| abstract |
A steel material for mechanical structures which comprises, in terms of percent by weight, 0.35 to 0.50% carbon, up to 0.15% silicon, 0.2 to 1.1% manganese, up to 0.020% phosphorus, 0.005 to 0.035% sulfur, more than 0.1 to 0.2% chromium, 0.05 to 0.5% molybdenum, more than 0.01 to 0.05% titanium, 0.01 to 0.05% aluminum, up to 0.01% nitrogen, 0.0005 to 0.0050% boron, 0.06 to 0.25% copper, 0.05 to 0.2% nickel, and iron and unavoidable impurities as the remainder, and which has a value of LD shown by the following equation (1) of 120 or lower. |