JP4049106B2 - Melting method of nickel-containing stainless steel - Google Patents

Description

  The present invention relates to a method for melting nickel-containing stainless steel, and in particular, to make the best use of inexpensive Ni and Cr sources in the melting process and to obtain the obtained nickel-containing stainless steel so-called “continuous casting”. The present invention relates to a technology for supplying a continuous casting machine without interruption.

  Usually, stainless steel is roughly classified into two types: chromium (symbol: Cr) -based stainless steel not containing nickel (symbol: Ni) and nickel-containing / stainless steel containing nickel. Conventionally, since nickel-containing stainless steel has to use a large amount of cold material such as stainless steel scrap, ferrochrome, ferronickel, etc., an arc furnace has been used for melting. On the other hand, with regard to chromium-based stainless steel, a method has been established in which a converter is used and ferronickel is melted and melted using hot metal as the iron source. -Melting was possible at cost.

  As described above, the production process of stainless steel is differentiated depending on whether it is chromium-based stainless steel or nickel-containing stainless steel, but the production of stainless steel is differentiated because the production lot is small. There was a problem that the yield and production efficiency were extremely low.

  Also, in the casting process of stainless steel, continuous casting is adopted for the purpose of improving the yield and production efficiency, but in order to maximize the efficiency of continuous casting, continuous continuous casting operation is desired, Since it takes a long time to dissolve a cold iron source such as scrap in an arc furnace and ferrochrome in a converter, the supply timing of the molten steel required for continuous casting and the discharge from the converter or arc furnace There was also a problem that the steel timing did not match.

  In view of such circumstances, a medium-carbon high-chromium molten metal obtained by melting a solid raw material containing high-carbon ferrochrome in an oxidizing atmosphere is electrically heated by a converter-like reaction vessel that is a first melting furnace. By moving to a holding furnace, melting the solid metal raw material such as scrap and ferronickel while heating this molten metal, and refining the molten metal thus obtained in a second smelting furnace having a finishing decarburization function A method for melting stainless steel that solves the above problem has been proposed (see, for example, Patent Document 1).

  However, the technique described in Patent Document 1 melts FeCr and scrap using the first melting furnace as an oxidizing atmosphere. In such an oxidizing atmosphere, the oxidation loss of Cr becomes large, so it is difficult to dissolve Cr ore, which is a Cr source that is even cheaper than scrap, and slag, dust, sludge, etc. containing Cr. Become. In addition, the first melting furnace can be used as a reducing atmosphere, and in addition to the Cr ore and Cr-containing slag, dust, sludge, scrap can also be dissolved in large quantities at the same time. The problem becomes longer and the time to reach the reduction temperature also becomes longer, so that it is impossible to produce molten iron containing Cr in time for the pitch of the continuous casting.

  In order to solve the above-mentioned conflicting problems, a method different from the technique described in Patent Document 1 has been proposed. As shown in FIG. 6, the Cr-containing molten iron obtained by melting Cr molten iron mainly using Cr ore, Cr-containing slag, dust, and sludge as the Cr source and the first melting furnace as the reducing atmosphere. Is held in a molten metal holding furnace having a heating function, and scrap is melted in the molten metal holding furnace, and Cr-containing molten iron is supplied to a decarburizing and refining apparatus in the next process according to the refining schedule (patent) Reference 2). In the example shown in FIG. 6, a converter-type smelting reduction furnace and a vertical furnace-type smelting reduction furnace filled with lump coke are used together as the first melting furnace, and a normal converter is used as a decarburization refining furnace. In addition, a vacuum decarburizer (VOD), which is a secondary decarburization furnace, is also used. According to the method described in Patent Document 2, the molten steel is supplied to a continuous casting machine that performs so-called “continuous casting” without interruption while making the most of an inexpensive Cr source for melting high Cr molten iron. Can do. In this case, in order to melt nickel-containing stainless steel, Ni source metal nickel, scrap, and the like are charged in the molten metal holding furnace and the second melting furnace. This is because if the Ni source is melted in the process before the molten metal holding furnace, the Ni concentration in the molten metal holding furnace increases, which hinders the subsequent melting of Cr-based stainless steel.

On the other hand, typical nickel metal as an expensive Ni source is generally several times more expensive than FeCr, which is an expensive Cr source, and in terms of cost, stainless steel with a particularly high nickel content. In order to melt, it is very important to use a large amount of inexpensive Ni source (for example, Ni-containing stainless steel scrap, nickel sludge, etc.). However, in the technique of Patent Document 1, it is difficult to dissolve Cr ore, Cr-containing slag, etc., which are inexpensive Cr sources. On the other hand, in the technique of Patent Document 2, emphasis is placed on mass use of inexpensive Cr sources. Therefore, the Ni content varies greatly, and the inexpensive Ni source cannot be used in large quantities. Therefore, the present situation is that there is no melting method using a large amount of inexpensive Ni source and Cr source at the same time for high nickel-containing stainless steel.
Sho 57-161020 JP 2003-155515 A

  In view of such circumstances, the present invention supplies the obtained nickel-containing / stainless steel molten steel to a continuous casting machine that performs so-called “continuous casting” without interruption even if inexpensive Cr sources and Ni sources are used in a larger amount than before. The object is to provide a method for melting possible nickel-containing stainless steel.

