JP2002038281A - Member for high-temperature use superior in corrosion resistance and high-temperature erosion resistance and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a corrosion resistance and a high-temperature erosion resistance of a member used in a high temperature and corrosive environment in which particles fly coming at high speed. SOLUTION: A steel base material is provided with a surface treatment layer comprising a layer mainly consisting of iron boride of 20-50 μm thickness on the base material side and a layer mainly consisting of nickel boride of 10-30 μm thickness thereupon, by means of forming a nickel plated layer on a surface with nickel electroplating and then boronizing the layer in a molten salt bath.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-temperature member, and more particularly to a high-temperature member such as a steam turbine blade used in a high-temperature corrosive atmosphere and in an environment where particles fly at a high speed. It relates to improvement of high temperature erosion resistance.

[0002]

2. Description of the Related Art Conventionally, the surface of a member has been hardened in order to improve abrasion resistance and erosion resistance. As a method of hardening the surface, for example, a method of modifying the surface layer of the member, such as induction hardening treatment, carburizing treatment, and nitriding treatment, may be mentioned. There is also a method in which a high-hardness coating is formed on the surface of the member by plating, vapor deposition, or the like to harden the surface. As a method of forming a high hardness coating, for example, there is electroless nickel plating. The coating of the electroless nickel plating has a high hardness of 350 Hv or more as it is at room temperature, and has a high hardness of about 1000 Hv when heat-treated at 400 ° C. In addition, electroless nickel plating film,
It is also excellent in corrosion resistance, and is said to be a film suitable for applications requiring both corrosion resistance and erosion resistance.

However, the electroless nickel plating film has a
In a temperature range up to about 0 ° C., a certain degree of hardness can be maintained, but at a higher temperature, for example, a temperature range of 500 ° C. or more, the hardness is significantly reduced, and the erosion resistance is significantly reduced. There's a problem.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a high-temperature member excellent in corrosion resistance and high-temperature erosion resistance and a method of manufacturing the same.

[0005]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have developed a surface-hardened layer having both corrosion resistance and erosion resistance at a high temperature suitable for a high-temperature member, including a method for forming the same. I studied diligently. As a result, an electrolytic nickel plating film is formed on the member, and thereafter, the member is subjected to boration treatment in which the member is immersed in a molten salt bath.
A surface treatment layer having a layer mainly composed of nickel boride as an outer layer and an inner layer composed of iron boride can be uniformly formed in each part even in a complicated shape, and is a member excellent in corrosion resistance and high temperature erosion resistance. I found what I could do. According to the study of the present inventors, it is possible to remarkably improve the erosion resistance at high temperatures and also provide the corrosion resistance, for the first time, as a two-layer structure having nickel boride as the upper layer and iron boride as the lower layer. .

The present invention has been completed based on the above findings and further studies. That is, the present invention is a high-temperature member having a surface treatment layer on the surface layer of a steel base material, wherein the surface treatment layer comprises a layer mainly composed of iron boride in order from the base material side, and a nickel boride. A high-temperature member having excellent corrosion resistance and high-temperature erosion resistance characterized by comprising a main layer, and in the present invention, the layer mainly composed of iron boride has a thickness of 20 to 50 μm. Preferably, the layer mainly composed of nickel boride has a thickness of 10 to 30 μm, and in the present invention, the iron boride is made of FeB
, Fe ₂ B, and Fe ₂₃ B ₆ , and the nickel boride is preferably one or two of Ni ₂ B and Ni ₃ B.

In the second aspect of the present invention, the steel substrate is subjected to electrolytic nickel plating, and a nickel plating film is formed on the surface. A method for producing a high-temperature member having excellent corrosion resistance and high-temperature erosion resistance, which comprises forming a surface treatment layer on a surface layer of a material, and in the second invention, the surface treatment layer is made of a steel base material. A layer mainly composed of iron boride in order from the material side,
In the second aspect of the present invention, it is preferable that the boride treatment is performed by subjecting the steel substrate to a molten salt bath containing anhydrous borax and boride as main components. Preferably, the treatment is performed by immersion in the substrate.

