JP6604062B2 - Gas melting method for metal melting / smelting furnace and gas blowing nozzle for metal melting / smelting furnace - Google Patents

Description

  The present invention relates to a gas blowing method for a metal melting / smelting furnace and a gas blowing nozzle for a metal melting / smelting furnace.

  For stirring molten iron in a melting / smelting furnace such as a melting furnace or a converter, gas blowing from the bottom or side wall of the furnace is used. In general, a nozzle made of a heat and oxidation resistant material (for example, stainless steel (SUS) or the like) containing a large amount of Cr, Ni or the like embedded in a refractory is used for such gas injection.

  In addition, since the gas blowing is performed under a high temperature condition, the nozzle is made while ensuring the cooling state of the nozzle so that the nozzle made of SUS or the like does not melt or wear out. Here, in order to maintain cooling conditions and suppress melting and wear of the nozzle, a protective layer with a fixed amount of iron (solidified iron, commonly known as mushroom) solidified in a molten iron bath is attached to the tip of the nozzle It is known to form. In order to stabilize the operation, it is important how to stably maintain the mushroom at the nozzle tip.

  Conventionally, the generation and maintenance of mushrooms was controlled by blowing a large amount of cooling gas. In addition, as disclosed in Patent Documents 1 to 3 below, many proposals have been made to change the nozzle material (composition, melting point) as a method for suppressing wear of the stirring nozzle or tuyere. ing.

JP-A-57-76117 JP 58-91111 A JP 59-50111 A

  However, depending on the conditions of the molten iron bath, the techniques disclosed in Patent Documents 1 to 3 described above and the control based on the gas cooling ability may not be sufficient to suppress the dissolution and wear of the nozzle. In particular, under conditions where the C concentration in the molten iron bath is high, the temperature of the molten iron bath generally decreases, and the melting temperature of the nozzle increases with respect to the temperature of the molten iron bath. Melting and welding hardly occur between the mushroom and the nozzle. In such a case, the mushroom is likely to be peeled off from the nozzles due to fluctuations in the blowing gas pressure, mechanical shocks during scrap charging, or thermal shocks associated with changes in furnace temperature.

  Therefore, in order to maintain the cooling conditions and suppress the melting / wearing of the nozzles, it is important to control the cooling state of the nozzles while considering the temperature conditions of the molten iron bath. In addition to cooling the nozzle, it was important to stably control the melting / welding state between the nozzle and the mushroom.

  The present invention has been made based on the above improvement viewpoint. Based on various test experiments and considerations, the inventors of the present invention can significantly reduce wear of the stirring nozzle due to mushroom peeling by appropriately controlling the material of the stirring nozzle according to the temperature conditions of the molten iron bath. It came to obtain the knowledge that is possible.

  That is, an object of the present invention is to provide a metal melting / smelting furnace gas blowing method and a metal melting / smelting furnace gas blowing nozzle having high durability and stability.

  In order to solve the above-mentioned problems, the present inventors control the melting point (liquidus temperature) of the stirring nozzle to a predetermined range according to the temperature range of the molten iron bath, based on the above-described conventional problems. By doing so, it has been found that mushrooms can be stably generated at the tip of the nozzle, and the durability of the nozzle can be greatly improved. Furthermore, as a result of various test experiments and examinations, the present inventors obtained the following knowledge and completed the present invention.

  For example, in Patent Document 1 described above, the temperature of the molten iron is monitored, and when the molten iron temperature becomes equal to or higher than the melting point of the nozzle or slightly lower than the melting point, the tuyere is increased by increasing the ratio of the non-oxidizing gas. A technique for suppressing melting damage of the steel has been proposed. In the technique disclosed in Patent Document 1, since a thermal load of the nozzle is reduced by blowing a non-oxidizing gas, a certain effect of suppressing wear of the nozzle is recognized. However, Patent Document 1 does not disclose the stable formation of mushrooms that play a major role in protecting the nozzle. In order to suppress the wear of the nozzle, it is necessary to ensure the connectivity between the generated mushroom and the nozzle, but it is not possible to maintain a stable mushroom adhesion state simply by flowing a cooling gas. This leads to an increase in wear rate.

