Effect of Cold Rolling on the Microstructural Evolution and Mechanical Properties of Fe-25Mn-3Si-3Al-0.3Nb TWIP Steel

The microstructural evolution, deformation mechanism and mechanical properties of Fe-25Mn-3Si-3Al-0.3Nb steel in the process of cold rolling were studied by optical microscopy, scanning microscopy, transmission electron microscopy, X-ray diffractometry, tensile testing and microhardness tests. A high-density dislocation structure and a small number of strain-induced twins appeared in the microstructure of the steel at 30% strain. At 50% strain, the strain-induced twins in austenite increased conspicuously, and the lamella thickness of the twins decreased. At 70% strain, the original grains were clearly refined by the micro-shear bands and twinning intersections to form a large number of sub-grains, and some sub-grains were at the nanoscale. The steel still remained a single-phase austenite during cold rolling even if the strain was as high as 70%. The plastic deformation mechanism of the steel was not changed through the addition of 0.3 wt.% Nb, and both dislocation slipping and twinning were still the fundamental plastic deformation mechanisms for the steel. Furthermore, cold rolling led to a drastic rise in the strength and hardness of the steel, but a remarkable decrease in the elongation. The characteristics of micropore aggregation fractures could always be observed on the fracture surface of static tensile specimens with various strains.

Automated summary

The microstructural evolution, deformation mechanism, and mechanical properties of Fe-25Mn-3Si-3Al-0.3Nb steel in the process of cold rolling were investigated. High-density dislocation structures and strain-induced twins appeared at 30% strain, and their characteristics changed at higher strains. The addition of 0.3 wt.% Nb did not alter the plastic deformation mechanism of the steel. Cold rolling significantly improved the strength and hardness of the steel while reducing its elongation. Micro-pore aggregation fractures were observed on the fracture surface of specimens with different strains.