JPH05247622A - Roll for heat treatment furnace - Google Patents

Abstract

PURPOSE:To obtain a roll for heat treatment furnace having excellent adhesivity, wear resistance and build-up resistance by forming the thermal-sprayed intermediate layer and the thermal-sprayed film most upper layer adding stabilized zirconia to mullite raw powder with the thermal-spray in order on metal layer for combination formed on the roll surface. CONSTITUTION:On the metal layer (NiCr) for combination formed with the thermal-spray on the surface of the roll base material, the thermal-sprayed intermediate layer composed of mixed material of the mullite, metal for combination and zirconia (20-70vol.% to the mullite) containing 5-20wt.% one or more kinds of MgO, CaO and Y2O3, is formed. Successively, on this thermal-sprayed intermediate layer, the thermal-sprayed film uppermost layer composed of the mixed material of the mullite and the zirconia (20-70vol.% to the mullite) containing 5-20wt.% one or more kinds of MgO, CaO and Y2O3 is formed. By this method, the hearth roll having excellent high temp. adhesivity, wear resistance and build-up resistance and largely extending the service life, is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is provided in a heat treatment furnace,
The present invention relates to a roll for annealing and conveying a steel sheet, and particularly to a heat treatment furnace roll (hereinafter abbreviated as hearth roll) excellent in high-temperature peeling resistance, high-temperature wear resistance and build-up prevention.

[0002]

2. Description of the Related Art For example, a hearth roll arranged in a continuous annealing furnace has a surface for annealing and transporting a material to be heat-treated continuously in an oxidizing or reducing atmosphere at 600 to 1300 ° C. for a long time. It is subject to abrasion, and the oxides and iron powder adhered to the heat-treated material are adhered and deposited on the roll surface to form what is called build-up.

When unevenness due to wear or build-up occurs on the hearth roll, the steel sheet, which is the material to be heat-treated, is flawed while being conveyed, causing deterioration in quality.
In order to prevent such deterioration of the quality of the steel sheet, after periodically interrupting the operation and cooling the inside of the heat treatment furnace, an operator enters the furnace to grind the surface of the hearth roll, or to clean the roll itself. I am replacing them.

Therefore, in order to prevent abrasion and build-up, a mixture of mullite and a bonding metal is formed through a bonding metal layer formed on the surface of the roll base material by thermal spraying as in JP-A-59-226113. There has been proposed a roll in which the thermal spraying intermediate layer and the uppermost layer of the thermal spray coating of mullite are formed by thermal spraying.

[0005]

However, the thermal expansion coefficient of the mullite sprayed coating is much smaller than that of the bonding metal, and even when the sprayed layer is made into three layers as in JP-A-59-226113. , The thermal sprayed coating uppermost layer, the thermal spraying intermediate layer and the bonding metal layer have a large difference in thermal expansion coefficient, the stress generated between the coatings when thermal fluctuation occurs cannot be sufficiently relaxed, and the peeling resistance is poor. However, there is a drawback that mullite has a low hardness and is easily worn.

As a result of various studies, the inventors of the present invention have added alumina or stabilized zirconia having a large thermal expansion coefficient and high hardness to the mullite raw material powder used in the uppermost layer of the thermal spray coating and the intermediate spray layer to perform thermal spraying. The present invention has been completed by finding a coated roll that has excellent adhesion to a roll substrate, does not peel off, and has high wear resistance at high temperature and a large effect of preventing buildup.

That is, the present invention is a hearth roll having a coating layer formed on the roll surface, which is excellent in high-temperature peeling resistance, high-temperature abrasion resistance and build-up preventing effect when used in an oxidizing or reducing atmosphere. It is intended to provide.

