ULTRA-HIGH STRENGTH LOW CARBON HOT-ROLLED STEEL SHEET WITH EXCELLENT HALL EXPANSIBILITY AND WELDABILITY AND METHOD OF MANUFACTURING THE LOW CARBON HOT-ROLLED STEEL

摘要

PURPOSE: An ultra high-strength low-carbon hot-rolled steel sheet with superior hole expandability and solderability and a manufacturing method thereof are provided to simply achieve the target strength and hole expandability through control of hot-rolling process. CONSTITUTION: A method for manufacturing an ultra high-strength low-carbon hot-rolled steel sheet comprises the steps of: reheating slab to a reheating temperature of 120050C(S105), hot-rolling the slab at a finish rolling temperature of 850100C(S110), cooling the rolled plate to a martensite temperature range at a cooling rate of 100-250C/sec(S120), and coiling the cooled plate in the martensite temperature range(S130). The slab comprises carbon of 0.03-0.08 weight%, silicon of 0.001-0.6 weight%, manganese of 1.0-2.0 weight%, aluminum of 0.001-0.1 weight%, niobium of 0.01-0.05 weight%, boron of 0.003weight% or less, and iron and inevitable impurities.