JPS63103017A - Refining method by blowing in converter - Google Patents

Abstract

PURPOSE:To improve the efficiency of decarburization in a low carbon region and to enhance the yield of iron by increasing the amount of oxygen blown at a prescribed concn. of carbon and reducing the amount of oxygen blown to below the amount in the early stage of decarburization before a decarburization reaction attains to a rate determining the feed of carbon. CONSTITUTION:In the early stage of refining in which the concn. of carbon in molten steel is high and all of oxygen fed is consumed for decarburization, a prescribed amount of oxygen is blown to refine the molten steel. At the time when the concn. of carbon is reduced to 0.5-0.6% by the progress of decarburizaton, the amount of oxygen blown is increased to violently agitate the molten steel. The amount of oxygen blown is then reduced to below the amount in the early stage of decarburization before the concn. of carbon is reduced to <=0.2% at which the decarburizaton reaction attains to a rate determining the feed of carbon.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a converter blowing method that improves decarburization efficiency in a low carbon region at the final stage of decarburization.

[Prior art] In the pure oxygen top-blown converter method, M cables are absorbed into the molten steel at the collision surface between the oxygen jet and the molten steel (hereinafter referred to as the fire point), and the carbon in the molten steel reacts with this oxygen. The molten steel is decarburized by the generation of carbon monoxide partial pressure. At this time, the decarburization rate increases as the decarburization reaction progresses. In the middle stage of decarburization, the speed at which carbon in the molten steel reaches the fire point is sufficiently high, and the decarburization reaction becomes rate-limiting in oxygen supply, so the decarburization efficiency approaches 100%.

However, as decarburization progresses further and the carbon concentration in the molten steel decreases, the amount of carbon that reaches the fire point decreases, and the decarburization reaction becomes rate-limiting for carbon supply. The carbon concentration at the boundary where the decarburization reaction becomes rate-limiting from oxygen supply to carbon supply (hereinafter referred to as transition carbon m
When the carbon concentration is lower than the carbon concentration (referred to as carbon concentration), the decarburization rate decreases, the decarburization efficiency decreases, and the amount of oxygen that does not contribute to decarburization increases. Therefore, iron oxide generated by the reaction between oxygen and iron in molten steel increases, resulting in a decrease in iron yield.

In particular, when blowing dephosphorized hot metal, a small amount of dephosphorizing agent is required and the amount of slag in the molten steel is small, making it possible to reduce manganese ore or chromium ore in the converter. In this case, not only the iron yield but also the manganese yield or chromium yield decreases.

In order to solve these drawbacks, conventionally, a mixed gas with a ratio of argon gas to oxygen gas of 1 to 2 is blown in a mixed gas furnace to reduce the partial pressure of carbon monoxide in the converter and reduce the carbon concentration to 0.
Technology to preferentially decarburize molten steel until the carbon monoxide decreases to 0.5%, and reduce the pressure inside the converter to approximately 100 torr using a vacuum pump, etc. to lower the partial pressure of carbon monoxide, giving priority to molten steel. A technology that decarbonizes fuel is adopted.

[Problems to be Solved by the Invention] However, when blowing is performed using a mixed gas of argon and oxygen, the cost of argon gas is high and the oxygen supply rate is low, so the blowing time is 10 to 50 minutes. % extension.

Further, when the inside of the converter is depressurized using a vacuum pump or the like, there are problems such as high equipment costs and increased heat dissipation due to the depressurization.

This invention was made in view of such circumstances, and
To provide a converter blowing method with high thermal efficiency without prolonging blowing time or increasing blowing and equipment costs when decarburizing with high efficiency in a low oxygen region and preventing a decrease in iron yield. The purpose is to

[Means for solving problems]

The converter blowing method according to the present invention performs oxygen blowing at a predetermined feed rate of 1fi, increases the amount of oxygen feed when decarburization progresses and decreases to a predetermined carbon concentration, and then the decarburization reaction supplies carbon. It is characterized by reducing the feed rate to below 1 m at the initial stage of blowing before it becomes rate-limiting.

Effect] In the present invention, when oxygen blowing is carried out at a predetermined amount of oxygen supply, decarburization progresses and the decarburization rate increases. Then, when a predetermined carbon content of 1Ir51 is reached, the feed Mm is increased to strengthen the stirring force. Thereafter, before the decarburization reaction becomes rate-determining for carbon supply, the feed weight is reduced from the initial stage of decarburization. In this way, by adjusting the WA section of the oxygen feed 1 according to the decarburization speed, the blowing time is not extended, the equipment cost is low, energy efficiency is high, and highly efficient decarburization in the low carbon range can be achieved. .

[Example] Examples of the present invention will be specifically described below.

