JPS62136421A - Hearth roll for continuous annealing furnace - Google Patents

Abstract

PURPOSE:To aim at enhancing the wear resistance, build-up resistance and zigzagging resistance of a hearth roll, by flame-coating micropellets which are formed such that the powder of alloy consisting of a specific weight percent of Ni and the remainder of Ci, and the fine powder of chromium carbide are mixed, pelletized and sintered, onto the outer surface of the hearth roll. CONSTITUTION:The blending amounts of Ni-Cr alloy containing therein 50-80wt% of Ni and the remainder of substantial Cr, and a chromium carbide are such that the Ni-Cr alloy powder has 25 to 15% and the chromium carbide powder has the remainder. Further, micropellets having been sintered are sorted in a particle size range from 10-50mum, and are flame-coated onto the outer surface of a roll. These amounts are determined in consideration with facts such that less than 20wt% of Cr causes an insufficient hardness of the Ni-Cr alloy, resulting in deterioration of the wear resistance of a coating layer formed on the outer surface of the roll by flame coating together with the other components, but more than 50wt% of Cr causes the melting point of the Ni-Cr alloy to be excessively high, and such that it is necessary to prevent the binding force between the Ni-Cr alloy powder and the chromium carbide powder from lowering when they are sintered after mixing and pelletization. Further, less than 15% of the alloy causes the binding force to be weak while more than 25% of the alloy causes the hearth roll to be easily worn.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a hearth roll for conveying heat-treated materials disposed in a continuous heat treatment furnace, and in particular, the present invention has excellent wear resistance,
The present invention relates to a hearth roll disposed in a continuous heat treatment furnace for transporting a heat-treated material, which can prevent pick-up caused by build-up and suppress meandering of the heat-treated material.

(Conventional technology) Since the conveyor hearth rolls that carry and transport the materials to be heat treated in a steel heat treatment furnace are exposed to a high temperature atmosphere, the scale of the materials to be heat treated adheres to the roll surface, causing a so-called build-up phenomenon. . When this phenomenon occurs, flaws called pickups are formed on the surface of the heat-treated material (hereinafter referred to as the treated material) that is subsequently transported, and these flaws induce surface defects in the rolled product.

Conventionally, in order to suppress the build-up phenomenon described above, that is, to prevent scale from adhering to the roll surface, the roll surface has been coated with ceramic sludge or cermet, which is a mixture of ceramic and metal, by thermal spraying. As such rolls, rolls such as Queen (1) and (2) are known, for example.

(1) At205+ ZrO2+ Cr2O3+
A roll coated with one or more ceramics selected from WG + 0r3C2.

(2) Cr I Ni I Ni-Cr I Co
A roll coated with a cermet made of a mixture of one or more metals or alloys selected from Mo and the ceramic described in item (1) above.

(Problems to be Solved by the Invention) For example, a roll coated with a mixture of multiple types of ceramics or cermet disclosed in JP-A-59-126772 has three properties: wear resistance, build-up resistance, and meandering prevention property. There was a problem in that it did not yet have sufficient characteristics. The reason for this is that the thermal spray materials described in the above publication are simply in a mixed state and separate during thermal spraying, so the coating formed by thermal spraying is a heterogeneous coating in which the various mixed raw materials are unevenly distributed and segregated. It is.

(Means for Solving the Problems) The present invention aims to eliminate and improve the drawbacks or problems of conventional hearth rolls for continuous annealing furnaces whose surfaces are coated by thermal spraying, and the scope of the present invention is as set forth in the claims. By providing a hearth roll for a continuous annealing furnace, the above object can be achieved. That is, in the present invention, N soil 50~
Wear-resistant and build-resistant micro pellets made by mixing, granulating, and sintering alloy powder consisting of 80 wt%, the remainder substantially Or, and fine chromium carbide powder are thermally sprayed onto the rotating surface of the roll base. The present invention relates to a hearth roll for continuous annealing furnaces that has excellent upability and anti-meandering properties.

Next, the present invention will be explained in detail.

The content of Ni and Or in the Ni-Cr alloy is approximately 80 wt%, with the remainder being substantially Or.

In addition, the blending amount of Ni - (3+ alloy and chromium carbide is 25 to 15% Ni - Cr alloy fine powder, and the balance is chromium carbide powder. After sintering, the micro pellets are classified into particle sizes in the range of 10 to 50 μm. It has been
This is thermally sprayed onto the roll surface.

Next, the reason for limiting the composition of the Ni-0+ alloy used in the present invention will be explained.

