Excellent welded structure steel plate and a manufacturing method thereof weldability and fatigue crack propagation properties

摘要

PROBLEM TO BE SOLVED: To provide a steel sheet having improved fatigue crack propagation resistance without being restricted by propagation directions, and excellent strength, extensibility, toughness and weldability.;SOLUTION: A steel sheet has a composition containing C, Si, Mn, P, S and the balance Fe with inevitable impurities, and having a carbon equivalent Ceq of 0.42 mass% or less, a weld crack sensitivity composition Pcm of 0.28 mass% or less, and a structure having a bainite structure at 1/4 position of sheet thickness, in which the total area fraction of the bainite structure and a ferrite structure is 80% or more, the balance has a pearlitic structure and/or a martensite structure is over 80%, the balance has a pearlitic structure and/or a martensite structure, further X ray diffraction intensity ratios of a (110) face parallel to a sheet face at 1/4 position of the sheet thickness and at sheet thickness center position, (110)_Q and (110)_M, are 2.0 or less, and X ray diffraction intensity ratios of a (100) face and a (111) face parallel to sheet face at the sheet thickness center position, (100)_M and (111)_M, satisfy a specific relation.;COPYRIGHT: (C)2014,JPO&INPIT