JPH0437134B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> This invention performs highly efficient dephosphorization while minimizing the amount of slag-forming agents (quicklime, etc.) used throughout the entire steelmaking process, and uses manganese ore (including iron-manganese ore) as a refining agent. The present invention relates to a method for producing high-quality steel at a low cost by utilizing Mn and maximally melting and reducing it to increase the refining end point [Mn] concentration in a converter. <Background technology> In recent years, various studies have been conducted with the aim of developing means to stably melt low-phosphorus steel at even lower costs. Regarding the minimization of phosphorus and the stable production of low phosphorus steel, the following preliminary dephosphorization method of hot metal is used: (a) Preliminary dephosphorization is performed by injecting quicklime-based flux or soda ash into the hot metal in a torpedo. (b) A method in which preliminary dephosphorization is performed by injecting or blasting a quicklime-based flux onto the hot metal in the ladle; (c) A method in which quicklime-based flux is applied to the hot metal in the blast furnace casting bed trough. A method of preliminary dephosphorization by blasting has been proposed, and some of it has been put into practical use. However, in methods (a) and (b) above, dephosphorization is a “transitary reaction” that progresses during the floating process of the dephosphorizing agent.
Because the dephosphorization flux is not always efficiently used because it relies on the ``reactor reaction'', there is also the problem that the longer the treatment time, the more heat is removed during the treatment, which lowers the hot metal temperature. In method c), the dephosphorization treatment is performed on hot metal immediately after being tapped from the blast furnace, so the dephosphorization treatment temperature is as high as approximately 1400℃, and therefore it is difficult to reach a sufficiently satisfactory level of P content. Furthermore, when using quicklime etc. as flux for hot metal dephosphorization, considering the amount of quicklime etc. used in the subsequent converter blowing, both of the above methods Compared to the "method of omitting the preliminary dephosphorization step and performing dephosphorization only in a converter," the effect of reducing the amount of required slag forming agent (amount of quicklime, etc.) could not be said to be that remarkable. Based on the above situation, the present inventors first used two converter-type furnaces with both upper and lower blowing functions as schematically shown in Fig. 3, and one of them was used for dephosphorization. Furnace 1, the other is decarburization furnace 2
Then, a refining agent mainly composed of converter slag 4 generated in the decarburization furnace 2 is added to the hot metal 3 injected into the dephosphorization furnace 1, and bottom-blown gas is stirred by the stirring gas injection nozzle 5. At the same time, oxygen gas is blown upward from lance 6 to raise the temperature of hot metal 3 in dephosphorization furnace 1 to 1400℃.
After dephosphorizing the hot metal while maintaining the following conditions, the obtained dephosphorized hot metal is decarburized and final dephosphorized in the decarburization furnace 2 to produce steel with a normal phosphorus level or He established a "steel manufacturing method that enables low-phosphorus steel to be manufactured with good workability and at low cost," and proposed it as patent application No. 132517-1981. The above invention previously proposed by the present inventors is
``The amount of slag forming agent required throughout the entire steelmaking process is minimal when ``slag-metal countercurrent refining'' is used, which brings slag and metal into countercurrent contact.
In reality, it is almost impossible to fully realize countercurrent refining, and the only steelmaking method that has the potential to reduce the amount of slag used with the least amount of labor is the two-step dephosphorization process. Recognizing that there is no other way than to divide the process into stages and use the slag generated in the lower process as a dephosphorizing agent in the upper process,
Regarding the "steel manufacturing method by reusing converter slag," the following findings (A) are based on research aimed at solving problems in terms of work stability, dephosphorization efficiency, equipment cost, etc.