In the second aspect of the present invention, it is preferable to perform a solution treatment after the boring treatment.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The high temperature member of the present invention has corrosion resistance,
It is a member suitable for use in an environment where high-temperature erosion resistance is required. The environment in which corrosion resistance and high-temperature erosion resistance are required in the present invention refers to, for example, fine particles (iron oxide, hardness of about 500 Hv) generated from the inner wall of a boiler tube such as in a steam turbine blade. (Temperature: about 600 ° C).

The steel substrate used in the high-temperature member of the present invention is not particularly limited, but it is preferable to use a steel material that can be used at a high temperature and has excellent corrosion resistance and oxidation resistance. In the present invention, a hard surface treatment layer is provided on a surface layer in order to improve erosion resistance. The surface-treated layer has a high hardness not only at room temperature but also at a high temperature (preferably in a temperature range of 600 ° C. or higher), and mainly comprises a layer mainly composed of iron boride and a layer mainly composed of nickel boride from the substrate side. Layer. As described above, by forming the layer mainly composed of nickel boride as the upper layer, the corrosion resistance is improved by the presence of nickel boride.
In particular, corrosion resistance in an environment containing water vapor is improved, and relatively high hardness is maintained even in a high temperature range, so that erosion resistance is improved.

[0011] Further, since the layer mainly composed of iron boride is used as the lower layer, the surface hardness of the member can be increased to a high temperature due to the presence of iron boride which can maintain high hardness higher than nickel boride up to a high temperature range. It is possible to maintain and improve the erosion resistance, and even if the layer mainly composed of nickel boride is worn or worn, the layer mainly composed of iron boride having a higher hardness than nickel boride in the lower layer is used. The erosion resistance does not decrease, and the life of the member can be extended.

The layer mainly composed of iron boride according to the present invention includes:
Preferably, it refers to a layer containing at least 50% by area of iron boride of at least one of FeB, Fe ₂ B, and Fe ₂₃ B ₆ . Further, the layer mainly containing nickel boride in the present invention preferably means a layer containing nickel boride composed of one or two of Ni ₂ B and Ni ₃ B in an area ratio of 50% or more. .

The thickness of the layer mainly composed of iron boride is preferably adjusted in the range of 20 to 50 μm. If the thickness is less than 20 μm, the region of high hardness is too narrow and the erosion resistance of the member is reduced. On the other hand, when the thickness exceeds 50 μm, the processing time becomes longer and the productivity is reduced. Therefore, the thickness of the layer mainly composed of iron boride is preferably in the range of 20 to 50 μm.

The layer mainly composed of nickel boride has a thickness of 10
It is preferable to adjust the thickness to a range of about 30 μm. Thickness
If the thickness is less than 10 μm, the thickness of the layer is too small to improve the corrosion resistance by nickel boride, while if the thickness exceeds 30 μm, it is difficult to control the thickness of the lower layer. Next, a method for producing the high-temperature member of the present invention will be described.

First, an electrolytic nickel plating process is applied to a steel base material of the above-mentioned material. As the electrolytic nickel plating treatment, any of the generally known electrolytic nickel plating is suitable. The thickness of the nickel plating film to be formed is 10 ~ 30μm
It is preferred that If the thickness of the coating is out of this range, a layer mainly composed of nickel boride having a predetermined thickness cannot be formed.

This nickel plating film combines with B introduced by a subsequent boration treatment to form nickel borides, thereby improving corrosion resistance and high-temperature erosion resistance.
The steel substrate having a nickel plating film formed on the surface is then subjected to a boride treatment. The boration treatment is preferably performed by immersing the steel substrate in a molten salt bath containing anhydrous borax and boride as main components. By performing the treatment by immersing in a molten salt bath, it is possible to easily form a layer mainly composed of nickel boride and iron boride even to a complicated shape, for example, a so-called closed portion where the surface is not directly opened. Can be formed.

By this treatment, boron B diffuses from the surface into the nickel plating film and the steel base material. Then, nickel boride is formed in the nickel plating film, iron boride is formed in the steel base material, and a layer mainly composed of nickel boride is formed as an upper layer, and a layer mainly composed of iron boride is formed as a lower layer. . Thereby, a surface treatment layer having high hardness and corrosion resistance even at high temperatures can be formed, and corrosion resistance and erosion resistance at high temperatures are improved.

