JP2006283164A - Method for desulfurize-treating chromium-contained molten iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a desulfurize-treating method with which molten iron containing ≥5 mass% chromium can be desulfurized at high efficiency and at low cost, when a high chromium steel having a little sulfur content is produced by using the molten iron containing ≥5 mass% chromium obtained with a fusing-reduction smelting etc. <P>SOLUTION: The chromium-contained molten iron is desulfurized by injecting a desulfurizing agent mainly containing metallic Mg powder and lime powder into the chromium-contained molten iron containing ≥5 mass% chromium held in a refining vessel. At that time, the temperature of the chromium-contained molten iron is made to ≥1,300°C and carbon content in the chromium-contained molten iron is made to ≥3.0 mass% and further, it is desirable that the chromium-contained molten iron is the one obtained by the fusing-reduction smelting or melting and the one tapped from a holding furnace after once holding the molten iron in the holding furnace having a heating function for molten iron. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a desulfurization treatment method capable of desulfurizing hot metal containing 5 mass% or more of chromium with high efficiency and at low cost.

  Sulfur in high chromium steel, represented by stainless steel, forms a compound with elements such as Mn and Mo in some steel types, and has the property of increasing machinability and film property, but it has hot workability. Since there is a problem of deterioration, it is generally necessary to reduce the concentration.

  The current high-chromium steel melting method includes hot metal pretreatment, charging phosphorus with reduced phosphorus into the converter, and adding ferrochrome alloy to melt and decarburize the alloy. Or a method in which chromium ore is melt-reduced and smelted in a converter to obtain a chromium-containing crude molten metal (hereinafter referred to as “chromium-containing hot metal”), and this chromium-containing hot metal is decarburized and refined. . Among these, when using chrome-containing hot metal, in order to adjust the chromium concentration, chrome-containing hot metal and ordinary hot metal are combined to perform decarburization refining, or in a holding furnace having a hot metal heating function. In some cases, decarburization and refining may be performed using the chromium-containing hot metal that has been once held and then discharged. Since ferrochrome alloys are expensive, methods using chromium-containing hot metal are becoming mainstream.

  The process of obtaining chromium-containing molten iron by smelting and reducing chrome ore is roughly divided into three processes: 1) a heat-up process, 2) a smelting reduction process, and 3) a finishing reduction process. Most of the sulfur contained in the hot metal is transferred to slag by the reduction reaction in the smelting reduction process. However, the sulfur concentration in the chromium-containing hot metal obtained by this smelting is at most about 0.005% by mass, and the sulfur concentration must be further lowered when melting extremely low sulfur steel. Further, the chrome-containing hot metal and the normal hot metal may be used in combination with each other. In this case, the sulfur concentration in the chrome-containing hot metal is increased by the sulfur contained in the normal hot metal.

  In order to further reduce the sulfur concentration in the smelting reduction smelting process, it is necessary to increase the amount of quick lime, which is a desulfurizing agent, in the final reduction process. The amount of use must be increased, and there is a concern that not only the cost of the auxiliary raw material will be increased, but also that the load on the smelting reduction furnace will increase and the production amount will decrease due to the extended time of the finishing reduction process.

On the other hand, no special measures are taken in the smelting reduction process, and reduction smelting is performed by adding Fe-Si alloy, quick lime, special flux, etc. to the molten high chromium steel after completion of decarburization refining using chromium-containing hot metal. Thus, desulfurization treatment can also be performed. However, when melting ultra-low sulfur steel, the amount of Fe-Si alloy added for reduction treatment increases, thereby reducing the basicity of slag (CaO / SiO ₂ ) and reducing the desulfurization ability. Resulting in. Therefore, in order to prevent this, the amount of quicklime used must be increased, and the amount of fluorite added to promote hatching of quicklime will increase accordingly, resulting in a refining cost. This causes a problem of increasing. The same applies to the desulfurization in the secondary refining using a ladle refining furnace or a VOD furnace, and the load due to the processing also increases.

