Transformation kinetics of retained austenite in the tensile Luders strain range in medium Mn steel

Medium Mn steel usually exhibits Luders banding behavior accompanied with austenite-to-martensite transformation during deformation. In tensile tests with standard samples, Luders front exhibits steep gradients in thickness and strain, which brings difficulty in measuring the transformation kinetics in the Luders strain range. To overcome it, a special-shaped specimen was designed to introduce a gradient in tensile stress along the transverse direction and additional geometrical constraints. The measured transformation kinetics exhibited two stages. Most transformation occurred at the first half range and almost no transformation afterwards. This demonstrates that austenite-to-martensite transformation does not directly provide strain hardening for Luders band propagation. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.