JPH032312A - Production of low-phosphorus pig iron - Google Patents

Abstract

PURPOSE:To effectively raise Mn concentration in dephosphorized pig iron without adversely affecting dephosphorizing capacity by blowing Mn ore fines through furnace-bottom tuyeres into iron bath at the time of dephosphorizing molten pig iron. CONSTITUTION:A dephosphorizing agent is added to molten pig iron and oxygen gas is top-blown while performing bottom-blown gas agitation, by which the dephosphorization of the molten pig iron is carried out. At this time, Mn ore fines 9 are blown through furnace-bottom tuyeres (bottom-blowing nozzles) 9 into the iron bath, or, Mn sintered ores prepared by exerting sintering by the addition and mixing of powdered slagging agent and coke fines are added from the upper part of the furnace together with the dephosphorizing agent 8, or, both means mentioned above are simultaneously carried out. Simultaneously, dephosphorizing treatment is performed while maintaining the temp. of the molten pig iron by top-blowing oxygen gas 7 through a top-blowing lance 6. By this method, the dephosphorizing treatment for molten pig iron and the raising of Mn concentration in molten pig iron by means of smelting reduction of Mn oxide can be simultaneously attained.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention simultaneously increases the [Mn] concentration in hot metal during hot metal dephosphorization treatment to achieve high [Mn]? The present invention relates to a method for dephosphorizing hot metal to increase [Mn] in order to advantageously manufacture M-grade steel.

<Prior art and its challenges> In recent years, various studies have been conducted with the aim of developing stable melting methods for low-phosphorus steel at even lower costs. Regarding the minimization of the total cost of steelmaking and the stable production of low-phosphorus steel, the following preliminary dephosphorization method of hot metal is proposed. How to do it.

(bl) A method of performing preliminary dephosphorization by reblasting (spraying) injected quicklime-based flux to 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 the above methods (al and (b)), the dephosphorization relies on "a reaction that progresses during the floating process of the dephosphorizing agent (transitary reactor reaction)", so the efficiency of using the dephosphorizing flux is not necessarily good, and There is a 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 the dephosphorization treatment temperature is as high as about 1400° C., and therefore 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 conducted the first
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 and the other as a decarburization furnace 2, and the dephosphorization furnace 1 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. As a result, we established a steel manufacturing method that enables the production of steel with normal phosphorus levels or low phosphorus steel with good workability and low cost with an extremely small amount of slag forming agent, and proposed it as Japanese Patent Application No. 132517/1986. did.

The above 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. Although it is possible to use the least amount of slag refining agents, it is almost impossible to completely realize countercurrent refining in practice, and at present, the most labor-intensive steelmaking method that has the potential to reduce the amount of slag-forming agent used is Recognizing that there is no other way than to divide the dephosphorization process into two stages and use the slag generated in the lower process as a dephosphorizing agent in the upper process, we decided to develop steelmaking by reusing converter slag. The following findings (8) to (F) are based on research aimed at resolving problems in terms of work stability, dephosphorization efficiency, equipment cost, etc., i.e., (A) In the dephosphorization process 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 is too low, it will cause problems in the next process, and there will be problems such as increased loss of granulated iron to the slag after treatment. occurs, so the temperature is most preferably about 1200 to 1400°C, preferably about 1300 to 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, the processing temperature can be stabilized. and easily maintained.

(B) 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 satisfactory 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 collector) is necessary.

(G) Taking these conditions into consideration, a converter-type furnace is recommended as the hot metal dephosphorization treatment vessel, and it is also possible to
A combined blowing converter with both upper and lower blowing functions that can be performed by humans is ideal, and if this is used to carry out the above-mentioned "steel manufacturing method that includes a two-stage dephosphorization process", the slag forming agent will be used throughout the entire steel manufacturing process. Even if only a small amount of phosphor is used, dephosphorization can be carried out efficiently and 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).
12. Input stones to reduce Mnl loss and melt Mn during refining.
id [It also suggests that the aim is to increase Mnl;
It was also very useful when melting n-steel.

In particular, in response to the increasing demand for quality stabilization and cost reduction of thick steel plates in recent years, high Mnj! A lot of research is being carried out to melt ＠ at the lowest possible price.
The most effective method among these is to introduce manganese ore into the hot metal in the converter and perform oxygen blowing to achieve the final point [M
The method proposed above makes it possible to reduce the amount of slag-forming agent used, which reduces mW by inputting manganese ore.
4 [It became possible to increase Mnl more effectively.