  For this reason, a method for efficiently and inexpensively desulfurizing a hot metal containing chromium and a molten steel containing chromium has been proposed.

  For example, Patent Document 1 discloses a method of performing dephosphorization and desulfurization simultaneously by adding a refining agent comprising an alkaline earth metal oxide and an alkaline earth metal halide to a molten iron alloy containing chromium. Is disclosed. However, in this method, since dephosphorization is simultaneously performed under a thermodynamically disadvantageous condition, the amount of slag generated increases. Furthermore, since chromium and phosphorus are mixed in the generated slag, the treatment method is difficult.

Patent Document 2 discloses a method of simultaneously desiliconizing and desulfurizing a chromium-containing hot metal containing silicon and sulfur by injecting a powdered desulfurizing agent together with gaseous oxygen. However, in this method, since gaseous oxygen is blown into the hot metal, the oxygen potential in the metal increases, which is a disadvantageous condition for desulfurization. In addition, the basicity of the slag also decreases due to the desiliconization reaction. Therefore, there is a problem in that the amount of slag increases in order to advance the desulfurization reaction, and the processing cost increases accordingly.
JP 59-47350 A JP-A-4-99112

  The present invention has been made in view of the above circumstances. The object of the present invention is to provide a high chromium steel with a low sulfur content using a hot metal containing 5% by mass or more of chromium obtained by smelting reduction smelting or the like. An object of the present invention is to provide a desulfurization treatment method capable of desulfurizing hot metal containing 5% by mass or more of chromium at high efficiency and at low cost.

  The chromium-containing hot metal desulfurization processing method according to the first invention for solving the above-mentioned problem is that a chromium-containing hot metal containing 5.0% by mass or more of chromium contained in a refining vessel is coated with metallic Mg powder and lime powder. It is characterized in that the chromium-containing hot metal is desulfurized by blowing a desulfurizing agent mainly composed of.

  The chromium-containing hot metal desulfurization treatment method according to the second invention is the method according to the first invention, wherein the temperature of the chromium-containing hot metal before the desulfurization treatment is 1300 ° C. or more, and the carbon content before the desulfurization treatment of the chromium-containing hot metal Is 3.0 mass% or more.

  The chromium-containing hot metal desulfurization method according to the third invention is the first or second invention, wherein the chromium-containing hot metal is obtained by smelting or refining or melting, and has a heating function of the molten metal. It is characterized in that it is once held in a holding furnace and then discharged from the holding furnace.

  According to the present invention, a desulfurizing agent mainly composed of metallic Mg powder and lime powder is blown to desulfurize chromium-containing hot metal containing 5% by mass or more of chromium, so that desulfurization is performed at high speed and high efficiency with a small amount of slag generation. As a result, in the production of a high chromium content alloy, a reduction in manufacturing cost and realization of high productivity can be achieved, and an industrially beneficial effect is brought about.

  The present invention will be specifically described below. In the present invention, a chromium-containing hot metal containing 5.0% by mass or more of chromium contained in a refining vessel is blown with a desulfurizing agent mainly composed of metallic Mg powder and lime powder to desulfurize the chromium-containing hot metal.

  The desulfurization reaction of hot metal including this chromium-containing hot metal is generally represented by the ionic formula shown in the following formula (1).

The equilibrium constant Ks in the equation (1) is expressed by the following equation (2). In the formula (2), a _M (M = O, S, O ²⁻ , S ²⁻ ) is the activity of each component. As is clear from the equation (2), in order to promote the desulfurization reaction, the sulfur activity (a _S ) in the hot metal is increased thermodynamically or the oxygen activity in the hot metal is increased. What is necessary is just to reduce ( _aO ).

  By the way, it has been known for a long time that metallic Mg has an excellent desulfurization ability, and is used as a desulfurization agent. It is believed that the molten iron desulfurization reaction with metallic Mg melts in the hot metal after Mg added to the hot metal melts, and the dissolved Mg reacts with sulfur in the hot metal. This desulfurization reaction is represented by the following formula (3).

