JPH083613A - Iron-making and steelmaking method - Google Patents

Abstract

PURPOSE:To reduce the produced quantity of slag in a steelmaking process and to effectively utilize the slag by pre-dephosphorizing high phosphorus-containing molten iron from a blast furnace at an out-furnace pre-dephosphorizing process to produce high phosphorus-containing slag and charging the high phosphorus-containing slag obtd. in a converter into the blast furnace. CONSTITUTION:The pre-dephosphorizing process of molten iron is executed between a blast furnace smelting furnace and a converter refining process. In this pre- dephosphorizing process, the high phosphorus-containing molten iron having 0.17-0.50% P content from the blast furnace is pre-dephosphorized. Thus, the high phosphorus- containing slag having >= about 0.5% P content is produced and is discharged as a useful slag. On the other hand, pre-dephosphorized pig iron having about 0.1% P content obtd. by this process is refined in the converter to obtain a low phosphorus steel. The high phosphorus-containing slag produced is charged into the blast furnace as a part of raw materials for charging into the blast furnace. By this method, P content in the molten iron tapped to the pre-dephosphorizing process from the blast furnace is kept to 0.17-0.50%. By constituting this iron-making and steelmaking cycle, the slag quantity produced in the steel-making process is remarkably reduced and also, can efficiently be utilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of iron and steelmaking for reducing the amount of slag discharged from a steelmaking process and improving the utility value of the generated slag, thereby reducing waste slag. is there.

[0002]

2. Description of the Related Art At present, most of the steel in Japan is manufactured by the "pig steel integrated manufacturing process". this is,
"The ironmaking process in which iron ore is reduced with carbonaceous material in a blast furnace to obtain carbon-rich pig iron (blast furnace smelting process)" and "This molten iron is charged into a converter and decarburized by oxygen blowing to obtain steel. Steelmaking process "
It is a main process of the steel manufacturing method because it is an integrated process and is very advantageous in terms of manufacturing efficiency and manufacturing cost.

By the way, pig iron obtained by blast furnace smelting contains Si, P and the like as impurities derived from iron ore in addition to C (carbon) described above. Therefore, these impurities can be reduced in the steelmaking process. Regarding P of these impurities, iron ore used in Japan is P
Since the content is relatively small, the P concentration in the hot metal is usually 0.1% by weight.
Tolerable amount in products is 0.01% in most cases
Because of the following, special consideration is also given to the reduction of P.

Hot metal containing C, Si, P, etc. is generally subjected to oxygen blowing in a converter to reduce these elements. However, while decarburization and desiliconization proceed without problems with oxygen blowing, dephosphorization is a complicated reaction that depends on the basicity of slag, oxygen potential, temperature, etc. Careful adjustment of operating conditions is required to proceed. Especially, the influence of the processing temperature is large, and the end point temperature is 160
Converter refining above 0 ° C is disadvantageous for dephosphorization. For this reason, the amount of slag-making agent (particularly quick lime) to be put into the converter is increased, and a large amount of highly basic slag is produced to promote dephosphorization treatment (this method is called "conventional method"). , The process is shown in FIG. 3].

Thus, the converter slag generated in the converter refining reaches about 10 million tons per year. This enormous amount of converter slag is difficult to be effectively used as a roadbed material or the like due to hydration expansion mainly due to unsmelted lime, and most of it is currently disposed of in landfill. However, landfill treatment must be said to be an extremely low-level treatment method compared to the case where blast furnace slag is effectively used as a cement raw material, a roadbed material, or the like. Furthermore, landfilling is not a process that can be performed anywhere, and in particular, in recent years, it has become difficult to secure landfills. In view of such a situation, a method of effectively using converter slag instead of landfill treatment has been widely studied.

