| 摘要 |
PURPOSE:To produce clean steel of less nonmetallic inclusions and content of oxygen by deoxidizing molten steel with Al after oxidation decarburization and refining and further reducing the content of oxygen therein with treatment such as vacuum degassing, bubbling then further deoxidizing the same with Ca. CONSTITUTION:After molten steel is oxidation decarburized and refined, Al which is a deoxidizing agent is added thereto to remove the oxygen contained therein as Al2O3. Since this molten steel contains Al2O3 as the product of deoxidation in the form of nonmetallic inclusions and contains residual dissolved oxygen, the floating of the nonmetallic inclusions such as Al2O3 is accelerated by DH vacuum degassing treatment or bubbling treatment by an inert gas, whereby said inclusions are separated and the dissolved oxygen in the molten steel is reduced so that the T[O]in the molten steel is reduced to <=50ppm. Next, a Ca-contg. deoxidizing agent such as Ca-Si is added to the molten steel at <=0.5kg ratio in terms of Ca per ton of the molten steel to deoxidize the Ca as CaO and to convert the same to spheroidal nonmetallic inclusions of CaO- Al2O3, whereby the degradation in the material of the steel pipe in rolling or the like is prevented. |
