JP2960263B2 - Roll for heat treatment furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is provided in a heat treatment furnace,
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roll for heat treatment furnace (hereinafter, hearth roll) which is excellent in high-temperature peeling resistance, high-temperature abrasion resistance and build-up prevention, particularly for annealing and conveying a steel sheet.

[0002]

2. Description of the Related Art For example, a hearth roll disposed in a continuous annealing furnace has a surface which is to be continuously annealed and conveyed for a long time in an oxidizing or reducing atmosphere at 600 to 1300 ° C. to convey the material. Abrasion occurs, and oxides and iron powder adhering to the material to be heat-treated adhere and accumulate on the roll surface to form a so-called build-up.

When such irregularities due to abrasion or build-up occur on the hearth roll, they are flawed while the steel sheet as the material to be heat-treated is being conveyed, causing deterioration in quality. In order to prevent such steel sheet quality deterioration,
After the operation is periodically interrupted to cool the inside of the heat treatment furnace, an operator enters the furnace to grind the surface of the hearth roll or replace the roll itself.

[0004] For this reason, in the prior art, Japanese Patent Publication No. 57-29549
As described in Japanese Unexamined Patent Application Publication No. Hei 6 (1995) -195, the roll surface is plasma-sprayed with ceramics such as alumina and zirconia, and as described in Japanese Patent Application Laid-Open No. 63-250449, a Zr-based nitride or Zr Means for thermally spraying a non-oxide ceramic raw material powder such as a carbide have been proposed.

However, the thermal spray coating layer of zirconia or alumina deteriorates the bonding force between grains forming the thermal spray coating in a high-temperature atmosphere, and peels off the coating itself, resulting in poor peel resistance.
In addition, the coating obtained by spraying a Zr-based nitride or Zr-based carbide raw material powder also oxidizes during the thermal spraying to form zirconia, and undergoes transformation in a high-temperature atmosphere to deteriorate the intergranular strength. There is a disadvantage that peeling of the film itself occurs and peeling resistance is poor.

[0006]

SUMMARY OF THE INVENTION The present inventors have developed a coating which is to be applied to hearth rolls used in these oxidizing or reducing atmospheres, which is excellent in high-temperature peeling resistance, abrasion resistance and has a large build-up prevention effect. As a result of various studies on materials and coating methods, the present inventors have found a coated roll which has excellent adhesion to a hearth roll substrate, does not peel off, and has excellent high-temperature strength, and has completed the present invention. That is, the present invention provides a hearth roll in which a coating layer having excellent high-temperature peeling resistance, abrasion resistance and build-up prevention effect is formed on the roll surface when used in an oxide or reducing atmosphere. It was made for the purpose of doing.

[0007]

SUMMARY OF THE INVENTION The present invention has a thermal sprayed ceramic coating of a Zr-based nitride or Zr-based carbide raw material powder having an oxidation-resistant coating formed on its surface, and is excellent in exfoliation resistance, wear resistance and build-up resistance. And a roll for a heat treatment furnace.

The oxidation resistant film formed on the surface of the raw material powder may be a metal film formed by plating, mechanical coating, or the like, or a metal oxide formed by metal alkoxide treatment, mechanical coating, vapor deposition, CVD, PVD, or metal silicide. , Metal nitride and metal carbide coatings can be employed.

Hereinafter, the present invention will be described in detail. The substrate of the hearth roll is made of heat-resistant cast steel. A ZrN or ZrC raw material powder whose surface has been subjected to the above-mentioned oxidation-resistant treatment is sprayed on the surface of these substrates to form a ceramic film.

In the present invention, ZrN or ZrC is used as a thermal spraying material because it has low reactivity with iron oxide and is stable without causing transformation in a high-temperature atmosphere and does not decrease in intergranular bonding force. That's why.

However, when ZrN or ZrC is sprayed as a raw material powder as described in JP-A-63-250449, the raw material powder is oxidized to zirconia at the time of thermal spraying and undergoes transformation under a high-temperature atmosphere to form particles. The inter-strength decreased, the peel resistance was poor, and the original performance was not exhibited.

For this reason, in the present invention, an oxidation resistant film is formed on the surface of the raw material powder to prevent oxidation during the thermal spraying of the raw material powder, whereby the reactivity between the raw material powder and the iron oxide is low, and the interparticle strength is deteriorated in a high temperature atmosphere. A hearth roll coating excellent in peeling resistance, abrasion resistance and build-up resistance in which no cracking occurs was obtained.

However, when a metal film is formed on the surface of the raw material powder as an oxidation-resistant film, the metal is exposed on the surface of the film and the film easily reacts with iron oxide. It is preferable to set the following. When a metal oxide, metal silicide, metal nitride or metal carbide film is formed on the surface of the raw material powder as an oxidation resistant film, a material having relatively low reactivity with iron oxide is selected. It is possible to increase the thickness of the coating to 50% of the raw material powder particle size.

