EP3018219A1 - Device and method for creating a rust-free steel - Google Patents

Abstract

In a process for producing an austenitic or ferritic stainless steel from a first, in particular highly carbon-containing molten iron (2) fed to a converter (3), a solution is to be created which permits the production of a stainless steel melt based on one of a highly phosphorus-containing Raw or feed molten molten iron in an energy-efficient manner in the context of a refining process in the usual for the production of stainless steel melt production facilities, in particular converters allows. This is accomplished by first subjecting the first molten iron (2) in the converter (3) to dephosphorization, desiliconization and decarburization treatment followed by intermediate slagging to remove phosphorus and then placing the metallurgically treated first molten iron (2) in the converter (3) in a second treatment stage for producing the stainless steel sufficient chromium-containing, molten iron chromium (FeCr) alloy (5) supplied as second molten iron (6) and from the resulting mixture of molten iron by metallurgical refining a stainless steel melt (7) becomes.

Description

The invention is directed to a method for producing an austenitic or ferritic stainless steel from a first, in particular highly carbon-containing molten iron supplied to a converter designed for a metallurgical refining.
Furthermore, the invention is directed to an apparatus for performing such a method in a converter.

In order to produce high-quality austenitic or ferritic stainless steels or stainless steels, it is necessary to be able to set precisely low levels of phosphorus in the final melt. The problem here is that an effective Entphosphorung a pig iron or molten steel due to thermodynamic laws in the presence of a high chromium content in the corresponding melt is impossible. Due to the decreasing availability of low-phosphorus feedstocks which are suitable for the production of stainless steels or stainless steels, it is increasingly necessary to use high-phosphorus feedstocks for their production. This requires that in the production of an austenitic or ferritic stainless steel various additional intermediate steps or process stages must be provided so that from a high phosphorus-containing raw material produced molten iron, in particular pig iron melt, analogous to be carried out when using low phosphorus feedstock or raw material production process in a refining process the desired chromium-containing stainless steel or stainless steel can be processed molten. Typically, this refining is performed in converters such as AOD (argon oxygen decarburization) AOD-L (lance), MRP (metal refining process) or MRP-L (lance) converters in a blowing process. To make this possible even with hochphosphorhaltigem feed, is in the state of Technique previously carried out in special containers or production units dephosphorization treatment. This is associated with longer process times and heat losses due to intervening casting processes and charging processes compared to processes in which low phosphorus raw material or feed can be used. This is also associated with the disadvantage of higher production costs and an increased logistics problem, since the previous, running when using low phosphorus materials production process must now be interrupted by intermediate steps or intermediate stages or intermediate processes.

Methods and apparatus for stainless steel production without electrical energy supply based on liquid pig iron and FeCr solids are known from WO 2008/064797 A1 and the WO 2008/064798 A1 known. In this process, the amount of pig iron produced in a blast furnace is divided and placed in parallel in two classic "Twin" AOD-L converters and then subjected to the usual chemical processes in each converter in each converter in the respective converters.

The invention has for its object to provide a solution that allows the production of a stainless steel melt based on a high phosphorus raw or feed molten iron melt in an energy efficient manner as part of a refining process in the production of stainless steel melt production facilities, especially converters.

In a method of the type described in more detail, this object is achieved in that the first molten iron in the converter in a first treatment stage of a dephosphorization, desilication and decarburization with subsequent intermediate Schlackenabstich is subjected to phosphorus removal and then the metallurgical treated first molten iron in the converter in a second treatment stage a sufficient chromium-containing chromium-containing iron chromium (FeCr) alloy supplied as a second molten iron to produce the stainless steel and from the resulting mixture of iron melts by metallurgical refining a stainless steel melt is produced.

In a device of the type described in more detail, this object is achieved in that the converter is part of a twin-converter system, both converters, in particular AOD (argon oxygen decarburization) - or AOD-L (lance) - or MRP (Metal Refining process) - or MRP-L (lance) converters, designed to simultaneously carry out the process.

