JPH089730B2 - Decarburization refining method for molten steel containing chromium - Google Patents

Description

Detailed Description of the Invention

[0001]

[Industrial field] In decarburization refining of molten steel containing chromium, at the time of decarburization, a metal oxide containing 30% or more of chromium oxide is supplied to the top blowing oxygen fire point to improve recovery efficiency of valuable metals and decarburization rate. The present invention relates to a method for decarburizing and refining molten steel containing chromium, which aims to improve

[0002]

2. Description of the Related Art In a decarburizing method of blowing oxygen gas and diluent gas into a molten chromium-containing steel containing 11% or more chromium such as conventional stainless steel, metal oxide is added to oxygen in the metal oxide. It is disclosed, for example, in Japanese Patent Application Laid-Open No. 62-243711 that the valuable metal is reduced and recovered and used to reduce the added amount of the reducing agent. In this method, slag containing 15% or more of chromium oxide generated by decarburization refining is left in the furnace at the time of tapping, and the chromium oxide in the slag is reduced by [C] in the newly received crude molten steel. Is the way to do it. Thus, this method is a method of reducing the chromium oxide in the slag in the high [C] concentration region at the initial stage of decarburization, but the molten steel temperature at the initial stage of decarburization is generally 1
The temperature is about 500 ° C., the reduction rate is very low, and the reduction rate varies widely. Further, in this method, only the slag generated by decarburizing and refining is repeatedly used, and no additional chromium source is added, so that chromium is not effectively recovered.

As another example, Japanese Patent Laid-Open No. 59-10442.
There is a method shown in No. 0, and in a decarburizing method in which oxygen gas and a diluent gas are blown into molten steel, [C] 0.25% or less of metal oxide is added after the middle period of decarburization. This is a method of decarburizing mainly oxides. Thus, in the medium coal region, the decarburization rate depends on the agitation of the steel bath, so addition of a metal oxide does not lead to an improvement in the decarburization rate.

[0004]

In the decarburization refining of molten steel containing chromium, the efficiency of decarboxylation is improved by promoting the utilization of oxygen in the metal oxide containing chromium oxide as an oxygen source for the decarburization reaction. At the same time, it is possible to effectively measure the reduction and recovery of chromium, shorten the refining time, and reduce the refining cost.

[0005]

The present invention advantageously solves the above-mentioned problems, and the gist thereof is that carbon is 0.3%.
In the treatment of blowing oxygen gas from below and above the bath surface of the chromium-containing molten steel contained above , the molten steel temperature T _m , the molten steel bath
The amount of oxygen gas W _g blown from above the surface is expressed by equation (1) and (2)
By treating under conditions that satisfy the formula, 200
Along with the formation of the upper blown oxygen fire point above 0 ° C,
A metal oxide containing 30% or more of chromium oxide is supplied to the blown oxygen fire point for treatment.

T _m ≧ 1550 Expression (1) W _g ≧ 0.2 Expression (2)

Further, the processing is performed under the condition that the following expression (3) is satisfied.
This is a decarburization refining method for molten chromium-containing steel.

[0008]

[Equation 2]

[0009] T _m: soluble Steel Temperature [℃] W _g: Unit molten steel per oxygen gas blowing quantity from the molten steel bath surface on the upper吹酸Motohi point ^{[Nm 3 / min · T]} W A: metal oxides Supply amount [kg] W _m : Molten steel weight [kg] (% Cr ₂ O ₃ ) _A : Chromium oxide concentration in metal oxide [%] [% C] _i : At the start of the metal oxide supply (immediately before) Molten Steel Carbon Amount [%] The present invention will be described in detail below.

The decarburizing refining method for molten chromium-containing steel according to the present invention is, as shown in FIGS. 1 (a) and 1 (b), an AOD combined blowing method and a top-bottom blowing converter method. As the metal oxide containing 30% or more, chromium ore or chromium-containing slag is added to the top blowing oxygen fire point. In the figure, 1 is a lance, 2 is molten chromium-containing steel, 3 is slag, 4 is a side blowing tuyere,
5 shows a bottom blown tuyere.

