JPS5835566B2 - How to process hot metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of treating hot metal whose silicon content has been reduced by using a specific refining agent to proceed with a desulfurization and dephosphorization reaction while suppressing decarburization.

Many studies have been conducted regarding the reduction and removal of phosphorus in hot metal.
It is known from Japanese Patent No. 6-10771 and the like that dephosphorization of hot metal can be achieved by oxidizing a basic slag with good fluidity.

Then, the use of CaO as a slag material to generate basic slag, the use of oxygen gas and/or solid oxygen (e.g. iron ore, mill scale, etc.) as an oxidizing agent, and the fluidity of slag. It is known to use fluorite as a flux to increase the

However, in the dephosphorization treatment of hot metal based on the above method,
The input content of the slag material and iron oxide is as large as 100 to 200 ky/l, and a large amount of slag is discharged.

In addition, as a simultaneous dephosphorization and desulfurization technology for hot metal, CaC470=so
%, Ca10-20%, Mn03-10% is melted into a compound.CaCl2-C is characterized by a low melting point.
Tetsu-to-Hagane A2, Vot 64.1978, introduces a method of using aO-Mn0-based flux with a diameter of about 25 φ for hot metal.

According to this method, the maximum dephosphorization rate is 91%, and the sulfur can be reduced to 0.03%, and the dephosphorization and desulfurization effects are fully satisfactory.

However, as has been well known, halides such as CaF2 and CaCl2 have low melting points, and although they have the characteristic of lowering the melting point of slag containing large amounts and increasing fluidity, this flux There is a problem in that the erosive force of refractories is large and harmful gases are generated, so in actual operation of the above method, strong measures to extend the life of the refractory lining of the smelting furnace and smoke collection treatment for the large amount of chlorine-containing gas generated are required. Further, since the above-mentioned flux is used in an amount of approximately 25 wt% of the hot metal, a huge amount of slag is generated, and its treatment becomes a problem.

As described above, all conventional methods for dephosphorizing hot metal have problems in slag treatment because they inevitably generate a large amount of slag.

The present inventors investigated various fluxes regarding the fluidity of refined slag based on the problem of the amount of refined slag mentioned above, and found that fluorite, which has been commonly used in the past, Even if the temperature of CaO is varied in the range of -2 to -2, the hot metal temperature remains between 1300 and 140.
It was confirmed that a low temperature range of 0°C, which is preferable for dephosphorization, works on fluidizing the slag, but is not necessarily optimal for improving fluidity.

He confirmed that chlorides of alkali metals or alkaline earth metals are useful as fluxes, and has already provided a new method for treating hot metal in Japanese Patent Application No. 130039/1982 and Japanese Patent Publication No. 11368/1983.

The purpose of the above-mentioned prior invention is to quickly turn f and lCaO into slag using the heat of hot metal whose Si content is reduced by using a specific refining agent and iron oxide, and to turn the slag into slag in a preferable state and produce a small amount of slag. Therefore, it is important to perform dephosphorization treatment without suppressing decarburization.

The gist of the leading invention is that when hot metal is dephosphorized, Ca is added to 0.03 to 0.25 tons of Si.
CaC1,2 and/or KCt per part by weight of O1
By adding a refining agent consisting of 0.2 to 0.5 parts by weight and adding iron oxide in portions, the basicity (CaO/S i 02 ) of the refining slag is reduced to 3.5 to 8.0 and T
This is a method for treating hot metal characterized by maintaining the amount of Fe between 5 and 15.

However, in the above-mentioned earlier application, the amount of T and Fe was 5 to 1.
Since the value is kept at a relatively low value of about 5 yen, decarburization of hot metal can be suppressed and a considerably high desulfurization rate can be obtained.

However, as a result of further study by the present inventors, it was found that if it were possible to improve the desulfurization rate as well as dephosphorize the hot metal while maintaining the carbon content in the hot metal at a high level, the processing time could be shortened and the quality of the product could be improved. , etc., T in refined slag.

