JP6126355B2 - Hot metal desulfurization treatment method - Google Patents

Description

  The present invention relates to a method for desulfurizing a carbon-containing hot metal.

  In the production process of stainless steel, steel, etc., desulfurization treatment that removes sulfur content from the molten iron produced by melting the raw material to remove the sulfur content that causes embrittlement of the finished product when contained Is done. In the desulfurization process, for example, in the case of stainless steel, a desulfurizing agent is added to the hot metal that has been manufactured in an electric furnace and then transferred to a ladle, thereby reacting the desulfurizing agent with sulfur in the hot metal to slag the sulfur content. To separate. At this time, a method is adopted in which the desulfurization reaction of hot metal is accelerated by adding a desulfurizing agent to the hot metal while mechanically stirring the hot metal with an impeller (stirring blade) immersed in the hot metal in the receiving pan. This mechanical stirring type desulfurization treatment method is called a KR method.

In the KR method, a desulfurization agent mainly composed of CaO (quick lime, calcium oxide) that is inexpensive and easy to handle is used. The hot metal desulfurization reaction with CaO is generally represented by the following formula.
[S] + (CaO) → (CaS) + [O]
That is, S (sulfur) in the hot metal and CaO react to generate CaS (calcium sulfide) in the slag and O (oxygen) in the hot metal. In addition, a substance indicated with [] such as [S] is a substance in hot metal, and a substance indicated with () such as (CaS) is a substance in slag. is there.

Furthermore, a desulfurization agent containing CaO as a main component and containing an alumina-metal Al (aluminum) mixture as a deoxidation agent in order to accelerate the desulfurization reaction is also used. The alumina-metal Al mixture not only has the effect of promoting the reaction of generating oxygen in the above formula by removing O in the hot metal, but also prevents CaO from agglomerating and allows the alumina to hatch CaO in the desulfurizing agent. Thus, it has the effect of promoting the reaction of CaO.
For example, Patent Document 1 describes a desulfurization method in which a desulfurization agent in which an alumina-metal Al mixture is added to CaO powder is added to the bath surface of hot metal being stirred by a stirring blade. In the desulfurization method described in Patent Document 1, an alumina-metal Al mixture containing 10 to 50% by mass of metal Al is used. And in order to accelerate | stimulate the hatching of CaO, the mixture ratio of the alumina metal Al mixture in a desulfurization agent is made high when the temperature of hot metal is low, and is made low when the temperature of hot metal is high.

JP 2011-132666 A

The desulfurization agent described in Patent Document 1 has a high mixing ratio of alumina (Al ₂ O ₃ ) in an alumina-metal Al mixture, and forms a binary desulfurization agent composed of CaO—Al ₂ O _3. doing. For example, when stainless steel hot metal is desulfurized using a binary desulfurization agent composed of CaO—Al ₂ O ₃ , when the temperature during desulfurization is 1250 to 1400 ° C., CaO—Al at 1400 ° C. or lower. _Since there is no liquid phase in the binary desulfurization agent made of ₂ O _{3, the} effect of promoting the hatching of CaO by alumina is reduced. Furthermore, since the desulfurizing agent forms a solid phase, when the concentration of alumina is high, a solid solution phase composed of CaO—Al ₂ O ₃ is formed on the surface of the CaO particles, and the desulfurization reaction of CaO is caused by the formed solid solution phase. Is inhibited. Therefore, there is a problem that the desulfurization efficiency of the hot metal by the desulfurizing agent is lowered.
In addition, even if the content in the desulfurizing agent or the hot metal is oxidized in the atmosphere and the components in the desulfurizing agent are changed, and a liquid phase is present in the desulfurizing agent even at a temperature of 1250 to 1400 ° C., In the liquid phase, a CaO—Al ₂ O ₃ -based high viscosity slag is formed. For this reason, even if the desulfurizing agent is made into a liquid phase, the desulfurization efficiency is lowered.

The present invention has been made to solve such problems, and provides a hot metal desulfurization treatment method that improves desulfurization efficiency by reducing the formation of a CaO—Al ₂ O ₃ -based solid solution. Objective.

