EP0140001B1 - Process and device for the production of steel having an elevated degree of purity and a reduced gas content - Google Patents

Description

The invention relates to a process for the production of steels with a high degree of purity and low gas contents in steelworks and steel foundries, in which the steel is melted and deoxidized with the desired alloy components in a converter after it has been melted in its own unit, while at the same time flushing with inert gas is carried out and the melt is refined in the ladle by purging with inert gas.

Various processes are already known for producing steels with a high degree of purity and low gas contents.

The best known is the melting in the arc furnace or the melting in the arc furnace with subsequent freshening in a converter using mixed gases or under vacuum.

The production of the special steels only in the electric arc furnace is very expensive in terms of energy technology and problematic with regard to the degree of purity to be set.

The production of the steels mentioned in the arc furnace with subsequent freshening in previously known converters using mixed gases has the disadvantage that these converters, originally designed for the sole production of chromium steels, have a smaller specific reaction space than is required for the production of the steel qualities mentioned is. A high specific reaction volume with a high specific oxygen supply is a prerequisite for a high fresh and heating rate.

In addition, reoxidation of the melt by air entering the reaction space cannot be avoided during the deoxidation phase.

In addition, there is an intensive contact with atmospheric oxygen during the tapping of the reduced steel, which results in annoying oxidic impurities and thus leads to rejects in the product.

The production of the listed steels with subsequent freshening in a vacuum converter is more complicated and more complex in terms of apparatus and operator effort.

The above-mentioned methods continue to be difficult to drive and require a great deal of experience and the use of specialist personnel.

It is also known that in the manufacture of these steels a final treatment can be carried out in pans flushed with inert gas. However, here too, the exact setting of the desired values with regard to the alloy components, the temperature, the oxygen and hydrogen value and the degree of purity is not possible or is possible only with difficulty if the predetermined output values of the arc furnace or previously known converter cannot be set reproducibly.

With the three aforementioned methods, it is furthermore particularly disadvantageous that the desired metallurgical values cannot be set with sufficient accuracy, so that material errors are unavoidable which occur in the case of highly stressed system parts, e.g. in nuclear power plants, can no longer be tolerated.

It is accordingly an object of the invention to provide a method and a device for producing the abovementioned grades, which no longer adhere to the abovementioned disadvantages and which in particular make it possible to ensure a stable, reproducible quality of the steel, while at the same time increasing productivity, Reduction of reject risk and good controllability of the process.

The device for carrying out the method according to the invention should furthermore be of relatively simple construction and be able to be operated at low energy costs, it being possible to dispense with the use of vacuum and high operator expenditure.

The object is achieved according to the invention in the method mentioned at the outset in that the process gas supply during the converter treatment is regulated in the range from 0.5 to 2.0 Nm ³ / t / min, in that the carbon content of the steel is at least 0.5 during the fresh period % is reduced, that the process gas supply in the converter takes place through injection openings in the floor or near the floor, that a collecting slag containing deoxidizing substances is placed in the pan, that the outflowing steel is protected against reoxidation by an inert gas curtain and that during the purging phase an inert gas throughput of 0.01 to 0.05 Nm ³ / t is set in the pan.

In the fine rinsing phase, the formation of troublesome coarse inclusions is avoided.

In this connection, argon in particular can be used as the inert gas.

Furthermore, a temporary reduction in the size of the converter mouth can advantageously take place in the converter during the deoxidation phase.

Further advantageous refinements of the method according to the invention result from subclaims 3 to 5.

Features 2 to 4 of the characterizing part of the main claim are to be regarded as individual steps known per se in the production of steels with a high degree of purity. In summary, it can be said that the subject matter of the invention makes it possible to produce a particularly high-quality steel with little outlay on equipment and while avoiding the use of a vacuum while setting the steel to the desired metallurgical values, and in which a stable and reproducible quality Control is possible.

• - einfache Möglichkeit der genauen Einstellung der chemischen Analyse und Temperatur der Stähle
• - einfache Einstellung der Endschwefelwerte je nach Anforderung
• - bessere mechanische Werte in der Endproduktion
• - Verbesserung des Ausbringens
• - sichere Reproduzierbarkeit der Ergebnisse durch einfache Steuerbarkeit
• - energiesparende Nutzung der Rohstoffe
• - geringe Investitionskosten bei entsprechenden Qualitätszielsetzungen.

The invention is distinguished from previously known devices and methods

• - Easy possibility of precise adjustment of the chemical analysis and temperature of the steels
• - Easy adjustment of the final sulfur values depending on the requirement
• - better mechanical values in final production
• - Improve spreading
• - Reliable reproducibility of the results through simple controllability
• - energy-saving use of raw materials
• - low investment costs with appropriate quality objectives.

• Figur 1 die einzelnen Phasen I-V der Stahlerzeugung gemäß der Erfindung und
• Figur 2 die Temperaturführung während der einzelnen Phasen gemäß Figur 1.

