High Strength Stainless Austenitic CrMnN steels ‐ Part III: Electronic Properties

Some results of ab initio calculations and experimental studies of the C, N and C+N effect on the electron structure of austenitic CrMn steels are presented. It is shown that the total electron energy per atom decreases due to alloying in the sequence of carbon→nitrogen→carbon+nitrogen, which suggests a corresponding increase in the thermodynamic stability of the austenite. Alloying with nitrogen and nitrogen+carbon increases the density of electron states at the Fermi level in comparison with interstitial‐free and carbon‐alloyed steel. Measurements of conduction electron spin resonance (CESR) allow separating the contributions from free electrons which are responsible for the metallic character of interatomic bonds and from localized electrons involved in the covalent bonds. It is shown that, in contrast to carbon, nitrogen enhances the metallic character of atomic interactions with a maximum of the concentration of free electrons at some critical content of nitrogen (about 2 at.%). The combined alloying with carbon+nitrogen leads to two effects: (i) a larger concentration of free electrons and (ii) a shift of the critical content of interstitials towards higher values. The obtained results of the theoretical and experimental studies of the electron structure were used as a physical background for the development of super‐high–strength stainless austenitic steels.