The provision of a twin-converter system for carrying out the method according to the invention is advantageous because the two-stage, the first treatment stage and the second treatment stage comprehensive fresh process takes longer than a conventional refining process. By providing two converters in the twin converter system, which can be operated simultaneously and in parallel in the same sequence of process steps, the possibility is created to continue to enforce the usual molten pig molten metal despite the longer refining times such that long casting sequences in combination with short casting times Maintaining high plant productivity while maintaining high product quality remains ensured.

In order to provide an energy-efficient process for producing a stainless steel even when using hochphosphorhaltigem raw or feedstock in an upstream first melting process or smelting unit, the invention proposes to carry out the refining process in a converter, but in two successive, different treatment stages. The first generated in an upstream first melting unit Iron melt is fed to the converter and then treated, in particular in the context of a dephosphorization, desilication and decarburization treatment carried out by subjecting the first molten iron to a treatment gas in the first treatment stage of the refining process. At the end of this first treatment stage or after the first treatment stage, an intermediate Schlackenabstich to remove the passed over in the above freshness treatment in the phosphorus phosphorus. Subsequently, a molten iron chromium (FeCr) alloy is added as a second molten iron in the remaining in the converter first molten iron in a second treatment stage, which provides the necessary for the production of stainless steel high nickel content. The iron melt now formed in the converter is then subjected in the usual way to a metallurgical refining under the action of treatment gas so that the desired stainless steel melt is present at the end. This can then be treated as usual in subsequent secondary metallurgical treatment stages and further processed before it is then cast, for example, as part of a continuous casting process.

The fact that the invention provides for a split of the freshness process, wherein the first part in the first treatment stage, the Entphosphorungs-, desilication and decarburization treatment of the still little chromium-containing and not high chromium enriched first molten iron provides, and only in the subsequent second treatment stage by the supply the molten iron chromium (FeCr) alloy is supplied to the increased chromium content necessary for the production of the stainless steel, the use of hochphosphorhaltigem material to produce the molten iron melted and melted in a previous step is possible. The otherwise problematic in the first Entphosphorungs-, Entsilizierungs- and decarburization process removal of chromium is avoided because only after this first treatment stage, the sufficient chromium-containing, second molten iron is supplied to the converter. This solves the problem that an effective Entphosphorungsbehandlung in the presence of higher chromium levels in a melt due to thermodynamic conditions is not possible.

Another advantage of the method according to the invention is that at least the first and second treatment stage and thus the process of preparing and refining the molten iron in the converter takes place without electrical energy supply. Preferably, the previous melting unit, in which the first molten iron to be used is produced, is also a blast furnace. However, this may also be an electric arc furnace. In any case, the invention is characterized in that the generation of the stainless steel melt in the converter is carried out without supplying electrical energy to the first molten iron.

The converters in which the process according to the invention can be carried out are conventional containers used in the refining of molten iron, namely AOD or MRP containers. The invention is therefore further characterized in that the first treatment stage and the second treatment stage in an AOD (argon oxygen decarburization) or AOD-L (lance) or MRP (metal refining process) or MRP-L (lance). Converters are performed.

In cases where an austenitic stainless steel is to be produced, it is advantageous that the converter for producing an austenitic stainless steel as the first molten iron, in particular high, phosphorus-containing pig iron or a Nickelroheisen or a molten FeNi alloy is supplied, thereby the invention features in a further embodiment.

In the production of ferritic stainless steel, however, it is advantageous that the converter to produce a ferritic stainless steel first Iron melt is supplied to a nickel-free pig iron, whereby the invention is also distinguished in design.