From the above studies, attention has been paid to the possibility of using converter slag as a pig iron material (blast furnace charging material) as one means of effectively utilizing converter slag.
However, since the converter slag has a high basicity as described above, it had a sufficient smelting ability as a pig iron material, but it also had the following problems. That is, a considerable amount of P (phosphorus) transferred in the steelmaking process exists in the converter slag in the form of phosphorus oxide, but since the reducing atmosphere is in the blast furnace furnace, the converter slag containing phosphorus oxide is present. When is used as a pig iron material, the phosphorus oxide is reduced in the blast furnace, and the P content in the slag is almost completely transferred to the hot metal. Therefore, the P content in the hot metal making process is circulated between the hot metal and the converter slag and is not discharged to the outside of the system, and new P content due to iron ore is added one after another, so that P content in the hot metal is increased. Gradually becomes thicker. As a result, the limit of dephosphorization in the converter is finally exceeded.

However, means for avoiding such a situation have been studied, and in the method proposed in, for example, JP-A-55-94420 and JP-B-3-66372, the hot metal is removed in advance outside the converter furnace. By performing phosphorus treatment, the P content in the hot metal is transferred to the slag (this slag is referred to as "dephosphorization slag"), and after this is discharged out of the system, this pre-dephosphorized hot metal (dephosphorized hot metal is dephosphorized). ) Is subjected to converter refining [this method is called "prior invention method"]. In other words, if the hot metal preliminary dephosphorization treatment is performed outside the furnace in this manner, the slag generated in the converter (converter slag) contains almost no P, and as shown in FIG. Even if it is used as a pig iron material, the concentration of P in the hot metal in the blast furnace becomes negligible and can be ignored.

In the above-mentioned "prior invention method" which employs the process shown in FIG. 4, a slag forming agent is also used when pre-dephosphorizing hot metal outside the furnace. ”
It has an advantage in that the dephosphorization treatment temperature is lower than that of the conventional method, so that the amount of slag generated is considerably smaller than that in the “conventional method”. Specifically, in the "conventional method", the amount of slag generated is about 70 to 100 kg per ton of hot metal, but in the case of the preliminary dephosphorization outside the furnace, it is only about 50 kg per ton of hot metal.

However, since the dephosphorization slag generated by the external dephosphorization outside the furnace contains P in a relatively high concentration (the P concentration in FIG. 4 is a typical example), it should be used as a pig iron material. I couldn't. Therefore, in the "prior invention method", although the converter slag that is generated can be used as a pig iron material, the dephosphorized slag that is generated by preliminary dephosphorization outside the reactor must be resorted to landfill, and the landfill must be relied on. The amount of dephosphorization slag that requires disposal is 30 to 50% compared to the amount of landfill required slag that is generated by the “conventional method”
It just decreases. However, since the dephosphorization slag generated by the preliminary dephosphorization outside the furnace contains a large amount of P compared to the converter slag generated by the "conventional method", use this as a raw material for fertilizers, phosphoric acid, etc. It is not unthinkable, but such a P content of about dephosphorization slag could not be considered as a realistic measure because the cost was not balanced.

On the other hand, in Japanese Patent Publication No. 59-37322, "In the case of a steelmaking method using a special" pure oxygen bottom blowing converter ", if the P concentration of the hot metal to be treated is up to 0.26% by weight, Based on the finding that the increase in the amount of quick lime used due to the increase is very small, "the P concentration in the hot metal discharged from the blast furnace is 0.26
"Upper-blowing converter slag" is used in which the "upper-blowing converter slag" is used as a blast furnace charging material within a range not exceeding the weight percentage, and the resulting blast-furnace pig is treated in the "pure oxygen bottom-blown converter". Reuse method "has been proposed. However, in this method, when refining the above-mentioned blast furnace pig iron, it is not possible to apply the "oxygen top blowing converter (including those that also use bottom blowing such as stirring gas)" that is commonly used It had a problem that "pure oxygen bottom blown converter" had to be used, and therefore it could not be said to be "a converter slag recycling method that can be generally adopted in any factory". Moreover, since the allowable value of P concentration required for blast furnace pig iron is not so high, the amount of top blowing converter slag that can be used as a blast furnace charging material is limited, and “slag discharged from a pure oxygen bottom blowing converter” is used. As for “,” it did not indicate a way other than disposal at landfill sites.

In view of the above, the object of the present invention is to reduce the amount of slag generated in the steelmaking process as much as possible and to expand the effective use range of the generated slag without requiring special equipment. The purpose of this is to establish a method for iron and steelmaking that can extremely reduce unnecessary waste of slag.

