JPS61246312A - Method for controlling form of inclusion in molten steel in ladle - Google Patents

Abstract

PURPOSE:To decrease and suppress the inclusions in a molten steel effectively by blowing a CaO desulfurizing agent together with an inert gas to the molten steel which is deoxidized to stir and refine the molten steel then blowing an inert gas thereto and stirring the molten steel. CONSTITUTION:The CaO desulfurizing agent or Ca alloy is blown together with the inert gas through a lance to the molten steel which is deoxidized in the ladle to stir the molten steel. The non-metallic melt by the reaction of the non-metallic oxide (resulted product of desulfurization) contained in the molten steel and Ca or Ca alloy is thereby floated and is further fused with existing slag to form high-basicity slag. The inert gas is blown through a lance or a plug provided in the bottom of the ladle to stir the molten steel after the blowing and refining, by which the molten steel and the high-basicity slag are thoroughly stirred so as to contact with each other. The acceleration of the desulfurization, the floating of the inclusions in the molten steel and the capturing of the inclusions by the high-basicity slag are thus executed.

Description

[Detailed description of the invention] Industrial applications TECHNICAL FIELD The present invention relates to control of the form of inclusions in steel heated inside a ladle.

BACKGROUND OF THE INVENTION In general, molten steel produced in a converter, electric furnace, etc. contains a considerable amount of #203 and SiO2-based nonmetallic inclusions. These inclusions are broadly classified into three types, A, B, and C based on their composition, and the A and B types in particular have a high degree of inhibition of steel quality due to their characteristic morphology.

In addition, as a method for eliminating the quality inhibition of steel due to inclusions, many methods have been proposed in which a Ca alloy is added to molten steel containing the inclusions for refining. As a representative example of this, for example, Fe
A method of coating molten steel with basic slag of 0.04% or less and blowing Ca or a Ca compound through a lance using a neutral carrier gas (hereinafter simply referred to as A9 deoxidizing Ca injection), or a special method. As shown in 1987-48711, after molten steel is degassed to reduce active oxygen to 10 PPM or less, the pure amount of Ca is 0.05 kg/T or more, Ca/S
A method of injecting Ca or Ca alloy from a lance (hereinafter simply referred to as vacuum degassed Ca injection), etc. has been proposed so that the value is 0.05 to 0.080.

However, these methods either add A9 alloy to molten steel and perform strong deoxidation, or greatly reduce oxygen in the steel by vacuum degassing treatment, and then add Ca or Ca alloy to remove carbon dioxide.
Since a high yield of a is obtained, the cost of deoxidizing agent and degassing treatment becomes extremely high.

In addition, these methods have drawbacks such as when the desulfurization agent and Ca or Ca alloy are added and refining is completed, inclusions in the molten steel increase, resulting in a decrease in quality and a low desulfurization rate. have.

Problems to be Solved by the Invention The object of the present invention is to provide an excellent method for controlling the form of inclusions in ladle molten steel, which eliminates the above-mentioned drawbacks and can effectively reduce and suppress inclusions.

Means for Solving the Problems The present inventors have discovered that when controlling the form of inclusions in molten steel in a ladle, conventional methods require the addition of deoxidizing agents or degassing treatment, which increases costs. It was found that molten steel was conversely contaminated by the desulfurization agent or the oxidation products of Ca alloy powder.

Further, Ca in steel is unstable compared to other elements, and depending on the treatment method, it rapidly oxidizes and floats, so that the function of controlling the shape of inclusions newly formed in molten steel disappears. Based on these findings, in order to control the morphology of inclusions, it is necessary to suppress the loss of added Ca in steel, and to prevent inclusions generated by reactions caused by the injection of desulfurization agents mixed into molten steel or Ca alloys. It is important to effectively float and remove oxidation products caused by refractories, slag, and refractories.

Therefore, in the present invention, a quicklime-based desulfurization agent and powder of Ca alone or a Ca alloy are added to molten steel in a ladle for a predetermined period of time A.
Stirring and refining is performed while blowing together with inert gas such as r gas and N2 gas. Next, by blowing only an inert gas into the molten steel in the ladle for a predetermined period of time, the desulfurization refining process and the flotation separation of inclusions contained in the steel are extremely effectively promoted. By controlling the morphology of inclusions, it is possible to obtain a highly clean steel that is rendered harmless and has a low [S].

By injecting the desulfurizing agent, Ca alloy, etc., the non-metallic fusion products mixed in the molten steel (desulfurization products) and the non-metallic fusion products caused by the reaction between Ca or Ca alloy float to the surface, and the existing slag fuses with to form a highly basic slag.

