KR20040024583A - Continuous casting roll for casting molten baths and method for producing one such continuous casting roll - Google Patents

Abstract

The present invention includes a roller body 2 made of a metal material, and a coating layer 4 made of a metal material having a hardness greater than that of the roller body 2 is coated on the roller body 2. A casting roller for molten metal casting, in particular a casting roller for molten steel casting. The casting roller according to the present invention has an increased service life and improved use characteristics. This feature is that when the coating layer 4 is considered over the thickness D of the coating layer, the hardness in the region adjacent to the roller body 2 is lower than the hardness in the region of the free surface 5. Is achieved.

Description

MOLTEN BATHS AND METHOD FOR PRODUCING ONE SUCH CONTINUOUS CASTING ROLL}

The two casting rollers used for strip casting steel in such a device, also called "twin roll casting machine", are internally cooled while rotating in opposite directions about the axes of the rollers arranged parallel to each other during the casting process, It defines the boundary of the long side of the casting gap formed between them. Since sufficient liquid molten metal is continuously supplied into the casting gap, a molten metal pool is formed above the casting gap. The molten metal that reaches the casting roller from this molten metal pool is solidified and moved into the casting gap by the casting roller. Within the casting gap, a casting strip made of a solid outer shell formed at the site in contact with the casting roller and still flowable molten metal is formed, which is passed to the next process after passing through the casting gap.

In order to ensure good thermal conductivity of the casting roller, at least the outer surface area of the casting roller is made of copper alloy. By doing so, good heat dissipation can be achieved. However, in practical operation, since the casting rollers are subjected to large mechanical and thermal stresses, considerable wear occurs on the copper material used to manufacture the casting rollers.

For this reason, casting rollers used for casting steel typically have a coating layer on the outer side that is harder than the material of the casting roller. A method of forming a coating layer on a copper roller body of a casting roller is known from EP 0801 154 B1. According to the method known in the patent, the outer surface of the copper casting roller is coated with a nickel coating layer by a special process step, so that the final casting roller is coated with a high hardness wear resistant coating layer to come into contact with the molten metal. This nickel coating protects the copper roller from mechanical damage and reduces the thermal deformation of the roller. At the same time, since the coating layer region has a low thermal conductivity, the coating layer region reaches a higher temperature than the region of the copper roller body having better thermal conductivity. By a higher temperature outer coating layer, the surface of the casting strip is improved.

In the case where the casting roller has a coating layer of the type described above, there is a problem that the specific coated coating layer and the roller body supporting the coating layer have different thermal expansion behavior. If this difference is too large, cracking or peeling may occur in a portion of the coating layer. This part of the roller body is in direct contact with the molten metal, resulting in additional wear.

In order to solve this problem, a method of coating two separate coating layers on the copper roller body such that the inner coating layer coated on the roller body is more thermally expandable than the outer coating layer in direct contact with the molten metal is disclosed in European Patent Publication. Suggested in EP 0 421 908 B1. Although the inner coating layer is colder than the outer coating layer by cooling the rollers, by the method described above, the outer coating layer is tensioned on the inner coating layer. In this case, it is preferable that the inner coating layer is made of copper, and the outer coating layer is made of steel, nickel or chromium. This type of double coating has the disadvantage that adhesion problems may occur at additional boundary layers formed between the first and second coating layers if the process conditions are not appropriate or the material composition is not uniform. In addition, according to EP 0 421 908 B1, problems relating to the reliability and wear resistance of the coating layer may also occur during actual operation.

The present invention relates to a casting roller for molten metal casting, in particular a casting roller for molten steel casting, having a roller body made of a metal material and having a coating layer made of a metal material having a higher hardness than the roller body material being coated on the roller body. will be. Casting rollers of this type are used in devices for continuously casting molten steel into strips.

