KR20010011732A - Refining method and porcelain anamelling steel manufacturing by it - Google Patents

Abstract

PURPOSE: A method for refining steel for porcelain enamel containing a high oxygen content and steel for porcelain enamel manufactured by the same are provided to prevent refractories erosion and provide steel for porcelain enamel containing a high oxygen content of which total oxygen is high by adding Mn and oxidizing the molten steel. CONSTITUTION: In a method for manufacturing steel for porcelain enamel, a molten steel is injected into a Tundish and continuously cast after the refining process in which a molten steel in a ladle is carburized and oxidized in RH. The molten steel in a ladle is comprised of a constituent of which oxidizing power is lower than that of Mn. The oxidization is carried out within the range of dissolved oxygen of 250 to 280 ppm by putting Mn into the molten steel. The steel for porcelain enamel has 300 to 400 ppm of total oxygen, and deoxidized by Mn.

Description

REFINING METHOD AND PORCELAIN ANAMELLING STEEL MANUFACTURING BY IT}

The present invention relates to a steel used as a base steel sheet of the enamel processing product, and more particularly, a method for refining high-oxygen enamel steel with high total oxygen in the final steel by Mn deoxidation, and the enamel steel produced by the refining method. It is about.

Generally, a product manufactured by applying inorganic glaze to a steel sheet and firing it at a high temperature is called enamel steel, and this product has the characteristics of being beautiful and excellent in corrosion resistance, such as glass, with the strength of metal. Enamel steel is mainly used for steel furniture and building exterior materials.

Fish scale is considered to be the most important property in the Enamel River. The fish scale refers to a defect in which the enamel layer is peeled off in the shape of fish scales on the surface of the steel sheet after enameling the steel sheet. Fish scale is a defect caused by hydrogen, and the solid solution of hydrogen is increased because the temperature of steel sheet is high during enameling process, but since the temperature is low after firing process, hydrogen dissolved in steel sheet diffuses to the surface to form enamel layer. Destroys and exits into the atmosphere.

In order to prevent fish scale defects, it is known that a space for absorbing hydrogen in the steel is required, that is, a large amount of (1) precipitates or (2) oxides are formed in the material.

(1) A technique for securing fish resistance with precipitates is to precipitate titanium sulfide (JP-A-56-51553), titanium carbide, boron nitride, etc., and the method of managing precipitates by controlling steel design and manufacturing conditions The technology is concentrated.

(2) Steel grades having fish resistance with oxide are usually called high oxygen enamel steel. High oxygen enamel steel is known to be good for fish resistance when the total oxygen is higher than 250ppm, the amount of oxide increases. Therefore, molten steel refining technology is the most important because it must be cast in a state of high dissolved oxygen.

The enameled steel is very low carbon (C: 0.005% or less), which is in consideration of formability. Therefore, the enamel steel decarburizes the molten steel refined in the converter to ultra low carbon in the RH refining process (see FIG. 1). Al and Si are used as a deoxidizer.

However, these deoxidizers have many disadvantages in that they are applied as deoxidizers of high oxygen enamel steel. Al deoxidizer has very high affinity with oxygen, so it is easy to adjust to the target range of oxygen in molten steel, but since a large amount of deoxidation product, alumina (Al ₂ O ₃ ) is present in molten steel, it blocks the nozzle in the continuous casting process. In addition, alumina is a needle-like hard structure, which is not directly drawn together with the material during rolling, which is a direct cause of surface quality deterioration. When adjusting the oxygen concentration in molten steel with Si, since Si bond rate (affinity) with oxygen is much slower than that of Al, unoxidized Si components remain in the molten steel until casting is completed, and Si is an element that degrades the plating property. There is a disadvantage in reducing enamel when remaining in the material. In addition, since SiO ₂ is rapidly removed in the RH refining process because of the high flotation separation rate, high dissolved oxygen was required in the tundish to secure higher total oxygen in the material.

The present inventors have made various attempts to develop a refining technology for producing high oxygen enamel steel, but Mn has a lower oxygen affinity than Al and Si, but its affinity with oxygen is higher than that of other elements, so that MnO is well formed in molten steel. The produced and especially produced MnO has a high specific gravity, so that the beak injury is not well in the molten steel, it is possible to obtain the target total oxygen even if the dissolved oxygen in the tundish, paying attention to the present invention was completed and proposed.

An object of the present invention is to provide a molten steel refining method that can increase the total oxygen of the cast while lowering the dissolved oxygen of the molten steel in the tundish of the continuous casting process. Furthermore, the present invention has a purpose of providing a high oxygen enamel steel having a total oxygen of 300 ~ 400ppm and deoxidized with Mn and excellent in fish scale properties.

