JPH01142009A - Steel making method - Google Patents

Abstract

PURPOSE:To efficiently and inexpensively manufacture high-quality and high- manganese steel by refining the molten iron in a dephosphorizing furnace with a refining agent obtained by adding manganese ore to the converter slag in a decarburizing furnace, and refining the dephosphorized molten iron in the decarburizing furnace. CONSTITUTION:One of the two converter-type furnaces is used as the dephosphorizing furnace 1 and the other as the decarburizing furnace 2 and molten iron 3 is refined. In this steel making method, the converter slag 4 generated in the decarburizing furnace 2 and the dephosphorized slag 4' consisting essentially of manganese ore are added as the refining agent to the preliminarily desiliconized and desulfurized molten iron 3 charged in the dephosphorizing furnace 1, and refining is carried out at <=1,400 deg.C by the bottom-blown gas agitation and the top-blown gaseous oxygen. In this way, the molten iron is dephosphorized, and the molten iron [Mn] is increased. The dephosphorized molten iron 3 is then transferred to the decarburizing furnace 2, the ordinary slag forming agent such as quick lime and manganese ore are charged, and refining is resumed. By this method, molten iron is decarburized, and the refining end point [Mn] of the molten iron is increased.

Description

[Detailed Description of the Invention] <Industrial Field of Application> The present invention is directed to the use of slag-forming agents (quicklime, etc.) throughout the entire steelmaking process.
In addition to performing highly efficient dephosphorization while minimizing the amount used, we also use manganese ore (including iron-manganese ore) as a refining agent and maximize the melting and reduction of it to reduce the [Mn] concentration at the end of refining in the converter. The present invention relates to a method for producing high-quality steel at a low cost by increasing the amount of steel.

<Background technology> In recent years, various studies have been conducted with the aim of developing means to stably produce 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 carried out by injecting quicklime-based flux or soda ash into the hot metal in a torpedo. Method.

(bl) A method of preliminary dephosphorization by injecting or blasting quicklime-based flux into hot metal in a ladle.

(A method in which preliminary dephosphorization is performed by blasting quicklime-based flux to the hot metal in the C1 blast furnace casthouse gutter.

have been proposed, and some have even been put into practical use.

However, in methods (a) and (middle) above, the dephosphorization is limited to "reactions that proceed during the floating process of the dephosphorizing agent (transitary reactor reaction)," so the efficiency of using the dephosphorizing flux is not necessarily good. There is also the problem that the longer the treatment time, the more heat is removed during the treatment and the temperature of the hot metal decreases. It has been pointed out that since the dephosphorization treatment is carried out at a high temperature of about 1400° C., it is difficult to achieve a sufficiently satisfactory P content.

Furthermore, when using quicklime etc. as a hot metal dephosphorization flux, considering the amount of quicklime etc. used in the subsequent converter blowing, both of the above methods are effective in eliminating the preliminary dephosphorization step. It could not be said that the effect of reducing the required amount of slag forming agent (amount of quicklime, etc.) was not so remarkable compared to the method of dephosphorizing using only a converter.

Therefore, based on the above situation, the present inventors first decided to
As shown schematically in the figure, two converter-type furnaces having both upper and lower blowing functions are used, and one of them is used as a dephosphorization furnace 1, the other as a decarburization furnace 2, and the dephosphorization furnace 1 is used. 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 molten iron 3, and oxygen gas is added from the lance 6 while bottom blowing gas is stirred by the stirring gas blowing nozzle 5. After dephosphorizing the hot metal while keeping the temperature of the hot metal 3 in the dephosphorization furnace 1 below 1400 ° C. by top blowing, the obtained dephosphorized hot metal is decarburized and final dephosphorized in the decarburization furnace 2. Established a "steel manufacturing method that enables the production of normal phosphorus level steel or low phosphorus steel with good workability and at low cost with an extremely small amount of slag forming agent" and proposed it as patent application No. 132517/1982. .