However, the method proposed above focuses on adding manganese ore in the decarburization furnace, and thereby
Mnl: The main aim is to increase the a degree,
The addition of manganese ore in the dephosphorization furnace does not place much emphasis on the addition of manganese ore, but is added as a secondary additive to the dephosphorization refining agent whose main components are [converter slag + iron oxide + fluorite]. It was just a thing.

The amount of manganese ore that can be added to the decarburization furnace at this time is determined by the "dephosphorization temperature and hot metal [C] concentration" and the "decarburization furnace end temperature and hot metal [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 15 to 20 kg per ton of molten iron.
The decarburization furnace end point [Mnl tri degree is also 0.7
The amount was only about 0.9% by weight.

On the other hand, products that require a higher Mn content [
The Mnl tM degree is often quite high, around 1.5% by weight, so it is necessary to compensate for the deficiency by adding expensive ferromanganese, etc. The above method proposed by the present inventors From this point of view, subsequent studies have led to the strong recognition that there are some shortcomings.

That is, in order to further reduce the production cost of high Mrf4 by reducing the Fe I:I manganese addition amount after refining, it is necessary to further increase the degree of Because there is a limit to the amount of manganese ore that can be added and melted down, it was not possible to simply increase the amount of manganese ore added in the decarburization furnace.

However, manganese ore is added to dephosphorized pig iron by hot metal pretreatment to further improve the end point [Mn] tM degree when molten steel with a high Mn concentration 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 achieve this. 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, but the cost of blown oxygen will also increase, and the blowing time will be extended (
(Decrease in productivity), increase in [S] from coke, increase in slag from coke, increase in amount of quicklime added to neutralize gangue9 Increase in amount of slag as a result of increase in amount of gangue and quicklime Although it is recognized that there is a cost reduction effect to the extent that there is a decrease in the manganese ore reduction yield, etc., when comparing the same amount of [Mn] increase as when manganese ore is added and melted and reduced without adding coke, coke It could not be denied that the benefits during use would be smaller.

Therefore, the object of the present invention is to add a dephosphorizing agent to hot metal poured into a converter-type furnace having both top and bottom blowing functions, and to top blow oxygen gas while stirring the bottom blowing gas. When aiming at low-cost dephosphorization of hot metal, it was also necessary to find a means to effectively increase the [Mn3 r= degree of dephosphorized pig iron without adversely affecting the dephosphorizing ability.

<Means for Solving the Problems> In order to achieve the above object, the present inventors conducted extensive research from various viewpoints, and as a result, the following new knowledge was obtained. That is, (al) In the hot metal dephosphorization method previously proposed in Japanese Patent Application No. 13251/1983, when manganese ore is added to increase the degree of [Mn]?W of the dephosphorized hot metal to 5.1, the manganese ore is powdered. Either it is blown into the hot metal from the bottom blowing tuyere of a dephosphorization furnace, or it can be used as a Mn source, such as "manganese sintered ore made by adding and mixing manganese ore powder with slag-forming agents such as limestone and silica sand, and coke powder". If this is added together with a dephosphorizing agent (quicklime, fluorite, converter slag, etc.) and refined, the added manganese ore will also effectively act as an oxidizing agent for hot metal dephosphorization. ,) in the dephosphorized hot metal processed in the dephosphorization furnace without having any adverse effect on the volume quality or operation [it is possible to maximize the MnlFi degreefb) and the obtained high If dephosphorized pig iron with [Mn]C degree is stored in a decarburization furnace and a slag agent containing manganese ore is added for decarburization refining, the overall amount of slag forming agent used is as small as possible. Phosphorus dekatsu [Mnl? It is possible to stably produce steel with a high W degree at low cost and with high efficiency.

(C) Therefore, the end point [Mn] in decarburization furnace refining is noticeably higher than that in conventional methods (the end point is much higher than the limit value when manganese ore addition blowing is performed only in a decarburizer). [Mn]?ffi degree), it is possible to significantly reduce the amount of manganese alloy iron.