[0008]

The gist of the present invention will be described below. Through the bonding metal layer formed on the surface of the roll base material by thermal spraying, mullite, the bonding metal and MgO, CaO, Y
_A thermal spraying intermediate layer comprising a mixture of zirconia (20 to 70 vol% with respect to mullite) containing 5 to 20% by weight of ₂ O ₃ and 1% or more of mullite and MgO, CaO, Y ₂ O _3. Heat-treatment furnace roll with excellent peeling resistance, wear resistance, and build-up resistance formed by thermal spraying the uppermost layer of thermal sprayed coating made of a mixture of zirconia (20 to 70 vol% with respect to mullite) ..

[0009] A thermal spraying intermediate layer composed of a mixture of mullite, a bonding metal and alumina (20 to 70 vol% with respect to mullite) and a mullite and alumina (mullite) through a bonding metal layer formed on the surface of the roll base material by thermal spraying. 20 to 70 vol% of the mixture), the uppermost layer of the thermal spray coating is formed by thermal spraying and has excellent peel resistance, abrasion resistance and build-up resistance. Heat treatment furnace rolls The present invention will be described in detail below.

The hearth roll substrate is made of heat resistant cast steel. These substrates were sprayed with a bonding metal layer on the surface, mullite in the middle, a spraying intermediate layer consisting of a mixture of bonding metal and 20 to 70 vol% alumina or stabilized zirconia with respect to mullite, and mullite as the uppermost layer. A thermal spray coating uppermost layer is formed of a mixture of 20 to 70 vol% alumina or stabilized zirconia with respect to mullite.

In the present invention, alumina or stabilized zirconia is added to the thermal spray coating because these ceramics have high thermal expansion, the difference in thermal expansion coefficient between the bonding metal layer, the thermal spray intermediate layer and the uppermost thermal spray coating layer is reduced. This is because the peel resistance and the wear resistance of the coating can be improved due to the high hardness, and the reactivity with iron oxide is low and the buildup resistance is not deteriorated.

From the results of this evaluation, when 15 vol% of alumina or stabilized zirconia was added to the mullite raw material powder, the effect of improving the peeling resistance due to the addition of alumina and stabilized zirconia was not confirmed. On the other hand, when 80 vol% was added, it was found that the coating film could not be densified and the buildup resistance was deteriorated because alumina and stabilized zirconia had high melting points. From this, the amount of alumina or zirconia added is 20 to 70 vol%
Must.

The details and results of this test will be described below.

The ceramic coating of the present invention was tested for peeling resistance, abrasion resistance and buildup resistance. Of these, 50 × 50 × 10 mm for peeling resistance and abrasion resistance tests
50 × 3 on the build-up resistance test on the SUS base material
Samples obtained by performing thermal spraying shown in Table 1 were used as a top coat (the uppermost layer of the thermal spray coating), an inner coat (a thermal spray intermediate layer), and a bond coat (a metal layer for bonding) on a 0 × 5 mm SUS substrate. Table 2 shows the physical property values of the raw material powder used in the preparation of the thermal spray coating.

[0015]

[Table 1]

[0016]

[Table 2]

First, a peel resistance test was conducted on the developed product. The peeling resistance test was performed by measuring the number of times of peeling when the sample was held at 1000 ° C. for 15 minutes and then repeatedly subjected to thermal shock of holding for 15 minutes in water. As a result, as shown in Table 3, the present invention is considerably superior in peeling resistance to the comparative materials with a small amount of alumina or stabilized zirconia added, and it is found that the addition of these ceramics improves the peeling resistance. It was

[0018]

[Table 3]

Next, the following experiment was conducted in order to investigate the high temperature wear resistance of the developed product. 900 on the sample surface
High temperature wear resistance was investigated by sliding a ball of material SUJ2 at a temperature of ₂ ° C. in an atmosphere of N ₂ —H _{2 of} 5% for a load of 2 kg, a sliding speed of 0.2 m / s and a sliding distance of 720 m. As a result, as shown in Table 4, it was found that the developed product was superior in high temperature wear resistance to the comparative material. It is considered that the wear resistance of the comparative material containing a large amount of alumina and stabilized zirconia was low because the melting points of alumina and stabilized zirconia were high and the coating could not be densified during thermal spraying.

