PURPOSE: To remarkably improve the toughness of a weld heat-affected zone (HAZ) at a lower temp. even in case of a high tension steel by restricting the compsn. of the high tension steel and cooling the HAZ in a prescribed temp. range in a specified time.
CONSTITUTION: The compsn. of a high tension steel is composed of, by weight, 0.03W0.20% C, 0.05W0.50% Si, 0.50W3.0% Mn, 0.50W10.0% Ni, ≤0.010% P, ≤0.010% S, 0.01W0.10% Al, ≤0.0060% N, 0.0003W0.0030% B, 0.01W1.50% each of one or more among Cu, Cr and Mo and the balance Fe with inevitable impurities. The steel is subjected to multilayer build-up welding and the HAZ of the steel is cooled so that it is cooled from 800°C to 500°C in a time τ (sec) satisfying the formula. Thus, toughness at about -40W-60°C or below can be ensured for the HAZ in spite of the high tension steel.
HAJI TOSHIAKI
YAMAMOTO KOICHI
AIHARA SHUJI
