JPH1180821A - Method for desulfurizing molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the effective desulfurization while suing desulfurizing agent having low blending ratio of metallic Mg by injecting a metallic Al source so that Al concn. in molten iron becomes in a specific range and successively, injecting the desulfurizing agent composed of the metallic Mg, CaO, CaF2 and Al2 O3 in the specific ratio. SOLUTION: Firstly, in order to promote the desulfurizing reaction, the metallic Al source is injected into the molten iron so that the Al concn. in the molten iron becomes 0.010-0.014 wt.% for the purpose of removing oxygen content obstructing the desulfurization to deoxidize the molten iron with Al. By using Al, it can be restrained that Mg is consumed by the oxygen causing the loss of Mg, and further, the desulfurizing reaction with CaO is promoted. Successively, the desulfurizing agent composed of, by weight, 3-10% Mg, 50-70% CaO, 5-30% CaF2 and 5-20% Al2 O3 , is injected into the molten iron to desulfurize the molten iron, and thus, the molten iron can efficiently be desulfurized. Further, as the metallic Al source, it is profitable to practically use the inexpensive Al dross.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, as the demand for producing high-grade steel has increased, there has been a strong demand for a method for producing low-sulfur steel at low cost. As a hot metal desulfurization method, CaO, CaC ₂ , soda ash and the like have been used for a long time. Above all, soda ash has an extremely high desulfurization ability and has been widely used as a method for stably producing low-sulfur steel. However, the use of soda ash has disadvantages in that the refractory is severely eroded and the resulting slag cannot be effectively used as a cement raw material or a roadbed material. On the other hand, it has long been known that metallic Mg has an excellent desulfurization ability.
No. 9919, metal Mg 15-20
%, And a method using a desulfurizing agent in which CaO is mixed.

[0003]

However, when desulfurization is carried out using a desulfurizing agent containing a high metal Mg as disclosed in JP-A-7-179919, a large refining effect can be obtained, but a large amount of expensive metal Mg is added. As a result, the desulfurization treatment cost increases and the economic burden increases. An object of the present invention is to provide a method for desulfurizing hot metal in which a desulfurization agent having a low compounding ratio of metallic Mg can be used to obtain a desulfurization ratio equivalent to that of the conventional art.

[0004]

Means for Solving the Problems The present invention has been made to solve the above-mentioned problems. Means 1 of the present invention is to dissolve metal such that the Al concentration in the hot metal is 0.010 to 0.040% by weight. An Al source is blown into the hot metal, followed by metallic Mg
3 to 10% by weight, 50 to 70% by weight of CaO,
And ₂ 5 to 30 wt%, it is a method of desulfurizing molten iron by blowing agent consisting of Al ₂ O ₃ 5 to 20 wt% in the hot metal. Further, the means 2 uses Al dross as the metal Al source.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted various studies on a flux having a high desulfurization ability even with a low Mg content. First, in order to promote the desulfurization reaction, in order to remove oxygen that inhibits desulfurization from the hot metal, it was considered that the hot metal was desulfurized after being deoxidized. That is, after the hot metal is first deoxidized with metal Al, a desulfurizing agent is blown into the hot metal,
This is a method for desulfurizing hot metal efficiently.

When the hot metal is deoxidized with Al and the oxygen concentration in the hot metal is reduced, Mg is prevented from being consumed and lost due to oxygen, and the effective content of Mg is increased. Furthermore, CaO
As can be seen from the reaction formula shown in the following formula, the oxygen O on the reaction product side is removed, so that the desulfurization reaction proceeds rightward and desulfurization is accelerated. This effect is more effectively exhibited as the addition amount of metal Al increases, the deoxidation of the hot metal is strengthened and the equilibrium O decreases. CaO + S → CaS + O

As a deoxidizing agent for hot metal, there are metal Si and metal Ti in addition to metal Al. However, in the case of deoxidation with metallic Si, a strong reaction layer of 2CaO.SiO _{2 is} formed on the surface of CaO, and further reaction is inhibited, so that effective desulfurization cannot be expected. Also, the use of metal Ti is costly and not practical. When metal Al is used, the cost is taken into consideration, and as an Al source, low cost Al dross (industrial waste generated during Al refining:
It is advantageous to utilize an Al content of 10-55%).

Next, the desulfurizing agent blown into the hot metal subsequent to the Al deoxidation promotes desulfurization by CaO added simultaneously with Mg. It was conceived to mix CaF ₂ and Al ₂ O ₃ effective for slagging into a desulfurizing agent.
That is, as a flux to obtain effective desulfurization effect at low cost, the Mg desulfurization and CaO desulfurization utilizing full at the same time, and focusing on a small amount _{Mg-CaO-Al 2 O 3} -CaF 2 desulfurization agent.

Therefore, the present inventors conducted various basic experiments in order to clarify the above-mentioned Al deoxidation and the optimum composition of the desulfurization flux to be subsequently blown into the hot metal. In each experiment, Al dross was used as an Al source to be blown into the hot metal before adding the desulfurizing agent, and the Al content was 32%. The initial [S] concentration of the hot metal is 0.028 to 0.0
It was set to 32%. The experimental temperatures were all set to 1300 ° C.

First, in order to clarify the appropriate degree of deoxidation of hot metal by the metal Al source, desulfurization treatment was performed by changing the amount of the metal Al source (using Al dross) before blowing the desulfurizing agent. As for the composition of the desulfurizing agent, Mg is 7% and CaO is 55%.
To 65%, CaF ₂ is 10~20%, Al ₂ O ₃ is 10 to
It was adjusted to 15%. The result is shown in FIG. As is clear from the figure, a high desulfurization rate was obtained when the Al concentration in the hot metal before the desulfurizing agent was blown was 0.01% or more. Also, A
If the 1 concentration is 0.04% or more, the desulfurization rate is saturated, and adding an Al concentration exceeding this is disadvantageous in cost.

