HIGH-TENSION STEEL MATERIAL WITH EXCELLENT SUITABILITY FOR WELDING WITH HIGH-ENERGY-DENSITY HEAT SOURCE AND WELDED STRUCTURE THEREOF

摘要

A steel material which has excellent suitability for welding with a high-energy-density heat source; and a welded structure of the same. They are characterized in that the steel material and the part influenced by welding heat and optionally the welded metal part are extremely reduced in carbon content, i.e., have a carbon content of 0.0050 to 0.025 wt.%, preferably 0.0050 to 0.020 wt.%, excluding 0.020 wt.%, and contain 0.1 to 0.5 wt.% silicon, up to 2.5 wt.% manganese, up to 0.003 wt.% sulfur, up to 0.05 wt.% aluminum, 0.0003 to 0.0040 wt.%, preferably 0.0010 to 0.0025 wt.%, excluding 0.0010 wt.%, boron, and up to 0.0035 wt.% nitrogen, optionally further contain one or more of copper, nickel, chromium, molybdenum, niobium, vanadium, and titanium, and optionally further contain one or more of calcium and REMs, and that these have a structure comprising 90 wt.% or more ultralow-carbon-content bentonite and up to 5 wt.% carbide in terms of existence proportion.