JP3414811B2 - Recovery method of residual alloy components in slag after refining when smelting low alloy steel - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen refining apparatus using a bottom-blowing gas injection facility, and an alloy remaining in slag after refining during melting of low alloy steel. A method for recovering components. [0002] In the case of producing low-alloy steel (Cr content: about 1.0%) using an oxygen refining facility such as a converter, Cr ore or semi-reduced Cr ore is used as a Cr source. ing. However, when using these oxide-based materials,
Since the rate of reduction of Cr oxides such as Cr ₂ O ₃ by C in the hot metal is slow, it is impossible to completely recover Cr contained in the raw material during refining. [0003] On the other hand, as a method of recovering the Cr content remaining in the slag, high Cr steel such as stainless steel is used.
A method is generally used in which a reducing agent such as FeSi or Al is added to slag, and the slag and molten steel are stirred by a bottom blown gas. [0004] When the above-mentioned method is applied to slag produced by melting low-alloy steel, the following problems occur. That is, when smelting low alloy steel,
Since the concentration is at most about 1% and P in the molten steel can be removed into the slag during refining, the process of reducing the raw material P is unnecessary when the low alloy steel is melted. However, when slag is forcibly reduced with a reducing agent such as FeSi or Al, P is also reduced in addition to Cr and re-dissolved and enriched in molten steel. Become. [0005] In the case of high Cr steel such as stainless steel, a large amount of Cr remaining in the slag is equivalent to 2 to 4% in terms of molten steel, so that a large amount of reducing material such as FeSi or Al is used. Need to be added. On the other hand, when decarburizing and refining low alloy steel to which the present invention is applied, the slag after decarburizing refining contains 10% or more of iron oxide. It has a sufficient P removal capacity, and the P removal reaction proceeds during the decarburization refining. When a reducing agent such as FeSi or Al is added to slag after decarburizing and refining of low alloy steel, the added reducing agent reduces Cr-based oxides in the slag, but at the same time reduces iron oxide in the slag. Cr by FeSi or Al etc.
The reduction efficiency is extremely reduced and the production cost is increased. Further, if a strong reduction is performed to completely reduce the Cr-based oxide remaining in the slag after the decarburization refining, the iron oxide in the slag is completely reduced, and the slag has almost no ability to remove P. P that has moved to the slag during refining moves again into the molten steel. [0008] It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide a method for recovering alloy components remaining in slag after refining during low alloy steel smelting. Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies, and as a result, have found that the concentration of iron oxide in the slag after the decarburization refining and the Cr ₂ O ₃ in the slag Concentration control,
The present inventors have found that there is a close relationship between the amount of bottom blown gas at the time of adding a reducing agent and the basicity of slag after reduction, and have completed the present invention. [0010] Namely, the present invention based on the above findings, using oxygen refining facilities, when Cr content is melted 0.5 to 2.0% low alloy steels, Cr ore as Cr-based raw materials or semi-reduced Cr
In the low alloy steel smelting method using ore, immediately before or after the end of decarburization refining, a carbon-based reducing agent is added into the oxygen refining facility, and the iron oxide concentration (T.Fe) in the slag after decarburization refining is added. ) Is reduced in advance to a state of 10% or less, and after the completion of the preliminary reduction by the carbon-based reducing agent, the amount of FeSi necessary to reduce the Cr ₂ O ₃ concentration in the slag to 3%
And a metal-based reducing agent such as Al or the like, the bottom blowing gas is adjusted to be in the range of 0.05 to 0.3 Nm ³ / min · t simultaneously with the addition of the reducing agent, and the basicity of the slag after reduction ( The gist of the present invention is a method for recovering residual alloy components in slag after refining during smelting of a low alloy steel , wherein the composition is controlled so that CaO / SiO ₂ ) is in the range of 2.5 to 3.5. The structure and operation of the present invention will be described. In the present invention, the pre-refining for recovering the remaining alloy components in the slag after the refining works as follows. In other words, immediately before or after the end of the decarburization refining, by adding a carbon-based reducing agent into the oxygen refining facility, at the contact interface between the added carbon material and the decarburized refining slag, a reduction reaction of iron oxide is performed. The slag is formed by the generated CO gas. The slag forming increases the apparent slag surface area, increases the reaction boundary area with the subsequently added metal-based reducing agent, and reduces the Cr content in the slag even when the stirring by the bottom blow gas is small. The reaction proceeds easily. Since the iron oxide concentration (T.Fe) in the slag after the decarburization refining is reduced to 10% or less by the preliminary reduction using the carbon material, the reduction efficiency of the metal-based reducing material added subsequently is reduced. Improves. When a reducing agent is added, it is necessary to adjust the bottom blown gas so as to be in the range of 0.05 to 0.3 Nm ³ / min · t. 0.05Nm ³ / mi
