Atomic Interactions and Mechanisms of Strengthening in Nitrogen Steels

摘要

A review of theoretical and experimental studies concerning the physical nature of favorable nitrogen effects in steels is presented. Using ab initio calculations and experimental studies of the electron structure, it is shown that the substitution of carbon by nitrogen enhances the metallic character of interatomic bonds. The spatial distribution of free electrons is non-homogeneous and their increased concentration is found in the vicinity of nitrogen atoms, which causes their effective negative charge. The nitrogen-caused improvement of fracture and impact toughness, excellent cryogenic properties and abnormally large grain-boundary strengthening are explained based on the atomic interactions. A mechanism of pseudo-cleavage at high nitrogen contents in austenitic steels is discussed.