JP5549198B2 - Steel making method using steel scrap - Google Patents

Description

  The present invention relates to a method for producing steel with less impurities by effectively using iron scrap having various kinds and contents of components, and more specifically, iron scrap and hot metal produced in a blast furnace (hereinafter, “ The hot metal is manufactured in an arc furnace using an iron source as an iron source, and the blast furnace hot metal is further mixed and diluted with the manufactured hot metal, and the diluted steel is used to convert the molten steel in the converter. It relates to a method of manufacturing.

The iron source used in the steelmaking process is mainly blast furnace hot metal obtained by reducing iron ore in a blast furnace, but with the aging of iron scrap, buildings and machinery products generated in the processing process of steel materials. A considerable amount of iron scrap is generated. In the manufacture of steel products, blast furnace hot metal requires a lot of energy to reduce and melt iron ore, whereas iron scrap requires only heat of melting, and iron scrap is used in the steelmaking process. In this case, there is an advantage that the amount of energy used for reducing heat of iron ore can be reduced. Therefore, from the viewpoint of energy saving and prevention of global warming by reducing CO _2, it is desired to promote the use of iron scrap.

  At present, most of iron scrap is consumed in an arc furnace and is used for producing so-called general-purpose steel such as bar steel and shaped steel. On the other hand, in the integrated steelworks, steel scrap is directly put into a steelmaking furnace such as a converter, and the converter uses the combustion heat of carbon contained in the blast furnace hot metal as the heat of melting of the iron scrap. Therefore, the mixing ratio of iron scrap cannot be increased extremely. Moreover, when low-grade iron scrap is used as an iron source in both the arc furnace and the converter, there is a problem that it is difficult to adjust the composition of the molten steel to be produced.

  There are many proposals to improve productivity and save energy even in arc furnaces mainly composed of iron scrap as an iron source, and one of them is to use blast furnace hot metal as an iron source for melting. Methods have been proposed for reducing time or reducing power consumption.

  For example, in Patent Document 1, prior to charging a solid material such as iron scrap into an arc furnace, a temporary molten metal guide is provided on the discharge port of the arc furnace to secure a runner, and then the solid material is placed in the arc furnace. A technique is disclosed in which a raw material is charged and energized, and a blast furnace hot metal is charged into the arc furnace through the runner during the energization. According to Patent Document 1, by setting the blending ratio of the blast furnace hot metal to about 30% by mass, the productivity of the arc furnace is improved and the power consumption can be reduced.

  Further, Patent Document 2 discloses that in an arc furnace, together with raw materials such as iron scrap, blast furnace hot metal at a rate of 30 to 85% by mass of the entire charge, and the charging time of the iron scrap melting rate of 30 to 40%. As a stage, a technique of charging from a furnace top to a part surrounded by solid raw materials such as iron scrap in the center of the furnace is disclosed. According to Patent Document 2, not only the productivity of the arc furnace is improved, but also the impurities in the steel are reduced by the dilution effect by the blast furnace hot metal, and even low-grade iron scrap can be effectively reused. .

  However, in Patent Document 1 and Patent Document 2, the molten iron is refined (called “decarburization refining”) to the stage of molten steel (usually the carbon concentration is less than 1% by mass) in an arc furnace, and after the refining, the molten steel is melted from the arc furnace. In an arc furnace, a large amount of oxygen gas must be supplied to the molten iron in the furnace to perform decarburization and refining. In addition to the melting time of iron scrap, more decarburization time is required. , The time spent for one melting and refining process becomes longer. In addition, since blast furnace hot metal is used together as an iron source, the amount of iron scrap melted per smelting and refining process is small compared to the furnace capacity, and the refining time will be longer due to decarburization refining. However, the amount of iron scrap dissolved per unit time does not necessarily increase. Judging from these, it must be said that it is difficult to consume a large amount of iron scrap as an iron source.

Furthermore, since an arc furnace is not originally intended for refining hot metal containing a high concentration of carbon, it generally does not have a large-scale exhaust gas recovery facility such as a converter. In the case of decarburization and refining, CO gas and CO ₂ gas, which are reaction products of carbon and oxygen gas in the hot metal, produced by decarburization reaction, compared with decarburization and refining in a converter It is hard to say that the latent heat and sensible heat of the exhaust gas is effectively recovered.