Next, the optimization of the composition of the desulfurizing agent added after Al deoxidation was examined. First, in order to clarify the appropriate amount of Mg for obtaining a desulfurizing effect with a small amount, the Al concentration in the hot metal before adding the desulfurizing agent was adjusted to 0.02 to 0.03%, and the composition of the desulfurizing agent was changed to CaO. 60-65% of CaF ₂ 10 to 20 percent, for Al ₂ O ₃ 5-15%, an experiment was conducted to blow Furatsukusu were uniformly mixed by changing the mixing ratio of Mg to the molten iron.

FIG. 2 shows the results. As is clear from the figure, if Mg is less than 3%, the desulfurization effect by Mg itself is insufficient, and the desulfurization rate remains at a low value. When the Mg content is 10% or more, the desulfurization rate is saturated.
Formulations in excess of 10% are only meaningful at the expense of cost. Therefore, the proper mixing ratio of Mg in the flux is 3 to 10%.

Next, the Ca expected from the Mg desulfurization
In order to clarify the compounding amount of CaF ₂ (which has an effect of increasing desulfurization ability by mixing with CaO and at the same time promoting slagging of CaO) to enhance the desulfurizing effect of O, changing the _second mixing ratio, 2
A desulfurization experiment was performed using the same experimental method as that described above. At this time, the composition of the flux was Mg 8%, CaO 50-65%, Al
₂ O ₃ was adjusted to 10 to 15%. The experimental results are shown in FIG. As can be seen from the figure, when the mixing ratio of CaF ₂ is lower than 5%, the desulfurization accelerating effect of CaF ₂ cannot be sufficiently obtained, and the desulfurization rate remains low. On the other hand, if the compounding ratio of CaF ₂ exceeds 30%, the desulfurization rate decreases due to the decrease in the compounding ratio of CaO itself. Therefore,
Proper blending ratio of CaF ₂ is 5-30%.

Furthermore, to clarify the proper amount of contributing Al ₂ O ₃ in the slag formation promoting flux, Al ₂ O
_The desulfurization experiment was performed by changing the compounding ratio of No. 3 and using the same experimental method as in FIGS. At this time, the composition of the flux was 8% for Mg, 50 to 65% for CaO, and 10 to 20% for CaF _2.
Aligned. The experimental results are shown in FIG. As can be seen from the figure, when the blending ratio of Al ₂ O ₃ is lower than 5%, the effect of promoting the desulfurization of Al ₂ O ₃ cannot be sufficiently obtained, and the desulfurization rate remains low. On the other hand, when the mixing ratio of Al ₂ O ₃ is 20
%, The desulfurization rate decreases due to the decrease in the CaO blend ratio itself, and the flux desulfurization ability decreases due to excess Al ₂ O ₃ . Therefore, Al ₂ O ₃
Is 5 to 20%. On the other hand, regarding the mixing ratio of CaO, the above-mentioned CaF ₂ and Al ₂ O ₃
Is specified as an appropriate mixing ratio, and 50 to 70% of CaO is an appropriate mixing ratio.

[0015]

【Example】

 1. A concentration in hot metal It is described in Table 1. 2. Hot metal temperature 1300-1330 ° C 3. Reaction vessel and amount of hot metal Hot metal pot 350t 4. 4. Method of adding Al source and desulfurizing agent Injection by immersion lance 5. Flux carrier gas Nitrogen gas Details and results of operating conditions are summarized in Table 1.

[0016]

[Table 1]

Table 1 shows Examples and Comparative Examples of the present invention. In Examples, high desulfurization rates of 81 to 89% were obtained. on the other hand. Comparative Example 1 lacks Al concentration in the hot metal, Comparative Example 2 lacks Mg, Comparative Example 3 contains C
aO deficiency, CaF ₂ deficiency in Comparative Example 4, A
It becomes l ₂ O ₃ of insufficient compounding, since out of the proper range of the present invention, the desulfurization rate has remained 65 to 71% and low.

[0018]

According to the present invention, low-cost and efficient hot metal desulfurization can be performed, so that high-grade steel such as low-sulfurized steel can be easily produced at the same time as drastic reduction in desulfurization processing cost. The effect on this type of industrial field is extremely large.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the Al concentration in hot metal and the desulfurization rate.

FIG. 2 is a diagram showing a relationship between a Mg compounding ratio and a desulfurization rate.

FIG. 3 is a diagram showing the relationship between the mixing ratio of CaF ₂ and the desulfurization rate.

FIG. 4 is a diagram showing the relationship between the mixing ratio of Al ₂ O ₃ and the desulfurization rate.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Makoto Moriguchi 1 Nishinosu, Oita, Oita City, Oita Prefecture Nippon Steel Corporation Oita Works

Claims (2)

[Claims] 1. The method according to claim 1, wherein the hot metal has an Al concentration of 0.010 to 0.0
A metal Al source was blown into the hot metal so as to be 40% by weight, and subsequently, 3 to 10% by weight of metal Mg and CaO 50
And 70 wt%, and CaF ₂ 5 to 30 wt%, Al ₂ O ₃
A method for desulfurizing hot metal, comprising blowing a desulfurizing agent of 5 to 20% by weight into hot metal. 2. The desulfurization method according to claim 1, wherein Al dross is used as said metal Al source.