JPH0387310A - Hearth roll having excellent build-up resistance - Google Patents

Abstract

PURPOSE:To manufacture a hearth roll having excellent build-up resistance by forming film layer composed of the specific ratio of NC, Cr, Al, Y and Co on surface of the roll body. CONSTITUTION:The film layer composed of wt.% of 5-70% NC, 15-28% Cr, 4-15% Al, 0.1-1.0% Y and the balance Co with inevitable impurities, is formed on the surface of roll body in >= about 50mu thickness with plasma thermal spray, etc. Then, a part of NC may be substituted with one or more kinds of TiC, SiC, MoC and TaC in each <=5% and oxide series ceramic (Al2O3, etc.) in <=15%. By this method, the hearth roll having excellent high temp. wear resistance and build-up resistance, is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hearth roll with excellent build-up resistance.

(Prior art) Hearth rolls, which are the inner rolls of heat treatment furnaces, are used at high temperatures, so surface-treated rolls with excellent build-up resistance, peeling resistance, and abrasion resistance are used. As the capacity of heat treatment furnaces increases, build-up phenomenon on the roll surface occurs frequently due to the rise in furnace temperature, resulting in a decline in product quality.

(Issue 8 to be Solved by the Invention) An object of the present invention is to provide a hearth roll that is excellent in build-up resistance, peeling resistance, and abrasion resistance and is compatible with increasing heat treatment furnace capacity.

(Means for Solving the Problems) The present inventors carried out build-up reproduction tests on various materials, and found that niobium carbide can be effective in terms of build-up resistance, especially CoCrjVY.
It was confirmed that the build-up resistance of metals and metal oxides in the coating layer of heat-resistant alloys can be greatly improved, and that the hardness of the coating layer can be increased and the wear resistance at high temperatures can be significantly improved. .

The gist of the present invention is as follows.

(1) On the surface of the roll body, 5-70% niobium carbide, 15-28% Cr, 4-15% IV, Y0
．． A hearth roll with excellent build-up resistance characterized by forming a film layer containing 1 to 1.0% of Co and the remainder being Co and unavoidable impurities.

(2) The above-mentioned item 1, wherein the film layer further contains 5% or less each of one or more of titanium carbide, molybdenum carbide, tantalum carbide, and silicon carbide, and 15% or less of oxide ceramics. Hearth roll with excellent build-up resistance.

The present invention will be explained in detail below.

First, the reasons for limiting the composition ranges of each additive element and the carbide and oxide ceramics will be explained.

Cr: Cr strengthens the coating layer matrix and
,0. It is an essential additive component to form an oxide film and improve oxidation resistance at high temperatures. However, when added in large quantities,
Since it causes the formation of chromium carbide and embrittlement of the coating layer matrix, the amount added is set at 15 to 28% in consideration of this.

jV:Aj is also added to form an oxidation-resistant film in the film layer matrix and to improve the oxidation resistance at high temperatures, but a small amount has no effect, and an excessively large amount will cause the matrix to become brittle. Considering these points, the amount added should be 4 to 15.
%.

Y: Y densifies the oxidation-resistant film of the film layer matrix, improves adhesive strength, and significantly improves the high temperature performance of the film layer. If added in large quantities, the effect will decrease,
Considering these points, it does not work effectively on the strength of the oxidation-resistant film of the matrix, and the amount added is set at 0.1 to 1.
It was set to 0%. Note that it is also possible to use a rare earth element as a substitute for Y.

Co: Co is selected as the base component of the heat-resistant matrix of the coating layer, and has excellent oxidation resistance and heat resistance, and plays the role of a binder for dispersed carbide and oxide ceramics. Therefore, a necessary amount is added as a balance amount other than the limiting components, but addition of up to about 50% is sufficient.

Niobium carbide: Niobium carbide is an essential component in order to improve the important effects of the present invention, namely, build-up resistance and to prevent welding of the conveyed metal and its oxides to the roll surface. When the content is low, build-up will be significant, while when the content is excessive, the toughness of the coating layer will be impaired. Taking these points into consideration, the content should be reduced to 5.
It was defined as ~70%. Although carbon is included in the coating layer by adding niobium carbide, the actual amount of carbon in the coating layer is about 3% at most on average.

Titanium carbide, molybdenum carbide, tantalum carbide, silicon carbide: These carbides are components used as carbides that partially replace niobium carbide in the present invention, and by adding these carbides that have similar characteristics to niobium carbide, only niobium carbide can be obtained. It was confirmed that the characteristics of the case and the road gap can be obtained. However, when added in large amounts, the build-up resistance and oxidation resistance of the coating layer are reduced, so the upper limit for both is set at 5%.

Oxide-based ceramics: Oxide-based ceramics are auxiliary components for improving the build-up resistance and high-temperature wear resistance of the coating layer.The action of these high-temperature heat-resistant oxides improves the build-up resistance of the coating layer. has been further improved, and
The dispersion strengthening of these oxides improves the high-temperature strength of the coating layer and improves its wear resistance. However, if added in large amounts, it will damage the toughness of the film layer, so if added in a maximum of 15%
up to.

Ceramics include single types such as Al2O and Aj
, O3MgO, and other composite oxides can also be used.

Next, the characteristics of a coating layer obtained by plasma spraying using thermal spray powders made of these various components will be explained using examples.

Table 1 shows the relationship between the component composition and usage characteristics of the coating layer obtained by plasma spraying and high-velocity gas spraying using the thermal spraying material corresponding to the coating layer composition according to the present invention. High-temperature hardness, room-temperature adhesion strength, and Fe5 in build-up tests at 750°C are indicators of wear resistance.
0. Looking at the baking properties of the powder, it can be seen that the properties of the film layer having the composition according to the present invention are excellent.

FIG. 1 illustrates the build-up resistance test method, in which the roll 2 is moved and Fe, 0. Look at the build-up of Powder 3. The verdict is A.

Comprehensive judgment will be made based on the degree of burn-in on side B.

In this example, the coating layer was formed using several buses of plasma spraying and a high-speed gas spraying system (the high-speed gas spraying system means an external combustion explosion method with a flame speed of Matsuha 3 or higher and other explosive methods). The thickness of the sprayed coating layer is 50t to provide heat resistance!
It is better to set it to more than m. It goes without saying that graded coating methods using materials with slightly different compositions, use of ceramic-based thermal spraying as a base thermal spraying method, and reduced pressure thermal spraying methods can also be applied. It is also effective to heat the film layer and perform a diffusion treatment. The loose film layer can also be oxidized to provide heat resistance in a reducing atmosphere. Furthermore, other methods which do not involve thermal spraying and which can form a coating layer having the composition according to the present invention are also naturally included in the present invention.

(Effects of the Invention) The hearth roll having a film layer according to the present invention has excellent high-temperature wear resistance and build-up resistance.

Note that the technical idea of the present invention can be applied to other mechanical members, so the industrial utility value of the present invention is extremely large.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the procedure for a build-up test. ■=test piece, 2: roll, 3: Fe50. powder. Test piece (30x50x5t), roll (load 8.5k)
g) Kyenoki movement

Claims (2)

[Claims] (1) On the surface of the roll body, niobium carbide is added in weight% from 5 to 50% by weight.
70%, Cr15-28%, Al4-15%, Y0.1
A hearth roll with excellent build-up resistance characterized by forming a film layer containing ~1.0% of Co and the remainder being Co and unavoidable impurities. (2) The film layer further contains 5% or less of each of one or more of titanium carbide, molybdenum carbide, tantalum carbide, and silicon carbide, and 15% or less of oxide ceramics. The hearth roll described in 1 with excellent build-up resistance.