| 摘要 |
PURPOSE:To obtain a steel having uniformly and highly improved strength and toughness by subjecting a billet, which is incorporated with elements for forming nitride and carbonitride and is formed by continuous casting or ingot making and blooming, to a pretreatment for intermediate hot rolling at a solubilizing temp. then hot rolling the billet. CONSTITUTION:A billet is produced by a continuous casting or ingot making and blooming method from a molten steel which is adjusted to the component compsn. of a high tension steel for a steel plate, etc. and is incorporated with >=1 kind among elements for forming nitride and carbonitride, such as Nb, V or the like, in a melting furnace. Such billet is heated to the temp. at which the nitride and carbonitride are solubilized or above and thereafter the billet is subjected to hot rolling to an intermediate thickness followed by quick cooling. Then the nitride and carbonitride solubilized in the billet are converted to fine precipitate. Such steel material is heated to the austenitizing temp. below the solubilizing temp. for the nitride and carbonitride and is subjected to the hot rolling wherein the rolling ends at the temp. for initiating ferrite transformation or above. The steel material obtd. after the end of rolling is cooled by forced cooling in the temp. region of a part or the whole down to an ordinary temp. before said material starts ferrite transformation. |
