Recent studies on the nature and state of carbon atoms in iron

Abstract

Carbon is the most important alloying element in steels and Fe–C alloys have been studied intensively. Carbon has various functions and has a strong influence on the transformed structures and mechanical properties. There are plenty of experimental data of Fe–C alloys but we still have many unsolved problems. The first-principles calculation and molecular dynamics (MD) method can evaluate effects of the slight change of the position and distribution of carbon atoms on energy and physical properties. So they are very useful for clarifying the nature and state of carbon in steels and for solving the problems which cannot be made clear by experiments. The electronic structure of carbon in iron, diffusion of carbon, site occupation of carbon atom in martensite, tetragonality, C–C interaction, carbon cluster and spinodal decomposition of martensite are the topics of this review paper. The studies using first-principles calculation and MD method are mainly reviewed. How much of the unsolved issues are clarified and what kind of problems remain are shown.