The present invention has been made based on the above findings, etc.
[A dephosphorizing agent (dephosphorizing slag agent) is added to the hot metal poured into a converter type furnace that has both upper and lower blowing functions, and oxygen gas is blown upward while stirring the bottom blowing gas to dephosphorize the hot metal. When carrying out
As shown in FIG. 2, manganese ore powder (including ferromanganese ore powder) 9 is blown into the iron bath from the bottom tuyere (bottom blowing nozzle) 5, or as shown in FIG. (Dephosphorization slag agent) 8 and “manganese sintered ore made by adding and mixing powdered slag agent and coke powder to powdered manganese ore”
10 is added from the upper part of the furnace, or both of these methods are carried out at the same time, and oxygen gas 7 is blown upward from the top blowing lance 6 to maintain the temperature of the hot metal, and the dephosphorization process is carried out. It is characterized by the fact that it is possible to simultaneously achieve hot metal dephosphorization treatment and increase in hot metal [Mn] concentration by melting and reducing manganese oxides.

<Effect> In addition, [Mn] of dephosphorized hot metal? The reason why manganese ore is added to the dephosphorization furnace in order to increase the degree of W is either blown into the furnace bottom through the tuyere in the form of powder or used in the form of manganese sintered ore for the following reason.

Reasons for producing manganese ore powder Manganese ore has manganese oxide as its main component and mainly contains Si 02+ AN z Ox as gangue, but its melting point is 1700° C. or higher and it is hardly soluble. Therefore, if manganese ore is added from the upper part of the furnace under the temperature condition of 1400°C or less during dephosphorization treatment, the dissolution of the manganese ore is slow, and the progress of the increase in [Mnl] due to smelting reduction is delayed, and the Mn OQfj1 in the slag is The temperature rises, leading to a sudden rise in the slag melting point, and dephosphorization is also adversely affected due to deterioration of slag fluidity.

However, when powdered manganese ore is blown into the molten iron from the bottom tuyere, M110g+ 2C=Mn+ 2Co ・
... (1) As a result of the rapid progress of the reduction reaction, the manganese yield is dramatically improved, and the fluidity of the slag is maintained well, and the dephosphorization ability is not deteriorated.

That is, the injected manganese ore powder rises through the hot metal while being dispersed in the hot metal, but in this case, the reaction of equation +1) is rapid because the reaction interface area between the manganese ore and the hot metal is very large. , and when the amount of manganese oxide in the manganese ore decreases due to this reaction, Mn0-5iO
□-ARzO, a low melting point (1200-1300°C) slag of the system is generated, and dissolution proceeds rapidly. In other words, some manganese oxides are quickly reduced while the injected manganese ore powder rises in the iron bath, so when it reaches the slag layer above the iron bath, the progress of dissolution is accelerated. It is.

As a result, the fluidity of the top slag can be maintained well, and the reaction between the top slag and the iron bath occurs quickly, and the reduction of manganese oxides in the slag allows the increase in Mnl and the dephosphorization reaction to proceed smoothly. .

Therefore, there is no negative effect on dephosphorization, and at the same time [
This means that Mnl can be increased with high yield.

The particle size of the manganese ore powder to be blown in may be about 1 mesh or less, but from the viewpoint of flow, it is preferably about 100 mesh or less.

Reasons for using manganese sintered ore Even if manganese ore is added directly from the top of the dephosphorization furnace, the increase in [Mnl] due to smelting reduction is slow, and as described above, dephosphorization is also adversely affected. When manganese sintered ore, which is prepared by adding and mixing powdered slag-forming agents such as limestone and dolomite and coke powder to shaped manganese ore and then calcining the mixture, is added as a Mn source, the dissolution of the manganese ore proceeds extremely quickly. As a result, the reduction reaction of manganese oxides proceeds rapidly, making it possible to increase [Mnl] in the hot metal with a high yield, and maintaining good fluidity of the slag, so that the dephosphorization ability does not deteriorate.

In other words, the sintered ore has a much lower melting point than manganese ore, and therefore quickly turns into slag even under low-temperature conditions of 1400° C. or lower, such as during hot metal dephosphorization treatment. It also has an upper and lower blow mechanism. As the slag-metal reaction progresses quickly due to bottom-blown gas agitation from the bottom blowing surface of a converter-type furnace, manganese oxides are reduced at a high yield, making it possible to increase [Mnl]. . Moreover, since the fluidity of the slag is maintained well, the dephosphorization reaction also proceeds smoothly.

Therefore, as in the case of injecting manganese sintered ore from the bottom tuyere, it is possible to increase [Mnl] with a high yield while sufficiently maintaining the desired dephosphorizing ability.