  At this time, the produced MgS reacts with oxygen in the atmosphere or oxygen in the molten iron, and when MgS becomes MgO, a phenomenon in which sulfur returns to the hot metal, so-called “resulfurization” occurs. Therefore, when desulfurizing with metal Mg, CaO powder is added simultaneously with the metal Mg powder, and the reaction of the following formula (4) is generated to suppress resulfurization.

  By utilizing the above reaction, the Mg-based desulfurization agent is usually used as a desulfurization agent in hot metal desulfurization treatment for ultra-low sulfur ordinary steel.

By the way, when considering the desulfurization reaction by Mg, the equilibrium constant Ks of the above-mentioned formula (3) is expressed by the following formula (5). In the equation (5), a _M (M = MgS, S, Mg) is the activity of each component.

Therefore, as is clear from the formula (5), in order to promote the desulfurization reaction with Mg, it is also possible to increase the activity of Mg in addition to increasing the activity of sulfur in the hot metal as described above. It is done. The activity of Mg in the hot metal is expressed as the product of the concentration (mass%) and the activity coefficient f _Mg, and the activity coefficient f _Mg is expressed by the interaction aid coefficient e. The activity (a _Mg ) is represented by the following formula (6). In the formula (6), X is an element such as carbon or silicon contained in the hot metal.

  Therefore, judging from the equation (6), in order to increase the activity of Mg in the hot metal, an element having a positive value of the interaction assistant coefficient e and a large value of the interaction assistant coefficient e is added to the hot metal. Or the activity of Mg is increased by adding a high-concentration component element to the hot metal in the component specifications of the steel material that is positive in the interaction aid coefficient e and made from the hot metal. become.

  Special steel typified by stainless steel and high alloy steel generally has a high concentration of additive elements. Therefore, when the influence of various elements added in large amounts on Mg in molten iron, that is, the literature value of interaction aid coefficient e, was examined, the value of interaction aid coefficient e on chromium Mg was expressed by the following equation (7). As shown, it was positive and a relatively large value of 0.01.

  Therefore, it is considered that the activity of Mg increases as the chromium concentration in the hot metal increases, and the reaction represented by the formula (3) is promoted. That is, from this, it was found that it is effective to use a metal Mg-based desulfurizing agent for desulfurization treatment of high chromium steel such as stainless steel. Here, specifically, the high chromium steel refers to one having a chromium content of 5.0% by mass or more.

Furthermore, in order to promote the reaction of the formula (3), it is necessary to increase the activity (a _S ) of sulfur. Conventionally, it is known that the influence of carbon on the activity coefficient of sulfur in hot metal is large, that is, the value of the coefficient of interaction coefficient between sulfur and carbon in hot metal is as large as 0.034. . For this reason, in the case of desulfurization treatment of high chromium steel, it is optimal to carry out at the stage of chromium-containing hot metal having a high carbon concentration, rather than in a low carbon concentration region as after decarburization refining. The carbon content in the chromium-containing hot metal may be 3.0% by mass or more.

  Further, since the desulfurization reaction is a reduction reaction, the higher the temperature of the chromium-containing hot metal during the desulfurization reaction, the more preferable the desulfurization reaction is promoted. At the same time, it is preferable because the adhesion amount of the metal to the processing container (for example, hot metal ladle) is reduced as the temperature increases. From these, it is preferable that the temperature of the chromium-containing hot metal before the desulfurization treatment is 1300 ° C. or more. This chromium-containing hot metal is obtained mainly by the smelting reduction smelting of chromium ore or by adding a ferrochrome alloy to ordinary hot metal and melting it. In addition, the blast furnace hot metal and ferrochrome are charged in the smelting reduction furnace in advance or afterwards, and the chrome containing hot metal produced by the smelting reduction is mixed with these to adjust the chromium content and carbon content. Good. Further, a chromium-containing hot metal in which the chromium content and the carbon content are adjusted may be prepared by combining the hot metal melted by smelting reduction smelting with the normal hot metal melted in a blast furnace after hot water.