1 is a manufacturing process diagram of enamel steel

2 is a graph showing the relationship between cast iron total oxygen and the endogenous fish scale

3 is a graph showing the relationship between dissolved oxygen and melt speed of shroud nozzle

4 is a graph showing the relationship between the dissolved oxygen content of the tundish molten steel and the total oxygen in the cast steel;

5 is a graph showing the behavior of dissolved oxygen in the molten steel refinement process from degassing equipment (RH) to tundish

In the refining method of the present invention for achieving the above object, in the manufacturing method of the enameled steel in which the molten steel of the ladle is sucked up by the RH refining furnace, decarburized and deoxidized, the deoxidized molten steel is charged into a tundish and continuously cast. The molten steel of the ladle is composed of a component having a lower oxidizing power than Mn; The deoxidation includes deoxidation of dissolved oxygen in a range of 250 to 280 ppm by introducing Mn into molten steel.

In addition, the enamel steel of the present invention has a total oxygen of 300 ~ 400ppm and comprises a deoxidized with Mn.

Hereinafter, the present invention will be described in detail.

The present invention embodies a method for refining molten steel in which molten steel can be increased while maintaining the dissolved oxygen in molten steel as low as possible by using Mn as a deoxidizer.

Al and Si deoxidizers known so far have high affinity with oxygen, making it easy to control the concentration of oxygen in molten steel, but in order to obtain the target total oxygen in the cast steel, the dissolved oxygen must be high. There was a high possibility of causing deterioration of sex. In addition, the Al ₂ O ₃ or SiO ₂ inclusions produced therefrom were also poor in rollability, causing deterioration of surface quality.

In the present invention, when Mn is applied as a deoxidizer of enameled steel in the course of research to solve this problem, since MnO is well formed and its specific gravity is high, separation in molten steel is not easily performed. It was noted that total oxygen could be increased. That is, MnO generated in the deoxidation process and MnO produced by the reaction of dissolved oxygen and Mn in the subsequent process act to increase the total oxygen in the slab. This MnO oxide was effective for endogenous fish scales because it formed a site where hydrogen could be deposited by making many interfaces with a matrix.

As described above, the present invention has the greatest feature of using Mn as a deoxidizer in the refining process of enamel steel. In the case of using Mn as a deoxidizer, the main component of molten steel should be composed of a component having less oxidizing power than Mn. The oxidizing power of the components that may be contained in the enamel steel is as follows.

Al〉 Ti〉 Si〉 Mn〉 Fe〉 P

Here, Si is inevitably contained as the five major components of the steel, it is preferably limited to at least 0.02% or less. Considering the oxidizing power as an example of the steel of the present invention may be composed of C, Mn, P, S, Si, specifically C: 0.005% or less, Mn: 0.30% or less, P: 0.020% or less, S: 0.015% or less, Si: 0.02% or less, and is composed of the remaining Fe and other unavoidable components.

In the present invention, the dissolved oxygen is preferably 700-800 ppm in consideration of decarburization and Mn deoxidation before RH refining of the molten steel of the ladle. The molten steel is decarburized according to a conventional method, and then Mn is used as the deoxidizer according to the present invention. Other input conditions except for the target dissolved oxygen follow the conventional method. In other words, the molten steel of the ladle is sucked up in the RH refining process, decarburized and then Mn is added. At this time, the target dissolved oxygen is finally determined by how total oxygen is performed in the cast steel.

Preferably, the Mn deoxidizer is added in two portions from the end of decarburization to the end of deoxidation. This allows for fine control within a range of control targets that target dissolved oxygen.

In addition, in the case of the conventional ultra low carbon steel refining, the vacuum in the vacuum chamber was maintained at a high vacuum of 5 Torr or less from the start of the treatment to the end of the treatment to remove the carbon in the molten steel as much as possible. In contrast, in the present invention, it is preferable that the vacuum degree in the vacuum chamber is set to a low vacuum of 30-50 Torr during Mn deoxidation refining. This is because a low vacuum degree can lower the molten steel reflux rate, thereby reducing the floating separation removal rate of manganese oxide generated by manganese injection.

Hereinafter, the reason for determining the target dissolved oxygen through the target total oxygen of the cast steel reflecting the fish scale resistance when RH refining using Mn as a deoxidizer according to the present invention.

First, as can be seen in Figure 2, the higher the total oxygen in the cast steel is less likely to occur fish scale. Therefore, the total oxygen of the cast steel as high as possible is advantageous to the fish scale resistance, the casting must be made by increasing the amount of dissolved oxygen in the molten steel during casting. However, when casting with a high dissolved oxygen amount, there is a fear that the melt loss of the refractory becomes severe, resulting in molten steel leakage or deterioration of casting workability.