The manganese sintered ore is produced by adding a powdered slag-forming agent such as limestone or dolomite to manganese ore powder, and then adding and mixing coke powder. 1100-14 at
It can be manufactured by firing at 00°C. During this firing, the manganese ore powder is assimilated with the powdered slag forming agent and becomes MMno-5.
A low melting point (1100 to 1300°C) slag mainly composed of in PdlzOz-CaO-MgO is produced and sintered.

It is desirable to mix the slag forming agent during the production of manganese sintered ore so that [(χCaO+2Mg0)/(χSing)) in the sintered ore is 0.3 to 2.0.

This is the dephosphorization treatment temperature (14
This is to promote slag formation of manganese sintered ore (manganese ore) at temperatures below 00°C. Outside this range, slag formation and reduction will be delayed, and as a result, there is a concern that the manganese yield will deteriorate.

In addition, the smaller the particle size of manganese sinter is, the better it is in order to improve the slag formation in the dephosphorization furnace, but since manganese sinter is inherently rich in slag formation, the particle size Even if it is about 100 cranes, there will be no particular inconvenience, and even if it is larger than this, it can be used.

By the way, when carrying out the hot metal dephosphorization treatment according to the present invention, it is preferable to adjust the treatment temperature in the dephosphorization furnace to 1400° C. or lower. This is because 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 1400° C. or higher.

However, if the temperature is too low, the loss of granular iron to the slag increases, and there is also a problem in increasing the [Mn]c5 degree in the molten steel in the subsequent decarburization furnace.

That is, the melting reduction of manganese ore is Mn0z + 2 [C] = [Mn] + 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 m degree, the more. 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 desired temperature of the hot metal to be treated, etc.
Generally, it should be less than 2ONm'8, usually 5 to 1ONm'/
l is effective. Incidentally, the amount of decarburization at this time is 0.5%
That's about it.

However, when manganese ore powder is injected from the bottom tuyere,
Inject a large amount (more than 10 kg) of manganese ore powder [
In order to increase Mnl, it is necessary to burn a larger amount of [C] in the hot metal with oxygen in order to compensate for the heat of the endothermic reaction (reduction reaction of Mn).

However, in order to increase the amount of Mn added in the decarburization furnace as described above, it is advantageous to make the [C] level after dephosphorization as high as possible.

Therefore, by blowing carbonaceous powder (coke, coal, etc.) into the iron bath together with manganese ore powder from the bottom blowing tuyere, [C]
An effective method is to suppress the decrease in [C] level after dephosphorization treatment and to make the [C] level as high as possible.

In the method of adding carbonaceous material from the top of the furnace, if powdered material is used, most of it will scatter, and if lumpy material is used, the carburizing speed will be extremely slow, so the [C] increasing effect cannot be sufficiently achieved. I can't perform.

The particle size of the carbonaceous powder that is injected together with the manganese ore powder is
As with manganese ore powder, it may be about l ni or less, but from the viewpoint of transportation, it is preferably about 100 mesh or less.

Regarding the method of blowing manganese ore powder and carbonaceous powder, they may be blown from the same or different sidings.

The amount of carbon material injected is desirably an amount equivalent to the reduction of manganese ore and the removal of carbon by oxygen feeding, and in this case, the decrease in [C] due to the dephosphorization process can be suppressed to a minimum.

It is also possible to blow powdered slag-forming agents (quicklime, fluorite, etc.) together with the manganese ore powder from the bottom blowing tuyere.

The currently used "top and bottom blowing combined blowing converter" is the most preferable as the "converter-type furnace with both top and bottom blowing functions" used in the method of the present invention, but the dephosphorization furnace in particular has different refining conditions. Because it is milder than a decarburization furnace, the furnace interior can be made even smaller, so even if a new furnace is used specifically for dephosphorization, there is not much of an impact on the cost.

As the refining agent (dephosphorization slag agent) in the dephosphorization furnace, those whose main components are quicklime, fluorite, and converter slag generated in the decarburization furnace are used, for example, quicklime: 0 to 80 weight%.

Fluorite: 0-50% by weight.

Converter slag: 0-80m1% A formulation with the following composition is recommended.

This refining agent is, of course, not limited to the above composition, and may additionally contain quicklime, CaC1z,
Nano・Sing, Na1COz, etc. may be added. 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 the same size as used in -M.

The amount of smelting reduction of manganese ore powder or manganese sinter (itself acts as an oxidizing agent) varies depending on the amount added, but for example, when inputting 1110 kg/l, the amount of increase in [Mn] is 0.
．． It is about 3 to 0.4%. It goes without saying that iron-manganese ore may be used instead of manganese ore used as manganese ore powder or manganese sinter.

