Submerged arc-welding method of steel for high strength pressure vessel

The invention discloses a submerged arc-welding method of thick steel slab for large pressure vessel with tensile strength of 610-670 MPa, which solves the currently existing defects that the impact energy of deposited metal and the actual joint tenacity can not meet the welding requirements for the production of large high-strength thick steel slab structure. A measure adopted by the invention is as follows: the method comprises the following steps of: adopting pressure vessel steel with tensile strength of 610-760 MPa and thickness of 44mm to 55mm; using matched welding materials: the tensile strength of a welding wire is 610-670 MPa with diameter of 4.0mm and welding flux SJ105Q is adopted; adopting an unsymmetrical double-side V-shaped groove with an angle of 60 degrees as the groove of submerged arc-welding and a blunted edge of 4mm; continuously welding at the butt joint till weld seams are filled up under the conditions of 700A welding current, 36V voltage, 30cm/min speed and 50kJ/cm energy input; using a welding flux roasting system of 350 DEG C multiplied by 1h; and adopting interlayer temperature of 100 DEG C to 150 DEG C. In the invention, preheating is not required before welding and heat treatment is not needed after welding and joints have good low temperature impact toughness and safety storage.