In order to solve the above problems, the desulfurization treatment method of hot metal according to the present invention, there is provided a desulfurization treatment method of hot metal desulfurizing molten pig iron containing 2-5 wt% of C at a temperature above 1250 ° C., and CaO A desulfurizing agent composed of an aluminum mixture containing 2% by mass or more of CaO and containing 85% by mass or more of metal Al is added to the hot metal stirred by a stirring blade.
Furthermore, the aluminum mixture may be formed by an aluminum can.
The hot metal may contain 10 to 30% by mass of Cr.

According to the hot metal desulfurization processing method according to the present invention, it is possible to improve the hot metal desulfurization efficiency by reducing the formation of a CaO—Al ₂ O ₃ solid solution.

It is a schematic diagram which shows the general flow of the manufacturing method of stainless steel. It is a schematic diagram which shows the state at the time of the desulfurization process by the desulfurization process method which concerns on embodiment of this invention.

Embodiments Hereinafter, a hot metal desulfurization method according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the present embodiment, a case will be described in which desulfurization is performed during the production of stainless steel.

First, referring to FIG. 1, stainless steel is manufactured by performing a melting step (A), a primary refining step (B), a secondary refining step (C), and a casting step (D) in this order. .
In the melting step (A), scraps and alloys as raw materials for stainless steel are melted in an electric furnace 1 to produce a stainless steel hot metal 2, and the generated stainless steel hot metal 2 is passed through a receiving pan 3 to a smelting furnace. Is poured into the converter 4. Further, in the primary refining step (B), a rough decarburization treatment is performed to remove carbon contained in the stainless steel hot metal 2 in the converter 4 by blowing the oxygen through the nozzle 4a. Stainless steel melt and slag containing carbon oxide and impurities are generated. Further, the molten stainless steel produced in the primary refining step (B) is delivered to the molten steel pan 5 and transferred to the secondary refining step (C).

  In the secondary refining process (C), the molten stainless steel still containing carbon or the like is put together with the molten steel pan 5 into a vacuum degassing apparatus (VOD) 6 which is a vacuum refining furnace, and final decarburization treatment and final component adjustment are performed. Done. And these processes are performed, and the stainless steel molten of a desired component structure produces | generates. In the casting step (D), the molten steel pan 5 is taken out from the vacuum degassing device 6 and set in a continuous casting device (CC) 7. The molten stainless steel in the molten steel pan 5 is poured into the continuous casting apparatus 7 and further cast into, for example, a slab-shaped stainless steel piece 8 by a mold provided in the continuous casting apparatus 7. The cast stainless steel piece 8 is hot-rolled or cold-rolled into a hot-rolled steel strip or a cold-rolled steel strip in the next rolling step.

  The stainless steel hot metal 2 transferred from the electric furnace 1 to the receiving pan 3 is subjected to desulfurization treatment before being poured into the converter 4. In addition, the hot metal 2 which forms stainless steel contains Cr (chromium), and the content thereof is 10% by mass to 30% by mass.

Referring to FIG. 2, in the desulfurization treatment, impeller 11 that is a stirring blade of stirring device 10 is immersed in hot metal 2 in receiving pan 3, and the surface (bath surface) of hot metal 2 in receiving pan 3. The discharge nozzle 14 of the desulfurizing agent charging device 13 for discharging the desulfurizing agent 100 to the bath surface is disposed above the surface. The stirring device 10 includes an impeller 11 and an electric motor 12 coupled to the impeller 11, and the impeller 11 is rotationally driven by the electric motor 12.
Then, the electric motor 12 is operated in the stirring device 10 to rotate the impeller 11, and the desulfurizing agent charging device 13 is operated while stirring the hot metal 2 in the receiving pan 3 by the impeller 11. The desulfurizing agent 100 is sprayed from the discharge nozzle 14 on the bath surface. The desulfurization agent 100 performs a desulfurization reaction with the hot metal 2, takes out the sulfur content (S) contained in the hot metal 2 as slag, and the extracted sulfur content is contained in the slag 2 a floating on the bath surface of the hot metal 2. It is. The desulfurization agent 100 is stirred and mixed together with the molten iron 2 to accelerate the desulfurization reaction.

