METHOD FOR GENERATING RESIDUAL COMPRESSIVE STRESS IN STAINLESS STEEL AND NI-BASED SUPERALLOY, AND METHOD FOR REPAIRING STRESS CORROSION CRACK BY UNDERWATER WELDING

摘要

PROBLEM TO BE SOLVED: To impart a residual stress to a molten part by melting underwater the surface of stainless steel or a Ni-based superalloy using a plasma arc welding torch (PTA torch) that is provided with a suitable water eliminating device, performing repair welding for cracks, and quenching in accordance with the movement of the torch. SOLUTION: A PTA torch 10 for underwater melting or welding is equipped with a conical or cylindrical water eliminating device 16 at the tip end of a gas lens 14; with the skirt of the device coming into contact with the surface 41 of a base material to be processed, the surrounding water is eliminated by a shield gas from an inactive gas supply line 11, enabling a local waterless area to be obtained forming a stable beam 42 and a molten metal pool 45. In addition, the body of the water eliminating device 16 is provided with minute and numerous holes for diffusing extra shield gas. With this torch 10 moved in the direction of the arrow 47, the surface 41 of the base material is continuously melted and cooled. Incidentally, as necessary, a welding material may be added to the molten pool 45.