JP3345622B2 - Hot metal pretreatment 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 pretreatment of hot metal, and more particularly to a method for pretreatment of hot metal in which desulfurization and dephosphorization are carried out effectively using Mg-based flux after desiliconization and dephosphorization, and is widely used in the steelmaking field. You.

[0002]

2. Description of the Related Art Hot metal spouted from a blast furnace is housed in a container such as a mixed iron car, and is blown with inert gas through a lance, and different fluxes are blown into the hot metal to desiliconize, dephosphorize,
Pretreatment for desulfurization is widely practiced. Generally metal M
g is known to have excellent desulfurization ability,
A single composition or a mixed composition with CaO is used as a desulfurizing agent. However, there have been the following problems in addition to the conventional use of metallic Mg as a desulfurizing agent. (B) The price of Mg is high, and the cost required for desulfurization increases. (B) Since the boiling point is low and the vapor pressure is high, the higher the temperature, the lower the reaction efficiency. (C) In the desulfurization of hot metal with Mg-based flux,
The generated MgS reacts with the following formula (1) to form MgO.
And S, the resulfurization after the treatment is liable to occur. Since MgS ten (O) → MgO ten S ........................ (1) further Mg oxygen or FeO and in Furatsukusu in the slag in the hot metal (1) tends to react by expression expensive forme blowing There is a problem that Mg is not effectively used for desulfurization.

[0003] As a result, hitherto, the blast furnace slag has conventionally been used only for hot metal in which only a small amount of slag is present, that is, hot metal in the case where desiliconization and dephosphorization are not performed, and S ≦ 0.005 even after desulfurization. % Was not obtained. Further, by injecting a mixed powder of Mg and CaO, M
It is known that the efficiency of the desulfurization reaction of g is improved. However, since the Mg and CaO are simultaneously infused or added directly to the hot metal, the composition of the slag CaO / SiO ₂ cannot be adjusted appropriately, and furthermore, the generation (MgS) of the slag by the above formula (1) is caused by oxygen of the slag. In addition to resulfurization due to the presence of sulfur, there is a problem that rephosphorization easily occurs due to FeO in the slag after the dephosphorization treatment.

[0004]

Although the Mg flux has been found to have an excellent effect on desulfurization, the conventional method for simultaneously proceeding dephosphorization and desulfurization has many problems as described above, and furthermore, has a problem in terms of the basic unit. Soaring costs,
There were two major problems: resulfurization of hot metal. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and particularly to provide a pretreatment method for hot metal that can prevent resulfurization and improve the reaction efficiency of Mg-based flux.

[0005]

The gist of the present invention is as follows. (1) In a pretreatment method of molten iron in which flux is blown into a molten iron housed in a container such as a mixed iron car to perform desiliconization, dephosphorization, desulfurization, etc., the flux is blown to desiliconize and dephosphorize, and then dedusting A step of injecting a flux containing CaO into the hot metal or adding the flux onto the hot metal to adjust the slag basicity to CaO / SiO ₂ ≧ 2.0; A step of injecting gas using a powder desulfurizing agent containing CaO as a flux, or adding the powder desulfurizing agent to hot metal, and a step of injecting gas into the hot metal and performing bubbling stirring. A method for pretreating hot metal, comprising: (2) The powder desulfurizing agent is metallic Mg: 5 to 50% by weight, C
aO: 95 to 50% by weight is contained, the hot metal pretreatment method according to the above (1),

The details of the present invention will be described with reference to the accompanying drawings. First, a mixed flux of ordinary iron oxide and lime is blown into hot metal to perform desiliconization and dephosphorization. Next, desiliconization and dephosphorization slag are removed. Next, the basicity of the slag CaO / SiO ₂ is adjusted prior to the desulfurization treatment. That is, CaO
Is injected into the hot metal, or
aO is added to the hot metal to adjust CaO / SiO ₂ ≧ 2.0. FIG. 1 shows the results of an investigation carried out by the present inventors by changing the desulfurization reaction efficiency of Mg flux to a basicity of 1.0 to 4.0. That is, the desulfurization reaction efficiency of the Mg-based flux is sharply improved in the region of CaO / SiO ₂ > 1,
The basicity continues to rise to CaO / SiO ₂ = 4, but in order to secure the desulfurization reaction efficiency to at least 35%, CaO /
It is necessary that SiO ₂ ≧ 2. The present inventors also investigated the relationship between the basicity of the slag and the amount of rephosphorization during the desulfurization treatment, and obtained FIG. That is, the basicity of slag CaO /
In the case of SiO ₂ <2, a phenomenon of phosphorus reversion during desulfurization treatment occurred. In order to prevent this rephosphorization, CaO / SiO ₂
≧ 2. For the above two major reasons, in the present invention, the basicity of CaO
Adjustment to / SiO ₂ ≧ 2 is limited as an essential requirement.

Next, the mixing ratio of the powder desulfurizing agent in the mixed composition of metallic Mg and CaO according to the present invention will be described. The composition ratio varies depending on the S content in the hot metal and the target desulfurization amount. Metal Mg: 5 to 50% by weight CaO amount: 95 to 50% by weight, and the maximum by the minimum amount of expensive Mg The mixing ratio is determined with the aim of the reaction efficiency of the reaction. In the desulfurization treatment of the metal Mg and CaO with the powder desulfurizing agent according to the present invention, gas is always blown into the hot metal to perform bubbling stirring. This is the condition required to improve the reaction efficiency by uniformly mixing the powder desulfurizing agent injected into or into the hot metal to improve the reaction efficiency. Efficiency could be significantly improved.

