Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1991-03-06
1992-10-20
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C21C 702
Patent
active
051566710
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for the dephosphorization of chromium-containing molten pig (high carbon) iron with a reduced oxidation loss of chromium.
Recently a good deal of attention has been paid to processes for preparing chromium-containing molten pig iron or molten ferrochromium, as starting molten hot metal in the preparation of stainless steel, wherein an electric furnace is not used in order to save power. For example, there has been proposed a process wherein scrap is molten by combustion heat of a carbonaceous material such as cokes and at the same time a chromium ore is melt reduced by the carbonaceous material. In this case, since the oxygen potential in the materials is very low during the melt reduction, almost 100% of phosphorus contained in the materials transfers to the molten hot metal. Accordingly, in order to commercially carry out the processes for preparing starting molten hot metal in the preparation of stainless steel, wherein a carbonaceous material is used, it is essential to develop and establish a technology for the dephosphorization of molten pig iron containing chromium in high concentrations.
However, the dephosphorization of chromium-containing molten pig iron is very difficult, since chromium lowers the activity of phosphorus. In fact, if chromium-containing molten pig iron is processed by a known oxidation dephosphorization method which is effective for the dephosphorization of ordinary molten pig iron substantially free from chromium, the chromium contained is preferentially oxidized, posing such problems that the slag formed is solidified to retard the dephosphorization reaction and that the basicity of the slag is lowered to adversely affect the dephosphorization. In other words, while oxidation dephosphorization methods using materials of CaO-FeO series or CaO-CaF.sub.2 series are well known for the dephosphorization of ordinary molten pig iron, when such oxidation dephosphorization methods are as such applied to the processing of chromium-containing molten pig iron, the oxidation of chromium preferentially proceeds and the desired dephosphorization of phosphorus does not substantially proceed.
For the dephosphorization of chromium-containing molten pig iron, there have been known methods wherein the chromium-containing molten pig iron is brought in contact with CaC.sub.2, Ca-CaF.sub.2 or CaC.sub.2 -CaF.sub.2 under a non-oxidizing atmosphere. These methods, however, require the non-oxidizing atmosphere and pose problems in treating the formed slag.
To solve the problems, JP B 61-149,422 proposes a method wherein a flux of NaF-CaO series containing from 30 to 70% by weight of NaF is blown into chromium-containing molten pig iron by means of a non-oxidizing gas. This method, however, consumes a quantity of the expensive NaF-containing flux.
JP B 57-32,688 teaches that when an alkali metal carbonate such as LiCO.sub.3 is caused to contact with chromium-containing molten pig iron which contains more than a certain amount, the dephosphorization of the chromium-containing molten pig iron proceeds. This method again requires an expensive dephosphorizing agent.
JP B 61-403 discloses a method for the dephosphorization of chromium-containing molten pig iron wherein a flux of BaO-BaCl.sub.2 series is used. The BaO used therein is again an expensive alkaline substance. Furthermore, it is recommended to use chromium oxide as the oxygen source for the dephosphorization, for the reason that use of iron oxide or gaseous oxygen for that purpose will oxidize chromium.
JP B 63-481 teaches that when a slag comprising from 10 to 40% by weight of CaO, from 5 to 40% by weight of FeO, from 40 to 80% by weight of CaF.sub.2 and not more than 10% by weight of SiO.sub.2 is contacted and stirred with chromium-containing molten pig iron having an Si content of not higher than 0.2% and a C content of at least 4%, the dephosphorization of the chromium-containing molten pig iron proceeds.
As discussed above, there have been proposed various methods for dephosphorizing chr
REFERENCES:
patent: 4356032 (1982-10-01), Morishita
Fukui Katsunori
Mukai Masato
Nakajima Yoshio
Nisshin Steel Co. Ltd.
Rosenberg Peter D.
LandOfFree
Method for dephosphorization of chromium-containing molten pig i does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for dephosphorization of chromium-containing molten pig i, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for dephosphorization of chromium-containing molten pig i will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-189518