| 摘要 |
PURPOSE: A low alloy cold-rolled steel sheet having an excellent weldability and strength and a manufacturing method thereof are provided to implement control-cooling in hot rolling, to implement soft reduction in cold rolling, and then to implement annealing, thereby improving yield strength, yield ratio, elongation rate, and bendability. CONSTITUTION: A low alloy cold-rolled steel sheet having an excellent weldability and strength includes 0.01 to 0.12 wt% of C, 0.1 to 2.0 wt% of Si, 0.5 to 2.5 wt% of Mn, 0.001 to 0.10 wt% of P, below 0.020 wt% of S, 0.02 to 0.30 wt% of Sol.Al, below 0.020 wt% of N, 0.1 to 1.2 wt% of Cr, 0.0010 to 0.0080 wt% of B, remnant Fe, and other inevitable impurities. The sheet further includes 0.003 to 0.08 wt% of Ti and 0.003 to 0.08 wt% of Nb. The sheet satisfies a formula(1) and a formula(2) below. The formula(1) is C+Mn/6+Cr/5<=0.55, and the formula(2) is C+Mn/20+Si/30+2P+4S<=0.27. A microstructure includes above 95 % of ferrite and below 5 % of bainite and martensite based on area. |
