Study on nitrogen in martensitic stainless steels

Pressure metallurgy is a means of increasing the nitrogen content and thereby the resistance of stainless martensitic steels to pitting corrosion. The present study on their constitution and heat treatment reveals that even at normal pressure more nitrogen is dissolved in the melt if the carbon content increases, because the fraction of ferrite is reduced during solidification. Nitrogen is dissolved more readily during austenitisation than carbon which lowers the C/N ratio at hardening temperature and thus is likely to improve the corrosion resistance of martensite after quenching. As the stability of retained austenite is increased by nitrogen a strain induced transformation by ausforming is discussed.