Extra-thick sheet submerged-arc welding technique

The present invention discloses an extra-thick sheet submerged-arc welding technique. The technique comprises the following technological parameters and steps: 1) connector preparation: X-type beveled edges are adopted by extra-thick sheets; 2) preheating: first heating a back side of an extra-thick sheet and then a front side of the extra-thick sheet, a preheating temperature being 150 DEG C to 160 DEG C, and a heating rate being not higher than 105 DEG/h; 3) backing welding: after preheating, using flux-cored wire gas shield welding for backing welding for two paths to form two layers, and using submerged-arc welding to fill at least two paths to form one layer, maintaining interlayer temperature to be not higher than 230 DEG C; 4) turning over after an inter-welding deformation is not larger than 6-8 mm; 5) backside welding: after carbon gouging and back chipping, backing welding according to the step 3) after the extra-thick sheet reaches a preheating requirement according to the preheating method described in the step 2); 6) stress relief treatment; and 7) carrying out post heating treatment at 200 DEG C/2h after the welding, then slowly cooling the extra-thick sheet to be at the room temperature. With adoption of the technique provided by the present invention, rooting welding deformation is reduced, welding residual stress for subsequently filling a cover face is also reduced, and thus turn-over times in welding of the extra-thick sheet are reduced.