Dynamic Torsional Deformation Behavior of Ultra-Fine-Grained Dual-Phase Steel Fabricated by Equal Channel Angular Pressing

Abstract

Dynamic torsional deformation behavior of an ultra-fine-grained dual-phase steel fabricated by equal channel angular pressing (ECAP) was investigated and compared with that of an equal channel angular pressed (ECAPed) ultra-fine-grained low-carbon steel. Tensile and dynamic torsional tests were conducted on these two steels, and the deformed microstructures were observed to investigate the dynamic deformation behavior. The ECAPed low-carbon steel consisted of very fine, elongated ferrite-pearlite grains of 0.5 mu m in size, and the ECAPed dual-phase steel consisted of ferrite-martensite grains of 1 mu m in size. The dynamic torsional test results indicated that maximum shear stress of the dual-phase steel was lower than that of the conventional steel, but that fracture shear strain was higher in the dual-phase steel. Some adiabatic shear bands were observed at the gage center of the dynamically deformed torsional specimen of the low-carbon steel, but they were not observed in the dual-phase steel because localized deformation was alleviated by the increased strain hardenability. These results suggested that the ECAPed ultra-fine-grained dual-phase steel could be a good way to increase the fracture resistance under dynamic loading as the formation of adiabatic shear bands was reduced or prevented.