METHOD FOR CUTTING-OFF STEEL PLATE BY LASER BEAM

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PROBLEM TO BE SOLVED : To provide a method for cutting-off steel plates by a laser beam, wherein the method is suitable for cutting-off thick steel plates to be used in welded structures, such as ship-building, civil engineering, architecture, bridges, construction machines, tanks, and steel pipes. SOLUTION : A horizontally placed steel plate is cut-off by a laser beam with a sweepback angle of 5 to 30°, wherein the steel plate preferably contains the following chemical components : 0.01 to 0.20 mass% of C, 0.80 mass% or less of Si, 0.4 to 2.5 mass% of Mn, 0.03 mass% or less of P, 0.01 mass% or less of S, 0.15 mass% or less of Al, 0.01 mass% or less of N, 0.007 mass% or less of O, and if necessary, one or two elements of Ti, Cu, Ni, Cr, Mo, Nb, V, B, Ca, Mg, and rare earth metals (REM). Further, the steel plate preferably has a selective oxidation layer with a thickness of 0.5 μm or more from a scale interface to a base metal, and contains 0.35 to 0.80 mass% of Si. COPYRIGHT : (C)2006, JPO&NCIPI