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 - 500 N/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 strong pinning effect. The newly developed steels also use the intragranular ferrite (IFG) like titanium oxide bearing steel (TiO steel). In mass-production heats, gamma grain size is restricted below 200 micron under conditions of 1400 deg 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 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 YS 550 N/mm2, the production of steel plates up to 70 mm in thickness was carried out. The properties of welded joints for the 70 mm thick plates of YS 500 N/mm2 steel have been evaluated under heat input in 0.7 kJ/mm of flux-cored arc welding (FCAW) and 3.5 kJ/mm of sub-merged arc welding (SAW). Thex have shown excellent CTOD and Charpy impact properties at welded joints; and have moreover indicated good weldability when carbon euqivalent has been restricted to 0.22 or lower.
Production of high-strength and high-toughness steel for offshore structures
Produktion von Stahl mit hoher Festigkeit und hoher Bruchzähigkeit für Offshore-Strukturen
2003
7 Seiten, 10 Bilder, 5 Tabellen, 12 Quellen
Conference paper
English
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