JPH031097B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a continuous casting mold that is highly durable and does not cause breakout. Continuous casting molds are usually made of copper or its alloy, which has high thermal conductivity, and are coated with various heat-resistant and wear-resistant materials. Many problems still remain regarding the seizability of the shell. In particular, recently, for some reason during operation, the solidified shell that is in the growth process breaks through the mold powder film used to provide lubricity, comes into direct contact with the inner surface of the mold, and seizes there, causing the solidified shell to break. The so-called restrictive breakout that occurs as a result of this has become a major problem. This restrictive breakout is mainly caused by seizure of the solidified shell due to insufficient supply of mold powder, so the present invention aims to eliminate this cause and provide a method for manufacturing a mold with high wear resistance.
The gist is that an undercoat material made of nickel or nickel alloy is attached to the surface of a mold body made of copper or copper alloy, a nickel-based self-fusing alloy sprayed layer is attached to the undercoat material, and the upper surface of the sprayed layer is By further attaching a chromium layer to the chromium layer and then carburizing it, carbon is diffused and penetrated from the surface of the chromium layer, and from the side of the chromium layer in contact with the nickel-based self-fusing alloy sprayed layer, the same sprayed layer is removed. This method of manufacturing a continuous casting mold is characterized in that the chromium layer is converted into chromium carbide from both sides by reacting carbon and chromium contained therein. In order to prevent such peeling of the surface coating layer, the surface coating layer may be extended to include not only the inner surface of the mold body but also part or all of the side wall surface. In particular, in the case of a mold that is sandwiched between a pair of opposing long-side molds and is used as a short-side mold with a variable width, the both side walls are moved while being in contact with the long-side molds. Therefore, it is important from the point of view of imparting wear resistance. The present invention will be described in detail below with reference to the drawings. First, to describe a method of forming a surface coating layer only on the inner surface of the mold body, as shown in FIG. A thickness of about 100 μm is attached, and a nickel-based self-fusing alloy sprayed layer 3 is attached to a thickness of 0.2 to 0.7 mm on the upper surface. A chromium layer 4 is then applied to the top surface by plating or other means. Note that after the undercoat material 2 made of nickel or nickel alloy is attached, heating is usually performed at 300 to 400° C. for one hour or more as a dehydrogenation treatment. The nickel-based self-fusing alloy to be used contains carbon as an essential component, that is, has a composition as shown in the table below, since it is necessary to cause a carbonization reaction with chromium on the upper surface in a later treatment.

[Table] After the surface coating layer is applied in multiple stages as shown in Figure 1, it is carburized. The carburizing treatment in this case may be solid carburizing, gas carburizing, vacuum carburizing, or ion carburizing, but if the mold body is made of pure copper, its mechanical strength will decrease if the temperature is too high. Therefore, it is preferable to use a precipitation hardening type copper alloy such as chromium-copper, chromium-zirconium-copper, or beryllium-copper, which can be strengthened even at high temperatures by subsequent rapid cooling, aging, and reheating. Through this carburizing treatment, carbon penetrates into the chromium layer 4 on the surface and is converted into chromium carbide 5 from the surface. At the same time, the chromium layer 4 in contact with the nickel-based self-fluxing alloy sprayed layer 3 is heated during the carburizing process. Carbon and chromium contained in the sprayed layer 3 undergo a carbonization reaction, and the chromium layer 4 is also changed into a chromium carbide layer 5 here. In this case, by adjusting the temperature and time of the carburizing treatment, the chromium layer 4 that still remains and is sandwiched between the chromium carbides 5 (see Figure 2) and all of it can be changed to the chromium carbide 5. Two types are obtained: one with a different shape (see Fig. 3). For convenience of explanation, the coating layers in Figures 2 and 3 are drawn as if they are separate, but in reality, the areas between the mold body and the undercoat material and between each coating layer are adjacent to each other. They are diffused into each other to form a diffusion layer, and all the coating layers are tightly adhered to each other through these diffusion layers. When the continuous casting mold according to the method described so far is shown in perspective, the coating layer is attached only to the inner surface of the mold body, as shown in Figure 4, but as shown in Figures 5 and 6. As shown in the figure, there are molds in which the coating layer wraps around part or all of the sides of the mold body, making it difficult for the coating layer to peel off. This is effective for short-sided molds that are sandwiched between different long-sided molds. Although not shown, a surface coating layer may also be applied to part or all of the upper and lower end surfaces of the mold body to further improve adhesion and to improve the corrosion resistance and wear resistance of these parts. In addition, in the case of continuous casting molds, due to the usage conditions, heat removal properties are particularly required in the upper part of the mold, and wear resistance is particularly required in the lower part of the mold. The thickness of the sprayed layer or chromium layer is gradually increased toward the bottom of the mold, the bottom of the mold is carburized at a higher temperature and/or for a longer period of time than the top, or surface grinding is performed after carburizing. It is possible to obtain various forms as shown in FIGS. As described above, in the method of the present invention, after attaching each coating layer by appropriate means, the mold body and each coating layer are chemically bonded through the diffusion layer formed between them by a simple method of carburizing. The sprayed layer is remelted and part or all of the chromium layer becomes chromium carbide at that location, and this chromium carbide has an Hv2000
It has the above hardness and excellent wear resistance and corrosion resistance. Even if microscopic cracks peculiar to the chrome plating layer occur, chromium carbide is formed in the cracks, and as a result, no cracks appear, which helps the mold powder to flow evenly, and because it is highly heat resistant. The molten steel and solidified shell do not seize and so-called restraint breakout does not occur. Therefore, it has the effect of allowing stable operation over a long period of time.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the state before carburization in the method of the present invention, Figs. 2 to 4 are explanatory diagrams of molds obtained by the method of the present invention, and Figs. 5 and 6 are illustrations of the same coating layer. 7 to 9 are explanatory diagrams in which the thickness of the same coating layer is gradually increased toward the bottom of the mold. In the figure, 1: mold body, 2: undercoat material,
3: Nickel-based self-fusing alloy sprayed layer, 4: Chromium layer, 5: Chromium carbide.

Claims (1)

[Claims] 1. An undercoat material made of nickel or nickel alloy is mounted on the surface of a mold body made of copper or copper alloy, and a nickel-based self-fusing alloy sprayed layer is mounted on the undercoat material. A chromium layer is further attached to the top surface of the sprayed layer, and then carburized to diffuse and penetrate carbon from the surface of the chromium layer, as well as from the side surface of the chromium layer in contact with the nickel-based self-fusing alloy sprayed layer. A method for manufacturing a continuous casting mold, characterized in that the chromium layer is converted into chromium carbide from both sides by reacting carbon and chromium contained in the sprayed layer. 2. The method for manufacturing a continuous casting mold according to claim 1, characterized in that the sprayed layer of a nickel-based self-fluxing alloy is gradually thickened from the upper part of the mold to the lower part of the mold. 3. A method for manufacturing a continuous casting mold according to claim 1 or 2, characterized in that the chromium layer is made thicker from the upper part of the mold to the lower part of the mold. 4. Claims 1 to 3, characterized in that the undercoat material, the nickel-based self-fusing alloy sprayed layer, and the chromium layer are wound and extended to a part or all of the inner surface of both sides of the mold body. A method for manufacturing a continuous casting mold according to any one of the above.