DD214389A1 - METHOD FOR THE TREATMENT OF LIQUID STEEL WITH GASOFMAL MEDIA - Google Patents

Abstract

The invention pursues the goal of achieving a higher alloying output, a better alloy distribution, a better pouring behavior, better and uniform material properties as well as a higher block steel output in a spooling gas treatment of the liquid steel in the ladle following the blowing process in the converter. The essence of the invention is to subject liquid steel melts outside the smelting unit to a sputtering treatment with a specially composed gaseous medium. The spülmedium consists of a nitrogen-oxygen mixture with concentration proportions of 79-96% nitrogen and 21-4% oxygen, preferably with concentrations of 88-96% nitrogen to 12-4% oxygen. The sputtering is carried out at a Spuelgasdruck of 150-500kPa, preferably at a Spuelgasdruck of 200-300kPa. During the spooling process, the sputtering gas pressure is varied so as to set a higher spooling gas pressure (250-300kPa) at the beginning of spooling and a lower spooling gas pressure (150-200kPa) in the last third of the spouting time. Residual gas accumulating in the oxygen production, which corresponds to the abovementioned composition, can be used as a flushing medium.

Description

(Title of the invention

Process for treating liquid steel with gaseous media

Anwe area of the invention

The invention relates to a process for the treatment of liquid steel, in particular of liquid steel from bottom-blowing oxygen converters, with gaseous media outside the converter or melting unit for the purpose of

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j improvement of Legierungsausbringens and the steel quality * char act eristic of the known technical solutions

For the purge gas treatment of liquid steel outside the smelting unit, for example in ladles, several publications are available. A detailed description The process and plant technology developed for this purpose is described in the report of the Standing Commission of the CMEA for Black Metallurgy entitled "Process for improving the steel quality and increasing the output outside the furnace "of January 1978. This report confirms that quality improvements and economic benefits can be achieved by purifying the liquid steel in the ladle. "These can be summarized as follows:

- Acceleration of the deoxidation kinetics as a result of better mixing of the steel

- Better separation of non-metallic inclusions

- Homogenization of the liquid molten steel.

All of the solutions outlined in the above report involve the use of inert gases to achieve the flushing effects. The most suitable flushing media in the RGW report are argon and nitrogen »

Also in DE-OS 2 253 630, a neutral or inert gas is cited as purge gas, which has the task to allow a more uniform distribution of pan additives as purge gas ·

In DE-OS 2,419,070 a process for the production of steel with improved Zähigkeiteeigenschaften is described. This method involves the injection of calcium silicon with a carrier gas not described in detail. This requires expensive injection devices. The achievable effects are impaired by high material costs for the fine-grained calcium silicon to be injected.

Another laid-open specification DE-OS 1 924 403 relates to the injection of purge gas in the form of Ar ₂ , N ₂ , Clo, CGI. or CF * under consideration of certain geometric conditions »

Finally, publications in the journal "Neue Hütte", 22 (1977) 4, page 217-222, relate to the inert gas purging of 200 t and 80 t melts from the SM furnace. Achievable benefits include better castability, homogenization, and alloy savings. Also in these publications are called usable purge gases argon and nitrogen ».

All of the mentioned methods have the disadvantage that expensive inert gases, such as argon and nitrogen, are blown in as flushing media and additional facilities for transport and storage are required. «

Further disadvantages are that the tapping slag has to be removed and special refractory material is necessary for the ladle delivery. This results in considerable additional costs.

Object of the invention

The invention has the aim of achieving a higher manganese yielding, a better alloy distribution, a better sprue behavior, better and more uniform material properties as well as a higher block steel yield at a purge gas treatment of the plunger steel in the ladle following the blowing process in the converter.

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The invention has the object of providing liquid steel melts outside of the melting unit, for example, in ladles, a rinsing treatment with a specially composed reaction inert gaseous medium to undergo. According to the invention the object is achieved in that for the rinsing treatment as a purge nitrogen, oxygen mixture with relatively low It has been found that, in contrast to known solutions, which require the use of technically pure inert gases as flushing media, also oxygen-containing purge gas mixtures can be used if certain technological conditions are met "Thus, according to the invention, a gaseous nitrogen oxygen mixture with concentration fractions of 79 96 % nitrogen and 21 - 4 % oxygen used as a purge gas, preferably concentrations of 88 '96 % nitrogen and 12 - 4 % oxygen are maintained «The Spülbehandl The reaction takes place at a purge gas pressure of 150 500 kPa, preferably at a purge gas pressure of 200 300 kPa and with a purge gas of 10 - 60 l / t of liquid steel, wherein the purge gas pressure is varied during purging. The variation of the purging gas pressure takes place in such a way that at the beginning of purging a higher pressure, for example 250-300 kPa, is set and the rinsing process is completed at a low pressure of 150-200 kPa.

