ROOT PASS WELDING

摘要

The present invention relates to a root welding method comprising: (a) a step of bonding a backing material with a toughness decrease suppressing layer formed to suppress a toughness decrease of a root welding unit in between parent metals placed at a certain distance; and (b) a step of forming a root welding unit on top of the backing material. Since nickel is contained in the toughness decrease suppressing material, the toughness of the root welding unit can be increased. The growth of crystal grain of the root welding unit can be suppressed by niobium, titanium, and vanadium, which suppress the crystal grain of the root welding unit. Since nickel, niobium, titanium, and vanadium are precipitated on a molten pool, the growth of the austenite crystal grain can be suppressed since they work as an austenite stabilizer during cooling.