JP2007231398A - Method for refining molten steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a refining method which can maximize the amount of scrap iron to be used, which contains at least one element among Ni, Mo and Cu as an alloy component, without leaving the scrap iron unmelted, when smelting a molten steel containing at least one element among the alloying elements, by using the scrap iron and molten pig iron as iron sources. <P>SOLUTION: The method for smelting the molten steel containing one or more elements among Ni, Mo and Cu as the alloy component comprises the steps of: charging the scrap iron containing one or more elements among Ni, Mo and Cu as the alloy component to a converter 1 for dephosphorization smelting; subsequently charging the molten pig iron 8 into the converter for dephosphorization smelting to dephosphorize the mixture; and then charging the dephosphorized molten pig iron 10 obtained through the dephosphorization treatment into a converter 4 for decarburization smelting to decarburization-refine the molten pig iron 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a refining process in which hot metal is refined by combining a dephosphorization converter and a decarburization refining converter, and molten steel containing at least one of Ni, Mo and Cu as an alloy component is smelted. More specifically, the present invention relates to a refining method for melting the molten steel by increasing the amount of iron scrap containing Ni, Mo, and Cu as alloy components.

Various elements made of Ni, Cr, Mo, Cu and the like are added to the steel material as alloy components according to the respective applications. Therefore, the iron scrap containing these alloy components is mixed with the recovered iron scrap. The recovered iron scrap is used as a main iron source in the electric furnace steelmaking process, and is also used as an iron source supplementing the hot metal in the converter steelmaking process using blast furnace hot metal as the main iron source. In recent years, the reduction of CO ₂ gas generation amount from the viewpoint of preventing global warming has been desired, since the generation amount of CO ₂ gas is reduced, and also increased the amount of steel scrap in BOF steelmaking Operations are taking place.

  Among these alloy elements contained in iron scrap, Ni, Mo and Cu have a smaller affinity for oxygen than Fe. Therefore, in converter decarburization refining hot metal using oxygen gas, Ni, Mo, and Cu dissolved therein cannot be removed from the hot metal and remain in the molten steel after refining. From the material of the steel material, there are also steel materials that Ni or Mo, Cu is not necessary or cannot be added, so iron scrap containing Ni, Mo, Cu as an alloy component is classified according to the alloying element contained after being recovered, It is used at the time of melting steel materials containing each element as an alloy component.

  In the conventional converter steelmaking process, when using Ni, Mo, Cu contained in iron scrap as raw material for component adjustment, iron scrap containing Ni, Mo, Cu as alloy components is converted into the converter before refining. Then, after the hot metal was charged, oxygen gas was supplied to decarburize and refine the hot metal. And after decarburization refining, based on the analysis results of molten steel in the furnace, in order to compensate for the deficiency of Ni, Mo, Cu, alloy iron, metallic nickel, metallic copper, etc. are added at the time of steel removal from the converter Ingredient adjustment was performed.

  However, in this refining method, if the amount of iron scrap containing Ni, Mo, Cu as an alloy component is excessive, the component specification value will be exceeded, so to prevent this, Ni, Mo, Cu The amount of iron scrap containing as the alloy component was suppressed, and a method of supplementing the deficiency with alloy iron at the time of steelmaking was adopted. That is, the amount of inexpensive iron scrap used as a raw material for component adjustment is suppressed, and expensive alloy iron, metallic nickel, and the like are used. In addition, since converter decarburization has a limit in dephosphorization reaction, the amount of iron scrap with a high phosphorus content is naturally limited.