In Patent Document 2, the material of the nozzle inner tube is made of copper or copper alloy, and the material of the nozzle outer tube is made of a copper alloy having a tensile strength of 35 kg / mm ² or more, thereby improving thermal conductivity. In addition, a technique for ensuring the strength of the nozzle is disclosed. As a result, mushrooms around the tuyere can be generated firmly, so that melting and blocking of the tuyere can be prevented. According to the technique disclosed in Patent Document 2, a good result can be obtained because a large and large mushroom can be formed by using copper having high heat conductivity or a copper alloy having high strength. However, since the melting point of the nozzle made of copper or copper alloy is significantly lower than the temperature of the molten iron, when the mushroom is peeled off from the nozzle, it is inevitable that the wear of the nozzle proceeds greatly.

  In Patent Document 3 above, carbon steel or stainless steel, which is a material having a high melting point and heat deformation, is used for the outer tube of the nozzle, and in addition to the high melting point and heat deformation, an acid resistance is used for the inner tube of the nozzle. A technology has been proposed to reduce the tuyere melting loss and improve the furnace bottom life by using a material containing 50% or more of Ni, Co or Ni + Co, which is a material having high chemical conductivity and high thermal conductivity. . The technique disclosed in Patent Document 3 is characterized in that the material used for the inner pipe has oxidation resistance and high thermal conductivity, but even if only the oxidation resistance and thermal conductivity are controlled, It is difficult to stably form mushrooms and suppress peeling. Therefore, with the technology disclosed in Patent Document 3, it is difficult to avoid a significant increase in wear rate when mushroom peeling occurs.

  With respect to these problems, in the present invention, it is possible to avoid an increase in nozzle wear due to mushroom peeling by stabilizing the connectivity between the nozzle and the mushroom. The mushroom formed at the nozzle tip portion by the cooling gas increases the bondability by welding the joint portion with the nozzle. However, if the melting point of the nozzle is higher than the molten iron temperature, the weld bondability is lowered.

  Generally, in converter blowing, a stainless steel nozzle containing Cr or Ni at a high concentration such as SUS304 is often used. Conventionally, the molten iron temperature at the end of blowing is increased to near 1700 ° C. and becomes higher than the melting point of SUS304 (about 1400 to 1460 ° C.). In such a case, although the molten iron is cooled by the cooling gas at the tip of the nozzle, there is also molten iron at a temperature higher than the melting point of the nozzle, so that the mushroom formed by the nozzle and the cooling gas is welded and bonded. Mushrooms were stable and easy to form.

  On the other hand, in recent years, with the expansion of the amount of hot metal preliminary treatment, there has been an increase in treatments for blowing in a lower temperature range. In such a case, even at the end of blowing, the molten iron temperature is as low as about 1350 to 1400 ° C., which is lower than the melting point of a stainless steel nozzle such as SUS304. The same applies to iron bath melting furnaces and electric furnaces that produce hot metal using scrap as the main raw material. Although the thermal load on the nozzle is smaller than that in converter decarburization blowing, the nozzle and mushroom In terms of welding and bonding, the reaction is difficult to proceed.

  Therefore, in order to improve the welding / bonding property between the nozzle and the mushroom, it is necessary to appropriately control the melting point of the nozzle with respect to the processing temperature range of the molten iron. The inventors of the present invention can improve the welding / bonding property between the nozzle and the mushroom and reduce the wear rate of the nozzle by setting the melting point of the nozzle to be lower than the highest temperature in the molten iron processing temperature range. I found it. Further, the present inventors have found that when the melting point of the nozzle is too low, when the nozzle is newly used or when the mushroom is peeled off, the melt wear amount of the nozzle becomes excessive. Accordingly, it has been found that the melting point of the nozzle does not have to be too low with respect to the processing temperature range of the molten iron and is preferably within a predetermined range.

  The present invention has been completed on the basis of the above findings, and the gist thereof is the selection of the material of the blowing nozzle shown in the following [1] and [4]. Moreover, it is preferably the structure of the blowing nozzle shown in [2] and [3].

[1] The melting temperature TN of the material of the gas blowing nozzle used in the melting and refining of the molten metal and the maximum temperature TM of the molten metal melting bath satisfy the formula (1),
The highest temperature TM is, Ri 1300 ℃ ~1450 ℃ der,
A gas blowing method for a metal melting / smelting furnace, wherein the material of the gas blowing nozzle includes Cr, Ni, and Mo.
0.8 <TN / TM <1.0 Formula (1)

  [2] The gas blowing method for a metal melting / smelting furnace according to [1], wherein the member made of the material having the melting temperature TN is used for a part of the gas blowing nozzle.

