Effect of Grain Size on Tensile Properties of TWIP Steel

Abstract

The effect of the grain size of TWIP (twinning induced plasticity) steel on both the strength and ductility in the quasi-static tensile test at room temperature was studied. 31%Mn-3%Al-3%Si steels were cold-rolled to a reduction in thickness of 88% and subsequently annealed at various temperatures ranging from 600°C to 1100°C. The post annealing produced recrystallized grains with mean grain sizes ranging from 0.60 μm (at 600°C) to 62.3 μm (1100°C), while small amounts of the dislocation cell structures and Mn compounds were observed in the specimen annealed at temperatures lower than 620°C. The 0.2% offset stress and tensile strength become higher with decreasing mean grain size as determined by Hall-Petch relationship; whereas the uniform elongation and total elongation become smaller. However, the warm-annealed TWIP steels with ultrafine grained microstructures still keep preferred ductility. The possible reason why the grain refinement of the TWIP steel easily provides the preferable strength ductility balance was discussed.