In addition, the above-mentioned invention previously proposed by the present inventors states that [the required amount of slag forming agent throughout the entire steelmaking process is sometimes determined by "slag-metal countercurrent refining" in which slag and metal are brought into contact with each other in a countercurrent manner. The least amount is fine, but in reality it is almost impossible to fully realize countercurrent refining, and it is currently listed as the steelmaking method with the least amount of labor and the potential to reduce the amount of thinning agent used. Recognizing that the only way to achieve this goal is to divide the dephosphorization process into two stages and use the slag generated in the lower process as a dephosphorizing agent. The following findings from research aimed at resolving problems in terms of work stability, dephosphorization efficiency, equipment cost, etc. based on the "steel manufacturing method by reusing converter slag" (A) to (F), In other words, (^) 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 not only cause problems in the next process, but also cause problems in the slag after treatment. The temperature is 1,200 to 1,400°C, preferably 13
The best temperature is about 0~1350°C. However, in actual work, it is extremely difficult to maintain the above temperature because the addition of the dephosphorizing agent itself is a major factor in lowering the processing temperature, but by blowing a small amount of oxygen gas during the dephosphorization process, is stable and easily maintained.

(i3) In order to fully utilize the dephosphorizing ability of the flux and increase the dephosphorizing efficiency, it is necessary to adjust the treatment temperature as described above, as well as to lack sufficient stirring to achieve a dephosphorizing equilibrium state. However, in order to achieve sufficient and efficient stirring in a short time for highly efficient dephosphorization of high-temperature hot metal, gas stirring using gas blown from the bottom of the processing vessel is most preferable.

(C) In addition, in order to perform an efficient dephosphorization process, the processing vessel must have sufficient freeboard (distance from the scene to the top of the vessel) for slag forming.

(D) In order to reduce erosion of the processing vessel refractories due to slag and increase dephosphorization work efficiency, it is preferable to use a basic lining.

(E) In order to increase the efficiency of dephosphorization in a steelmaking process that includes a two-stage dephosphorization process, the efficiency of removing slag from the processing container cannot be ignored, and it is essential to use a processing container that allows easy removal of slag. .

(F) In order to mass-produce high-quality steel with good workability, sufficient exhaust gas treatment equipment (dust collection*) is necessary.

(G) Considering these conditions, a converter-type furnace is ideal as a hot metal dephosphorization treatment vessel, especially a combined blowing converter that has both upper and lower blowing functions that can introduce stirring gas from the bottom of the furnace. When this is used to carry out the above-mentioned "steel manufacturing method including two-stage dephosphorization process", sufficiently efficient dephosphorization can be achieved even if the amount of slag forming agent used throughout the entire steel manufacturing process is extremely small. High-quality steel can be mass-produced with high efficiency.

It was completed based on.

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 cost. It was extremely advantageous.

Moreover, this proposal requires Mn during converter refining (decarburization furnace refining).
Input ore to reduce [Mn] loss during refining and to reduce molten steel [
It also suggests that efforts should be made to increase Mn], which is extremely useful even when producing high-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 means of
? The method proposed above makes it possible to reduce the amount of slag-forming agent used, which makes it possible to more effectively increase the molten steel [Mn] by adding manganese ore. became possible.

However, the method proposed above focuses on adding manganese ore in the decarburization furnace, and thereby
The main aim is to increase the concentration of manganese ore in the dephosphorization furnace, and it is not so important to add manganese ore in the dephosphorization furnace. It was merely a secondary addition to the phosphorus refining agent if desired.

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]Na degree." Therefore, in reality, the amount of manganese ore that can be added in the decarburization furnace, which is the main source of addition, is 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. It was only about % by weight.

On the other hand, products that require a higher Mn content [
Mn] concentration is often quite high, around 1.5% by weight (
Therefore, it is necessary to compensate for the deficiency by adding expensive ferromanganese, etc. From this point of view, the above method proposed by the present inventors has some shortcomings. This has come to be strongly recognized through consideration of the following.

In other words, in order to further reduce the manufacturing cost of high Mn steel by reducing the amount of ferromanganese added after refining = 8-, it is necessary to further increase the [Mn] concentration at the end point of the decarburization furnace.
Due to the above-mentioned reasons, there is a limit to the amount of manganese ore that can be added and melted down, so it was not possible to simply increase the amount of manganese ore added in the decarburization furnace.

