Effect of austenitization temperature on microstructure, crystallographic aspects, and mechanical properties of AISI 420 martensitic stainless steel

The effect of austenitization temperature on crystallographic aspects of martensite and mechanical properties for AISI 420 martensitic stainless steel with 0.33%C was investigated in this study. The samples were characterized by X-ray diffraction (XRD), electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD) techniques, and dilatometry, hardness, and tensile tests. The refining mechanism observed for the steel with the increase of austenitization temperature consisted of increased interfaces formed by variants that showed high misorientation. The formation of blocks with smaller widths and more irregular Bain groups refined the microstructure. The increment of carbon in solid solution due to increased carbide dissolution with increasing austenitization temperature is the main effect on microstructure refinement. The blocks also showed a misorientation gradient between two lower misorientation variants (V1/V4 variant pair). The refining mechanism and increased carbon in solid solution promoted the increase in YS, UTS, and hardness. The higher percentage of retained austenite reduced the yield strength and altered the mechanical behavior of the sample austenitized at 1100 °C.