JP2001192720A - Converter steel making process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a converter steel making process for recycling of slag after decarburization refining at hot. SOLUTION: The converter steel making process using coolants having a large amount of iron oxide for cooling slag after decarburization refining in a fifth stage in executing a first stage of charging the molten iron or the molten iron and the scrap as main raw materials to a converter, a second stage of executing desiliconizing and dephosphorizing, a third stage of discharging the formed slag, a fourth stage of executing decarburization blowing thereafter and a fifth stage of tapping steel allowing the slag to remain after the decarburization refining, then returning to the first stage and repetitively executing up to the fifth stage by recycling the slag made to remain in the fifth stage in the desiliconizing and dephosphorizing of the second stage. Accordingly, the time for cooling the slag may be shortened, quicklime as au auxiliary raw material may be saved and the dephosphorization efficiency above ordinary operation may be obtained by using iron ores, etc., as the coolants in hot recycling of the decarburization slag. The recycling of the slag may be achieved without worrying out the problem of the unslagged off lime in the dephosphorizing slag.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter steelmaking method for hot reuse of slag after de-C refining.

[0002]

2. Description of the Related Art Conventionally, refining of hot metal in a converter involves charging a blast furnace hot metal into a converter, feeding a flux mainly composed of quick lime, and removing P and C from the hot metal by oxygen blowing to remove steel. The method of melting was common. After that, the refining function over multiple processes is centralized in the converter to significantly reduce the energy loss of the hot metal, and to significantly reduce the fixed costs (equipment costs and labor costs) of the processes before and after the converter. The method is disclosed in, for example, JP-A-2-181989.

According to the invention, as a first step, molten iron is charged into a converter, and as a second step, flux addition and oxygen blowing are performed to remove Si and P, thereby reducing the P content to a predetermined level. As a third step, the converter is tilted to discharge the slag generated in the second step, and then, as a fourth step, decarbonization is performed to a predetermined C content by flux addition and oxygen blowing in the same converter. As a fifth step, the slag generated in the fourth step is left in the converter and the steel is returned to the first step, and the steps up to the fifth step are repeatedly performed. This is a method in which the slag generated in the process is not returned to the first process, and the entire amount of slag is discharged after tapping in the fifth process.

Japanese Unexamined Patent Publication No. 8-199218 discloses a process of receiving iron without discharging slag generated by pre-charging using an upper-bottom blow converter type refining apparatus (process 1), and removing hot metal. In the converter steelmaking method in which a phosphorus refining step (step 2), a waste step (step 3), a de-C step (step 4), and a tapping step (step 5) are continuously performed, after step 5, slag is removed. The furnace is allowed to stand upright with it remaining in the furnace, and nitrogen, Ar, CO, C
A converter steelmaking method is described in which a gas in which one or two or more types of O ₂ are mixed is blown, and then the C-removed slag for carrying out step 1 is recycled.

[0005] Further, the technology disclosed in Japanese Patent Application Laid-Open No. 4-72007 discloses a method of charging molten iron, removing P and removing S, removing slag, removing C, removing steel, and removing C slag. This is a method for producing molten steel in which the process of charging hot metal is continuously performed.

On the other hand, JP-A-5-25527 discloses that a dephosphorizing agent containing continuous casting slag and / or ingot slag and iron oxide and, if necessary, converter slag is added to hot metal to obtain a required oxidation. There is disclosed a method for dephosphorizing hot metal, which comprises producing a hot slag and stirring the hot slag and the hot metal.

[0007]

Problems to be Solved by the Invention
In the method according to Japanese Patent No. 989, de-P,
Since it is implemented in a process that continuously performs the de-C step, energy loss when moving from the de-P step to the de-C step can be reduced, and the fixed costs (equipment costs and labor costs) can be significantly reduced. can do.