At this time, the temperature of the hot metal 2 during the desulfurization treatment is set to 1250 ° C to 1400 ° C.
This is because the hot metal 2 discharged from the electric furnace 1 (see FIG. 1) does not solidify before being transferred to the subsequent desulfurization process and the primary refining process (B), the temperature required is 1250 ° C. This is because it is desirable to set the temperature to 1400 ° C. or lower in order to minimize the input melting power in the electric furnace 1. However, in the case of a hot metal component having a high melting point, the temperature of the hot metal 2 during the desulfurization treatment may exceed 1400 ° C.
Moreover, if the temperature of the hot metal 2 during the desulfurization process is lower than 1250 ° C., the hot metal 2 may be solidified during the desulfurization process, which makes operation difficult.
Therefore, the desulfurization treatment is performed in a state where the temperature of the hot metal 2 during the desulfurization treatment is 1250 ° C. to 1400 ° C.

If the hot metal 2 is not sufficiently dissolved during the desulfurization treatment, the fluidity of the hot metal 2 is lowered, and the effect of promoting the reaction between the hot metal 2 and the desulfurizing agent 100 by stirring is lowered. For this reason, the melting point of the hot metal 2 is controlled so as to be sufficiently melted at 1250 ° C. to 1400 ° C., and this melting point is controlled by adjusting the content of C (carbon) in the hot metal 2. The melting point of the hot metal 2 decreases as the C content increases to about 5%, and increases when it exceeds about 5%.
However, if the C content increases, the amount of decarburization in the primary refining step (B) and the secondary refining step (C) increases and the production efficiency decreases, so the C content in the hot metal 2 is: The upper limit is 5% by mass. On the other hand, in order to lower the melting point of the hot metal 2 so that the hot metal 2 is sufficiently dissolved at 1250 ° C. to 1400 ° C., the content of C in the hot metal 2 needs to be 2% by mass or more. Further, when the C content in the hot metal 2 is lowered, the equilibrium oxygen concentration in the hot metal 2 is increased, so that the amount necessary for the desulfurization treatment of metal Al (aluminum) contained in the desulfurizing agent 100 described later is greatly increased. However, it becomes economically inefficient. For this reason, the content of C in the molten iron 2 is required to be 2% by mass or more. That is, the C content in the hot metal 2 is set between 2% by mass and 5% by mass.

Further, the desulfurizing agent 100 contains CaO powder as a main component and further contains an aluminum mixture as a deoxidizing agent.
The CaO powder is preferably classified by a sieve having a size of 5 mm or less (particle diameter ≦ 5 mm) in order to ensure the desulfurization reaction area on the surface of the CaO particles.
The aluminum mixture contains metal Al in a proportion of 85% by mass or more. As the aluminum mixture, those obtained by cutting or crushing an aluminum can into pellets, or those obtained by cutting or crushing other aluminum products into pellets or powders are used. Then, those aluminum mixture contains besides metallic Al is most impurities resulting from the aluminum cans and aluminum products, _alumina: containing little (Al 2 _O 3 aluminum oxide). That is, alumina is not added to the aluminum mixture. The aluminum mixture is alumina, which is formed by the natural oxidation of the surface of the pelletized or granular metal Al in the air, or the oxidation of the metal Al pieces or metal Al particles and impurities that naturally react. It is a grade containing aluminum. For this reason, aluminum ash or the like in which the content of metal Al is about 35% by mass and most of the other 65% by mass is alumina is not used as an aluminum mixture because of the high concentration of alumina. In addition, aluminum ash is comprised by the slag etc. which generate | occur | produce at the time of refining in manufacture of aluminum.

In the desulfurizing agent 100, the aluminum mixture made of pellet-like or powder-like metal Al as described above is added to the CaO powder in an amount between 2% by mass and 10% by mass of the CaO powder.
In the receiving pan 3, S (sulfur) contained in the hot metal 2 reacts with CaO and metal Al contained in the desulfurizing agent 100 to become CaS (calcium sulfide), and CaS is a bath surface of the hot metal 2. The slag 2a is formed by separating and floating above. Thereby, a sulfur component is removed from the hot metal 2, that is, desulfurized. At this time, the desulfurization reaction shown by the following formula (1) occurs in the receiving pan 3.
3 [S] +3 (CaO) +2 (Al) → 3 (CaS) + (Al ₂ O ₃ ) (1)
Note that the alumina produced by the desulfurization reaction also forms the slag 2a.