An iron melt supplied to the converter as the first melt advantageously has a chromium content of only up to 5% by weight so as not to impair the dephosphorization treatment provided in the first treatment step. The invention is therefore characterized in another embodiment also in that the converter as the first molten iron melt with a content between 0 wt .-% and 25 wt .-% nickel (Ni), a content of up to 5 wt .-% Chromium (Cr) and high levels of carbon (C), phosphorus (P) and silicon (Si) is supplied.

In the subsequent second treatment step, the converter is then fed as a second molten iron, a high chromium containing, for example, 60-65 wt .-% chromium-containing molten iron chromium (FeCr) alloy as a second molten iron, which is also characterized by a low phosphorus content of <0.05 wt .-%, in particular <0.04 wt .-%, phosphorus. The invention is therefore in an advantageous embodiment further characterized in that the converter as a second molten iron, a molten iron chromium (FeCr) alloy containing more than 50 wt .-% chromium (Cr), in particular between 60 and 65 wt .-% Chromium (Cr), and a low phosphorus content is supplied.

In the second treatment stage, cooling agents and / or alloying agents and / or slag formations and / or reducing agents can then be supplied in freshly customary amount and manner of the resulting molten iron or crude steel melt, which the invention also provides.

The stainless steel melt produced in the converter with completion of the second treatment stage can then be further treated in the usual way. In this regard, the invention provides in an advantageous embodiment that the stainless steel melt produced in the converter by means of metallurgical refinement is fed to a ladle and / or a subsequent secondary metallurgical treatment.

As a particularly efficient possibility from an energy point of view, to produce the iron melt to be supplied to the converter as the first molten iron in an upstream melting aggregate, the melting in the blast furnace offers itself. The invention therefore also provides, in a further embodiment, for the converter to be supplied with a molten pig iron melted in a blast furnace as the first molten iron.

Overall, the inventive method is characterized in that it is carried out in each case, in particular an AOD or AOD-L converter, but two of these converters are operated in particular simultaneously with the inventive method. The high-carbon-containing first molten iron molten in an upstream melting unit is decarburized, dephosphorized and desilvered in the respective converter and, in particular, brought to the desired final contents. Thereafter, a chromium-containing, molten iron chromium (FeCr) alloy of the first iron melt located in the converter is added and in the context of a second treatment stage of the refining process with the addition of further treatment agents such as coolant and / or alloying agent and / or slag and / or reducing agent to the desired stainless steel melt processed. Since this process no Zwischenerhitzungen and Umchargieren are necessary, as would be necessary when performing the first treatment stage in a separate converter, the method is characterized by a low logistics outlay. In addition, temperature losses, which would be necessary by re-heating at a Umchargieren the melt, avoided. In particular, this is the energy efficiency of the process guaranteed. The investment costs, for example the provision of cranes, charging devices or similar units remains reduced.

The invention is explained in more detail below by way of example with reference to a drawing. This shows in the single figure, a primary melting unit 1, in which a high-carbon raw material or feedstock, a first high-carbon-containing molten iron 2 is melted. The first molten iron 2 is a high-phosphorus pig iron melt, molten nickel pig iron or ferro-nickel molten pig iron which, for example in the embodiment described here, has a composition of approximately 3% by weight carbon (C), approximately 2% by weight silicon (Si ), more than 0.05% by weight of phosphorus (P), 0-25% by weight of nickel (Ni), less than 2.5% by weight of chromium (Cr) and iron as the remainder. This first molten iron 2 is fed at a temperature of about 1500 ° C one or both AOD converters 3 of the twin converter system 4. Here, the temperature of the first molten iron during transport in a pan is so high that covered during transport to the AOD converter 3 temperature loss is covered, taken into account and compensated.