  By the way, Patent Document 1 proposes a method of efficiently melting a large amount of alloy raw material in a steelmaking process that combines hot metal dephosphorization treatment and hot metal converter decarburization refining. That is, the alloy raw material is placed in an empty hot metal container and heated by the retained heat of the hot metal container, and then the hot metal container receives the hot metal and melts the stored alloy raw material. In this method, the hot metal is dephosphorized in a vessel, and the hot metal is charged into a converter and decarburized and refined. According to the method of Patent Document 1, even if the phosphorus content of the alloy raw material is high, it can be dealt with by dephosphorization treatment, but since the dephosphorization treatment is carried out in the hot metal vessel, the stirring power of the hot metal is not sufficient, If the amount of alloy raw material is increased, the alloy raw material may remain undissolved. If the alloy raw material remains undissolved, the alloy element concentration in the hot metal is estimated to be low, and the alloy raw material to be blended in the converter decarburization refining in the next step becomes excessive, which may exceed the component standard value.

In Patent Document 2, when one of the two converter-type furnaces is a dephosphorization furnace and the other is a decarburization furnace, when molten steel is produced from hot metal, light iron scrap is loaded into the dephosphorization furnace. A method is disclosed in which molten iron is dephosphorized to melt light-weight iron scrap in the hot metal, and the resulting dephosphorized hot metal is refined in a decarburizing furnace to melt the molten steel. However, the lightweight iron scrap in Patent Document 2 is a simple iron source, and does not disclose anything about using the alloy component in the lightweight iron scrap as a component adjusting raw material.
JP-A-5-171243 Japanese Patent Laid-Open No. 1-147011

  As described above, when melting a molten steel containing at least one of Ni, Mo, and Cu as an alloy component, in the conventional method, one or more of Ni, Mo, and Cu are alloyed. There has been a problem that iron scrap contained as a component is not sufficiently effectively used as a raw material for component adjustment, or that iron scrap remains undissolved when it is tried to be used effectively.

  The present invention has been made in view of the above circumstances. The object of the present invention is to use iron scrap containing at least one of Ni, Mo, and Cu as an alloy component as a raw material for component adjustment. When molten steel containing at least one of Ni, Mo and Cu as an alloy component is melted from scrap and hot metal produced at a hot metal production facility such as a blast furnace, unmelted iron scrap is generated. The present invention is to provide a molten steel refining method capable of maximizing the use amount of the iron scrap without making it.

  The method for refining molten steel according to the first invention for solving the above-mentioned problem is to install iron scrap containing one or more of Ni, Mo and Cu as an alloy component in a dephosphorization refining converter. Then, hot metal is charged into the dephosphorizing and refining converter to carry out a dephosphorizing process, and then the dephosphorized hot metal obtained by the dephosphorizing process is charged into the decarburizing and refining converter. Decarburization refining is performed, and molten steel containing one or more of Ni, Mo, and Cu as an alloy component is melted.

  The method for refining molten steel according to a second invention is characterized in that, in the first invention, the iron scrap is a high phosphorus-containing iron scrap having a phosphorus content of 0.2% by mass or more.

  The method for refining molten steel according to the third invention is the deficiency relative to the target value in the first or second invention based on the component analysis values of Ni, Mo, Cu of the dephosphorized hot metal obtained by the dephosphorization treatment. In order to compensate for this, the decarburizing and refining converter is charged with iron scrap containing one or more of Ni, Mo and Cu as an alloy component.

  According to the present invention, molten steel containing one or more of Ni, Mo and Cu as an alloy component is melted by a refining method combining a converter for dephosphorization and a converter for decarburization and refining. At the time of dephosphorization treatment in a dephosphorization converter, iron scrap containing one or more of Ni, Mo and Cu as alloy components is charged at the time of melting from The stirring power of the hot metal in the refining converter is strong, the iron scrap is melted without being melted, and a large amount of iron scrap can be used as a raw material for component adjustment. Moreover, since it is premised on the dephosphorization treatment, even high phosphorus-containing iron scrap having a high phosphorus content can be used as a raw material for component adjustment without any problems. Furthermore, based on the component analysis values of Ni, Mo, and Cu in the hot metal after the dephosphorization treatment, the deficiency in the converter for decarburization and refining is reduced to one or more of Ni, Mo, and Cu as alloy components. When supplemented with iron scrap, most of the alloy components of Ni, Mo, and Cu can be satisfied with the iron scrap, and the use of expensive alloy iron or metallic nickel can be suppressed. In addition, since the iron scrap is added in two stages of a dephosphorization refining converter and a decarburization refining converter, the component adjustment is performed smoothly and there is no fear of component removal.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic view showing a process of a molten steel refining method according to the present invention.

