Effect of Cold-Rolling and Annealing Treatments on the Microstructure and Mechanical Properties of AISI 309S Austenitic Stainless Steel

Microstructural evolutions and mechanical properties of a cold-rolled 309S austenitic stainless steel were investigated after reversion annealing in the temperature ranges of 700-1000°C for 3-20 min. The specimen was first cold-rolled at room temperature to 90% thickness reduction. The microstructure was analyzed by optical and SEM methods and the mechanical behavior was studied by tensile tests and hardness measurement. The results depicted that negligible strain-induced ά-martensite was formed after cold-rolling. In addition, elongated austenite grains were observed after deformation followed by annealing below 700°C which was a signature of the recovery process. The recrystallization of the deformed austenite was dominant above 800°C, while recrystallization followed by grain growth were seen at 900°C. Moreover, the significant grain growth was observed at 1000°C. The optimum annealing temperature and time for achievement of a uniform recrystallized grain were at 800°C for 3 min which resulted in considerable grain refinement. The grain refinement led to improvement of mechanical properties of investigated austenitic stainless steel. The hardness value of refined austenite grains was 195% greater than that of the as-received steel. Finally, current work can shed some light on the effect of grain refinement on the control of microstructural and mechanical property of austenitic stainless steels.