However, if the amount of slag discharged in the third step is small, the P removed in the slag in the second step returns to the molten steel in the fourth step again, so that P is removed again in the fourth step. The need arises, and the amount of flux such as quicklime must be increased, leading to an increase in cost. Moreover, in this fourth step, P
Since the slag having a higher concentration is reused in the second step, the removal of P from the second step is increased and the cost is increased. If the amount of slag discharged in the third step is small as described above, it is impossible to avoid an increase in overload for performing de-P, resulting in an increase in cost.

In Japanese Patent Application Laid-Open No. Hei 8-199218, bumping during hot metal charging is prevented by cooling slag, but Ar, CO, CO ₂ is used as a cooling gas while the converter is upright. Since it is used, the slag on the surface is supercooled, and it takes time until the slag is melted at the time of the next de-P treatment, which leads to an increase in the treatment time. Because of this P
The reaction efficiency deteriorates.

Further, in the method disclosed in Japanese Patent Application Laid-Open No. 4-72007, no heat loss occurs due to the transfer of hot metal, but the decharged C slag has a high (T · Fe), so that the next charge in the molten state is high. When hot metal is charged, there is a problem that so-called bumping occurs in which hot metal and slag spout out of the furnace by reacting rapidly with C in the hot metal. To avoid this, limestone or scrap is added to the slag as a cold material before charging the hot metal, and the converter is tilted several times.However, the added coolant is cooled in the slag. Requires a long period of time, thereby causing a problem that productivity is significantly impaired.

When a coolant containing CaO is used, a portion of the CaO in the coolant remains in the slag-removed slag without leaving slag, which hinders the use of the slag for roadbed materials and the like. Was. In order to utilize the slag, a processing period (aging period) for applying the slag to the roadbed material is required.
, Which requires a period of time, which leads to an increase in equipment, labor, time and other costs. When a relatively large (100 mm or more) scrap is used as a coolant, heat transfer from the slag to the coolant takes a long time (5 minutes or more).
Therefore, there is a problem that productivity is reduced.

On the other hand, in JP-A-5-25527, a P-removing agent containing continuous casting slag and / or ingot slag and, if necessary, converter slag is added to hot metal. Since the temperature is as high as 1500 ° C. or more and has a dense structure, there is a problem that melting is incomplete at a furnace temperature during the de-P treatment. If the dissolution becomes incomplete, the slag not only does not function as a de-P
This leads to increased variation and heat loss, leading to significant cost reduction.

[0013] The present invention provides a converter steelmaking method in which the amount of quicklime is reduced and the productivity is high by slag that has been left at the time of charging hot metal and safely recycles decarbonized slag without causing bumping. In the converter to achieve
It is an object of the present invention to provide a method for cooling slag.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional method, and its gist lies in the following means. (1) The first step of charging hot metal or hot metal and scrap as main raw materials into a converter, the second step of removing Si and P, the third step of discharging generated slag, and the subsequent C blowing The fourth step is to remove the slag after de-C refining, and the fifth step is to return to the first step.
In de-P, the slag left in the fifth step is recycled and used.
A converter steelmaking method in which a coolant containing a large amount of iron oxide is used for cooling the slag after the C-free refining in the fifth step when repeatedly performing the five steps.

(2) The amount of the coolant used as the coolant is 3 to the amount of the slag after the de-C refining remaining in the fifth step.
The converter steelmaking method in the converter according to (1), which is 0 to 150%. (3) The converter steelmaking method according to (1) or (2), wherein iron ore, sintered ore, and ironmaking dust are used as the coolant used in the fifth step.

(4) In the second step, continuous casting slag and / or ingot slag and / or converter slag are used as auxiliary materials to be used in addition to the slag left in the furnace (1) to (3). 2.) The converter steelmaking method according to any one of (1) to (3). (5) The converter steelmaking method according to any one of (1) to (4), wherein in the second step, the end point temperature of the de-Si / de-P treatment is 1300 ° C to 1350 ° C. (6) In the fourth step, the concentration of Al ₂ O ₃ in the decarbonized slag during the decarbonizing blowing is 2 to 5% (1) to (5).
Converter steelmaking method according to any one of the above.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted various studies on the cooling of C-removed slag. As a result, the material used as a coolant does not hinder the removal of P in the second step, P
If it is possible to exert a useful effect for cooling, it is possible to obtain an effect having both the effect of cooling and the effect of removing P, and to use a material containing a large amount of iron oxide having a useful effect as a coolant for that purpose. I paid attention.

