LAUSR

Martensitic structures in steels are characterized by a high density of dislocations and a fine substructure. They typically exhibit hardness which can be improved by interstitial elements such as carbon and nitrogen. Therefore, martensite with high contents of carbon and nitrogen is an important microstructure for strengthening steel. It is introduced in commercial steel products, such as hard steels for tools, hardened surface layers of machine structural steels, and steel sheets for automobiles. Recently, the improvement of high-strength industrial steels was necessitated to cope with economic and environmental demands. Hence, the applications of high-carbon and high-nitrogen martensite are expected to expand and therefore, a deeper understanding of their structures and properties is essential. Carbon steel martensite has been extensively investigated for many decades. The morphology of its microstructure,1–6) substructure of dislocations and twins,3–8) crystallographic character,9,10) and mechanical properties6,11–14) were deeply examined based on carbon content. Even in high carbon martensitic steels with a carbon content of more than 1 mass%, the microstructure,14,15) habit planes,14,15) and hardComparison of Microstructure and Hardness between Highcarbon and High-nitrogen Martensites