We considered making the amount of Fe even lower than in the previous application.

That is, decarburization of hot metal is an oxidation reaction, desulfurization is a reduction reaction, and dephosphorization is an oxidation reaction.
The smaller the amount, the better, and the larger the amount of T and Fe is to promote dephosphorization.
Decreasing the amount of e results in inhibiting dephosphorization.

As a result of intensive studies to solve these conflicting problems, we found that by strongly stirring the hot metal bath by mechanical means, especially an impeller, the dephosphorization reaction rate was significantly accelerated, and as a result, the amounts of T and Fe were kept lower than in the previous application. However, the dephosphorization rate was maintained at a comparable value, and the desulfurization was successfully achieved compared to the previous application.

However, the limit of the NU value of T and Fe is 3.

This is T even with strong stirring using an impeller. This is because when the value of Fe becomes 3φ or less, the dephosphorization rate decreases significantly.

Note that the upper limit values of the amounts of T and Fe were set to be less than 5 in relation to the lower limit values of the amounts of T and Fe in the previous application.

The contents of the present invention will be explained in detail below.

One of the features of the present invention is that CaC per part by weight of CaO'
1, and/or KCt is used as a refining agent containing 0.2 to 0.5 parts by weight, and iron oxide, so-called solid oxygen, is used as a refining aid.

In the above refining agent, CaO acts as a slag material, and CaO
Cl2 and/or KCt act as a flux.

As this flux, chlorides of alkali metals or alkaline earth metals have a similar effect, but among these chlorides, CaCl2. KCb'k was selected based on conditions such as the CaO slag formation rate, flux cost, and use of the generated slag, which will be described later.

Examples of the iron oxide include iron ore, sintered ore, mill scale, and iron oxide powder.

The above-mentioned refining agent and iron oxide are added separately or in a mixed manner in amounts that are distantly related to the refining conditions described below.

When the charged refining agent, iron oxide, and hot metal are brought into contact with each other under forced stirring, first, silicon in the hot metal is oxidized by iron oxide to produce 5IO2.

This Si02, FeO from iron oxide, and CaC added
Alternatively, KCl slags CaO.

In this case, CaCl2 or KCl has the effect of promoting slag formation even with a low FeO composition.
If the amount of 1 is less than 0.2 parts by weight based on CaO, no slag effect can be expected with a low FeO composition, and the consumption of iron oxide increases.

Not only does this prolong the slagation time, but it also makes it impossible to obtain refined slag that is highly reactive and has good fluidity.

From this point of view, in order to promote slag formation, CaCl2 or KC
The larger the amount of t is, the more preferable it is, but if the amount of CaCl2 or KCl exceeds 0.5 parts by weight based on CaO, as shown in FIG. Alternatively, the concentration of vaporized CaCl2 or KCl and chloride gas increases, which is undesirable because it has a large effect on the load on environmental protection equipment.

From this point of view, the ratio of CaCl2 or KCt to the amount of CaO is determined to be 0.2 to 0.5.

Furthermore, a high ratio of CaCl2 or KCl impedes the characteristics of the refining agent of the present invention as an inexpensive dephosphorization and desulfurization agent, since these compositions are not cheap.

Next, as mentioned above, the silicon in the hot metal is oxidized to form SiO
Generate 2.

The amount of SiO2 produced is determined by the basicity (Ca
b/5in2).

As shown in Figure 3, the basicity of the refined slag affects the dephosphorization rate.

For the above reasons, the present invention uses sold hot metal containing silicon.

If the silicon content in the hot metal exceeds 0.25%, it is necessary to use a large amount of refining agent and iron oxide to produce the desired refining slag. Not only is the objective not achieved, but the lowering of the hot metal temperature is also a problem, which significantly limits the decarburization treatment conditions carried out as a subsequent step of the method of the present invention.

