Development of NK-HIWEL steels suitable for high-heat-input welding

This paper deals with the notch toughness of weld HAZs made by high-heat-input welding. New ideas to improve the HAZ toughness with a radical reduction of free-N in HAZ were applied to the C-Mn steel for LPG, the EH36 grade steel for large-scale arctic offshore structures, and the high-tensile-strength C-Mn steel used in low-temperature regions. The HAZ toughness of these steels was investigated. As a result, it was demonstrated that these NK-HIWEL series steels of the high-Al, low-N, micro-Ti type produce welds of excellent toughness, even under high-heat-input welding conditions.