Evolution of the microstructure and mechanical properties of a V-containing microalloyed steel during coiling

The microstructural evolution during coiling and its effects on the mechanical properties of a vanadium microalloyed steel were investigated. Samples were held at 500 °C for 80 s (S1), 600 s (S2), 3600 s (S3), and 18000 s (S4) to capture the various stages of microstructure evolution. Experimental results demonstrated that nano precipitates (<10 nm) nucleated during holding at 500 °C were heterogeneously distributed. These precipitates mainly contained V and N were more commonly found in areas with a high value of the Kernel Average Misorientation (KAM) because these areas have a larger number of dislocations which act as nucleation sites for the precipitates. The tensile flow curves of the samples show extended elastoplastic regions that are related to the heterogeneity of the microstructure as well as the presence of microscopic residual stresses. The precipitation strengthening effect is not very large and is offset by softening which is caused by the aging of bainite and the associated recovery of dislocations.