On the other hand, as the silicon content in the hot metal decreases, the amount of refining slag controlled within a specific range described below can be proportionally reduced.

Furthermore, the lower the amount of Si, the faster the dephosphorization rate itself.

However, when the silicon content is less than 0.03%, the amount of SO2 produced from the hot metal is limited, and the absolute amount as refining slag to smoothly achieve dephosphorization is insufficient. Phosphorus results are no longer available.

For the above reasons, the present invention adopts molten pig iron with a diameter of Si of 0.03 to 0.25, and adds the above-mentioned refining agent and iron oxide to it and stirs it strongly to turn CaO into slag and form molten refining slag. It is something to do.

As the above-mentioned strong stirring means, for example, a mechanical stirring means using a rotary blade is advantageous in order to efficiently dephosphorize a small amount of T, Fe''Q, and if necessary, the bubbling effect of inert gas can be used. Known means such as physical stirring means using kinetic energy or stirring means using kinetic energy of falling flow can be used alone or in combination.

Next, one of the characteristics of the present invention is the basicity of the smelting slag (
CaO/Sr02) is to be maintained at 3.5-8.

The hot metal to be treated in the method of the present invention may be stored in a certain amount in a container such as a ladle, or in a channel furnace where a certain amount of hot metal flows continuously, or in a combination of the two. There are so-called batch type and continuous type modes.

The method of the present invention can be carried out regardless of the presence of hot metal in any of the above embodiments, and as a means of maintaining the basicity of the refined slag within the predetermined range, it is possible to carry out the method in accordance with the silicon content of the treated hot metal. Inject a determined amount within the range of 12-30 kp/l.

When the entire required amount of this refining agent is added at once and forcefully stirred, CaCl2. It can be easily turned into slag by the action of KC.

In addition, the silicon content of the hot metal is relatively high, so the refining agent is
If the amount is 0 kg/l or close to it, the absolute amount to be added will be large and some of the refining agent may form lumps, so it is better to add the refining agent in two or three times.

Next, the iron oxide becomes a FeO source necessary for slag formation, desiliconization, and dephosphorization of the refining agent.

The refining agent used in the present invention is CaCl2. By blending KCt in a predetermined ratio and in combination with strong stirring, the formation of CaO into slag progresses rapidly with a small amount of FeO.

Here, in order to shorten the dephosphorization and desulfurization treatment time, it is essential to quickly turn the refining agent into slag.

Therefore, in the present invention, strong stirring is carried out and at the initial stage of treatment, 15 to 301
A relatively large amount of iron oxide selected from within the range of i/t is added, and thereby the slag formation of CaO proceeds smoothly and rapidly.

When slag formation progresses to the desired state and dephosphorization actively progresses, it is necessary to suppress decarburization as much as possible.
Since the decarburization reaction increases in proportion to the amount of iron oxide added, the amount of T and Fe suitable for dephosphorization and desulfurization can be maintained by dividing the iron oxide into portions at this stage.

For example, in the case of hot metal stored in a batch method, there are methods in which a portion of the input amount is continuously added within a time corresponding to about 70 to 90% of the dephosphorization and desulfurization treatment time, and In the case of flowing hot metal, a method can be adopted in which a portion of the input amount is continuously introduced in accordance with the amount of iron passing per unit time.

What is important when implementing this method of splitting iron oxide is that the reduction rate of FeO in the smelting slag is relatively fast.
, by introducing an XFeo source.

According to experiments conducted by the present inventors, it is practically preferable to add the liquid in divided doses at least once every four minutes.

For example, if the total treatment time is 20 minutes, iron oxide should be divided into at least five times.

As mentioned above, by adding iron oxide at least in parts, the slag formation of the supplied CaO proceeds smoothly and stably, and the proportion of FeO in the obtained refining slag can be stably controlled, and in addition, Since the supply of oxygen source is suppressed, the decarburization reaction can be suppressed.

