Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1998-04-23
2000-07-25
Willis, Prince
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75387, 75375, C21C 104
Patent
active
06093235&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to a process for decarburizing a steel melt for the production of high-chromium steels by blowing in oxygen in which the decarburization rate is continuously measured and the amount of oxygen to be blown in is adjusted depending on the measured values. The decarburization rate is determined from the CO content and CO2 content in the exhaust gas and from the flow of exhaust gas.
2. Discussion of the Prior Art
DE 33 11 232 C2 discloses a process for decarburizing steel melts in which the process quantities by which the decarburization process is to be controlled are calculated on the basis of a theoretical model describing the course of decarburization in the steel melt. For this purpose, oxygen and a diluting gas are blown into the melt and the injected quantities are controlled corresponding to the course of decarburization by adjustable gas flow control means. The controlling of the injected quantities is carried out so that the extent of decarburization and the carbon content of the melt during the melting process is calculated with reference to the model and is compared with predetermined values. When the calculated value agrees with the predetermined value, the proportion of dilution gas and the gas quantity injected into the melt are changed in a predetermined manner. Accordingly, in this process, the characteristic quantities in the model, i.e., those inputted in the computing program, are compared with actual measured quantities and, by comparing the predetermined reference values and the calculated actual values, the control of the decarburization process is carried out so that the actual course of the process corresponds as far as possible to the course of the process simulated in the computer. The decarburization process can be controlled exactly by this computer-controlled decarburization process.
While this process is suitable for the decarburization of steel melts, this process based on the employed model is not suitable to determine exactly the time at which the point of transition from the decarburizing reaction to the metal oxidation is reached.
This results in increased chromium loss and accordingly additionally required quantities of reducing materials, for example, ferrosilicon and lime, as basic neutralization of the silicon content in the slag, and finally in a reduced life of the ladle or converter.
SUMMARY OF THE INVENTION
It is the object of the present invention to control, in an exact manner, the decarburization of a steel melt for the production of high-chromium steels by blowing oxygen into the melt such that, in particular, unwanted chromium oxidation is avoided and a strong decarburization of the melt and a minimum metal slagging are still achieved.
Pursuant to this object, and others which will become apparent hereafter, one aspect of the present invention resides in a process for decarburizing a steel melt for producing high-chromium steel. The process includes the steps of injecting oxygen into the melt, continuously measuring a rate of decarburization and continuously adjusting the amount of oxygen injected depending upon the measured values.
According to the invention, the following controlled variables are calculated by means of a computer on the basis of measured or predetermined values: the duration of the Al--Si oxidation phase at the start of the decarburization process, the duration of a principle decarburization phase immediately following the Al--Si oxidation phase until the transition point from the decarburization reaction to the metal oxidation is reached, and the decarburization rate in the principal decarburization phase, wherein the decarburization rate is determined in turn from the CO and CO2 content in the exhaust gas and the exhaust gas flow.
The process is conducted so that the injected oxygen quantity is increased at an accelerated rate immediately following the Al--Si oxidation phase to the oxygen quantity of the principal decarburization phase until the calculated dec
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patent: 3816720 (1974-06-01), Bauer et al.
patent: 4564390 (1986-01-01), Gupta et al.
patent: 5584909 (1996-12-01), Kim
Mannesmann AG
McGuthry-Banks Tima
Willis Prince
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