  Furthermore, after holding these chromium-containing hot metal in a holding furnace having a function of heating the molten metal, when using the hot metal discharged from the holding furnace, it is possible to adjust the temperature and components of the chromium-containing hot metal. Yes, it is possible to set the hot metal conditions optimal for the desulfurization treatment. Therefore, it is more effective to use the chromium-containing hot metal discharged from such a holding furnace as a hot metal for desulfurization treatment. At this time, the high chromium steel scrap may be additionally melted in the holding furnace.

  As a hot metal desulfurization treatment method, a powder desulfurization agent is usually injected through an injection lance immersed in the hot metal or a blowing tuyere installed in the refining vessel, or on the hot metal contained in the refining vessel. There are a method of adding a desulfurizing agent and stirring, and a method of mechanically stirring the hot metal and the desulfurizing agent with a stirring bar such as an impeller, etc., but the injection method is simple and preferable in terms of equipment.

  Moreover, the desulfurization agent injected into the chromium-containing hot metal is a mixed powder of metal Mg powder and lime powder from the above-mentioned examination, and the composition thereof is 10-50 mass% of metal Mg and 50-90 mass of lime powder. It is preferable to use a desulfurizing agent mixed at a ratio of%. As the lime powder, a substance containing or generating CaO such as quick lime powder and limestone powder can be used, and quick lime powder is preferable.

  Further, the carrier gas for blowing the desulfurizing agent is not particularly specified, but nitrogen gas which is a non-oxidizing gas is generally used. However, for extremely low nitrogen stainless steel, using Ar gas is more efficient because it reduces the load during subsequent decarburization refining and secondary refining.

  As described above, according to the present invention, a desulfurization agent mainly containing metallic Mg powder and lime powder is blown to desulfurize chromium-containing hot metal containing 5% by mass or more of chromium, so that a small amount of slag is generated. The desulfurization process can be performed at high speed and high efficiency.

  Hereinafter, the present invention will be described in more detail with reference to the embodiment in the desulfurization treatment facility shown in FIG. As shown in FIG. 1, in the desulfurization treatment facility 1, an injection lance 4 that can move up and down in the hot metal ladle 3 is held by a swivel carriage 5, and the injection lance 4 is attached to an injection tank 9. The stored desulfurizing agent is configured to be injected into the chrome-containing hot metal 2 stored in the hot metal ladle 3. A dust collection hood 6 and a dust collection duct 7 are installed above the hot metal ladle 3. The desulfurization treatment facility 1 is provided with a hopper 8 for receiving the desulfurizing agent, and the desulfurizing agent is appropriately supplied from the hopper 8 to the injection tank 9.

  In the desulfurization treatment facility 1 configured as described above, a desulfurization treatment was performed by injecting a desulfurization agent into the 185-ton chromium-containing hot metal 2 accommodated in the hot metal ladle 3 via the injection lance 4.

  Here, as the chrome-containing hot metal, (1) the hot metal discharged after performing the smelting reduction smelting of chromium ore using the top bottom blowing converter type smelting reduction furnace, the blast furnace hot metal and the vertical smelting reduction furnace A chromium-containing hot metal (hereinafter referred to as “chromium-containing hot metal A”) obtained by combining high-chromium hot metal obtained by melting and reducing a chromium-containing sludge; The hot metal discharged after smelting and reducing smelting of chromium ore is once held in a holding furnace equipped with a heating function, and obtained by smelting and reducing chrome-containing sludge in a blast furnace hot metal and vertical smelting reduction furnace. The chrome-containing hot metal (hereinafter referred to as “chromium-containing hot metal B”) was prepared by combining the hot chrome-containing hot metal in a holding furnace, further melting the chrome-containing steel scrap appropriately in the holding furnace, and then tapping the hot water. The type was used.

