the effect of thermomechanical treatment on the microstructure and mechanical behavior of an austenitic steel containing 1.4% al and 17.5% mn

The aim of this research was to evaluate the effect of different thermomechanical treatments on the microstructure and investigate some of the mechanical properties of a twip steel rich in mn & al. to this end, a block of a twip steel with nominal composition fe-17.5mn-1.36al-0.8c was cast and then subjected to hot rolling followed by cold rolling and heat treatment. cold rolling was performed before heat treatment in order to reduce grain size and improve the tensile and fatigue properties. x-ray diffraction technique was used before and after the heat treatment to study the structure of the phases present in the microstructure. no sign of martensitic transformation after cold deformation was observed. however, by increasing the amount of cold deformation, the number of mechanical twins and slip bands increased, which resulted to an increase in hardness and strength values. the best tensile and fatigue result was obtained after 47% thickness reduction and annealing at 715˚c for 10 min. under these conditions, the mean grain size reduced from 138 to 9 μm resulting in an increase in yield strength from 395 to 510 mpa; and the fatigue life improvement from the mean life of 10200 for the cast sample to 21500 cycles for the treated sample, when these samples underwent fatigue tests at a stress range of 650 mpa and r=0 (i.e., σmin = 0). in addition, the diameter and depth of dimples in fracture surfaces decreased by reducing the grain size, so the fracture mode remained ductile, and an adequate plastic deformation occurred before failure.