JPH0665709A - Roll for heat treatment furnace - Google Patents

Abstract

PURPOSE:To form a coating layer having large preventing effect on build-up and excellent high temp. peeling resistance and wear resistance on the surface of a roll in a hearth roll used in oxidizing or reducing atmosphere. CONSTITUTION:In the roll for heat treatment being formed with a thermally sprayed oxidation-resistant ceramic film composed of Zr-based nitride or carbide on the surface, even at the time of use in the oxidizing or reducing atmosphere in an annealing furnace at 600-1300 deg.C for long time, the roll has excellent build-up resistance, peeling resistance and wear resistance.

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 referred to as a hearth roll) which is excellent in high temperature peeling resistance, high temperature abrasion resistance and build-up prevention.

[0002]

2. Description of the Related Art For example, a hearth roll disposed in a continuous annealing furnace has a surface thereof 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 wear, and the oxides and iron powder adhered to the heat-treated material are adhered and deposited on the roll surface to form so-called build-up.

If such 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 quality deterioration of steel sheet,
After periodically interrupting the operation to cool the heat treatment furnace, an operator enters the furnace to grind the surface of the hearth roll and replace the roll itself.

For this reason, Japanese Patent Publication No. 57-29549
As described in JP-A No. 63-250449, a roll surface is coated with ceramics such as alumina or zirconia by plasma spray coating, or as described in JP-A-63-250449. A means for spray-coating a non-oxide ceramic raw material powder such as a system carbide has been proposed.

However, the thermal spray coating layer of zirconia or alumina is inferior in peeling resistance because the bond strength between the grains forming the thermal spray coating is deteriorated in a high temperature atmosphere to cause peeling of the coating film itself.
A coating obtained by spraying a Zr-based nitride or Zr-based carbide raw material powder also oxidizes the raw material powder during thermal spraying to become zirconia, transforms in a high temperature atmosphere, and deteriorates the intergranular strength. There is a drawback that peeling itself occurs and the peeling resistance is poor.

[0006]

DISCLOSURE OF THE INVENTION The inventors of the present invention have a coating having excellent high temperature delamination resistance, abrasion resistance, and great build-up prevention effect, which should be applied to hearth rolls used in these oxidizing or reducing atmospheres. As a result of various researches on materials and coating methods, the present invention has been completed by finding a coating roll that has excellent adhesion to a hearth roll substrate, does not peel off, and has excellent high temperature strength. That is, the present invention provides a hearth roll in which a coating layer having excellent high-temperature peeling resistance, wear resistance, and a large 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]

The present invention has a peeling resistance, wear resistance and build-up resistance having a sprayed ceramic coating of Zr-based nitride or Zr-based carbide raw material powder having an oxidation-resistant coating formed on the surface thereof. The main point is a roll for a heat treatment furnace.

The oxidation resistant coating formed on the surface of the raw material powder is a metal coating 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 silicidation. Materials, metal nitrides and metal carbide coatings can be used.

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

In the present invention, ZrN or ZrC is used as the thermal spraying raw material because it has a low reactivity with iron oxide and is stable and does not undergo a decrease in intergranular bonding force in a high temperature atmosphere. This is because.

However, as described in JP-A-63-250449, when ZrN and ZrC are sprayed as the raw material powder, the raw material powder is oxidized during the thermal spraying to become zirconia, which undergoes transformation in a high temperature atmosphere to form grains. The strength was decreased, the peel resistance was poor, and the original performance was not exhibited.

For this reason, in the present invention, an oxidation resistant coating is formed on the surface of the raw material powder to prevent oxidation during the thermal spraying of the raw material powder, so that the interparticle strength is deteriorated in a high temperature atmosphere having low reactivity with iron oxide. A film for a hearth roll having excellent peeling resistance, abrasion resistance, and build-up resistance that does not occur is obtained.

However, when a metal coating is formed on the surface of the raw material powder as an oxidation-resistant coating, the metal is exposed on the surface of the raw material and the coating easily reacts with iron oxide, so the thickness of the metal coating is 10% of the particle diameter of the raw material powder. The following is preferable. Also, when forming a metal oxide, metal silicide, metal nitride, or metal carbide coating as the oxidation-resistant coating on the surface of the raw material powder, select a material that has relatively low reactivity with iron oxide, 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 in order to evaluate the peeling resistance, abrasion resistance and buildup resistance of the ceramic coating of the present invention. 5 for peeling resistance and abrasion resistance test
For the 0 × 50 × 10 mm SUS base material and the build-up resistance test, a sample obtained by spraying the SUS base material of 50 × 50 × 10 mm shown in Table 1 was used. 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]

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

[0018]

[Table 3]

In order to investigate the high temperature wear resistance of the product of the present invention,
The following experiment was conducted. A sample similar to that used in the peel resistance test was used in this test. The surface of this sample is made of material S in an atmosphere of N ₂ —H ₂ 5% and 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 the high temperature wear resistance. As a result, as shown in Table 4, it was found that the present invention has excellent wear resistance. It is considered that this is because the coating film of the present invention was densified.

[0020]

[Table 4]

Next, the following experiment was conducted in order to investigate the build-up resistance of the product of the present invention. The test apparatus used for the experiment is shown in FIG. SCH22 (25Cr-20Ni-0.
A half-moon shaped pressure roll 6 having a radius of 35 mm was manufactured using 4C) as a material and slid back and forth on each of the two sprayed samples 4 and 4 ', and an evaluation device capable of reproducing the occurrence of buildup was used. Two sprayed samples 4 and 4 ′ were prepared by double-sided spraying 4 and single-sided spraying 4 ′, and the build-up raw material 5 (between the half-moon pressure roll 6 and the two samples 4, 4 ′ was used. Iron oxide powder Fe ₃ O ₄ : true specific gravity 5.18: particle size distribution 10 μm or less) is sprinkled and stored in the tray 3. These devices are placed in a pot type electric furnace 2, N ₂ -H ₂
The pressure roll 6 is reciprocated for 4 hours at a constant temperature of 850 ° C. in a reducing atmosphere of 5% 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 in direct contact with the half-moon roll 6 is the A surface, the back surface is the B surface and the surface facing the C surface is the C surface, and the buildup resistance after the test is shown in Table 5 using the buildup resistance index. , And the respective evaluation points were totaled and compared. Further, the buildup resistance of the thermal sprayed sample was evaluated by the average value of the adhered area ratio of Fe ₃ O ₄ which is the buildup 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 has a higher build-up resistance index than any of the comparative materials, and has a small area coverage of Fe ₃ O ₄ powder, and is excellent in build-up resistance. It is considered that this is because the Fe ₃ O ₄ powder is hard to be caught in the coating because the binding force between the grains in the coating is increased and the grains do not fall off by preventing the raw material powder from being oxidized.

[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. To further improve the peel resistance, a so-called cermet layer in which a 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 peel resistance, abrasion resistance and build-up resistance, and greatly contributes to the roll life extension.

[Brief description of 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 raw material 6 Pressure roll

Claims (1)

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