JPS59145718A - Blowing method of gas in nozzle for refining molten metal - Google Patents

Abstract

PURPOSE:To extend the service life of a bottom blowing tuyere and to reduce the cost of the gas used by using the gas contg. a large amt. of non-oxidative gas or reducing gas as the stirring gas to be blown from the bottom after the mid-period of combined blowing. CONSTITUTION:Gas contg. 40-100vol% non-oxidative gas such as Ar, N2 or the like and/or reducing gas such as CO, methane, propane or the like is used as the stirring gas to be blown after the mid-period of blowing in a combined blowing method wherein oxygen is top blown with an upper lance 7 to the molten iron 5 and slag 6 in a converter 1 consisting of a shell 2 and refractories 3 and the stirring gas is blown from the tuyere 4 in the bottom, whereby the wear of the tuyere 4 is suppressed while the cost of the stirring gas is taken into consideration and the service life of the tuyere is made at least equivalent to the life of the converter. It is further preferable for the decreased temp. of the tuyere 4 hence decreased wear thereof to increase the cooling capacity by blowing the stirring gas to be blown after the mid-period of blowing at a rate of 1-3 times the rate of blowing before the mid-period of blowing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention improves the service life of the bottom blowing tuyere in the top and bottom blowing method (combined blowing method) of molten metal, and makes it possible to use the converter instead of the furnace. The present invention relates to a method for blowing gas, the purpose of which is to make the gas used cost-effective.

The top-bottom blowing method uses a converter (as shown in Figure 1).
Oxygen is blown upward from the top of the molten iron (5) and slag (6) in the converter (1) using a lance (7), and stirring gas is blown through the tuyere (4) provided at the bottom of the converter (1). This is a refining method that strengthens the stirring and mixing of molten iron and slag, thereby promoting the reduction of iron oxides remaining in the slag, improving the iron yield, increasing the blowstop Mn, and dephosphorizing. Note that (2) 1 in the figure is an iron shell, and (3) is a refractory. An example of the separate notice provided at the bottom of the converter (1) is shown in FIG. 2. (8) is plowed with a gas box made of iron plate, (9)
) is a non-porous refractory (for example, MgO).

A large number of pores (10) are provided in the MgO-" CaO-based refractory, Mg0-C-based refractory) so that a predetermined flow rate of gas can be injected into the furnace. Note that (3') in the figure indicates the permanent tension (6 are lined refractories.

In addition, in the conventional composite blowing method, this tuyere (4)
CO2, A as the type of gas injected for stirring molten iron.
r, N2. Oxygen, air, etc. were each used in their own form. However, although using an expensive gas such as Ar alone is preferable in terms of tuyere life, it is disadvantageous in terms of cost, and CO2 has been mainly used.
．． Oxygen was also used in some cases.

However, when such an oxidizing gas is used as a bottom blowing gas, the wear and tear of the tuyeres is severe, and the life of the refractory (which must have a lifespan equal to that of the refractory lining the converter) is extremely high. -I couldn't do it.

Therefore, there is a problem that the superiority of the above-mentioned refining method is lost, and improvements to this problem have been desired.

Therefore, in order to improve the service life of the tuyeres, the inventors studied the wear rate and wear mechanism, and found that there are cases in which an oxidizing gas such as CO2 is used as the bottom blowing gas, and cases in which Ar
, I learned that the mechanism and rate of wear are different when using a non-oxidizing gas such as N2 or a reducing gas such as CO. In this case, a slag layer with high FeO content (wt% of the slag component is FeO: 50%, M
MgO: 35%, MnO: 15%) is generated to a thickness of 1.0 to 1.5 mist, and this generated slag erodes MgO and carbon, which are the main components of the tuyere refractories, resulting in wear and tear. proceed.

On the other hand, in the tuyeres injected with non-oxidizing gas such as Ar or N2 or reducing gas such as CO, the above-mentioned high-Fe
No wear was observed due to O slag pressure, and only wear was caused by converter slag. As a result, the difference in wear rate due to the difference between high FeO slag and converter slag is that the latter is approximately 60 to 70% slower;
Therefore, it will greatly affect the service life of the tuyere! Knew. However, Ar, which has the advantage of slowing down the wear rate of the tuyere, is too expensive to use alone, and the use of N2 alone increases [N]7 in the steel, resulting in poor product quality. There are things I need to improve on retention.

