Solidification mode and microstructure of nitrogenous stainless steels

This article reports the solidification mode, microstructure, and element distribution of phases in 18Mn18CrN stainless steels with four kinds of N contents. N content significantly affects the solidification mode and microstructure of 18Mn18CrN alloy systems. The solidification mode of 18Mn18CrN stainless steels changes from Mode F to A as the N content increases from 0.07% to 0.72%. Additionally, the microstructure of 18Mn18CrN stainless steels changes from ferrite + austenite Widmanstätten dual-phase structure to ferrite + austenite dual-phase structure and a single phase of austenite as the N content increases. N content also affects the morphologies of austenitic phases. The lath-like or needle-like austenite phase changes into interdendritic and equiaxed austenite phases with the increase of N content. Ridges are present in interdendritic and equiaxed austenite grains, and the amount of ridges increases as the N content increases. There is a relationship between the ridges and the segregation of Cr, Mn and Fe elements in austenite phases during the solidification process. Moreover, this solidification segregation is retained to room temperature microstructure.