METHOD FOR PRODUCING LARGE THICKNESS LOW YIELD RATIO HIGH TENSILE STRENGTH STEEL PLATE

摘要

PROBLEM TO BE SOLVED: To provide a method for producing a low yield ratio high tensile strength steel plate with which in the large thickness high tensile strength steel plate having ≥550MPa tensile strength and exceeding 40mm thickness, the low yield ratio and the high strength can be achieved in both of 1/4 thickness position and 1/2 thickness position as the small characteristic difference in the plate thickness direction without needing Q'(quenching) and T(tempering) process.;SOLUTION: When the large thickness high tensile strength steel plate having ≥40mm plate thickness is produced by heating a slab to 1000-1300°C and accelerated-cooling with the water-cooling to ≤500°C after hot-rolling, the cooling from the surface of the steel plate is controlled so that the difference of the cooling speed at the temperature zone of at least 700-500°C at the 1/4 thickness position and the 1/2 thickness position in the plate thickness direction at the accelerated-cooling time becomes within 15%.;COPYRIGHT: (C)2007,JPO&INPIT