JP-A-6-41627 JP-A-8-109408

  As mentioned above, there is a technology for melting iron scrap by blending blast furnace hot metal in the arc furnace as a means to efficiently dissolve iron scrap in an energy-saving manner. However, in the above conventional technology, decarburization refining is performed in the arc furnace. Due to the processing time for decarburization and refining, productivity is deteriorated due to a decrease in iron scrap melting ability, and latent heat and sensible heat in exhaust gas during decarburization and refining are effectively recovered. There is a problem that can not be.

  Furthermore, in recent years, demands for quality characteristics of steel have become stricter, and demands for reducing the concentration of trump elements such as copper and tin have increased, but conversely, in the iron scrap market, the amount of iron scrap stocks in Japan has increased. Accordingly, the concentration of the trump element in the waste scrap has been increasing, and when iron scrap is used as the iron source, it is very difficult to ensure the quality of the steel product.

  The present invention has been made in view of such circumstances. The purpose of the present invention is to efficiently dissolve iron scrap in an energy-saving manner when manufacturing molten steel using iron scrap as an iron source, It is to provide a steel making method using iron scrap, which can produce steel with few impurities even when using iron scrap having various contents.

  A steelmaking method using iron scrap according to a first aspect of the present invention for solving the above-described problem is to charge an iron furnace using hot metal produced in iron scrap and a blast furnace as an iron source, and in the arc furnace, the iron The scraps are melted to produce hot metal containing carbon, the hot metal produced is discharged from the arc furnace, and the hot metal produced in the blast furnace is further mixed with the hot metal that has been discharged, and the mixed hot metal is converted into a converter. And molten steel is produced by oxygen blowing in the converter.

  The steelmaking method using iron scrap according to the second invention is the steelmaking method according to the first invention, wherein the blending ratio H (H (%)) of the blast furnace hot metal charged into the arc furnace is 100 / (the blast furnace hot metal composition). Amount + iron scrap blending amount)) is 75% or less.

  The steelmaking method using iron scrap according to the third invention is characterized in that, in the second invention, the blending ratio H of the blast furnace hot metal is 30% or more and 65% or less.

  A steelmaking method using iron scrap according to a fourth aspect of the present invention is the steelmaking method according to any one of the first to third aspects, wherein the carbon concentration of the hot metal produced by supplying the carbonaceous material into the arc furnace is 4.0 mass. In the oxygen blowing in the subsequent converter, 100 kg or more of iron scrap per ton of molten steel to be produced is used as an iron source.

  A steelmaking method using iron scrap according to a fifth aspect of the present invention is any one of the first to fourth aspects, wherein the hot metal is discharged from the arc furnace, or is manufactured in a blast furnace after being discharged from the arc furnace. The hot metal mixed with hot metal is desulfurized.

  According to the present invention, in an arc furnace, iron scrap is melted together with blast furnace hot metal as an iron source, and hot metal generated by this melting is discharged without decarburizing and refining, so iron scrap per unit time The amount of melting is increased, and it is realized that iron scrap is efficiently and energy-savingly melted. Also, the hot metal discharged from the hot water is mixed with the blast furnace hot metal, and after mixing, oxygen blowing in the converter, that is, decarburization refining is performed. Therefore, even if iron scraps with different types and contents of components are used, it is possible to produce steel that is diluted with blast furnace hot metal and contains less impurities, while at the same time converting blast furnace hot metal to be refined. Since the furnace is equipped with exhaust gas recovery equipment, it is possible to effectively recover latent heat and sensible heat in the exhaust gas during decarburization refining.

It is the schematic which shows the example which melt | dissolves iron scrap using an blast furnace hot metal in an arc furnace. It is a figure which shows the relationship between the mixture ratio H of a blast furnace hot metal, and an iron scrap melting capability.

  Hereinafter, the present invention will be described in detail.

  The inventors of the present invention have repeatedly studied a method for producing a steel having a small amount of impurities even when using iron scrap having various kinds and contents of components while efficiently dissolving a large amount of iron scrap with energy saving. . The examination results are described below.

