Effects of Thermomechanical Treatment on Microstructural and Mechanical Behavior of an Austenitic Steel Contains ۱.۴% Al and ۱۷.۵% Mn

The aims of this research were to evaluate the effects of different thermomechanical treatments on the microstructure and investigate some of the mechanical properties of a TWIP steel rich in Mn & Al. So, a block of a TWIP steel with nominal composition Fe-۱۷.۵Mn-۱.۳۶Al-۰.۸C 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 the grain size and improve the tensile and fatigue properties. X-ray diffraction technique was used before and after the heat treatment to evaluate the possibility of any phase formation. 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 band increased resulted to an increase in hardness and strength. The best tensile and fatigue result were obtained after ۴۷% thickness reduction and annealing at ۷۱۵˚C for ۱۰ min. Under these conditions, the mean grain size reduced from ۱۳۸ to ۹ μm resulted to an increase in yield strength from ۳۹۵ to ۵۱۰ MPa, and the fatigue life improvement from the mean life of ۱۰۲۰۰ for the cast sample to ۲۱۵۰۰ cycles for the treated sample, when these samples underwent fatigue tests at a stress range of ۶۵۰ MPa and R=۰. In addition, the diameter and depth of dimples in fracture surfaces decreased by reducing the grain size but the fracture mode was remained ductile and adequate plastic deformation occurred before failure.

کلیدواژه ها:

TWIP steel ، Heat Treatment ، Fatigue ، Fractography ، Thermomechanical processing