LU86225A1 - METHOD FOR PRODUCING HIGH QUALITY STEEL - Google Patents

Description

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Process for the production of high quality steel • | : The invention relates to a method for producing high quality; Steel, as part of an oxygen inflation process.

"5 ä In the present optics, high-quality is a steel that i has the lowest possible levels of phosphorus, sulfur and non-metallic inclusions.

i, 1 3 Λ; 10 One method of achieving the desired carbon content in a melt is to stop decarburization in good time. The disadvantage of this method is that it does not allow steels with a high carbon content and at the same time a low one

Gain phosphorus content.

ξ \ 15 a j If you still aim for low phosphorus levels, then you need to | processing of pig iron (dephosphorization, desulfurization, desilicon) is unavoidable. Such pretreatments, which are primarily explained by Japanese steel manufacturers in numerous publications j 20, take place outside the converter, in stationary or

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; in mobile pans and require a lot of equipment. In addition, the necessary temperature losses j must be accepted or compensated for by heating units.

t! 25 It should be noted that only in steels in which the i; Desired carbon content achieved by stopping decarburization î; low levels of bullets.

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Another method, which is cheaper to achieve low phosphorus levels in the steel, is to e.g. Blown 0.05% C With this method; However, after decarburization, the steel contains a relatively large amount of 5 oxygen, depending on the conditions, about 500 to over 1000 ppm, the removal of which using conventional means not only requires large amounts of expensive substances, but also leads to the formation of inclusions.

10 The applicant has set itself the task of developing a process that allows the production of high quality steel, the? ; ’Content of non-metallic inclusions is reduced to a minimum.

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; 15 This object is achieved by the method according to the invention; which is characterized by the combination of several steps which; be described as follows.

; The first step is decarburization in the converter, by inflating 20 oxygen, with the addition of the additives required for slagging silicon and phosphorus. Decarburization produces hardness and the slag becomes reactive due to the absorption of oxygen, with a certain amount of phosphorus being absorbed into the slag. The decoction

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; is carried out up to a carbon content below 0.10 Z C, preferably below 0.05% C, regardless of which carbon content is targeted in the finished steel.

j j The second step is a treatment of the essentially decarburized and oxygen-rich bath, in the converter, with coal; 30 fabric.

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This step is carried out by introducing shredded coal, preferably anthracite, into the melt at the greatest possible speed. This leads to an extraordinarily violent reaction in which the metal bath simultaneously deoxidizes; and is carburized. It should be emphasized that, in contrast to the | conventional deoxidation in the pan by means of a combination of i - 3 - i: »'tion of coal, ferromanganese, ferrosilicon, aluminum, etc. the deoxidation product here is exclusively gaseous and therefore cannot lead to inclusions. The large amounts of carbon monoxide formed in this way cause the metal phase to swirl vigorously with the slag phase.

; According to the invention, everything is done to take advantage of the reactivity of the slag. For this reason, the reaction is carried out as described so that the bath movement and the mixing of bath and slag are as intensive as possible. An advantageous one

The procedure provides for the carbon to be inflated through a special lance, the carbon particles which are suspended in an inert carrier gas being heated to high speeds i; be accelerated. It has also proven to be beneficial; 15 Mix the bath and the slags even more intensively during the blowing in of carbon by flushing them with inert gas through the floor.

If the oxygen content is approximately 250-400 ppm 0, the second process step is terminated. At this point the coal is! 'Melt content of the melt still very low, about 0.04-0.07% C. The

Applicant has found that in the course of the second step, the carbon added primarily melts the melt primarily deoxy; before carburization occurs. Indeed, through that); 25 blowing in carbon on the one hand and flushing the floor on the other hand reduced the »product CxO to the thermodynamic equilibrium value which corresponds to the respective temperature and gas pressure conditions in the metal bath i. E.g .: Before blowing:% C = 0.032, ppm 0 = 900; After blowing:% C »0.057, ppm 0 = 350.

1 30; At the same time, it is found that the reaction has led to a surprisingly extensive dephosphorization of the bath.

If particularly low phosphorus end values are sought, e.g. 35 0.008% P or less, according to the invention one becomes a "Na20 carrier, i.e. suitable compounds which give off Na2Ü during thermal decomposition, e.g. by blowing it in together with the carbon!"

