JP3226768B2 - Slag reforming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reforming slag, and more particularly to a method for reducing the production cost of high cleanliness steel using industrial waste.

[0002]

2. Description of the Related Art Generally, slag reforming technology is used as one method for producing high cleanliness steel or low sulfur steel. This utilizes absorption separation of inclusions by slag during molten steel stirring and low sulfurization of molten steel by slag desulfurization.In either case, ladle slag has a sufficiently low oxygen potential and controls the desired slag composition. There is a need to. As a means for controlling such slag composition, a ladle refining method (LF method) is known. This is a facility that has a heating and stirring function, and adds slag forming material and slag reducing material to control slag. However, special equipment is required and the cost of refractories, electrodes, power, etc. increases The point is the challenge.

[0003] In addition, a method of adding a slag-making material or a slag-reducing material at the stage of tapping work from a steelmaking furnace to a ladle to control the slag composition has been widely performed (Japanese Patent Publication No. Sho 62-39205).
However, compared to the ladle refining method, there are problems in the reduction efficiency and slagging property of slag, and in order to solve these problems, a method of controlling slag near the minimum melting point composition (Japanese Patent Laid-Open No. 6-330138), A method of stirring in a slag using a mixed molded product of a gas generating substance (Japanese Patent Publication No. 2-19168) has been proposed.

In the former, it is necessary to control the slag to an extremely narrow composition, and there is a risk that the slag entrainment may cause deterioration of the slab quality depending on the casting conditions, which may lower the viscosity of the slag. Further, in the latter case, there is a problem that the production cost is increased due to the use of a special slag reforming material, and the invention of a low-cost and high-efficiency slag reforming method capable of controlling a wide range of slag composition has been expected. .

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of such a situation, and is intended for industrially easily available industrial waste in carrying out slag reforming for obtaining high cleanliness steel. An object of the present invention is to provide an inexpensive and highly efficient slag reforming method capable of controlling a wide range of slag composition by using a material.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a material containing, as a main component, metals Al, Al ₂ O ₃ and AlN generated in the refining stage of aluminum when slag is reformed in a molten steel ladle. The so-called industrial waste is described in (1) below.
A slag reforming method characterized by being added to a so-called undeoxidized ladle molten steel (without adding a deoxidizing material) within a range of an addition amount defined by a formula and during tapping. . 1.0 ≦ (addition amount of industrial waste) × T [N] / (total steel output) ≦ 6.0 where T [N]: total nitrogen content (% by weight) contained in the added industrial waste The unit of (amount of added industrial waste) is kg, and the unit of (total steel output) is t.

[0007]

The present invention is constructed as described above. The point is that slag forming is generated and controlled in ladle slag reforming using N in industrial waste as defined in the claims. By selectively agitating power to the ladle slag by, while improving the slag reduction efficiency and promoting slagging,
This is a method for preventing N in industrial waste from remaining in molten steel as much as possible, and in particular, a method for achieving its purpose at low cost using industrial waste.

Hereinafter, the present invention will be described in detail.
The present inventors investigated the yield of N in molten steel when using industrial waste generated in the Al refining stage. Fig. 1 shows the relationship between the blow-off C and the [N] before the RH treatment at that time when the industrial waste was added to the tapping for the total tapping amount of 280t that was subjected to converter refining. It is the result of the investigation. Level 1 is the industrial waste (Al: 24%,
(Al ₂ O ₃ : 55%, T [N]: 3.6%) was added at an amount of 450 t at the time of tapping of 60 t, and then Al: 70 kg
The level 2 is a case in which Al; 70 kg was added at the time of a tapping amount of 60 t, and then 450 kg of the same industrial waste was added.

As shown in FIG. 1, when Al, which is a deoxidizer, is added in advance, the value of [N] before the RH treatment is high. That is, N from the industrial waste concerned
In order to suppress the yield, it was found that the industrial waste should be added without adding the deoxidizing agent. Furthermore, the present inventors conducted a test to determine the upper limit of the amount of addition of the industrial waste in a state where the deoxidizing agent was not added.

FIG. 2 shows that before tapping C: 0.10 to 0.12.
% And a result of investigating the relationship between the added amount of the industrial waste and the N before the RH treatment for a charge with a steel output of 280 t. Each level is based on the composition of the industrial waste used. Level 1 is Al: 35%, Al ₂ O ₃ : 45%, T [N]:
2.1%, Level 2 is Al: 24%, Al ₂ O
₃ : 55%, T [N]: 3.6%, level 3 is A
_{l: 12%, Al 2 O} 3: 67%, T [N]: 5.1%
Were used. As shown in FIG. 2, at any level, the amount of industrial waste added exceeds the range of (the amount of industrial waste added) × T [N] / (total steel output) ≦ 6.0. In this case, it was found that N in the molten steel after addition increased.

