THERMO-MECHANICAL CONTROL PROCESS TYPE 590 MPa CLASS H-SHAPED STEEL

摘要

PROBLEM TO BE SOLVED: To provide a TMCP type 590 MPa class H-shaped steel having a yield point of 440 to 540 MPa, tensile strength of 590 to 740 MPa and a yield ratio of 80% or less, where Charpy absorption energy at 0°C of a base material and HAZ is 47 J or more, a CTOD value at -40°C of a weld joint of small heat input weldment of HAZ is 0.50 or more and a CTOD value at 10°C of a weld joint of large heat input weldment is 0.15 or more.SOLUTION: There is provided thermo-mechanical control process type 590 MPa class H-shaped steel containing C:0.041 to 0.06%, Si:0.03 to 0.6%, Mn:0.3 to 1.6%, P:0.03% or less, S:0.001 to 0.01%, Cu:0.1 to 0.5%, Ni:0.1 to 1.5%, Cr:0.11 to 1.0%, Mo:0 to 0.29%, V:0.005 to 0.100%, Nb:0.005 to 0.070%, Ti:0.005 to 0.030%, B:0 to 0.0005%, Al:0.003% or less, N:0.0080% or less, and O:0.0005 to 0.0050%, and including a composite inclusion having MnS existing around Ti oxide. An area ratio of MnS in a cross section of the composite inclusion is 10% or more and less than 90%, a ratio of MnS in a boundary surface of the composite inclusion is 10% or more and a number density of the composite inclusion with a particle diameter of 0.5 to 5.0 μm is 10 to 100/mm.SELECTED DRAWING: None