[0012]

Therefore, the inventors of the present invention have conducted extensive studies to achieve the above object, and have obtained the following findings. That is, the present inventors, as a result of various studies,
In order to reduce the amount of slag that must be disposed of in landfills, the slag that is generated (especially the slag generated in the steelmaking process) will be put to effective use by taking measures to increase its usefulness. I thought it necessary to reduce the amount of slag generated. Then, first, it was concluded that it is most practical to increase the P concentration of slag generated in the steelmaking process and use it as a fertilizer or a phosphorus-containing raw material such as phosphoric acid.

However, in the "conventional method" in which dephosphorization is performed during converter refining in which decarburization is the main constituent, the P concentration of the produced slag is determined by the refining temperature (which greatly affects the P distribution ratio). Increasing it adversely affects the product quality (steel quality) and cannot be adopted. However, when hot-metal preliminary dephosphorization is performed, the temperature is lower than that of converter (decarburization) blowing, so high-efficiency dephosphorization can be performed with a small amount of slag, and a slag with a high P concentration is formed. be able to. Moreover, in this case, if the P concentration of the blast furnace pig iron to be subjected to the preliminary dephosphorization outside the furnace is in a high range exceeding a certain value, the P concentration of the dephosphorized slag generated by the preliminary dephosphorization also becomes extremely high, and fertilizer, phosphoric acid, etc. It becomes a phosphorus-containing raw material that can be used as a manufacturing raw material.

In addition, the converter slag produced in the final converter blowing after the preliminary dephosphorization outside the furnace is circulated as a part of the charging raw material of the "blast furnace for supplying pig iron to the preliminary dephosphorization step outside the furnace". By doing so, it becomes possible to maintain the P concentration of the blast furnace pig iron in a high range, and the blast furnace pig iron tapped from the blast furnace is "molten pig iron for generating high P dephosphorization slag by the preliminary dephosphorization outside the furnace". Moreover, it is not necessary to dispose of the converter slag.
On the other hand, if preliminary dephosphorization of hot metal is performed outside the furnace, the converter (decarburization)
Since the treatment is carried out at a temperature lower than that of blowing, highly efficient dephosphorization can be performed with less slag, and the amount of dephosphorized slag itself can be reduced.

Therefore, contrary to the conventional wisdom, hot metal having a higher P concentration is subjected to a steelmaking process, first subjected to preliminary dephosphorization outside the furnace, and then blown to a converter to blow molten iron to such an extent that low-phosphorus steel can be produced. Medium P
After generating high P dephosphorization slag by reducing
This dephosphorized hot metal is blown into a converter for decarburization and finish dephosphorization, and the converter slag generated at this time is used as a part of the blast furnace charging raw material to “supply the hot metal to the preliminary dephosphorization process outside the furnace. By constructing the iron and steelmaking operation cycle of charging into the steel, the amount of slag generated in the steelmaking process can be significantly reduced, and the slag generated also has a significantly high P concentration, and fertilizers or phosphoric acid, etc. It can be effectively used as a phosphorus-containing raw material.

The present invention has been completed on the basis of the above-mentioned findings and the like. "The preliminary dephosphorization process of hot metal outside the furnace between the blast furnace smelting process and the converter refining process for iron and steelmaking is performed. In addition to this, in the preliminary dephosphorization process of the hot metal outside the furnace, the high phosphorus-containing hot metal having a P content (P concentration) of 0.17 to 0.50% by weight is preliminarily dephosphorized to produce a useful slag having a high P concentration. On the other hand, after the preliminary dephosphorized pig iron obtained at this time is smelted in a converter to obtain low phosphorus steel, the phosphorus-containing slag produced in the converter smelting or this phosphorus-containing slag and other converter operations are produced. P content (P concentration) in the hot metal tapped from the blast furnace by charging the blast furnace with the converted converter slag as a part of the blast furnace charging raw material
Is maintained at 0.17 to 0.50% by weight, the slag discharge from the system in the steelmaking process is substantially stopped only during the preliminary dephosphorization of the hot metal outside the furnace, and the discharge amount is reduced, and the slag discharged from the system is reduced. It is possible to reduce waste slag by ensuring effective utilization based on the high P concentration ”.

