JP5504955B2 - Manufacturing method of molten steel - Google Patents

Description

  The present invention relates to a method for producing molten steel by using hot metal and iron scrap as main raw materials and performing secondary refining in a secondary refining facility following decarburization refining in a converter or decarburization refining in a converter. Specifically, the present invention relates to a method of manufacturing a molten steel having a component composition having a desired material characteristic in consideration of the amount of trump elements brought mainly from iron scrap.

  When producing molten steel by decarburization refining in a converter or converter decarburization refining and subsequent secondary refining in a secondary refining facility, the steel product produced from the molten steel has the material characteristics required by the customer. Refining is performed on molten steel so as to achieve a component composition satisfying the above. There are various types of steel products (referred to as “steel grades”) depending on the application, and in order to increase the efficiency of the refining process, multiple steel grades with similar component compositions are converted together from the customer's order. In general, a refining equivalent amount (referred to as “one charge” or “one heat”) in a furnace is constituted and refining is performed based on this amount.

  However, in recent years, with the diversification of demands of customers for steel products, various new steel types have appeared, and there are many cases where it is difficult to configure one charge with steel types having similar composition. It has become. If it waits until the order of a similar component composition is put together in one charge by converter decarburization refining, the malfunction that supply of the steel product to the consumer who had the order first will be overdue will occur. In such a case, in order to give priority to the delivery date to the customer, it was necessary to compose a charge with the intention of generating a large amount of surplus material.

  In view of such a situation, in recent years, a method for determining a molten steel component by paying attention to material properties of steel products has been proposed. For example, Patent Document 1 requires CEQ (CEQ = C + Mn / K, where K is a constant determined by the manufacturing process), which is a factor that determines the material properties of steel products, and is necessary from the contents of orders from customers. A method is proposed for determining the components of the converter steel from the obtained CEQ range and the component values of the order contents, thereby efficiently consolidating and producing a plurality of steel types. ing.

  Further, in Patent Document 2, manufacturing information storage means for accumulating past results, and mechanical properties obtained when steel products are manufactured based on input instruction values are used in the data of the manufacturing information storage means. A method for organizing orders with different specifications from a plurality of customers into one production lot while estimating mechanical properties of a steel product using a DB-type material prediction system comprising: Then, chemical components that satisfy the specifications of each order are set, the mechanical properties in the chemical components are estimated using a DB type material prediction system, and the mechanical properties of all steel products to be aggregated are estimated. A method has been proposed in which each order is aggregated as a production lot of the chemical component when the value satisfies the specification of the order.

JP-A-10-260702 JP 2009-20807 A

  According to Patent Document 1 and Patent Document 2 described above, it is possible to efficiently collect orders made up of a plurality of steel types to form a charge, and to efficiently manufacture steel products. However, in recent years, including steel products manufactured by these methods, even steel products having a predetermined compositional composition for which the steel output component is a target are often excessive quality such as exceeding the required strength, or Unexpected situations such as deviation from material characteristics have occurred. In particular, when a plurality of steel types are aggregated, the target component is in a narrow limited range (pinpoint), so the tendency to occur is remarkable.

  The present inventors have pursued this cause, and as a result, the above phenomenon has been forced to use low-grade iron scrap even in integrated steelworks due to the recent tightening of demand for ironmaking raw materials. It became clear that it was caused by this. In other words, low-grade iron scrap contains various impurities, so-called trump elements such as Cu, Ni, and Mo, which are difficult to remove by ordinary hot metal pretreatment and converter decarburization refining, are ignored. However, it was unavoidable that the material was mixed in an amount that could not be obtained, and it was revealed that the material properties of the manufactured steel product deviated from the expected range.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to use molten steel and iron scrap as main raw materials, and to consolidate a plurality of steel types into one charge based on material characteristics. It is to provide a method for producing molten steel that can produce molten steel without causing problems in the quality of the steel product or excessive quality, even when low-grade iron scrap is frequently used in production. .

