Effect Of Increased Nitrogen On Controlling The M-A Constituent Of Low Carbon Mo-V-Ti-B Steel

Low-carbon Mo-V-Ti-B steel can produce the Multi-phase,acicular(AF)/granular bainite(GBF)as the matrix and the martensite austenite(M-A)constituent as second phase,by controlling the appropriate cooling technology and the given nitrogen content.The Time-Temperature-Transformation diagram;Continuous-Cooling-Transformation diagram were studied,and the process of how to producing different types matrix with M-A constituent were identified.The element diffusion characteristics of low-carbon Mo-V-Ti-B steels with three different nitrogen content(30 ppm,120 ppm and 165 ppm)in mid-temperature domain were simulated by using the DICTRA software.The effect of nitrogen content in controlling the nitrogen and carbon synergistic diffusion and the elements distribution in metastable austenite(?')were identified clearly.The resultant materials with three different nitrogen content which were prepared using a Gleeble-3500 thermal simulator were observed and the M-A constituent were examined.Thus,the effect of nitrogen content on the M-A constituent of low carbon Mo-V-Ti-B steel was comprehensively expounded.The results showed that the amount of the M-A constituent increased with the increased nitrogen content during the continuous cooling transformation process;increased nitrogen content facilitated the diffusion of nitrogen atoms during the ???+?' process,reduced the diffusion of carbon,regulated the carbon and nitrogen atoms concentration distribution in ?' and increased the martensite transformation temperature(Ms);the microstructure was observed consisted by AF and GB;the amount of AF and the M-A constituent increased.Nitrogen(carbon)atoms enrichment enhanced(decreased)in M-A constituent with increased nitrogen content;thus adjusted the internal structure of the M-A constituent transform from the twin-type M-A to lath-type M-A.