1 is a perspective view of a casting roller;

2 is an enlarged detail view of a cross section of a casting roller;

** Description of reference numbers **

1: casting roller 2: roller body

3: outer surface of roller body 4: coating layer

5: outer surface of coating layer (free surface) D: thickness of coating layer 4

It is an object of the present invention to provide a casting roller having a long service life and improved use characteristics as compared with the above known technology, and also to disclose a method of manufacturing such a casting roller.

In the apparatus of this type, when the coating layer coated on the roller body is considered throughout the thickness, the object of the present invention is reduced by reducing the hardness at the boundary area between the coating layer and the roller body than the hardness at the free surface of the coating layer. Can be achieved.

In the present invention, the roller body is coated only with a single coating layer which is preferably based on a nickel alloy. However, such a coating layer is comprised so that the hardness of the boundary area with a roller main body may be lower than the hardness of the outer surface which directly contacts a molten metal. Since the hardness increases from the roller body toward the outer side of the coating layer thickness, the coating layer is ductile in an area adjacent to the roller body. Thus, in this area, the coating layer absorbs the deformation of the copper jacket of the roller body and ensures good adhesion of the coating layer on the roller body. Thus, by preventing the risk of the coating layer being separated from the roller body during the operation, it is possible to ensure a long-term continuous and reliable operation of the casting roller. At the same time, according to the present invention, since the hardness at the outer circumferential portion of the casting roller is high, the surface of the casting roller has good abrasion resistance, thus improving the service life.

By varying the composition of the free surface area of the coating layer and the area adjacent to the roller body, the hardness distribution of the coating layer coated on the roller body can be changed. For example, in certain electrolytes used during the coating process, the proportion of elements that improve the hardness of the coating material may be increased. In this way, the alloy composition changes over the thickness of the coating layer. An alloying element is distributed so that ductility is low while hardness is lower in the area | region adjacent to a casting main body than the outer peripheral part of a casting roller. In this case, if a coating layer is formed based on the nickel alloy, it is preferable to use sodium citrate, sulfur or the like which is suitable as the hardness increasing element.

Instead of or in parallel with the method of changing the composition to affect the hardness distribution, the coating process may be controlled such that the microstructure of the area of the coating layer adjacent to the roller body is softer than the microstructure of the outer free surface area. To achieve this, a method of increasing the plating current starting from the minimum during the coating process may be used. Due to the low plating current strength at the beginning of the coating process, a coating layer region having fine grains and excellent ductility is formed first. Subsequently, as the plating current strength increases, the hardness of the coating layer increases as the tissue coarsens and the thickness increases.

In each case, the coating process should be controlled so that a homogeneous coating structure with optimum material properties is obtained in the particular area in question (the boundary layer between the roller body and the coating layer; the outer surface of the coating layer). This can be reliably achieved by adding a hardness increasing element to the electrolyte or by altering the plating current, in which case in each case the hardness increases continuously over the thickness of the coating layer. Depending on the particular coating material, thickness and specific working influence used, it may be appropriate in this case to have a tendency to increase linearly or gradually with hardness from the outer periphery of the roller body to the outer surface of the coating layer.

According to a practical experiment, the casting roller according to the present invention satisfies the requirement that the casting roller should have when the hardness of the coating layer is 150 HV to 250 HV in the roller body and the boundary region and 400 HV to 500 HV in the free surface region. In particular, when the coating layer is formed based on the nickel material, the above conditions are established.

Other preferred embodiments according to the invention are specified in the dependent claims.

Preferred embodiments related to the following representative embodiments described based on the drawings will be described in more detail.

The casting roller 1 is equipped with the roller main body 2 in which the outer side surface 3 was made from the same material. Inside the roller main body 2, the cooling apparatus (not shown) which cools the roller main body 2 during casting operation is provided.

The coating layer 4 based on the nickel alloy is coated on the outer surface 3 of the roller body 2 by an electrodeposition process. The hardness change of the coating layer 4 linearly increasing over the thickness D of the coating layer 4 starting from the outer side 3 is shown by a horizontal line in FIG. 2, and is electrodeposited during the coating process to obtain this hardness change. The intensity of the current increased linearly. In this way, by gradually forming the coating layer 4 at the beginning of the coating process, the coating layer 4 in the region in contact with the outer surface 3 of the roller body 2 has a fine structure and a hardness in the range of 150 HV to 250 HV. At the same time, ductility increased. Thus, the coating layer in the thickness area adjacent to the casting body can bear the expansion of the roller body 2 generated by the heat during casting.

