| 摘要 |
<p>PURPOSE: To accelerate the flotation and removal of Al2 O3 type nonmetallic inclusions and to improve hydrogen induced cracking resistance by adding calcium to a molten steel having an oxygen content of a prescribed value or below under reduced pressure and controlling the form of the Al2 O3 type nonmetallic inclusions in the molten steel. CONSTITUTION: After the total oxygen content in the molten steel in the course of RH treatment reaches <=20ppm, calcium or/and calcium alloy are added. As to the preferred steelmaking process, desulfurizing treatment with CaO flux, RH treatment, and continuous casting are performed in the order named. Further, as to the addition of Ca to the molten steel in the course of RH treatment, Ca is added to the lower part of a ladle by the well known method, such as powder injection method and wire feeder method. Because the added Ca reacts, uniformly in a short time, with the Al2 O3 inclusions in the molten steel by the vigorous agitation in RH treatment and rapidly rises to the surface in the form of inclusions containing large amounts of 12CaO-7Al2 O3 , having the equilibriously lowest melting point and excellent in floatability, cleanliness can be improved.</p> |
