Effect of strain-induced martensite on the formation of nanocrystalline 316L stainless steel after cold rolling and annealing

This work aimed to study the effects of cold rolling temperature and pre-strain on the volume fraction of strain-induced martensite in order to obtain nanocrystalline structures of 316L stainless steel. Hot rolling and cold rolling followed by annealing treatments were conducted under different conditions. The microstructures and the volume fraction of phases were characterized by scanning electron microscopy and feritscope tests, respectively. The hardness and tensile properties of the specimens were also measured. The results showed that decreasing the rolling temperature while increasing pre-strain leads to increased the volume fraction of martensite accompanied by decreased saturating strain and, further, that this behavior affects the degree of grain refinement. The smallest grain size of about 30-40 nm was obtained via 30% pre-strain at 523 K and subsequent conventional cold rolling at 258 K with a strain and a strain rate of 95% and 0.5 s(-1), respectively, followed by annealing at 1023 K for 300 s. Uniaxial tensile tests at room temperature showed that this specimen exhibits very high tensile strength of about 1385 MPa. (C) 2009 Elsevier B.V. All rights reserved.