A boron steel consisting of 0.18% to 0.35% C, 0.06% to 0.15%, Si, 0.50% to 1.00% Mn, 0.40% to 0.90% Cr, 0.01% to 0.05%, Al, 0.01% to 0.04% Ti, no more than 0.012% N, no more than 0.003% O, 0.0005% to 0.0030% B, and the balance Fe and impurities contained inevitably in manufacturing the steel, all percentages being based on the weight of the steel. The ratio of Ti to N is 3.4 to 6.0. The boron steel has an improvement in the reduction of heat-treatment distortion, surface oxidation in carburization and material cost, and also has superior hardenability, mechanical strength and fatigue strength.
Hot-rolled steel sheet which then can be cold-rolled, coated, the steel in the sheet having the following composition by weight: 0.15%<carbon<0.5% 0.5%<manganese<3% 0.1%<silicon<0.5% 0.01%<chromium<1% titanium<0.2% aluminum<0.1% phosphorus<0.1% sulfur<0.05% 0.0005%<boron<0.08%, the remainder being iron and impurities inherent in processing, the sheet ensuring a very high mechanical resistance after thermal treatment and the aluminum-based coating ensuring a high resistance to corrosion.
