On the Work-Hardening Behavior and Tensile Properties of a TWIP Steel when Cu or Al is Introduced into the Alloy Composition

Abstract

Taking account the wide interest in aluminum-free TWIP steels, we melted and cast a simple and inexpensive Fe–22Mn–0.6C–1.5Cu alloy. Cold-rolled sheets were annealed at different temperatures, mechanical properties were measured, and microstructure was analyzed. We also compare this material’s behavior with that shown by the classical Fe–22Mn–0.6C–1.5Al alloy. The TEM characterization showed that heating the sheets at 500, 750 and 850 C activated recovery anneal, partial recrystallization and complete recrystallization, respectively. The Cu-TWIP steel showed a higher ultimate tensile strength than Al-TWIP steel. The thermo-mechanical process that generated the favorable behavior is rolling at 20 C+an 850 C anneal; the values are rmax = 1372 MPa and Sr = 47.3 pct. The main deformation mechanism for all conditions was twinning together with dislocation glide. The alloy annealed at 850 C also shows the best formability among the cases analyzed. However, it performs worse than brass and Al-TWIP steel. The serrations due to dynamic strain aging that appear in the true stress/strain curves of the Fe–22Mn–0.6C–1.5Cu alloy may inhibit the selection of this alloy for certain applications.