  As a means for melting iron scrap, a method using an arc furnace is generally used. However, in an arc furnace, the heat receiving efficiency of input energy until the iron scrap starts to melt and becomes liquid is low. Therefore, in order to improve this, a method of increasing the thermal efficiency of the next-charged iron scrap by leaving a part of the pre-charged molten steel produced by melting the iron scrap in the arc furnace has been performed. Therefore, in an arc furnace having a blast furnace in the vicinity, a method of reducing the electric power for melting iron scrap by charging the blast furnace hot metal into the arc furnace has been put into practical use. However, in the past, refining to the molten steel stage where the carbon concentration is low in the arc furnace, that is, decarburization refining is performed by supplying oxygen gas to the molten metal in the arc furnace, and this decarburization refining takes time. Thus, the optimum value for the productivity of melting iron scrap is determined by the blending ratio of blast furnace hot metal and iron scrap.

  On the other hand, trump elements such as copper and tin mixed in iron scrap are hardly removed in current steelmaking processes such as arc furnaces and converters, and components in molten steel are determined by the concentration mixed in iron scrap. The The content of these trump elements is small in the blast furnace hot metal, and therefore the concentration of these trump elements can be diluted by using the blast furnace hot metal in combination, so that the merit of using the blast furnace hot metal is great. However, when the blending ratio H of the blast furnace hot metal in the arc furnace is large, the effect of diluting the trump element is large, but the carbon concentration of the molten metal to be produced becomes high, and the subsequent decarburization refining time is extended accordingly. Therefore, the blending ratio H of the blast furnace hot metal is naturally limited.

  From these examination results, in order to solve the above problems, the blast furnace hot metal is charged into an arc furnace, the iron scrap is melted using the heat of the blast furnace hot metal, and the hot metal produced by this melting (hereinafter, “ Without decarburizing and refining the arc furnace hot metal), the hot metal is discharged from the arc furnace in a hot metal state with a high carbon concentration, and the blast furnace hot metal is further mixed into the arc furnace hot metal after the hot water, and the mixture is converted into a converter. It was found that it was effective to blow oxygen into molten steel.

  That is, by using blast furnace hot metal in the arc furnace, it is possible to enjoy high thermal efficiency when melting iron scrap, and since the decarburization refining is not performed in the arc furnace, the time for one treatment can be shortened. After that, the concentration of the trump element can be further diluted by mixing new blast furnace hot metal with the arc furnace hot metal melted in the arc furnace. Note that the arc furnace hot metal discharged from the arc furnace is a hot metal with a high carbon concentration. Unlike molten steel, the amount of dust generated when mixed with new blast furnace hot metal is small, and the boiling of the molten metal due to CO boiling is not possible. Can be prevented.

  The present invention has been made on the basis of such knowledge, and was charged into an arc furnace using iron scrap and blast furnace hot metal as an iron source, and the iron scrap was melted in the arc furnace to contain carbon. The arc furnace hot metal produced is discharged from the arc furnace, the blast furnace hot metal is further mixed with the arc furnace hot metal after being discharged, and the mixed hot metal (arc furnace hot metal + blast furnace hot metal) is charged into the converter. And producing molten steel by blowing oxygen in the converter.

  Below, this invention is demonstrated along a process.

  FIG. 1 is a schematic diagram showing an example of melting iron scrap using blast furnace hot metal in an arc furnace. In FIG. 1, reference numeral 1 is a DC arc furnace, 2 is a melting chamber, 3 is a furnace lid, 4 is an upper electrode, 5 is a furnace bottom electrode, 6 is a hot metal charging iron, 7 is a charging pan for containing the blast furnace hot metal, 8 is a crane, 9 is a blast furnace hot metal, 10 is a tap, 11 is an oxygen gas supply lance, 12 is a carbonaceous material supply lance, and 13 is iron scrap.

  After the furnace lid 3 is removed, the iron scrap 13 is charged into the melting chamber 2, and after the iron scrap 13 is charged, the molten iron is inserted through the hot metal charging rod 6 installed through the side wall of the DC arc furnace 1. The blast furnace hot metal 9 is charged into the melting chamber 2 from the charging pan 7 lifted by the crane 8. When a predetermined amount of the blast furnace hot metal 9 is charged, the supply of the blast furnace hot metal 9 from the charging pan 7 is finished, a direct current is fed between the upper electrode 4 and the furnace bottom electrode 5, and the upper electrode 4 and the furnace bottom are supplied. An arc is generated between the electrode 5 or between the charged iron scrap 13 and the upper electrode 4. And the iron scrap 13 is melt | dissolved with the generated arc heat, and an arc furnace hot metal (not shown) is produced | generated. When a predetermined amount of iron scrap 13 cannot be charged by one charging, the iron scrap 13 can be additionally loaded in the melting chamber after the melting of the iron scrap 13 proceeds to some extent.

