Patent Publication Number: US-2003230163-A1

Title: Method of and plant for producing products from carbon or stainless steel

Description:
[0001] The present invention relates to a method of and a plant for producing products from carbon or stainless Steel in an electrical arc furnace-converter with two metallurgical vessels.  
       [0002] One method (DE 196 23 671 A1) contemplates the use of two electrical furnaces, in which delivered scrap is melted, two crucible furnaces for further chemical treatment of metal, two vacuum stations, two continuous casting machines, an equalizing furnace, and a rolling train, and is effected by controlling the material flows in two economically ineffective, requiring large investments, parallel lines of two electrical arc furnaces, two crucible furnaces, two vacuum stations, and two complete continuous casting installations.  
       [0003] For controlling material flows between the two lines, a plurality of crossing elements is necessary, which further noticeably increase the costs. While considering constructional costs, the costs associated with conducting the process have not been taken in account. Such a process cannot, therefore, justify the necessary investment and the economic inefficiency by improvement in the steel production process. These drawbacks cannot compensate the melt exchange that was not described here in detail in the steel production process. These drawbacks cannot compensate the melt exchange that was not described here in detail  
       [0004] The present invention is based on a system of two metallurgical vessels which are alternatively heated and the melt content of which is alternatively oxidized with oxygen (DE 196 21 143 A1). To this end, respective top lances above the vessels and a pivoting electrode arrangement between the two vessels which, however, can only be used with one vessel at a time, are required. The following installations are adapted to the melt times of both metallurgical vessels.  
       [0005] According to this method, no melts with a different analysis can be produced, which is not even contemplated.  
       [0006] The object of the present invention is the system of two metallurgical vessels capable of being simultaneously operated but in different portions of the process, which can be changed based on arbitrary analysis of following each other melts, e.g., in accordance with a production program of a steel manufacturer that takes into account the customer contract.  
       [0007] The set object is achieved according to the present invention by combination of features of claim 1. The basis of the invention forms the process described in DE 196 21143A1 and which is effected in an electrical arc furnace-converter with two metallurgical vessels and wherein, according to the invention, during melting, an electrode system pivots over each metallurgical vessel, and during oxidation with oxygen, a top lance is introduced in each metallurgical vessel and one or several side lances are introduced into a metallurgical vessel for oxidation, and an immediate quality change from carbon melt to stainless melt or vice versa is effected by oxidation with oxygen with the top lance and/or by oxidation with oxygen with at least one side lance or in reverse order during tapping periods which depend on the operation of an immediately adjoining continuous casting machine.  
       [0008] The advantage is a flexibility of a steel manufacturer which, in accordance with the customer guidelines, produces one sort of steel and which can, without large expenses, change the quality in a new run. Up to the present, a prejudice dominated among the experts against production of different qualities in one and the same metallurgical vessel shortly one after another.  
       [0009] The invention contemplates that the top lance is set during oxidation above a slag layer, and the side lance is set during oxidation beneath the slag layer. Thereby, the bath movement can be tailored to the corresponding process step.  
       [0010] The advantage of so-called CONARC®-process (protected mark of the assignee herein) vessels can further be enhanced by planning tapping periods for both metallurgical vessels and the changing periods for the continuous casting machine so that they are less than 90 minutes.  
       [0011] During production of stainless steels, it is advantageous when during a dephosphorization phase of a phosphorous-reach pigizon, scrap or other iron carriers, and/or ferrochromium, and/or ferronickel or other alloying means such as refrigerants and additives (such as slag-forming constituents) are added to a quantity of iron sponge, and the melt is oxidized with a top lance.  
       [0012] At that, it is contemplated that the oxidation is effected with less than 400 Nm 3 /min of oxygen or oxygen mixture.  
       [0013] Further measures for influencing the bath movement consist in that during the oxidation phase of the melt, a quantity of stainless scrap, and/or ferrochromium, and/or ferronickel is supplied, and during finish oxidation with at least one side lance and, if necessary, the top lance, less than 100 Nm 3 /min of oxygen or oxygen mixture is fed.  
       [0014] One modification contemplates that during oxidation with the top lance and/or at least one side lance, turbulence of the melt and/or the slag layer is kept low, and that inner wall of the metallurgical vessel remains free of slag formations.  
       [0015] At that, it is of no importance that cooling plates, which are located in the upper region of the electrical arc furnace-converter, are covered with slag.  
       [0016] Another measure relates to removal of residual melt of a preceding melt during quality change. To this end, it is contemplated that the metallurgical vessel is tilted, during tapping, until a complete discharge of the slag and the melt. To this end, a particular metallurgical vessel in form of a vessel with a nose is contemplated.  
       [0017] In a further embodiment, it is contemplated that the produced liquid steel after vacuum treatment in a vacuum installation and, if necessary, in a crucible furnace station, is cast in a continuous casting machine, with a cast strand being rolled and wound into coils of carbon steel or stainless steel.  
       [0018] Also, the continuous casting process and the hot rolling process of carbon steel or stainless steel can be effected in an, already used in practice, compact strip production plant (CSP).  
       [0019] It is further advantageous that a product of a continuous casting process and of a rolling process of carbon steel or stainless steel is formed in an elongate product in the continuous casting machine.  
       [0020] The plant is likewise based on the state of the art according to DE 196 21 143 A1 which discloses a plant for producing products from carbon steel or stainless steel in an electrical arc furnace-converter with two metallurgical vessels with lowerable or rotatable top lances associated with each metallurgical vessel and with an electrode system arranged between the metallurgical vessel and pivotable over each metallurgical vessel.  
       [0021] The object of the invention, with regard to the plant, is achieved by a plant in which each metallurgical vessel consists of a tiltable or stationary metallurgical vessel and in which in addition to the top lances one or several side lances are provided, and in which the electrode system arranged between the two metallurgical vessels and following vacuum installation crucible furnace-station, continuous casting machine, hot rolling train, continuous rolling mill or reversing cold rolling mill for flat or elongate products, and a coiler all lying on a common line, are provided. Also a single top lance oscillating between the two vessels, can be provided.  
       [0022] It is advantageous when the rolling technology is tailored to the rolled product. To this end, it is suggested to provide several rolling trains in the common line.  
       [0023] In the latter case, one rolling train can be formed as a continuous cold rolling mill or as a reversing cold rolling mills.  
       [0024] For production of selected sorts, a discaling process is contemplated. It is effected with a pickling installation provided between two following each other rolling trains located in the common line.  
       [0025] An entire product range produced up to now, can be produced to this end, the continuous casting machine is designed for production of elongate products, broom profiles, billet profiles, and thin slab cross-sections, with the rolling mill being correspondingly adjusted. 
     
