ES2273014T3 - PROCEDURE OF METALLURGICAL TREATMENTS ON A METALLIC BATH. - Google Patents

Abstract

Method of metallurgical treatment on a metal bath, comprising: a first treatment that involves the presence or formation of an acid slag on the surface of said metal bath; and a second treatment that involves the presence or formation of a basic slag on the surface of said metallic bath; characterized in that the two treatments are carried out without intermediate dechlorination simultaneously in two separate zones and ensuring on the surface of said metallic bath a physical separation between an acid slag zone and a basic slag zone.

Description

Metallurgical treatments procedure on a metallic bath

Technical field to which the invention relates

The present invention relates in a manner general to a metallurgical treatment procedure on a metallic bath More particularly, it refers to the procedure of this class that includes a first treatment that involves the presence or formation of an acid slag on the surface of a metallic bath and a second treatment that involves the presence or formation of a basic slag on the surface of this bathroom metal.

State of the art

Such a procedure is, for example, a procedure for treating crude steel in cauldron, in the that an overheating of the steel bath is carried out by aluminothermia before performing a desulfurization treatment (en that is, a treatment to reduce the sulfur content) and / or of defosforation (i.e. a treatment to reduce the content of match). During aluminothermal heating, it is done react aluminum with oxygen, which forms an acid slag of Al 2 O 3 on the surface of the steel bath. Now the desulfurization or defosforation treatment that needs a basic slag on the surface of the steel bath, is inhibited by the presence of an acid slag of Al 2 O 3 in the steel bath surface. Therefore, it is necessary first remove the acid slag from Al 2 O 3 before Be able to start the desulfurization and / or defosforation treatment. However, such intermediate runoff significantly increases the total duration of treatment and is not possible in any post of metallurgical treatment

To increase the performance of a Aluminothermal reheating of a metallic bath in a cauldron, it is known to perform this overheating under a hood (see, for example, the patent US-A-4518422). By injection of a inert gas, a "window" is first formed in a layer of initial slag that covers the metallic bath. Then the bell above this "window" until its edge Lower be submerged in the metallic bath. The reagents of the aluminothermia, namely aluminum and oxygen, are added by under this bell. At the same time, stirring is performed of the metallic bath by injection of an inert gas. It will be appreciated that the hood allows to realize the overheating by aluminothermic under a protected atmosphere and with a minimum loss in the environment. When aluminothermal reheating is finished, Remove the bell The slag around the bell is mixed with the slag of Al_ {2} O_ {3} formed under the hood, which provides a slag whose content inhibits a treatment of desulfurization and / or subsequent defosforation due to its content high of Al 2 O 3 (> 40%).

Another procedure of the type defined in the preamble is a procedure in which a crude foundry bath or a bath of ferroalloys must suffer at the same time a disappointment by oxygen injection (i.e. a treatment to lower the silicon content) and a desulfurization and / or defosforation. The oxygen injection disappointment produces an acid slag of SiO 2 on the surface of the metal bath. Now the subsequent desulfurization treatment requires the presence of a basic slag on the surface of the steel bath and is inhibited for a SiO_2 content greater than 10%. It follows from this that the acid slag formed during disillusionment must be removed before starting the desulfurization treatment. As already explained, such intermediate slag significantly increases the duration of the procedure and is not possible in any port of metallurgical treatment

Object of the invention

The objective of the present invention is optimize the development of a metallurgical procedure in which a first treatment involves the presence or formation of a acid slag on the surface of a metal bath and a second treatment involves the presence or formation of a slag Basic on the surface of this metallic bath.

Exhibition of the invention

According to the invention, this objective is achieved. carrying out the two treatments without intermediate defoiling simultaneously in two separate zones and securing on the surface from the metallic bath a physical separation between a slag zone acid and a basic slag zone. In order to save the maximum of time, the two treatments will take place simultaneously. Be you will appreciate that, in all cases, the time necessary for the intermediate defoiling and both treatments can be performed in a single metallurgical treatment port that is not necessarily equipped to carry out a slag removal (the final dehorning can be done elsewhere).

In a preferred embodiment, one of the two treatments are performed under a deep bell whose edge bottom is submerged in the metal bath, and the other treatment It takes place around this deep bell. This deep bell ensures physical separation between the two slag zones in the bathroom surface, allowing at the same time to do one of the two treatments under a protected atmosphere with a minimum of losses Towards the environment. However, if you do not want to take advantage of these Additional advantages of a deep bell, however, can be also use a simple separation wall to secure in the metal bath surface a physical separation between an area of acid slag and a basic slag zone. This separation wall can cooperate with the edges of a metal cauldron to divide the metal bath surface in two juxtaposed areas, or it can form a kind of ring to delimit an "islet" in the interior of the surface of the metallic bath.