The solution according to the invention includes nitrogen-oxygen mixtures obtained in oxygen production plants with the defined concentrations of nitrogen and oxygen which are known under the technical name "residual gas" while adhering to the aforementioned rinsing parameters without detrimental effect on the quality of the steel for rinsing liquid Steel are applied.

Embodiment .

In a bottom-blowing oxygen converter, a steel grade of steel grade 9 S Mti 28 was produced with the following directional analysis:

* 0,14 % G. «0,05 % Si 0,90 - 1,30 % Mh = 0,100 % Έ 0,240 - 0,320 % S

The mission consisted of 22 tons of liquid Thomas pig iron and 5 tons of scrap metal. At the end of the blowing process, a temperature measurement was performed, which corresponded to the technological requirements with 1943 K. Afterwards, a steel pre-sample was taken and analyzed. The pre-sample analysis yielded 0, 5 % Mn, 0.052 % P and 0.030 % S. Thereafter, the liquid slag was dumped over the converter mouth. The residual slag remaining in the converter was then licked with lime to co-run to avoid the slag when cutting off the steel. After provision of the pouring trolley was tapped. During the tapping, the addition of 360 kg of ferro-manganese carbure and 86 kg of sulfur was carried out at about 1/4 Pfannenfüllgrad, In contrast to unsweetened batches was no Ferro-manganese Zusatζ in the converter. All ferro-manganese was added to the pan.

After completion of the tapping, the transport of the Plüssigstahls was carried out by pouring trolley to the rinse. The transport time was 30 seconds. Before the beginning of rinsing, the steel temperature was measured by means of an immersion lance. This measurement yielded 1823 K. Subsequently, the purge gas treatment was carried out with a nitrogen-oxygen mixture (94 % N ₂ , 6 % O ₂ ).

The flushing time was 2.5 minutes at a purge gas pressure of 300 kPa in the first two-thirds and 200 kPa in the last third of the purge period. The purging gas was approximately _e 625 1 «Pur injecting the purge gas a fireproof sheathed lance was used · A slag exchange did not take place" After the rinse temperature measurement was performed again · This measurement gave 1,803 K * Then the batch was determined by casting carriage in the The casting hall was lowered and poured down into molds of the N 390 format · The analysis of the final sample showed the following composition:

0.13 % C 0.01 % Si 1.02 % Mn

0.056 % P 0.285 % 5

By omitting the otherwise required partial alloy in the converter, the necessary to achieve the required directional analysis ferro-manganese additive reduced under comparable conditions by 80 kg / batch · The batch weight was 25 t of liquid steel · The batch was purged trouble-free, the ladle showed after completion of the casting no approaches »

Claims (4)

invention claim 1. A process for the treatment of liquid steel with gaseous media, in particular of liquid steel from bottom-blowing oxygen converters, characterized in that low-oxygen nitrogen-oxygen mixtures are used for purging of liquid steel in ladles at varying purge gas pressure. 2. The method according to item 1, characterized in that oxygen-poor nitrogen-oxygen Geraische with a concentration of 79 - 96 % nitrogen and 21 - 4 % oxygen, preferably with a concentration of 88 - 96 % nitrogen and 12 - 4 % oxygen at a purge gas pressure of 150-500 kPa, preferably at 200-300 kPa and a purge gas amount of 10 - 60 l / t liquid steel are used as purge gases 3 ♦; Process according to points 1 and 2, characterized in that the purge operation is started with a higher purge gas pressure of 250-300 MPa and completed with a lower purge gas pressure of 150-200 MPa and the lower pressure is maintained for at least 1 minute at the end of the purge process, 4 · Method according to points 1 to 3, characterized in that in the oxygen production accumulating residual; gas, preferably with a concentration of 88-96 % nitrogen and 12-4 % oxygen is used as purge gas ·