Carbon, Nitrogen and Hydrogen in Steel: Similarities and Differences in their Effect on Structure and Properties

Interstitials N, C and H in steels are compared in terms of their effect on the electronic structure and stacking fault energy, atomic distribution, phase transformations and precipitation, mobility of dislocations, mechanisms of deformation, strengthening and fracture. It is shown that the observed similarities and differences are essentially controlled by the decrease of the electron state density at the Fermi level of the iron due to carbon and its increase due to nitrogen and hydrogen. The increase in the concentration of vacancies with increasing content of interstitials and its possible role in mechanical properties are considered. The nature of nitrogen- and hydrogenincreased localized plasticity of austenitic steels is discussed and some consequences for their fracture are analyzed.