WELDING JOINT OF LARGE HEAT INPUT WELDING AND WELDING METHOD THEREOF

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PURPOSE : A welded joint of large input heat welding and a welding method thereof are provided to improve toughness at low temperature in the welded metal and the zone affected by welding heat by welding a steel plate through the large input-heat electro-gas welding with welding input-heat more than 100 KJ/cm. CONSTITUTION : A welded joint is obtained by welding a steel plate through the large input-heat welding with the welding input-heat more than 100 kJ/cm. The welding metal for the welded joint contains C of 0.03 - 0.12 mass%, Si of 0.10 - 0.80 mass%, Mn of 0.80 - 2.50 mass%, Ni of 0.50 - 3.00 mass% , less than Cr of 0.50 mass%, less than Mo of 0.50 mass%, Ti of 0.01 - 0.10 mass% and rare earth elements of 0.0010 - 0.0050 mass%. The welding metal satisfies f(Q) is bigger than or the same with (B) and (B) is bigger than or the same with 0.01 (Q is the welded input-heat) to B content (B), and has the composition composed of the balance iron with inevitable impurities. Toughness at low temperature is improved in the welded metal and the welded heat affected zone by welding the steel plate with the large input-heat welding over 100 kJ/cm welding input-heat.