Improvement of Fracture Toughness, Kc, of Welded Joints : Development of Higher Toughness YP47 (460 N/mm~2) Class Steel Plates for Ultra-large Container Ships - 2

摘要

To improve the efficiency of maritime transport, Nippon SteelrnCorporation has developed YP47-class steel plates instead ofrnconventional YP40 steel plates and applied them to actual largerncontainer ships. The development concept and performances of YP47rnsteel plates were reported in the previous conference, ISOPE 2010. Inrnthis paper, we focus on fracture toughness, that is, the technologies forrnmicrostructure control to secure brittle crack initiation toughness inrnwelded joints. In order to improve fracture toughness grain refinementrnis the most important. To achieve this, fine particles of oxides and/orrnsulfides were dispersed and an appropriate amount of boron was addedrnto the steel. Furthermore, to reduce the brittle phase that can be arncleavage trigger, the chemical composition of the steel was optimizedrnincluding a reduction in silicon content. It was confirmed that weldedrnjoints prepared by combining steel plates and welding materials exhibitrnexcellent properties evaluated by the Charpy impact test and deepnotchrntest.