Elevated Temperature Tensile Behavior of a Nb-Mo Microalloyed Medium Mn Alloy under Quasistatic Loads

Wenlong Wu,Haijun Pan,Minghui Cai,Zeyu Zhang,Weigong Tian

doi:10.3390/met12030442

Abstract

The elevated temperature tensile behavior of a Nb-Mo microalloyed medium steel was investigated over the −50 to 150 °C temperature range. The ultimate tensile strength was significantly reduced with increasing deformation temperature, but both YS (yield strength) and EI (total elongation) values changed slightly. The best product of UTS (ultimate tensile strength) and EI (~59.5 GPa·%) can be achieved at the deformation temperature of 50 °C, implying an excellent combination of strength and ductility. Furthermore, the change in strain hardening rate as a function of deformation temperature was further explained by the following two aspects: the dependence of mechanical stability of retained austenite on deformation temperature as well as the dependence of deformation mechanism on deformation temperature. Theoretical models and experimental observations demonstrate that the dominant deformation mechanism of the present medium Mn steel changed from the single transformation-induced plasticity (TRIP) effect at −50 to 50 °C to the multiple TRIP + TWIP (twinning-induced plasticity) effect at 50–150 °C.

Highlights

Medium Mn steels (4–12 wt.%) as a candidate in the advanced high-strength steel family have gained widespread attention due to having a high strength level of ≥1000 MPa while maintaining excellent elongation of ≥30% [1–5]
The excellent overall tensile properties of medium Mn steels largely rely on the stability of austenite, which controls the activation of transformation-induced plasticity (TRIP) or twinning-induced plasticity (TWIP)
The phases of the annealed samples are identified as ferrite (α) and retained austenite (γ) grains, based on their morphological features, as arrowed in yellow

Summary

Introduction

Medium Mn steels (4–12 wt.%) as a candidate in the advanced high-strength steel family have gained widespread attention due to having a high strength level of ≥1000 MPa while maintaining excellent elongation of ≥30% [1–5]. The excellent overall tensile properties of medium Mn steels largely rely on the stability of austenite, which controls the activation of transformation-induced plasticity (TRIP) or twinning-induced plasticity (TWIP). Lots of efforts have been conducted to tailor the stability of retained austenite (RA) [6]. The stability of retained austenite is influenced by many factors, such as chemical compositions [7,8], grain size [9,10] and morphology [11,12]. Deformation temperature is another key parameter affecting the stability of retained austenite and its transformation behavior [6,12]. This is partly because the transformation behavior of retained austenite depends on the stacking fault energy (SFE) of steel, which is usually a function of deformation temperature.

Methods

Results

Discussion

Conclusion