As part of a conventional blowing process in the respective AOD converter 3, the first molten iron 2 is now subjected to a dephosphorization, desilication and decarburization treatment in a first treatment stage. By means of an inflation process using a top lance, the initial carbon content of the first molten iron 2 is reduced to a value of <0.1% by weight. After the decarburization and the dephosphorization of the first molten iron 2 carried out in parallel, phosphorus is removed from the treated first molten iron 2 after completion of the blowing process of the first treatment stage via a subsequent intermediate slag tap. If it should be necessary due to a high silicon content, another intermediate Schlackenabstich during the blowing process of the first Treatment level to be performed. After the first treatment stage, the first molten iron 2 used in the exemplary embodiment in the respective AOD converter 3 then has the following composition: less than 0.05% by weight of carbon (C), less than 0.02% by weight of silicon (Si ), less than 0.02% by weight of phosphorus (P), 0-25% by weight of nickel (Ni), less than 0.5% by weight of chromium (Cr) and iron (Fe) as the remainder. In the refining process in the first treatment stage, coolant and / or slag images can be supplied in the usual way. This, in the first treatment stage treated first molten iron 2 having the above composition is then fed in the respective AOD converter 3 as chromium carrier a molten iron chromium (FeCr) alloy 5 as the second molten iron 6. For example, the second molten iron 6 has the following composition in the embodiment: about 3 wt% carbon (C), about 5 wt% silicon (Si), less than 0.04 wt% phosphorus (P), 60 The second molten iron 6 has a temperature of 1500 ° C, with which they the respective AOD converter 3, after after the first treatment stage or as Completed the end of the first treatment stage the slag or the Schlackeabstich has been performed is supplied. After supplying the second molten iron 6 to the already treated in the AOD converter first molten iron 2, the total mixture is brought in a blowing step with a high oxygen / nitrogen ratio by gas to a carbon content of 0.7 wt .-%. Here, the temperature rises relatively quickly to a high operating temperature, which prevents chromium slagging, ie the chromium oxidation losses are kept low at this temperature. At this time, coolants such as high-carbon ferroalloys are added to the molten bath so that the temperature can be maintained at the desired high level. A condition for this is that a large amount of refrigerant is supplied to the converter from a bunker. The combined blowing process is performed without interruption, however different gas compositions between individual blowing steps can be used. Decarburization is carried out until a final carbon content of about 0.03 to 0.05 weight percent carbon is achieved. The temperatures and the carbon content are measured and tested, since these values are the blowing time of each step with different proportions of oxygen and inert gas depends. Depending on the desired steel quality, nitrogen or argon is used for rinsing. After oxygen blowing, a reduction phase is necessary. By adding reducing agents with simultaneous argon purging or stirring, high levels of chromium in the slag can be recycled back into the molten iron or molten steel. Subsequently, calcium oxide is added to the steel bath or molten iron, so that a slag having a sufficient basicity and a sufficient desulfurization capacity is formed. Then the usual chemical analyzes and temperature determinations are carried out before the tapping of the produced stainless steel melt 7 from the respective AOD converter 3 takes place.

The above-explained and carried out in the second treatment stage individual process steps of the refining process basically correspond to those, as they are otherwise usual when performing refining.

At the end of the second treatment step, a stainless steel melt 7 is then obtained in the embodiment, the content of ≤ 0.05 wt .-% carbon (C), about 0.4 wt .-% silicon (Si), less than 0.04 Wt .-% phosphorus (P), about 8 to 12 wt .-% nickel (Ni), about 16 to 24 wt .-% chromium (Cr), and iron (Fe) as the remaining portion.

The obtained stainless steel melt 7 is then tapped into a ladle 8 at a temperature of about 1650 ° C and fed with this a ladle furnace 9, in which the stainless steel melt 7 a secondary metallurgical treatment is subjected before it is then cast in a casting plant 10, in particular a continuous casting plant. The time from tapping to tapping is approximately 120 minutes for each of the two AOD converters 3.

The example described above relates to the production of an austenitic stainless steel. If a ferritic stainless steel number is to be produced, in the first treatment stage the first molten iron 2 is exclusively nickel-free pig iron.