(F), that is, (A) In the dephosphorization treatment of hot metal, it is better to keep the treatment temperature as low as possible from the viewpoint of dephosphorization efficiency, but if the temperature becomes too low, it will cause problems in the next step, Since the problem of increased granular iron loss to the slag after treatment occurs, the temperature is
The best temperature is about 1200-1400°C, preferably about 1300-1350°C. However, in actual work, it is extremely difficult to maintain the above temperature because the addition of the dephosphorizing agent itself becomes a major factor in lowering the processing temperature. However, by blowing a small amount of oxygen gas during the dephosphorization process, (B) In order to fully utilize the dephosphorizing ability of the flux and increase the dephosphorization efficiency, it is necessary to maintain the dephosphorization equilibrium state in addition to adjusting the treatment temperature as described above. Although adequate agitation is essential to achieve
In order to achieve sufficient and efficient stirring in a short time for highly efficient dephosphorization of high-temperature hot metal,
Gas agitation using gas injected from the bottom of the processing vessel is most preferable. distance)
(D) In order to reduce erosion of the processing vessel refractories caused by slag and increase dephosphorization work efficiency, it is preferable to use a basic lining. (E) Steel manufacturing including a two-step dephosphorization process In order to increase the efficiency of dephosphorization in the method, the efficiency of removing slag from the processing container can be ignored, and it is essential to use a processing container that allows easy removal of slag. Sufficient exhaust gas treatment equipment (dust collector) is required for mass production. (G) Taking these conditions into consideration, a converter-type furnace is recommended as the hot metal dephosphorization treatment vessel, and stirring gas is introduced from the bottom of the furnace. A composite blowing converter with both upper and lower blowing functions is ideal, and if this is used to carry out the above-mentioned "steel manufacturing method including a two-stage dephosphorization process," the slag-forming agent will be removed throughout the entire steel manufacturing process. It was completed based on the following principles: Even if the amount used is extremely small, sufficient dephosphorization can be performed and high-quality steel can be mass-produced with high efficiency. The method previously proposed by the present inventors can stably produce low-phosphorus steel with low-cost operation that minimizes the amount of slag-forming agent used, and provides high-quality steel at a low price. It was extremely advantageous. Moreover, the proposal also suggests that Mn ore be input during converter refining (decarburization furnace refining) to reduce [Mn] loss during refining and increase molten steel [Mn]. It was also very useful when melting Mn steel. In particular, in recent years, in response to the increasing demand for quality stabilization and cost reduction of thick plate steel materials, research has been actively conducted to produce high-Mn steel at the lowest possible price. The most effective method is the "converter refining method in which manganese ore is introduced into the hot metal in the converter and oxygen blowing is performed to increase the end point [Mn] concentration," but the method proposed above This makes it possible to reduce the amount of slag-forming agent used,
This made it possible to increase the molten steel [Mn] more effectively by adding manganese ore. However, the method proposed above focuses on adding manganese ore in the decarburization furnace, and the main aim is to increase the [Mn] concentration at the end of the decarburization furnace. The addition of manganese ore did not place much emphasis on it, and was merely a secondary addition, if desired, to the dephosphorization refining agent, whose main components were [converter slag + iron oxide + fluorite]. . The amount of manganese ore that can be added in the decarburization furnace at this time is determined by the "dephosphorization temperature and hot metal [C] concentration" and the "decarburization furnace end temperature and molten steel [C] concentration." Therefore, in reality, the amount of manganese ore that can be added in the decarburization furnace, which is the main source of addition, is at most only about 15 to 20 kg per ton of molten iron, and the [Mn] concentration at the end of the decarburization furnace is 0.7 to 0.9% by weight. It was only a matter of degree. On the other hand, the [Mn] concentration of products that require a high Mn content is often quite high, around 1.5% by weight, so it is necessary to make up for the deficiency by adding expensive ferromanganese, etc. From this point of view, it has been strongly recognized