Weldable steel excellent in the toughness of the bond in a single layer welding with a large heat-input

A weldable steel excellent in the toughness of the bond in a single layer welding with a large heat-input more than 60,000 J/cm, which contains 0.03 to 0.22% of carbon, 0.02 to 0.80% of silicon and 0.40 to 2.00% of manganese in coexistance of 0.005 to 0.1% of rare earth metal and 0.0005 to 0.01% of boron, the remainder being substantially iron. Said weldable steel can be further improved by containing at least one of not more than 0.1% of niobium, not more than 0.1% of vanadium, not more than 0.5% of copper, not more than 1.0% of nickel, not more than 0.8% of chromium, not more than 0.5% of molybdenum, not more than 0.1% of selenium, not more than 0.1% of aluminum, not more than 0.1% of titanium and not more than 0.1% of zirconium.