Patent ID: 6156263
Filing Date: 2000-12-05
Classification: C21C

Abstract:
An apparatus for refining molten steel for manufacturing ultra low carbon steel comprising: an RH vacuum-degassing device consisting of a vessel and a snorkel composed of an up-leg and a down-leg, andthe apparatus further comprising:a plurality of gas injection lance nozzles each consisting of an inner tube and an outer tube and installed above a molten steel level on a side wall of said vacuum vessel of said vacuum-degassing device at a height 1.9 to 3.0 times the radius of said vacuum vessel so as to inject gas toward the molten steel within said vacuum vessel;said inner tube including a neck portion forming a jet stream of a super-sonic velocity;said outer tube injecting a cooling gas for cooling said inner tube,wherein each of said lance nozzles has a leading end portion, and each of said lance nozzles is installed such that said leading end portion is disposed evenly with an inner wall of said vessel; andsaid neck portion has a straight cylindrical portion, and the inner circumferential surface of said inner tube is expanded with a constant angle .theta.3 of 3.degree. to 10.degree. toward said leading end portion from said neck portion and an angle .theta.1 between said gas injection lance nozzle and said side wall of said vessel is 20.degree. to 35.degree..