  The method for producing molten steel according to the first invention for solving the above-mentioned problems is required for producing molten steel as a target component by decarburizing and refining in a converter using hot metal and iron scrap as main raw materials. The concentration of the trump element in the molten metal in the converter is calculated from the composition and mass of the hot metal and iron scrap charged to the converter, for the target component value range that is provisionally determined based on the material characteristics of the steel product. , Refining conditions in the converter so that the range of the target component value that has been tentatively determined based on the influence of the trump element on the material characteristics is corrected, and the molten steel component falls within the corrected target component value range. And adjusting the additive amount of the component adjusting material.

  The method for producing molten steel according to the second aspect of the present invention includes decarburization and refining in a converter using hot metal and iron scrap as main raw materials, produced by the decarburization and refining, and steel discharged from the converter to a ladle. When refining molten steel in a secondary refining facility to produce molten steel of the target component, decarburization refining in the converter uses a target component value that is provisionally determined based on the required material properties of the steel product. The molten steel composition is adjusted at a concentration lower than the range, the concentration of the trump element of the molten steel discharged from the converter is analyzed, and the above provisionally determined based on the influence of the trump element on the material characteristics The range of the target component value is corrected, and the refining conditions and the component adjustment material addition amount in the secondary refining equipment are adjusted so that the molten steel component falls within the corrected target component value range.

  According to the present invention, when producing molten steel using hot metal and iron scrap as a main raw material, even when low-grade iron scrap is frequently used, the composition of the molten steel is considered in consideration of the influence of the trump element. Since the component composition is adjusted to match the material properties of the product, it is possible to manufacture molten steel without causing problems in the quality of steel products and in excess quality. In addition, in order to offset the influence of the trump element on the material properties of steel products, it is often necessary to reduce the amount of alloy components such as Mn. From this point of view, the amount of component adjustment materials such as alloy iron is reduced. In addition, an unexpected effect of economically producing steel can be obtained.

  Hereinafter, the present invention will be specifically described.

  The present invention includes a first method for producing molten steel as a target component by decarburizing and refining in a converter using hot metal and iron scrap as main raw materials, and a converter using hot metal and iron scrap as main raw materials. The second method of producing molten steel of the target component by performing decarburization and refining the molten steel produced by this decarburization refining and delivered to the ladle from the converter in the secondary refining equipment Two types of methods having different manufacturing processes are provided, and each method will be described below.

  First, the 1st method (1st form) which manufactures the molten steel of a target component only applying the decarburization refining in a converter is demonstrated.

  If the converter to be used supplies oxygen gas (industrial pure oxygen gas) to the hot metal and iron scrap charged in the converter and can decarburize and refine the hot metal, the top blow Any type such as a furnace, a bottom blown converter, and an upper bottom blown converter may be used. In addition, the hot metal used is generally obtained by reducing iron ore in a blast furnace, but it may be obtained by melting iron scrap in a cupola-type vertical furnace, It may be obtained by other smelting reduction smelting methods. These hot metal prior to decarburization and refining in the converter from the viewpoint of efficiently adjusting the composition of the molten steel by reducing the load on the decarburization and refining of the converter, or reducing the amount of slag generated. It is preferable to perform hot metal preliminary treatment such as preliminary desiliconization, preliminary dephosphorization or preliminary desulfurization.

  Iron scrap may be charged directly into the converter, but it is charged in advance in a hot metal transport container such as a torpedo car before receiving and a hot metal charging pan in the converter, and preheated with the heat retained in these containers, It is preferable to receive the molten iron therein because the melting time in the converter can be shortened. In the present invention, hot metal and iron scrap are mainly used as the main raw material (iron source) for producing molten steel, but a mold or a metal bar may be used in combination.

