Method for determining slag, method for processing slag using the same, and method for manufacturing steelmaking slag.

Abstract

To provide a slag determination method, a slag treatment method using the same, and a steel-making slag production method, capable of avoiding generation of a large amount of defective slag that does not satisfy a quality standard determined by a standard such as JIS in a water immersion expansion test without construction of large-scale equipment and a large amount of operation cost.SOLUTION: A slag determination method of the present invention is a method for determining the properties of slag discharged from a converter. The slag is determined to be a non-defective product or a defective product by comparing an index value indicating the amount of free lime in the slag at the time of completion of a refining treatment process with a threshold value indicating a predetermined expansion limit of the slag. Slag discharged in a slag discharging process is treated by using the slag determination method. Further, slag determined to be a non-defective product by using the slag determination method is used as steelmaking slag.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for determining slag for steelmaking slag generated in a converter, a method for treating slag using the same, and a method for producing steelmaking slag.

Background Art

[0002] In the steelmaking process of a steelworks, in a converter, an oxidation refining treatment (desiliconization, dephosphorization, decarburization treatment) for producing molten steel is performed by adding an oxygen source such as oxygen gas to molten iron. In this oxidation refining treatment, slag is generated by an oxidation reaction of added auxiliary materials and impurity components in molten iron. After this slag is recovered, it is reused as raw materials for various applications.

[0003] One of the uses of the slag generated in a converter is a roadbed material. When using slag as a roadbed material, it is necessary to satisfy the quality standards defined by standards such as JIS for the water immersion expansion rate. For example, according to the JIS standard, it needs to be 1.5% or less. In order to reduce the water immersion expansion rate of slag, it is necessary to keep the amount of free lime in the slag low. Therefore, a method is used in which a threshold value of an index for estimating the amount of free lime from the slag composition is set, and the amount of auxiliary materials added during the oxidation refining treatment is set in advance so as to be controlled below the threshold value to control the water immersion expansion rate of the slag.

[0004] However, even when trying to perform the oxidation refining treatment with the preset amount of auxiliary material added, in order to prevent abnormal reactions during the oxidation refining treatment, it is necessary to appropriately change the amount of oxygen and the amount of auxiliary material added according to the situation of the refining reaction. Therefore, there are cases where the slag composition does not become as preset. In that case, slag with the amount of free lime in the slag not being kept low is mixed with other slag in the slag yard, and does not satisfy the quality standards defined by standards such as JIS in the water immersion expansion test, which has been the cause of generating a large number of defective products. FIG. 3 is a diagram showing one aspect of a conventional treatment method for determining good / defective products of slag generated in the refining treatment process of a converter as a conventional process.

[0005] As shown in Figure 3, the slag generated in the converter is stored in the slag field of the converter yard in batches of 1 charge each, and slag shipment lots are managed in large units such as 300 charges per lot. As a result, even a few charges of slag that have not had their free lime content suppressed may be mixed in, causing them to fail to meet the quality standards set by JIS and other standards in water immersion expansion tests. In such cases, steam aging treatment must be performed on the entire 3,000 tons of steelmaking slag, resulting in a significant workload and high costs.

[0006] A method to avoid such problems is disclosed, for example, in Patent Document 1. In this method, a modifier that fixes the CaO in the converter slag is added to the molten converter slag, and an oxygen-containing gas is blown onto the molten converter slag to oxidize it by granulating it to a particle size of 10 mm or less at least once. By doing so, a method is shown in which hydration expansion is prevented by modifying the CaO in the converter slag. However, this method is difficult to apply because it requires large-scale equipment and costs to modify the molten slag outside the converter. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2003-155511 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Conventional methods control the water immersion expansion rate of slag by setting a threshold for an index that estimates the amount of free lime from the slag composition, and pre-setting the amount of auxiliary materials added during the oxidative refining process to keep it below that threshold. However, with this method, even when attempting to perform the oxidative refining process with the pre-set amount of auxiliary materials added, it was necessary to appropriately change the amount of oxygen and auxiliary materials added according to the state of the refining reaction in order to prevent abnormal reactions during the oxidative refining process. As a result, there were cases where the slag composition did not turn out as pre-set. In such cases, slag in which the amount of free lime in the slag was not suppressed to a low level mixed with other slag in the slag depositing area, and failed to meet the quality standards set by JIS and other standards in the water immersion expansion test, resulting in the problem of generating a large amount of defective product, up to 3,000 tons at once.

