Effect of Cooling Path on Microstructure Features and Tensile Properties in a Low Carbon Mo-V-Ti-N Steel

The two-stage controlled rolling and cooling of a low carbon Mo-V-Ti-N steel at different cooling paths was simulated through a Gleeble 3500 system. The microstructure and tensile properties of each sample were examined by estimating their dependence on the cooling paths. It was indicated that a mixed microstructure of polygonal ferrite (PF), acicular ferrite (AF), granular bainitic ferrite (GBF), and a martensite-austenite (M-A) constituent was developed in each sample. Results showed that application of the reduced cooling rate and elevated finishing cooling temperature led to the increases in the effective ferrite grain size and the precipitate amount despite a decrease in dislocation density, which eventually resulted in the overall yield strength. It also led to an increasing amount of M-A constituent, which lowered the yield ratio and, thereby, enhanced the capacity for strain hardening. In addition, the underlying mechanism for the correlations among the cooling path, the microstructure, and the yield strength was considered.