| 摘要 |
PURPOSE:To produce the high tensile steel of over 50kg/mm<2> class of superior weldability by quenching the steel plate, which has been improved of its weldability through the reduction in the addition amount of strength-intensifying-alloy components and the reduction of carbon equivalent, right after rolling thereby compensating the decrease in strength owing to the decrease in the alloy components. CONSTITUTION:The steel which contains C; 0.03-0.09%, Si; 0.05-0.40%, Mn; 0.07-1.80%, Al<0.10% and further, if necessary, contains one or two or more kinds of Cu<0.50%, Ni<0.50%, Cr<0.30%, Mo<0.30%, V<0.10%, Ti<0.10% and whose carbon equivalent expressed by formula I is 0.32 or less. After this steel is hot rolled, it is immediately quenched from the temperature above 770 deg.C down to the temperature below 600 deg.C. At this time, the mean cooling rate between 770- 600 deg.C is made rapid cooling of more than (28Mn%-17) deg.C/sec. This yields the high tensile structural steel of not less than 50kg/mm<2> class of superior weldability. |