[0009] Furthermore, the method disclosed in Patent Document 1 has the problem that it cannot be applied to actual slag manufacturing processes because it requires large-scale equipment and high operating costs to modify the molten slag outside the converter.

[0010] The objective of this invention is to propose a method for determining slag, a method for processing slag using this method, and a method for manufacturing steelmaking slag, which can avoid generating a large amount of substandard slag that does not meet the quality standards set by JIS or other standards in water immersion expansion tests, without requiring the construction of large-scale facilities or high operating costs. [Means for solving the problem]

[0011] The present invention provides a method for determining the properties of slag discharged from a converter, characterized by comparing an index value indicating the amount of free lime in the slag at the end of the refining process with a predetermined threshold value indicating the expansion limit of the slag (non-expansion threshold), thereby determining whether the slag is good or bad. In this invention, the properties of the slag are determined by determining whether the slag is good or bad as described above.

[0012] Furthermore, in the slag determination method according to the present invention configured as described above, (1) In the slag discharge process, when slag generated in multiple oxidation refining processes is discharged into the same slag receiving pot, the index values ​​indicating the amount of free lime in the slag from each of the multiple refining processes, calculated at the end of each of the multiple refining processes, are combined and used to make a single judgment of whether the slag is good or bad. (2) The determination of whether a batch of products are good or bad is made by calculating the average index value of the index values ​​indicating the amount of free lime in the slag, which were calculated at the end of each of the multiple refining processes, and comparing the average index value with the threshold value. (3) The determination of whether a batch of products are good or bad is made by comparing the index value indicating the amount of free lime in the slag calculated at the end of each of the multiple refining processes with the threshold value, and determining that any product containing a bad product is a bad product. This is considered to be a more preferable solution.

[0013] Furthermore, the slag processing method of the present invention calculates the composition of the slag at the end of the refining process according to the slag determination method described above, calculates the index value from the calculated slag composition, compares the threshold value with the index value, and if the comparison result determines that the slag is good quality, the slag discharged in the slag discharge process is placed in the good quality slag storage area, and if it is not determined to be good quality, it is determined to be a candidate for non-good quality.

[0014] Furthermore, in the slag processing method according to the present invention configured as described above, (1) Analyze the slag sample determined to be a candidate for non-good quality, calculate a second index value in the slag from the composition of the sample analysis results, and if the slag is determined to be good quality as a result of comparing the second index value with the threshold, place the slag discharged in the slag discharge process into the good quality slag storage area. If the slag is not determined to be good quality as a result of comparing the second index value with the threshold, it is determined to be non-good quality, and place the slag discharged in the slag discharge process into the non-good quality slag storage area. (2) The slag that has been determined to be of poor quality shall, after cooling, undergo crushing and sizing treatment as necessary, and be recycled to the converter, or be modified into good quality slag by extending the slag aging period beyond the usual time. This is considered to be a more preferable solution.

[0015] Furthermore, the steelmaking slag manufacturing method of the present invention determines whether the slag is good or bad by comparing an index value indicating the amount of free lime in the slag at the end of the refining process with a predetermined threshold value indicating the expansion limit of the slag, and uses the slag determined to be good as steelmaking slag. [Effects of the Invention]

[0016] According to the present invention's method for determining slag, a method for processing slag using the same, and a method for manufacturing steelmaking slag, a predetermined non-expansion threshold of the slag is compared with a free lime content index value. The slag is determined based on the value of the free lime content index value relative to the non-expansion threshold, and is then separated into good and bad products. As a result, it is possible to avoid the generation of a large amount of defective slag that does not meet the quality standards set by JIS and other standards in water immersion expansion tests, which would otherwise result in a heavy workload and high costs such as multiple steam aging treatments. Furthermore, this also has the effect of eliminating the need for large-scale equipment investment and substantial operating costs. [Brief explanation of the drawing]

