KR102089131B1 - Method for manufacturing high clean steel - Google Patents

Abstract

Disclosed is an invention related to a method for manufacturing highly clean steel. Method of manufacturing a high-clean steel of the present invention includes the step of laminating molten steel refined in a converter to a ladle; And a step of adding quicklime and millscale to the molten steel; and the millscale is introduced at 0.1 to 0.4 kg per ton of the molten steel.

Description

Manufacturing method of high clean steel {METHOD FOR MANUFACTURING HIGH CLEAN STEEL}

The present invention relates to a method for manufacturing high-clean steel. More specifically, the present invention relates to a method for manufacturing high-clean steel having excellent inclusion removal effect through slag viscosity control using mill scale, a by-product of the rolling process.

The ultra-low carbon steel used for automotive exterior materials requires a high level of surface quality. In order to cope with these demands, it is necessary to control the number of inclusions, which are impurities that are essentially generated in the steelmaking process, when manufacturing ultra-low carbon steel for automotive exterior materials.

If the inclusions cannot be removed in the steelmaking process, clogging occurs in the performance process and defects are caused by the inflow of the inclusions. Therefore, it is necessary to efficiently remove these inclusions.

Background art of the present invention is disclosed in Republic of Korea Patent Publication No. 10-0215105 (August 16, 1999, the name of the invention: method of manufacturing high-clean steel).

According to an embodiment of the present invention, it is to provide a method for producing high-clean steel having excellent slag viscosity control effect in molten steel and inclusion removal effect in molten steel.

According to an embodiment of the present invention, to provide a method for manufacturing a high-clean steel that is excellent in the effect of improving the quality of molten steel and can prevent nozzle clogging in a continuous casting process.

One aspect of the present invention relates to a method for manufacturing high-clean steel. In one embodiment, the method of manufacturing high-clean steel comprises: stepping ladle refined molten steel in a converter; And a step of adding quicklime and millscale to the molten steel; and the millscale is introduced at 0.1 to 0.4 kg per ton of the molten steel.

In one embodiment, the mill scale may include hot rolled mill scale powder generated in a hot rolling process.

In one embodiment, the quicklime may be added 0.2 to 0.5 kg per ton of the molten steel.

In one embodiment, the method of manufacturing a high-clean steel comprises the steps of bubbling a molten steel in which the quicklime and mill scale are added in a bubbling stand to control the temperature and dissolved oxygen of the molten steel; Transferring the bubbling molten steel to a vacuum degassing (RH) facility to process the vacuum degassing; And continuously casting the vacuum degassed molten steel.

When applying the high-clean steel manufacturing method of the present invention, the slag viscosity control effect in molten steel and the removal effect of inclusions in molten steel are excellent, thereby producing high-quality molten steel and preventing nozzle clogging during the continuous casting process.

1 relates to a method for manufacturing high-clean steel according to one embodiment of the present invention.
Figure 2 is a comparison of the removal efficiency of inclusions, according to the difference in the viscosity of slag in the molten steel.
3 is a graph showing a change in the viscosity of slag according to an increase in iron oxide content in molten steel slag.
4 is a graph showing an increase in iron oxide content and a recovery rate of aluminum in slag according to a change in the input volume of molten steel mill scale.
5 is a photograph showing a surface defect of a comparative example high-clean steel product for the present invention.

Hereinafter, the present invention will be described in detail. At this time, in the description of the present invention, when it is determined that the detailed description of the related known technology or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted.

In addition, terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to a user's or operator's intention or practice, and thus the definition should be made based on the contents of the present specification describing the present invention.

High clean steel  Manufacturing method

One aspect of the present invention relates to a method for manufacturing high-clean steel. 1 relates to a method for manufacturing high-clean steel according to one embodiment of the present invention. Referring to Figure 1, the high-clean steel manufacturing method (S10) molten steel step; And (S20) quick lime and mill scale input step; includes. More specifically, the method for manufacturing the high-clean steel comprises: (S10) stepping a molten steel refined in a converter into a ladle; And (S20) adding quicklime and millscale to the molten steel.