  In FIG. 1, 1 is a converter for dephosphorizing and refining, 4 is a converter for decarburizing and refining, 7 is a hot metal vessel, 8 is hot metal, 10 is dephosphorized hot metal, and 11 is molten steel. In the present invention, first, in the converter 1 for dephosphorization and refining, iron scrap containing one or more of Ni, Mo and Cu as an alloy component is added to the hot metal 8. The dephosphorization treatment is performed, and then decarburization refining is performed in the decarburization refining converter 4 using the dephosphorization molten iron 10 obtained by the dephosphorization treatment, so that one or two of Ni, Mo and Cu are used. Molten steel 11 containing at least a seed as an alloy component is produced. That is, the alloy component of Ni, Mo, and Cu contained in the iron scrap is used as the alloy component of the molten steel 11 to be melted. In this case, as a matter of course, iron scrap containing a component not included in the molten steel 11 as an alloy component is not used. That is, when the molten steel 11 contains only Mo as an alloy component, iron scrap containing Ni and Mo as an alloy component is not used.

  A small amount of Ni, Mo, Cu is also contained in the steel produced by the blast furnace-converter pig steel integrated method. Therefore, “one or more of Ni, Mo, Cu” in the present invention is used. "Scrap containing iron as an alloy component" and "molten steel containing one or more of Ni, Mo, Cu as alloy components" are any one of Ni, Mo, Cu or It is iron scrap and molten steel containing 0.03% by mass or more of two or more types. Iron scrap and molten steel having a content of these elements of less than 0.03% by mass, that is, iron scrap and molten steel containing these elements as inevitable impurity components are outside the scope of the present invention.

  The hot metal 8 used in the present invention is a hot metal manufactured in a hot metal manufacturing facility such as a blast furnace, and the hot metal 8 manufactured in the hot metal manufacturing facility is received by a hot metal transport container (not shown) such as a hot metal pan or a torpedo car. Then, the hot metal 8 is conveyed to the dephosphorization refining converter 1.

In order to efficiently perform the dephosphorization process with a small amount of dephosphorizing refining agent, Si in the hot metal 8 may be removed in advance (referred to as “pre-desiliconization process of hot metal”) before the dephosphorization process. When performing the preliminary desiliconization treatment, it is preferable to reduce the Si content of the hot metal 8 to 0.2% by mass or less, desirably 0.1% by mass or less. As means for lowering the Si content of the hot metal 8 to this range, an oxygen source such as oxygen gas or iron oxide is supplied to the hot metal 8 manufactured by the hot metal manufacturing facility, and Si contained in the hot metal 8 by these oxygen sources. Can be used to forcibly remove Si as an oxide. When the preliminary desiliconization process is performed, the generated slag (SiO ₂ ) is removed before the dephosphorization process.

  The hot metal 8 thus obtained is subjected to dephosphorization treatment in the dephosphorization refining converter 1. In the present invention, it is necessary to perform a dephosphorization process using the converter 1 for dephosphorization and refining. The dephosphorization treatment can be performed in a hot metal transfer container such as a hot metal ladle or a torpedo car. However, the dephosphorization refining converter 1 has a larger freeboard than these hot metal transfer containers, and the hot metal 8 is vigorously stirred. This is because the dephosphorization process can be performed quickly with a small amount of the dephosphorizing refining agent used, and the iron scrap to be charged is rapidly dissolved because the stirring power is large.

  The dephosphorizing refining converter 1 is provided with an upper blowing lance 2, and oxygen gas is blown from the upper blowing lance 2 toward the bath surface of the hot metal 8. Further, a stirring gas blowing tuyere 3 is installed at the bottom of the dephosphorizing and refining converter 1 so that stirring gas such as nitrogen gas or rare gas is blown into the hot metal 8 from the stirring gas blowing tuyere 3. It has become. Further, a raw material such as quick lime, fluorite, bauxite, and iron ore is stored on the furnace of the dephosphorizing and refining converter 1 and the raw material is supplied from the hopper to the dephosphorizing and refining converter 1. A raw material cutting device (not shown) is installed.