  In the ladle 3, the hot metal 2 is stirred and mixed with the desulfurizing agent 100 by the impeller 11, so that the CaO of the desulfurizing agent 100 is widely dispersed in the hot metal 2 and increases the chance of contact with S in the hot metal 2. Therefore, the desulfurization reaction is promoted. Further, since the metal Al having deacidification removes the oxygen component separated from CaO to the outside of the hot metal 2, the reaction of the formula (1) is promoted to the right, that is, to generate CaS, so that the desulfurization reaction Is promoted.

  In addition, in the desulfurization agent 100 added to the hot metal 2, when the addition ratio of the aluminum mixture with respect to CaO is less than 2% by mass, the Al used in the formula (1) is insufficient, and therefore when desulfurization treatment is performed for a predetermined time. The desulfurization efficiency of the is significantly reduced. On the other hand, even if the addition ratio of the aluminum mixture with respect to CaO in the desulfurizing agent 100 exceeds 10% by mass, the S content in the hot metal 2 to be desulfurized does not change, so the desulfurization efficiency is 10% by mass. It becomes almost unrelated to the case. For this reason, the addition ratio of the aluminum mixture with respect to CaO is set between 2 mass% and 10 mass%.

Further, since the hot metal 2 and the desulfurizing agent 100 are stirred and mixed by the impeller 11 and the desulfurization reaction is promoted, the alumina produced as slag has a CaO—Al ₂ O ₃ solid solution phase on the surface of the CaO particles. Even if it is formed, its amount is small and has little influence on the hatching of CaO.
Therefore, the CaO contained in the desulfurizing agent 100 suppresses the formation of a CaO—Al ₂ O ₃ based solid solution phase on the surface thereof, so that the desulfurization reaction at the CaO surface layer is promoted and the reaction is made of metal Al. Therefore, S is efficiently removed from the hot metal 2.

(Example)
Hereinafter, two examples of desulfurization treatment by the desulfurization treatment method according to the embodiment for the stainless steel hot metal in the receiving pan 3 and a desulfurization agent in which the purity of metal Al in the aluminum mixture is less than 85 mass% are used. Thus, a comparative example in which desulfurization treatment is performed is verified. In addition, CaO which is a main component of the desulfurizing agent was CaO powder (particle size ≦ 2 mm) classified by a 2 mm sieve mesh.
Moreover, the hot metal to be desulfurized is a Cr-containing hot metal containing 10 to 30% by mass of Cr and 2 to 5% by mass of C.

  As shown in Table 1 below, in the examples and comparative examples, the hot metal (weight 80 tons) generated in one charge in the electric furnace 1 is transferred to the receiving pan 3 and the maximum rotation speed 120 rpm (rotation per minute) The impeller 11 was rotationally driven by a stirring device 10 of a few), and a desulfurizing agent was added to the hot metal while stirring to desulfurize the impeller 11. Furthermore, the desulfurization treatment time, that is, the stirring time of the hot metal by the impeller 11 was set to 10 minutes, and the temperature of the hot metal was maintained between 1250 ° C. and 1400 ° C. during this 10 minutes. That is, the desulfurization treatment temperature was between 1250 ° C and 1400 ° C.

  Table 2 describes the composition of the desulfurization agent used in the examples and comparative examples.

In Example 1, aluminum can pellets are used as the aluminum mixture to be added to the desulfurization agent, and the aluminum can pellets have a purity of 97 mass% and contain metallic aluminum. Furthermore, in Example 1, the aluminum can pellets were added at a rate of 3 mass% with respect to the CaO powder.
In Example 2, metal aluminum powder is used as the aluminum mixture added to the desulfurizing agent, and the metal aluminum powder contains metal aluminum with a purity of 85% by mass. Furthermore, in Example 2, metal aluminum was added at a ratio of 3% by mass with respect to the CaO powder.

