JPH0586449B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is a roll that is disposed in a heat treatment furnace and conveys a material to be heat treated, and has excellent wear resistance.
This invention relates to a heat treatment furnace roll (hereinafter referred to as a hearth roll) that prevents build-up from occurring. (Conventional technology) For example, when continuously annealing a steel plate, 300 to 1200
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 roll, causing deterioration in the quality of the steel plate, and sometimes production operations are immediately stopped and the hearth roll is removed. The surface of the machine 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 zirconia, alumina, etc. onto the roll surface, 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. Therefore, the present applicant previously disclosed in Japanese Unexamined Patent Publication No. 60-2661 a heat-treated roll comprising a coating layer of an inorganic material containing 30 to 70% Cr ₂ O ₃ and the remainder consisting of Al ₂ O ₃ . Also, Japanese Patent Application No. 144176/1987 has provided a heat-treated roll having a coating layer of a solid solution inorganic material containing 70 to 90% Cr ₂ O ₃ and the remainder Al ₂ O ₃ . (Problems to be Solved by the Invention) The present invention solves the problem of the composition of the Cr ₂ O ₃ -Al ₂ O ₃ solid solution of the hearth roll coating layer consisting of Cr ₂ O ₃ and Al ₂ O ₃ and the contaminants. As a result of focusing on the ingredients,
An object of the present invention is to invent and provide a hearth roll that has better build-up resistance than the prior invention. (Means for Solving the Problems) The present invention provides a solution having a weight ratio of 1:9 to 9:1.
Contains 97% by weight or more of Cr ₂ O ₃ −Al ₂ O ₃ solid solution, and has 0.01% by weight or more and 0.5% by weight or less of metal Cr generated by reduction by gas during roll surface spraying, with the remainder being unavoidable. This is a hearth roll with a surface layer made of impurities. The present invention will be explained in detail below. Generally, Al ₂ O ₃ (melting point 2045℃), Cr ₂ O ₃ (melting point 2275℃)
℃) has a high melting point, poor reactivity with metals, high hardness, and wear resistance. However, Cr ₂ O ₃ and Al ₂ O ₃ on the hearth roll surface
When a coating layer is formed, if it is used at a temperature of 700° C. or higher and the temperature is lowered, peeling will occur during the first heat history, making it difficult to use as a hearth roll. As a countermeasure to this problem, studies have been conducted focusing on the fact that Cr ₂ O ₃ and Al ₂ O ₃ form a complete solid solution over the entire region. Therefore, it was found that by dissolving 10 to 90% by weight of Al ₂ O ₃ in Cr ₂ O ₃ , it becomes thermally stable and suppresses peeling of the coating layer. Therefore, various coating layers made of Cr ₂ O ₃ - Al ₂ O ₃ solid solution in a weight ratio range of 1:9 to 9:1 have been used as hearth rolls, but in some cases build-up occurs between each roll. Ba,
There were some that did not occur at all. Therefore, as a result of intensive consideration of this build-up mechanism, we found that
It has been found that build-up occurs when metallic Cr is present in an amount exceeding 0.5% in a Cr ₂ O ₃ -Al ₂ O ₃ solid solution. Next, Table 1 shows the results of the peeling resistance test and Table 2 shows the results of the build-up test, which were used as the basis for the numerical limitations of the coating material according to the present invention. Peeling resistance test is 30×50×
Various Cr ₂ O ₃ −Al ₂ O ₃ on the outermost surface of 5 mm SCH22 cast steel
A sample with a solid solution coating layer formed (sprayed) was
Peeling resistance was determined by repeating heating at °C for 30 minutes and then immersing it in water, and checking the number of times peeling occurred. In the build-up test, iron oxide powder, which is the build-up raw material, is placed between two flat plates of the sample prepared using the same procedure as the peeling resistance test, and a load is applied on top of the iron oxide powder.
Gives a movement similar to that of two flat plates being rubbed together,
Adjust the atmosphere to N ₂ (95%) - H ₂ (5%) and
It was heated at .degree. C. for 5 hours, and after cooling, the surface condition of the coating layer was observed to determine the build-up property.

[Table] As can be seen from this result, in the Cr ₂ O ₃ - Al ₂ O ₃ solid solution, when the ratio of the solid solution is in the range of 1:9 to 9:1 as in Nos. 3 to 5, the durability is 10 times or more. It can be seen that the peeling resistance is significantly improved. The composition of the coating layer used in this test other than the Cr ₂ O ₃ -Al ₂ O ₃ solid solution is Cr ₂ O ₃ that has not been converted into a solid solution.
and Al ₂ O ₃ and unavoidable impurities SiO ₂ , TiO ₂ ,
These include CaO, MgO, Fe ₂ O ₃ , etc.

[Table] Composition of Cr ₂ O ₃ -Al ₂ O ₃ solid solution is 1:9 by weight
It can be seen that in the range of ~9:1, when the Cr ₂ O ₃ -Al ₂ O ₃ solid solution is 97% by weight or more and the metal Cr content is 0.5% by weight or less, build-up is less likely to occur.
(No. 10, 11, 12, 15, 16, 17, 19, 20, 21) Among them, especially when the metal Cr content is 0.2% by weight or less, it becomes extremely small (No. 11, 12, 16, 17, 20, 21),
Furthermore, the metal Cr content is 0.01% (No.12, No.17, No.21)
In this case, no build-up was observed in experiments. Techniques for reducing the metal Cr in the Cr ₂ O ₃ - _{Al 2} O ₃ solid solution include, for example, oxidation treatment, pickling, etc. in the manufacturing process of the solid solution powder, and using a non-reducing atmosphere during thermal spraying. There are methods to suppress the reduction of Cr ₂ O ₃ . Examples will be described below. (Example) No. 11 shown in Table 2 was placed on the outermost surface of the heat-resistant cast steel roll.
Coating layers No. 17, 20, and No. 14 were formed by thermal spraying and ground to a surface smoothness of 100 μm or less to obtain rolls for heat treatment furnaces. Furthermore, as a conventional product, we have prepared a roll made of heat-resistant cast steel. Table 3 shows the results of using the five types of heat treatment furnace rolls described above in an actual steel sheet heat treatment furnace (temperature 800 to 1050°C, _N2 - _H2 - _H2O atmosphere) for 3000 hours.

【table】

[Table] As can be seen from Table 3, no build-up was observed in the product of the present invention even after 3000 hours of use. (Effects of the Invention) As shown in the above examples, the build-up resistant coating layer according to the present invention does not cause build-up even when used for a long time, contributing to extending the life of the roll.

Claims (1)

[Claims] 1 Cr ₂ O ₃ − in a weight ratio of 1:9 to 9:1
Metal containing 97% by weight or more of Al ₂ O ₃ solid solution and reduced by gas during roll surface spraying.
A roll for a heat treatment furnace having a surface layer containing Cr of 0.01% by weight or more and 0.5% by weight or less, with the remainder being unavoidable impurities.