High tensile strength steel material having a tensile strength of 700 MPa or more that has both weldability and toughness, and a method for producing the same

摘要

PPROBLEM TO BE SOLVED: To provide a high-tensile-strength steel material with a tensile strength of a 700 MPa grade or higher having both weldability and toughness, and to provide a manufacturing method therefor. PSOLUTION: This steel material includes, by mass, 0.005-0.08% C, 0.01-0.40% Si, 0.10-3.0% Mn, 0.010-0.10% Al, 0.10-3.0% W, 0.010-0.080% Nb and 0.010-0.50% V, and has boundaries between large inclined grains containing a lath structure of a bainite or martensite phase, in which intermetallic compounds containing W precipitate at a spacing of 100 nm or shorter. The intermetallic compounds have an average particle diameter of 1 m or smaller, and contain more than 0.005% W by a measured value by quantitative analysis with the use of an X-ray fluorescence analysis technique for an extraction residue obtained by a constant potential electrolysis. The large inclined grains contain the bainite or martensite phase so as to occupy 50% or higher of the total area in a visual field when a cross section is observed through an optical microscope. PCOPYRIGHT: (C)2007,JPO&INPIT