The first treatment is, for example, a chemical overheating that takes place under a hood deep under a protected atmosphere that produces a scum acidic under this bell. Chemical heating means here a strongly exothermic oxidation of an element generally metallic, such as, for example, aluminum (aluminothermia) or silicon (silicothermia).

The first treatment can also be a oxygen injection disappointment treatment, in particular in the framework of a foundry or ferroalloy treatment (such as ferronickel) with high contents of silicon. This oxygen injection disappointment treatment it is also advantageously carried out under a deep bell whose lower edge is submerged in the metallic bath.

The second treatment is, for example, a desulfurization and / or defosforation treatment that makes intervene a basic slag formed, for example, by adding lime, sodium carbonate, magnesium, etc. This treatment can take place around the deep bell below which Make the first treatment.

Within the framework of a disillusionment treatment by oxygen injection, desulfurization treatment and / or defosforation advantageously comprises the addition of limestone, in particular of castina, to the metallic bath. It is an agent cheap and very effective desulfurizer, but its decomposition in the bathroom metallic results in a strongly endothermic reaction that has tendency to cool the metallic bath. Now in combination with an oxygen injection disappointment, this cooling effect it hardly causes problems, since the disillusionment reaction, which is strongly exothermic, still produces an excess of hot.

When a deep bell is used to ensure a physical separation on the surface of the metallic bath between an acid slag zone and a basic slag zone, it proceeds advantageously as follows: it is formed first, by injection of an inert gas, a "window" in a slag bell initial covering the surface of the metallic bath; this is covered "window" with the help of a deep bell whose bottom edge is submerged in the metallic bath; one of the two is done treatments under the deep bell and the other around the deep bell, simultaneously shaking the bath metallic by injection of an inert gas; and at the end of the two treatments, stirring stops, deep bell is removed and the two slags are removed immediately after. The detention of agitation before the withdrawal of the deep bell allows prevent the two slags from mixing too much, which could be detrimental to the outcome of the procedure.

Other peculiarities and characteristics of procedure according to the invention will become more clearly manifest from some examples presented below to illustrative title, also referring to the attached figure 1, which shows a schematic illustration of the implementation of a procedure according to the invention.

Detailed description of some advantageous embodiments of the invention

Figure 1 is used to describe more in detail, by way of illustration of the present invention, the development of a metallurgical process comprising a desulphurization treatment in the cauldron of a crude steel bath, preceded by a chemical overheating in this cauldron's bath steel.

Figure 1 shows a metallurgical cauldron 10 in a metallurgical treatment post during commissioning practice of the procedure mentioned above. In the initial state, this cauldron 10 contained a bath of raw steel 12 from the converter or electric oven, as well as a slag layer Basic residual lining the steel bath. At the port of metallurgical treatment was first formed by injecting a inert gas a window 14 in the waste slag cauldron, is say that an area of the steel bath surface has been released 12 at least partially of the residual slag that covered it. By a bell has been positioned above this window 14 deep 16, so that its lower edge 18 is submerged in the metallic bath 12 in at least 20 cm (the more important the bubbling of metallic bath 12, the more important the immersion depth of the bottom edge of the bell 16). Remains to emphasize that a possible execution of such a deep bell 16 is describes, for example, in patent application WO 98/31841, specifying, however, that the bell used herein procedure should not necessarily be a rotating bell.

Below the bell 16 there is a Overheating of the steel bath by aluminothermia. To this end, it add aluminum and oxygen is insufflated under bell 16, as indicated schematically by arrows 18 and 20. Simultaneously, it stirring the metal bath 12 with the help of a gas inert that is injected, preferably with the help of a spear lateral 22, in the metallic bath 12. The aluminum reacts with the oxygen in a strongly exothermic reaction. This reaction gives as a result the formation of an acid slag of Al 2 O 3 below bell 16. In figure 1, this acid slag from Al 2 O 3 is designated by reference 24.

According to the state of the art, it went back up the bell 16 at the end of the chemical reheating to effect a removal of residual slag heavily contaminated with the slag of Al_ {2} O_ {3} formed under bell 16. A then, the desulfurization treatment was carried out on the steel bath freed from slag. Indeed, it is known that, for be able to carry out a desulfurization and / or defosforation treatment with the help of a basic scum, it is necessary that the content of Al 2 O 3 of this slag is less than 40%.

According to the present invention, the desulfurization and / or defosforation treatment around the bell 16 without performing an intermediate slag removal. To this finally, a formation agent of a basic slag 28 in the metallic bath 12 around the hood 16. This basic slag forming agent 28 may be, by example, lime, limestone, castin, sodium carbonate, magnesium, etc. The bell 16 prevents the acid slag of Al_ {2} O_ {3} formed below bell 16 mix with the basic slag around bell 16, which allows both treatments Simultaneously without intermediate defoiling. Preferably, it first of all, the overheating due to aluminothermia is carried out and desulfurization and / or defosforation treatment begins in when the steel bath has reached a temperature enough.

