Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Patent
1989-04-13
1990-10-09
Lechert, Jr., Stephen J.
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
75708, C22B 3400
Patent
active
049617842
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of smelting reduction of Cr raw materials such as Cr ores or Cr ore pellets.
BACKGROUND OF THE INVENTION
High Cr steel like stainless steel has been conventionally produced using ferrochromium as raw material. In view of saving energy and securing low production cost, smelting reduction process has been recently considered as being potentially attractive. This process produces high Cr molten metal directly using Cr raw ores (explanation will refer to "Cr ore" as an 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, proposal 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 proposal blows respectively O.sub.2 from the bottom tuyeres and O.sub.2 and N.sub.2 from the side blowing 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 No. 61-279,608 (1986).
However, each of the above mentioned methods has many problems in that the Cr reduction speed is low and treatments take considerable time. With respect to the background of the prior art, the following drawbacks are known.
1. The workers in the art believed that reduction of Cr ore progresses by action of C in carbonaceous materials after Cr ore had been molten in the slag, and the melting of Cr ore is assumed to determine Cr reduction. Therefore, important technical interests for shortening the treating time were focused on specifying of the slag composition. But Cr ore is inherently less to be molten, and it is limited to speed up the reduction by accelerating the melting of Cr ore.
2. For accelerating the melting speed of Cr ore in the slag and the reduction speed, it has been 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 a furnace upper part. If the post combustion ratio was increased, the temperature of an exhaust gas went up, but there was no technique which efficiently transmitted a sensitive heat of the exhaust gas to the molten metal, and as a result, 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 feed. Therefore, in general it has been considered that the post secondary combustion ratio could not be heightened very much.
For dealing with the above stated problems of the prior art, the inventors made studies on the mechanisms of the smelting reduction and the decarburization, and the actual measures therefor, and subsequently they found following facts.
(1) As having been said above, it was assumed that Cr ore was reduced by the carbonaceous materials staying in the slag after Cr ore was molten in the slag, but it has been found that almost all of the actual reductions were made by actions of C in the molten metal beneath the slag as the reducing material. Therefore, the reduction speed was determined by contacting of the molten metal to Cr ore heated at the high temperature not by melting of Cr ore into the slag, so that the reduction speed could be effectively heightened by positively contacting of the molten metal to the ores.
(2) It was a basic concept in the prior art that the post combustion which is combustion of CO.sub.2 generated by reduction of carbon in the ore increased in view of the technical limit with respect to increasing of the heat transfer efficiency and consumption of the refractories. If O.sub.2 was blown so that the post combustion was mainly caused in the slag to forcibly agitate the slag, the heat transfer efficiency could be heightened-effectively. Thus, by the high post combustion and the high heat tr
REFERENCES:
patent: 4130417 (1978-12-01), Breuer et al.
patent: 4783219 (1988-11-01), Mori et al.
Inoue Shigeru
Iwasaki Katsuhiro
Kawakami Masahiro
Takahashi Kenji
Tanabe Haruyoshi
Kojima Moonray
Lechert Jr. Stephen J.
Nigohosian, Jr. Leon
NKK Corporation
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