The boride treatment is preferably performed under the condition that the layer mainly composed of iron boride is formed in a range of 20 μm to 50 μm. If the thickness of the layer mainly composed of iron boride is less than 20 μm, the erosion resistance is reduced. On the other hand, if the thickness is more than 50 μm, the processing time becomes longer and the productivity is reduced.
After forming the surface treatment layer on the steel base material surface layer, it is preferable to perform a solution treatment according to the base material composition in order to maintain desired base material characteristics.

[0019]

EXAMPLE A steel substrate (dimensions: 50 × 50 × 6 mm) was subjected to electrolytic nickel plating to form a 5 to 30 μm thick electrolytic nickel plating film on the surface. Next, these steel substrates were subjected to a boride treatment of dipping in a molten salt bath containing anhydrous borax and boride as main components to form a surface treatment layer having a predetermined thickness. After that, a solution treatment was performed to obtain a high temperature member having a surface treatment layer. As a comparative example, a member was prepared in which an electroless nickel plating film was formed on the same steel base material as described above in a thickness of 50 μm.

About the obtained member, the structure of the surface treatment layer,
The thickness was investigated, and the corrosion resistance and erosion resistance were further investigated. (1) Investigation of Structure The cross section in the plate thickness direction of the obtained member was polished, the structure was imaged with an optical microscope, and the thickness of each surface treatment layer was measured from the obtained photograph. Also, regarding the cross section of the obtained high temperature member,
The phases constituting each layer of the surface treatment layer were identified by X-ray diffraction.

(2) Investigation of Corrosion Resistance and Erosion Resistance The obtained high temperature member was subjected to a salt spray test in accordance with JIS Z 2371. The condition of the salt spray was 2 hours at room temperature, and the corrosion loss after the test was determined. Corrosion resistance is
Comparative example (electrode No.
The corrosion weight loss in 8) was set to 1.0, and the ratio was evaluated.

After heating the obtained high-temperature member to 500 ° C., the fine particles (iron oxide) are heated at room temperature at a speed of 40:40.
After projecting at m / s for 5 min, the wear and loss on wear were measured. The erosion resistance was evaluated by the ratio of the loss of abrasion loss of the comparative example (member No. 8) in which an electroless nickel plating film was formed to 1.0. Table 1 shows the results.

[0023]

[Table 1]

Table 1 shows that all of the examples of the present invention have high high-temperature hardness, and are excellent in corrosion resistance and erosion resistance at high temperatures.

[0025]

According to the present invention, even a member having a complicated shape can form a uniform surface treatment layer at each part, and a high temperature member having excellent corrosion resistance and high temperature erosion resistance can be processed through a complicated process. It can be manufactured without any problems, and the service life of the high-temperature member can be prolonged.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a configuration of a surface treatment layer of a high-temperature member of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel base material 2 Layer mainly composed of iron boride 3 Layer mainly composed of nickel boride

Claims (6)

[Claims] 1. A high temperature member having a surface treatment layer on a surface layer of a steel base material, wherein the surface treatment layer mainly includes a layer mainly composed of iron boride and a nickel boride in order from the substrate side. A high-temperature member having excellent corrosion resistance and high-temperature erosion resistance, comprising: 2. The layer mainly composed of iron boride has a thickness of 20 to 50.
μm, and the layer mainly composed of the nickel boride has a thickness of 10 μm.
The high-temperature member according to claim 1, wherein the thickness is from 30 µm to 30 µm. 3. A steel substrate is subjected to electrolytic nickel plating, a nickel plating film is formed on the surface, and then the steel substrate is subjected to boride treatment to form a surface treatment layer on the surface of the steel substrate. A method for producing a high-temperature member having excellent corrosion resistance and high-temperature erosion resistance. 4. The method according to claim 3, wherein the surface treatment layer comprises a layer mainly composed of iron boride and a layer mainly composed of nickel boride in order from the steel substrate side. A method for manufacturing a high-temperature member. 5. The boring treatment according to claim 3, wherein the boring treatment is performed by immersing the steel base material in a molten salt bath containing anhydrous borax and boride as main components. A method for producing the high-temperature member according to the above. 6. The method for producing a high-temperature member according to claim 3, wherein a solution treatment is performed after the boring treatment.