JP2002285319A - Member for high temperature use having excellent oxidation resistance and wear resistance, and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a member for high temperature use which has a surface treated layer usable at high temperatures, and has excellent oxidation resistance and wear resistance, and to provide a production method therefor. SOLUTION: A base material made of a low carbon metallic material containing <=0.40 mass% C is subjected to carburization treatment to form a carburized layer, preferably, having a thickness of 50 to 500 μm. Next, the base material is dipped into a chromium-containing molten salt held at >=850 deg.C. In this way, a chromium carbide layer having a thickness of 1 to 30 μm is formed on the surface layer. The chromium carbide layer preferably consists of a layer of Cr7 C3 alone or Cr23 C6 alone, or a mixed layer of Cr7 C3 and Cr23 C6 or further mixed with Cr3 C2 .

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 a method of manufacturing the same, and more particularly to an improvement in oxidation resistance and wear resistance of a high-temperature member used at a high temperature, such as a mechanical part around an engine.

[0002]

2. Description of the Related Art Conventionally, to improve the wear resistance, the surface of a metallic material member has been hardened.
Examples of the means for hardening the surface include a method of modifying the surface layer of the member, such as a metal infiltration method such as induction hardening, carburizing, nitriding, or chromium diffusion coating.

[0003] For example, Japanese Patent No. 3049763 discloses a Cr diffusion method in which plasma carburizing is performed on the surface of steel containing Cr as a base material component, and then embedded in a powder containing metallic Cr and heated under a H ₂ gas flow. After infiltration treatment, Fe, Cr
A surface modification treatment method for a Cr-containing steel, which forms a mixed structure of a composite carbide composed of Fe and Cr and a matrix composed of Fe, Cr and C, and improves corrosion resistance and wear resistance is disclosed. Here, the Cr diffusion and infiltration treatment is usually called a chromizing treatment, in which a material to be treated is embedded in a mixed powder composed of a metal Cr powder, alumina powder, and ammonium chloride powder, and H ₂ gas is introduced. 950 while flowing
This is a method of heating at 1100 ° C. for 5 to 15 hours to diffuse and infiltrate Cr into the surface layer of the material to be treated.

The surface layer of a steel material treated by the technique described in Japanese Patent No. 3049763 is, for example, C: 5.8 wt%, Cr:
35 wt%, Fe: composite carbide having a residue, C: 0.4 wt%,
Cr: 8 wt%, Fe: a composite structure with a matrix having a residue, the area ratio of carbide is 80%, and the hardness is about Hv 1000 to 1200. Therefore, the wear resistance at room temperature is certainly improved. However, when this steel material is used for a long time in an atmosphere exceeding 600 ° C as a high-temperature member, it has a complex carbide containing Fe, so its hardness is reduced and internal oxidation at locations exposed to high temperatures is severe. Become
Oxidation resistance and wear resistance are significantly deteriorated.

[0005] As described above, the members manufactured by the technique described in Japanese Patent No. 3049763 have a remarkable lack of oxidation resistance and wear resistance, and are suitable for application to high temperature members whose use conditions exceed 600 ° C. Had left the problem. Further, according to the technique described in Japanese Patent No. 3049763, after the chromizing treatment, the resulting coating film has a surface rough defect, leaving a practical problem.

[0006]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems of the prior art and has a surface treatment layer suitable for high-temperature members used at high temperatures, such as mechanical parts around an engine. It is another object of the present invention to propose a high-temperature member having excellent oxidation resistance and abrasion resistance and a method for producing the same.
In the present invention, “excellent in oxidation resistance” means that the temperature is 800 ° C.
Even in a high temperature environment nearby, the inside of the surface treatment layer is not oxidized and the surface treatment layer does not peel off.

[0007]

Means for Solving the Problems The present inventors have intensively studied various factors affecting oxidation resistance in order to achieve the above-mentioned object. As a result, the present inventors considered that in order to obtain a member having excellent oxidation resistance and wear resistance, the surface treatment layer should be a layer made of pure chromium carbide only, in particular, Cr ₇ C ₃
It is necessary to form a chromium carbide layer mainly composed of

Then, the present inventors first form a carburized layer of a predetermined depth on the surface of the member, and then treat it in a molten salt bath containing Cr to obtain a low carbon material having a C content of 0.4% by mass or less. It has been found that a surface treatment layer consisting purely of chromium carbide can be formed even with a metal member. The present invention has been completed based on the above findings and further studies.

That is, a first aspect of the present invention is a high temperature member having a surface treatment layer on a surface layer of a metal material base material, wherein the surface treatment layer has a hardness of Hv 1000 to 1800 and a thickness of 1 mm.
A high-temperature member having excellent oxidation resistance and wear resistance, characterized in that the chromium carbide layer is a layer made of Cr ₇ C ₃ ;
Alternatively, a layer in which Cr ₇ C ₃ and Cr ₂₃ C ₆ are mixed is preferable. As the base material made of a metal material, it is preferable to use a low-carbon metal material of C: 0.40% by mass or less. Further, the base material made of a metal material may be made of a metal material having a C content of more than 0.40% by mass.