At the end of the desulfurization treatment and / or defosforation, all agitation of the metallic bath 12 stops before of raising bell 16 again. Then the two are removed slags together.

It should be noted that the treatment carried out under the bell could also be, for example, a treatment of disappointment of foundry or ferroalloys, in particular of Ferronickel, by oxygen injection. In this case, the silicon reacts with the insufflated oxygen below the hood to form an acid scum of SiO2 below the hood. Around the bell a treatment of desulfurization and / or defosforation as described more above. The bell prevents the acid slag from SiO_ {2} formed below bell 16 mix with the basic slag surrounding the cauldron 16, which allows both treatments Simultaneously without intermediate defoiling. Indeed, for a desulfurization and / or effective defosphorus treatment, it is necessary that the SiO_ {2} content of the basic slag does not exceed at 10%

Example 1

This example refers to a treatment in converter crude steel cauldron, which aims at a 80% desulfurization of this steel.

Initial state : A metallurgical cauldron contains 160 t of raw converter steel and 600 kg of refining waste slag. The results of the analysis are as follows: 0.04% of C, 600 ppm of O, 0.010% of S. The temperature of the steel bath is 1,600 ° C. 200 kg of Al deoxidation and 600 kg of CaO have been added to the laundry.

Aluminothermal reheating: The first treatment is an overheating by aluminothermia that is carried out, as described with respect to figure 1, under a deep hood located above an area of the steel bath previously released from its slag layer. residual. A temperature rise of the steel bath of about 90 ° C is obtained by injection of 530 kg of aluminum and 350 m 3 of oxygen in 7 min (flow rate of 50 m 3 / min of O 2 ). Stirring below the bell is carried out by argon injection with the help of a side lance with a flow rate of 0.2 m 3 / min.

Desulfurization : The second treatment is an 80% desulfurization that takes place around the hood. As a desulfurizing agent, a powder composed of 60% CaO and 35% Al 2 O 3 is used, the remainder being impurities. The addition of Al 2 O 3 is to regulate the flow of the slag obtained. Other slag agents can also be added.

The desulfurizing agent is injected with the help of a submerged head spear, using argon as carrier gas. Before starting the injection of the desulfurizing agent, it is used the injection lance to pre-agitate the bath of steel. To this end, the injection lance is fed for 5 min with a flow rate of about 0.5 m 3 / min of argon, cutting the desulfurizing agent feed. This preliminary agitation allows, in particular, to homogenize the bath temperature of steel before desulfurization. They are then injected into a time interval of about 12 min, 960 kg of agent Desulfurizer mentioned above (solid flow rate of around 80 kg / min) with a flow rate of about 1 m3 / min of argon as carrier gas The treatment is terminated with the same launches intense agitation for 5 min with a flow of about 1 m 3 / min of argon, cutting again the desulfurizing agent feed. Then it stops all shaking action and the bell is raised again.

Final state :

Steel: 0.04% C, 0.002% S, temperature approximate: 1,600ºC.

Slag: about 1,000 kg of Al_ {2} O_ {3} formed under the hood, plus about 2,500 kg of desulfurization slag around the hood.

Remark :

If you want to obtain only a desulfurization Moderate steel, there is no need to inject a desulfurizing agent in the bathroom with the help of a spear. In effect, the residual slag that is around the hood may already contain a sufficient amount of desulfurizing agents to obtain a moderate desulfurization of the steel. Enough then with removing the steel bath around the hood to do so react with the residual slag that floats on its surface and add, if appropriate, slag agents to regulate, in particular, the consistency of the slag.

Example 2

This example refers to a treatment in cauldron of gross smelter that aims at a disappointment and a desulfurization of the foundry.

Initial state : A metallurgical cauldron contains 100 t of crude smelter whose analysis results are the following: 4.5% of C, 0.8% of Si, 0.10% of S. The temperature of the foundry bath is 1,350 ºC. The foundry is covered with a residual slag layer of a basic nature.

De-initiation treatment: An oxygen-injected disinitiation treatment is carried out, as described above, under a deep hood located above a bath area previously released from its residual slag layer. 450 m 3 of oxygen are injected under the hood in 10 min (flow rate of 45 m 3 / min of O 2). Stirring below the bell is carried out by argon injection with the help of a side lance with a flow rate of 0.2 m 3 / min.

Desulfurization : Desulfurization takes place around the bell. As the desulfurizing agent, a powder composed of 70% CaCO 3 and 30% Na 2 CO 3 is used. Other slag agents can also be added.