During the coating process, the electrodeposition current was increased continuously and linearly, with the result that the coating layer formed more rapidly and the grain became coarse. By this method, the hardness of the coating layer increased linearly in the direction of the outer surface 5 in contact with the molten metal, whereby the maximum hardness at the outer surface 5 of the coating layer was in the range of 400 HV to 500 HV, thereby providing excellent wear resistance. .

Claims (21)

For molten metal casting having a roller body 2 made of a metal material and having a coating layer 4 made of a metal material having a hardness greater than that of the roller body 2 is coated on the roller body 2. In casting rollers, especially casting rollers for molten steel casting, The coating layer 4 is cast for molten metal casting, characterized in that the hardness in the region adjacent to the roller body 2 is lower than the hardness in the region of the free surface 5 over the thickness D of the coating layer. roller. The method of claim 1, The coating layer (4) is a casting roller for molten metal casting, characterized in that the composition in the region adjacent to the roller body (2) and the composition in the region of the free surface (5) is different. The method according to claim 1 or 2, The coating layer (4) is a casting roller for molten metal casting, characterized in that the microstructure in the region adjacent to the roller body (2) is softer than the microstructure in the region of the free surface (5). The method according to any of the preceding claims, The casting roller for molten metal casting, characterized in that the hardness of the coating layer (4) continuously increases from the region adjacent to the roller body (2) to the free surface (5). The method of claim 4, wherein The hardness of the coating layer is a casting roller for molten metal casting, characterized in that it increases linearly. The method of claim 4, wherein The hardness of the coating layer is a casting roller for molten metal casting, characterized in that there is a tendency to increase gradually. The method according to any of the preceding claims, The hardness of the coating layer 4 is in the range of 150 HV to 250 HV in the region adjacent to the roller body 2 and in the region of the free surface 5 in the range of 400 HV to 500 HV. . The method according to any of the preceding claims, The roller body (2) is a casting roller for molten metal casting, characterized in that at least the outer surface (3) on which the coating layer (4) is coated is made of copper alloy. The method according to any of the preceding claims, The coating layer (4) is a casting roller for molten metal casting, characterized in that formed on the basis of a nickel alloy. In the manufacturing method of the casting roller 1 which coats the roller main body 2 by the electrodeposition method the coating layer 4 which consists of metal coating materials, During the coating process, the electrodeposition current is increased starting from the minimum value, characterized in that the casting roller manufacturing method. The method of claim 10, Casting roller manufacturing method characterized in that to increase the electrodeposition current continuously. The method of claim 11, Casting roller manufacturing method characterized in that to increase the electrodeposition current linearly. The method of claim 11, And gradually increasing the electrodeposition current. The method according to any one of claims 10 to 13, The coating layer is formed on the basis of the nickel alloy casting roller manufacturing method, characterized in that. In the manufacturing method of the casting roller 1 which coats the roller main body 2 by the electrodeposition method the coating layer 4 which consists of metal coating materials, During the coating process, increasing the proportion of the elements in the electrolyte which increases the hardness of the coating material. The method of claim 15, And continuously increasing the proportion of the elements that increase hardness. The method of claim 16, And linearly increasing the proportion of the elements that increase hardness. The method of claim 16, And gradually increasing the proportion of the elements that increase hardness. The method according to any one of claims 15 to 18, The coating layer is formed on the basis of the nickel alloy casting roller manufacturing method, characterized in that. The method according to any one of claims 15 to 19, A method for producing a casting roller, comprising adding sodium citrate to the electrolyte as a hardness increasing element. The method according to any one of claims 15 to 19, A process for producing a casting roller, wherein sulfur is added to the electrolyte as a hardness increasing element.