Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1989-04-25
1990-07-31
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75544, C21C 532, C21C 534
Patent
active
049447998
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of directly producing stainless molten steel from Cr ores or Cr ore pellets via a one smelting container consecutively.
BACKGROUND OF THE INVENTION
High Cr steel like stainless steel has been conventionally produced using ferrochromium as raw materials. In view of saving energy and securing low production cost, a so-called smelting reduction process is recently considered potentially attractive, which obtains high Cr molten metal directly using Cr raw ores (explanation will refer to "Cr ore" as example hereinafter). In the smelting reduction method, Cr ores, carbonaceous materials and others are supplied into a reduction furnace for directly obtaining high Cr molten metal.
For the smelting reduction method, there have been several proposals hitherto. One of them blows respectively O.sub.2 from bottom tuyeres and N.sub.2 from side blowing tuyeres at the same time as blowing O.sub.2 from a top lance. Another of them blows respectively O.sub.2 from the bottom tuyeres and O.sub.2 and N.sub.2 from the side tuyeres at the same time as blowing O.sub.2 from the top lance. The latter is disclosed in, for example, Japanese Patent Application Laid-Open 61-279,608 (1986).
However, each of the above mentioned methods has big problems that the Cr reduction speed is low and treatments take much time. With respect to the backgrounds of the prior art, following drawbacks will be taken up. materials after Cr ore had been molten in the slag, and the melting of Cr ore was assumed to determine Cr reduction. Therefore, important technical interests for shortening the treating time were focused to specifying of the slag composition. But Cr ore was inherently less to be molten, and it was limited to speed up the reduction by accelerating the melting of Cr ore. reduction speed, it was considered to make a post combustion of CO gas in the furnace and utilize the heat thereby. An existing method has been adopted, which blew O.sub.2 for the post combustion from the furnace upper part. If the post combustion ratio was increased, the temperature of an exhaust gas went up, but there has not been a technique which efficiently tansmitted a sensitive heat of the exhaust gas to the molten metal, and as a result, a heat transfer efficiency was lowered and the exhaust gas at high temperature was removed inevitably. The heated exhaust gas considerably damaged the wall refractories and those of an exhaust gas food. Therefore, in general it has been considered that the post combustion ratio could not be heightened so much.
For finally obtaining the stainless molten steel from the Cr raw ore efficiently and economically, it is of course desirable to continuously carry out a smelting reduction and a subsequent decarburizion blowing in the same furnace. However, the prior art has not made studies on a method that the decarburizing treatment was carried out after smelting reduction in the same furnace for reasons as follows. considerably loss of Cr by its oxidation (called as "Cr oxidation loss" hereinafter), and therefore although the smelting reduction was carried out in the converter, the decarburization had to depend on a vacuum system which was less in Cr oxidation loss such as RH-OB system. the existing smelting reduction method did not want the agitating gas so much. Therefore, if the container of the same converter type was used, it had been considered that a furnace for the smelting reduction had to have a structure different from that of the decarburizing container. decarburization in the same container, the slag generated by the smelting reduction had to be removed, but an ordinary electric furnace could not remove the slag. decarburization method. Accordingly, if the both treatments were performed in the same container the whole treating time was made very long and lowered the productivity, and the furnace refractory would be considerably injured, so that the operation was made difficult.
For dealing with the above stated problems of the prior art, the inventors made studies o
REFERENCES:
patent: 3854932 (1974-12-01), Bishop
patent: 4178173 (1979-11-01), Gorges
patent: 4783219 (1988-11-01), Mori
Inoue Shigeru
Iwasaki Katsuhiro
Kawakami Masahiro
Takahashi Kenji
Tanabe Haruyoshi
Kojima Moonray
NKK Corporation
Rosenberg Peter D.
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