Effect of Isothermal Annealing on Microstructural Morphology of Martensite in a Super-Martensitic Stainless Steel Subjected to Different Prior Conditions

Abstract

A super-martensitic stainless steel of the Fe-Cr-Ni family was investigated for morphological changes during isothermal annealing after subjecting it to different prior conditions. The key issues during thermomechanical treatment included determination of conditions for austenite stability and reversibility and deciding the appropriate prior treatments for the cold worked alloy before subjecting it to isothermal annealing. The study evaluated the effect of isothermal annealing on the recrystallization kinetics, phase reversion, and microstructural changes in the alloy. Intercritical isothermal annealing was carried out on samples in the range 750-900 degrees C for short time periods in the range of 1-2.5min. The recrystallization behavior and microstructural changes were studied by electron backscatter diffraction, X-ray diffraction, and Vickers's hardness measurements. Martensite morphology showed significant changes during the isothermal annealing process with dependence on prior matrix substrate. The tensile properties were also evaluated. The cold rolled (CR) and isothermally annealed samples provided an improved combination of strength and ductility at the optimum heat treatment parameters.