[3] The gas blowing nozzle is a double nozzle including an inner nozzle and an outer nozzle,
The gas blowing method for a metal melting / smelting furnace according to [2], wherein the member having the melting temperature TN is used for the outer nozzle.

[4] A gas injection nozzle used for melting and refining molten metal,
The melting temperature TN of the material of the gas blowing nozzle and the maximum temperature TM of the molten metal melting bath satisfy the formula (1),
The highest temperature TM is, Ri 1300 ℃ ~1450 ℃ der,
A gas blowing nozzle for a metal melting / smelting furnace, wherein the material of the gas blowing nozzle includes Cr, Ni, and Mo.
0.8 <TN / TM <1.0 Formula (1)

  In the present invention, by selecting the material of the blowing nozzle using the above index, mushrooms are used in various furnaces having greatly different processing temperature ranges such as converters, hot metal pretreatments, iron bath melting furnaces, electric furnaces, etc. It is possible to promote the stable formation of the nozzle and suppress the nozzle wear. Therefore, according to the present invention, in the metal melting / smelting furnace, it is possible to maintain the stable adhesion state of the solidified iron generated at the tip of the blowing nozzle that supplies the stirring gas. This makes it possible to perform stirring with high durability and stability in a metal melting / smelting furnace.

It is the graph which plotted the iron adhesion amount with respect to the molten iron temperature TM. It is the graph which plotted the iron adhesion amount with respect to the difference of molten iron temperature TM and nozzle melting | fusing point TN. It is the graph which evaluated the nozzle abrasion property with respect to the parameter | index which divided | segmented nozzle melting | fusing point TN with the molten iron temperature TM. It is the schematic diagram which showed an example of the nozzle structure which concerns on one Embodiment of this invention.

  The present invention relates to a method for melting or refining a metal, and more particularly to a method for stably cooling a blowing nozzle (hereinafter also simply referred to as a nozzle) for supplying a stirring gas in stirring a molten iron bath.

  The present inventors made various nozzles with different compositions for the material of the stirring nozzle for stirring in the metal melting / smelting furnace, and performed immersion in molten iron and a gas blowing test. From the results of these tests, the gas blowing method having high durability and stability shown in [1] to [3] described above, and the gas blowing nozzle having high durability and stability shown in [4] described above. Was completed. Hereinafter, the reason why the present invention is defined in the above range will be described in detail, and the preferable range of the present invention will be described in detail.

a) Influence of nozzle material on nozzle durability Conventionally, a nozzle made of a material containing at least one of Cr and Ni has been used as a blowing nozzle for gas stirring in consideration of oxidation resistance. . Such a blowing nozzle is mainly used in a refining furnace such as a converter. In a refining furnace or the like, the molten iron temperature at the start of the treatment is low, but in the latter half of the treatment, the molten iron temperature is high and is higher than the melting point of the nozzle.

  Here, the nozzle tip forms a protective layer by adhering mushrooms obtained by solidifying molten iron with the blown gas to maintain durability. In addition, since the molten iron temperature is equal to or higher than the melting point of the nozzle at the end of the process, a part of the nozzle tip is melted to form a strong bonded state with the solidified molten iron.

  On the other hand, in a refining furnace or an iron bath melting furnace having a low processing temperature, the molten iron temperature at the end of the processing is about 1300 to 1450 ° C. Therefore, for example, in a nozzle using SUS304, which is used for general purposes, the nozzle melting point (about 1400 to 1450 ° C.) is often higher than the molten iron temperature. For this reason, a mushroom formed by solidifying molten iron is formed at the nozzle tip, but the connectivity at the nozzle tip is not strong and is easily peeled off by impact during processing.

  Therefore, in order to strengthen the mushroom adhesion, it is necessary to appropriately select the melting point of the nozzle material in accordance with the processing temperature condition of the furnace. In order to clarify the influence of the nozzle material, the present inventors immersed the molten iron in the molten iron for a predetermined time while blowing the gas to the nozzles of different materials under the condition that the temperature of the molten iron was changed. The adhesion of was evaluated.

