| 摘要 |
PURPOSE:To obtain a welded H-beam having excellent strain age hardening property by hot rolling steel contg. specific contents of C, Si, Mn, N, then subjecting the same to a cooling treatment under specific conditions as a treatment for provision of strain age hardening property, then to skin pass rolling to apply cold strains and welding said steel. CONSTITUTION:Steel is composed, by wt%, of 0.02-0.25C, <1 Si, <2 Mn, 30- 200ppm N, and if necessary 1 or 2 kinds among <0.1 Nb, <0.12 V, <0.5 Cu, <1 Cr, <0.1 Ni, and the balance Fe and unavoidable impurities. This steel is hot rolled and is air cooled to temps. between 550-750 deg.C and immediately after this cooling or after the steel is held at these temps. of 2min, the steel is cooled quickly down to the coiling temp. lower than 500 deg.C at 20-80 deg.C/sec cooling rate. Or after hot rolling, the steel plate is cooled quickly to <=500 deg.C at 5-15 deg.C/sec cooling rate. This steel plate is subjected to skin pass rolling to apply 0.5-4% cold strain thereto and is welded to H-beam. |