  The mass and components of these main raw materials to be charged into the converter are known in advance. The composition of the hot metal can be known by taking a sample from the hot metal after the pretreatment and analyzing it. Steel scrap has a clear source, such as scrap generated in steelworks. For example, if it is a slab crop, it is a representative component of the slab, and if it is scrap of a coil, it is a representative of the coil. Component). There are also grades in iron scrap (city scrap) in the city, and its components can be specified almost. And the average composition of the main raw material charged in a converter is calculated | required by calculation from the compounding ratio of these main raw materials.

  In the present invention, for each charge in the converter, a range of provisional target component values is determined in advance on the basis of the material properties from the customer required for the molten steel. In this case, as a method for determining the range of the provisional target component value, a method disclosed in Patent Document 1 or Patent Document 2 can be used. In particular, it is preferable to use the method disclosed in Patent Document 2 because a plurality of different steel types can be accurately aggregated.

  The feature of the present invention is that the range of the provisional target component value determined based on the above-mentioned material characteristics is not fixed as it does not move (that is, it is set as a static target value), but is charged in the converter. It is to grasp the influence on the material properties of the playing element brought by the main raw material, and to correct the range of the temporary target component value in consideration of this influence (that is, to dynamically correct).

  In order to evaluate the material properties of steel products required by customers when correcting the range of provisional target component values, the well-known carbon equivalent (Ceq), weld crack sensitivity (Pcm), etc. are used. . Usually, a demand is made from a consumer as a range having a certain upper and lower limit as a material characteristic. Therefore, the range of the target component value is corrected by obtaining the upper limit value and lower limit value of the specific target component from the upper limit value and lower limit value of the material characteristics by the following method.

For example, taking as an example the relationship between tensile strength (TS) and carbon equivalent (Ceq) (thick plate materials also affect the plate thickness t, which is evaluated), the tensile strength (TS ) Is expressed by the following formula (1), and the carbon equivalent (Ceq) is expressed by the following formula (2). From the formulas (1) and (2), Focusing on certain C and Mn, the following equation (3) is obtained. However, in the formulas (2) and (3), [% C], [% Mn], [% Cu], [% Ni], [% Mo] are the contents of each element in steel (mass% ) And a, b, c, and d are coefficients. In the formula (2), other elements such as Si, Cr, and V are omitted.
TS = f (Ceq, t) (1)
Ceq = [% C] + a × [% Mn] +… + b × [% Cu] + c × [% Ni] + d × [% Mo]… (2)
[% C] + a × [% Mn] = g (TS, t, [% Cu], [% Ni], [% Mo])… (3)
Using the obtained equation (3), the target composition of C and Mn, which was the temporary target component value, is corrected to a new target component value corresponding to the concentrations of Cu, Ni, and Mo that are playing elements.

  And decarburization refining in a converter is performed by determining or changing the refining conditions and the component adjustment material addition amount so as to be within the corrected target component value range. The range of the target component value may be corrected before the start of refining in the converter to determine the refining conditions, or after the start of refining, the refining conditions that have already started can be changed dynamically. May be.

  In this way, molten steel is manufactured by decarburization refining in a converter. After decarburization and refining, the molten steel is removed from the converter to the ladle and subjected to light treatment such as argon gas and bubbling to equalize the temperature and components of the molten steel, or continuously cast, or secondary refining equipment After continuous degassing, cast continuously into slabs, blooms, billets, etc.

  In the case of special steels that require form control of extremely low-sulfur steel or non-metallic inclusions, component adjustment should be performed by adding a small amount of Ca or REM to the molten steel in the tundish or mold of the continuous casting equipment. However, in the case of other steels, the molten steel composition upon arrival at the continuous casting equipment determines the composition of the final product. In addition, even in the case of special steel that adjusts components by adding a small amount of Ca or REM in the tundish or mold of the continuous casting equipment, components other than Ca and REM still arrive at the continuous casting equipment. The molten steel composition at the time determines the composition of the final product.