However, the end point [Mn] i1 when manganese ore is introduced into dephosphorized pig iron by hot metal pretreatment and molten steel with a high M ntR is refined in a converter (normal refining using only one converter).
! It is also known that it is effective to add a carbonaceous material such as coke as a means to further improve the carbon content. 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). ), [S] rise from coke.

The rise of gangue from coke, the increase in the amount of quicklime added to neutralize the gangue, and the decrease in the manganese ore reduction yield due to the increase in the amount of slag as a result of the increase in the amount of gangue and quicklime, etc. Although the cost reduction effect is recognized, it is the same as when manganese ore is added without adding coke and melted and reduced [When compared in terms of Mnl increase, it could not be denied that the benefit when using coke is 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 raise the end point [Mn] 911 degrees 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 they continued their research to find a steel manufacturing method that is efficient and has low manufacturing costs, they obtained the following findings. That is, (a) Although the previously proposed method did not require the addition of manganese ore in the dephosphorization furnace, if blowing is performed in the dephosphorization furnace with manganese ore as an essential refining agent, this manganese ore In addition to acting well as an oxidizing agent for dephosphorization,
It becomes possible to easily maximize the [Mn] tllff degree of hot metal dephosphorized in a dephosphorization furnace. Then, if a slag-forming agent containing manganese ore is further added to this high [Mn] tM = degree dephosphorization pig iron and refined in a decarburization furnace, it will be possible to obtain low-phosphorus and [Mn ] ? It is now possible to stably melt high-grade steel at a low cost and with high efficiency. (bl) 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 in the method previously proposed by the present inventors, ``in order to secure FeO in the slag and promote dephosphorization, a refining agent (dephosphorization agent) is added in the dephosphorization furnace. It was recognized that it is essential to include iron oxide in In this case, even if you use a dephosphorizing agent that does not contain iron oxide [converter slag + manganese ore] or a mixture of fluorite, the manganese ore will effectively act as a substitute for iron oxide and will work well. (C1) Therefore, if a refining agent containing manganese ore is used as a dephosphorizing agent in the dephosphorization furnace in place of iron oxide, which was an essential component other than the converter slag, iron oxide addition is possible. Of course, it is possible to proceed with sufficiently good dephosphorization while reducing the cost required for
In addition to promoting dephosphorization, manganese ore itself has [C]
(d) As a result of these, subsequent decarburization The end point [Mn] in furnace refining becomes higher (the end point [Mn] is much higher than the limit value when performing manganese ore addition blowing only in a decarburization furnace).
), and significant savings in manganese ferroalloys can be achieved.

This invention was made based on the above-mentioned knowledge. ``As shown in FIG. In a steelmaking method in which hot metal is refined using decarburization furnace 2, hot metal 3 injected into dephosphorization furnace 1 is mixed with converter slag 4 generated in decarburization furnace 2 and manganese ore (here, "iron-manganese ore"). ”
A refining agent whose main component is mangon ore) is added, and while the bottom-blown gas is stirred by the stirring gas injection nozzle 5, oxygen gas is blown upward from the lance 6 to raise the temperature of the hot metal. A process of dephosphorizing the hot metal and raising the hot metal [Mn] while keeping the temperature below 1400°C, and adding a normal slag forming agent and manganese ore to the obtained dephosphorized hot metal and refining it in the decarburization furnace 2. By including decarburization and the process of increasing the smelting end point [Mn] of molten iron, high quality steel with a low phosphorus level and high ['Mn]' content can be produced with an extremely small amount of slag forming agent. It is characterized by being easy to work with and can be manufactured at low cost.

Reason for adjusting the treatment temperature in the dephosphorization furnace to below 1400℃□
The reason is that if the hot metal treatment temperature is higher than this, only decarburization will progress and the amount of oxidizing agent in the slag will decrease, and thermodynamically, dephosphorization will deteriorate at temperatures above 1400°C.

However, if the temperature is too low, the loss of granular iron to the slag will increase, and [Mn] '1 in the molten steel in the subsequent decarburization furnace
There are also problems in increasing the degree of lls.

