Partially-recrystallized, Nb-alloyed TWIP steels with a superior strength-ductility balance

We investigated the effect of Nb micro-alloying in the range of 0.01 to 0.1 wt% on the microstructures and mechanical properties of Fe17Mn0.6Cl.5Al (wt%) TWIP steel. EBSD analysis shows that the Nb addition retards recrystallization in both the hot-rolled steels and cold-rolled and annealed steels. The Nb addition in the cold rolled and annealed TWIP steel leads to an increase in yield strength. This phenomenon is due to a combined effect of precipitation hardening and a low degree of recrystallization. Recovery annealing of the cold-rolled TWIP steels at 650 degrees C results in a good combination of yield strength and ductility. The steels containing 0.01 wt % and 0.025 wt% of Nb show a superior combination of UTS x TE exceeding 40,000 MPa.% and yield strength higher than 800 MPa. The design of TWIP steels utilizing both precipitation hardening and partial re crystallization opens a way to develop steels with a superior combination of yield strength and ductility.The authors gratefully acknowledge the support of CBMM and the POSCO Technical Research Laboratories