If attention is paid only to the cooling of the decarbonized slag, limestone and scrap can be used in the auxiliary material used in the converter, but as mentioned above, the added slag Of unslagging of the coolant at the time (when the time in the second step is less than the time required for dissolving CaO in the coolant) or when the shape of the scrap is relatively large The problem of the deterioration of the performance arises.

On the other hand, in order to carry out the de-P reaction efficiently,
It is desirable to control the iron oxide concentration in the slag to be high. In the de-Si / P phase, since a large amount of C is present in the metal, iron oxide in the slag is easily reduced, and it is difficult to control the iron oxide concentration in the slag to a high level. However, once the CaO-FeO, iron oxide and forming a CaO-Fe ₂ O ₃ KeiTorukarada is less likely to be reduced, it helps to increase the control of iron oxide concentration in the slag.

In order to promote the formation of CaO-FeO and CaO-Fe ₂ O ₃ -based melts, it is considered effective to increase the chances of contact between slagging CaO and iron oxide. A material containing a large amount of iron oxide containing a large amount of slag (at least 50% or more of iron oxide is desirable)
It has been found that it is desirable to perform cooling at room temperature. In other words, conventionally, auxiliary materials containing scrap or unslagged CaO have been generally used as a coolant.
Instead, iron ore, sinter,
If iron-making dust or the like (hereinafter simply referred to simply as iron ore) is used, there is no need to worry about the problem of unslagging, and an effective iron oxide can be contained in advance at the time of removing P. , And concluded that it could have excellent utility.

[0021] Here, iron-made dust refers to dust that is mainly contained in iron oxide among dusts generated in steelworks such as converter dust and continuous cast scale and mill scale. It is a body or a briquette of 50 mm or less.

In the case where C-removed slag is re-used hot for de-P treatment, it is necessary to cool or deoxidize slag in order to suppress bumping phenomenon and slag forming at the time of charging hot metal. Was known. In the past, as described above, limestone and scrap coolant have been used for cooling slag.However, in the current converter operation that is directed to mass production, a short time is required to increase productivity. Slag needs to be cooled. For this reason, under the cooling condition in which the bumping phenomenon and the slag forming can be completely avoided, the slag is supercooled, and there has been a problem that the de-P reaction efficiency is deteriorated.

In the present invention, iron ore containing a large amount of iron oxide, which has not been conventionally used, is used as a cooling material when the C-removed slag is reused hot for the de-P treatment. is there. It is thought that by mixing iron ore in advance with slag removal in the slag cooling process and forming slag, CaO-FeO, CaO-Fe ₂ O ₃ -based melt, which is advantageous for improving the P removal efficiency, is generated promptly. Therefore, it is possible to easily solve the conventional problem that has caused deterioration of the P removal reaction efficiency.

In addition, it is more effective to carry out stirring by top blowing or bottom blowing when mixing the de-C residue and the coolant. Furthermore, since it does not contain unslagged CaO, it does not cause unslagged CaO remaining in the slag at the time of P removal. In addition, since iron ore generally has a small shape of 50 mm or less, slag cooling can be performed in a short time (within 2 minutes), and productivity is not hindered.

As described above, CaO—FeO, CaO—Fe
_A coolant that can simultaneously solve the problems of improving the de-P reaction by the ₂ O ₃ -based melt, preventing unslagged lime from remaining in the de-P slag, and achieving slag cooling in a short time is an iron ore containing a large amount of iron oxide. Only stones.

