Effect of Microalloying Elements (Ti, V and Nb) on the Hot Ductility Behavior of High-Mn Austenitic Fe-22Mn-1.5Al-1.5Si-0.45C Twip Steel

TWIP steels, with an excellent combination of strength and ductility, have been attracting great attention as a new group of materials in many industrial applications. This research work studies the influence of single microalloying elements (Ti, V and Nb) on the hot ductility behavior of high-Mn austenitic TWIP steels. For this purpose TWIP steels were melted in an induction furnace and casted into 70 mm x 60 mm cross section ingots. Uniaxial hot tensile test in the temperature range of 700-1100 °C under a constant true strain rate (10^-3 s^-1) were carried out to evaluate the hot ductility as a function of reduction in area (%RA). X-ray diffraction (XRD) was used to corroborate the stability of the austenite phase. SEM-EBSD technique was used to identify recrystallized grains, and TEM analysis using carbon replica technique was carried out to determinate the precipitates nature on the broken specimens. In general, V and Nb-microalloyed TWIP steels exhibit the highest peak stress values (265 and 284 MPa, respectively) at 700°C. Likewise, these steels show a significant improvement in the hot ductility value (86 and 73 %RA, respectively) in the temperature range of 800-900 °C. On the other hand, Ti-microalloyed TWIP steel exhibits the lowest hot ductility value (35 %RA). The hot ductility improvement in V-microalloyed TWIP steel is associated with its ability to form fine VC particles, which rise the strengthening and promote the dynamic recrystallization (DRX). Thus, grain refinement by DRX promotes the isolation of cracks along grain boundaries, which prevents their growth and coalescence, and therefore this phenomenon significantly increases the percentage of reduction in area. Finally, grain boundary sliding was recognized as the failure mechanism associated with second-phase particles precipitated at the grain boundaries, which play an important role on the mechanism of nucleation and propagation of void-cracks.