THE DYNAMIC PHASE TRANSFORMATION AND FORMATION OF NANOCRYSTALLINE STRUCTURE IN SUS304 AUSTENITIC STAINLESS STEEL SUBJECTED TO HIGH PRESSURE TORSION

SUS304 austenitic stainless steel was deformed by high pressure torsion (HPT) at room temperature at different the rotation speed. By using X-ray diffraction (XRD) and transmission electron microscopy (TEM), the quantitative phase analysis and microstructural evolution along the progress of HIPT were investigated. The present results show that the deformation-induced dynamic phase transformation (DPT) not only from austenite (y) to martensite (alpha') but also alpha' to gamma occurred and equaixed nanocrystalline y grains are generated by HPT at high rotation speed. It is proposed that in austenitic stainless steel nanocrystalline gamma grains structure is formed by combination of forward (gamma -> alpha' ) and reverse (alpha -> gamma) DPT induced by HPT at high strain rate.