After blowing and refining the powder, continuously blowing inert gas,
The molten steel and the high basicity slag are sufficiently stirred and brought into contact to promote desulfurization, float inclusions in the molten steel, and capture the inclusions with the high basicity slag.

This inert gas injection makes it possible to desulfurize and clean the molten steel at the same time, and also remove the [Ca] dissolved in the steel.
loss can be minimized.

Suppression of the disappearance of [Ca] dissolved in steel is achieved by injecting and refining Ca alone or powder of Ca alloys such as Ca-5i and Ca-AQ, and then eliminating inclusions that are newly generated due to elution of refractories, air oxidation, etc. It is important to control the morphology of Ca to C-based, and a [Ca] value of at least 20 PPM is required at the time of injection.

After the desulfurization agent and Ca alone or Ca alloy are injected for refining, the inert gas injection time is important. As shown in FIG. 1, the inert gas blowing conditions need to be 150 to 50 ONQ/min for 1 to 4 minutes.

If the blowing time is shorter than 1 minute, the inclusions will hardly float, and furthermore, desulfurization will not be possible due to insufficient stirring.

On the other hand, if stirring is continued for longer than 4 minutes, [
[Ca] is oxidized and disappears.

For this reason, the shape control function of [Ca] in the steel decreases, and the inclusions in the steel increase due to the inclusions generated by the elution of refractories or air oxidation during the process up to the injection of molten steel. and lead to quality deterioration.

By blowing the inert gas for 1 to 4 minutes, loss of [Ca] in the steel can be suppressed, and the molten steel can be desulfurized and cleaned at the same time. In this way, the present invention achieves unprecedented control over the form of inclusions and high cleanliness by blowing and refining the desulfurization agent and powder of Ca alone or Ca alloy, and stirring them together using an inert gas. Moreover, an excellent steel with low [S] can be obtained.

EXAMPLE An example of the method for controlling the form of inclusions in molten steel in a ladle according to the present invention will be described below.

When pouring molten steel refined in a converter into a ladle, a prescribed deoxidizing agent and ferroalloy are added to produce Al1-9i guild steel, for example, Al1-9i guild steel, or ■ to ■, as shown in Table 1. Like Si
- Obtain killed steel. After deoxidizing and adjusting the composition, a desulfurizing agent consisting of CaO powder mixed with 5 to 10% fluorspar is added to the molten steel at a concentration of 200 to 80% through a refractory-coated lance and a powder supply device.
0kg/170T pot. This desulfurizing agent is blown into A
The experiment was carried out using t gas as the carrier gas. Subsequently, 80 to 250 kg of Ca-5i powder was blown into the pot as a Ca source by the same means as described above to perform desulfurization and control of the morphology of inclusions.

After this, 1 liter of Ar gas was added from the ventilation plug provided at the bottom of the ladle.
It was supplied at a rate of 50 to 50 ONi/min, and stirring and refining was performed for 1 to 4 minutes. The compositions and blowing conditions of each of these are shown in Table 1, and their effects are compared with the conventional method in Figures 2 and 3.The results show that the water droplet has an extremely high desulfurization rate and is stable. In addition, the amount of steel debris caused by inclusions is greatly reduced,
Steel of extremely high quality was obtained.

In addition, this quality improvement is due to the effect of suppressing the loss of Ca added in the steel at the initial stage, and since the amount of Ca in the steel is maintained high, the effect of suppressing inclusions that are formed between the time of blow refining and the time of tundish injection is also sufficient. Met.

Effects of the Invention As described above, by using the method for controlling the shape of inclusions in molten steel in a ladle according to the present invention, it is possible to eliminate the presence of inclusions in molten steel without deforming and strengthening the molten steel, and without causing an increase in cost due to degassing treatment. You can easily control the shape of objects.

In addition, it is possible to obtain high-quality steel with low [S] and high cleanliness due to high desulfurization, which cannot be obtained by the conventional method of simply adding a desulfurization agent and Ca alone, or a Ca alloy, and has extremely excellent inclusions. This is a shape control method.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the index of inclusions (12.5 g or more) in molten steel in a tundish during inert gas stirring and continuous casting. FIG. 2 is a diagram showing the desulfurization rate in water droplet and conventional methods. FIG. 3 is a diagram showing the product waste removal index of the one-piece method and the conventional method.

Claims (1)

[Claims] C is added to the deoxidized molten steel through a lance together with an inert gas.
Inclusions of molten steel in a ladle, characterized in that an aO-based desulfurization agent and Ca or Ca alloy are injected, stirred and refined, and then an inert gas is blown in and stirred through the lance or a plug provided at the bottom of the ladle. Form control method.