  Using the dephosphorization refining converter 1 having such a configuration, the hot metal 8 is dephosphorized.

  First, iron scrap containing one or more of Ni, Mo, and Cu as an alloy component is charged into the dephosphorization refining converter 1. The amount of iron scrap charged is within a range of 90% or less with respect to target values within the Ni, Mo and Cu component standard ranges of the molten steel 11 finally melted in the decarburizing and refining converter 4. Set with. That is, even if Ni, Mo, and Cu in the iron scrap are recovered at a yield of 100%, the iron scrap is set so that the target value of each standard component of Ni, Mo, and Cu in the molten steel 11 is 90% or less. Limit the amount of charge. Even if the iron scrap contains a high concentration of phosphorus, there is no problem because it is dephosphorized. Specifically, even if the iron scrap is a high phosphorus content iron scrap containing 0.2 mass% or more of phosphorus, as long as it contains one or more of Ni, Mo, Cu as an alloy component, the component It can be used as a raw material for adjustment. When the phosphorus concentration is less than 0.2% by mass, dephosphorization can be performed by decarburization and refining in the converter of the next step without performing dephosphorization and there is no problem.

  Next, the hot metal 8 is charged into the dephosphorization refining converter 1. As the hot metal 8 to be used, any composition can be used, and a preliminary desulfurization process or a preliminary desiliconization process may be performed before the dephosphorization process. Incidentally, the main chemical components of the hot metal 8 before the dephosphorization treatment are: C: 3.8 to 5.0% by mass, Si: 0.3% by mass or less, S: 0.05% by mass or less, P: 0.00%. It is about 08-0.2 mass%. However, if the amount of slag 9 produced in the dephosphorization refining converter 1 during the dephosphorization process increases, the dephosphorization efficiency decreases. As described above, the produced slag 9 is reduced to increase the dephosphorization efficiency. Therefore, it is preferable to previously reduce Si in the hot metal to 0.2% by mass or less, desirably 0.1% by mass or less by preliminary desiliconization treatment. Moreover, if the hot metal temperature is in the range of 1200 to 1350 ° C., dephosphorization can be performed without any problem.

After the molten iron 8 is charged, a predetermined amount of a dephosphorizing refining agent such as quick lime, converter slag, and sodium carbonate is placed on top. Before and after the introduction of the dephosphorizing refining agent, oxygen gas is supplied from the top blowing lance 2 while blowing the stirring gas from the stirring gas blowing tuyere 3. In addition, when the blowing function of the dephosphorizing refining agent is added to the upper blowing lance 2, it may be blown and added from the upper blowing lance 2 in place of the upper charging. Further, fluorite (CaF ₂ ), bauxite (Al ₂ O ₃ ) or the like may be added to the dephosphorization refining agent as a hatching accelerator.

The hot metal 8 is vigorously stirred by the stirring gas blown from the stirring gas blowing tuyere 3 and the added dephosphorizing refining agent is also stirred with the hot metal 8, and the dephosphorizing refining agent forms slag 9. Further, the oxygen gas supplied from the top blowing lance 2 reacts with P in the hot metal to form P ₂ O ₅ , and the formed P ₂ O ₅ is quickly absorbed by the slag 9 to remove the hot metal 8. The phosphorus reaction proceeds rapidly. At the same time, iron scrap containing one or more of added Ni, Mo and Cu as an alloy component is also vigorously stirred with the hot metal 8 and melts by receiving the heat of the hot metal 8.

  Note that if the oxygen source during the dephosphorization process is only gaseous oxygen gas, the hot metal temperature will rise excessively and the dephosphorization reaction may be inhibited. Therefore, if necessary, a solid oxygen source such as mill scale or iron ore may be used. It may be added. These addition amounts can be appropriately changed according to the Si concentration, P concentration, C concentration and the like in the hot metal.