That is, the melting reduction of manganese ore proceeds through an endothermic reaction of Mn0z → -2 [C] → [Mnl + 2CO (the cooling capacity of manganese ore is about 2.5 times that of scrap). Therefore, the amount that can be added to manganese ore (the amount that can be reduced by melting) depends on the temperature of the hot metal and [C]? ! The higher the degree, the more it occurs. Therefore, completing the dephosphorization process while the hot metal temperature and [C]s degree are high increases the amount of manganese ore that can be added in the decarburization furnace and increases the Mnl concentration at the end point 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 the [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, the treatment temperature in the dephosphorization furnace is preferably maintained as high as possible within the range of 1400°C or less.

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 desired temperature of the hot metal to be treated, etc.
Generally, it should be less than 2ONm3, usually 5 to 1ONm3/
l is effective. Incidentally, the amount of decarburization at this time is 0.5%
That's about it.

As for the above-mentioned "converter type furnace with both top and bottom blowing functions", the currently used "top and bottom blowing combined blowing converter" is the most preferable. Since the dephosphorization process is also mild, the furnace mouth body can be made even smaller, so even if a new one is installed exclusively for dephosphorization, there will be no significant impact on the cost.

As the refining agent (dephosphorization agent) in the dephosphorization furnace, one 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: 10-60% by weight.

Fluorite 20-30% by weight A formulation with the following composition is recommended.

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, or CaCj! 2
+ NazO' 5t()z, NazCO3, etc. may be added. Further, instead of manganese ore, iron-manganese ore may be used as described above. 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 sludge formation, but there is no problem as long as it is of the level commonly used.

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 for ensuring 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 [Mnl ta degree] 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 flux becomes very poor in slag formation, and Since the oxidizing power in the slag necessary for dephosphorization cannot be secured, 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"? [The converter slag has been turned into slag once, so the flux is well converted into slag.] and [The converter slag contains 10 to 25% by weight of iron oxide.]
This is thought to be due to the fact that this and the oxidizing power of the manganese ore combine to secure the oxidizing power necessary for dephosphorization.

The amount of manganese ore reduced by melting (itself acts as an oxidizing agent) varies depending on the amount added, but for example, the amount of manganese ore added is 10
The increase in [Mn] in kg/l is about 0.3 to 0.4%.

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, MnO
Mn content in the form of [% by weight]] and hot metal [
Figure 2 shows the relationship between the ratio of Mn] (Mn distribution ratio) and the slag basicity.As is clear from Figure 2, the higher the basicity, the greater the ] becomes smaller. In other words, the higher the slag basicity, the more easily manganese oxide is reduced, and it can be confirmed that this tendency becomes strongest and becomes constant in the region where the slag basicity is 2.5 or more ( Note that desulfurization progresses more easily as the flag basicity increases, and it has been confirmed that when Cab/Sing is 3, the desulfurization rate is about 60%).

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 it is usually 30 to 6
0kg/or so is fine.

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 to form slag of the dephosphorization fluff. (When using a molten substance like this, it is poured into a dephosphorization furnace through a pot lined with a refractory). It may be used after cooling and solidifying the material and crushing it 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 ability to form slag in the dephosphorization furnace, but since converter slag is inherently highly slag-formable, the particle size is less than 100 fins. Even if the size is larger, it will not cause any particular inconvenience, and it can be used even if it is larger than this.

The timing of the converter slag to be used is preferably that of the previous charge, but it goes without saying that it may also be that which came out of the decarburizing furnace before that or that which was generated in the decarburizing furnace of another factory.

The stirring gas blown from the bottom of the furnace is Ar, CO21CO.
, N, , O□, air, etc. may be used.

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 0.2 Nm'
/l), but it is of course possible to increase the amount even more with the aim of improving the dephosphorization rate.