When iron ore is taken as an example, the amount of the coolant used is 30 to 150% based on the amount of slag after de-C refining remaining.
(Against slag). This amount is 30%
If it is less than the value, the effect as a coolant will be weakened, the slag cannot be solidified and remains in a molten state, and when charged with hot metal in the next process, it will react rapidly with C in the hot metal, bumping phenomenon will occur and hot metal and Slag gushes out of the furnace. Also, if this amount is 150
%, The slag is in a supercooled state, a part of the slag is not melted in the second step, and the efficiency of the P removal reaction is reduced.

Further, in the present invention, it is possible to effectively use slag such as continuous solidified slag, ingot slag, and converter slag (normal iron slag, de-C slag) that have been cooled and solidified. These slugs
It has been known that it has a useful composition as a de-P agent, but its melting point is higher than the furnace temperature at the time of de-P treatment and it has a dense structure, so that However, in many cases, complete slag formation is not achieved by ordinary Si / P removal treatment in which the reaction proceeds in the coexistence of slag phase and solid-liquid. If the slag is not completely formed, not only does the slag not function as a de-P agent, but also the dispersion of the de-P is increased due to variation in the amount of molten slag, and heat loss is caused by heating the solid slag that does not contribute to the reaction. Therefore, it has been difficult to use it in large quantities.

The inventors of the present application focused on the slagging behavior of the cooled and solidified continuous casting slag, ingot slag, converter slag, etc. in the environment inside the converter during the de-P treatment, and conducted an in-situ observation experiment. As a result, slagging of continuous solidified slag, ingot slag, converter slag, etc., which is cooled and solidified, is strongly affected by the state of the surrounding slag phase, and when the surrounding slag is completely in the liquid phase. It was found that a complete slagging state was obtained in a short time.

On the other hand, the present invention is characterized in that, in the cooling process of the decarbonized slag remaining in the furnace, the chlorinated slag is mixed with iron ore in advance to form slag, so that the composition of the decarbonized slag changes. The melting point can be expected to decrease. Therefore, the slag cooled and solidified by this method and the slag cooled and solidified by limestone and scrap, which are the conventional methods, are de-Si / P-free.
An in-situ observation experiment was performed to confirm the state at the furnace temperature during the treatment. As a result, the C
The slag completely became a liquid phase at about 1250 ° C., whereas in the case of the conventional method, a complete liquid phase could not be obtained even at 1350 ° C., which is the de-P treatment temperature.

In this method, the slag in the furnace becomes a single-phase liquid phase immediately after the start of the de-P treatment, and the surface of the slag newly charged into the converter furnace as a P-removing agent is entirely covered with a low-melting liquid slag. Will be Even if the slag has a high melting point and a dense structure and poor slagging properties, chemical dissolution into the low-melting liquid slag on the solid phase surface occurs actively, and complete slagging is obtained. Because it is easy to use, it can be used in large quantities as a de-P agent.

The hot metal de-P treatment end point temperature is 1300
It is desirable to control the temperature within a range of not less than 1350 ° C. As described above, the melting point of slag mixed with de-C slag and iron ore to form a slag is about 1250 ° C., and a temperature of 1300 ° C. or higher is required to ensure the presence of molten slag. On the other hand, from the viewpoint of the de-P reaction efficiency, when the temperature becomes 1350 ° C. or higher, iron oxide in the slag is reduced, and the oxidizing power of the slag is reduced. For this reason, a temperature of 1350 ° C. or less is required.

Al in slag at the time of de-C treatment after de-P treatment
It is desirable that the concentration of ₂ O ₃ is also within a certain range. Al ₂ O ₃ has a function as a melting point depressant for slag, and is effective in reducing the ratio of unslagged lime in slag. The effect is almost constant under the condition of (% Al ₂ O ₃ ) = 2% or more and the unslagged CaO ratio is 2% or less.
In order to reduce the amount of O, it is desirable that (% Al ₂ O ₃ ) = 2% or more. On the other hand, Al ₂ O ₃ also has the property of increasing the viscosity of the molten slag, so that high concentrations cause slopping. Since the occurrence frequency of the slopping becomes remarkable when (% Al ₂ O ₃ ) = 5% or more, (% A ₂ O ₃ )
l ₂ O ₃ ) = 5% or less is desirable.

