is prone to segregate. Besides, the ASTM standard doesn’t give the control range of N. In this paper, the influence of the C, N contents on the microstructure and properties, such as the grain size, tensile properties under room temperature or 580 °C, the room-temperature impact toughness and the intergranular corrosion resistance were investigated by the tensile and impact testing machines, combined with other testing methods such as OM and intergranular corrosion performance testing. The findings demonstrate that there are slight changes in grain size, tensile properties, and impact toughness of the alloys with C (0.04%～0.06%) or with N (0.05% to 0.07%). Although the hot-rolled alloy plates with the C contents of 0.04% to 0.06% generally show good intergranular corrosion resistance, the corrosion rate increases with the increasing C content. The rate of the intergranular corrosion resistance tends to decrease with the increase of the N content. Based on the results, the recommended control limits of the C and N content of the engineered 316H stainless steel parts are determined.