Further essential features of carrying out the process according to the invention in an AOD or AOD-L converter are the feeding of a first molten iron 2, for example an iron-nickel (FeNi) - or even a chromium-containing melt, into the AOD converter 3; the dephosphorization, desilication and decarburization of the first molten iron in the AOD converter 3; a reduction of the partial pressure of the system by increased inert gas rates and reduced oxygen rates in different blowing stages of the first and / or second treatment stage to minimize the metal losses due to oxidation; performing an oxidation process in the AOD converter 3 by introducing both oxygen and alternatively argon or nitrogen through side blow holes; the provision of a storage or bunker system located above the AOD converter 3, from which ferroalloys, coolant and additives can be fed to the respective molten iron or steel bath; performing a reduction phase after oxygen blowing by adding reducing agents with simultaneous argon stirring to transfer high levels of chromium from the slag back into the steel bath and to obtain sufficient chromium content; the tapping of the hot melt and transporting the same in the ladle 8 after Schlackenabstich to a secondary metallurgical treatment, for example in the ladle furnace. 9

Claims (11)

Process for producing an austenitic or ferritic stainless steel from a first, in particular high-carbon, molten iron (2) fed to a converter (3) designed for metallurgical refining,
characterized,
that the first molten iron (2) in the converter (3) is subjected in a first treatment stage a dephosphorization, Entsilizierungs- and decarburization treatment with subsequent intermediate slag to phosphorus removal and subsequently the metallurgically treated first molten iron (2) in the converter (3) in a second treatment stage, a sufficiently rich chromium-containing chromium-containing iron chromium (FeCr) alloy (5) is fed as second molten iron (6) to produce the stainless steel and a stainless steel melt (7) is produced from the resulting mixture of molten iron by metallurgical refining. A method according to claim 1, characterized in that the production of the stainless steel melt (7) in the converter (3) without electrical energy supply to the first molten iron (2) is performed. Method according to claim 1 or 2, characterized in that the first treatment stage and the second treatment stage are in an AOD (argon oxygen decarburization) or AOD-L (lance) or MRP (metal refining process) or MRP-L (lance). - Converters (3) are performed. Method according to one of the preceding claims, characterized in that the converter (3) for producing an austenitic stainless steel as the first molten iron (2), in particular high, phosphorus-containing pig iron or a Nickelroheisen or a molten FeNi alloy is supplied. Method according to one of claims 1 - 4, characterized in that the converter for producing a ferritic stainless steel as the first molten iron (2) is supplied to a nickel-free pig iron. Method according to one of the preceding claims, characterized in that the converter (3) as the first molten iron (2) is a melt with a content between 0 wt .-% and 25 wt .-% nickel (Ni), a content of up to 5 Wt .-% chromium (Cr) and high levels of carbon (C), phosphorus (P) and silicon (Si) is supplied. Method according to one of the preceding claims, characterized in that the converter (3) as a second molten iron (6) is a molten iron chromium (FeCr) alloy (5) containing more than 50 wt .-% chromium (Cr), in particular between 60 and 65 wt .-% chromium (Cr), and a low phosphorus content is supplied. Method according to one of the preceding claims, characterized in that the resulting molten iron or stainless steel melt (7) in the second treatment stage, coolant and / or alloying agent and / or slag and / or reducing agent are supplied. Method according to one of the preceding claims, characterized in that the stainless steel melt (7) produced in the converter (3) by means of metallurgical refinement is fed to a ladle (8) and / or a subsequent secondary metallurgical treatment. Method according to one of the preceding claims, characterized in that the converter (3) as the first molten iron (2) is fed to a pig molten pig molten in a blast furnace. Device for carrying out the method according to one of the preceding claims in a converter (3), characterized in that the converter (3) is part of a twin-converter system (4) whose two converters (3), in particular AOD (argon oxygen Decarburization) - or AOD-L (lance) or MRP (Metal Refining Process) or MRP-L (lance) - converter, designed to simultaneously carry out the method according to any one of claims 1-10.

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