Or: If Or is less than 20 wt%, the hardness of the Ni-0+ alloy will be insufficient, and as a result, when the coating layer is formed by thermal spraying on the roll surface as one component of the micro pellet with other components, the coating layer On the other hand, if the Or content exceeds 50%, the melting point of the Ni-Cr alloy becomes too high, and the Ni-Cr alloy powder and fine chromium carbide powder are mixed and granulated and then sintered. Crr needs to be within the range of 20 to 50 wt%, since the bonding strength during this process decreases and it becomes impossible to form good micropellets.

Ni: Ni is 100% in total with the content of Or above
It is necessary to

Next, the reason for limiting the composition of the constituent elements of the micropellet of the present invention will be explained.

The Ni-0+ alloy functions as a binder material when sintered to form micropellets, but if the Ni-Cr alloy is less than 15 wt%, the bonding strength is weak and the micropellets will break. On the other hand, if the Ni-Cr alloy is more than 25 wt%, the content of chromium carbide will be relatively reduced.
After thermal spray coating, the hardness of the coating decreases and the wear resistance deteriorates, so the Ni-Cr alloy is
It is necessary to keep it within the range of wt%.

Next, the reason for limiting the particle size of the micropellets will be explained.

If the particle size is smaller than 5 μm, an overmelted state will occur due to the high heat source during thermal spraying, such as combustion flame or plasma flame.
In some cases, chromium carbide may evaporate, or decomposition and decarburization of chromium carbide may occur, making it impossible to form a normal film.On the other hand, if the particle size is larger than 50 μm, contrary to the case of a small particle size, it may not be possible to form a normal film. The particle size of the micropellets must be within the range of 5 to 50 μm, since the sprayed coating becomes molten and has many pores, which can cause build-up if such a roll is used.

Next, the present invention will be explained with reference to examples.

Example 1゜nickel chromium alloy and chromium carbide)”t-■ in Table 1
After agglomerating and sintering in the component ratios shown in ~■ to form micro pellets, the particle size was adjusted to 5 to 50 μm, and then thermally sprayed onto test materials for a wear test and a build-up test.

For comparison, a mixed material of nickel chromium alloy and chromium carbide was prepared with the same component ratio as in ■ to ■, and the same tests were conducted.

(4) Creation of test piece A thermal spray material (particle size 5 to So1
1 m).

This was used as the test material SOH22 (50 x 5 QsuIlx
5m+) to form a film thickness Q, 5m.

(B) Abrasion test method The abrasion test method was based on JIS-18615, and the weight difference between 400D and S before and after abrasion was measured and compared using a Suga abrasion tester.

(C) Build-up resistance test method 5S41 material was heated and held at a temperature of 800° C. for 10 hours to generate scale on the surface. This was placed on the surface of each test piece and pressed with a load of fi1 to 50097cm2 in a heating furnace (atmosphere: temperature 1200℃, 95%N2.5%02
"Contains PPM H2O)" for 24 hours.Then, take out the test piece and measure the degree of scale adhesion on its surface.The degree of scale adhesion is expressed as the ratio of scale adhesion surface to the contact area with the scale piece (3341 material). .

The results of each test are shown in Table 1. As is clear from the table,
It was found that the examples of the present invention had excellent abrasion resistance, had extremely little scale adhesion, and therefore had good build-up resistance. In particular, regarding the hardness that affects wear resistance, the present invention has a micro Vickers hardness DPI (300 gf) or more at room temperature, whereas
The coating obtained by spraying the same ratio of mixed materials is DPI (300g
f) 650 is the limit.

Example 2 83 wt% chromium carbide - 17 wt% nickel chromium (75 wt% nickel and 25 wt% chromium in a nickel chromium alloy) was agglomerated and sintered to form micro pellets, and the material whose particle size was adjusted to 10 to 50 μm was plasma-treated. 150μ is applied to the surface of the continuous annealing furnace nozzle roller using thermal spraying equipment.
It was coated with a thickness of m and was used on an actual machine.

As a result, the lifespan of a hearth roll sprayed with a mixture of chromium carbide and nickel chromium alloy of the same ratio and composition was 88.
In contrast, the 71-slower of the present invention could be used effectively for two years without wear or pick-up, and no occurrence of meandering was observed.

(Effects of the Invention) As described above, use of the roll of the present invention can increase durability and greatly contribute to stabilizing furnace operation and improving efficiency.

Claims (1)

[Claims] 1. The rotating surface of the roll base is coated by thermal spraying with micro pellets obtained by mixing, granulating and sintering an alloy powder consisting of 20 to 50 wt% Cr and the remainder substantially Ni and fine chromium carbide powder. Hearth roll for continuous annealing furnace. 2. The hearth roll according to claim 1, wherein the micro pellets are comprised of 25 to 15 wt% of nickel-chromium alloy fine powder, and the remainder substantially of chromium carbide fine powder. 3. The hearth roll according to claim 1 or 2, wherein the particle size of the micropellets is within the range of 5 to 50 μm.