[0011] In Thus, the first invention of the present invention, per the decarburization refining of chromium-containing molten steel, reducing the use of oxygen gas, and for measuring the increase in decarburization rate, including chromium oxide 30% or more
This is a method of supplying metal oxides such as chrome ore and slag (hereinafter, mainly referred to as metal oxides) to the high-temperature top-blown oxygen hot spot, and the second invention further decarburizes oxygen in the metal oxides. For effective use, the temperature during addition, the amount of top-blown acid fed and the amount of metal oxide supplied are limited. In the present invention, the addition of chromium ore or slag changes the chromium oxide concentration in the slag during decarburization to 2 Cr +3 O = (Cr ₂ O
Obtained from the equilibrium relationship ₃₎ (Cr ₂ O ₃₎ concentration
Effectively suppress the oxidation of the steel [Cr] to be maintained at a higher concentration than.

In the present invention, the metal oxide containing 30% or more of chromium oxide added to the top-blown oxygen hot spot contains chromium ore or chromium oxide such as slag produced as a by-product during refining of molten steel containing chromium. Table 1 shows an example of the metal oxide used.

[0013]

[Table 1]

When chrome ore or slag is used, it can be in a powder form or a lump form and can be used properly depending on the addition device. It is preferable to use a lump in the case of addition by a chute, and a powder in the case of addition from a top blowing lance hole. The mode of addition of such chromium ore or slag will be described based on an example of an oxygen gas supply pattern in the composite blowing of the present invention shown in FIG. In this pattern Cr
In order to suppress oxidation, the amount of acid sent is controlled on the low carbon side. In the present invention, when the chromium ore or slag is supplied, the supply mode is as follows.

The chromium ore or slag may be added all at once, but in order to prevent the temperature of the molten steel from lowering and to promote the reduction of the metal oxide efficiently, it is preferable to add it in portions or continuously. At the start of decarburization, the molten steel temperature is low, and the temperature rises as decarburization proceeds. Therefore, the supply of chromium ore or slag is started when the molten steel temperature reaches or exceeds the predetermined temperature. The [C] concentration in the molten steel at the start of this supply is [C] _i . The higher the [C] _i concentration, the more efficiently the reduction of the metal oxide proceeds. In the case of divisional addition or continuous addition, the next supply is performed before the metal oxide in the previously supplied ore or slag is completely reduced, and the final supply is such that the [C] concentration in the molten steel is 0.3. It is necessary to carry out under the condition that is above%.

In the present invention, the reason why the chromium-containing molten steel to be treated has a carbon content of 0.3% or more is to limit the range in which the effects of the present invention can be effectively obtained as described below.

FIG. 3 shows the relationship between the [C] concentration in the molten steel and the decarbonation efficiency. The decarboxylation efficiency shows the ratio of oxygen used for decarburization. If the concentration of [C] is less than 0.3%, the efficiency of decarboxylation will decrease sharply. In other words, Cr in molten steel
Oxidation progresses, and the Cr ₂ O ₃ concentration in the slag sharply rises. Even if Cr oxide is added in such a state, a sufficient effect cannot be obtained.

That is, the [C] concentration in the molten steel when Cr oxide is added is 0.3% or more, preferably 0.5% or more.

As described above, the higher the [C] concentration in the molten steel,
Since the reduction of the metal oxide proceeds efficiently, the supply of the metal oxide is started after the steel is received (usually when the steel has a [C] concentration of 1.5 to 2 at a temperature of 1550 ° C. or higher). ．
0%) It is desirable to carry out as early as possible in decarburization.

Next, the reasons for limiting the oxygen gas injection amount W _g per unit molten steel from the bath surface, the chromium ore or slag supply amount W _A , and the molten steel temperature T _{m in} the present invention will be described.

In FIG. 4, W _g is 1.0 Nm ³ / min · T,
[C] _i is 1.2 to 1.5%, W _m is 60,000 k
molten steel temperature T when g and W _A are set to 800 to 1500 kg
The relationship between _m and the reduction rate index of Cr oxide is shown. The reduction rate index is a value indexed with 1 when T _m = 1550 ° C.

The higher the molten steel temperature is, the higher the reduction rate is, and it is possible to maintain the reduction rate at a high level especially by T _m in the equation (1).

T _m ≧ 1550 ° C. Equation (1) In FIG. 5, [C] _i is 1.2 to 1.5% and W _m is 60,00.
0 kg, W _A 800 to 1500 kg, T _m 1600
The relationship between the amount of acid W _g to be blown upward, the temperature difference between the blown oxygen blowing fire point and the molten steel, and the reduction rate index of Cr oxide at ˜1750 ° C. is shown. The reduction rate index is such that W _g is 0.
It is a value indexed as 1.0 in the case of 2 Nm ³ / min · T. W _g is as the temperature of the fire point part is increased greatly, when the W _g and 0.2Nm ³ / min-T or more, soluble
Steel temperature is 450 ° C higher than 1550 ° C (Fig. 4)
As a result, the temperature of the hot spot becomes 2000 ° C. or higher, which increases the reduction rate, and in particular, W _g in the formula (2) exerts a remarkable effect.

