Effect of Solution Carbon and Nitrogen on the Microstructural Size and Crystallography of Lath Martensite in Fe–N and Fe–C Alloys

Abstract

Microstructures of lath martensite that contains bcc or bct martensite crystals in Fe–C alloys are known to depend on the carbon content of the alloys. The effect of nitrogen content on microstructure, however, has not yet been elucidated. This study elucidates the effects of carbon and nitrogen content on microstructures via local crystallographic analysis. We found that the packet sizes are similar when the nitrogen content in the alloys are the same as the carbon content, with the packet size decreasing with increasing carbon and nitrogen content. The block and sub-block thicknesses in low nitrogen lath martensite are smaller than those in low carbon lath martensite, whereas those in medium and high carbon and nitrogen lath martensites are similar. Martensite lath thickness and dislocation density in the Fe–N alloy laths are lower than those in the Fe–C alloys laths, and the distribution of misorientation angles between adjacent the blocks and sub-blocks in Fe–N alloys is similar to that in Fe–C alloys.