The second invention is a method for producing a high-temperature member having a surface treatment layer on a surface layer of a low carbon metal material base material having a carbon content of 0.40% by mass or less. A first step of forming a carburized layer on the surface layer of the low-carbon metal material base material, and then heating the low-carbon metal material base material having the carburized layer formed on the surface layer in the first step at 850 ° C. or higher. Immersed in a molten salt bath containing chromium held at a thickness of 1 to 30 having a hardness of Hv 1000 to 1800 on the surface layer of the low carbon metal material base material.
and a second step of forming a chromium carbide layer having a thickness of .mu.m. It is preferable that the thickness of the carburized layer is 50 to 500 μm. In the second aspect of the present invention, it is preferable that the chromium carbide layer is a layer made of Cr ₇ C ₃ or a layer in which Cr ₇ C ₃ and Cr ₂₃ C ₆ are mixed.

[0011] The third invention is a method for producing a high-temperature member comprising a surface treatment layer on the surface of a metal-made base material containing C: more than 0.40% by mass of carbon. Oxidation and abrasion resistance, characterized by immersing a base material made of a metal material in a molten salt bath containing chromium maintained at 850 ° C or higher to form a chromium carbide layer having a thickness of 1 to 30 μm on the surface layer. A method for producing a high-temperature member having excellent heat resistance, and in the fourth invention, the chromium carbide layer is a layer made of Cr ₇ C ₃ ;
Alternatively, a layer in which Cr ₇ C ₃ and Cr ₂₃ C ₆ are mixed is preferable.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The high temperature member of the present invention has a surface treatment layer on a surface layer of a metal material base material. As a surface treatment layer, a chromium carbide layer having a hardness Hv of 1000 to 1800 and a thickness of 1 to 30 μm is formed. In the high-temperature member of the present invention, the chromium carbide layer formed on the surface layer is composed of Cr and C, and is composed of pure carbide having no solid solution such as Fe other than Cr and C. By making the surface treatment layer a layer composed of such pure chromium carbide, the hardness of the surface layer is H
v1000 to 1800, which improves wear resistance and 80
Oxidation resistance is improved without exfoliation even in a high temperature environment around 0 ° C.

The chromium carbide layer to be formed includes pure chromium carbide, such as Cr ₇ C ₃ alone, Cr ₂₃ C ₆ alone, or Cr ₇ C ₃ , Cr ₂₃ C ₆ , or even Cr ₃ C _2. A mixed chromium carbide layer is preferred. On the other hand, if the thickness of the formed chromium carbide layer is less than 1 μm, the film formation is poor, the wear resistance is reduced, and the oxidation resistance is also reduced, so that practical functions can hardly be expected. On the other hand, if the thickness of the chromium carbide layer exceeds 30 μm, the chromium carbide layer has a high hardness and a compressive stress, which may cause a chipping phenomenon. Therefore, in the present invention, the thickness of the surface treatment layer (chromium carbide layer) formed on the surface layer is limited to 1 to 30 μm.

The base material of the high-temperature member is a low-carbon metal material of C: 0.40% by mass or less, especially a low-carbon steel material of C: 0.40% by mass or less, for example, austenitic heat-resistant steel material such as SUS310S, SUH-23, Inconel and the like. It is preferred to use Conventionally, such low-carbon metallic materials (low-carbon steel materials)
Even at a high temperature of 0 ° C., a stable chromium carbide layer could not be formed without oxidation or the like.

When a metal material (steel) containing more than 0.40% by mass of C is used as a base material, since the C content is high, it contains Cr without a carburizing treatment as a pretreatment. A surface treatment layer comprising a desired chromium carbide layer can be formed by immersion in a molten salt bath. Next, the method for producing a high-temperature member of the present invention,
explain.

C: 0.40% by mass as base material for high temperature member
It is preferable to use the following low-carbon metal materials, among them, steel materials of C: 0.40% by mass or less, for example, SUS310S, SUH-23, Inconel material and the like. First, oxides on the surface of the low carbon metal material base material are removed by polishing, sputtering or the like, and then carburizing treatment is performed to form a carburized layer on the surface layer of the base material.
The thickness of the carburized layer is preferably from 50 to 500 μm. If the thickness of the carburized layer is less than 50 μm, the amount of carbon (C) contributing to the formation of chromium carbide will be insufficient, and a long time immersion in a molten salt bath will be required to form a desired chromium carbide layer. Becomes an etching state, resulting in a poor surface condition. On the other hand, if the thickness of the carburized layer exceeds 500 μm,
The intrinsic properties (mechanical strength, heat resistance) of the substrate may be impaired.