In Comparative Example 1, aluminum ash is used as the aluminum mixture to be added to the desulfurizing agent. The aluminum ash contains metal Al with a purity of 35% by mass, and most of the other 65% by mass is alumina. Further, in Comparative Example 1, aluminum ash having a low content of metal Al is added more than in Examples 1 and 2 with respect to CaO powder to ensure the amount of metal Al, and is added at a rate of 10% by mass. It was done. Therefore, the addition ratio of metal Al to the CaO powder in the desulfurization agent of Comparative Example 1 is close to the addition ratio of metal Al to the CaO powder in the desulfurization agent of Example 1.
The desulfurizing agents of Examples 1 and 2 and Comparative Example 1 were added to the hot metal at a rate of 5 to 10 kg per ton of hot metal.

  As described above, as a result of stirring the hot metal with the impeller 11 for 10 minutes while adding the desulfurizing agent, the ratio of S contained in the hot metal in Examples 1 and 2 and Comparative Example 1 was measured. Usually, the content concentration of S in the hot metal after the desulfurization treatment needs to be suppressed to 10 to 110 ppm. In Examples 1 and 2 and Comparative Example 1, it was determined to be defective when the S concentration in the hot metal exceeded 110 ppm. The determination result is shown in Table 3 below.

The number of hot metal charges subjected to the desulfurization treatment in Table 3 is the number of hot metal charges generated in an electric furnace and then desulfurized in each example. Thus, the number of charges determined as desulfurization failure. The desulfurization failure determination rate is the ratio of the number of desulfurization failure determination charges to the number of hot metal charges subjected to the desulfurization process in each example.
As shown in Table 3, the desulfurization failure determination rate correlates with the ratio (purity) of metal Al in the aluminum mixture of the desulfurization agent, and the desulfurization failure determination rate is highest in Example 1 where the purity of metal Al is the highest. In Comparative Example 1, which is low and the purity of metal Al is the lowest, the desulfurization failure determination rate is the highest. Furthermore, the desulfurization failure determination rates in Examples 1 and 2 in which the purity of the metal Al is 85% by mass or more are close to each other and greatly separated from Comparative Example 1. And the desulfurization defect determination rate and the purity of metal Al are not in a proportional relationship.

In Example 1 and Comparative Example 1, as described above, the addition ratio of metal Al to CaO in the desulfurization agent is close, but the desulfurization failure determination rate is greatly different. This is because the CaO—Al ₂ O ₃ solid solution formed by the alumina contained in the desulfurization agent of Comparative Example 1 abundantly inhibits the desulfurization reaction by CaO. On the contrary, the desulfurization agent contains almost no alumina. In Example 1, which does not, it can be seen that CaO efficiently performs the desulfurization reaction without being affected by the CaO—Al ₂ O ₃ solid solution of alumina.

Thus, the hot metal desulfurization treatment method according to the embodiment of the present invention is a hot metal desulfurization treatment method of desulfurizing hot metal 2 containing 2 to 5 mass% of C at a temperature of 1250 ° C. or higher. In this desulfurization treatment method, a desulfurizing agent 100 in which an aluminum mixture containing metal Al at a ratio of 85 mass% or more is added at a ratio of 2 mass% or more with respect to CaO is added to the hot metal 2 stirred by the impeller 11. . At this time, the content of metal Al is increased while the content of alumina contained in the desulfurizing agent 100 is kept low. Therefore, since the production amount of the CaO—Al ₂ O ₃ solid solution by alumina and CaO is kept low, inhibition of the desulfurization reaction of CaO by this solid solution is reduced, and the desulfurization efficiency by CaO can be improved. Furthermore, the desulfurization agent 100 also contains a large amount of metal Al, which is a deoxidizer, to accelerate the desulfurization reaction of CaO and improve the desulfurization efficiency.

  Moreover, although the hot metal desulfurization method according to the embodiment has been applied to the production of stainless steel, it may be applied to the production of other metals.

  2 hot metal, 3 ladle, 11 impeller (stirring blade), 100 desulfurization agent.

Claims (3)

A hot metal desulfurization method for desulfurizing hot metal containing 2 to 5% by mass of C at a temperature of 1250 ° C. or higher,
A hot metal desulfurization treatment method comprising adding a desulfurization agent comprising CaO and an aluminum mixture containing 2% by mass or more of metal Al to 85% by mass or more of CaO to hot metal stirred by a stirring blade. .   The desulfurization processing method according to claim 1, wherein the aluminum mixture is formed by an aluminum can.   The desulfurization method according to claim 1 or 2, wherein the hot metal contains 10 to 30% by mass of Cr.

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