Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1996-07-15
1999-02-09
Ryan, Patrick
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75507, 75433, 75414, 75392, 148501, 148503, 148500, C21C 102
Patent
active
058688170
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to a refining process, using a converter having a bottom-blowing function, in steel production. The present invention relates, in more detail, to a converter refining process wherein molten iron is refined by desiliconization and dephosphorization in the same converter, intermediate slag discharge is conducted, and the molten iron is successively refined by decarbonization, and to the operation conditions of the dephosphorization refining.
PRIOR ART
Demand for quality of steel materials has become more strict as the utilization technologies become advanced and diversified, and the need for the production of a high purity steel has further increased. In order to meet such a requirement for the production of such a high purity steel, molten iron pretreatment installations or secondary refining installations have been enlarged and arranged in a steel production process. Since dephosphorization is particularly efficient in the molten iron stage where the temperature level is low, precedent dephosphorization is generally carried out in the molten iron pretreatment step. In precedent dephosphorization, there are refining vessel systems such as a torpedo car system, a ladle system and a two converter system where decarbonization is conducted in a separate furnace. Any of the systems can be carried out by charging flux such as CaO and iron oxide either through top addition or injection, and agitating through nitrogen bubbling or nitrogen bubbling and oxygen top blowing in combination. For example, Japanese Patent Publication Kokai No. 58-16007 discloses a Process for Dephosphorizing and Desulfurizing Molten Iron wherein a CaO flux is blown into a molten iron, together with a carrier gas, while oxygen is being top blown, the molten iron is subsequently dephosphorized so that the slag basicity and the iron oxide content subsequent to the treatment become at least 2.0 and up to 15%, respectively, top blowing oxygen is then stopped, and the molten iron is desulfurized by blowing a desulfurizing agent without forcibly removing the slag. Moreover, Japanese Patent Publication Kokai No. 62-109908 discloses a Process for Desiliconizing, Dephosphorizing and Desulfurizing Moten Iron wherein a dephosphorizing flux containing CaO as its main component is added to a molten iron surface from the initial stage of pretreating the molten iron, oxygen or an oxygen source in a solid state is added to the molten iron surface while iron oxide flux powder is being blown into the molten iron with a carrier gas, and the flux is changed to an alkali type flux after the desiliconization stage to conduct dephosphorization and desulfurization simultaneously. In addition to the Japanese Patent Publications mentioned above, Japanese Patent Publication Kokai No. 63-195209 discloses a Process for Producing Steel wherein two converters, a top-blowing converter and a bottom-blowing converter, are used, one is employed as a dephosphorizing furnace and the other is employed as a decarbonizing furnace, the converter slag produced in the decarbonizing furnace is recycled to the dephosphorizing furnace, and the dephosphorized molten iron obtained by dephosphorization is charged into the decarbonizing furnace.
As described above, in order to make the decarbonization step in a converter efficient and improve the productivity therein by carrying out the desiliconization step and the dephosphorization step as a primary refining process in the molten iron stage, steel companies have directed, their attention to separate refining and have conducted studies and realized installations of this type.
In view of only the capacity of the dephosphorization step according the process as mentioned above, a relatively low phosphorus content level can be achieved. However, the step has the following drawbacks: the treating time is long and the heat loss at the time of treating is large; it takes much time to supply the molten iron to a converter; and, even when two converters are utilized, a decrease in the molten iro
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10th Anniversary of 2D Committee by Japan BOT Group, LD Committee, 235, (1969).
Arai Masayuki
Hirata Hiroshi
Ikemizu by Keiko
Kawai by Noriko
Koizumi Fumio
Elve M. Alexandra
Nippon Steel Corporation
Ryan Patrick
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