  When the arc furnace hot metal is produced, in order to efficiently melt the iron scrap 13, the blending ratio H of the blast furnace hot metal 9 is preferably 75% or less, desirably 30% or more and 65% or less. The blending ratio H of the blast furnace hot metal 9 is a value defined by “H (%) = Blast furnace hot metal blending amount × 100 / (Blast furnace hot metal blending amount + iron scrap blending amount)”.

  In this case, as the arc furnace hot metal is generated, a flux such as quick lime is charged into the melting chamber 2 to form molten slag on the arc furnace hot metal, thereby preventing the arc furnace hot metal from being oxidized and keeping warm. Is preferred. If the oxygen gas supply lance 11 and the carbon material supply lance 12 can be inserted into the melting chamber after energization, oxygen gas is supplied from the oxygen gas supply lance 11, and coke, It is preferable to spray carbon materials such as coal and graphite toward the molten iron or molten slag in the melting chamber. The sprayed carbon material reacts with the sprayed oxygen gas to generate combustion heat and acts as an auxiliary heat source to save power consumption. In addition, since a carbon material plays the role which raises the carbon concentration of an arc furnace hot metal, it is preferable to supply the carbon material of the quantity larger than the chemical equivalent of the oxygen gas supplied.

  When a predetermined amount of arc furnace hot metal has accumulated in the melting chamber, the melting chamber 2 is tilted to the side of the tap 10 by means of a tilting device (not shown), and the arc furnace hot metal is removed from the tap 10 to a holding container such as a ladle ( Take out hot water to (not shown). After pouring hot water, iron scrap 13 and blast furnace hot metal 9 are newly charged into the melting chamber 2, and melting of the next heat is started.

  The higher the carbon concentration of the hot metal discharged from the arc furnace, the higher the heat margin in the subsequent converter refining process. In other words, in the oxygen blowing process in the subsequent converter, iron scrap blending It becomes possible to increase the ratio. As described above, when iron scrap is melted in the presence of blast furnace hot metal, the molten iron produced by melting is mixed with the blast furnace hot metal to dilute the carbon concentration of the blast furnace hot metal. Therefore, it is preferable to dissolve the iron scrap while spraying and adding carbonaceous materials such as coke, coal, and graphite from the carbonaceous material supply lance 12 to the generated arc furnace hot metal so as to compensate for this dilution. In this case, only the melting period of the iron scrap is sufficient for carburizing the arc furnace hot metal by adding the carbon material, and it is not necessary to extend the processing time for carburizing. As described above, when supplying oxygen gas, it is necessary to supply a carbon material in an amount larger than the chemical equivalent of the supplied oxygen gas for carburizing.

  In the present invention, the blast furnace hot metal is mixed with the discharged arc furnace hot metal in order to dilute the concentration of the trump elements of the hot metal brought about by iron scrap after the hot water from the arc furnace.

  By the way, coke and coal contain 0.1% by mass or more of sulfur (0.5 to 0.7% by mass in the case of coke), and arc by using these carbon materials in an arc furnace. Increases the sulfur concentration in the molten iron. Therefore, the desulfurization treatment can be applied to the arc furnace hot metal discharged from the arc furnace or the hot metal molten iron mixed with the blast furnace hot metal (arc furnace hot metal + blast furnace hot metal: hereinafter referred to as “mixed hot metal”). preferable.

  This desulfurization treatment can be applied to various desulfurization treatments such as a method of injecting a desulfurization agent mainly composed of a CaO-Mg-based flux through a lance. It is preferable to desulfurize the desulfurizing agent and the arc furnace hot metal or mixed hot metal with an impeller using a so-called mechanical stirring desulfurization apparatus. The target sulfur concentration in the hot metal after desulfurization is about 0.002 to 0.010 mass%.

  In addition, when performing a desulfurization process with respect to the arc furnace hot metal before mixing with a blast furnace hot metal, the blast furnace hot metal mixed after a desulfurization process uses what carried out the desulfurization process. In addition, dephosphorization is further performed on the mixed hot metal in which the blast furnace hot metal is mixed with the arc furnace hot metal after the desulfurization treatment, or the mixed hot iron that has been desulfurized after the mixing of the arc furnace hot metal and the blast furnace hot metal. It is also possible to perform processing.

