By the utilization of new fine particles, steels refining the heat affected zone (HAZ) structure have been developed. This has made possible the mass-production of offshore structural steels which have high-strength of 460–500N/mm2 in yield strength (YS) and excellent crack-tip opening displacement (CTOD) properties. These newly developed steels for offshore structures have been mass-production to over 45,000 tons. The new particles are dispersed finely in the developed steels and show a strong pinning effect. The newly developed steels also use the intragranular ferrite (IGF) like titanium oxide bearing steel (TiO steel). In mass-production heats, γ grain size is restricted below 200 μm under conditions of 1400°C for 60 seconds. The improvement of HAZ toughness and the utilization of the thermo-mechanical control process (TMCP) has restrained the increase in carbon equivalent (Ceq,PCM) far as possible. By application of these technologies, it has been possible to mass-produce steels with high-strength, excellent CTOD properties and good weldability. As for steel plates of YS500N/mm2, the production of steel plates up to 70mm in thickness was carried out. The properties of welded joints for the 70mm-thick plates of YS500N/mm2 steel have been evaluated under heat input in 0.7kJ/mm of flux-cored are welding (FCAW) and 3.5kJ/mm of sub-merged arc welding (SAW). They have shown excellent CTOD and Charpy impact properties at welded joints; and have moreover indicated good weldability when PCM has been restricted to 0.22% or lower.
- Ocean, Offshore, and Arctic Engineering Division
Production of High-Strength and High-Toughness Steel for Offshore Structures
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Nagai, Y, Fukami, H, Inoue, H, Nakashima, T, Kojima, A, Kajitani, T, Adachi, T, & Yoshida, Y. "Production of High-Strength and High-Toughness Steel for Offshore Structures." Proceedings of the ASME 2003 22nd International Conference on Offshore Mechanics and Arctic Engineering. Volume 3: Materials Technology; Ocean Engineering; Polar and Arctic Sciences and Technology; Workshops. Cancun, Mexico. June 8–13, 2003. pp. 319-325. ASME. https://doi.org/10.1115/OMAE2003-37436
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