The desulfurizing agent is injected with the help of a submerged spear, using argon as carrier gas. Are injected in a time interval of about 20 min approximately 1,000 kg of the aforementioned desulfurizing agent (solid flow rate of about 50 kg / min) with about 1 m3 / mn of argon as carrier gas After having stopped all agitation action, it you can raise the bell again and remove the two slags together.

Final state :

Pretreated foundry: 4.3% of C, 0.4% of Si, 0.02% of S, approximate temperature: 1400ºC.

Slag: about 860 kg of SiO_ {2} formed under the hood, plus approximately 700 kg of slag of desulfurization around the bell.

Observation regarding the treatment of the foundry :

In the classical desulfurization of the foundry in a single stage, a mixture is very often used as desulfurizer Mg-CaC2 or Mg-CaO. Is about Desulphurizers very effective but also very expensive. Are used especially because they produce limited cooling of the bathroom metal. However, the combination of desulfurization with a strongly exothermic disappointment allows a source to be used desulfurizer more refrigerant, but cheaper, such as, for example, limestone (CaCO_3) or castina. For the rest, the decomposition of CaCO 3 or Na 2 CO 3 in the water bath steel also generates oxygen that contributes to the disappointment of the Casting (1 kg of CaCO3 or Na2CO3) reduces the need of oxygen de-initiation in about 0.1 m 3). For another side, it is preferable to use a mixture of CaCO3 + Na 2 CO 3 in order to obtain a more fluid slag and of limit the losses due to iron drag during the uncrossed However, the use of Na_ {2} CO_ {3} requires also limit the temperature to 1,400 ° C in order to avoid a loss of Na 2 CO 3 by vaporization.

Observation regarding a ferroalloy treatment :

It will be appreciated that a bath of ferroalloys, in particular a ferronickel bath, it can also be the object of a combined treatment of desiliciación and desulfurization, such as presented in example 2 for casting.

However, in the case of ferronickel, taken by way of example, it is generally sought to make a much more important disappointment (reduction of Si content in more than 1%). By de-initiation by an oxygen jet gas would be obtained, in the absence of effective cooling, a heating of the order of 300 ° C or even more.

As is done in certain procedures of smelting of smelters, a coolant can be used as mineral or an iron oxide obtained as a coproduct in the steel manufacturing. However, with the proposed procedure, which combines desiliciación and desulfurization, is particularly suitable to use castin (CaCO3) and / or carbonate sodium (Na2CO3) as a desulfurizing agent, since these the latter are both very refrigerant and desulfur effectively, to condition of not being diluted by a contribution of silica (SiO_ {2}).

Leaving aside the quantitative aspect (Si reduction by 1 to 2% instead of 0.2 to 0.4% for blast furnace conditions), the proposed procedure for foundry is applied similarly to ferroalloys, adjusting the proportions of oxygen and refrigerant / desulfurizer.

Claims (10)

1. Metallurgical treatment procedure on a metallic bath, comprising: a first treatment that involves the presence or the formation of an acid slag on the surface of said bath metal; Y a second treatment that involves the presence or the formation of a basic slag on the surface of said bath metal; characterized in that the two treatments are carried out without intermediate defoiling simultaneously in two separate zones and ensuring on the surface of said metallic bath a physical separation between an acid slag zone and a basic slag zone. 2. Method according to claim 1, in which one of the two treatments is performed under one deep bell whose bottom edge is submerged in said bath metallic, and the other treatment is carried out around said deep bell 3. Method according to claim 2, wherein said first treatment is a treatment of chemical heating that takes place under said hood deep 4. Method according to claim 3, wherein said chemical heating treatment is a aluminothermal or silicothermic treatment. 5. Procedure according to any one of the claims 1 to 4, wherein said second treatment is a desulfurization and / or defosforation treatment based on a basic scum. 6. Method according to claim 1, wherein said first treatment is a treatment of disappointment of foundry or ferroalloys, in particular of Ferronickel, by oxygen injection. 7. Method according to claim 6, in which said treatment of injection disappointment of oxygen is effected under a deep bell whose edge bottom is submerged in said metal bath, and said second treatment is a desulfurization and / or defosforation treatment effected around said deep bell. 8. Procedure according to any of the claims 6 or 7, wherein said second treatment is a lime based desulfurization and / or defosforation treatment. 9. Method according to claim 8, wherein said second treatment comprises the addition of limestone, particularly castina, to said metallic bath. 10. Procedure according to any of the claims 1 to 9, wherein: at the beginning of said procedure, the surface of said metallic bath with a slag layer residual; a window is formed in said slag layer residual by injection of an inert gas; said window is covered with the help of a deep bell whose bottom edge is submerged in said bath metal; one of the two treatments is performed under said deep bell and the other around said bell deep, simultaneously stirring the metal bath by injection of an inert gas; Y at the end of the two treatments, it stops said agitation, said deep bell is removed and removed immediately after the two slags.