FIGS. 1 and 2 are explanatory views of an example of the iron-making and steel-making process according to the method of the present invention. FIG. An example of the case where the generated converter slag is charged into the blast furnace as a part of the blast furnace charging raw material, and Fig. 2 shows that in addition to this converter slag, "converter slag generated by other converter operation" is also included. Examples of charging the blast furnace as a part of the blast furnace charging raw material are shown.

[0018]

When the "invention method" shown in FIG. 1 or 2 and the "prior invention method" shown in FIG. 4 are compared, the two seem to be similar in appearance, but There is a big difference in technical ideas. In other words, conventionally, as the P concentration in the hot metal increases, the load of dephosphorization increases, so efforts have been made not to increase the P concentration in the hot metal used for converter smelting. While the preliminary dephosphorization of the hot metal is positioned as a measure for reducing the P concentration of the hot metal to be used in the above, the "invention method" is the opposite of these ideas. In addition to using a high-concentration one, the position of the hot metal pre-dephosphorization dephosphorization is rather to keep the hot metal P concentration at a high level. The slag that occurs in is generated.

As described above, one feature of the present invention is that the hot metal having a high P concentration is preliminarily dephosphorized outside the furnace to generate the dephosphorization slag having a high P concentration. It opens the way for effective use as fertilizer or phosphorus-containing raw material such as phosphoric acid. The "useful slag with a high P content" as used in the present invention means that the P content is as high as 5% by weight or more (usually a high concentration close to 15% by weight) and a fertilizer or a phosphorus-containing raw material such as phosphoric acid. It means slag that can be effectively used as. Further, the preliminary dephosphorization outside the furnace may be carried out by using a generally used ladle, a top speed or a converter already known to be suitable as a container for the preliminary dephosphorization.
In any case, since the treatment is carried out at a lower temperature than converter (decarburization) refining, highly efficient dephosphorization is possible with a small amount of slag, and it is possible to generate dephosphorized slag having a high P concentration in this respect. It also leads to a reduction in the amount of dephosphorized slag that is discharged after being discharged.

In order to stably produce good quality steel having a low P concentration in the iron and steelmaking process, P should be discharged at the same rate as P is brought into the metal as an impurity in the iron ore. However, the "relationship between the P concentration in slag and the amount of slag" when discharging P brought in from iron ore as slag (of course, slag generated in the "steel making process") is described in the "Conventional method", A comparison between the “prior invention method” and the “invention method” is shown in FIG. As can be seen from FIG. 5, when manufacturing steel with the same P concentration, the “conventional method” and “prior invention method” discharge a large amount of slag with a low P concentration, whereas "Invention method"
Only a small amount of high-concentration slag needs to be made, and the amount of slag discharged can be greatly reduced.

Here, the most effective and practical means for producing the dephosphorization slag having a high P concentration during the preliminary dephosphorization of the hot metal is to use the hot metal having a high P concentration. That is, the dephosphorization ability of slag is expressed by the following equation (equation related to P distribution ratio). From this equation as well, in order to increase the concentration of P contained in the slag having a certain dephosphorization ability, it is necessary to increase the concentration of P contained in the metal coexisting with the slag, so that the concentration of P contained in the slag is high. It is understood that the P concentration of the hot metal to be subjected to the preliminary dephosphorization outside the furnace must be increased in order to generate phosphorus slag.

In the method of the present invention, the P concentration of the hot metal applied to the preliminary dephosphorization outside the furnace is preferably in the range of 0.17 to 0.50% by weight. This is because if the P concentration is lower than this range, the P concentration in the slag does not become sufficiently high due to the P distribution ratio, and the effect of reducing the amount of dephosphorized slag generated is low, and there is a way to effectively use the dephosphorized slag. Can't open On the other hand, when the hot metal P concentration is higher than the above range, the hot metal P concentration does not decrease to the desired value even by the preliminary dephosphorization of the hot metal, and the P concentration is still high even after the pretreatment, so the converter Even if refined, it cannot be dephosphorized to the required level.

