Effect of Gradient Structure Induced by Torsion at Different Temperatures on the Mechanical Proper-ties of Austenitic Steel

As one of the most widely used stainless steel in industrial production and daily life, 304 austenitic steel is of FCC (Face-Centered Cubic) structure. This study investigated the strengthening and toughening mechanisms of 304 austenitic steel at different temperatures. The characteristics of gradient twin structure and gradient phase distribution resulting from pre-torsion under different temperatures were presented. The combination of twin and phase gradients leads to the strength-ening and toughening in 304 austenitic steel in the subsequent tension. The number of twin structure gradually increases from core to edge and the number of twin types also increases: in the central region, the main type of twinning is primary twinning, and a large number of secondary twins are observed at the edge with a large shear strain of 0.52. As temperature decreases, the grain size gradually refines and the number of twin structure increases respectively. Pre-torsion at different temperature re-sults in a significant increase in ultimate strength and yield strength at corresponding temperatures. The simultaneous at-tainment of both strength and ductility in 304 austenitic steel with pre-torsion is in striking contrast to the usual strength-duc-tility trade-off in steels.