Meanwhile, in the present invention, “extremely low carbon steel” may be a steel type containing 50 ppm or less of carbon (C). For example, it may be a steel type containing 30ppm or less.

Hereinafter, a method for manufacturing a high-clean steel according to the present invention will be described in detail step by step.

(S10) Yonggang  Course Level

The above step is a step of elevating molten steel refined in a converter into a ladle. In one embodiment, the molten iron can be charged to the converter, oxygen is blown and decarburized to prepare molten steel, and the ladle can exit.

(S20) quicklime and Millscale  Input phase

The step is a step of injecting quick lime (CaO) and millscale to the molten steel.

In one embodiment, the quicklime is included for the purpose of controlling slag basicity in desulfurization and molten steel. In one embodiment, the quicklime may be added 0.2 to 0.5 kg per ton of the molten steel. The control effect of slag basicity in the desulfurization and molten steel under the above input conditions may be excellent.

In one embodiment, the mill scale refers to an iron oxide film formed on a steel surface during hot rolling or cold rolling, and iron oxide (FeO, Fe ₃ O ₄ And Fe ₂ O ₃ ) as a main component. In one embodiment, the mill scale powder, hot rolled mill scale powder or the like may be used.

Also, the “inclusion” may include sulfide inclusions and oxide inclusions. In one embodiment, the sulfide inclusion may include a sulfide-based compound and a compound such as MnS. In one embodiment, the oxide inclusions may include deoxidation products, oxides precipitated during the temperature drop and solidification process of molten steel, various foreign materials such as various slags, steelmaking raw materials, and refractory pieces. For example, the oxide inclusion may include a silicate-based compound and an alumina-based compound. For example, it may be an alumina-based compound.

On the other hand, inclusion removal efficiency is highly related to the viscosity of slag in molten steel. Typically, the inclusion removal time (τ) can be expressed by Equation 1 below:

[Equation 1]

In Equation 1, the ΔC utilizes a state diagram of CaO-Al ₂ O ₃ -SiO ₂ which is known to represent the amount of change in the removal force of inclusion removal between the saturated slag (Csat) and the initial slag (Co). ΔC can be calculated.

In addition, when applying the same temperature and the same inclusion size when removing the inclusion, Equation 1 may be represented by Equation 2:

[Equation 2]

In Equation 2, η and ΔC are as defined in Equation 1.

Referring to Equation 2, it can be seen that the inclusion removal time τ is proportional to the viscosity η of the slag, and therefore, in order to reduce the inclusion removal time τ, the viscosity of the slag η must be lowered.

2 is a comparison of the removal efficiency of inclusions according to the difference in the viscosity of slag in molten steel. Referring to FIG. 2, in the case of a high-viscosity slag, the reaction area between the inclusion and the slag is small, which is disadvantageous for inclusion absorption, while in the case of a low-viscosity slag, the reaction area between the inclusion and the slag increases, which is advantageous for inclusion absorption and thus removal efficiency. This can increase.

3 is a graph showing a change in viscosity of slag according to an increase in iron oxide content in molten steel slag. Referring to Figure 3, it can be seen that the viscosity of the slag is inversely proportional to the iron oxide (FeO) content. That is, when the iron oxide content in the slag increases, the viscosity of the slag decreases, and when the iron oxide content decreases, the slag viscosity increases.

Iron oxide (FeO), the main component of the mill scale, reacts with the aluminum (Al) component in molten steel to recover aluminum.

In one embodiment, the mill scale is 0.1 to 0.4 kg per ton of the molten steel. When the mill scale is less than 0.1kg, it is difficult to secure the effect of lowering the viscosity of molten steel slag, and surface defects of steel products and nozzle clogging may occur during continuous casting, and when it exceeds 0.4kg, iron oxide of slag and aluminum in molten steel The aluminum recovery rate may decrease rather by reacting as follows:

[Equation 3]

3 FeO + 2 Al → Al ₂ O ₃ + 3 Fe

4 is a graph showing the increase in iron oxide content and the aluminum recovery rate in the slag according to the change in the input of the molten steel mill scale. Referring to the results of FIG. 4, it can be seen that when the mill scale is added in excess of 0.4 kg, iron recovery efficiency of the slag reacts with aluminum in the molten iron and aluminum in the molten steel as follows.

