Progress in TMCP Technology and Expansion of Its Range of Application

More than twenty years have passed since the development and commercialization of water-cooling-type TMCP (Thermo-Mechanical Controlled Processing) steel. At present, the technology is used in various areas as a reliable process. Features of TMCP steel are excellent weldability and toughness, which make it extremely useful as a tank material. This paper aims to contribute to the safety and workability improvement in the tank construction field as in other areas by the effective use of TMCP steel. The paper first describes the characteristics of material properties and workability of TMCP steel and the metallurgy to realize these characteristics. It then introduces a several examples of recent development in the application of TMCP technology. The use of TMCP steel realizes better toughness in high-heat-input welding, improved low-temperature toughness and sour gas resistance, in addition to reduced weld pre-heating temperature thanks to its low carbon content. Recently, because of its excellent characteristics, it has become possible to apply TMCP steel to nuclear energy areas, medium- to high-temperature regions, and ultra-high strength types such as 780 MPa and 950 MPa. Examples of the latest commercial application include surface ultra fine grain steel whose excellent brittle crack arrestability is comparable to that of high-Ni steel for cryogenic use, and ultra-thick structural steel plate that allows super-high welding heat input over 100kJ/mm.