The P concentration of the hot metal subjected to preliminary dephosphorization outside the furnace was set to 0.17.
~ 0.50% by weight is "molten iron tapped from the blast furnace"
It is necessary to increase the P concentration in the medium and adjust it to 0.17 to 0.50% by weight, which is higher than in the case of ordinary hot metal. Therefore, in the present invention, the converter slag generated when the dephosphorized pig iron is refined (decarburization and finish dephosphorization) in the converter is charged into the blast furnace as a part of the blast furnace charging raw material. The blast furnace charging raw material here includes not only the raw material directly charged into the blast furnace but also the raw material charged in the form of sinter or pellets,
In the latter case, converter slag is used as a raw material for sinter or pellets.

That is, in the preliminary dephosphorization outside the furnace according to the present invention, P
Although the hot metal obtained has a higher P concentration than the dephosphorized iron obtained by ordinary preliminary dephosphorization, the problem is that the hot metal thus obtained is called "dephosphorized hot metal" in order to generate high-concentration dephosphorized slag. If a large amount of slag-forming agent is used during furnace (decarburization) refining to form high basicity slag, this can be solved sufficiently, which is a particular obstacle to stable production of desired low phosphorus steel. Never give. Not only that, the converter slag generated at this time contains a large amount of uncalcified quick lime, so if it is charged into the blast furnace as a part of the blast furnace charging raw material, it not only leads to a reduction in the basic unit of the pig iron raw material, but also 3 Since it absorbs P from the molten steel at a level of about 10% by weight or less, when charged into the blast furnace, P contained in the converter slag in the form of oxide is reduced due to the reducing atmosphere in the furnace. In the "blast furnace smelting in Japan using iron ore with a relatively low P content," it helps to increase the P concentration in the hot metal in the blast furnace and maintain the level of 0.17 to 0.50% by weight. It is possible to stably supply hot metal having a high P concentration to the preliminary dephosphorization outside the furnace.

Moreover, as described above, since the converter slag generated in the converter refining after the preliminary dephosphorization outside the furnace is charged into the blast furnace as a part of the blast furnace charging material, the converter slag is discarded. It does not cause any difficult problems. Further, in the present invention, a slightly larger amount of slag-forming agent is used when refining the dephosphorized pig iron in the converter (decarburization), but the cost increase due to the increase in the basic unit of the converter slag is caused by the blast furnace charging raw material. There is no problem because it is offset by the "cost reduction due to the reduction of the basic unit of the pig iron raw material for virgin", which is brought about by the use as.

In this case, as shown in FIG. 2, in addition to the phosphorus-containing slag produced by the converter smelting of the preliminary dephosphorized pig iron according to the present invention, the converter slag produced by another converter operation (conventional pig iron Slag (e.g., slag generated from the integrated steel process) is also charged into the blast furnace as part of the blast furnace charging raw material ", the residual lime in the converter slag can be effectively used as a raw material for pig iron production. It also leads to further reduction of input materials. In addition, there is no need to worry about the disposal of converter slag (such as slag generated from the conventional pig iron integrated process) generated in other converter operations, and the slag generation amount reduction effect can be maximized.

It should be noted, in particular, according to the present invention method the amount of slag to be discharged out of the system can easily be less molten steel ton 20 kg, reduced to _^1/3 to _^1/5 of the prior art To do.
Moreover, the slag discharged to the outside of this system can be effectively used as a raw material for phosphate fertilizers and industrial phosphoric acid because the concentration of phosphorus oxide contained therein becomes as high as about 15% by weight.

Next, the present invention will be described more specifically by way of examples.

【Example】

[Example 1] The method of the present invention was applied to an actual iron and steelmaking process to obtain the following results. First, the converter slag generated in the integrated pig steel factory employing the process shown in FIG. 3 was continuously charged into the blast furnace as a raw material for pig iron production. Therefore, the P concentration in the tapped hot metal gradually increased from about 0.10% by weight at the beginning.

