Alloying effects on the microstructure and phase stability of Fe-Cr-Mn steels

Austenitic Fe-Cr-Mn stainless steels interstitially alloyed with nitrogen have received considerable interest lately, due to their many property improvements over conventional Fe-Cr-Ni alloys. The addition of nitrogen to Fe-Cr-Mn stabilizes the fcc structure and increases the carbon solubility. The benefits of increased interstitial nitrogen and carbon content include: enhanced strength, hardness, and wear resistance. This study examines the effect of carbon, silicon, molybdenum, and nickel additions on the phase stability and tensile behavior of nitrogen-containing Fe-Cr-Mn alloys. Nitrogen and carbon concentrations exceeding 2.0 wt.% were added to the base Fe-18Cr-18Mn composition without the formation of nitride or carbide precipitates. Minor additions of molybdenum, silicon, and nickel did not affect nitrogen interstitial solubility, but did reduce carbon solubility resulting in the formation of M23C6 (M=Cr, Fe, Mo) carbides. Increasing the interstitial content increases the lattice distortion strain, which is directly correlated with an increase in yield stress.