Manufacturing method of 50㎏ / ㎠ class high tensile strength steel with excellent fracture toughness

摘要

The present invention relates to a method for manufacturing 50 kg / mm2 class high tensile strength steel used for ship's side shell and upper deck by thermal processing control (hereinafter referred to as TMCP). And to provide a method of manufacturing 50㎏ / ㎠ class high tensile strength steel with excellent fracture toughness of the weld joint.;In order to achieve the above object, the present invention, in the manufacturing method of 50kg / mm2 high-tensile strength steel, in weight%, C: 0.12-0.14%, Si: 0.15-0.40%, Mn: 1.15-1.35%, P: 0.020% Below, S: 0.008% or less, Ti: 0.010 ~ 0.015%, N: 20 ~ 60ppm, steel slab composed of balance Fe and other unavoidable impurities is heated to a temperature range of 1150-1250 ℃, and the residual pressure drop rate is 75 ± 5. Rough rolling up to% starts rolling in the temperature range of 950-990 ° C, and finishes the primary finishing rolling in the recrystallization temperature range up to 50 ± 10% of the residual pressure reduction rate, and then 10-30 ° C lower than the recrystallization stop temperature. Start rolling at and finish secondary finishing rolling in the temperature range directly above or below Ar _3, and then accelerated cooling at a rate of 5 ~ 15 ℃ / sec to a temperature range of 550 ~ 610 ℃, and then has excellent fracture toughness The technical gist of the manufacturing method of high-tension steel of 50㎏ / ㎠