Controlling Mechanical Behavior of TWIP Steels by Tuning Texture and Stacking Faults

Abstract

We developed an Fe–22Mn–0.6C–1.5Al TWIP steel and investigated how thermo-mechanical processes affect the mechanical properties. In this alloy, the low stacking fault energy (SFE) activates the formation of mechanical twins, which reduces the dislocation mean free path during plastic deformation. Thus, a high strain hardening rate is observed. Two processes provided the best combination of yield stress, maximum strength, and strain to fracture: (1) rolling at 20 °C and annealing at 750 °C, and (2) rolling at 600 °C and annealing at 850 °C. Although the dominant deformation mode was dislocation glide combined with twinning, the crystallographic textures were significantly different. The first processing path developed the typical low SFE-FCC rolling texture, which is favorable for twinning. However, the texture developed by the second process shows components typical of medium/high SFE metals. Correlation between microscopy and Rietveld analysis using MAUD showed that a large number of twins formed during rolling at 20 °C and also during annealing at 750 °C. This fact influenced the strain hardening despite the favorable texture. Meanwhile, although the formation of twins during rolling at 600 °C was inhibited, the high number of extrinsic SFs available contributed to twinning during tensile deformation. Both samples achieved more than 1100 MPa ultimate tensile strength and 45 to 50 pct strain to fracture.