Next, the basicity (CaO/SiO2) of the refined slag was set to 3.
The technical reason for limiting the amounts of 5-8, T, and Fe to less than 3-5% will be described.

As shown in Figure 3, the basicity of the refined slag affects the dephosphorization rate.

As is clear from the graph presented, the lower the basicity, the lower the dephosphorization rate.

Therefore, in order to achieve the dephosphorization treatment that is the objective of the present invention, the lower limit of basicity must be maintained at 3.5 or higher.

By maintaining the basicity of 3.5 or more, the dephosphorization rate of hot metal is approximately 8.
The value is 0% or more.

As shown in Figure 2, CaO of CaCl2 or KCl
CaO/SiO2 even if the ratio to 0.2 to 0.5
It has been found that the Ct- concentration in the exhaust gas during treatment increases rapidly when the basicity (Cao/S 102 ) becomes less than 3.5. From this point of view as well, the basicity (Cao/S 102 ) needs to be 3.5 or more.

If the basicity of the refined slag is further increased from 3.5, the dephosphorization rate will be significantly improved.

However, even if the basicity is increased to a value exceeding 8, the dephosphorization rate is no longer significantly improved and the cost of the refined slag is simply increased.

At such a high basicity, in actual operation, CaO is insufficiently converted into slag, resulting in smelting slag with poor fluidity.
As shown in the figure, this method is not practical because it significantly increases the proportion of iron mixed into the refining slag, resulting in iron loss.

However, in the method of the present invention, the basicity (C
aO/S102) is limited to 3.5 to 8.

Adjustment and maintenance of the above basicity of 3.5 to 8 can be grasped by theoretical calculations based on the relationship between the silicon content of the limited hot metal to be treated and the amount of refining agent input, and it is possible to adjust and maintain the basicity according to the silicon content in the hot metal. The refining agent is added in an amount adjusted to have the optimum basicity and minimum slag amount within the range of 12 to 30/l.

Next, regarding the amount of T and Fe in the refining slag in the method of the present invention, as mentioned above, CaCl2 and/or KCl in the refining agent brings about the slag effect of CaO by the action of strong stirring even in the low FeO amount range. .

The amounts of T and Fe in the refined slag vary depending on the temperature of the hot metal, the silicon content in the hot metal, the amount and method of iron oxide input, and the stirring method.

Figure 4 shows the relationship between the stirring intensity of the hot metal bath (impeller and gas bubbling), the amount of T and Fe in the smelting slurry, and the dephosphorization rate. It can be seen that the ratio (so% or higher) is maintained.

This is due to the fact that slag formation is promoted by the strong stirring by the impeller and the reaction rate is significantly accelerated.

Next, Figure 5 shows the relationship between the amount of T and Fe in the refined slag and the desulfurization rate.The lower the amount of T and Fe, the better the desulfurization rate.Moreover, strong stirring by an impeller improves the desulfurization rate. is remarkable.

According to the present invention, when carrying out the above-described dephosphorization and desulfurization treatment of hot metal, even though FeO is present in the refined slag, the basicity is 3 because the amounts of T and Fe are at a low level.
．． Desulfurization treatment is carried out at a high rate when it is 5 to 8.

On the other hand, normally when desulfurizing hot metal, CaO
It is known that a desulfurization rate of 60% can be ensured by using -CaFe refined slag.

However, when FeO is present in this refined slag, the desulfurization rate is only about 20 or more even if the basicity is 3.5 or more, but according to the method of the present invention, the desulfurization rate is several times higher. was achieved.

As described above, the method of the present invention involves adding a refining agent consisting of 0.2 to 0.5 parts by weight of CaCl2 and/or KCl to 1 part by weight of Ca to hot metal containing 0.03 to 0.25 Si, and Iron is added in parts or continuously, and C
The basicity (CaO/SiO2) is maintained at 3.5 to 8 using SiO2 from aO1 hot metal, FeO from iron oxide, and CaCl2 and/or KCl, and T is increased by particularly strong stirring. , Fe amount is 3~
Even if the amount is less than 5, slag can be stably generated and rapid dephosphorization and desulfurization treatment can be performed.