  Next, a second method (second embodiment) for producing molten steel of a target component by refining molten steel discharged from a converter to a ladle in a secondary refining facility will be described. Here, the secondary refining equipment is an RH vacuum degassing apparatus, a DH vacuum degassing apparatus, a ladle refining furnace, a VAD furnace, a VOD furnace, or the like, and may be properly used according to the grade of steel to be manufactured.

  When passing through the secondary refining equipment, hot metal and iron scrap are used as the main raw material in the decarburization refining in the converter as in the first embodiment. In the second embodiment, it is not necessary to calculate the amount of trump elements brought into the converter by the main raw material, but the composition of the molten steel after the steel is discharged from the converter to the ladle is required. It is necessary to adjust a molten steel component so that it may become a density | concentration lower than the range of the target component value temporarily determined based on the material characteristic of steel products. This is because, in the second embodiment, the final component adjustment is performed in the secondary refining equipment, so the molten steel composition in the ladle produced from the converter takes into account the amount of trump elements in the secondary refining equipment. This is because it is necessary to adjust the component within a possible range. Usually, it is often difficult to remove an excessively added component with the secondary refining equipment, and therefore, the concentration is adjusted in a concentration range lower than the range of the target component value that has been temporarily determined. In extreme cases, it is not necessary to add a component adjusting material such as iron alloy.

  In order to ensure that the concentration is adjusted to a level lower than the target component value range that has been determined, the amount of the trump elements brought into the converter by the main raw material is set as in the first embodiment. You may calculate and may determine the target ingredient at the time of converter steelmaking. However, in this case as well, the target component value that is temporarily determined is not the target component value at the time of converter steelmaking, but the target component that is temporarily determined, as in the case where the amount of the trump element is not considered. It is necessary to adjust at a density lower than the range of values. Specifically, with respect to the range of the target component value determined temporarily, in the case of C, about 0.02% by mass, in the case of Mn, about 0.1-0.2% by mass, a low value is set. It is sufficient to use it as the target component for converter steelmaking.

  Otherwise, decarburization refining is performed in accordance with the first embodiment described above.

  In the secondary refining at the secondary refining equipment, the components composition that satisfies the material properties of steel products required by customers by refining finish decarburization, desulfurization, deoxidation, etc., adding the necessary alloying elements Adjust to. At this time, in the second embodiment, the concentration of the trump element in the molten steel after the steel from the converter is analyzed, the effect on the material properties of the trump element is grasped, and this effect is taken into Correct the target component value range. Then, secondary refining is performed by determining or changing the refining conditions and the component adjustment material addition amount so as to fall within the range of the corrected target component value.

  Since trump elements such as Cu, Ni, and Mo are generally difficult to remove by decarburization refining in the converter, the amount brought from the main raw materials such as hot metal and iron scrap is taken out from the converter as it is. It remains in the steel being steeled. However, iron scrap is a mixture of several types of steel depending on the brand, and the composition may be non-uniform. In the molten steel when the steel is actually removed from the converter, the content of the trump elements in the molten metal calculated from the information on the main raw material charged in the converter The content of playing cards may be different.

  In the second embodiment, in the secondary refining equipment having the function of final component adjustment, the material characteristics of the trump element are affected based on the content of the trump element in the molten steel actually discharged from the converter. Considering the impact, the target component value range is modified so that material properties satisfying customer requirements can be obtained, so molten steel that is even more suited to the material properties required by customers. Can be manufactured.

  The method for determining the range of the tentative target component value and the method for evaluating the material characteristics of the steel product required by the customer when correcting the range of the tentative target component value by the component composition are the first described above. What is necessary is just to follow according to a form. The produced molten steel is cast into slabs such as slabs, blooms and billets by a continuous casting machine as in the first embodiment.

  As described above, according to the present invention, when manufacturing molten steel using hot metal and iron scrap as the main raw material, even when low-grade iron scrap is frequently used, the component composition of the molten steel Considering the influence, the composition is adjusted to match the material characteristics of the steel product, so that it is possible to produce molten steel without causing problems in quality and over-quality of the steel product.

