Behaviour of nitrogen dissolution in Fe–Cr–Ni–Mo system stainless steels

Abstract

A study has been performed to understand the behaviour of nitrogen dissolution into six different alloys of the Fe–Cr–Ni–Mo system stainless steels with partial pressures of N₂ gas at 0·25, 0·5 and 1 atm. Some experiments were also conducted at 0·9 and 0·95 atm N₂ pressure. It was confirmed that the alloy systems obeyed Sievert’s law with nitrogen contents <0·52% apart from the Fe–29Cr–30Ni–8Mo system at 1723 K with nitrogen contents higher than 0·58%. Therefore, the critical point at which the deviation took place lay in between 0·52 and 0·58%N in this steel. The self-interaction coefficient of nitrogen was obtained as 0·056 with the Fe–29Cr–30Ni–8Mo alloy system at 1723 K. Therefore, interaction between nitrogen atoms should be accounted for along with the consideration of the equilibrium constant K obtained by varying N₂ partial pressure if designing alloy systems whose nitrogen contents are higher than 0·58%.