The present inventors conducted the following experiments to evaluate the peeling resistance, abrasion resistance and build-up resistance of the ceramic coating of the present invention. 5 for peel resistance and wear resistance test
A SUS substrate having a size of 0 × 50 × 10 mm and a sample obtained by spraying the thermal spray of Table 1 on a SUS substrate having a size of 50 × 50 × 10 mm were used for the build-up resistance test. Table 2 shows the physical property values of the raw material powders used in forming the thermal spray coating.

[0015]

[Table 1]

[0016]

[Table 2]

In this evaluation, the electroless plating was carried out to obtain about 0.
Nickel-plated ZrN, ZrC powder having a thickness of 5 μm and ZrN, ZrC powder having a ZrSi ₂ coating having a thickness of about 10 μm by mechanical coating were used. The product of the present invention was first subjected to the following experiment in order to investigate the peeling resistance. The peel resistance test was performed on the sample at 1000 ° C 15
The measurement was performed by measuring the number of times of peeling when the thermal shock of holding in water for 15 minutes after repeated holding was repeated. As a result, as shown in Table 3, it was found that the present invention was excellent in peel resistance.

[0018]

[Table 3]

In order to examine the high temperature wear resistance of the product of the present invention,
The following experiment was performed. In this test, the same sample as that used in the peel resistance test was used. The surface of this sample was placed in an atmosphere of N ₂ -H ₂ 5% at a temperature of 850 ° C.
A UJ2 ball was slid at a load of 2 kg and a sliding speed of 0.2 m / s for a sliding distance of 720 m to investigate high-temperature wear resistance. As a result, as shown in Table 4, it was found that the present invention was excellent in wear resistance. This is probably because the coating of the present invention was densified.

[0020]

[Table 4]

Next, in order to investigate the build-up resistance of the product of the present invention, the following experiment was conducted. FIG. 1 shows the test apparatus used for the experiment. SCH22 (25Cr-20Ni-0.
4C), a crescent-shaped pressure roll 6 having a radius of 35 mm was manufactured, and reciprocally slid on the two sprayed samples 4, 4 'to use an evaluation device capable of reproducing the occurrence of build-up. Two sprayed samples 4 and 4 'were sprayed on both sides and one sprayed on one side 4', and a build-up material 5 (between the half-moon shaped pressure roll 6 and the two samples 4 and 4 'was used. (Iron oxide powder Fe ₃ O ₄ : true specific gravity 5.18: particle size distribution 10 μm or less), and housed in tray 3. These devices are placed in a pot type electric furnace 2 and N ₂ -H ₂
The pressure roll 6 is reciprocated at a constant temperature of 850 ° C. for 4 hours in a 5% reducing atmosphere to cause build-up. In the drawing, reference numeral 1 denotes an atmosphere gas introduction pipe, 7 denotes a pressure rod, 8 denotes a load material, 9 denotes a counterbalance, 10 denotes a seal plate, and 11 denotes a reduction gear.

In the above reproduction experiment, as shown in FIG.
The surface directly in contact with the half-moon roll 6 is designated as surface A, the surface opposite to surface B is designated as surface C, and the build-up occurrence state after the test is evaluated using a build-up resistance index as shown in Table 5. , And the respective evaluation points were compared with each other. Further, the build-up resistance of the thermal sprayed sample was evaluated based on the average value of the adhesion area ratio of Fe ₃ O ₄ as a build-up source.

[0023]

[Table 5]

Table 6 shows the results of the build-up resistance test.
It was found that the product of the present invention had a higher build-up resistance index than any of the comparative materials, a small area ratio of Fe ₃ O ₄ powder adhered, and excellent build-up resistance. This is considered to be because the oxidation of the raw material powder was prevented, the bonding force between the grains in the film was increased, and the particles did not fall off, so that the Fe ₃ O ₄ powder was less likely to bite into the film.

[0025]

[Table 6]

In this test, CoCr was used as the metal component.
AlY was used, but CoNiCrAlY, NiCrA
Similar results were obtained with the 1Y system. In order to further improve the peeling resistance, a so-called cermet layer in which metal is added to the top layer may be used.

[0027]

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

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a build-up test evaluation device and method.

FIG. 2 is a partially enlarged view of FIG.

[Explanation of symbols]

 4,4 'thermal spray sample 5 build-up material 6 pressure roll

Claims (1)

(57) [Claims] 1. A roll for a heat treatment furnace having a sprayed ceramic coating of a Zr-based nitride or Zr-based carbide raw material powder having an oxidation-resistant coating formed on the surface.