Referring to FIG. 1, in one embodiment of the present invention, the method for manufacturing high-clean steel comprises: (S30) molten steel bubbling treatment step after the quick lime and mill scale input step (S20); (S40) vacuum degassing step; And (S50) continuous casting step; may further include.

(S30) Yonggang Bubbling  Processing stage

The step is a step of controlling the temperature and dissolved oxygen of the molten steel by bubbling the molten steel in which the quicklime and mill scale are added in a bubbling stand.

(S40) Vacuum Degassing  Processing stage

The step is a step of transferring the bubbling molten steel to a vacuum degassing (RH) facility to process the vacuum degassing.

(S50) Continuous casting step

The step is a step of continuously casting the vacuum degassed molten steel.

When applying the high-clean steel manufacturing method of the present invention, the slag viscosity control effect in molten steel and the removal effect of inclusions in molten steel are excellent, thereby producing high-quality molten steel and preventing nozzle clogging during the continuous casting process.

Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, this is provided as a preferred example of the present invention and cannot be interpreted as limiting the present invention by any means.

Example  And Comparative example

Example

The molten steel refined in the converter was discharged to the ladle, and quicklime (0.2 to 0.5 kg per ton of molten steel was added) and hot rolled mill scale (0.3 kg per ton of molten steel) were added to the molten steel. The molten lime and the mill-scale molten steel are bubbled in a bubbling stand to control the temperature and dissolved oxygen of the molten steel, and the bubbling molten steel is vacuum degassed (RH) equipment. After transferring, the vacuum degassing treatment was performed, and then the vacuum degassed molten steel was continuously cast to prepare a slab.

Comparative example  One

A slab was prepared in the same manner as in Example 1, except that 0.45 kg per ton of molten steel was added to the hot-rolled mill scale.

When preparing the high-clean steel of Examples and Comparative Examples 1, the content (% by weight) of iron oxide (FeO) in the slag and the aluminum recovery rate (% by weight) in molten steel are measured and are shown in Table 1 below.

Referring to the results of Table 1, it was found that when the mill scale input amount of the present invention was applied, the iron oxide content in the slag was increased, and the recovery rate of the aluminum component in the molten steel was excellent. On the other hand, in the case of Comparative Example 1 in which the present invention was applied in excess of the mill scale input, it was found that the inclusion removal efficiency was lowered than in the above Example.

5 (a) below shows the surface defects of a conventional high-clean steel product (Comparative Example 2) manufactured without introducing the mill scale of the present invention, and FIG. 5 (b) shows the surface defects of Comparative Example 2 This is an enlarged photo of the site. Referring to FIG. 5, it can be seen that in Comparative Example 2 of the present invention, a steel scab defect occurred on the product surface, and the surface quality was deteriorated.

Simple modifications or changes of the present invention can be easily implemented by those skilled in the art, and all such modifications or changes can be considered to be included in the scope of the present invention.

Claims (4)

Step of ladle the refined molten steel in the converter;
Adding quicklime and millscale to the molten steel;
Controlling the temperature and dissolved oxygen of the molten steel by subjecting the molten lime and the mill scale to the molten steel in a bubbling stand;
Transferring the bubbling molten steel to a vacuum degassing (RH) facility to process the vacuum degassing; And
Containing; continuously casting the vacuum degassed molten steel;
The quicklime is added 0.2 ~ 0.5kg per ton of the molten steel,
The mill scale is a method of manufacturing high-clean steel, characterized in that 0.1 ~ 0.4kg per ton of the molten steel.
According to claim 1,
The mill scale, high-clean steel manufacturing method characterized in that it comprises a hot-rolled mill scale powder generated in the hot rolling process.
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