  The mixed hot metal, which has been subjected to desulfurization treatment, preferably further dephosphorized, is charged into a converter, and in the converter, oxygen blowing from an upper blowing lance or a bottom blowing nozzle is performed, and the carbon in the mixed hot metal and Phosphorus is removed by oxidation to produce molten steel from mixed hot metal.

  In the oxygen blowing in the converter, carbon in the molten iron is combined with oxygen and removed as CO gas, but the latent heat of the CO gas can be recovered as energy by the exhaust gas recovery facility of the converter. When producing molten steel by decarburizing and refining in a conventional arc furnace, exhaust gas recovery equipment such as a converter is not generally installed in the arc furnace due to the huge equipment costs. Even when possible, the latent heat / sensible heat of CO gas is recovered as steam energy, and the energy efficiency of recovery is low.

  Furthermore, when decarburizing and refining in a converter, the temperature of the molten metal is raised mainly by the heat generated by the decarburization reaction, but the calorific value is proportional to the carbon concentration in the mixed hot metal, so the carbon concentration of the mixed hot metal is high. In some cases, it is possible to dissolve a cold iron source such as iron scrap. For example, in a normal converter refining method based on the premise of CO gas recovery from exhaust gas, when the carbon concentration of the mixed hot metal at the time of charging is 4.5 mass%, the mixed hot metal at 1300 ° C. is 1600 ° C. or higher. The amount of heat for the temperature rise to become molten steel and the heat margin that can melt iron scrap at room temperature of about 10% by mass relative to the mass of the mixed hot metal, but the carbon concentration of the mixed hot metal at the time of charging However, if it is about 3.0 mass%, there is only the amount of heat for heating the mixed hot metal, and iron scrap can hardly be dissolved.

  By the way, by carburizing and securing the carbon concentration of the arc furnace hot metal to 4.0% by mass or more, if the carbon concentration of the blast furnace hot metal mixed with the arc furnace hot metal after that is about 4.5% by mass, The present inventors have confirmed that 100 kg or more of iron scrap per ton of molten steel produced can be used in combination in oxygen blowing in a converter.

  In the present invention, when iron scrap is melted in an arc furnace, since the blast furnace hot metal is used as an iron source, the carbon concentration of the arc furnace hot metal generated by the carbon in the blast furnace hot metal becomes high, and carbon during the melting Since the carbon concentration of the arc furnace hot metal can be increased by adding the material, the carbon concentration of the mixed hot metal is high, and there is an ability to further dissolve iron scrap in the converter.

  As described above, according to the present invention, in the arc furnace, iron scrap is melted together with blast furnace hot metal as an iron source, and the hot metal generated by this melting is discharged without decarburizing and refining. The amount of iron scrap melting per unit time is increased, and it is realized that energy scrap is efficiently and efficiently melted. Also, the hot metal discharged from the hot water is mixed with the blast furnace hot metal and mixed, and then oxygen blowing in the converter. Since decarburization and refining is carried out, even if iron scrap with various types and contents of components is used, it is possible to dilute with blast furnace hot metal to produce steel with less impurities, and at the same time, Since the converter for refining is equipped with exhaust gas recovery equipment, it is possible to effectively recover the latent heat and sensible heat in the exhaust gas during decarburization refining.

  Although the arc furnace shown in FIG. 1 is a DC arc furnace, the present invention can be applied without any problem even if an AC arc furnace is used. In addition, the method of using biomass raw materials for carburized materials can reduce carbon dioxide emissions, which is one of the causes of global warming, because biomass is carbon neutral. From the viewpoint of global warming, It is preferable to use a biomass raw material. Furthermore, although the method of carburizing is carried out by top blowing projection from the lance, it may be injection into the bath from above, and a dedicated nozzle is buried in the bottom of the furnace and bottom blowing injection is performed. It doesn't matter. What is necessary is just to implement with the optimal equipment by the balance of capital investment and efficiency. Furthermore, the arc furnace itself is not limited to the type shown in FIG. 1, and there is no problem even if it is a type of arc furnace having a preheating chamber for preheating iron scrap.

  Hereinafter, the present invention will be described in detail with reference to examples.