[0017] [Figure 1] This diagram illustrates one aspect of the generation and treatment method of oxidized slag produced during the refining process of a converter. [Figure 2] This diagram illustrates one method for determining and separating good and bad quality oxidized slag generated during the refining process of a converter. [Figure 3] This diagram illustrates one conventional method for determining whether slag generated during the refining process of a converter is of good or bad quality. [Modes for carrying out the invention]

[0018] In the following detailed description, many specific details will be described by exemplifying embodiments of the present invention to provide a complete understanding of the present invention. However, it is clear that one or more embodiments can be implemented without such specific details. Also, for the sake of brevity, well-known structures and devices are shown in schematic diagrams in the drawings.

[0019] <Regarding the method for manufacturing steelmaking slag for implementing the slag determination method of the present invention> In the steel manufacturing method according to the present embodiment, hot metal discharged from a blast furnace is charged into a converter and subjected to oxidative refining treatment to produce molten steel. Hereinafter, hot metal and molten steel are collectively referred to as molten iron. The hot metal to be subjected to oxidative refining treatment may be previously subjected to hot metal pretreatment such as desiliconization treatment, dephosphorization treatment, and desulfurization treatment in other refining facilities.

[0020] In the present embodiment, as shown in FIG. 1, first, after charging molten iron, which is hot metal, into the converter, an inert gas is blown into the molten iron from a plurality of bottom blowing tuyeres, and oxygen gas is injected into the molten iron from an upper blowing lance, thereby performing a refining treatment step of oxidative refining treatment. Oxidative refining treatment is a treatment in which an oxygen source is added to hot metal to oxidize and remove impurity components such as carbon and phosphorus in the hot metal. In the present embodiment, by oxidative refining treatment, a decarburization reaction in which at least carbon in the molten iron is removed and a dephosphorization reaction in which phosphorus in the molten iron is removed proceed. Hereinafter, the addition of oxygen gas (oxygen source) to the molten iron by the injection of oxygen gas from the upper blowing lance is also referred to as blowing.

[0021] In the refining process, the decarburization reaction proceeds, oxidizing and removing carbon from the molten iron, producing molten steel with a low carbon concentration. Furthermore, in the refining process, auxiliary materials such as slag-forming agents are introduced into the converter to promote the dephosphorization reaction. At this time, multiple types of slag-forming agents with different component compositions are added in amounts corresponding to the target slag composition. The amount of auxiliary materials such as slag-forming agents is predetermined according to various blowing conditions, including the composition and temperature of the molten iron before oxidation refining, the target composition and target temperature of the molten iron after oxidation refining, the efficiency of the refining reaction, and the free lime content in the slag after oxidation refining. The determined amount is then added at the beginning of the oxidation refining process. In the slag composition, the ratio of the CaO concentration (mass%) to the SiO2 concentration (mass%) ((%CaO) / (%SiO2)) is called the basicity. Furthermore, the amount of auxiliary materials to be added is calculated in advance before the oxidation refining process based on the mass balance, including the composition of the molten iron and the planned amount of oxygen to be added. However, additional auxiliary materials may be added during the refining process to suppress slag and granular iron blasting, depending on the blasting situation. In the refining process, auxiliary materials are added, followed by blowing, and the oxidation refining process is completed when the composition and temperature of the molten iron reach the target.

[0022] First, the amount of oxides contained in the main raw materials (metals recovered from scrap and slag) charged into the converter before the oxidation refining process is calculated. Furthermore, the amount of auxiliary raw materials added during the oxidation refining process, the amount of oxides generated by the oxidation of components in molten iron by the oxygen source, the amount of slag carried over from the previous oxidation refining process, and the amount of elution from the refractory bricks lining the converter are calculated, including some estimations as needed. Based on these calculated values, the amount of slag in the converter and the calculated slag composition are derived. The estimated basicity of the slag calculated from this calculated slag composition is also called the calculated basicity. From this calculated slag composition, a free lime content index value indicating the amount of free lime in the slag according to the embodiment is calculated.