  Of the materials containing Cr, Ni, Mo, and the like, two types of materials, ie, a material A (melting point 1430 ° C.) and a material B (melting point 1390 ° C.) with different melting points, are used as the nozzle material. The temperature was changed in the range of from 1C to 1250C every 50C. The result of plotting the iron adhesion amount against the molten iron temperature TM is shown in FIG. The iron adhesion amount was determined from the average value of the maximum and minimum diameters of the adhering iron measured from the cross-sectional shape of the adhering iron in the cross section perpendicular to the nozzle length direction.

  In FIG. 1, the data with ● and ▲ indicate that the weldability between the nozzle and the adhered iron is good. Specifically, this state is a state in which the nozzle surface is melted and has a strong bonded state with the attached iron.

  Next, FIG. 2 shows the result of arranging the difference between the molten iron temperature TM and the nozzle melting point TN on the horizontal axis. As shown in FIG. 2, it is understood that the meltability between the nozzle and the adhered iron is good under the condition where the nozzle melting point is lower than the molten iron temperature. Further, it can be seen that the material B having a lower nozzle melting point has a higher iron adhesion amount and can produce a mushroom which is a protective layer of the nozzle in a better state.

  On the other hand, when the nozzle melting point is extremely low, the amount of dissolved nozzle is increased due to high heat load under conditions where mushrooms are not attached (for example, when a new furnace is started, when a nozzle is replaced, or when mushrooms are removed during processing). It will occur. FIG. 3 shows the results of evaluating the nozzle wear resistance under conditions in which the nozzle melting point was greatly changed. FIG. 3 is a graph plotting nozzle wear rate against nozzle melting point / molten iron temperature (TN / TM). The nozzle wear rate was evaluated as the amount of nozzle wear per charge (number of times molten iron was supplied to the furnace), and was measured by inserting a rod-shaped measuring ruler into the nozzle from the rear of the nozzle between charges. .

  As a result of arranging the nozzle melting point TN by an index obtained by dividing the nozzle melting point TN by the molten iron temperature TM, it was found that when TN / TM is 0.8 or less, the amount of wear of the nozzle is remarkably increased. Therefore, the nozzle melting point should be selected as long as the nozzle melting point / molten iron temperature (= TN / TM) is larger than 0.8 and smaller than 1.0. Here, the molten iron temperature is the maximum temperature of the molten iron being processed. A more preferable range of nozzle melting point / molten iron temperature (= TN / TM) is 0.85 or more and 0.95 or less.

  The nozzle melting point TN can be controlled within the above-described range by controlling the amount of additive elements such as Cr, Ni, and Mo contained in the nozzle material, for example. For example, the melting point of the nozzle material tends to decrease as the amount of additive elements such as Cr, Ni, and Mo contained in the nozzle material increases. Therefore, the total content of Cr, Ni, and Mo in the nozzle material is preferably 30% by mass or more. Moreover, it is preferable that a nozzle material contains 15 mass% or more of Cr. Specific examples of such a nozzle material include SUS316 and Hastelloy.

  The structure of the blowing nozzle may be a known blowing nozzle structure, but is preferably a structure described in detail below. Moreover, such a blowing nozzle can be manufactured using a known method.

b) Nozzle structure When the nozzle material is controlled so as to satisfy the nozzle melting point described above, it is important to contain a large amount of additive elements such as Cr, Ni, and Mo in the nozzle material. When the additive element has a relatively low concentration, the strength of the nozzle material can be maintained. However, when the concentration of the additive element is increased, there is a concern that the strength of the nozzle material may be reduced.

Therefore, the entire nozzle may be manufactured with a material that satisfies the above-mentioned nozzle melting point condition, or only a part of the nozzle may be manufactured with a material that satisfies the above-mentioned nozzle melting point condition. For example, when the additive element of the nozzle material becomes a high concentration, a main nozzle is manufactured with a high-strength material such as SUS304 (melting point 1400 to 1450 ° C.), and a material with a higher alloy composition is embedded in a part of the nozzle. It is also possible to exert a desired effect by performing such processing. Thus, high alloy low melting point material of the embedding free that part of the nozzle, the strength of the entire nozzle while maintaining, by high-alloy low melting point materials embedded to maintain the weldability of the nozzle and the mushroom It becomes possible.

  FIG. 4 shows an example of application of the above method. FIG. 4 is a schematic view showing an example of a cross section obtained by cutting a nozzle according to an embodiment of the present invention along a plane perpendicular to the axial direction. As shown in FIG. 4, for example, the nozzle 1 is a double nozzle including an inner nozzle 100 made of SUS304 and an outer nozzle 200 made of SUS304. Further, an embedded material 300 made of a high alloy material (for example, Hastelloy (melting point: about 1290 ° C.)) is embedded in a part of the outer nozzle 200. According to such a structure, it is possible to improve the adhesion of mushrooms while maintaining the strength of the entire nozzle under high temperature conditions.