In addition, in order to increase the addition yield of manganese ore powder or manganese sintered ore, it is advantageous to set the slag basicity to 2.5 or more. The reason for this will be explained using FIG. 4.

Figure 4 shows “(Mn) in the slag of the dephosphorization furnace (actually MnO
Mn content expressed in weight percent) and hot metal [
This figure shows the relationship between the ratio of Mn] to slag basicity (Mn distribution ratio) and slag basicity.As is clear from Figure 4, the higher the basicity, the more ] becomes smaller.In other words, the higher the slag basicity, the easier it is for manganese oxide to be reduced;
．． It can be confirmed that this tendency becomes strongest and becomes constant in the region of 5 or more (note that desulfurization progresses more easily as the slag basicity increases, and when CaO/SiO□ is 3, the desulfurization rate is 60%). It has also been confirmed that the
.

The amount of refining agent (dephosphorization slag agent) used in the dephosphorization furnace is determined by the [P] level of the steel to be melted, but usually 30
~60kg/weight is sufficient.

Now, as the converter slag used as part of the refining agent in the dephosphorization furnace, the molten slag generated in the decarburization furnace is preferable from the viewpoint of thermoeconomics and slag formation of the dephosphorization flux. (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 slag formation in the dephosphorization furnace, but since the converter slag is naturally rich in slag formation, the particle size is less than 100 ms. 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.

By the way, when implementing the treatment 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 treatment 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 amount of molten iron 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, it is a good idea to adjust the Si content of the hot metal to 0.3% or less, preferably 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 1 250 tons of hot metal having the composition shown in 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, and Dephosphorization treatment was carried out for about 12 minutes by adding a mixed 10 kg/l of iron ore as a dephosphorization slag agent and a dephosphorization agent from the upper part of the furnace.

As the dephosphorization slag agent, in case 1, 8 kg/l of quicklime and 4 kg/l of fluorite were used, and in case 2, the converter slag was cooled to 30 kg/l.
25kg/l and 8k of fluorite crushed to a particle size of mm or less
g/l was added.

The operating conditions of the dephosphorization furnace used (upper and lower double blowing combined blowing converter) were as shown in Table 2, and the operating conditions were the same for Case 1 and Case 2.

The composition of the dephosphorized hot metal thus obtained is shown in Table 3. In case 1, [P] is 0.025%;
[Mn] is 0.12%, and in case 2, [P]
The results showed that [Mn] was 0.015% and [Mn] was 0.14%.

Comparative Example 2 Desulfurization and iron with the composition shown in Table 4 poured into a dephosphorization furnace.
250 tons of desiliconized hot metal, a dephosphorizing slag agent, and manganese ore (particle size of 30 dragons or less) as a dephosphorizing agent.

χT, Mn=50) was added in a mixed state from the upper part of the furnace to perform dephosphorization treatment.

The blending conditions for the dephosphorizing slag agent were the same in Case 3 as in Case 1 of Comparative Example 1, and in Case 4 as in Case 2. Note that the test conditions other than the above were the same as in Comparative Example 1.

The components of the dephosphorized hot metal obtained in this way are shown in Table 5. In case 3, the dephosphorization was poor at [P]: 0.040%, and [Mn] was also 0.35%. It was confirmed that the manganese yield was low.

In addition, in case 4, the dephosphorization is slightly worse with [P]: 0.025%, and [Mn] is 0.47%, which is better than case 3, but the manganese yield is sufficiently high. It has been confirmed that it is not possible to obtain

Furthermore, when the properties of the slag after the dephosphorization treatment were investigated, it was found that in both cases 3 and 4, the slag was not completely melted (it was in a semi-molten state). was bad. This deterioration in slag formation is thought to be the cause of dephosphorization and a decrease in manganese yield.

The reason why case 4 gave relatively better results than case 3 is that because converter slag was used in case 4, it was less effective than other dephosphorization slag agents (quicklime, fluorite, etc.). This is thought to be due to the good slagability.