[0023] After the oxidation refining process, the converter is tilted to discharge the molten iron in a tapping process. The discharged molten iron is collected in a ladle (not shown) located below the converter and sent to the next process. After the tapping process, slag remains in the converter. The slag remaining in the converter is then discharged downwards from the furnace opening as the converter is tilted in the opposite direction from the tapping process.

[0024] The discharged slag is collected in a slag receiving pot located below the converter, and then discharged and cooled in a slag storage area. It is also sorted into good and bad grades as needed.

[0025] Subsequently, after crushing and magnetic separation, an aging treatment is performed to convert the free lime in the slag into calcium hydroxide. The aged oxidized slag is then subjected to a water immersion expansion test according to the JIS A 5015 test method to determine whether it is suitable for shipment as roadbed material. Good quality products are shipped as roadbed material.

[0026] <Regarding the present invention's method for determining slag, a method for processing slag using the same, and a method for manufacturing steelmaking slag> In this embodiment, as shown in Figure 2, the composition of the slag is calculated at the end of the refining process, and the free lime content index value in the slag is calculated from the calculated slag composition. This free lime content index value is then compared with a predetermined non-expansion threshold for the slag. If the comparison results in a good product, the slag discharged in the slag removal process is placed in the good product slag storage area. If it is not determined to be a good product, it is determined to be a candidate for a non-good product.

[0027] Furthermore, the determination method may be designed to classify a product as good if the free calcium content index value is below the non-expansion threshold (or less than the non-expansion threshold). Alternatively, a product may be classified as a candidate for non-good if the free calcium content index value is above the non-expansion threshold (or exceeds the non-expansion threshold). This design depends on the characteristics of the free calcium content index value, and the relationship is not limited.

[0028] In this embodiment, if the free lime content index value is below the non-expansion threshold, it is determined to be a good product, and the slag discharged in the slag removal process is placed in the good product slag storage area. If the free lime content index value exceeds the non-expansion threshold, it is determined to be a candidate for a non-good product.

[0029] One example of a free lime content index value is the following equation (1). In equation (1), first, the amount of CaO contained as a compound in the minerals in the slag is estimated based on the amount of oxides such as SiO2, Al2O3, Fe2O3, and P2O5 in the slag, and the relative abundance of oxides to CaO in each mineral. Then, the amount of CaO contained as a compound in the minerals is subtracted from the amount of CaO in the slag composition, and the remainder is often used as the free lime content.

[0030] Free calcium content index value (estimated formula) ≈ T.CaO-CaO(in 2CaO·SiO2)-CaO(in 2CaO·Al2O3)-CaO(in 2CaO·Fe2O3)-CaO(in 3CaO·P2O5)···Formula (1)

[0031] One example of a method for pre-defining the non-expansion threshold of slag is as follows: First, slag generated from multiple blowing processes is cooled together in a slag deposit area, and then a sample is taken. From the compositional analysis of the sample slag, a free lime content index value is calculated using formula (1), etc. Subsequently, the free lime content index value is compared with the results of a water immersion expansion test performed on the slag according to the JIS A 5015 test method to determine the threshold value that satisfies the quality standards for roadbed material.

[0032] For slag that has been determined to be a candidate for non-quality, a sample of the slag is analyzed, and a second free lime content index value in the slag is calculated from the composition of the sample analysis results. If the calculated second free lime content index value is below the non-expansion threshold, it is determined to be quality, and the slag discharged in the slag removal process is placed in the quality slag storage area. On the other hand, if the second free lime content index value exceeds the non-expansion threshold, it can also be determined to be non-quality, and the slag discharged in the slag removal process is placed in the non-quality slag storage area. The comparison between the second free lime content index value and the non-expansion threshold (settings such as "greater than or equal to," "less than or equal to," "less than," "greater than," etc.) can be designed in the same way as described above.