[0033]

(Example 1) As an example, a 330-t converter was used, C-removed slag was left in a 20 to 40 kg / t furnace, iron ore was charged at 15 to 20 kg / t, and slag was cooled. For the present invention, and for comparison, the conventional scrap cooling was performed (slag cooling conditions were almost the same), and molten iron was charged for melting in the next converter. A total of 10 to 30 kg / t of the continuous cast slag, ingot slag, and converter slag that have been cooled and solidified are charged, the de-P treatment is performed at an end temperature of 1300 to 1350 ° C. for de-Si and de-P processing, and the generated slag is discharged. 1 and 2 show an example in which the Al ₂ O ₃ concentration in the decarbonized slag was set to 2 to 5% in the decarbonizing blowing after the above.

The time required for cooling the slag (the time from the introduction of the coolant to the confirmation of the solidification of the slag) was 1.5 minutes on average for slag cooling with iron ore, whereas the average time for slag cooling with scrap was 5. 3 minutes.

FIG. 1 shows the relationship between the basicity of slag and T.Fe, and FIG. 2 shows the basicity of slag and P after de-P treatment.
It shows the relationship between the concentrations. As is clear from the figure, in the case of the present invention, T.Fe is higher than in the conventional method, and the P concentration after the de-P treatment is lower.

The T.Fe in the slag is proportional to the iron oxide concentration in the slag. It is understood that the use of the present invention makes it possible to control the concentration of iron oxide in the slag to a high level, and thus it is possible to efficiently perform the de-P reaction.

(Example 2) In a case where a 330-t converter was used as an example, C-removed slag was left in a 20 to 40 kg / t furnace, iron ore was charged at 15 to 20 kg / t, and slag was cooled and solidified. In the case of the present invention) and the case where the decalcified slag is left in a 20 to 40 kg / t furnace, limestone is charged at 15 to 20 kg / t, and the slag is cooled and solidified (comparative example), The continuous casting slag, the ingot slag, and the converter slag which were charged with hot metal for the production and cooled and solidified as auxiliary materials were 10-30 k in total.
g / t, and end point temperature of de-Si and de-P treatment 1300-1
The de-P treatment was performed at 350 ° C., and in the de-C blowing after discharging the generated slag, in the slag after the de-P treatment when the Al ₂ O ₃ concentration in the de-C residue was 2 to 5%. FIG. 3 shows an example in which the remaining state of the cooled and solidified continuous casting slag, ingot slag, and converter slag was investigated.

In the case of this method, the slag in the Si-removing and P-removing phases was uniform, and the particles of the converter slag were not recovered. On the other hand, in the case of the conventional method, particles of the converter slag were recovered from the slag in the de-Si / P phase. From this fact, it can be seen that according to the present method, the slag property of the cooled and solidified slag in the de-Si / P phase is improved.

(Example 3) As a working example, a 330-t converter was used, leaving decarbonized slag in a furnace of 20-40 kg / t, charging iron ore of 15-20 kg / t, cooling and solidifying the slag,
Continuous casting slag, ingot slag, and converter slag cooled and solidified at the time of de-Si / de-P treatment are fed in a total of 10 to 30 kg / t to remove Si.
・ De-C after de-P treatment and discharge of generated slag
FIG. 4 shows an example of measuring the temperature dependence of the P ₂ O ₅ concentration in the Si-free and P-free slag when the Al ₂ O ₃ concentration in the C-removed slag is 2 to 5% in the blowing. Was.

The P ₂ O ₅ in the slag has a high value when de-P is efficiently performed. In this embodiment, the P ₂ O ₅ in the de-Si / P-free slag has a maximum value of 5 in a certain temperature range. It was stable with little variation at ~ 7%.

As shown in FIG.
It can be seen that ° C has a high de-P efficiency and is an optimal operation condition.