  In order to confirm the effect of the nozzle having high durability according to the present invention, the following examples and comparative examples were tested and the results were evaluated.

  The material of the bottom blowing double nozzle was changed in an iron bath melting furnace, and the durability evaluation was performed. In the iron bath melting furnace, raw materials containing scrap and iron oxide were charged into a hot metal bath for melting.

  In the bottom blown double tube nozzle, the inner nozzle uses material A (melting point 1430 ° C.), and the outer nozzle uses material B (melting point 1390 ° C.), material C (melting point 1330 ° C.), or material D (melting point 1270 ° C.). ) Were used to manufacture nozzles according to Examples 1 to 3, and their durability was evaluated. Also, the inner nozzle uses material A (melting point 1430 ° C.), the outer nozzle uses material A (melting point 1430 ° C.), and a nozzle partially embedded with material D (melting point 1270 ° C.). The nozzle which concerns on Example 4 which has a structure shown in FIG. 4 was manufactured, and durability was evaluated.

  For comparison, in the bottom blown double tube nozzle, the material of the inner nozzle is material A (melting point 1430 ° C.), and the material of the outer nozzle is material A or material E (melting point 1090 ° C.). The nozzles according to Comparative Examples 1 and 2 were manufactured, and the durability of the nozzles was evaluated.

  Here, fine gas coal was flowed from the inner nozzle using nitrogen gas as a carrier gas, and nitrogen gas was flowed from the outer nozzle as cooling gas. The temperature of the molten iron reached 1400 to 1450 ° C. after the treatment, and the temperature was lower than this temperature during the dissolution treatment. Therefore, the temperature of the molten iron reached after the treatment was set as the molten iron temperature TM.

  Table 1 shows the results of evaluating the durability of the nozzle.

  As can be seen from the results in Table 1, it is understood that the wear rate of the nozzle can be reduced by setting TN / TM within the range of 0.8 to 1.0. Further, in Example 4 in which the material C (melting point 1330 ° C.) is embedded in a part of the outer nozzle as shown in FIG. 4, the wear rate is slightly increased compared to Example 2 in which the entire outer nozzle is changed to the material C. It can be seen that a sufficient effect can be obtained.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  In the above description, the melting point TN of the nozzle material is controlled so that the nozzle melting point / molten iron temperature (TN / TM) satisfies the relationship of the formula (1). However, the present invention is not limited to this example. For example, it goes without saying that the nozzle melting point / molten iron temperature (TN / TM) may satisfy the relationship of the formula (1) by controlling the molten iron temperature TM. In such a case, for example, the molten iron temperature TM is preferably controlled in the range of 1300 ° C to 1450 ° C.

1 nozzle 100 inner nozzle 200 outer nozzle 300 embedding material

Claims (4)

The melting temperature TN of the material of the gas blowing nozzle used in the melting and refining of the molten metal and the maximum temperature TM of the molten metal melting bath satisfy the formula (1),
The highest temperature TM is, Ri 1300 ℃ ~1450 ℃ der,
A gas blowing method for a metal melting / smelting furnace, wherein the material of the gas blowing nozzle includes Cr, Ni, and Mo.
0.8 <TN / TM <1.0 Formula (1)   2. The gas blowing method for a metal melting / smelting furnace according to claim 1, wherein the member having the melting temperature TN is used for a part of the gas blowing nozzle. The gas blowing nozzle is a double nozzle comprising an inner nozzle and an outer nozzle;
The gas blowing method for a metal melting / smelting furnace according to claim 2, wherein the member made of the material having the melting temperature TN is used for the outer nozzle. A gas injection nozzle used for melting and refining molten metal,
The melting temperature TN of the material of the gas blowing nozzle and the maximum temperature TM of the molten metal melting bath satisfy the formula (1),
The highest temperature TM is, Ri 1300 ℃ ~1450 ℃ der,
A gas blowing nozzle for a metal melting / smelting furnace, wherein the material of the gas blowing nozzle includes Cr, Ni, and Mo.
0.8 <TN / TM <1.0 Formula (1)

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