through subsequent studies that the above-mentioned method previously proposed by the present inventors is still unsatisfactory. In other words, in order to further reduce the manufacturing cost of high-Mn steel by reducing the amount of ferromanganese added after refining, it is necessary to further increase the [Mn] concentration at the end point of the decarburization furnace. - Because there is a limit to the amount of manganese ore that can be reduced by smelting, it was not possible to simply increase the amount of manganese ore added in the decarburization furnace. However, it is possible to further improve the end point [Mn] concentration when molten steel with a high Mn concentration is refined in a converter (normal refining using only one converter) by adding manganese ore to the dephosphorized pig iron produced by hot metal pretreatment. It is also known that it is effective to add a carbonaceous material such as coke. However, even if this method is applied to decarburization refining using the method proposed earlier, not only will the cost increase due to the use of coke, the cost of blown oxygen will also increase, and the blowing time will be extended (leading to a decrease in productivity). ), increase in [S] from coke, increase in gangue from coke, increase in amount of quicklime added to neutralize gangue, and increase in amount of slag as a result of increase in amount of gangue and quicklime. Although a certain degree of cost reduction effect is recognized due to a decrease in the amount of residue, etc., when comparing the amount of increase in [Mn] that is the same as when manganese ore is added and melted and reduced without adding coke, the amount of increase in [Mn] when using coke is It could not be denied that the benefits would be smaller. <Means for Solving the Problems> Therefore, the present inventors devised a system for converting hot metal by using one of two converter-type furnaces with both upper and lower blowing functions as a dephosphorization furnace and the other as a decarburization furnace. It is possible to effectively increase the end point [Mn] concentration in the decarburization furnace by taking advantage of the previously proposed steelmaking method of refining, and without using the method of adding coke that has the disadvantages mentioned above. As we continued our research to find a steel manufacturing method that is efficient and has low production costs, we obtained the following findings. That is, (a) the previously proposed method did not require the addition of manganese ore in the dephosphorization furnace, but if blowing is performed in the dephosphorization furnace with manganese ore as an essential refining agent, this manganese ore In addition to sufficiently acting as an oxidizing agent for dephosphorization, it is also possible to easily maximize the [Mn] concentration of hot metal dephosphorized in a dephosphorization furnace. Then, if a slag-forming agent containing manganese ore is further added to this dephosphorized pig iron with a high [Mn] concentration and it is refined in a decarburization furnace, it will be possible to achieve a low phosphorus and [Mn] concentration with the least amount of slag-forming agent used. (b) Generally, the refining agent (flux) for hot metal dephosphorization has quicklime, iron oxide, and fluorite as its main components.
Iron oxide is considered to be an essential component, and the method previously proposed by the present inventors also
It was recognized that in order to secure FeO and promote dephosphorization, it is essential to include iron oxide in the refining agent (dephosphorization agent) added in the dephosphorization furnace (therefore, the dephosphorization agent Converter slag + iron oxide + fluorite] was considered to be good), but in this case, as a dephosphorizing agent, it does not contain iron oxide
(c) Therefore, even if fluorite is mixed with manganese ore, the manganese ore will act effectively as a substitute for iron oxide and good dephosphorization will proceed. If a refining agent containing manganese ore is used as a dephosphorizing agent in a dephosphorization furnace instead of iron oxide, which was an essential component of iron oxide, the cost required for adding iron oxide can be reduced and sufficient dephosphorization can be achieved. (Of course, manganese ore not only promotes dephosphorization, but also works to effectively increase the [Mn] of the dephosphorized pig iron by being reduced with [C] etc.). (d) As a result, the final point [Mn] in the subsequent decarburization furnace refining becomes higher (when performing manganese ore addition blowing only in the decarburization furnace). A much higher end point [Mn] concentration than the limit value can be obtained). Significant savings in manganese ferroalloy are possible. This invention was made based on the above knowledge, and it is said that ``As shown in Fig. 1, one of the two converter-type furnaces having both upper and lower blowing functions is dephosphorizing furnace 1, and the other is In a steelmaking method in which hot metal is refined using the decarburization furnace 2, the hot metal 3 injected into the dephosphorization furnace 1 is
