Microstructure and deformation behavior of metastable duplex stainless steel at high rolling reductions

The current investigation is a part of project concerning microstructure and texture in a series of ferrite-austenite stainless steels after deformation and annealing. The present paper focuses on deformation behavior of constituent phases in a metastable duplex type steel subjected to cold-rolling in the range of high reductions. Optical microscopy was used to examine changes in the morphology and the formation of ferrite-austenite band-like structure. Transmission electron microscopy was applied to analyze the microstructure and deformation mechanisms within the bands of austenite and ferrite. Additional research included the examination of texture changes in both constituent phases. Special attention was paid to deformation mechanisms operating within ferrite-austenite banded structure at high rolling reductions, including the formation of micro-shear bands, the occurrence of micro-twinning as well as deformation induced martensitic transformation. Transmission electron microscopy analysis indicates that the phase transformation occurred most likely through direct (gamma ->alpha') mechanism and obeyed predominantly Kurdjumov-Sachs orientation relationship. Within strongly fragmented two-phase microstructure at high strains the formation of alpha'-martensite proceeded in most cases at internal interfaces in micro-bands from the operating deformation systems.