Development of YP460 Class Steel Plate with Excellent Brittle Crack Arrestability for Large Container Ships

摘要

Since brittle fracture occurred at a hull structure of large size containerships has a possibility to cause catastrophic damage, structural integrityshould be ensured by prevention to initiate brittle crack and / orprevention of brittle crack propagation in case it may occur(arrestability). Especially, research for crack arrestability of steel plateshas been widely conducted in order to compile guidelines forarrestability requirements. In addition, a recent trend in container shipsis a huge increase in ship size over 15,000 TEU class appropriate fortransport efficiency and low cost operation. Consequently high strength(YP460) steel plates with not only heavy thickness but high crackarrestability performance are in high demand with the trend ofenlargement of ships.In general, crack arrestability of steel plate is related to the impactproperty of the plate through microstructure refining by TMCP process,particularly by means of lowering heating temperature and rollingtemperature. JFE Steel Corporation has developed an innovativesolution for compatibility of high arrestability and high strength forheavy thickness steel plate over 70mm, by means of texture controlledTMCP process with chemical compositions optimization.The developed YP460 (EH47 grade) heavy thickness steel plate has anexcellent arrestability over 15,000 N/mm~(3/2), adequately more thandouble for guidelines on brittle crack arrest design issued by someclassification societies. Characteristics of the plate, manufactured byTMCP process, are highly oriented transformation texture forprevention of brittle crack propagation in addition to excellent impacttoughness. Alloy design of the developed steel is relatively high carbonequivalent (Ceq.) but low carbon content in order to satisfy requiredtensile properties for every thickness portion. Moreover, the steel alsoexhibits low cold cracking susceptibility equal to conventional YP390steel plates due to its low PCM design, consequently good weldability.