A Study on Using Hot-Rolled Steel Sheet for Ship Superstructure

Application of the hot-rolled steel sheet for the members of superstructure, where the strength requirement of these parts in ships is not severe, is expected as a solution to reduce the hull construction cost. Because the hot-rolled steel sheet is applied after recoiling by cold working to return it to a flat plate, the material properties is deteriorated due to excessive plastic working and the residual stress induced by the plastic work might affect for the thermal cutting and welding. There is a possibility that the hot-rolled steel sheet has poor properties comparing with the flat rolled steels applied for hull parts where the structural integrities are required by the classification societies’ rules. The difference of properties between the hot-rolled steel sheet and the flat rolled steel are investigated in this research. Investigated items are mechanical properties, microstructures, initial residual stress distributions, hardness distributions, distortion after thermal cutting and laser-arc hybrid welding.