When dephosphorization treatment is carried out under the above conditions, dephosphorized pig iron with a desired high [Mn] concentration can usually 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 added manganese ore. 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 it improves the [Mn] tM degree of the molten steel at the end point. Therefore, 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 this invention,
If possible, it is better to perform a preliminary desulfurization treatment on the applied hot metal. The first reason 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 concern about increasing the molten steel S content in the charge. 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, the Si content of hot metal should be 0.3% or less if possible.
Preferably, it is a good idea to adjust it to 0.2% or less. In addition, if it is desired to raise the hot metal temperature after treatment due to the conditions of the decarburization furnace, it may be advantageous to set the Si content of the hot metal to about 0.2%, so it should be determined according to 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 an upper and lower double blowing combined blowing converter used as a dephosphorization furnace. 25 kg/l of converter slag generated in a similar type of decarburizing furnace by cooling and solidifying it and crushing it to a particle size of 30 W or less, 12 kg/l of iron ore with a similar particle size, and 8 kg/l of fluorite. were added in a mixed state to perform dephosphorization treatment for 13 minutes.

The dephosphorization furnace and decarburization furnace used were both 25'O ton top and bottom double blowing combined blowing converters capable of gas injection and stirring from the bottom of the furnace, and the operating conditions were as shown in Table 2. was adopted.

The dephosphorized pig iron thus obtained (composition is shown in the middle row of Table 1) was tapped into a hotpot and then poured into a decarburization furnace, and additionally 8 kg/l of quicklime and 5 kg of dolomite were poured into the decarburizing furnace. /l,
Main blowing was carried out after adding 1 kg/l of fluorite and 20 kg/l of manganese ore.

The converter slag generated at this time was 25 kg/l, 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 small as 13 kg, and [P] in the mesh was 0.011% by weight and [Mn] as shown in the lower part of Table 1.
] 0.82% by weight was obtained.

In addition, the reason why [Mn] increases after dephosphorization in Table 1 is because
This is because (MnO) in the converter slag generated in the decarburization furnace was as high as 18% by weight.

Example 1 250 tons of desulfurized and desiliconized hot metal having the composition as shown in the upper part of Table 3 was poured into a dephosphorization furnace, and 25 kg/l of converter slag generated in the decarburizing furnace and 8 kg/l of fluorite were added. In addition, dephosphorization was performed under the same conditions as in the comparative example, except that 12 kg of manganese ore with a particle size of 30 mm or less was added instead of iron ore.

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.

As described above, according to the method of the present invention in which manganese ore is used instead of iron ore as a refining agent in the dephosphorization furnace, it is possible to secure an increase in [Mn] higher than 0.23% compared to the case of the comparative example. confirmed.

Example 2 Desulfurization and desiliconization hot metal 25 with the components shown in the upper row of Table 4
Converter slag generated in the decarburizing furnace as a dephosphorizing agent (refining agent in the dephosphorizing furnace): 25 kg/l.

Manganese ore: 12kg/l.

Quicklime: 7kg/l.

Fluorite: Converter blowing was carried out in the same manner as in Example 1, except that a 10 kg/l mixture was used.

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 is 0.31% higher than that of the comparative example [M
n] means that the increase has been secured.

<Summary of Effects> As explained above, when manganese ore is generally used in a decarburization furnace, about half of it is not reduced to Mn and remains in the slag as oxide =26-, but this invention According to this method, since the slag is reused as hot metal dephosphorization flux, the residual ore is effectively utilized, which is useful for "reducing [Mn] loss" or "increasing [Mn]" in the hot metal dephosphorization step. In addition, since manganese ore is added to the decarburization furnace and reduced, the end point in the decarburization furnace [
Mn] 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 entire steelmaking process, resulting in extremely useful effects industrially. It is possible.

[Brief explanation of the drawing]

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 earlier. In the drawings: 1...Dephosphorization furnace 1 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 (2)

[Claims] (1) In a steelmaking method in which hot metal is refined by using one of two converter type furnaces with upper and lower blowing functions as a dephosphorization furnace and the other as a decarburization furnace, the hot metal is injected into 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, and the hot metal is heated while maintaining the hot metal temperature at 1400°C or less by blowing oxygen gas upward while stirring the bottom blowing gas. A process of dephosphorization and raising of hot metal [Mn], a normal slag-forming agent and manganese ore are added to the obtained dephosphorized hot metal and smelting in a decarburization furnace, and the end point of decarburization of hot metal and refining of molten iron [ 1. A steelmaking method comprising: a step of increasing Mn]. (2) The steelmaking method according to claim 1, wherein the hot metal to be treated has been subjected to preliminary desiliconization treatment to reduce the Si content to 0.30% by weight or less.