JPS5822318A - Refining process for molten steel - Google Patents

Abstract

PURPOSE:To shorten reducing and desulfurizing period and to prolong the life of a furnace-body as well as to reduce the amount of blowing gas by means of tapping the molten steel into a laddle in a short time, after doxidizers are added in the decarburization-refining for molten steel. CONSTITUTION:At the refining etc. of stainless-steel by dilute decarburization, molten steel is agitated by blowing inert gas thereinto immediately after finishing decarburization, and simultaneously deoxidizers are added. Then, the molten steel is tapped into a laddle in the period less than three minutes. After the molten steel is inert gas-treated at least five minutes, said steel is left as it is and is cast. Strong agitation between the slag and the metal in the tapping stream at a tapping process may be generated by this process, thereby carrying out the reducing reaction effectively. Further, the melted loss for refractory material is prevented, and the inert gas-amount brown into the furnace in order to promote the reducing reaction may be economized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for reduction refining or desulfurization refining of molten steel after completion of decarburization refining.

Decarburization refining methods for molten steel, such as MuOD (MurgonOxy
The biggest problem in the stainless steel refining method by dilution decarburization, typified by the Gen I) @eaburlzatlan method, is how to reduce the cost of refractories and inert gas.

As shown in Figure 1, in the AOD method, a mixed gas of oxygen gas and inert gas is blown into the converter from nine tuyeres 3 attached to the bottom side wall of the converter 2 containing molten steel 1, so the energy for stirring the molten steel is extremely large. For this reason, the surface of refractories that come into contact with molten steel is violently washed by the high-temperature molten steel, resulting in extremely rapid wear and tear.Although the quality of refractories has been improved in recent years, and the operating method of the AOD method has also made significant progress. , which is far from the 1,000 or more cycles that is the furnace body lifespan of a common steel converter.

In order to extend the life of the furnace body as much as possible, it is necessary to shorten the one-heat refining time as much as possible and to omit the period in which refractories are most likely to be eroded during the one-heat refining process.

As a very general method to know the amount of refractories that have been eroded, for example, in a MOD furnace, it is generally Mg0-C.
Since a refractory of the slag or MgO-CaO type is used, it is sufficient to calculate the amount of increase in MgO in the slag during each refining process.

Using this method, Mg in the slag during each refining process is
Figure 2 shows the amount of increase in O. As is clear from this figure, M in the slag during the reduction period and desulfurization period after the completion of decarburization.
A significant increase in the amount of gO is observed. Therefore, it is expected that the erosion of refractories will be significantly reduced if the reductive desulfurization stage can be omitted, and by shortening the refining time, it is expected that the amount of inert gas injected during this period will be significantly reduced. Based on this idea, the inventors repeated various experiments, and as a result, they were able to significantly shorten the reductive desulfurization period, significantly extend the life of the furnace body, significantly reduce the cost of refractories, and reduce the amount of blown gas by shortening the refining time.・He developed a method for refining molten steel that enables significant reductions.

The present invention will be explained in detail below based on an example in which the present invention is applied to the AOD method.

Hereinafter, an example in which the method of the present invention is applied to an AOD method and a conventional MuOD refining method will be compared and explained with reference to FIG. Figure 3 1 shows the conventional AOD method, in which the ratio of oxygen and alponic injected into the rounding process is changed according to the changes in the amount of carbon in the steel to efficiently decarburize the carbon in the steel. Decarburization is performed to prevent oxidation, but generally the chromium in steel is 2-
Because it is oxidized before and after, 1s solvent (CaO etc.) is used after decarburization.
and a reducing agent (F.-81, etc.) were added, and the molten steel was stirred by inert gas injection K for an appropriate period of time to oxidize and reduce nine chromium, and desulfurization was performed using a solvent added at the same time as the reducing agent. It was later produced.

On the other hand, in the present invention, as shown in Fig. 3 bK, immediately after the decarburization is completed, an inert gas (such as alponic gas) is injected into the molten steel, and a reducing agent (F.-81, etc.) is added while stirring the molten steel. After dispersing the agent and making it easier to dissolve, the steel is tapped. Note that it is desirable to continue stirring the molten steel for 0.5 to 1 minute between the end of reducing agent addition and the time of steel tapping. This is particularly important in the reduction process.

Therefore, the time required for this step must be kept as short as possible.

In the present invention, the time from the addition of the reducing agent to the start of steel tapping is limited in relation to the progress of the reduction reaction, in other words, the reduction rate. That is, it was found that when 3 minutes or more elapsed after the addition of the reducing agent, the reduction reaction rapidly proceeded within a short period of time.

Therefore, during this period, the melting loss of the refractory is particularly large.