Example 1 Desulfurization of the component composition shown in Table 6 poured into a dephosphorization furnace.
A mixture of 250 tons of desiliconized hot metal and a dephosphorizing slag agent was added from the top of both the upper and lower blowing converters, and 1.5 kg of manganese ore powder (particle size of 100 mesh or less) was added from the bottom blowing tuyeres using N2 gas as a carrier gas. The dephosphorization treatment was performed for 12 minutes in total by blowing in an amount of mln-t for 8 minutes (total blowing amount 12 kg/l), and then blowing only N2 gas for the following 4 minutes.

The amount of bottom-blown N2 gas including carrier gas during and after manganese ore injection was 0.15N of/m.
It was adjusted to be 1 nt.

The blending conditions for the dephosphorizing slag agent were the same in case 5 as in case 1, and in case 6 as in case 2. Note that the test conditions other than the above were the same as those in Comparative Example 2.

The composition of the dephosphorized hot metal obtained by such treatment is shown in Table 7, and in case 5, [P] is 0.026%.
In case 6, [Mn] is 0.48%, and in case 6, [P] is 0.0.
At 15%, [Mn] was 0.58%, which significantly improved the dephosphorization rate and manganese yield compared to Case 3 and Case 4.
Results comparable to those of Case 1 and Case 2 were obtained.

From these results, it is clear that according to the method of the present invention, manganese ore can be melt-reduced at a high yield without deteriorating dephosphorization, and it is possible to effectively increase [Mn] in dephosphorized hot metal. be.

Example 2 A dephosphorization treatment test was conducted using an upper and lower blowing converter using 250 tons of desulfurized and desiliconized hot metal having the composition shown in Table 8. The test conditions were as follows: Manganese ore powder (particle size of 100 mesh or less) and coke powder (particle size of 100 mesh or less) were each fed from the bottom tuyere using N2 gas as a carrier gas.
kg/m1n- and 0.3 kg/min, 1 at t
Blow for 3 minutes (total of 26 kg and 3.9 kg, respectively)
kg/l), and only N2 gas was blown from the bottom for the next 4 minutes, resulting in a total of 17 minutes of dephosphorization treatment. Note that even after the manganese ore powder and coke powder were blown, the amount of bottom-blown N2 gas containing carrier gas was adjusted to 0.15 Nnf/5 in-t.

The mixing conditions for the dephosphorizing slag agent were the same in case 7 as in case 1, and in case 8 as in case 2. Note that the test conditions other than the above were the same as in Example 1.

The composition of the dephosphorized hot metal thus obtained is shown in Table 9, and it can be seen that good results were obtained in both dephosphorization and manganese yield.

Here, in order to compensate for the heat by increasing the amount of manganese ore injected, the top blowing oxygen time was increased to 5 minutes (the top blowing oxygen amount was 3 N of
/l) Dephosphorization treatment was carried out for an extended period of time ([C] at the acid storage site and manganese ore storage site was approximately 0°25% more than in Example 1).
), and by coke dust injection, [C
It was confirmed that 1fi&low could be prevented and the [C] level after dephosphorization could be maintained at a high level.

Example 3 250 tons of desulfurized and desiliconized hot metal having the composition shown in Table 1θ was poured into a dephosphorization furnace (both upper and lower blowing converter), and a dephosphorization slag agent and a composition of composition shown in Table 11 were added. Manganese sintered K (particle size 3
0): 12 kg/l was added in a mixed state from the upper part of the furnace to perform dephosphorization treatment.

The mixing conditions for the dephosphorizing slag agent were the same in case 9 as in case 1, and in case 10 as in case 2. Note that the test conditions other than the above were the same as those in Comparative Example 2.

The manganese sintered ore used was manufactured by the following method.

That is, the same manganese ore used in Comparative Example 2 was crushed to a particle size of 3 C or less, limestone powder and dolomite powder with a particle size of 3 C or less were added to this manganese ore powder, and coke powder was further added and mixed. Sintered using a Dwight Lloyd sintering machine. In addition, limestone powder.

Dolomitewa) and coke powder content are 20kg, 60kg and 100kg per ton of manganese ore powder, respectively.
It is g.

The composition of the dephosphorized hot metal thus obtained is shown in Table 12. In case 9, [P] was 0.027% and [Mn
] is 0.48%, and in case 10, [P] is 0.48%.
014% and [Mn] was 0.59%, both the dephosphorization rate and manganese yield were significantly improved compared to Case 3 and Case 4, and results comparable to Case 1 and Case 2 were obtained. It was done.