[0033] The slag samples described above may be collected by inserting a sample-collecting ladle or similar tool into the slag discharged into the slag receiving pot, or by inserting a sample-collecting ladle or similar tool into the slag discharged to the slag accumulation area after being discharged into the slag receiving pot. For the subsequent task of separating good and bad quality slag, it is more preferable to collect samples from the slag discharged into the slag receiving pot. After the samples collected by the above method have cooled, they are often analyzed using an analytical instrument employing techniques such as X-ray fluorescence, and the compositional analysis results are obtained as fractions of mass of oxides such as CaO, SiO2, MnO, Fe2O3, Al2O3, and P2O5.

[0034] In the aforementioned slag discharge process, when slag generated from multiple oxidation refining processes is discharged into the same slag receiving pot, there is also a method of collectively determining whether the slag is good or bad by combining the free lime content index values ​​in the slag calculated at the end of each refining process.

[0035] In that case, the determination of whether a product is good or bad may be made by comparing the average index value calculated from the free lime content index values ​​in the slag, which are calculated multiple times at the end of each of the aforementioned refining processes, with the non-expansion threshold.

[0036] Alternatively, the determination of whether a batch of slag is good or bad may be made by comparing the free lime content index value in the slag, calculated multiple times at the end of each refining process, with the non-expansion threshold, and determining that a batch is bad if even one batch contains a bad product.

[0037] The slag that has been determined to be of poor quality can be recycled to a converter after cooling, followed by crushing and sizing as needed, or it can be modified into good quality slag by extending the slag aging period beyond the usual time.

[0038] In the embodiment of the present invention relating to the method for manufacturing steelmaking slag, slag determined to be of good quality using the slag determination method described above is used as steelmaking slag. For example, in the embodiment relating to the method for manufacturing steelmaking slag of the present invention, an index value indicating the amount of free lime in the slag at the end of the refining process is compared with a predetermined threshold value indicating the expansion limit of the slag to determine whether the slag is of good quality or not, and slag determined to be of good quality is used as steelmaking slag. This makes it possible to manufacture steelmaking slag suitable for applications such as roadbed material. [Examples]

[0039] Using a steel manufacturing method similar to that of the above embodiment, molten iron was refined in a converter. The free lime content index value in the slag generated during the refining process was calculated, and the free lime content index value was compared with the non-expansion threshold. If the free lime content index value was below the non-expansion threshold, it was judged as good quality, and the slag discharged in the slag removal process was placed in the good quality slag deposit area. If the free lime content index value exceeded the non-expansion threshold, it was judged as poor quality, and a sample of the slag was analyzed again. A second free lime content index value in the slag was calculated from the composition of the sample analysis results. If the second free lime content index value was below the non-expansion threshold, it was judged as good quality, and the slag discharged in the slag removal process was placed in the good quality slag deposit area. If the second free lime content index value exceeded the non-expansion threshold, it was judged as poor quality, and the slag discharged in the slag removal process was placed in the poor quality slag deposit area.

[0040] For the analysis of slag samples deemed to be non-compliant, a sample was taken by inserting a sample-collecting ladle into the slag discharged into the slag receiving pot. The collected sample was then cooled, crushed, and sized, and analyzed using an X-ray fluorescence analyzer. The results obtained as percentages by mass were used.

[0041] Furthermore, in calculating the free lime content index, when slag generated from multiple oxidation refining processes was discharged into the same slag receiving pot, a method was used to combine the free lime content index values ​​in the slag calculated at the end of each refining process and perform a single judgment of good or bad quality.

[0042] The aforementioned determination of whether a batch of slag is good or bad was carried out using the following two methods. In one method, the free lime content index value was calculated at the end of each of the multiple refining processes. This average index value was then calculated and compared with the non-expansion threshold. In the other method, the aforementioned determination of whether a batch of slag is good or bad was carried out by comparing the free lime content index value in the slag, calculated at the end of each of the multiple refining processes, with the non-expansion threshold, and determining that a batch was bad if even one batch contained a bad product.