Next, the behavior of N in molten steel will be described. According to the investigation by the present inventors, most of N in industrial waste generated in the Al refining stage was AlN. Therefore, A existing in the vicinity of the surface of metal Al particles or Al ₂ O ₃ particles
1N comes into contact with undeoxidized molten steel prior to the progress of deoxidation of the molten steel and reacts preferentially with oxygen atoms, so that Al ₂ O ₃
And N atoms are generated. At this time, since the generated N atoms locally increase in concentration, they do not easily cause floating separation in the molten steel as N ₂ gas to increase N in the molten steel.

On the other hand, when the industrial waste is added after adding the deoxidizing material or when excessively added to undeoxidized molten steel, the concentrations of both Al and N in the molten steel increase, Since the decomposition of AlN was dominated by local equilibrium, it was presumed that the N concentration sufficient for bubble generation did not increase, and that the N atoms diffused and dissolved in the molten steel increased. As described above, the present inventors have investigated the physical properties of the substance in detail and elucidated the melting mechanism in molten steel, thereby setting the upper limit for suppressing the yield of N in molten steel with respect to the amount of addition in the actual operation. I could specify it.

Further, the present inventors have determined that the N
We have developed a slag reforming method using slag. Before tapping C:
For a charge of 0.15 to 0.20% and a tapping amount of 280 t, the relationship between the amount of the industrial waste and the slag (% T.Fe + MnO) before the RH treatment was investigated. The slag reforming procedure at this time is performed as shown in FIG.
[Al] value before RH treatment was 0.020 for Al addition during tapping.
It was adjusted to be 0.030%. Each level corresponds to the components of the industrial waste used, and level 1 is Al: 35
%, Al ₂ O ₃ : 45%, T [N]: 2.1%, and Level 2 was Al: 24%, Al ₂ O ₃ : 55%, T
[N]: 3.6%, Level 3 is Al: 12%, A
l ₂ O ₃ : 67%, T [N]: 5.1%, respectively.

FIG. 3 shows the results. As shown in FIG.
When the industrial waste is added in an amount of 1.0 ≦ (industrial waste addition amount) × T [N] / (total steel output), RH treatment is performed at any level. In the previous slag, (% T.Fe + MnO) ≦ 1.5%, and it was confirmed that the slag modification was performed efficiently. 4 shows the amount of industrial waste added and the slag before RH treatment (% T.Fe + M
FIG. 3 is a diagram showing a processing procedure of slag reforming in the investigation of the relationship of (nO).

The function of N in the slag reforming will be described below. Part of the AlN contained in the substance, particularly those contained in Al ₂ O ₃ grains, reaches the slag surface and decomposes in the slag. At this time, AlN is F in the slag.
By contacting with eO, MnO, etc., Al ₂ O ₃ and N atoms are generated. This reaction is exothermic and promotes the slagging reaction. In addition, the generated N atoms generate N ₂ gas bubbles in the slag layer, causing physical phenomena such as an increase in internal stirring in the slag layer and a volume expansion of the slag layer. Therefore,
The slag modifier added to the slag quickly infiltrates and can efficiently reduce lower oxides in the slag. From the above results, the lower limit value for performing the slag reforming with high efficiency using the N contained in the substance was specified.

The so-called aluminum dross generated during the refining process of aluminum is different from A in the refining process.
Although a product with a l content is generated, a product with a high content of metal Al is subjected to refining to recover the metal Al. Therefore, as an industrial waste, the metal Al content: 5 to 5
0 (% by weight), Al ₂ O ₃ content: 20 to 70 (% by weight), AlN content: 5 to 20 (% by weight), and Al ₂ O with a decrease in the metal Al content. ₃ or Al
N content increases.

In the practice of the present invention, the metal Al content: 20 to 40 (% by weight), Al ₂ O
( ₃₎ Content: 25 to 50% by weight is recommended. When the metal Al content is high or the Al ₂ O ₃ content is low, the substance dissolves quickly,
The rate at which the decomposition of 1N proceeds in the molten steel increases, and the slag stirring force may decrease. Therefore, when the present invention is used alone and other slag stirring means is not used, the above range is recommended. When the metal Al content is high,
Alternatively, when the content of Al ₂ O ₃ is low, the ratio of the powder of the substance becomes high, and depending on the addition conditions, the working environment and the addition yield may be deteriorated. Therefore, the above range is recommended depending on the dust collection conditions.

The present invention does not limit the kind of the slag reducing agent added to the slag after tapping at all. When the slag is reformed in the molten steel ladle, at least the metal generated in the refining stage of aluminum is used. A so-called industrial waste containing Al, Al ₂ O ₃ and AlN as its main components is subjected to a so-called undeoxidized ladle within the range of the addition amount defined by the above formula (1) and during tapping. The above problem can be solved as long as it is added to molten steel (to which no deoxidizing agent is added).

[0019]

EXAMPLES The effects of the present invention are compared with those of the conventional method in Table 1 below.
Shown in All examples are steel grades equivalent to JIS-S10C.