A refining agent whose main components are the converter slag 4 generated in the decarburization furnace 2 and manganese ore (hereinafter collectively referred to as "manganese ore" including "iron-manganese ore") is added, and the stirring gas is blown. A process of dephosphorizing the hot metal and raising the hot metal [Mn] while keeping the temperature of the hot metal below 1400°C by blowing oxygen gas upward from the lance 6 while stirring bottom-blown gas through the pouring nozzle 5, and By adding a normal slag-forming agent and manganese ore to phosphorous hot metal and refining it in the decarburization furnace 2, and including the process of decarburizing the hot metal and increasing the refining end point [Mn] of the molten iron, the amount of phosphorus can be reduced to an extremely small amount. It is characterized by the ability to produce high-quality steel with a low phosphorus level and high [Mn] content using a slag-forming agent with good workability and at low cost. The reason why the treatment temperature in the dephosphorization furnace is adjusted to 1400℃ or less is that if the hot metal treatment temperature is higher than this, decarburization will proceed and the amount of oxidizing agent in the slag will decrease, and thermodynamically the temperature will be lower than 1400℃. If the temperature is above ℃, dephosphorization will deteriorate. However, if the temperature is too low, the loss of granular iron to the slag increases, and there are also problems in increasing the [Mn] concentration in the molten steel in the subsequent decarburization furnace. That is, the melting reduction of manganese ore proceeds through an endothermic reaction of MnO ₂ +2[C]→[Mn]+2CO (the cooling capacity of manganese ore is about 2.5 times that of scrap). Therefore, the amount of manganese ore that can be added (the amount that can be reduced by melting) increases as the temperature and [C] concentration of the hot metal increases. Therefore, completing the dephosphorization process while the hot metal temperature and [C] concentration are high increases the amount of manganese ore that can be added in the decarburization furnace and increases the final [Mn] concentration in the decarburization furnace. preferable. Here, in order to easily complete the dephosphorization process while the temperature and [C] concentration are high, the first idea is to raise the temperature and [C] concentration of the hot metal poured into the deP furnace as high as possible. Large changes in the tapping temperature and [C] concentration of blast furnace pig iron are problematic both technically and cost-wise. Therefore, it is important to keep the temperature and [C] concentration of the hot metal (ie, the sum of the sensible heat and latent heat of the hot metal) as low as possible during the dephosphorization process. Therefore, it is preferable to maintain the treatment temperature in the dephosphorization furnace as high as possible within the range of 1400°C or lower. This treatment temperature is maintained by blowing oxygen gas from the top blowing lance or by blowing oxygen gas from the bottom tuyere. In other words,
The oxygen gas injection in the dephosphorization furnace is performed to ensure the dephosphorization treatment temperature. Therefore,
The top-blowing oxygen lance here may be a normal converter lance, but it may also be a new small flow rate lance for dephosphorization. The amount of oxygen gas used is determined by the temperature and silicon content of the hot metal before treatment, the temperature of the converter slag, the warmth of the dephosphorization furnace, the target temperature of the hot metal to be treated, etc., but is approximately 20Nm ³ /t. It may be less than 5 Nm 3 /t, and usually 5 to 10 Nm ³ /t is effective. Incidentally, the amount of decarburization at this time is about 0.5%. ``Converter type furnace with both upper and lower blowing functions''
The currently used "top-bottom blowing combined blowing converter" is the most preferable, but especially for dephosphorization furnaces,
Since the refining conditions are milder than in a decarburization furnace, the furnace itself can be made even smaller, so even if a new one is built specifically for dephosphorization, there will not be much of an impact on the cost. As the refining agent (dephosphorization agent) in the dephosphorization furnace, a substance whose main components are converter slag generated in the decarburization furnace and manganese ore is used. For example, converter slag: 40 to 80% by weight , Manganese ore: 10 to 60% by weight, Fluorite: 0 to 30% by weight. In addition, since manganese ore is somewhat disadvantageous in terms of slag formation compared to iron oxide, it is better to actively add fluorite, and it is better to add more fluorite than when adding iron oxide. desirable. This refining agent is of course not limited to the above composition, and quicklime may be added in addition,
