| 摘要 |
PURPOSE:To obtain titled steel without any surface defect in the stage of an ingot and without clogging in a nozzle in the stage up to said stage by limiting the time for adding Al, rare earth elements, B and Ti in the stage of stirring and deoxidizing molten steel for production of steel contg. B, Ti for welding with a large heat input. CONSTITUTION:The uniform mixing time tauo of the system in the stage of stirring and deoxidizing of the molten steel melted for the purpose of producing steel contg. B and Ti for welding with a large heat input is determined as a standard. Al is added dividedly at every (0.5-2.0)tauo until the point of the time of (0.8- 3.0)tauo before the intended time for ending said stage, so that the molten steel is made into the aluminum killed state. Rare earth elements are added at the point of the time of (0.8-3.0)tauo before the above-described intended time to disperse the ultrafine particles of Al oxide, REM oxide and REM oxisulfide in the steel. Thereafter, B and Ti are added thereto and the steel material is obtained in the stage conforming to a conventional method. |