  When the dephosphorization process is completed, the dephosphorized hot metal 10 obtained by the dephosphorization process is poured into the hot metal container 7. The slag 9 is discharged separately. A sample for analysis of the dephosphorization hot metal 10 is taken from the dephosphorization hot metal 10 staying in the dephosphorization refining converter 1 or the hot metal vessel 7. The chemical component analysis of the collected sample for analysis is performed, and the chemical component of the dephosphorized hot metal 10 is grasped.

  Next, decarburization refining is performed in the decarburization refining converter 4 using the obtained dephosphorized hot metal 10, and molten steel containing one or more of Ni, Mo, and Cu as alloy components 11 is melted. The decarburizing and refining converter 4 includes an upper blowing lance 5 and a stirring gas blowing tuyere 6. Similarly to the above-described dephosphorization refining converter 1, a raw material storage hopper and a raw material cutting device for supplying the raw material from the hopper to the decarburization refining converter 4 are installed.

  Using the decarburization refining converter 4 having such a configuration, decarburization refining of the dephosphorized hot metal 10 is performed as follows.

  First, in the target alloy element among Ni, Mo, and Cu, the difference between the target value within the standard range of the molten steel 11 that is the purpose of melting and the chemical component value of the dephosphorized hot metal 10 is obtained. From the obtained difference, the shortage is determined, and based on the determined shortage, an additional amount of iron scrap containing one or more of Ni, Mo, Cu as an alloy component is obtained, and the obtained additional amount The iron scrap of the minute is charged into the decarburizing and refining converter 4. If the amount of the alloy component is insufficient with only the alloy component supplied from iron scrap, adjustment is made by adding alloy iron, metallic nickel, metallic copper, or the like. Moreover, if there is a heat margin even if these are added, normal iron scrap may be added. The alloy component supplied from iron scrap containing one or more of Ni, Mo and Cu as an alloy component is 90% or less with respect to the target value within the standard range. When addition of the alloy component is required but not required for some reason, addition of the alloy component is not performed and normal iron scrap is added.

  Next, after the dephosphorization hot metal 10 is charged into the decarburizing and refining converter 4 and quick lime is further added, the top gas is blown up while blowing nitrogen gas or a rare gas as the stirring gas from the stirring gas blowing tuyere 6. Oxygen gas is supplied from the lance 5. In this case, Mn ore as an inexpensive Mn source may be fed into the decarburization refining converter 4 as necessary. The quicklime and the Mn ore added as necessary melt to form the slag 12. The added Mn ore is reduced by the carbon of the desiliconized molten iron 10 during the decarburization refining, and the reduced Mn moves to the molten steel 11. The carbon contained in the desiliconized hot metal 10 reacts with the oxygen gas supplied from the top blowing lance 5 to become CO gas, and decarburization refining proceeds, and the dephosphorized hot metal 10 is melted into the molten steel 11.

  If decarburization refining is performed to a predetermined carbon concentration, decarburization refining is terminated, and the obtained molten steel 11 is put into a ladle (not shown) and conveyed to the next step. At the time of steel output, Fe—Mn alloy iron, Si—Mn alloy iron, metallic aluminum, and the like are added to the molten steel 11 as necessary to adjust the components of the molten steel 11. The molten steel temperature at the time of steel production is determined by the lead time determined from the arrangement of each facility in the steelmaking factory and cannot be generally specified, but, for example, about 1620 to 1650 ° C. is sufficient.

  Thus, by melting the molten steel 11 containing one or more of Ni, Mo and Cu as an alloy component, at least one alloy component of Ni, Mo and Cu is converted into Ni. In addition, iron scraps containing one or more of Mo and Cu as alloy components can be satisfied, and the use of expensive alloy iron or metallic nickel can be suppressed. Further, since the iron scrap is added in two stages of the dephosphorizing and refining converter 1 and the decarburizing and refining converter 4, the component adjustment is performed smoothly and the components are not removed.

