(Session 9A)Development of Thick YP460 MPa Class Steel Plates for Large Heat-input Welding for Very Large Containerships

摘要

In connection with a recent trend toward large scaled containerships, it becomes more important than ever to ensure hull girder longitudinal strength around the deck openings in order to assure the safety and reliability of the hull construction. For this reason, YP460 MPa class steel plates have been applied, which exceed YP390 MPa class, the highest strength standard of the conventional TMCP (Thermo Mechanical Control Process) steel.For practical application of YP460 MPa class steel, it is necessary to ensure further safety of the ships, as well as to apply high efficiency large heat-input welding.This report describes the development concept of YP460 MPa class steel plates, and the material characteristics of the base metal and welded joints.To reduce MA that may cause the HAZ (Heat Affected Zone) toughness deterioration, C addition and Ceq were reduced as much as possible. In addition, TiN was added for the purpose of refinement of the HAZ structure, and to prevent enlargement of γ grains from large heat-input welding.To achieve the YP460 MPa class high strength, transformation toughening using a uniform intense cooling process was applied.Improvements of the base metal fracture toughness were achieved by refinement of crystal grains using strictly temperature controlled TMCP.