JPH05445B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Application of the Invention) The present invention relates to a roll for a heat treatment furnace (hereinafter referred to as a hearth roll) which is disposed in a heat treatment furnace and conveys a material to be heat treated, and which has particularly excellent wear resistance and prevents build-up. ). (Prior art) For example, when continuously annealing a steel plate, 600 to 1000
The steel sheets are passed through an oxidizing or reducing atmosphere at a temperature of Adhering oxides or iron powder adhere and accumulate on the surface of the hearth roll, forming what is called a build-up. When such wear and build-up occur, the surface of the steel plate is damaged while it is being conveyed on the hearth rolls, causing deterioration of the quality of the steel plate, and sometimes production operations are immediately halted and the hearth is removed. The surface of the roll is forced to be ground and maintained. For this reason, attempts have been made to change the material of the hearth roll, or to thermally spray coat the roll surface with zirconia, alumina, etc., as described in Japanese Patent Publication No. 57-29549. However, many of these known attempts have not been fully satisfactory in terms of hot wear resistance or prevention of build-up. (Purpose of the Invention) The present inventors have conducted various research into coating materials and coating methods that have excellent wear resistance and build-up resistance that should be applied to hearth rolls used in these oxidizing or reducing atmospheres. As a result, they discovered a coated roll that has excellent adhesion to the hearth roll substrate, does not peel off, and has excellent high-temperature strength, and completed the present invention. That is, the present invention provides a hearth roll for conveying heat-treated materials, which has a coating layer formed on its surface that has excellent wear resistance and build-up resistance when installed and used in an oxidizing or reducing atmosphere. It was made for that purpose. (Structure and operation of the invention) The present invention will be described in detail below. The base of the hearth roll is made of heat-resistant steel. On the surface of these substrates, a cermet layer containing 30 to 70% by weight (hereinafter abbreviated as %) of silicon carbide, silicon nitride, or a mixture thereof with a minimal amount of metallic silicon is formed by thermal spraying. . First, the influence of silicon metal in silicon carbide, silicon nitride, or a mixture thereof will be described. Normally, when producing silicon carbide or silicon nitride, when metal silicon is carbonized or nitrided as a starting material, unreacted metal silicon may remain. In addition, when performing reduction carbonization using silicon oxide as a starting material,
May generate metallic silicon. If metallic silicon is present in silicon carbide, silicon nitride, or a mixture thereof in the cermet layer of the hearth roll, iron powder adhering to the steel plate will adhere and accumulate at high temperatures, making it easy to cause build-up.
Iron powder is placed on a fired body of silicon carbide and silicon nitride containing different amounts of metallic silicon, and in a non-oxidizing atmosphere at 900°C, it is pressed with a half-moon roll and rubbed for 4 hours to prevent the iron powder from adhering. The sedimentation properties were investigated. The results are shown in Figure 1. When the metal silicon content is 1% or more, the adhesion area of iron powder increases rapidly, making it unsuitable. However, when the metal silicon content is 1% or less, it shows extremely excellent build-up resistance. . High purity silicon carbide,
Silicon nitride has excellent build-up resistance and is a hard material because it is difficult to form reaction products with Fe and Fe oxides at temperatures below 1000℃, and because it is a covalent bond and is stable, it has little reactivity at high temperatures. Therefore, it also has excellent wear resistance. Next, the amounts of silicon carbide, silicon nitride, and mixtures thereof added as cermets will be described. It is extremely difficult to thermally spray high-purity silicon carbide and silicon nitride as they are, so Co,
It is necessary to create a thermal spray coating with high strength and strong adhesion by forming a matrix using Cr, Mo, Ni, Al, W, Y, or a mixture or alloy of two or more of them. . Regarding build-up resistance, the higher the content of silicon carbide and silicon nitride, the better the properties.
If it is not contained above, sufficient build-up resistance cannot be maintained in practical use. Further, even if the build-up resistance is excellent, it is meaningless if the thermal spray coating peels off from the heat-resistant steel of the roll base, and adhesion strength sufficient to prevent this peeling is required. In order to ensure this adhesion, the cermet layer contains
The higher the content of heat-resistant metals such as Co, Cr, Mo, Ni, Al, W, and Y, the better the adhesion and the better the peeling resistance. It was confirmed that in order to prevent the thermal spray coating from peeling off, the amount of metal as a binder must be at least 30% or more. In this way, in order to ensure build-up resistance and peeling resistance properties and to perform the function as a hearth roll, the appropriate blending amount of silicon carbide, silicon nitride, or a mixture thereof is 30 to 70%, and is preferably 30% to 70%. The upper limit is 60%. Example A hearth roll coated with 0.7% silicon metal, 25% silicon carbide, and 75% Co-Cr alloy to a thickness of 400μ.A hearth roll coated with 0.7% silicon metal, 35% silicon carbide, and 65% Co-Cr alloy to a thickness of 360μ. Hearth roll coated by thermal spraying to a thickness of 420 μm Hearth roll coated by thermal spraying to a thickness of 420μ with 50% silicon carbide containing 0.7% metallic silicon and 50% Co-Cr alloy 65% silicon carbide containing 0.7% metallic silicon and Co-Cr alloy Hearth roll coated with 35% alloy by thermal spraying to a thickness of 390μ Hearth roll coated by thermal spraying of 78% silicon carbide with 0.7% silicon metal and 22% Co-Cr alloy to a thickness of 350μ Silicon carbide 63 with 1.6% silicon metal %, Co-Cr alloy 37% to a thickness of 410μ Hearth roll Metallic silicon 0.8% silicon nitride 20%, Co-Cr alloy 80% spray-coated to a thickness of 450μ 0.8% silicon carbide and silicon nitride (17:
83) mixture 60%, Co-Cr alloy 40% 410μ
A hearth roll coated by thermal spray coating with a thickness of 390 μm A hearth roll coated with a thermal spray coating of 0.8% silicon metal, 81% silicon nitride, and 19% Co-Cr alloy at a thickness of 390 μ Hearth roll using heat-resistant steel SCH22 Each of the above hearth rolls was tested in an actual machine for a long time in a non-oxidizing atmosphere at an operating temperature of 750°C. The results are shown in Table 1. As shown in Table 1, the roll of the present invention,
, showed very excellent build-up resistance and durability, while other test products were prone to build-up or peeling of the sprayed layer. Furthermore, the same material as ~ was thermally sprayed onto a heat-resistant steel surface of 100 x 100 mm, heated to 800°C for 1 hour, and then water-cooled repeatedly, and the number of times it took to peel off was shown in Figure 2 as a peeling index. It was confirmed that peeling resistance decreased as the amount of metal decreased, and it was found that the amount of metal as a metal binding material was required to be 30% or more, preferably 40% or more.

[Table] (Effects of the Invention) As shown in the above examples, the roll of the present invention has extremely excellent build-up resistance and greatly contributes to extending the life of the roll.

[Brief explanation of the drawing]

Figure 1 is a graph of the relationship between the adhesion of various samples to iron powder and the amount of metal silicon contained in the sample, and Figure 2 is the relationship between the peeling index of various samples and the amount of metal added as a binder. This is a diagram.

Claims (1)

[Claims] 1 Contains 30 to 70% by weight of silicon carbide, silicon nitride, or a mixture thereof with a metal silicon content of 1% by weight or less, and the remainder is Co, Cr, Mo, Ni, Al, W, Y alone or in a mixture of two or more. 1. A roll for a heat treatment furnace, characterized in that the base body of the hearth roll is coated with a thermally sprayed cermet layer made of an alloy.