  The inventor has intensively studied to achieve the above object, and the results have been embodied in the present invention.

  That is, the present invention is obtained by melting Cr-containing molten iron in a reducing atmosphere using one or more of an iron source, Cr ore, Cr-containing slag, dust, and sludge in a first melting furnace in a reducing atmosphere. The molten iron containing Cr is held in a molten metal holding furnace having a heating function, and then the molten iron containing Cr is supplied to the second melting furnace in accordance with the refining schedule in the second melting furnace in the next step. When performing decarburization and component adjustment, the Cr-containing molten iron held in the molten metal holding furnace is transferred to another melting furnace in accordance with the refining schedule of the second melting furnace, and an inexpensive Ni source is input. In this method, the nickel-containing stainless steel is melted by melting and adding Ni to the Cr-containing molten iron and then supplying it to the second melting furnace to decarburize and adjust the components.

  In this case, the another melting furnace may be the first melting furnace. The second melting furnace is preferably a converter and / or a vacuum decarburizer.

  According to the present invention, it is possible to supply the obtained nickel-containing / stainless steel molten steel without interruption to a continuous casting machine that performs so-called “continuous casting” by using a large amount of inexpensive Cr source and Ni source. Similarly, stainless steel not containing nickel can be continuously supplied to the continuous casting machine without interruption.

  Hereinafter, the best embodiment of the present invention will be described based on the background of the invention.

  In order to dissolve a large amount of inexpensive Ni source in Cr-containing molten iron, as in the prior art, if Ni source is input by a decarburization refining apparatus, it cannot meet the demand for a continuous casting machine that performs “continuous casting”. Inexpensive Ni sources not only vary in Ni content, but also many are low, so it takes time to melt. Therefore, in order to perform “continuous casting”, it is necessary to set an upper limit on the input amount.

  Therefore, the inventor reviewed the manufacturing process of the molten stainless steel and thought that it would be sufficient to use another melting furnace having an action of melting the Ni source in order to melt the cheap Ni source in a larger amount. . That is, instead of supplying the Cr-containing molten iron stored in the molten metal holding furnace directly from the molten metal holding furnace to the decarburization refining apparatus, it is transferred to another melting furnace at a timing earlier than the conventional refining schedule, A desired amount of Ni is dissolved in advance in the Cr-containing molten iron. This is because the Cr-containing molten iron containing Ni can be supplied through the decarburizing and refining device without delaying the “continuous casting” in the continuous casting machine.

  As another melting furnace in the present invention, any furnace may be used as long as it can dissolve Ni into Cr-containing molten iron under a reducing atmosphere so as not to oxidize Cr and Ni in molten iron. Specifically, it is preferable to replace the existing converter type smelting reduction furnace that performs smelting reduction of Cr ore or the like with another melting furnace referred to in the present invention. This is because the equipment cost is unnecessary and it is economical. The process according to the present invention in that case is as shown in FIG. That is, in a conventional stainless steel production line indicated by a solid arrow, a converter-type smelting reduction furnace is used as another melting furnace, and Cr-containing molten iron is transferred from the molten metal holding furnace as indicated by a dotted arrow. It moves to a smelting reduction furnace, throws in an inexpensive Ni source, dissolves Ni, and immediately supplies the obtained Cr-containing molten iron containing Ni to the decarburization refining apparatus to perform decarburization and component adjustment. . In the present invention, when the Ni source is melted in such another melting furnace, the Cr source may be simultaneously added to the melting furnace in addition to the Ni source to further melt Cr. . This is because Cr does not adversely affect the dissolution of Ni.

  In carrying out the present invention, a converter, that is, a top blowing converter or a top bottom blowing converter may be used as the decarburization refining apparatus. However, when stainless steel such as low carbon and extremely low carbon is desired, the molten steel discharged from the converter may be further decarburized using a vacuum decarburizer (eg, VOD, RH, etc.). preferable.

  Furthermore, in the present invention, it is preferable to use a converter type smelting reduction furnace and a vertical smelting reduction furnace filled with lump coke as the first melting furnace. The converter-type smelting reduction furnace uses FeCr and Cr ore as the Cr source, and the vertical smelting reduction furnace uses Cr-containing slag, dust, sludge, and other Cr sources as excellent sources for melting Cr-containing molten steel. Because.