CaCl <sub>2</sub> , Na <sub>2</sub> O.SiO <sub>2</sub> , Na <sub>2</sub> CO <sub>3</sub> or the like may be added. Further, instead of manganese ore, iron-manganese ore may be used as described above. and,
The smaller the particle size of these dephosphorizing agent raw materials other than the converter slag is, the more preferable it is from the viewpoint of slag formation, but there is no problem as long as it is of a generally used size. By the way, as already mentioned, in the method previously proposed by the present inventors, the important components of the dephosphorizing agent in the dephosphorizing furnace are [converter slag + iron oxide + fluorite], and among these, the dephosphorizing agent in the dephosphorizing furnace is In addition to slag, iron oxide was also considered essential to ensure a high dephosphorization rate. However, the present inventors investigated a method of using manganese ore instead of iron oxide used as the oxidizing agent, and in this case, the same dephosphorization rate as when using iron oxide could be obtained, and the The present invention was completed by discovering that it is possible to increase the [Mn] concentration while maintaining the temperature and [C] concentration of molten iron at the same level as when iron oxide is used. However, when using the conventional quicklime-based hot metal dephosphorizing agent (quicklime + iron oxide + fluorite), even if manganese ore is mixed as described above instead of iron oxide,
The slag formation of the flux is very poor, and the oxidizing power in the slag necessary for dephosphorization cannot be secured, so that good dephosphorization does not proceed. However, in the case of a dephosphorizing agent based on converter slag (converter slag + iron oxide + fluorite), why can good results be obtained even if the component "iron oxide" is replaced with "manganese ore"? ``Since the converter slag has been turned into slag, the flux is well converted into slag,'' and ``Since the converter slag contains about 10 to 25% by weight of iron oxide, this and manganese slag must be mixed.'' This is thought to be due to the fact that the oxidizing powers of the ores combine to secure the oxidizing power necessary for dephosphorization. The amount of smelting reduction of manganese ore (itself acts as an oxidizing agent) varies depending on the amount added, but for example, with an input amount of 10 kg/t, the increase in [Mn] is 0.3 to 0.4
It is about %. In this case, in order to increase the addition yield of manganese ore, it is advantageous to set the slag basicity to 2.5 or more. The reason for this will be explained using FIG. 2. Figure 2 shows “(Mn) in the slag of the dephosphorization furnace [actually
Figure 2 shows the relationship between the ratio of Mn in the form of MnO (expressed in weight percent) to hot metal [Mn] (Mn distribution ratio) and slag basicity. As is clear from the above, it can be seen that (Mn)/[Mn] decreases as the basicity increases.In other words, the higher the slag basicity, the easier manganese oxide is reduced, and the region where the slag basicity is 2.5 or more It can be confirmed that this tendency becomes strongest and becomes constant (note that desulfurization progresses more easily as the slag basicity increases, and CaO/SiO ₂
It has also been confirmed that the desulfurization rate is about 60% when is 3). In order to increase the basicity of slag, there is a method of increasing the amount of converter slag in the decarburization furnace, but quicklime may be added as an auxiliary together with the converter slag. The amount of refining agent (dephosphorizing agent) used in the dephosphorizing furnace is determined by the [P] level of the steel to be melted, but is usually about 30 to 60 kg/t. Now, as the converter slag, which is the main component of the refining agent used in the dephosphorization furnace, the molten slag generated in the decarburization furnace is preferable from the viewpoint of thermoeconomics and the ability of the dephosphorization flux to form slag. (If the molten material is used in this way, it is poured into the dephosphorization furnace through a pot lined with refractory material.) Considering ease of handling, etc., the material obtained in the decarburization furnace is used. It may be used after being cooled and solidified and crushed into granules or chunks (in addition,
Also at this time, from a thermal standpoint, the higher the slag temperature, the better.) However, in this case, the smaller the particle size is, the better it is in order to improve the slag formation in the dephosphorization furnace, but since the converter slag is inherently highly slag formation, the particle size is 100 mm.