(Example 4) As a working example, a 330-t converter was used. De-C slag was left in a 20 to 40 kg / t furnace, iron ore was charged at 15 to 20 kg / t, and slag was cooled and solidified.
The ratio of uncalcified lime in the de-C treatment following the de-Si and de-P treatment when a continuous casting slag, ingot slag, and converter slag cooled and solidified during the de-Si and de-P treatment are added in a total amount of 10 to 30 kg / t. FIG. 5 shows an example in which the dependency of the frequency of occurrence of slopping on the concentration of Al ₂ O _{3 in} slag during the de-C treatment was measured.

The lower the unslagged lime, the higher the lime utilization efficiency and the more advantageous the cost. Under the test conditions, Al ₂ O ₃ was 2
If it is higher than 2%, the upper limit of variation of unslagized lime ratio is 2%
It was almost constant below.

From FIG. 5, it can be seen that the Al ₂ O ₃ concentration is optimally 2% or more based on the ratio of uncalcified lime and 5% or less from the frequency of occurrence of slopping.

[0045]

According to the present invention, by using iron ore or the like as a coolant at the time of hot reuse of de-C slag, it is possible to shorten the slag cooling time and to save quicklime as an auxiliary material. It can be expected to obtain a de-P efficiency higher than the normal operation using scrap, lime, etc. as a coolant.

Further, since the problem of unslagged lime in the P-free slag can be solved, slag can be reused without impairing productivity. Furthermore, the slag that has been cooled and solidified can be used in large quantities as a P-removing agent because it is easy to obtain a complete slag state.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between basicity of slag and T · Fe.

FIG. 2 is a diagram showing a relationship between basicity of slag and P concentration after de-P treatment.

FIG. 3 is a view showing a slag formation state in a removal of Si from a continuous cast slag / ingot slag / converter slag solidified by cooling;

FIG. 4 is a diagram showing the temperature dependence of (% P ₂ O ₅ ) in the slag after the Si removal from the P treatment;

FIG. 5: Ratio of unslagged lime in slag after sludge removal
Ping occurrence (% Al_Two O _Three Figure showing dependency

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C21C 5/36 C21C 5/36 (72) Inventor Keisuke Okuhara 1st Nishinosu Oaza, Oita City, Oita Prefecture Nippon Steel Corporation Oita Works, Ltd. (72) Inventor Masanobu Kumakura, Oita, Oita, Oita, Nishi-no-Shi, 1 Nippon Steel Co., Ltd. F-term in Oita Works (reference) 4K002 AB01 AB04 AE06 AF04 BD04 4K014 AA01 AA03 AB04

Claims (6)

[Claims] 1. A first step of charging hot metal or hot metal and scrap as a main raw material into a converter, a second step of removing Si and P, a third step of discharging generated slag, and then removing C. A fourth step of blowing, a fifth step of tapping while leaving slag after de-C refining, and then returning to the first step to remove the S in the second step.
In i. De-P, the slag left in the fifth step is recycled and used, and when repeating the above-mentioned five steps, the coolant containing a large amount of iron oxide is used for cooling the slag after the de-C refining in the fifth step. Converter steelmaking method characterized by using 2. The amount of the coolant used as the coolant is 30 to 1 with respect to the amount of the slag after the C-free refining remaining in the fifth step.
2. The converter steelmaking method according to claim 1, wherein the ratio is 50%. 3. The converter steelmaking method according to claim 1, wherein iron ore, sinter, or ironmaking dust is used as a coolant used in the fifth step. 4. The method according to claim 2, wherein in the second step, continuous casting slag and / or ingot slag and / or converter slag are used as auxiliary raw materials in addition to the slag left in the furnace. 4. The converter steelmaking method according to any one of 1 to 3. 5. The converter steelmaking method according to claim 1, wherein, in the second step, the end point temperature of the Si / P removal treatment is 1300 ° C. to 1350 ° C. 6. The method according to claim 1, wherein, in the fourth step, the concentration of Al ₂ O ₃ in the decarbonized slag during the decarbonizing blowing is 2 to 5%. Converter steelmaking method.