Study of the Fabrication Method of 590 MPa Steel (SA440) with High Tensile Strength and High Ductility

摘要

Harumi 1-choume development is a big project which includes three high rise buildings (bight over 150 m) and ten middle/low rise buildings in Tokyo. The structural steel frame of these high rise buildings was designed involving box sections and pipes using a new steel material 5A440 which has 590 MPa tensile strength. The box section has been man-ufactured by welding with much higher heat input after assembling steel plates, and the pipe section has been manufac-tured by bending a steel plate. 5A440 is a particular material manufactured by undergoing heat treatment, including dou-ble quenching and tempering. The upper and lower limits of the yield strength (YP) and tensile strength (Th), and also yield ratio (YP/Th) are strictly regulated for this material. However; after the fabrication of this steel with much heat input or plastic deformation, there was a fear that the property of the material might have varied and YP, Ts and YR might have exceeded the specified extent. In order to meet the requirement after the fabrication, we studied the heat treatment process of the pipe products, manufactured by bending, and the manufacturing process for the box products through pro-duction tests. From the result of these experiments, we studied the conditions of heat treatment and welding process which comply with the requirements. Consequently, Kawasaki Steel confirmed that it can ensure good mechanical prop-erty of pipes to which heat treatment in applied after receiving plastic deformation, and also obtain a good weld metal of the fabricated box section.