400 MPA-GRADE FINE-GRAIN HOT ROLLED STEEL BAR AND MANUFACTURING PROCESS THEREFOR

摘要

A 400 MPa-grade fine-grain hot rolled steel bar and a manufacturing process therefor, which relate to the field of hot-rolled steel bar production. The steel bar comprises the following components in mass percentage: 0.20-0.25% of C, 0.3-0.8% of Si, 1.2-1.6% of Mn, 0.01-0.04% of P, 0.01-0.04% of S, 0.005-0.03% of Ti, 0.001-0.08% of Cr, 0.0001-0.008% of V, 0.0001-0.008% of Nb, 0.0001-0.008% of Al, 0.01-0.02% of O, and 0.003-0.01% of N, the rest being Fe and inevitable impurities. The described steel bar further comprises manganese silicate inclusions, titanium oxide manganese sulfide multiphase inclusions, manganese sulfide inclusions and other inevitable inclusions. The manufacturing process comprises: molten steel smelting, continuous casting, continuous cast billet heating and steel bar rolling. According to the described method, by combining the optimization of the components and inclusions with smelting, continuous casting and rolling improvement as well as an inclusion induced fine grain strengthening mechanism, the strength of the steel bar is improved, the amount of precious alloy elements added is reduced, and the low-cost and high-quality production of a hot-rolled steel bar is achieved.