Recently, the amount of handling of the sea container increases rapidly by rapid economic growth in the east Asian nations including China. Therefore, needs of the enlargement of the container ship have risen in the shipping company's trying to decrease the cost of transportation, to suppress the fare, and the ship's trying to load with a lot of containers. Therefore, thickness of steels is becoming. So, the weight of the hull is increasingly and the welding operation is becoming difficult. To reduce these problems, Nippon Steel developed YP47 steel which is high tensile force more than conventional YP40 steel and applied it to actual ship. Double integrity is the main concept to develop YP47 steel. One is the quality which is hard to initiate brittle crack, and the other is prevention brittle crack spread even if brittle crack occurred (arrestability). This concept is the one generally applied in the tank field, and we applied to new development steel. This arrestability had been researched by the industry-university cooperation up to now, and the conclusion that the crack that occurred in the welding was highly the possibility of missing to the parent material by the influence such as the residual stresses and arrested. However, that the steel plate to be investigated is YP36 steel plate and plate thickness by thinness with about 35mm in high tensile steel. So, it is not investigated in high tensile steel and 40mm thickness and over like YP47 steel. This paper refers in detail about the arrestability which is one of "double integrity" put up as a development objective.
While internationalization in a market is developed and increases in the marine transportation amount in recent years, steel development which corresponds to building of a high added value ship is being desired.