| 摘要 |
PURPOSE: To produce at a high speed a low alloy welded steel tube having an excellent toughness of a joined part by welding a steel plate which contains prescribed chemical components as a stock at a prescribed speed or above, with a laser beam of a specified output or above. CONSTITUTION: This steel plate is composed of, by wt.%, 0.02-0.30 C, <=0.80 Si, 0.10-2.0 Mn, 0.002-0.08 Al, <=0.04 Ti, <=0.0060 O, <=1.0 Cu, <=3.0 Ni, <=1.0 Cr, <=1.5 Mo, <=0.1 V, <=0.1 Nb, <=0.003 B, <=0.0050 Ca, <=0.02 Y, <=0.02 rare earth element, the content of Al, Ti and O satisfying the formula of Ti(%)/Al(%)×O(%)<5.0×10<3> and the balance iron with inevitable impurity. The steel plate is formed into an open tube while feeding to a forming roll group, irradiated with the laser beam of output 8KW or above and welded at the speed of 6.0m/min or above while its edge part is shielded with an inert gas pressurized by a squeeze roll. |