W _g ≧ 0.2 Nm ³ / min · T (2) Formula W _g is 0.2 to 1.0 Nm ³ / min · T, T _m
The showing the relationship between the ratio which is decarburized by subjected <br/> supply oxygen ratio (h) and oxygen in Cr oxides to metal oxides in the case of a 1,600-1,750 ° C..

The horizontal axis represents the amount of oxygen [O] _A supplied and supplied by the metal oxides by the amount of oxygen [O] _m required to decarburize [C] Δ [% C] _m in molten steel. Divided value; h =
[O] _A / [O] _m, which is expressed by the following equation.

[0026]

[Equation 3]

The vertical axis represents the value obtained by dividing Δ [% C] _A decarburized by [O] _{A in} molten steel [C] by Δ [% C] _m ; k = Δ [% C] _A / Δ [% C] _m . That is, in the case of "% C" _m decarburization Δ the [C] in the molten steel, the chromium oxide (% Cr ₂ O ₃₎ with respect to the increase in the supply amount W _A of the metal oxide containing _A, the metal oxide C in
It shows the rate of decarburization of [C] in molten steel using r ₂ O ₃ as an oxygen source.

As shown in FIG. 6 , in the range of h ≦ 0.5, k increases substantially in proportion to the increase of h, that is, the increase of the metal oxide supply amount W _A.

However, in the range of h> 0.5, the increase of k corresponding to the increase of h becomes slower. Also, h <0.
In the range of 05, the amount of decarburization becomes very small and it is not effective. Therefore, it is more effective to supply the metal oxide within the range of 0.05 ≦ h ≦ 0.5.

That is, the following equation is obtained from 0.05 ≦ h ≦ 0.5.

[0031]

[Equation 4]

The decarburization amount Δ [% C] _m is given by the following equation, where the [C] concentration in the molten steel at the completion of decarburization according to the present invention is [% C] _e .

Δ [% C] _m = [% C] _i − [% C] _e [% C] _e is 0.3% or more, preferably 0.5% or more, so that the range of W _A is (3 ) Got the formula.

[0034]

[Equation 5]

[0035]

The metal oxide (Cr ₂ O added in the present invention
₃ ) is consumed by the decarburization reaction by the following formula, and at the same time, it is reduced to [Cr] and recovered in molten steel.

(Cr ₂ O ₃ ) +3 [C] → 2 [Cr] + 3CO (g)
For this reason, the amount of oxygen gas required for decarburization can be small, and the Cr source can be supplemented with inexpensive chromium ore or slag.

The reaction of the above formula is accelerated at high temperatures and high [C] concentrations. In the method of injecting oxygen by the upper blowing lance to proceed the decarburization reaction, when a certain amount or more of oxygen gas is supplied so as to form a high-temperature hot spot on the steel bath surface, so-called secondary combustion and steel The temperature of the top-blown oxygen hot spot rises due to the reaction with the bath . The reaction is promoted by adding a metal oxide to this region.

CO + 1/2 O ₂ → CO ₂ ... In the decarburization reaction, the rate-determining process changes depending on the [C] concentration. On the low [C] concentration side, the rate-determining process is the transfer of [C], and by strengthening the stirring, the transfer of [C] is promoted,
Decarburization rate increases. Adding a metal oxide in this state does not lead to an improvement in the decarburization rate. On the other hand, on the high [C] concentration side, the supply of oxygen is a rate-determining process, and increasing the supply amount of oxygen improves the decarburization rate. Therefore, the addition of the metal oxide can improve the decarburization rate.

Further, the added metal oxide (Cr ₂ O ₃ )
As a result, the (Cr ₂ O ₃ ) concentration in the slag becomes high, so that the following formula progresses, that is, in the molten steel [C
r] can be suppressed and Cr ₂ O ₃ reducing S
The amount of i is small.

4 [Cr] +3 O ₂ → 2 (Cr ₂ O ₃ ) ...