[0020]

[Table 4]

The following experiment was conducted to evaluate the build-up resistance of the developed product. The test apparatus used for the experiment is shown in FIG. Radius 3 made from SCH22 (25Cr-20Ni-0.4C)
A half-moon pressure roll 6 of 5 mm was manufactured and reciprocally slid on each of the two sprayed samples 4 and 4 ', and an evaluation device capable of reproducing the occurrence of buildup was used. The two sprayed samples 4, 4'use the one 4 sprayed on both sides and the one 4'one surface sprayed on the SUS substrate, and build between the half-moon shaped pressure roll 6 and the two samples 4, 4 '. Raw material 5 (iron oxide powder F
e ₃ O ₄ , true specific gravity of 5.18, particle size distribution of 10 μm or less), and store in tray 3. These devices are placed in a pot-type electric furnace 2 and 900 ° C. in a reducing atmosphere of N ₂ —H ₂ 2%.
The pressure roll 6 is reciprocally moved for 4 hours at a constant temperature to cause buildup. In the figure, 1 is an atmosphere gas introduction pipe, 7 is a pressure rod, 8 is a load material, 9 is a counter balance, 10 is a seal plate, and 11 is a speed reducer.

In the above reproduction experiment, as shown in FIG.
The surface that directly contacts the half-moon roll 6 is surface A, the back surface is surface B, and the surface C that faces surface B is the surface C, and the buildup resistance after the test is shown in Table 5. Using an index, the respective evaluation points were summed and compared. In addition, the buildup resistance of the thermal sprayed sample was evaluated by the average value of the adhesion area ratio of Fe ₃ O ₄ which is the buildup source.

[0023]

[Table 5]

Table 6 shows the build-up resistance test results.
The newly developed material has a build-up resistance index and F higher than the comparative material.
It was found that the adhering area ratio of the e ₃ O ₄ powder was excellent and the build-up resistance was also excellent. It is considered that this is because alumina or zirconia, which is difficult to react with iron oxide, was added.
On the other hand, the build-up resistance of the comparative material is inferior because the melting points of alumina and stabilized zirconia are high, the coating is not densified during thermal spraying, and iron oxide easily gets caught in the coating and build-up occurs. It is thought that it is easier to do. This time, NiCr was used as the metal component,
Similar results were obtained with the CoCrAlY, CoNiCrAlY, and NiCrAlY systems.

[0025]

[Table 6]

[0026]

As described above, the hearth roll of the present invention is remarkably excellent in high temperature delamination resistance, abrasion resistance and build-up resistance, and greatly contributes to the roll life extension.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of a buildup test evaluation apparatus and method, and FIG. 2 is an explanatory diagram of a buildup test evaluation apparatus and method.

[Explanation of symbols]

4, 4 ': Thermal spray sample, 5: Build-up raw material,
6: Pressure roll.

Claims (2)

[Claims] 1. A mullite, a bonding metal, and MgO, through a bonding metal layer formed on the surface of a roll base material by thermal spraying.
A thermal spraying intermediate layer made of a mixture of zirconia (20 to 70 vol% with respect to mullite) containing 5 to 20% by weight of CaO and Y ₂ O ₃ , and mullite, MgO and Ca.
Peeling resistance formed by thermal spraying the uppermost layer of the thermal sprayed coating made of a mixture of zirconia (20 to 70 vol% with respect to mullite) containing 5 to 20% by weight of O and Y ₂ O ₃ in one or more weight%,
Heat treatment roll with excellent wear resistance and build-up resistance 2. A thermal spraying intermediate layer comprising a mixture of mullite, a bonding metal and alumina (20 to 70 vol% with respect to mullite) through a bonding metal layer formed by thermal spraying on the surface of a roll base material, and mullite and alumina. (20-70 vol% with respect to mullite) A heat treatment furnace roll with excellent peeling resistance, abrasion resistance and build-up resistance formed by thermal spraying the uppermost layer of thermal spray coating