[Invention Example 1]
About 70 tons of blast furnace hot metal is charged through a charging pan into an arc furnace having a furnace diameter of 6 m, a height of 4 m, a furnace capacity of 140 tons, and a transformer capacity of 100 MVA shown in FIG. 70 tons were charged. The graphite upper electrode was energized to start melting, and oxygen gas was supplied from the oxygen gas supply lance to 5000 Nm ³ / h, and coke was supplied from the carbon material supply lance to the arc furnace at a supply rate of 90 kg / min. . It takes about 30 minutes for the entire amount of iron scrap to melt, and the carbon material unit, oxygen gas unit, and power unit in the generated arc furnace hot metal (total mass of blast furnace hot metal and iron scrap) are 20 kg / t, 19 Nm ³ / t, 170 kWh / t.

  About 140 tons of generated arc furnace hot metal was discharged from the outlet of the arc furnace into a blast furnace pan that had previously received about 70 tons of blast furnace hot metal and mixed with the blast furnace hot metal. In addition, the carbon concentration of the molten iron in the arc furnace at the time of tapping from the arc furnace is 2.3 mass%, the temperature is 1398 ° C, the carbon concentration of the blast furnace molten iron for mixing is 4.5 mass%, and the temperature is 1400 ° C. there were. Thereafter, the mixed hot metal is charged into a hot metal ladle, and about 140 tons of blast furnace hot metal (carbon concentration: 4.5 mass%, temperature: 1400 ° C.) is further charged into the hot metal ladle. Mixed hot metal was obtained.

  In order to desulfurize the mixed hot metal, an impeller for stirring the molten metal is immersed in the mixed hot metal from above the hot metal ladle, and a desulfurizing agent mainly composed of lime is charged (charging amount = 8 kg / hot metal-t). The mixed hot metal and the desulfurizing agent were stirred for a minute with an impeller to desulfurize the mixture. The sulfur concentration of the mixed hot metal after the desulfurization treatment was 0.002% by mass.

The mixed hot metal after the desulfurization treatment is charged into the converter, and a flow rate of 60000 Nm is supplied from the top blowing lance while flowing nitrogen gas and Ar gas at a flow rate of 0.1 Nm ³ / (min · hot metal-t) through the bottom blowing nozzle. Decarburization refining was performed by supplying oxygen gas at ³ / h for 13 minutes. The carbon concentration of the molten steel at the end of decarburization refining was 0.04% by mass, the temperature was 1630 ° C., and the copper concentration was 0.05% by mass. Thereafter, the molten steel was poured into a ladle and cast into slab slabs with a continuous casting machine.

[Invention Example 2]
The present invention was carried out using the same arc furnace as that used in Example 1 of the present invention. Invention Example 2 is a test in which the amount of carbon material supplied during melting in the arc furnace was increased in order to increase the carbon concentration of the arc furnace hot metal as compared with Invention Example 1 described above.

About 70 tons of blast furnace hot metal was charged into the arc furnace through a charging pan, and then about 70 tons of iron scrap was charged. The upper electrode was energized to start melting, and oxygen gas was supplied from the oxygen gas supply lance to the inside of the arc furnace at a supply rate of 5000 Nm ³ / h and coke from the carbonaceous material supply lance to 110 kg / min. It takes about 30 minutes for the entire amount of iron scrap to melt, and the carbon material unit, oxygen gas unit, and power unit in the generated arc furnace hot metal (total mass of blast furnace hot metal and iron scrap) are 25 kg / t, 19 Nm ³ / t, and 171 kWh / t.

  About 140 tons of generated arc furnace hot metal was discharged from the outlet of the arc furnace into a blast furnace pan that had previously received about 70 tons of blast furnace hot metal and mixed with the blast furnace hot metal. The carbon concentration of the molten iron in the arc furnace when discharging from the arc furnace is 3.1% by mass and the temperature is 1402 ° C. The carbon concentration of the blast furnace hot metal for mixing is 4.5% by mass and the temperature is 1400 ° C. there were. Thereafter, the mixed hot metal is charged into a hot metal ladle, and about 140 tons of blast furnace hot metal (carbon concentration: 4.5 mass%, temperature: 1400 ° C.) is further charged into the hot metal ladle. Mixed hot metal was obtained. The mixed hot metal was subjected to a desulfurization process in the same manner as in Example 1 of the present invention.