In the present invention, slag is heated so that it does not come into contact with refractories, especially when the slag is in a period of high corrosion of large objects. That is, the steel is tapped into a ladle within 3 minutes after adding the reducing agent. In this tapping process, a strong stirring action between the slag and metal is obtained in the tapping stream, and the reduction reaction proceeds extremely efficiently, and the content of chromic acid in the slag is lower than that in the conventional method. It drops to almost the same level as at the end of the reduction period. In other words, by tapping the steel within 3 minutes after adding the reducing agent, it is possible to prevent corrosion of the refractory and achieve a highly efficient reduction reaction, and also to save on the inert gas that would normally be blown into the furnace to promote the reduction reaction. .

The molten steel contained in the ladle is injected with inert gas (alpha) for at least 5 minutes after tapping for the purpose of further supplementary reduction and, if necessary, slight composition adjustment and temperature control.
Continuous casting or ingot casting is performed after standing with blowing (gas, etc.).If standing with blowing of arunone gas after tapping is less than 5 minutes, the reduction reaction will be insufficient, and additions may be made to adjust the composition. The temperature of the molten steel in the ladle after the completion of tapping is set so that the casting temperature is maintained even if the alloy etc. are not uniformly melted and the inert gas is blown for 5 minutes or more.

Further, the amount of inert gas blown into the ladle is desirably 247 m1n- or more.

In the present invention, if a solvent such as CaO is added together with a reducing agent after decarburization is completed, desulfurization refining can be performed simultaneously in addition to reduction refining from K. However, if this solvent is added all at once after the decarburization is completed, the temperature of the molten steel will be lowered, so it will be necessary to keep the temperature high. This is undesirable from the viewpoint of corrosion of the refractory, and the desulfurization reaction may not proceed sufficiently at low temperatures.To prevent this, some or all of the solvent should be added before the decarburization is completed. It is important to preheat it. Moisture brought in by the solvent can be removed in advance from TakoreK.

With the method of the present invention, it takes approximately 1 hour from the end of decarburization to the start of steel tapping.
What used to take 5 minutes could be shortened to 3 minutes or less, and as a result, the refractory corrosion index could be reduced to about 50, compared to 100 for the conventional method. 11 The consumption index of inert gas such as aldine gas consumed from the end of decarburization to the start of casting was also reduced to 80 compared to 100 for the conventional method.

An example of decarburization refining of stainless steel will be shown below.

Example 1 After completion of decarburization, an amount of Fs-81 required for reduction was added, and 3 minutes after the addition, the steel was tapped into a ladle.

Example 2 After the completion of decarburization, argon gas is injected into the molten steel and the amount necessary for reduction is maintained?・-81 was added and 1 minute after addition, the steel was poured into a ladle and the steel was poured out.

Implementation 9113 Ca as part of the amount of solvent required for desulfurization before the completion of decarburization.
O was added, and after the decarburization was completed, while alginic gas was blown into the molten steel, the remaining CaO and the amount of Fe-8t necessary for reduction were added, and 1 minute after the addition, the steel was tapped into a ladle.

Example 4 Ca as part of the amount of solvent required for desulfurization before the completion of decarburization
O was added, and after decarburization, argon gas was blown into the molten steel while the remaining CaO and the amount of F-81 necessary for reduction were added, and 1 minute after the addition, the steel was tapped into a ladle. . Alu F7 gas was blown into the ladle self-melting steel for 5 minutes and then continuous casting was performed.

Figure 1 shows the Cr yield and product composition in each embodiment and the conventional example, and Figure 4 shows the Cr yield in the embodiment 3 and the conventional example.
8 shows the transition of r yield and molten steel.

Table 1

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the AOD method jIII11, Figure 2 is a diagram showing the refractory erosion amount index at each 1iK of refining,
Fig. 3 1 is an illustration of the normal AOD method, b is an explanatory diagram of the AOD method to which the present invention is applied, Fig. 4 1 is a diagram showing the transition of Cr yield and S in molten steel in the conventional method, and Fig. 4 C of Example 3 of the present invention
It is a figure showing the transition of r yield and molten steel 8. Rod 1 time 2nd figure I I f 4th C0) 10 20 3θ J5θ Do θ time (minutes) 1l to 2o 3o M jθ
Same amount at lθ now)

Claims (4)

[Claims] (1) A method for refining molten steel that aims at tapping the steel into a ladle within 3 minutes after adding the reducing agent. (2) A method for refining molten steel according to claim 1, characterized in that inert gas is injected simultaneously with the addition of a reducing agent. (3) A method for refining molten steel according to claim 1 or 2, characterized in that a solvent is added. (4) Jli! The method for refining molten steel according to claim 1, 2, or 3, characterized in that after tapping the steel into a ladle, the steel is allowed to stand for at least 5 minutes with inert gas blowing, and then cast.