  Hereinafter, the present invention will be described in more detail with reference to an example in which molten steel having a Mo component specification range of 0.20 to 0.22% by mass is produced.

  The hot metal discharged from the blast furnace was desiliconized in the blast furnace casting floor, and then transferred to a 300-ton capacity dephosphorization refining converter. 20 tons of Mo-containing iron scraps with a Mo content of 0.1% by mass were charged into the dephosphorizing converter, and then 299 tons of molten iron was charged. The chemical components of the molten iron charged were C: 4.1% by mass, Si: 0.14% by mass, Mn: 0.16% by mass, P: 1.15% by mass, S: 0.02% by mass, The temperature was 1295 ° C. Using quicklime as a dephosphorizing refining agent, oxygen gas was blown from an upper blowing lance, and nitrogen gas was blown from a stirring gas blowing tuyere as a stirring gas to perform a dephosphorization treatment. The dephosphorization time was 12.5 minutes, and the chemical components of the obtained dephosphorizing hot metal were C: 2.6% by mass, Si: 0.01% by mass, Mn: 0.12% by mass, P: 0. .15% by mass, S: 0.04% by mass, Mo: 0.0067% by mass, and the amount of discharged hot water was 295 tons.

  The dephosphorized hot metal was charged into a decarburizing and refining converter and decarburized and refined. At that time, 5 tons of Mo-containing iron scrap having a Mo content of 0.5% by mass and 1 ton of Mo raw material having a pure Mo content of 58% by mass were charged in advance into a decarburization refining converter. Also, 2 tons of normal steel scrap was charged. The temperature of the dephosphorizing hot metal at the time of charging was 1351 ° C.

  Quick lime, light calcined dolomite and the like were charged as a medium solvent, and oxygen gas was blown from an upper blowing lance, and Ar gas was blown as a stirring gas from a stirring gas blowing tuyere, and decarburization refining was performed. The dephosphorization time was 15 minutes, and Fe-Mn alloy iron, Si-Mn alloy iron, Fe-Si alloy iron, and a carburizing agent were added as component modifiers when steeling the ladle. The chemical composition of the molten steel in the ladle is as follows: C: 0.19 mass%, Si: 0.1 mass%, Mn: 0.39 mass%, P: 0.1 mass%, S: 0.03 mass%, Mo : 0.21% by mass, and the amount of hot water discharged was 291 tons.

  From this result, the Mo yield was determined to be 97.8%, and an extremely high yield was obtained. Further, in the converter for dephosphorization and refining, although 20 tons of Mo-containing iron scrap was charged, no undissolved residue was confirmed.

It is the schematic which shows the process of the molten steel refining method which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Converter for dephosphorization 2 Top blowing lance 3 Gas blowing tuyere for stirring 4 Converter for decarburizing refining 5 Top blowing lance 6 Gas blowing tuyere for stirring 7 Hot metal vessel 8 Hot metal 9 Slag 10 Dephosphorating hot metal 11 Molten steel 12 Slug

Claims (3)

  Iron scrap containing one or more of Ni, Mo and Cu as an alloy component is charged into a dephosphorizing and refining converter, and then molten iron is charged into the dephosphorizing and refining converter. Phosphorus treatment is performed, and then the dephosphorized hot metal obtained by the dephosphorization treatment is charged into a decarburization refining converter and decarburization refining, and one or two of Ni, Mo and Cu are performed. A method for refining molten steel, comprising melting molten steel containing at least a seed as an alloy component.   The method for refining molten steel according to claim 1, wherein the iron scrap is a high phosphorus content iron scrap having a phosphorus content of 0.2% by mass or more.   Based on the component analysis values of Ni, Mo, and Cu in the dephosphorized hot metal obtained by the dephosphorization treatment, in order to make up for the deficiency with respect to the target value, the decarburizing and refining converter is made of Ni, Mo, or Cu. The method for refining molten steel according to claim 1 or 2, wherein iron scrap containing one or more kinds as an alloy component is charged.

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