  In the converter, when performing decarburization and refining using the mixed hot metal after the desulfurization treatment, 40 kg of iron scrap per ton of molten steel to be produced is charged in the converter in advance, and the mixed hot metal after desulfurization is then installed. Then, decarburization refining was performed according to Example 1 of the present invention. The carbon concentration of the molten steel at the end of decarburization refining was 0.04% by mass, the temperature was 1630 ° C., and the copper concentration was 0.05% by mass. Thereafter, the molten steel was poured into a ladle and cast into slab slabs with a continuous casting machine.

[Invention Example 3]
The present invention was carried out using the same arc furnace as that used in Example 1 of the present invention. Invention Example 3 is a test in which the amount of carbon material supplied during melting in the arc furnace was increased in order to further increase the carbon concentration of the molten iron in the arc furnace as compared with Invention Example 2 described above.

About 70 tons of blast furnace hot metal was charged into the arc furnace through a charging pan, and then about 70 tons of iron scrap was charged. The upper electrode was energized to start melting, and oxygen gas was supplied from the oxygen gas supply lance to 5000 Nm ³ / h and coke from the carbon material supply lance was blown into the arc furnace at a supply rate of 140 kg / min. It takes about 30 minutes for the entire amount of iron scrap to melt, and the carbon material unit, oxygen gas unit, and power unit in the generated arc furnace hot metal (total mass of blast furnace hot metal and iron scrap) are 30 kg / t, 19 Nm ³ / t, and 172 kWh / t.

  About 140 tons of generated arc furnace hot metal was discharged from the outlet of the arc furnace into a blast furnace pan that had previously received about 70 tons of blast furnace hot metal and mixed with the blast furnace hot metal. In addition, the carbon concentration of the molten iron in the arc furnace at the time of tapping from the arc furnace is 4.5% by mass and the temperature is 1401 ° C. The carbon concentration of the blast furnace hot metal for mixing is 4.5% by mass and the temperature is 1400 ° C. there were. Thereafter, the mixed hot metal is charged into a hot metal ladle, and about 140 tons of blast furnace hot metal (carbon concentration: 4.5 mass%, temperature: 1400 ° C.) is further charged into the hot metal ladle. Mixed hot metal was obtained. The mixed hot metal was subjected to a desulfurization process in the same manner as in Example 1 of the present invention.

  In the converter, when decarburizing and refining using the mixed hot metal after the desulfurization treatment, 120 kg of iron scrap per ton of molten steel produced in the converter is charged in advance, and then the mixed hot metal after desulfurization is charged. Then, decarburization refining was performed according to Example 1 of the present invention. The carbon concentration of the molten steel at the end of decarburization refining was 0.04 mass%, the temperature was 1630 ° C, and the copper concentration was 0.04 mass%. Thereafter, the molten steel was poured into a ladle and cast into slab slabs with a continuous casting machine.

  By increasing the carbon content of the molten iron in the arc furnace in this way, the heat margin in the converter is expanded, and iron scrap can be further melted in the converter, and the hot water in the arc furnace is increased. By making the carbon concentration at that time 4.0% by mass or more, it was confirmed that converter decarburization refining can dissolve 100 kg or more per ton of molten steel from which iron scrap is produced.

[Comparative example]
About 140 tons of iron scrap is charged into the arc furnace used in Example 1 of the present invention, the upper electrode is energized to start melting, and oxygen gas is supplied from an oxygen gas supply lance to 3500 Nm ³ / h, a carbonaceous material supply lance. From above, coke was blown into the arc furnace at a feed rate of 60 kg / min. It takes about 45 minutes until the entire amount of iron scrap is melted, and the carbon material unit, oxygen gas unit, and power unit in the produced molten iron are 20 kg / t, 19 Nm ³ / t, and 370 kWh / t, respectively. Met.

  About 140 tons of molten iron produced was tapped into a ladle. The carbon concentration of the molten iron at the time of tapping from the arc furnace was 0.1% by mass, the temperature was 1610 ° C., and the copper concentration was 0.22% by mass. Then, this molten iron (molten steel) was desulfurized with an LF facility (ladder refining facility), and the molten steel after desulfurization was cast into a bloom slab with a continuous casting machine.

  In Table 1, the operation result of this invention example 1-3 and a comparative example is shown.

As shown in Table 1, according to the present invention, it becomes possible to melt iron scrap in a short time and with a small amount of electric power, and the molten steel to be produced has a low copper concentration, and the iron scrap is converted into an iron source of high-grade steel. It was realized to use as. Moreover, by carburizing in an arc furnace, it became possible to mix iron scrap in the converter, and it was confirmed that not only energy saving but also prevention of global warming by CO ₂ reduction was achieved.

