Nitrogen in iron and steel

A short review of beneficial effects of nitrogen in steel is given including mechanical and corrosion properties, and the data of interatomic interactions and distribution of solute atoms in solid solutions are discussed with the aim of explanation of the physical nature of nitrogen steels. The concept is presented according to which alloying by nitrogen enhances the metallic component of interatomic bonds and provides more homogeneous distribution of substitutional solutes through short range ordering of nitrogen atoms and strong chemical interaction between nitrogen and alloying elements, which results in the high thermodynamical stability of nitrogen austenitic steels. The opposite tendency to clustering and concentration inhomogeneity of austenitic steels due to carbon is shown. Inheritance of the atomic distribution by martensite is discussed in terms of short range atomic order and data on crystal structure of precipitations during tempering of nitrogen martensite are presented as compared to carbon and carbon + nitrogen martensites.