At a gas flow rate less than n · t, the reduction reaction of the slag-metal hardly proceeds, but conversely, 0.3 Nm ³ / min · t
At a gas flow rate exceeding the above, although the reduction rate of Cr is improved, the iron oxide concentration (T.Fe) in the slag after the reduction is reduced to 3% or less, and a P-reaction from the slag occurs. The basicity of the slag after reduction (CaO / Si
The composition must be controlled by CaO or the like so that O ₂ ) is in the range of 2.5 to 3.5. If this treatment is neglected, the melting point of the slag decreases after reduction, and when the molten steel is transferred from the smelting furnace to a moving container such as a ladle, a large amount of the slag flows out after the reduction and has a serious adverse effect on the subsequent processes. . In the present invention, it is possible to reduce and recover about 90% of Cr in the slag while controlling the recovery P and the slag outflow to the ladle by controlling such that the above conditions are satisfied. I can do it. Embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. Embodiment FIG. 1 is a side sectional view of a converter type refining apparatus having a bottom blowing function. In a smelting vessel, 95t of hot metal subjected to hot metal pretreatment and 5t of scrap are added as main raw materials. 1500 kg of calcined lime and 3000 kg of semi-reduced Cr ore as auxiliary materials
Added. Blow stop C = 0.06%, blow stop temperature = 17
Decarburization refining is performed so as to reach 00 ° C. When 100 kg of soil graphite and 500 kg of calcined lime were added to the furnace immediately before the end of blowing, the C concentration in steel was reduced to 0.06% by oxygen refining. The iron oxide concentration of the slag, whose Fe has increased to nearly 18%, has decreased to 8%. on the other hand,
The slag is produced by the reduction reaction of iron oxide by graphite.
The gas is formed by the gas. After the decarburization refining is completed, 400 k FeSi is introduced into the furnace.
g and the bottom blown gas is supplied at a flow rate of 0.1 Nm ³ / min · t.
Was stirred for about 6 minutes. As a result, as shown in Table 1, Cr was reduced and recovered with almost no recovery P. On the other hand, since the basicity of the reduced slag is also maintained at 3.3, the reduced slag has a relatively low liquid phase ratio, and the molten steel is transferred from the refining vessel to the ladle for transfer. Almost no slag flow was observed during the transfer. As a comparative example, after the decarburization refining was completed, FeSi was added to the furnace in a state where the preliminary reduction with soil graphite was not performed.
0 kg is added, and the bottom blown gas is supplied at a flow rate of 0.1 Nm ³ / min.
Table 2 shows the results of stirring for about 6 minutes under the condition of t. In the comparative example, the reaction area was small because FeSi was added without slag forming.
Since the slag and the reducing agent do not sufficiently react with the stirring at the bottom blown gas flow rate of about 0.1 Nm ³ / min · t, Cr is hardly reduced only by reducing the iron oxide in the slag. As another comparative example, FeSi was introduced into the furnace after the decarburization refining without pre-reduction with soil graphite.
400 kg is added, and the bottom blown gas is flowed at a flow rate of 0.5 Nm ³ / mi.
Table 3 shows the results of stirring for about 6 minutes under the condition of n · t. [Table 1] [Table 2] [Table 3] The flow rate of the bottom blow gas is 0.5 Nm 3 / min.
・ Under the strong stirring condition of t, the slag and the reducing material react sufficiently, so that Cr in the slag is almost reduced. Further, the iron oxide in the slag was completely reduced, and as a result, P removed from P during the decarburization refining completely returned to molten steel. As described above, the present invention is constructed as described above. Therefore, a low alloy steel is produced without a special low P treatment of raw materials in advance, and with little P recovery. Since the Cr content remaining in the slag after refining at the time of smelting can be reduced and recovered, it is extremely useful in industry.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side sectional view of a converter type refining apparatus having a bottom blowing function used in the present invention. [Description of Signs] 1-molten steel, 2-Cr containing slag, 3-oxygen lance, 4-furnace body, 5-hopper, 6-oxygen jet, 7-bottom tuyere,
8-bottom blowing gas.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C21C 5/28 C21C 5/36

Claims (1)

(57) [Claims] [Claim 1] Using an oxygen refining facility, and having a Cr content of 0.5
In the low alloy steel smelting method that uses Cr ore or semi-reduced Cr ore as a Cr-based raw material when melting low alloy steel of up to 2.0%, the carbon After the decarburization and refining, the iron oxide concentration (T.Fe) in the slag is preliminarily reduced to a state of 10% or less, and after the preliminary reduction by the carbon-based reducing material is completed, Of a metal-based reducing agent such as FeSi or Al necessary for reducing the Cr ₂ O ₃ concentration of the alloy to 3% , and simultaneously with the addition of the reducing agent, the bottom-blown gas is supplied at 0.05 to 0.3 Nm ³ / mi.
while it adjusted in the range of n · t, low alloy steel smelting, which comprises controlling the composition as the slag basicity after reduction (CaO / SiO ₂₎ is in the range of 2.5 to 3.5 Method of recovering residual alloy components in slag after refining.