Evolution of V (C,N) particles and microstructure analysis of V-N normalized steel under welding thermal cycle

The continuous cooling phase transformation of V-N microalloyed normalized container steel under welding thermal cycling was analyzed by welding thermal simulation method. The continuous cooling transformation microstructure and its composition were analyzed by optical microscope and scanning electron microscopy. The morphology and size of V (C,N) precipitates were analyzed by transmission electron microscopy. VN precipitation-time-temperature curve was calculated by solid solubility product formula. The simulated heat-affected zone continuous cooling transformation (SHCCT) curve was obtained. The microstructure and the phase composition at different cooling conditions were obtained. The critical t_8/5 for V (C,N) precipitation under welding thermal cycle was about 80 s. Effects of solid solution and precipitation state of V and N atoms on continuous cooling phase transformation and microstructure formation were discussed.