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The third process step consists in treating the largely deoxidized and partially carburized bath, taking into account the prevailing conditions with regard to bath temperature, oxygen content, carbon content, i.e. that the product C x 0 at • 5 the prevailing temperature is also a determining factor for the subsequent procedure.

• With regard to one of the essential aims of the invention, namely the suppression of the tendency to form inclusions, the method is oriented towards the fact that one gets into the pan; does not have to be provided with heating units, enters a melt that is as acidic as possible: its carbon content should be as close as possible to the intended final concentration. With a view to avoiding solid deoxidation products, the deoxidation should be carried out as far as possible using carbon, with only carbon monoxide and carbon dioxide being produced.

Accordingly, according to a first embodiment, the melt can be further treated in the converter with carbon, namely until: 20 the desired final concentration is reached. For example, is the latter

at around 0.10% C, the corresponding oxygen content is around 200 ppm 0. The rack is then tapped into the pan.

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A second embodiment provides for the further treatment of the carbon bath in the pan to be carried out in the

Converters limit the amount of carbon to be injected.

, The total amount of carbon is added in the form of a commercial carburizing agent during tapping into the pan and before the addition of alloying elements.

30 'Be it that the third step is carried out in the converter or in the pan, it is found that the normally expected rephosphorization is surprisingly omitted. In the applicant's view, this is due to the fact that during the second step, not only does the conversion of carbon with oxygen to carbon monoxide or carbon dioxide and the absorption of carbon in iron take place, but that the slag with the

Carbon enters into a kind of interaction, which at the beginning of the treatment enables the strong reactivity towards phosphorus and partly also sulfur to be exploited, which goes through a maximum * and at the end of the treatment changes into a wide passivity.

5 In any case, the slag then behaves passively and, despite treating the steel with reducing agents, does not indicate any phosphorus: the bath.

This passivity also allows the CxO balance in the converter; 10 by adding e.g. Ferromanganese, by blowing into it

Steel bath, i.e. while maintaining the same carbon content, * further reduce the bath's oxygen content; without rephosphorization. Although solid deoxidation products are formed here, due to the still high steel temperature and the much larger bath diameter: bath height ratio compared to a ladle, these deoxidation products do not lead to inclusions in the finished steel, but are completely eliminated from the melt and into the slag added.

: 20 Finally, as a fourth process step, the melt in the pan is treated with a deoxidizing and desulfurizing agent, preferably metallic calcium and synthetic slags. As a result, the oxygen supply of the melt, which is increased due to the inevitable drop in temperature, is intercepted again and predominantly large, globular reaction pro- products in the implementation of oxygen. Large globular bodies' show a greater degree of willingness to ascend and separate from the metal phase than is the case with small or - non-globular structures.

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The method according to the invention is aimed at the production of both semi-calmed and fully calmed steels.

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Claims (4)

1. A method of manufacturing high quality steel as part of a - * oxygen inflation process, characterized by the following 5 steps: (1) decarburization in the converter, by blowing oxygen to below 0.1% C; (2) a treatment of the melt, in the converter, with carbon, 10 whereby crushed coal is introduced into the bath with the greatest possible speed, so that the melt and slag start to boil until the oxygen content of the melt is about 250-400 ppm 0 or less and the carbon content is about 0.04-0.07% C or more; 15 (3) a targeted carburization of the melt, which is carried out depending on the position of the temperature, the product% C x% 0 and the desired C content in the converter or in the pan, whereby one decides with regard to the goal, one if possible, transfer 20 oxygen-free melt and the targeted carbon content to the pan; (4) treatment of the melt in the pan with a deoxidizing and at the same time desulfurizing agent, preferably 25 metallic calcium, and a synthetic slag. 2. -Procedure according to claim 1, characterized in that the carbon supply is accomplished by suspending shredded coal, preferably anthracite, in a carrier gas, through a lance on the bath surface. 3. The method according to claims 1 and 2, characterized in that; that in the course of the second step the dephosphorization. Addition of a Na2Ü carrier supports. 35 f:. - 2 - t 4. Process according to claims 1 to 3, characterized in that the deoxidation is supported in the course of the third step by adding ferromanganese. . 55. The method according to claims 1-4, characterized in that an inert gas stream is passed through the bottom into the bath in the course of the second and third steps in the converter. ? \ «