METHOD FOR MANUFACTURING HOT ROLLED STEEL SHEET FOR API STEEL PIPE USING MINIMILL PROCESS AND THE STEEL SHEET MANUFACTURED THEREBY

摘要

PURPOSE: A method for manufacturing hot rolled steel sheets for an API steel pipe by using a mini mill process and a hot rolled steel sheet through the same are provided to reduce excessive increase of yield strength due to low-temperature transformed structure after pipe milling. CONSTITUTION: A method for manufacturing hot rolled steel sheets for an API(American Petroleum Institute) steel pipe by using a mini mill process is as follows. A molten steel is composed of C 0.35 to 0.55wt.%, Mn 0.5 to 2.0wt.%, Si 0.05 to 0.8wt.%, Cr lower than 1.0wt.%, Ti lower than 0.5wt.%, residual Fe, and inevitable impurities. An ingot steel is casted into a 30 to 150mm thickness of thin slab(a). The thin slab is passes through roughing mill(20) in 850 to 1150°C temperature. The hot rolled strip(b) is finally rolled and coiled in about 700°C Bs(Bainite start) temperature.