JPS5896812A - Refining method by decarburization - Google Patents

Abstract

PURPOSE:To reduce the partial pressure of CO in a vapor phase part and to improve decarburization efficiency in a dilute decarburization method by blowing the diluting gas of a specific ratio of the content of gaseous oxygen to be blown into molten steel into the vapor phase in a furnace. CONSTITUTION:In the stage of dilute decarburization of steel, a diluting gas such as N2 and Ar or air at >=20% bottom blowing oxygen is blown from a furnace top into a vapor phase part in a decarburization period. Then decarburization efficiency is improved, and the time of the decarburization period and the unit of a reducing agent are decreased. In this method, if the % of Si which is a slag forming element is regulated to <=0.15% to regulate the amt. of the slag to be carried in to <=10kg/t-molten steel, the decarburization efficiency is further improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for further improving decarburization efficiency in a steel dilution decarburization method.

In general, if the temperature and content (Cr) of [C] in molten steel are constant, decarburization progresses as the partial pressure of CO gas in the gas phase that contacts the carbon in molten steel decreases. This CO gas partial pressure (hereinafter referred to as PC)
In order to lower the molten steel (abbreviated as O), the interface in contact with the molten steel is vacuumed, or diluent gas is blown in with oxygen.
This lowers PCO.

In the dilution decarburization method, a large amount of oxygen gas and diluent gas are injected into the molten steel from the bottom of the furnace or the side wall near the bottom of the furnace, so the contact interface between the dilution gas and the molten steel is very large. CO migrates to the surface, PCO is diluted, and membrane formation progresses easily. However, as mentioned above, the temperature in molten steel, [Cr)-
When a pco in equilibrium with is achieved, membrane production is stopped. In order to perform decarburization more efficiently, it is theoretically possible to inject a larger amount of diluent gas, but it is possible
Due to operational problems, it is impossible to blow in a large amount of the dilution gas (f) from the bottom of the furnace. In other words, sugura, shi of molten steel.

This increases the cooling effect of the gas, which has the opposite effect on decarburization. Furthermore, in order to avoid the problem of slush and sludge, it is necessary to relatively reduce the amount of oxygen blown, which leads to an extension of the refining time, which is undesirable as it significantly reduces productivity.

On the other hand, as already mentioned, since a large amount of gas is injected into the molten steel from the bottom of the furnace, the top surface of the molten steel is violently blown, and the contact interface between the gas phase and the molten steel on the top surface of the molten steel is also slightly blown. It can be easily estimated that the decarburization is considerably larger than vacuum decarburization, which does not contain any carbon.

If the PCO in this gas phase is lowered, P at the contact interface
It is thought that decarburization progresses more easily because the CO equilibrium is disrupted. However, in the old method, Pco # of this gas phase
Since the extraction from iKi1 steel is occupied by the dilution gas and CO gas that came out, basically the P in the dilution gas at the interface
Same as CO.

The present inventor estimates that if the PCO in the gas phase is further reduced, the ratio of oxygen spent on decarburization at the contact interface, that is, the decarburization oxygen efficiency will increase, and the gas phase is controlled by the atmosphere (Pco). As a result of conducting various experiments, it was found that decarburization was further promoted by blowing atmospheric dilution gas into the gas phase.

The present invention will be described in detail below with reference to specific examples.

Figure 1 shows the storage of S from the outer pipe of the double pipe tuyere installed on the bottom of the furnace @ wall.
Using an AOD furnace in which argon is injected into the molten steel through an inner pipe, a mixture of oxygen gas and argon as a diluent gas is injected into the molten steel. Air at a pressure of 3 to 10 kt/cs
The results show that the decarburization oxygen efficiency improves as the ratio with the bottom blown oxygen amount improves, both in the case of N2 and Ar and in the case of air. The ratio is almost saturated at 20-.

In other words, the gist of the present invention is to store s from the outer pipe of the double pipe tuyere,
In a method of decarburizing and refining f-sulfur by blowing a mixed gas of dilution gas and oxygen gas into molten steel from an inner tube,
This is a decarburization refining method in which at least 201 II of the amount of oxygen gas to be blown into the molten steel is injected into the gas phase in the furnace to dilute the atmosphere.

In the present invention, in addition to inert gases such as argon, the atmosphere diluting gases to be blown into the gas phase in the furnace include nitrogen, carbon dioxide gas, air, and well-known gases capable of lowering the Peg of hydrocarbon liquor. Any gas can be used.

Inert gases such as argon, carbon dioxide, and nitrogen are used as protective gases blown into the outer pipe of the double-pipe tuyere.

Water vapor or the like can be used, and other well-known gases such as inert gas such as argon, nitrogen gas, etc. can be used as the diluent gas blown from the inner tube. In addition to stainless steel, other steel types that undergo dilution decarburization can also be used.

In Figure 1, air has a greater effect than N2 and Ar because oxygen in the air reacts with the generated CO,
The effect of heat generation caused by
It is estimated that cleaning using an inert gas to promote the reduction of the temperature is also highly effective.

Next, a specific example is shown* 18 Cr-8N1 (8U8
304) When diluting and decarburizing stainless steel by blowing oxygen gas and argon from the inner tube of the double-tube tuyere installed on the side wall of the furnace bottom and argon from the outer tube, bottom-blown oxygen is used even during the decarburization stage. Amount 23 m”/T-5m of molten steel for 20 hours
The air from the molten steel is transferred from the top of the furnace to the gas phase at a pressure of 5 to 6 kp/
The results are summarized in Table 1.
As is clear from Table 1, by improving the decarburization oxygen efficiency, the decarburization period time and the required reducing agent consumption rate were both 92 to 9.
311G, and the amount of corrosion damage of large objects was reduced to 96-G compared to the conventional one due to the effect of time reduction.

As can be easily deduced from the detailed description of the present invention, in order to utilize the interface between the gas phase and the molten steel as widely and effectively as possible, the smaller the amount of slag floating on the molten steel, the more efficient it is. be. Therefore, the ingredients in the crude molten steel charged into the furnace, especially the slag-forming element [81]IG, are 0.15
By specifying the amount of slag to be 16 or less, and specifying the amount of slag brought in to be 10k)/less than one crude molten steel, the effect is further increased.

Table-1

[Brief explanation of the drawing]

Figure 1 shows an AOD furnace in which argon is injected as a protective gas from the outer pipe of a double-tube tuyere installed on the side wall of the furnace bottom, and a mixed gas of oxygen gas and argon as a diluent is injected into molten steel from the inner pipe. N is used as an atmosphere diluent gas from the top of the furnace during the decarburization period.
2 is a diagram showing the results of blowing Ar or air into the gas phase in the furnace at a pressure in the range of 3 to 10 #qI/l. Figure 1

Claims (2)

[Claims] (1) In a method of decarburization refining by injecting preservation gas from the outer pipe of a double-pipe tuyere and a mixed gas of dilution gas and oxygen gas from the inner pipe into molten steel, the air inside the furnace is 20% of the amount of acid 11gf injected into the molten steel by diluting the atmosphere into the phase.
- A method for refining arms and legs, which is characterized by infusing the above. (2)! (81) in steel is o, t 5% or less,
The decarburization refining method according to claim 1, wherein the amount of slag brought in is 10 kf/T-molten steel or less.