Even if it is smaller than this, no particular inconvenience will occur, and even if it is larger than this, it can be used. The timing of the converter slag to be used is preferably that from the previous charge, but it goes without saying that it may also be from the decarburizing furnace or from a decarburizing furnace at another factory. Stirring gases blown from the bottom of the furnace include Ar, CO ₂ ,
It may be any of CO, N ₂ , O ₂ , air, etc. The degree of agitation of the bottom gas in the dephosphorization furnace is the same as in normal double blowing combined blowing (0.03 to 0.2N
m ³ /t), but it is of course possible to increase the amount even more if you are aiming for a factory with a high dephosphorization rate. When dephosphorization is performed under the above conditions, usually
Dephosphorized pig iron with the desired high [Mn] concentration can be obtained within 20 minutes. When the dephosphorized pig iron with increased [Mn] in the dephosphorizing furnace is blown in the dephosphorizing furnace, carbonaceous material such as coke is added as a heat source to increase the amount of manganese ore added. Needless to say, it's a good thing. Blowing in a decarburizing furnace is basically the same as blowing ordinary hot metal that has been dephosphorized outside the furnace, but in order to improve the [Mn] concentration of the molten steel at the end point, Manganese ore is added in addition to slag-forming agents, mainly quicklime and dolomite. By the way, when implementing the steel manufacturing method according to the present invention, it is preferable to perform a preliminary desulfurization treatment on the applied hot metal if possible. The first reason for this is that the progress of desulfurization is extremely slow in this steelmaking method, but on the other hand, when hot metal that has not been desulfurized in advance is used, the S content in the converter slag increases, and the This is because there is also a concern that the molten steel S content in the charge may be increased. Note that the preliminary desulfurization may be performed by any of the commonly used hot metal desulfurization methods. Furthermore, the lower the Si content of the raw material hot metal used in this method, the better. This is because as the Si content in the hot metal increases, the basicity of the slag in the dephosphorization furnace decreases, the dephosphorization ability decreases, and the total amount of quicklime etc. used increases. Therefore, it is a good idea to adjust the Si content of hot metal to 0.3% or less, preferably 0.2% or less. In addition, if it is desired to raise the temperature of the hot metal after treatment due to the conditions of the decarburization furnace, it may be advantageous to set the Si content of the hot metal to around 0.2%, so it should be determined based on the local conditions of the factory. It is. Next, the present invention will be explained in more detail with reference to examples in comparison with comparative examples. <Example> Comparative example 250 tons of hot metal having the composition shown in the upper row of Table 1, which had been desulfurized and desiliconized in a torpedo, was poured into a top and bottom double blowing combined blowing converter used as a dephosphorization furnace.
In addition to this, converter slag generated in a similar type of decarburization furnace is cooled and solidified and crushed into particles with a particle size of 30 mm or less25
Kg/t, 12 Kg/t of iron ore and 8 Kg/t of fluorite having similar particle sizes were added in a mixed state and dephosphorization was carried out for 13 minutes. The dephosphorization and decarburization furnaces used are both 250-ton and upper-lower furnaces that can be stirred by injecting gas from the bottom of the furnace.

【table】

【table】

【table】

[Table] This is a double blowing combined blowing converter, and the operating conditions shown in Table 2 were adopted. The dephosphorized pig iron thus obtained (composition is shown in the middle row of Table 1) is tapped into a ladle and then poured into a decarburizing furnace. t, fluorite 1Kg/t and manganese ore 20
Main blowing was carried out after adding Kg/t. The converter slag generated at this time was 25 kg/t, and a series of operations were repeated in which it was added to the dephosphorization furnace as a dephosphorizing agent raw material for the next charge together with iron ore and fluorite, and dephosphorization was performed. As a result, the total amount of quicklime and dolomite used in the entire steelmaking process was as low as 13 kg/t, and as shown in the lower row of Table 1, [P] was 0.011% by weight and [Mn] was 0.82% by weight. % of molten steel was obtained. In Table 1, the increase in [Mn] after dephosphorization is due to (MnO) in the converter slag generated in the decarburization furnace.
This was due to the fact that the amount of carbon dioxide was as high as 18% by weight. Example 1 250 tons of desulfurized and desiliconized hot metal having the components shown in the upper row of Table 3 poured into a dephosphorization furnace were mixed with 25 kg/t of converter slag generated in the decarburization furnace and 8 kg/t of fluorite. In addition, 12 kg of manganese ore with a particle size of 30 mm or less can be used instead of iron ore.