In converter blowing, when the carbon concentration of molten steel is high, the decarburization reaction becomes the rate-limiting oxygen supply, and the supplied oxygen is approximately 100%
% consumed in decarburization. However, when decarburization progresses and the carbon concentration of the molten steel decreases, it is necessary to increase the stirring power of the molten steel in order to efficiently advance the decarburization reaction. For this reason, for example, when the carbon concentration reaches 0.5 to 0.6%, the amount of M fed is increased by 50 to 100% compared to the amount of oxygen fed at the initial stage of decarburization, thereby increasing the blowing pressure and stirring force of the molten steel. increase.

After that, as decarburization further progresses and the carbon concentration decreases, and the decarburization reaction becomes rate-limiting in carbon supply, the amount of oxygen that does not contribute to decarburization increases, oxidizing the effective components in the molten steel. For this reason, before the decarburization reaction reaches the carbon concentration that determines the rate of carbon supply, for example 0.2%, the amount of oxygen supplied is reduced to below the initial stage of decarburization. By controlling the amount of oxygen fed in this way, the decarburization efficiency in the low carbon region increases.

Next, the operation of this embodiment will be explained. First, molten steel is oxygen blown in a converter at a predetermined amount of oxygen. Then, when the carbon concentration of the molten steel reaches 0.5 to 0.6%, the amount of oxygen supplied is increased by 50 to 100%. This will increase the stirring power of the molten steel! 152 carbon reaction proceeds efficiently. after that,
Further decarburization progresses and the carbon concentration decreases, but when the carbon concentration is 0
．． Just before it reaches 2%, reduce the oxygen supply amount to less than the initial amount of decarburization. In this case, the amount of increase in excess oxygen in the molten steel is small. By simply adjusting the amount of oxygen fed in this way, the decarburization efficiency in the low carbon range increases and the yield of iron, etc. in molten steel improves.

Therefore, decarburization can be performed with high thermal efficiency and with high efficiency even in a low carbon range without prolonging the blowing time or increasing blowing and equipment costs.

Next, a specific example of converter blowing according to this embodiment will be described. Pre-treatment to reduce phosphorus content to approximately 0.01%
The molten pig iron was charged into a converter, and predetermined amounts of manganese oxide and chromium oxide were added as alloying components therein, and oxygen blowing was started. The feed rate 111ffi at this time was 35x103 Nm3/hour. Next, when the blowing progresses and the carbon concentration reaches 0.5%, the oxygen supply amount is increased by 45×103 Nm3/hour in specific example 1, and 55×103 Nm3/hour in specific example 2.
×10103N/hour. After that, the carbon concentration is 0
．． Shortly before the drop to 2%, the oxygen supply rate was reduced to 25 x 103 Nm'/h in both embodiments. In addition, the oxygen supply amount was kept constant at 35X10"Nm3 until the carbon concentration reached just below 0.2%, and then 25X
1 O3Nm3 was used as a comparative example. In addition, the first
The figure shows each blowing pattern. Next, the results of blowing under these conditions will be shown. FIG. 2 is a graph showing the relationship between carbon concentration and decarburization efficiency, with the horizontal axis representing the carbon concentration and the vertical axis representing the amount of decarburization per unit weight of oxygen efficiently supplied. According to this, it can be seen that the specific example has better decarburization efficiency than the comparative example at any carbon concentration. Also, send 1! Specific example 2, which has a high increase rate of II, has better decarburization efficiency than specific example 1. In Figure 3, the horizontal axis shows the carbon S degree at the end point of blowing, and the vertical axis shows the total iron concentration (total Fe concentration) such as Fed, Fe2O3, etc. in the slag, and the carbon concentration at the end point of blowing and the total Fe are plotted. It is a graph diagram showing a relationship. According to this, by lowering the carbon concentration to about 0.05%, the total Fe11
In contrast, in specific examples, the total Fe concentration is 20% or less, and in particular, in specific example 2, the total Fe concentration is about 10%. in this way,
In this specific example, the decarburization efficiency in the low carbon range is improved,
Iron yield increases.

[Effects of the Invention] According to the present invention, the amount of oxygen supplied is increased at a predetermined carbon concentration, and the amount is lowered to below the carbon layer at the initial stage of decarburization before the decarburization reaction becomes rate-determining the carbon supply. It can improve the decarburization efficiency and increase the iron yield. Therefore, it is possible to decarburize with high thermal efficiency and with high efficiency even in a low carbon range without prolonging the blowing time or increasing the blowing and equipment costs.

[Brief explanation of the drawing]

Figure 1 is a graph showing the oxygen supply pattern, Figure 2 is a graph showing the relationship between carbon concentration and decarburization efficiency, and Figure 3 is a graph showing the relationship between carbon 11 degrees at the end of blowing and total Fe. It is a diagram.

Claims (1)

[Claims] Oxygen blowing is carried out at a predetermined amount of oxygen supply, and when decarburization progresses and the carbon concentration decreases to a predetermined level, the amount of oxygen supply is increased. A converter blowing method characterized by reducing the amount of acid to below.