Example One ton of hot metal whose silicon content had been reduced in advance to a range of 0.203 to 0.25% was charged with a refining agent and iron oxide in a ladle under forced stirring by an impeller.

The refining agent used was CaCl20 per part by weight of Ca01.
．． It consists of 25 parts by weight, and the amount added is 13.5-
It is.

The refining agent and iron oxide were introduced using an eight-time split injection method.

The amount of iron oxide added was varied within the range of 15 to 25 kg, and stirring was performed using two types of impeller (200 rl) and gas bubbling (1007/min, t), and the amounts of T and Fe in the slag and dephosphorization were determined. The relationship between the three factors is shown in Figure 4.

As is clear from Fig. 4, in the case of strong stirring by an impeller, the dephosphorization rate is high (8
0% or more), and when the diameter is less than 3φ, the performance deteriorates rapidly even under strong stirring.

On the other hand, the results of desulfurization obtained by the above treatment are shown separately in FIG.

As is clear from this figure, it can be seen that the desulfurization rate improves as the amounts of T and Fe in the refined slag decrease.

The C content of the hot metal used was 4.2%, and the C content after treatment was 3.9% for the gas bubbling method and 4.1% for the impeller method.
%Met.

As detailed above, the present invention involves using a CaO-CaCl2 and/or KCl-based refining agent and iron oxide together to treat hot metal, and in particular, stirring the hot metal bath with strong mechanical stirring. As a result, the amount of T and f'e in the refined slag capable of high-level dephosphorization can be lowered to 3φ (the upper limit is less than 5φ), thereby improving the desulfurization rate and allowing the treatment to be carried out without reducing the carbon content. This method is extremely effective in shortening the time required for pretreatment of hot metal and securing a heat source during the subsequent decarburization treatment without slag.

Additional relationship The present invention is disclosed in Japanese Patent No. 1122315 (Japanese Patent Publication No. 113-1988
This is an additional invention of No. 68).

The first summary is Si0.003~0.25
% of hot metal, a refining agent consisting of 0.2 to 0.5 parts by weight of one or two types of CaCl2KCt per 1 part by weight of CaO was added, and iron oxide was added in portions to determine the basicity of the refining slag (CaO/5in2 ) from 3.5 to 8.0 and T, Fe
The point is to maintain the amount between 5 and 15%.

The present invention expands the amount of T and Fe in the refining slag that can be used by strongly stirring the hot metal bath from the lower limit of 5φ to 3, thereby maintaining the dephosphorization rate and suppressing decarburization while increasing the desulfurization rate. This is the first additional invention.

[Brief explanation of drawings]

Figure 1 shows the basicity (CaO/5in) of the refined slag of the present invention.
2) and granular iron mixed in the slag. Figure 2 shows the relationship between the basicity (Cab/S i02 ) of the refining slag and the Ct in the refining exhaust gas at different CaC, 12/Ca O - An explanatory diagram showing the relationship between concentration indexes, Figure 3 shows the basicity (CaO
/5in2) and the dephosphorization rate of hot metal. Figure 4 is a diagram showing the relationship between the stirring intensity of the hot metal bath, the amount of T and Fe in the refining slag, and the dephosphorization rate. Figure 5 is T in smelting slag
, a chart showing the relationship between the amount of Fe and the desulfurization rate.

Claims (1)

[Claims] 1 When dephosphorizing hot metal, SiO,03~o,
A refining agent consisting of 0.2 to 0.5 parts by weight of CaCl2 and/or KCl to 11 parts by weight of Ca is added to 2s% hot metal, iron oxide is added in portions, and the hot metal is vigorously stirred for refining. Basicity of slag (CaO/S
102) is maintained at 3.5 to 8.0 and the amount of T and Fe to less than 5φ to 3φ.