WELDING METHOD

PROBLEM TO BE SOLVED: To provide a welding technology capable of obtaining a sound fused junction part with deep penetration without blow hole or incomplete penetration. SOLUTION: The welding method includes a step (1) of forming an I-shaped joint part by butting end faces of two steel plates to each other, a step (2) of forming a sealed part 17a for sealing a gap formed on a surface side of the steel plates out of gaps G formed in the I-shaped joint part by melting the surface of the steel plates adjacent to the gap with arc, a step (3) of coating a penetration promoting agent 4a on the surface of the steel plates including the formed sealed part, a step (4) of melt-joining the I-shaped joint part from the surface side by melting and penetrating the surface of the steel plates with the promoting agent being coated thereon by arc, a step (5) of coating the penetration promoting agent on the butted part formed on the back side, and a step (6) of melt-joining the I-shaped joint part from the back side by melting the back side by arc until reaching the melt-joined part formed at least from the surface side. COPYRIGHT: (C)2009,JPO&INPIT