When the hot metal P concentration exceeds 0.15% by weight, it becomes difficult to reduce the P concentration in the molten steel to the required level by the process of FIG. 3, and particularly when it becomes 0.17% by weight or more, the P concentration decreases to the required level. At this point, a hot metal pretreatment dephosphorization process as shown in FIG. Here, at the beginning of introducing the hot metal pretreatment dephosphorization process shown in FIG. 1, the dephosphorization slag generated during the preliminary dephosphorization was also charged into the blast furnace as a pig iron raw material in the same manner as the converter slag. For this reason, the P concentration in the hot metal further increased and reached 0.20% by weight, but from this point, the ironmaking steelmaking method according to the present invention (the ironmaking steelmaking method in the process shown in FIG. 1) is continued in a steady state. did.

In this iron and steelmaking process, in the preliminary dephosphorization, an upper-bottom blow converter is used as a preliminary dephosphorization vessel, and the molten iron supplied from the blast furnace has a P concentration of 0.20% by weight, and the amount of the slag forming agent is 1 ton per ton.
After adding 5 kg, oxygen was blown in the upper and lower blow converters to remove phosphorus.
As a result, the P concentration in the hot metal dropped to 0.11% by weight,
The P concentration in the dephosphorized slag reached 7.3% by weight. This dephosphorized slag was discharged to the outside of the system.

Next, the dephosphorized pig iron thus obtained was charged into another upper-bottom blowing converter, and 95 kg per ton of slag-forming agent was added to carry out oxygen blowing. As a result, the P concentration of the obtained molten steel was reduced to 0.008 wt% as in the case of the conventional method. The converter slag generated by this converter blowing had a P concentration of 1.2% by weight, but this converter slag was charged into the blast furnace as a raw material for ironmaking.

Then, P supplied from the blast furnace in this way
Preliminary dephosphorization of high-concentration hot metal, converter smelting, and use of the converter slag generated by this converter slag as raw material for pig iron (loading into blast furnace) were repeated. The P concentration in the hot metal to be pig iron is stably maintained at 0.18 to 0.23% by weight, and the P concentration in the molten steel obtained by preliminary dephosphorization and converter refining is stably kept at 0.01% by weight or less. Was done.

The dephosphorization slag discharged outside the system at this time was within the range of 15 to 20 kg per ton of molten steel. This is the is _^1/3 or less "conventional method", the slag reduction effect is manifested by this process. The P concentration in the dephosphorization slag discharged to the outside of the system is in the range of 7.0 to 7.5% by weight. As a result of using this dephosphorization slag as a substitute for phosphate rock in a phosphoric acid plant, the dephosphorization slag is It was confirmed that it can be used in place of phosphate rock without problems.

[Example 2] The method of the present invention was applied to a pig iron making process having two blast furnace-steel making plants having almost the same production capacity, and the following results were obtained. First, converter slag generated at both steelmaking plants was continuously charged into one of the blast furnaces as a raw material for ironmaking. For this reason, the P concentration in the hot metal tapped from the blast furnace gradually increased from about 0.10% by weight at the beginning.

When the P concentration in the hot metal exceeds 0.15% by weight, it becomes difficult to reduce the P concentration in the molten steel to the required level without performing preliminary dephosphorization, and particularly when it is 0.17% by weight or more, the P concentration decreases to the required level. Will not come true, so at this point P
As shown in FIG. 2, the hot metal pretreatment dephosphorization process was introduced into the steelmaking plant that receives the concentrated hot metal. At the beginning of introducing the preliminary dephosphorization process as shown in FIG. 2, the dephosphorization slag generated during the preliminary dephosphorization was also charged into the blast furnace as a raw material for ironmaking in the same manner as the converter slag. . For this reason, the P concentration in the hot metal tapped from the blast furnace further increased and reached 0.30% by weight, but from this point, the iron and steel making method according to the present invention (the iron making in the process shown in FIG. 2 is performed. Steelmaking) was continued in a steady state.

In this iron and steelmaking method, in the preliminary dephosphorization, an upper-bottom blowing converter is used as a preliminary dephosphorization vessel, and the molten iron supplied from the blast furnace has a P concentration of 0.30% by weight, and the amount of the slag-forming agent is 3 tons per ton.
0 kg was added, and oxygen was blown in the upper and lower blow converters for dephosphorization.
As a result, the P concentration in the hot metal dropped to 0.10% by weight,
The P concentration in the dephosphorized slag reached 7.5% by weight. This dephosphorized slag was discharged to the outside of the system.

