Manufacturing Method of 50KGF / mm2 Class High Strength Structural Steel Sheet for Tensile Strength

摘要

The present invention relates to a method of manufacturing a tensile strength 50kgf / mm2 high tensile strength structural steel sheet, the purpose is to slow down the cooling rate of the slab after continuous casting, to precipitate a large amount of TiN and to uniformly precipitate TiN inside the slab In addition, by slowing down the reheating speed of the slab, a large amount of Ti in solid solution in the slab before heating is sufficiently precipitated with fine TiN, and effectively inhibits the growth of austenite grains during heating and hot rolling of the slab, thereby allowing fine structure after hot rolling. It is to provide a method of manufacturing a tensile strength 50kgf / mm2 high-tensile structural steel sheet having excellent mechanical properties by obtaining.;The present invention for achieving the above object is a method of manufacturing a tensile strength 50kgf / mm2 high tensile structural steel sheet, by weight ratio, C: 0.05-0.18%, Si: 0.5% or less, Mn: 0.9-1.8%, Al: The slab is heated at a rate slower than 100 ° C / hr immediately after continuous casting of molten steel consisting of 0.01-0.1%, Ti: 0.005-0.03%, P: 0.03% or less, S: 0.02% or less, and the remaining Fe and other unavoidable impurities. Air-cooled to and reheating the slab to a temperature range of 1100-1400 ° C. at a rate later than 50 ° C./min, followed by recrystallization control rolling to finish rolling at a temperature range of 1050-900 ° C., and then 4-15 ° C./min. The gist of the present invention relates to a method for manufacturing a tensile strength 50kgf / mm2 high tensile strength structural steel sheet which is cooled to a temperature range of 500-650 ° C. at an initial cooling rate and then air cooled to room temperature.