질소와 이트륨 첨가에 따른 듀플렉스강의 고온변형거동

Effect of alloying on the microstructure and mechanical properties of heat-resisting duplex stainless steel for retort used in Pidgeon process for Mg production was investigated in this study. 25Cr-(8, 10)Ni based duplex stainless steels were cast into rectangular ingots of which the dimension was 350x350x100 ㎣. Nitrogen and Yttrium were added in the range within 0.3 in weight percent. Phase equilibrium was calculated using the thermodynamic software FactSage® and the database of FSStel. For comparison, 310S stainless steel widely used heat-resisting austenitic stainless steel, and 20Cr-5Al alloy were also cast in this study. On ingots, dilatometry was carried out in the temperature range from RT to 1200°C and thermal expansion coefficients were evaluated. Addition of N and Y had no effect on the thermal expansion behavior. High temperature tensile and compression tests were conducted on the ingots at 1230℃, which is operation temperature employed for Mg production by Silicothermic reduction. The steel with N and Y showed much higher strength than 310S and 20Cr-5Al alloy in both tensile and compression tests. By thermal exposition at 1230℃ for 200 hrs, hardness of duplex stainless steel containing N and Y was found to increase, while those of 310S 20Cr-5Al alloy decreased.