[0020]

[Table 1]

Inventive Example 1 is a component C which was subjected to converter refining:
During the tapping of molten steel at 0.06% at a temperature of 1648 ° C., the relevant industrial waste (Al: 35%, Al ₂ O ₃ : 45%, T
[N]: 2.1%) was 1.8 kg / t-S, Al;
7 kg / t-S, FeSi; 3.0 kg / t-S, Fe
Mn: 5.0 kg / t-S, CaO: 4.0 kg / t-
S was added continuously in the order described, and A was added on the slag after tapping.
l: 0.45 kg / t-S was added as a slag reducing material, the components were adjusted in the RH process, and continuous casting was performed. As shown in Table 1, [N] was 28 ppm, and there was no effect of the addition of the industrial waste, and the oxygen potential in the slag before the RH treatment could be sufficiently reduced. According to the analysis result of the slab after continuous casting, T [O]: 11
ppm.

Inventive Example 2 is a component C which was subjected to converter refining:
During the tapping of molten steel at 0.08% and a temperature of 1631 ° C., the relevant industrial waste (Al: 35%, Al ₂ O ₃ : 45%, T
[N]: 2.1%), 1.8 kg / t-S, Al;
7 kg / t-S, FeSi; 3.0 kg / t-S, Fe
Mn: 5.0 kg / t-S, CaO: 2.5 kg / t-
S was added continuously in the order described, and A was added on the slag after tapping.
l: 0.45 kg / t-S was added as a slag reducing material, the components were adjusted in the RH process, and continuous casting was performed. As shown in Table 1, [N] was 19 ppm, which was not affected by the addition of the industrial waste, and the oxygen potential in the slag before the RH treatment was sufficiently reduced. According to the analysis result of the slab after continuous casting, T [O]: 9p
pm.

In Comparative Example 1, component C was subjected to converter refining:
0.07% Al in the tapping of molten steel at a temperature of 1640 ° C;
0.6 kg / t-S, the relevant industrial waste (Al: 24
%, Al ₂ O ₃ : 55%, T [N]: 3.6%).
5 kg / t-S, FeSi; 3.0 kg / t-S, Fe
Mn: 5.0 kg / t-S, CaO: 4.5 kg / t-
S was added continuously in the order described, and A was added on the slag after tapping.
l: 0.45 kg / t-S was added as a slag reducing material. As shown in Table 1, at the stage before the RH treatment, [N] was 61 ppm, which exceeded the desired range of the steel type, so the steel type was changed.

In Comparative Example 2, the components C were subjected to converter refining:
During the tapping of molten steel at 0.08% at a temperature of 1647 ° C., aluminum dross with a high Al content (Al: 60%, Al ₂ O ₃ :
20%, T [N]: 1.0%) to 2.0 kg / t-S,
FeSi; 3.0 kg / t-S, FeMn; 5.0 kg
/ T-S, CaO; 2.0 kg / t-S was added continuously in the order described, and Al: 0.45 kg /
This is the case where t-S is added as a slag reducing material. The charge is (% TF) in the slag before the RH treatment.
e + MnO) was high. The analysis result of the slab shows T
[O]: 28 ppm, and the desired cleanliness could not be secured.

[0025]

As described above, according to the present invention, ladle slag can be selectively agitated, and highly efficient slag reforming can be performed at low cost to improve the cleanliness of molten steel.

[Brief description of the drawings]

FIG. 1 shows a case where the industrial waste is added with the prior addition of the deoxidizer and the case where the industrial waste is added without the preceding addition of the deoxidizer. Diagram comparing and showing the relationship between C and [N] before RH processing

FIG. 2 is a diagram showing the relationship between the amount of addition and the value of [N] before RH treatment when the industrial waste is added to undeoxidized molten steel.

FIG. 3 is a graph showing the relationship between the amount of the industrial waste added and the slag (% T. Fe + MnO) before RH treatment.

FIG. 4 is a diagram showing a processing procedure of slag reforming in an investigation of the relationship between the amount of the industrial waste added and the slag before RH treatment (% T. Fe + MnO).

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Terashima 12 Nakamachi, Muroran-shi, Hokkaido Nippon Steel Corporation Muroran Works (56) References JP-A-6-200317 (JP, A) JP-A Heihei 6-108137 (JP, A) JP-A-6-228626 (JP, A) JP-A-4-72009 (JP, A) JP-A-4-88117 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21C 7/04 C21C 7/00

Claims (1)

(57) [Claims] When slag is reformed in a molten steel ladle, metals Al and A generated in a refining stage of aluminum are used.
A substance containing l ₂ O ₃ and AlN as its main components, so-called industrial waste, is added to undeoxidized molten steel in the ladle during tapping in a range of the addition amount defined by the following formula (1) A slag reforming method characterized by the above-mentioned. 1.0 ≦ (the amount of added industrial waste) × T [N] / (total steel output) ≦ 6.0 (1) where T [N] is the total amount of the added industrial waste The unit of nitrogen concentration (%) (the amount of added industrial waste) is kg, and the unit of (total steel output) is t.