[0008]

According to the present invention, before performing desulfurization treatment by adding Mg-based flux to indie or hot metal, the basicity of slag CaO / SiO ₂ is adjusted by adding CaO to indie or slag. since it subjected to a treatment prior to this a 2.0 or more, and deterioration in fluidity of the slag, Mg is less likely to be oxidized since a degree that almost solidified, MgS ten (O) → become MgO ten S (1) The reaction of the formula is suppressed, and Mg reacts effectively. Further, since the reaction represented by the following formula (2) is promoted: MgS-> 10 CaO → CaS-> MgO (2)
As S is absorbed in the slag, desulfurization is achieved.

[0009]

【Example】

Example 1 The components of the hot metal spiked from the blast furnace were as follows. C Si Mn P S 4.55% by weight 0.18 0.27 0.130 0.025 The hot metal after desiliconization and dephosphorization of this hot metal with a mixed flux of iron oxide and lime in a mixed iron car is as follows: It was like C Si Mn PS 4.55% by weight 0.01 0.020 0.040 0.022 The desiliconized and dephosphorized slag was sludge-removed by tilting a mixed iron wheel.
CaO is added to the remaining slag of the mixed iron wheel, and the basicity is CaO.
/ SiO ₂ ≧ 2.0 and 2.8 (metal Mg 30% by weight)
(A 70% by weight of CaO) was blown into the hot metal to perform a desulfurization treatment. The S content after desulfurization is 0.005.
%, No rephosphorization was observed during this desulfurization treatment. The reaction efficiency of the Mg-based flux at a basicity of 2.8 was 43%.

Example 2 A conventional method of simply blowing with a mixed flux of Mg metal and CaO, a method of blowing a flux containing CaO before desulfurization treatment, or adding CaO onto hot metal to add a basicity of CaO / After performing a pretreatment to make SiO ₂ ≧ 2.0,
A comparative test was conducted to compare the amount of Mg-based flux used with the method of the present invention to be desulfurized and the transition of the S content in the hot metal.
The results are as shown in FIG. As is clear from FIG. 3, when the S concentration of 0.005% by desulfurizing S = 0.025% in the hot metal, according FeS + Mg = MgS + Fe
Although desulfurization is performed, conventionally has consumes about four times the Mg theoretical calculated amount, to desulfurize the S of the above cases 0.2 k g / t
0.2 × For that (24.30 / 32.06) × 4 =
Although 0.60 kg / t of Mg metal was required, in the present invention, it was 2.2 to 2.5 times, that is, 0.2 × (24.
30 / 32.06) × 2.2 = 0.33 kg / t or
0.2 × (24.30 / 32.06) × 2.5 = 0.3
8 kg / t of Mg metal is sufficient. Therefore, the reaction efficiency could be significantly improved from the conventional 25-30 percent to 40-45 percent.

[0011]

According to the pretreatment method of the present invention, particularly desulfurization method, the slag of the hot metal which has been subjected to the desiliconization and dephosphorization treatment is subjected to slag removal and then contains CaO prior to the desulfurization treatment with Mg-based flux. Influx the flux or add it to the hot metal to add the basicity of slag CaO /
After adjusting to SiO ₂ ≧ 2, desulfurization was performed with Mg-based flux. During this desulfurization treatment, an inert gas was blown into the hot metal and subjected to bubbling stirring to obtain the following effects. (A) The desulfurization efficiency of Mg was significantly improved as compared with the conventional method. (B) The rephosphorization phenomenon conventionally observed during the desulfurization treatment was not observed at all and could be completely prevented.

[Brief description of the drawings]

FIG. 1 Prior to desulfurization treatment with Mg-based flux according to the present invention, by adjusting the basicity of slag to CaO / SiO ₂ ≧ 2.0, the Mg-based flux reaction efficiency is improved as the basicity increases. FIG.

FIG. 2 is a correlation diagram showing a relationship between basicity of slag and rephosphorization and dephosphorization in desulfurization treatment using a Mg-based flux.

FIG. 3 shows a basicity of slag CaO / SiO ₂ ≧ prior to desulfurization treatment with Mg-based flux in an example of the present invention.
Correlation diagram comparing the relationship between the S concentration (%) in hot metal and the amount of Mg-based flux used (Kg / t) between the case of adjusting to 2.0 and the conventional method without adjusting the slag basicity. It is.

Continued on the front page (72) Inventor Mitsuno Makino 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. None) Kawasaki Steel Corporation, Mizushima Works (56) References JP-A-63-238209 (JP, A) JP-A-63-86810 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , (DB name) C21C 1/00 C21C 1/02 102 C21C 1/02 110 C21C 1/04 101

Claims (2)

(57) [Claims] 1. A pretreatment method for hot metal in which a flux is blown into a hot metal housed in a container such as a mixed-iron car for desiliconization, dephosphorization, desulfurization, etc. Slag and blowing a flux containing CaO into the hot metal, or adding the flux onto the hot metal to add slag basicity CaO / SiO ₂ ≧ 2.0
And performing a gas injection using a powder desulfurizing agent containing metallic Mg and CaO to the hot metal as a flux, or adding the powder desulfurizing agent onto the hot metal,
Performing a bubbling agitation by injecting a gas into the hot metal, wherein the hot metal is pre-treated. 2. The method according to claim 1, wherein the powder desulfurizing agent contains 5 to 50% by weight of metal Mg and 95 to 50% by weight of CaO.