Study of Formation and Reversion of the Martensitic Phase Induced by Deformation of Lean Duplex Stainless Steel

Abstract

Lean duplex stainless steels consist of a low percentage of nickel and molybdenum, presenting twice as much resistance compared to austenitic stainless steel and their cost is about twice as low. However, this class of steels has microstructural instabilities, such as the formation of martensite induced by austenite deformation by cold rolling. This feature can significantly alter the properties of interest of this steel. The formation of the martensitic structure, as well as its reversion, is little studied in the steels of the austenitic–ferritic structure. The process of formation and reversal of the martensitic structure in cold rolled stainless steel duplex UNS S32304 was investigated through magnetic measurements, microhardness and X-ray diffraction analyzes. The deformation process allowed the formation of the -martensite phase from the austenite phase with an increase in the values of saturation magnetization, coercive field and micro-hardness values as well as a change in the intensity of the X-ray diffraction peaks. The heat treatment performed at $$650\,^\circ \hbox {C}$$ showed an increase in the peak intensity of the austenitic phase and a decrease in the saturation magnetization values, demonstrating a possible reversal of the martensitic structure. The SEM observations after annealing the Beraha’s etched samples revealed the possibility of a martensite transformation and reversion in a Lean duplex stainless steels.