Reverse transformation from α′ to γ in lightly and heavily cold-drawn austenitic stainless steel fibers

Abstract

The reverse transformation of the strain-induced martensite phase (α′) to the austenite phase (γ) is studied in lightly and heavily cold-drawn 316 L stainless steel fibers using thermomagnetic analysis. The transformation mechanisms of the two types of fiber are different. A three-region reverse transformation process for α′ to γ during the heating process in the two types of fiber is established. Throughout the reverse process, the transformation is dominated by a diffusion-controlled mechanism for the two types of fiber. Shear reversion occurs for the lightly cold-drawn 316 L fiber in region II. A shoulder appears in the TMA curve at around 625 °C for the heavily colddrawn 316 L fiber Transformations of existing α′ and reformed α′ via the diffusion-controlled and shear mechanisms occur in the temperature range of 625–640°C for the heavily cold-drawn 316L fiber. The transformation is attributed to the reformed α′ containing low Nieq content, which retards the reverse transformation of the phase via shear mechanisms until around 625°C.