High heat input welding characteristics and a manufacturing method excellent microalloyed high tensile steel ductility.

摘要

PROBLEM TO BE SOLVED: To provide a production method capable of stably obtaining a non-heat-treated high tensile strength steel plate provided with excellent toughness in a high heat input weld heat affected zone at which weld heat input reaches 200 kJ/cm or higher and excellent base material ductility (19% or higher of total elongation) and having a plate thickness of 50 mm or lower, and in which the yield strength of the base material is 460 MPa or higher.;SOLUTION: A steel stock having a specified componential composition is heated at 1,050 to 1,200°C, is subjected to hot rolling at a cumulative draft of 30% or higher in the temperature range of 900°C or lower and at a rolling finishing temperature of an Ar₃ transformation point or higher, and is cooled at a cooling velocity of 2°C/s or higher to (an Ar₃ transformation point-100°C) or lower, thereafter, the cooling is stopped, and the same is reciprocated to the temperature range of an AC₁ transformation point to an Ac₃ transformation point, is again cooled to below 450°C at a cooling velocity of 2°C/s or higher, and is subsequently air-cooled.;COPYRIGHT: (C)2016,JPO&INPIT