  In addition, this invention is not limited to the range of the said invention example, A various change is possible. For example, in the above invention example, the blending ratio of the blast furnace hot metal charged to the arc furnace and the iron scrap was 1: 1, but this ratio is optimum based on the purity of the iron scrap used and the target productivity. You can select the correct value. In addition, oxygen gas is supplied into the arc furnace when iron scrap is melted. However, if oxygen gas is not added, it is not possible to obtain a reduction in the amount of electric power due to combustion of the carbonaceous material. However, the use of oxygen gas may be determined based on the balance between productivity and processing cost.

  The present invention was carried out using the same arc furnace as that used in Example 1. This example is a test in which the blending ratio H of the blast furnace hot metal at the time of manufacturing the arc furnace hot metal was changed as compared with Example 1 described above.

  The amount of the blast furnace hot metal charged into the arc furnace through the charging pan was changed, and the iron scrap to be charged thereafter was combined to make a total of 140 tons. The case of not using hot metal is the case of the comparative example of Example 1. In this case, it took 45 minutes until the entire amount of iron scrap was dissolved. The iron scrap melting capacity of the arc furnace was compared by changing the hot metal mixture ratio H. The melting capacity is determined by the sum of the hot metal charging time, the iron scrap melting time, and the tapping / draining time. The shorter the total time, the larger the melting capacity. The hot metal charging time does not depend much on the amount of hot metal because the cross-sectional area of the hot metal charging iron is large, but the amount of power consumption increases as the amount of iron scrap charged increases. Becomes longer. Moreover, since the amount of hot water is constant, the hot water and waste time does not depend on the hot metal blending ratio H.

  The relationship between the blending ratio H of the blast furnace hot metal and the iron scrap melting ability is shown in FIG. In FIG. 2, the melting ability in the case of 100% iron scrap not containing blast furnace hot metal is indexed as 1.0. As shown in FIG. 2, by mixing up to 75% of blast furnace hot metal, the melting capacity of iron scrap is improved, and in particular, the melting capacity index is 1.1 times when the mixing ratio H is in the range of 30% to 65%. It was found that the effect was great.

  This is because the use of the blast furnace hot metal shortens the energization time due to the reduction in the power consumption rate and improves the heat receiving efficiency from the blast furnace hot metal. However, the effect decreased when the blending ratio H exceeded 50%, and when it exceeded 75%, the dissolving ability became less than 1.0. This is because if the blending ratio H becomes too high, the amount of iron scrap that dissolves during one melting decreases and the melting time is shortened, but the charging time, tapping and draining time do not change. This is because the per hour increases.

DESCRIPTION OF SYMBOLS 1 DC type arc furnace 2 Melting chamber 3 Furnace lid 4 Upper electrode 5 Furnace bottom electrode 6 Hot metal charging iron 7 Charging pan 8 Crane 9 Blast furnace hot metal 10 Outlet 11 Oxygen gas supply lance 12 Charcoal material supply lance 13 Iron scrap

Claims (4)

Steel scrap and hot metal produced in a blast furnace are charged into an arc furnace using an iron source, the iron scrap is melted in the arc furnace to produce hot metal containing carbon, and the produced hot metal is discharged from the arc furnace. And then mixing the molten iron produced in the blast furnace with the molten iron after tapping, charging the molten iron after mixing into the converter, and blowing the oxygen in the converter to produce molten steel , iron scrap In which the carbon concentration of the hot metal produced by supplying a carbonaceous material into the arc furnace is carburized to 4.0% by mass or more, and then oxygen blowing in a converter Then, the steelmaking method using iron scrap characterized by using together iron scrap of 100 kg or more per molten steel to be manufactured as an iron source .   The blending ratio H (H (%) = blast furnace hot metal blending amount x 100 / (blast furnace hot metal blending amount + iron scrap blending amount)) of the blast furnace hot metal charged into the arc furnace is 75% or less. A steel making method using the iron scrap according to Item 1.   The steelmaking method using iron scrap according to claim 2, wherein the blending ratio H of the blast furnace hot metal is 30% to 65%. Hot metal after pouring from the arc furnace or, characterized in that the hot metal molten iron produced in the blast furnace are mixed after tapped from the arc furnace desulfurization process, any one of claims 1 to 3 1 Steel making method using steel scrap described in 1.

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