An exemplary embodiment of the invention is described in more detail below with reference to drawings. Show it:

• Figure 1 shows the individual phases IV of steel production according to the invention and
• 2 shows the temperature control during the individual phases according to FIG. 1.

According to FIG. 1, the steel is melted in phase I, this being possible either in a cupola furnace, an induction furnace or an arc furnace or in a crucible heated by a lance.

In phase 11, the steel is tapped and provided with the desired alloy additives as well as additives that enable the necessary temperature increase in the fresh process according to phases 11 and 111.

In phases 11 and 111, the converter treatment with oxygen, nitrogen, air or argon or mixtures of these gases is carried out after the additives and additives have been introduced.

After the melt has been tipped into a pan in accordance with phase IV, a fine rinsing is carried out there and then in phase V either block, mold or continuous casting etc. can take place.

The above-mentioned processes are already known as individual steps in steel production.

Specifically, after the tapping from a smelting unit in accordance with phase I, alloy and additive elements are added and then the two-phase treatment mentioned is carried out in a converter. Rapid and intensive freshening takes place with a considerable increase in temperature from about 1500 to above 1700 ° C. by blowing in the known inert gas / air / oxygen mixture. This freshness can be supported with a lance. There is then a rapid deoxidation phase with a relatively low temperature reduction, in which the desired setting of the final analysis is largely carried out and in which the oxides generated during the freshening are largely reduced. After the rapid deoxidation phase with high gas throughputs, tapping takes place.

A fine rinsing phase with significantly lower gas throughputs, for example 0.01 to 0.05 Nm ³ / t, then takes place in the pan.

In this context, it is necessary that the mixing and control elements for the introduction of the required gases into a converter have an appropriate design and that the injection openings in the bottom or near the bottom of the converter are designed in such a way that they are also in phases with low gas throughput stay free of penetrating steel.

During the deoxidation phase, it is advantageous to reduce the converter opening. The device for reducing the converter opening can be designed such that it can remain on the converter when the melt is tapped.

In the further course of the process, the melt is emptied via the converter edge, the slag being tipped into the pan and forming part of the collecting slag there. During the tipping, the inert gas atmosphere is maintained in the converter and the outflowing steel is protected by means of a deoxidizing agent and using an inert gas shield to avoid reoxidation with atmospheric oxygen.

With this ladle aftertreatment, the desired metallurgical values with regard to chemical analysis, temperature and the degree of purity can be set precisely, the melt becoming such that later coarse inclusions can be avoided. Steels with better mechanical properties are created.

In phase V, the steel is then poured under pouring beam protection.

When carrying out the process, it should be noted that all the alloys used are dry and that all additions are added to the melt early enough that they are also thoroughly rinsed out.

All slag formers should be filled into the converter in advance and the batch should be decanted without slag. At least 0.5 percent carbon is freshened out in the converter.

The process gas supply must be controllable in the range from 0.5 to 2.0 Nm ³ / t / min with a suitable extraction of the flue gas quantities.

During the treatment time in the converter, a rinsing with at least 4 to 6 Nm ³ ar / t should be carried out, and the time until tapping after completion of the melt may not exceed 5 to 10 minutes.

It is also advantageous to adjust the tapping pan to be basic or neutral. It should be preheated well and equipped with one or more floor sinks.

The particular advantages of the method and the device according to the invention include in the fact that it can not only be used for the production of better steel in industrialized countries, but that, due to its simplicity and stable process management, it can also be used successfully in non-highly industrialized countries.

Claims (5)

1. Process for producing steels with a high percentage purity and low gas content in steelworks and steel foundries, in which the steel, after melting down with the required alloying constituents in an aggregate, is refined and deoxidized in a converter, with simultaneous flushing with inert gas and the melt being refined through flushing with inert gas after running off in the pan, characterised in that a converter with a specific reaction space of between 0.45 and 0.8 m³/t yield is used, in that the introduction of processing gas during converter processing is regulated at between 0.5 and 2.0 Nm³/t, in that the carbon content of the steel is reduced by at least 0.5% during the refining period, in that the introduction of processing gas into the converter is implemented by means of inlet openings in the base or near the base, in that collecting slag containing deoxidizing substances is added to the steel in the pan, in that the steel flowing out is protected against reoxidization by a shroud of inert gas and in that during the fine flushing stage in the pan there is an inert gas throughput of 0.01 to 0.05 Nm³/t.

2. Process according to claim 1 characterised in that during deoxidization the mouth of the converter is reduced at times.

3. Process according to claim 1 or 2 characterised in that the converter is emptied over its edge while the slag is tipped into the pan.

4. Process according to claims 1 to 3 characterised in that during running off of the converter the inert gas atmosphere remains in the converter.

5. Process according to one of claims 1 to 4 characterised in that the quantity of processing gas flowing through during the refining and deoxidization stages is a multiple, of at least 10 to 20, of the quantities of inert gas flowing through the pan in the fine flushing stage.

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