Recent development of niobium bearing structural steels for ships and infrastructures in Nippon Steel

Since niobium gives significant metallurgical effects on restraint of grain growth, retardation of recrystallization and precipitation hardening, it has been used as the main microalloying element in Thermo-Mechanical Control Process (TMCP) of steel plates. This paper describes the effect of Nb on microstructure evolution and the new Nb bearing structural steels recently developed by Nippon Steel such as YP460MPa heavy plates with high toughness, excellent arrestability and large heat input weldability for hull structures of mega-container ships, the high strength steels for seismic application of high-rise buildings with improved toughness of heat affected zone surrounding high heat input welded joints and the high performance steels for bridge structures with high yield strength and good weldability. (AU)