Dephosphorization treatment was carried out under the same conditions as in the above comparative example except that t was added. Next, the dephosphorized pig iron thus obtained (the composition is shown in the middle row of Table 3) was refined in a decarburization furnace under the same conditions as in the comparative example. As a result, molten steel as shown in the lower row of Table 3 was obtained, and it was revealed that the end point [Mn] in the decarburization furnace increased to 1.05% by weight. Of course, as in the comparative example, the amount of quicklime and dolomite used in the entire steelmaking process was small. In this way, it was confirmed that according to the method of the present invention, which uses manganese ore instead of iron ore as a refining agent in the dephosphorization furnace, it is possible to secure a higher increase in [Mn] by 0.23% compared to the case of the comparative example. Ta. Example 2 Converter slag generated in the decarburization furnace was used as a dephosphorizing agent (refining agent in the dephosphorization furnace) for 250 tons of desulfurized and desiliconized hot metal with the components shown in the upper row of Table 4: 25 kg/ Converter blowing was carried out in the same manner as in Example 1, except that the following mixtures were used: manganese ore: 12 kg/t, quicklime: 7 kg/t, and fluorite: 10 kg/t. The dephosphorized hot metal composition at this time is shown in the middle row of Table 4, and the final point molten steel composition in the decarburization furnace is shown in the lower row of Table 4. As is clear from Table 4, this refining made it possible to raise the end point [Mn] in the decarburization furnace to 1.13% by weight. This means that a 0.31% higher increase in [Mn] was ensured compared to the case of the comparative example. <Summary of effects> As explained above, when manganese ore is generally used in a decarburization furnace, about half of the
Although it remains in the slag as an oxide without being reduced to Mn, according to the present invention, the slag is reused as hot metal dephosphorization flux, so the residual ore is effectively utilized, and the "[ It is useful for “reducing [Mn] loss” or “increasing [Mn]”. Furthermore, since manganese ore is added to the decarburization furnace and reduced, the end point [Mn] in the decarburization furnace can be stably and inexpensively increased by about 0.2 to 0.3% by weight compared to conventional methods. Therefore, it is possible to reduce the amount of ferromanganese added by 3 to 4 kg per ton of crude steel, and it is also possible to achieve a significant reduction in the amount of slag forming agent required throughout the steelmaking process, which brings extremely useful effects industrially. It is possible.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of the process of the present invention. FIG. 2 is a graph showing the relationship between the Mn distribution ratio and the slag basicity in the dephosphorization furnace. FIG. 3 is a conceptual diagram of the process related to the steel manufacturing method proposed above. In the drawings, 1... dephosphorization furnace, 2... decarburization furnace,
3... Hot metal, 4... Converter slag, 4'... Dephosphorization slag whose main component is converter slag, 5... Stirring gas blowing nozzle, 6... Lance.

Claims (1)

[Scope of Claims] 1. A steelmaking method in which hot metal is refined by using one of two converter-type furnaces having upper and lower blowing functions as a dephosphorization furnace and the other as a decarburization furnace, wherein the dephosphorization furnace A refining agent mainly composed of converter slag and manganese ore generated in the decarburization furnace is added to the hot metal injected into the furnace, and oxygen gas is blown upward while stirring the bottom blowing gas to bring the temperature of the hot metal below 1400℃. The process involves dephosphorizing the hot metal and raising the hot metal [Mn] while maintaining the temperature, and adding a normal slag forming agent and manganese ore to the resulting dephosphorized hot metal and refining it in a decarburizing furnace, decarburizing the hot metal and increasing the molten iron. Refining end point [Mn]
A steel manufacturing method characterized by including a step of aiming at an increase in. 2. The steelmaking method according to claim 1, wherein the hot metal to be treated has been subjected to a preliminary desiliconization treatment to reduce the Si content to 0.30% by weight or less.