As can be seen in FIG. 3, it can be seen that the dissolved oxygen speed of the shroud nozzle increases sharply around 250 ppm of dissolved oxygen. Therefore, in consideration of the stability of casting workability, the upper and lower oxygen values of the tundish are preferably 250 ppm.

As shown in FIG. 4 (when the Mn deoxidizer is used), when the dissolved oxygen amount of the molten steel in the tundish is about 250 ppm, the total oxygen in the cast steel is about 400 ppm. As described above, when dissolved oxygen in the cast steel is more than 300ppm considering that the fish scale stability is secured (Fig. 2), it can be seen that the dissolved oxygen amount of the molten steel in the tundish should be 200ppm.

As can be seen from above, in order to secure fish scale resistance, dissolved oxygen in the molten steel should be 200-250ppm.

However, after the RH refining process, the molten steel is moved to the performance equipment and continuously cast while charging the molten steel with a tundish, wherein the temperature of the molten steel drops. The lower the temperature of the molten steel, the lower the oxygen solubility of the molten steel is reduced dissolved oxygen. In addition, dissolved oxygen causes an oxidation reaction with the valuable elements in the molten steel so that the dissolved oxygen gradually decreases with time. In consideration of the transfer time to the playing equipment in the RH refining process and the temperature drop at this time, the reduction of dissolved oxygen is about 30 ppm (Fig. 5).

Therefore, after deoxidation in the RH refining process, the target dissolved oxygen in the deoxidized molten steel should be 250-280 ppm.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

Table 1 shows the operation and quality performance of deoxidizers in the method of deoxidation after decarburization of molten steel in the RH refining process.

Deoxidation Method Dissolved oxygen in molten steel in tundish Cast Oxygen Total Oxygen Residual ingredients in the material Al Si Conventional example Al deoxidation 243-287ppm 271-311ppm 0.0011% 0.015% Si deoxidation 251-285ppm 287-321ppm - 0.035% Inventive Example Mn Deoxidation 212-240ppm 354-380ppm - 0.005% Results of 4-9 measurements, the average of residual components in the material

As shown in Table 1, in the case of Al or Si deoxidation, the total oxygen measured value in the slab was lower than the target value (total oxygen: 300 ppm or more). It can be seen that the Si component remains.

Example 2

RH refining process of the ladle steel with dissolved oxygen as shown in Table 1 below, which is composed of C: 0.03-0.05, Si: 0.01-0015, Mn: 0.15-0.2%, P: 0.02% or less, and S: 0.015% or less After degassing by sucking, deoxidation by adding Mn, the deoxidation steel was charged into a tundish and continuously cast to prepare a cast.

In the tundish, the dissolved oxygen of molten steel and the total oxygen in the slab state were investigated and shown in Table 2. The composition of the oxide in the slab was shown in Table 3.

division Dissolved oxygen in molten steel arriving at RH process Dissolved oxygen of molten steel from RH Dissolved oxygen in molten steel in tundish Total oxygen of cast steel One 780 ppm 280 ppm 240 ppm 380 ppm 2 234 ppm 370 ppm 3 740 ppm 255 ppm 238ppm 362 ppm 4 212 ppm 354ppm

division MnO FeO 1, 2 86% 13% In the case of 3, 4 90% 8%

As shown in Tables 2 and 3, the total oxygen in the cast steel is 350-380ppm level, the oxide produced in the cast steel is mainly due to the manganese oxide can be seen that the good fish-scale resistance (Fig. 1).

As described above, the present invention has the effect of providing a high total oxygen high enamel steel while preventing refractory loss.

Claims (7)

In the method for producing enameled steel in which the molten steel is decanted and deoxidized in RH, and then molten steel is injected into a tundish to continuously cast The molten steel of the ladle is composed of a component having a lower oxidation power than Mn; The deoxidation is a refining method of high oxygen enameled steel comprising deoxidation of dissolved oxygen in the range of 250 ~ 280ppm by adding Mn to the molten steel. The method of claim 1, wherein the molten steel before the RH refining treatment has a dissolved oxygen of 700 to 800ppm. The refining method according to claim 1, wherein the Mn is maintained in a low vacuum state of 30 to 50 Torr after the Mn is introduced. The refining method according to claim 1, wherein the molten steel in the tundish has a dissolved oxygen of 200 to 250 ppm. The method of claim 1, wherein the enamel steel is C: 0.005% or less, Mn: 0.30% or less, Si: 0.02% or less, P: 0.020% or less, S: 0.015% or less, and the remaining Fe and other unavoidable impurities Refining method Enamel steel deoxidized with Mn with total oxygen of 300-400ppm. 8. The enamel preparation according to claim 6, which is composed of C: 0.005% or less, Mn: 0.30% or less, Si: 0.02% or less, P: 0.020% or less, S: 0.015% or less, and the remaining Fe and other unavoidable impurities. River.