    
    
     [0026] In the single FIGURE of the drawings, a carbon steel scrap store  1 , a blast furnace  2  for pig iron, a stainless scrap store  3 , a ferrochromium store  4 , a ferronickle store  5 , a sponge iron and alloy carrier store  6 , and pig  7  form the basis of the process. Respective flows of the material are designated with  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a , and  7   a.    
     [0027] The material flows are processed in an electrical arc furnace-converter installation  8  with two metallurgical vessels  9  and  10 . An electrode system  11  pivots over each metallurgical vessel  9 ,  10 . For oxidation with oxygen, a top lance  12  is inserted into or is withdrawn from each vessel  9 ,  10  and, if necessary, is rotated.  
     [0028] Alternatively, liquid steel  14 , after being prodded for less than about 90 minutes, reaches a vacuum installation  15  and is transported therefrom into a crucible furnace-station  16 . The finished liquid steel  14  is then delivered with a ladle  17  to a continuous casting machine  18 , which is provided with a distributor  19  and a continuous casting mold  20 , and therefrom via a back-up rolling stand  21  and through a tunnel furnace  22 , the steel is fed to hot rolling train  23  and is finally coiled. Via a line  24 , the strand is guided through a pickling installation  25  and is finally rolled in a continuous cold-rolling mill  26  or a reversing cold-rolling mill  27  and is wound in coils  28  in a coiler  32 .  
     [0029] The top lances  12  are arranged in the electrical arc furnace-converter installation  8  during oxidation above a slag layer  29 , and side lances  13  are arranged during oxidation beneath the slag layer  29 .  
     [0030] During the dephosphorizing phase (in case phosphorus-reach pig iron is used), a quantity of sponge iron  6 , stainless scrap  3 , ferrochromium  4 , ferronickel  5 , or of other alloy means such as solid refrigerants or supplements, are used as slag-forming constituents, with the melt being oxidized by using the top lance  12 . Here, with the oxygen being supplied in an amount up to 400 Nm 3 /min, turbulence can occur.  
     [0031] In case of production of a stainless melt, during the oxidation phase of the melt, a quantity of stainless scrap  3 , and/or ferrochromium  4 , and/or ferronickel  5  and supplements are added, and less than 100 Nm 3 /min of oxygen is fed with a side lance  13  and, if necessary, with the top lance  12 . In this case, only a small turbulence is created in the melt.  
     [0032] During the oxidation with a top lance  12  and/or with at least one side lance  13 , the turbulence of the melt and/or of the slag layer  29  is kept low, so that the inner wall  31  of the metallurgical vessel  9 ,  10  remains free from slag formations.  
     [0033] The metallurgical vessel  9 ,  10  is tilted during tapping until a complete discharge of the thinly fluid schlag  29  and the fluid melt.  
     [0034] The liquid steel  14  is cast, after vacuum treatment in the vacuum installation  15  (VD/VOD) and, if necessary, in the crucible station  16 , in the continuous casting machine  18 , with the cast strand being rolled in the hot rolling train  23  and/or in the continuous rolling mill  26  and is wound in coils  28  or carbon steel or stainless steel.  
     [0035] Advantageously, the continuous casting process and the rolling process of carbon or stainless steel takes place in compact strip production plant, as shown.  
     [0036] At that, as it has already been proved in practice, a product, which is formed as a result of a continuous casting process of carbon or stainless steel, can be formed in the continuous casting machine  18  into a long product.  
     [0037] Each metallurgical vessel  9 ,  10  can be formed as a tilting vessel or as a stationary vessel. In addition to the top lance  12 , one or (preferably) two or more side lances  13  can be provided. Between the metallurgical vessels  9 ,  10 , there is provided the electrode system  11 , and the vacuum installation  15  (VD, VOD). The crucible furnace-station  16 , the hot rolling train  23 , the continuous cold-rolling mill  26  are provided downstream of the metallurgical vessels  9 ,  10  for flat or elongate products, or there are provided the reversing cold-rolling mill  27  and the coiler  28  in the line  24 .  
     [0038] Between the two, arranged one after another, rolling mills  23 ,  26  in the line  24 , a pickling installation  25  is inserted.  
     [0039] The continuous casting machine  18  is designed for production of elongate products, bloom profiles, billet profiles, and thin slab cross-sections. The used rolling mills are adapted to these products.