  Table 1 shows the composition of the chromium-containing hot metal after the smelting reduction smelting, the composition of the blast furnace hot metal, and the composition of the high chromium-containing hot metal obtained by smelting and reducing the chromium-containing sludge in the vertical smelting reduction furnace.

  Table 2 shows the composition of the two types of chromium-containing hot metal A and the composition of chromium-containing hot metal B used in this example.

Table 3 shows a list of processing conditions of the inventive examples and the comparative examples. The hot metal used was chromium-containing hot metal A and chromium-containing hot metal B shown in Table 2, and was desulfurized by injecting an Mg-based desulfurizing agent. In contrast, in the comparative example, the hot metal used was the same, but a CaO—CaF ₂ -based desulfurizing agent was used as a desulfurizing agent, and this CaO—CaF ₂ -based desulfurizing agent was injected for desulfurization treatment.

Here, as Mg type desulfurization agent, what mixed metal Mg powder in the ratio of 30 mass% and CaO powder in 70 mass% was used. Further, the lime-based desulfurizing agent used in Comparative Example, the CaO 90 wt%, fluorite and (CaF ₂₎ was used after blending in a ratio of 10 mass%. In both the inventive examples and the comparative examples, the blowing rate of the desulfurizing agent was 50 kg / min. During the desulfurization process, while performing sampling of the chromium-containing hot metal at an appropriate time, the desulfurization process was carried out until the sulfur concentration in the chromium-containing hot metal became 0.005% by mass or less. The temperature drop and slag generation amount of the hot metal inside were compared.

  In FIG. 2, transition of the sulfur concentration in the chromium-containing hot metal in the present invention example and the comparative example is shown. As shown in FIG. 2, it can be seen that the inventive example has a much faster desulfurization rate. Table 4 shows the results of the desulfurization treatment.

  Inventive Example 1 was lower in the basic unit of desulfurization agent used than Comparative Examples 1 and 2, and the amount of slag generated was small. Further, the treatment time was as short as 11 minutes, and the desulfurization treatment could be carried out effectively without causing any trouble in subsequent processes such as decarburization refining and continuous casting. Further, in Example 2 of the present invention using the chromium-containing hot metal B once held in the holding furnace, an effect that the hot metal temperature before the desulfurization treatment can be controlled by heating in the holding furnace is added, and the desulfurization rate is further increased. The amount of slag generated can be further reduced.

  On the other hand, in Comparative Examples 1 and 2 using a lime-based desulfurizing agent, the treatment time became longer, and the basic unit of use of the desulfurizing agent and the amount of slag generated increased. In addition, as the treatment time increased, the temperature drop of the hot metal also increased. From the above results, the superiority of the method of the present invention could be confirmed.

It is the schematic of the desulfurization processing equipment used in the Example. It is a figure which shows transition of the sulfur concentration of the chromium containing hot metal during a desulfurization process by comparing the example of the present invention and the comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Desulfurization processing equipment 2 Chromium-containing hot metal 3 Hot metal ladle 4 Injection lance 5 Revolving carriage 6 Dust collection hood 7 Dust collection duct 8 Hopper 9 Injection tank

Claims (3)

  A chromium-containing hot metal containing 5.0% by mass or more of chromium contained in a refining vessel is blown with a desulfurizing agent mainly composed of metal Mg powder and lime powder to desulfurize the chromium-containing hot metal. Desulfurization method for chromium hot metal.   The temperature before desulfurization treatment of the chromium-containing hot metal is 1300 ° C or more, and the carbon content before desulfurization treatment of the chromium-containing hot metal is 3.0 mass% or more. Desulfurization method for chromium-containing hot metal.   The chromium-containing hot metal is obtained by smelting or refining or melting, and is once held in a holding furnace having a heating function of the molten metal and then discharged from the holding furnace. The method for desulfurizing chromium-containing hot metal according to claim 1 or 2.

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