Next, the dephosphorized pig iron thus obtained was charged into another upper-bottom blowing converter, and 80 kg per ton of a slag-making agent was added to carry out oxygen blowing. As a result, the P concentration of the obtained molten steel
It was reduced to 0.009% by weight. The P concentration of the converter slag generated by this converter blowing was 1.2% by weight,
This converter slag was charged into the blast furnace as a part of the ironmaking raw material together with the converter slag generated in "another converter (see Fig. 2)". During this period, the P concentration of the hot metal or molten steel from "another blast furnace (see Fig. 2)" or "another converter (see Fig. 2)" was maintained at about 0.10% by weight and 0.01% by weight, respectively.

Then, the hot metal having a high P concentration supplied from the specific blast furnace is pre-dephosphorized and then smelted in the converter,
Further, both the converter slag generated by this converter refining and the converter slag generated by "another converter (see Fig. 2)" are used as the ironmaking raw material in the specific blast furnace (that is, from two steel mills). The generated converter slag is charged into the specific blast furnace), and the P concentration in the hot metal tapped from the specific blast furnace is stably maintained at 0.18 to 0.23% by weight. The P concentration in the molten steel obtained by preliminary dephosphorization and converter refining was stably maintained at 0.01% by weight or less.

The dephosphorization slag discharged to the outside of the system at this time was within the range of 15 to 20 kg per ton of molten steel. This is the is _^1/3 or less "conventional method", the slag reduction effect is manifested by this process. It was also confirmed that the P concentration in the dephosphorized slag discharged to the outside of the system was in the range of 7.0 to 7.5% by weight, which can be used as a substitute for phosphate rock in a phosphoric acid plant.

[0040]

[Summary of Effects] As described above, according to the present invention, the amount of slag discharged from the steelmaking process can be significantly reduced without requiring special equipment, and the slag discharged from the steelmaking process can be significantly reduced. An integrated process for pig iron and steel making that can effectively utilize slag as a raw material for phosphoric acid, fertilizer, etc. can be used to dramatically reduce the amount of "slag that needs to be disposed of" that is discharged to the outside of the iron and steel making process. It will bring about extremely useful effects in the industry, such as the opening of.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an outline of a pig iron making process according to the present invention.

FIG. 2 is a schematic explanatory view showing another example of the pig iron making process according to the present invention.

FIG. 3 is an explanatory diagram showing an outline of a pig iron making process according to a conventional method.

FIG. 4 is an explanatory view showing an outline of a pig iron making process according to the prior invention method.

FIG. 5 is a graph comparing “relationship between P concentration in slag and amount of slag” when discharging P brought in from iron ore as slag by the conventional method, the prior invention method and the present invention method.

Claims (2)

[Claims] 1. An external pre-dephosphorization step for hot metal is provided between the blast furnace smelting step and the converter refining step, and the P content is 0.17 to 0.50% by weight in the external hot pre-dephosphorization step for hot metal. After preliminarily dephosphorizing the high phosphorus-containing hot metal, a useful slag having a high P content is generated and discharged, while the preliminary dephosphorized iron obtained at this time is smelted in a converter to form a low phosphorus steel. By maintaining the P content in the hot metal tapped from the blast furnace at 0.17 to 0.50% by weight by charging the phosphorus-containing slag produced in the converter refining into the blast furnace as a part of the blast furnace charging raw material. A feature of the iron and steelmaking process that enables reduction of waste slag. 2. An external pre-dephosphorization step for hot metal is provided between the blast furnace smelting step and the converter refining step, and the P content is 0.17 to 0.50% by weight in the external hot pre-dephosphorization step for this hot metal. After preliminarily dephosphorizing the high phosphorus-containing hot metal, a useful slag having a high P content is generated and discharged, while the preliminary dephosphorized iron obtained at this time is smelted in a converter to form a low phosphorus steel. , P in the hot metal tapped from the blast furnace by charging the phosphorus-containing slag generated by the converter refining and the converter slag generated by another converter operation into the blast furnace as a part of the blast furnace charging raw material. Content 0.17 ~ 0.50
A pig iron and steelmaking method capable of reducing waste slag, which is characterized by maintaining the weight percentage.