[0043] By applying this embodiment, it was possible to prevent the generation of a large amount of defective slag that does not meet the quality standards set by JIS and other standards in water immersion expansion tests due to the mixing of good slag with poor slag. This made it possible to avoid the significant workload and high costs associated with multiple steam aging treatments. Table 1 below shows the results of applying this embodiment and the results when it is not applied.

[0044] [Table 1]

[0045] In determining whether a product was good or bad, the free lime content index value was calculated using the following formula (2). As the non-expansion threshold, first, slag generated from multiple blowing cycles was cooled together in the slag deposit area, and then a sample was taken. The free lime content index value was calculated from the compositional analysis values ​​of the sample slag using formula (2). Next, the calculated free lime content index value was compared with the results of a water immersion expansion test conducted on the slag according to the test method of JIS A 5015, and a threshold of 0.45 was set as the threshold for meeting the quality standard for roadbed material. If the non-expansion threshold was 0.45 or less, the product was judged to be good; if it exceeded 0.45, it was judged to be bad.

[0046] Free calcium content index value = (%CaO) - 1.87 × (%SiO2) - 1.1 × (%Al2O3) - 0.7 × (%T.Fe) × α - 1.18 × (%P2O5) ... Equation (2) Here, α is a coefficient obtained from the actual ratio of T.Fe value to Fe2O3 value in the slag. Since Fe2O3 cannot be directly determined as an analytical result in the X-ray fluorescence analysis used in this example, the actual ratio of T.Fe value to Fe2O3 value of the converter slag, obtained by another analytical method, is used as a substitute. In this example, α = 0.64.

[0047] In this embodiment, the calculation of the free lime content index value in the slag generated during the refining process, and the determination of whether the free lime content index value is below the non-expansion threshold, were automatically calculated using a process computer. When slag generated from multiple oxidation refining processes is discharged to the same slag receiving pan, the free lime content index values ​​in the slag from multiple processes, calculated at the end of each refining process, are combined and a single good / bad product determination is automatically calculated using the process computer. The results are automatically notified to the person in charge of the converter operation room and also to the person in charge of the slag field. The person in charge of the slag field is reliably notified by illuminating a red warning light (registered trademark) and sounding an alarm when a slag receiving pan containing bad slag is transported to the work area. This also introduces a mechanism to prevent the person in charge of the slag field from mistakenly placing good and bad slag in the wrong slag storage area.

[0048] To allow users to selectively use the following two methods, each method was introduced as a configuration option in the process computer: (1) A method of determining whether a batch of products are good or bad by calculating the average index value of the free lime content index values ​​in the slag, which are calculated multiple times at the end of each of the aforementioned refining processes, and comparing the average index value with the non-expansion threshold; and, (2) A method for determining whether a batch of slag is good or bad by comparing the index value of free lime content in the slag, calculated multiple times at the end of each refining process, with the non-expansion threshold, and determining that any batch containing any bad material is bad.

Claims

1. A method for determining the properties of slag discharged from a converter, wherein the slag is determined to be good or bad by comparing an index value indicating the amount of free lime in the slag at the end of the refining process with a predetermined threshold value indicating the expansion limit of the slag, according to a slag determination method, A method for processing slag, comprising: calculating the composition of the slag at the end of the refining process; calculating the index value from the calculated slag composition; comparing the threshold value with the index value; if the comparison results in a good product, placing the slag discharged in the slag discharge process into a good product slag storage area; and if it is not determined to be a good product, determining it as a candidate for a non-good product. A method for processing slag, comprising: analyzing a sample of slag determined to be a candidate for non-good quality; calculating a second index value in the slag from the composition of the sample analysis results; if the slag is determined to be good quality as a result of comparing the second index value with the threshold, the slag discharged in the slag discharge process is placed in the good quality slag deposit area; and if the slag is not determined to be good quality as a result of comparing the second index value with the threshold, it is determined to be non-good quality, and the slag discharged in the slag discharge process is placed in the non-good quality slag deposit area.

2. The slag processing method according to claim 1, wherein the slag determined to be of poor quality is recycled to the converter after cooling, and if necessary, subjected to crushing and sizing treatment, or modified into good quality slag by extending the slag aging period beyond the usual time.

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