  In addition, in the present invention, it is preferable that the molten metal holding furnace has a heating function to melt the scrap. The amount of scrap input to the first melting furnace can be reduced, the amount of heat supplied for scrap melting in the first melting furnace is reduced, the time required for heating is shortened, and the aforementioned Cr ore, slag, This is because the input amount of inexpensive Cr sources such as dust and sludge can be increased.

The present invention was implemented in a form in which the vertical smelting reduction furnace was used in combination with the process shown in FIG. The melting converter-type smelting reduction furnace is a so-called “top bottom blowing converter” furnace having a furnace capacity of 180 tons and provided with a lance for blowing oxygen gas upward and tuyere for blowing oxygen gas to the bottom. As a result, molten iron, Cr ore, and charcoal were used as the main raw materials to perform smelting reduction to produce Cr-containing molten iron. In addition, since this furnace melt | dissolves Ni in the Cr-containing molten iron transferred according to the refining schedule from the molten metal holding path furnace, it also gave the role as "another melting furnace" as used in the present invention. The vertical smelting reduction furnace is a known so-called “shaft furnace” filled with lump coke and having a furnace capacity of 140 m ³ . As a result, slag, dust, and sludge, which are inexpensive chromium sources, were melted and reduced to produce molten iron containing Cr. The molten metal holding furnace was capable of holding 1000 tons of Cr-containing molten iron previously melted in a converter-type smelting reduction furnace and a vertical smelting reduction furnace. Moreover, as the decarburization refining apparatus, the above bottom bottom blowing type converter having a furnace capacity of 180 tons and decarburization by so-called "secondary refining", vacuum degassing capable of accommodating a ladle with a capacity of 180 tons. A device (eg, VOD) was also utilized. The obtained molten stainless steel containing 8% by mass of Ni, 18% by mass of Cr and 0.05% by mass of C is obtained by a steel vertical slab (slab) having a thickness of 200 mm and a width of 1200 mm using a normal vertical / curved type continuous casting machine. It was done.

  The operation contents and conditions for performing the smelting reduction of the Cr source, the decarburization of the Cr-containing molten iron (in the case of including Ni), and the component adjustment were carried out by a well-known method. 3 is compared with the usage ratio of the expensive one (FeCr, metal Ni) and the cheap one (for example, when implemented in the process shown in FIG. 6) and shown in FIG. 3 and FIG. Keep it. According to the present invention, as shown in FIG. 4, it is apparent that the usage ratio of the inexpensive Ni source has been improved. In addition, the Ni source input position is another melting furnace (converter-type smelting reduction furnace) in the practice of the present invention, and in the conventional operation, the molten metal holding furnace and the decarburization refining apparatus are the top bottom blowing converter. is there.

  In addition, FIG. 2 shows the flow of molten iron and molten steel at the time of carrying out the present invention, and Cr-containing molten iron containing Ni can be continuously supplied to the decarburizing and refining apparatus, as in the case where nickel is not contained. It is clear that “continuous casting” of molten stainless steel has become possible. Further, according to the cost index obtained by setting the costs of Ni and Cr of the conventional method as 100, as shown in FIG.

It is process drawing explaining the melting method of the nickel containing stainless steel which concerns on this invention. It is a flow of molten iron and molten steel during the implementation of the present invention. It is a figure which shows the use ratio of an expensive and cheap Cr source. It is a figure which shows the usage-ratio of an expensive and cheap Ni source. It is the figure which compared the manufacturing cost of nickel-containing stainless steel in the case of implementation of this invention, and implementation of conventional operation. It is a figure which shows the conventional process which manufactures chromium-containing molten iron.

Claims (3)

In the first melting furnace, melt iron containing Cr in a reducing atmosphere using one or more of iron source, Cr ore, Cr-containing slag, dust, and sludge as the Cr source, and heat the resulting Cr-containing molten iron After holding in the molten metal holding furnace having the function, the Cr-containing molten iron is supplied to the second melting furnace in accordance with the refining schedule in the second melting furnace in the next step to decarburize and adjust the components. When performing, the Cr-containing molten iron held in the molten metal holding furnace is transferred to another melting furnace in accordance with the refining schedule of the second melting furnace, and an inexpensive Ni source is charged and melted to dissolve the Cr-containing molten iron. A method for melting nickel-containing stainless steel, wherein Ni is contained in molten iron and then supplied to the second melting furnace to decarburize and adjust components. The method for melting nickel-containing stainless steel according to claim 1, wherein the another melting furnace is the first melting furnace. The method for melting nickel-containing stainless steel according to claim 1 or 2, wherein the second melting furnace is a converter and / or a vacuum decarburization apparatus.

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