Moreover, generally, trump elements, such as Cu, Ni, and Mo, often have an effect of improving the properties of steel products such as strength, corrosion resistance, and weld crack sensitivity. This means that the addition amount of alloy elements such as Mn and C as well as Cu, Ni and Mo, which are scheduled to be added to ensure these properties, can be reduced. Therefore, if the method of the present invention is applied, it becomes possible to reduce the amount of alloying elements added, which contributes to resource savings and, in turn, to reduction of energy consumed and CO ₂ generated when producing these component adjusting materials. To do.

  An example will be described in which component adjustment is performed only by decarburization refining in a converter without going through secondary refining equipment.

  From the material properties required by the customer, the target component composition (corresponding to the range of provisional target component values) is C: 0.17 ± 0.02 mass%, Si: 0.15 ± 0.05 mass%, Mn The conventional method and the method of the present invention were compared when refining using a converter having a furnace capacity of 300 tons for a steel grade for a thick steel plate given as 0.63 ± 0.08 mass%.

  First, as a conventional example, converter decarburization refining was performed so as to meet the above target component composition without considering iron scrap and hot metal trump elements. The average value of refining with 10 charges, the Mn content in the molten steel at the time of blowing the converter is 0.14% by mass, and it was put into the ladle to adjust the ingredients when the steel was discharged from the converter. The basic unit of ferromanganese was 4.9 kg / mol.

  In the example of the present invention, iron scrap and hot metal playing card elements were calculated from the respective component compositions and charging amounts. The average value of 10 charges was Mo: 0.020 mass%, Cu: 0.090 mass%, Ni: 0.075 mass%.

On the other hand, the carbon equivalent (Ceq) in the final steel product calculated from the target component composition (corresponding to the range of the provisional target component value) by the following formula (4) was 0.275. However, in the formula (4), [% C], [% Mn], [% Cr], [% Mo], [% V], [% Cu], [% Ni] are in the steel of each element. It represents the content (mass%).
Ceq = [% C] + [% Mn] / 6 + ([% Cr] + [% Mo] + [% V]) / 5 + ([% Cu] + [% Ni]) / 15 ... (4)
The contribution to the carbon equivalent (Ceq) of the above-mentioned trump element corresponds to 0.015 from the equation (4). Therefore, the Mn content is reduced by that amount, and the target component value at the time of converter steelmaking is set. C: 0.17 ± 0.02% by mass, Si: 0.15 ± 0.05% by mass, Mn: 0.54 ± 0.08% by mass.

  The average value of refining with 10 charges and the Mn content in the molten steel at the time of blowing the converter is 0.14% by mass, and ferromanganese introduced into the ladle to adjust the components when the steel is discharged from the converter. The basic unit of Mn was an average of 4.0 kg / molten steel-ton in terms of pure Mn.

  Thus, by applying the present invention, it was possible to reduce the amount of ferromanganese added at the time of the converter steel to 0.9 kg / molten steel-ton by making Mn pure. Moreover, the material characteristics of the rolled thick steel plate satisfied the demands of each customer.

  Following the decarburization refining in the converter, an example in which the components are adjusted by secondary refining with the RH vacuum degassing apparatus will be described.

  From the material properties required by the customer, the target component composition (corresponding to the range of provisional target component values) is C: 0.19 ± 0.02 mass%, Si: 0.15 ± 0.05 mass%, Mn : About 0.85 ± 0.11 mass% steel grade for thick steel plate is decarburized and refined using a converter with a furnace capacity of 300 tons, and then secondary refined in an RH vacuum degasser In some cases, the conventional method and the method of the present invention were compared.

  First, converter decarburization refining was performed so as to be in a range lower than the above target component composition without considering iron scrap and hot metal trump elements as a conventional example. That is, since the final component adjustment is performed by the RH vacuum degassing apparatus, the target composition at the time of steel leaving the converter is C: 0.19 ± 0.02 mass%, Si: 0.15 ± 0.05 mass%, Mn: 0.75 ± 0.11% by mass. The average value of refining with 10 charges and the Mn content in the molten steel at the time of blowing the converter is 0.14% by mass. The basic unit of manganese was 6.0 kg / molten steel-ton in terms of the average Mn content.