[0041]

EXAMPLE Assuming that SUS304 stainless steel 60 ton treatment was performed, the method of FIG. 1 (b) was performed with the bottom blowing gas pattern of FIG.

Table 2 shows the composition at the start of decarburization refining of the treated chromium-containing molten steel.

[0043]

[Table 2]

60 ton of molten steel to be treated The chromium oxides to be added had the same symbols as in Table 1, and the addition timing and the mode were divided additions shown in Table 3. The bottom-blowing gas supply pattern was the same as the bottom-blowing gas supply pattern in FIG.

[0045]

[Table 3]

No. No. 7 does not supply Cr oxide No. 7 No. 7 and 8 were not blown with oxygen, and No. 7 was used. No. 9 has an oxygen gas flow rate outside the present invention, and No. 9 In No. 10, the molten steel temperature when Cr oxide was added was outside the present invention, and No. 10 Reference numerals 11 and 12 are examples in which the added amount of Cr oxide deviates from the conditions of the present invention.

The results of this implementation are shown in Table 4. This table shows No. No. carried out according to JP-A-59-104420. All 8 examples are shown by the index as 100.

[0048]

[Table 4]

[0049]

INDUSTRIAL APPLICABILITY The present invention significantly improves the efficiency of decarbonation in decarburizing and refining molten steel containing chromium, and at the same time effectively reduces and recovers chromium, shortens the refining time, and reduces refining costs. An advantageous effect is acquired.

[Brief description of drawings]

FIG. 1A is an explanatory diagram of an AOD composite blowing method for carrying out the present invention, and FIG. 1B is an explanatory diagram of an upper bottom blowing converter method.

FIG. 2 is a diagram showing a gas supply pattern of the composite blowing method according to the present invention.

FIG. 3 is an explanatory view of the reason for limiting the carbon content of the target chromium-containing molten steel of the present invention.

FIG. 4 is an explanatory view of the reason for limiting the molten steel temperature in the present invention.

FIG. 5 is an explanatory diagram of the reason for limiting the amount of top-blown acid fed by the present invention.

FIG. 6 is a diagram illustrating the reason for limiting the Cr oxide addition amount range.

[Explanation of symbols]

 1 ... Top blowing lance 2 ... Molten steel 3 ... Slag 4 ... Side blowing tuyere 5 ... Bottom blowing tuyere

Front page continued (72) Inventor Hiroshi Hirata 1-1-1 Emitsu, Yawatahigashi-ku, Kitakyushu, Fukuoka Prefecture Inside the 3rd Technical Research Laboratory, Nippon Steel Corporation (72) Ryoji Tsujino Emitsu, Hachimanto-ku, Kitakyushu, Fukuoka 1-1-1 Inside Nippon Steel Co., Ltd. 3rd Technical Research Laboratory (72) Inventor Hiroyuki Kajioka 1-1-1 Edamitsu, Hachimanto-ku, Kitakyushu City, Fukuoka Prefecture Inside 1-1 Nippon Steel Corporation 3rd Technical Research Laboratory (56) Reference JP-A-57-57814 (JP, A)

Claims (2)

[Claims] 1. A process for blowing oxygen gas from below and above the bath surface of molten steel containing chromium containing 0.3% or more of carbon .
The molten steel temperature T _m , the oxygen gas blown from above the molten steel bath surface.
Under the condition that the amount W _g satisfies the formulas (1) and (2)
By treatment, the surface of the bath will be blown by oxygen at 2000 ° C or higher.
A decarburization refining method for molten chromium-containing steel T _m ≧ 1550 , characterized in that a point portion is formed and a metal oxide containing 30% or more of chromium oxide is supplied to the above-mentioned blown oxygen fire point portion for treatment. (1) Formula W _g ≧ 0.2 (2) Formula T _m : Molten steel temperature when supplying metal oxide [° C.] W _g : Oxygen gas per unit molten steel from the molten steel bath surface to the upward blowing oxygen fire point Blowing amount [Nm ³ / min ・ T] Wherein removal of metal oxides containing chromium molten steel according to claim 1, wherein the supply amount W _A of metallic oxides when supplied to said (3) treating under conditions satisfying the formula Charcoal refining method [Equation 1] W _A : Supply amount of metal oxide [kg] W _m : Weight of molten steel [kg] (% Cr ₂ O ₃ ) _A : Chromium oxide concentration [%] [% C] _i : Metal oxide Molten steel carbon amount [%] at the start of supply (immediately before)