Effect of heat treatment on microstructures and tensile properties of ultrafine grained C-Mn steel containing 0.34 mass% V

An ultrafine grained (UFG) C-Mn steel containing a relatively large amount of vanadium was fabricated by equal channel angular pressing (ECAP) and its microstructures and tensile properties were examined. This investigation was aimed at demonstrating the effect of precipitation stage of vanadium precipitates in the course of the material processing on the tensile properties of the ultrafine grained C-Mn steel, especially strength and strain hardening capability. For this purpose, the two different heat treatments were carried out on the: present steel: (a) conventional normalization for vanadium precipitation before ECAP, and (b) isothermal transformation for vanadium precipitation during ECAP and subsequent annealing. The results showed that the second heat treatment was more effective on improving the thermal stability and the overall tensile properties of the steel by better uniform distribution of nano-sized vanadium precipitates which yielded an extensive interaction with lattice dislocations inside ultrafine ferrite grains. In addition, in this report, the feasibility enhancing the strain hardening capability of the UFG C-Mn steel was explored by comparing the microstructure and stress-strain curve of the steel prepared by the second heat treatment with those of the UFG C-Mn steel without vanadium.