  Subsequently, in the secondary refining in the RH vacuum degassing apparatus, 1.1 kg / molten steel-ton of metal manganese was added as pure Mn, and the final Mn content of the molten steel was adjusted to 0.85 mass%.

  On the other hand, in the examples of the present invention, iron scrap and hot metal playing card elements were calculated from the respective component compositions and charging amounts. In the average value of 10 charges, the trump element of the molten metal in the furnace was Mo: 0.016 mass%, Cu: 0.062 mass%, and Ni: 0.087 mass%.

  The target component at the time of converter steelmaking is 0.1% by mass lower than Mn: 0.85 ± 0.11% by mass of the target component composition (corresponding to the range of the provisional target component value), 0.75 ± Decarburization refining was performed at 0.11% by mass. In other words, the target components at the time of steel conversion from the converter were C: 0.19 ± 0.02 mass%, Si: 0.15 ± 0.05 mass%, Mn: 0.75 ± 0.11 mass%, The carbon equivalent (Ceq) calculated by the above formula (4) from the component composition was 0.315.

  The contribution of the trump element to the carbon equivalent (Ceq) corresponds to 0.013 from the equation (4). Therefore, the Mn content is reduced by that amount, and the converter steel output target component is set to C: 0. 19 ± 0.02 mass%, Si: 0.15 ± 0.05 mass%, Mn: 0.67 ± 0.11 mass%. The average value of refining with 10 charges and the Mn content in the molten steel at the time of blowing the converter is 0.13% by mass. The basic unit of manganese was an average value of 5.4 kg / molten steel-ton in terms of pure Mn.

  Subsequently, secondary refining was performed in an RH vacuum degassing apparatus, and final component adjustment was performed. Here, when the components of the molten steel produced from the converter were analyzed, C: 0.19% by mass, Si: 0.15% by mass, Mn: 0.75% by mass, and the trump element was Mo: 0.00. They were 020 mass%, Cu: 0.060 mass%, and Ni: 0.092 mass%.

  The carbon equivalent (Ceq) in the final steel product calculated from the target component composition (corresponding to the range of the provisional target component value) by the equation (4) was 0.332. Therefore, considering the contribution of the trump element to the carbon equivalent (Ceq), the final target component values are C: 0.19 ± 0.02 mass%, Si: 0.15 ± 0.05 mass%, Mn : 0.77 ± 0.11% by mass, in a RH vacuum degassing apparatus, manganese manganese is added as a pure Mn, 0.2 kg / molten steel-ton is introduced, and finally the Mn content of the molten steel is set to 0.1. It adjusted to 77 mass%.

  Thus, by applying the present invention, the addition amount of ferromanganese at the time of converter steelmaking is 0.6 Mn / mol steel-ton, and the addition amount of metallic manganese in the RH vacuum degasser The amount of pure Mn was reduced by 0.9 kg / molten steel-ton. Moreover, the material characteristics of the rolled thick steel plate satisfied the demands of each customer.

Claims (1)

  Decarburization and refining in the converter using hot metal and iron scrap as the main raw material, the molten steel produced by the decarburization and refining from the converter to the ladle is refined in the secondary refining equipment, When producing molten steel of the target component, in decarburization refining in the converter, the molten steel component is adjusted at a concentration lower than the target component value range that is temporarily determined based on the required material properties of the steel product. Then, the concentration of the trump element of the molten steel produced from the converter is analyzed, the range of the target component value that is provisionally determined based on the influence of the trump element on the material characteristics is corrected, and the molten steel component is A method for producing molten steel, comprising adjusting a refining condition and a component adjusting material addition amount in a secondary refining facility so as to fall within a range of a corrected target component value.