Abstract: The effect of nitrogen content on the microstructures and mechanical properties in simulated CGHAZ(coarse-grain heat-affected zone) of normalized vanadium microalloyed steel were studied by thermal simulation method. The results showed that nitrogen content has a significant effect on the low-temperature toughness, precipitates, impact fracture morphology and ultimate microstructures. The steel contains 31ppm or 210ppm nitrogen has the poor CGHAZ toughness. As nitrogen is 31ppm, there is slight Ti-enriched carbonitride and grain boundary ferrite, the large-sized ferrite side-plate is the major microstructure, which can be as the channel of crack causing the poor CGHAZ toughness. As nitrogen is 210 ppm, CGHAZ contains coarse grain boundary ferrite, the crack can spread along the coarse grain boundary ferrite leading to poor toughness. As nitrogen is 120ppm, CGHAZ contains thin (V,Ti)(C,N), the fine grain boundary ferrite and abundant acicular ferrite can be as impediment of crack spread, bringing preferable CGHAZ toughness.
Authors: Chai Feng, Shi Zhong-ran, and Yang Cai-fu
Keywords: Nitrogen content, Simulated CGHAZ, Vanadium microalloying, Normalized Steel