In line with the above findings, the inventors further developed the
As a result of considering the compositional changes in molten iron during blowing as shown in the figure, as well as the molten iron temperature, we found that the oxidation reaction of molten iron by CO2 when CO2Y is used as the bottom blowing gas does not result in the presence of Si02 in the high Fe0 layer. Since 81 is not present in the molten iron when the temperature of the molten iron becomes the highest, it was discovered that this phenomenon occurs after the middle stage of blowing, and the present invention was developed based on this knowledge.

That is, the present invention provides a composite blowing method in which oxygen is blown upward from the top of the molten metal using a lance and stirring gas is blown from the bottom, and the stirring gas blown after the middle stage of the blowing is replaced by a non-oxidizing gas and/or a stirring gas.
Alternatively, it is a method of blowing gas into a molten metal refining nozzle, characterized in that the gas contains 40 to 100% of reducing gas by volume.

In addition, the amount of stirring gas blown after the middle stage of the blowing is
Another feature is that the amount of gas injected is 1 to 6 times the amount of gas in the first stage of blowing.

The present invention aims to improve the service life of the bottom blowing tuyeres in the combined blowing method, and to make it possible to use at least one converter. For example, use CO2, which is inexpensive, and take into consideration that the oxidation reaction of the molten iron due to CO2 occurs as explained earlier after the middle stage of blowing, and in order to avoid this, change the type of blowing gas to cause the oxidation reaction. It contains 40 to 100% by volume of a non-oxidizing gas or a reducing gas, or two of these gases.

In this case, the selection of the gas type, the mixing ratio of the components, etc. must be determined with consideration given to the quality of the steel product to be obtained.

In addition, the reason why the lower limit of the mixing ratio of the above-mentioned non-oxidizing gases such as Ar and N2 and/or boiling reducing gases such as CO, methane, and propane as well as the punching gas is set at 40% is that the lower limit is 40%. This is because the effect of improving the useful life of the tuyere, which is the objective of the present invention, cannot be achieved significantly.

Furthermore, in the method of the present invention, it is preferable to increase the amount of blown gas by 1 to 6 times at the final stage of blowing in order to achieve the purpose of the present invention. This is because the temperature of the working surface of the tuyere refractory is lowered at the final stage of blowing, when the temperature is highest, so oxidation by high-temperature molten iron is reduced. The reason why the upper limit of the gas injection amount is set to six times is because there is no need to exceed this.

Table 1 below shows examples of the method of the present invention and comparative examples of the conventional method.

In Table 1, the average wear rate of the lining is 1.1 gourd/ch.
In the following cases, it is possible to use tuyeres between the converter and the furnace. In addition, the total cost ratio of tuyere and gas is shown for reference, but the method of the present invention is advantageous in terms of cost in all embodiments compared to the case of using only Ar gas and using one tuyere for one furnace. It is understood that Thus, according to the method of the present invention, it is possible to use the tuyere for one furnace without using the entire amount of expensive Ar (although it is possible to use inexpensive gas for one furnace).

[Brief explanation of the drawing]

Figure 1 is an explanatory longitudinal cross-sectional view of a top-bottom blowing converter, Figure 2 is a vertical cross-sectional view showing an example of nine tuyeres in a top-bottom blowing converter, and Figure 6 is a diagram showing changes in components in molten iron during blowing. , FIG. 4 is a diagram showing the temperature of molten iron during blowing. Agent: Patent Attorney: Mitsu Kimura Term: Muneharu Sasaki Figure 1- Figure 2 Figure 4 Collection ML Octopus (k$)

Claims (2)

[Claims] (1) In the combined blowing method, in which oxygen is blown upward from the top of the molten metal using a lance and stirring gas is blown from the bottom, the volume of the stirring gas, non-oxidizing gas and/or reducing gas that is blown in from the middle stage of blowing onwards. The gas should contain 40% to 100% of
Characteristic method of blowing gas into a molten metal refining nozzle. (2) In the molten metal refining nozzle according to claim 1, the amount of stirring gas blown after the middle stage of the blowing is 1 to 3 times the amount of gas blown before the blowing. How to blow gas.