Example 4 In manufacturing manganese sintered ore, manganese sintered ore was prepared with various combinations of slag-forming agents (limestone, dolomite, etc.) and dephosphorized under the same operating conditions as Case 9 of Example 3. Processing was carried out. In addition, in each test, the total amount of slag-forming agents (limestone, dolomite) and dephosphorization-forming slag agents (quicklime, light calcined dolomite fluorite) in manganese sintered ore, and
The blending ratio was kept constant.

The results of these tests are shown in FIG.

The results shown in Figure 5 confirm that the method of the present invention can effectively increase [Mn] while maintaining good dephosphorization.
It is also clear that it is preferable to adjust o)/5i02 to 0.3 to 2.0 in order to ensure a good dephosphorization rate and manganese yield.

The results shown in Figure 5 indicate that the manganese yield and dephosphorization rate are greatly affected by the quality of slag formation of manganese sintered ore at a low temperature range of 1400°C or lower. (CaO+Mg0)/StOz is 0.3~
If it is outside the range of 2.0, the slag formation of manganese sintered ore will be delayed,
As a result, it is thought that the manganese yield deteriorates and the dephosphorization also deteriorates due to the deterioration of the fluidity of the slag.

In addition, in the above example, only the results of bottom blowing of manganese ore powder or top addition of manganese sintered ore were shown to increase [Mn] in dephosphorized hot metal, but when both methods are carried out simultaneously Needless to say, good results were obtained.

<Summary of Effects> As explained above, according to the present invention, manganese ore (manganese ore powder , manganese sinter) can be smelted and reduced at a high yield to effectively increase the [Mn] in the dephosphorized hot metal, and the next step, decarburization furnace blowing, can significantly increase the [Mn] in the steel. This makes it possible to significantly reduce the amount of ferromanganese added, which makes it possible to significantly rationalize steel manufacturing costs, and brings extremely useful effects industrially.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram illustrating the process of the steel manufacturing method proposed above. FIG. 2 is an explanatory diagram of the method of the present invention. FIG. 3 is an explanatory diagram of another method according to the present invention. FIG. 4 is a graph showing the relationship between the manganese distribution ratio and the slag basicity in the dephosphorization furnace. FIG. 5 is a graph showing the relationship between (CaO+Mg0)/Stow in manganese sintered ore, manganese yield, and dephosphorization rate, obtained in Examples. In the drawings, 1... Dephosphorization furnace, 2... Decarburization furnace. 3... Hot metal, 4... Converter slag. 4'...Dephosphorization slag. 5... Stirring gas blowing nozzle (furnace bottom tuyere). 6...Lance, 7...Oxygen. 8... Dephosphorization slag agent, 9... Manganese ore powder. 10... Manganese sintered ore. Figure 1

Claims (5)

[Claims] (1) When dephosphorizing the hot metal by adding a dephosphorizing agent to the hot metal poured into a converter type furnace that has both top and bottom blowing functions, and performing bottom blowing gas agitation and top blowing oxygen gas, A hot metal dephosphorization method characterized by blowing manganese ore powder into an iron bath through a tuyere to simultaneously raise [Mn] in the hot metal and dephosphorize it. (2) The method for dephosphorizing hot metal according to claim 1, characterized in that carbonaceous powder is also blown into the iron bath together with manganese ore powder from the hearth bottom tuyere. (3) When dephosphorizing the hot metal by adding a dephosphorizing agent to the hot metal poured into a converter-type furnace with both top and bottom blowing functions, and performing bottom blowing gas agitation and top blowing oxygen gas, Manganese sintered ore, which is prepared by adding and mixing powdered slag-forming agent and coke powder to powdered manganese ore together with a phosphorizing agent, is added to the hot metal [
Mn] and dephosphorization are carried out at the same time,
Hot metal dephosphorization method. (4) When dephosphorizing the hot metal by adding a dephosphorizing agent to the hot metal poured into a converter-type furnace with both top and bottom blowing functions and by blowing oxygen gas upward while stirring the bottom blowing gas, Hot metal is produced by adding manganese sintered ore, which is made by adding and mixing a powdered slag-forming agent and coke powder to powdered manganese ore together with a phosphorous agent, and then firing the manganese ore powder into the iron bath through the bottom tuyere. A hot metal dephosphorization method characterized by simultaneously performing an increase in medium [Mn] and dephosphorization. (5) The hot metal according to any one of claims 1 to 4, characterized in that converter slag generated when dephosphorizing pig iron is blown in a decarburizing converter is used as a dephosphorizing agent component. Dephosphorization method.