The conditions for the carburizing treatment are not particularly limited. However, in order to obtain the above-described carburized layer depth, the heating temperature is set at 90 ° C.
It is preferable that the temperature is 0 to 1100 ° C and the holding time is 1 to 8 hours. As the method of carburizing treatment, generally known gas carburizing, plasma carburizing, solid carburizing and the like are all suitable.
Plasma carburization is preferred from the viewpoint of the surface roughness of the substrate surface and the ease of adjusting the carburization concentration and carburization depth.

The substrate made of a low-carbon metal material, on which a carburized layer, preferably a carburized layer having a thickness of 50 to 500 μm, is formed, is then Cr
And held for a predetermined time. The molten salt bath in which the substrate is immersed is at 850 ° C. or higher, preferably 1300 ° C.
It is kept at a temperature below ° C. If the bath temperature is below 850 ° C,
The diffusion rate of Cr is slow, and it takes a long time to produce a chromium carbide having a desired thickness, and the productivity is reduced. Meanwhile, 1300 ° C
If it exceeds 300, the viscosity of the treatment bath agent becomes small, and the substrate is directly oxidized upon contact with the air during cooling, which is not preferable in terms of quality. For this reason, the temperature of the molten salt bath is 850 ° C. or higher, preferably 13 ° C.
The temperature was set to 00 ° C. or lower. The immersion time of the member in the bath is preferably adjusted according to the bath temperature so that the thickness of the chromium carbide layer is 1 to 30 μm.

When the base material is a metal material having a C content of more than 0.40% by mass, preferably a steel material having a C content of more than 0.40% by mass, a Cr-containing molten salt bath is used without performing the above-mentioned carburizing treatment. By performing only the second step of immersion in chromium, a surface treatment layer composed of a chromium carbide layer can be formed. The molten salt bath suitable for the present invention is preferably anhydrous borax containing Cr. Thereby, a chromium carbide mainly composed of Cr and C mainly composed of Cr ₇ C ₃ can be formed on the surface layer of the member made of the low carbon metal material.

[0020]

[Example] C: Low carbon steel containing less than 0.4% by mass (dimensions: 60 × 60 × 3 mm) and C: carbon steel containing more than 0.4% by mass (dimensions: 60 × 60 × 3 mm) Oxides and dirt on the surface of the substrate were removed by polishing and sputtering, and the surface was cleaned. Next, when a low carbon steel material was used as the base material, the base material was subjected to a first step of forming a carburized layer having a thickness shown in Table 1 on the surface layer by plasma vacuum carburizing treatment.
The conditions of the plasma vacuum carburizing treatment were as follows: temperature: 1000 ° C,
Time: 1 to 8 h, and the thickness of the carburized layer was adjusted. The thickness of the carburized layer was determined by defining a region exceeding the average hardness in the vicinity of the center of the base material as a carburized layer and measuring the hardness in the vicinity of the surface layer using a micro-Vickers hardness tester. In the case where the carbon steel material containing C: more than 0.4% by mass was used as the base material, the first step was omitted.

Next, these substrates were subjected to a second step of immersion in a molten salt bath containing Cr to form a surface treatment layer comprising a chromium carbide layer on the surface of the substrate, thereby obtaining a high-temperature member.
The thickness of the formed surface treatment layer was determined by observing a cross section near the surface layer using an optical microscope or a super-electron microscope.
The type of the constituent phase of the formed surface treatment layer was identified for chromium carbide using X-ray diffraction. The hardness of the formed surface treatment layer was measured over the entire range of the formed surface treatment layer on the surface section of the member using a Vickers hardness tester, and the average value was measured for the hardness of the surface treatment layer. I did it.

As a conventional example, a low carbon steel material containing less than 0.4% by mass of C was subjected to plasma carburizing treatment and chromizing treatment to form a surface treatment layer having a thickness of 30 μm on the surface layer. Next, oxidation resistance and abrasion resistance of each of the obtained members were examined. The test method was as follows. (1) Oxidation resistance Each of the obtained members (size: 60 × 60 × 3 mm) was heated to 800 ° C., held for 40 hours, and then cooled. After the treatment, the surface condition of each member was visually observed, the presence or absence of oxidation and peeling was investigated, and the oxidation resistance was evaluated. X indicates that oxidation and peeling occurred in the entire member, Δ indicates that a part of the member occurred, and ○ indicates no occurrence. (2) Abrasion resistance A test piece (dimensions: 60 × 30 × 3 mm) was sampled from each of the obtained members, and the test piece was heated to 800 ° C. and then subjected to an Ogoshi-type abrasion test. After the test, the specific wear amount was calculated from the width of the wear mark of each test piece, and the degree of damage was evaluated. When the degree of damage was large, the abrasion resistance was poor: poor, and when the degree of damage was small, good: good.

Table 1 shows the obtained results.

[0024]

[Table 1]

Each of the examples of the present invention does not cause internal oxidation or peeling even at a high temperature of 800 ° C., is excellent in oxidation resistance, is excellent in abrasion resistance, and has excellent characteristics as a high temperature member. You can see that. On the other hand, in the conventional example, 80
At a high temperature of 0 ° C., internal oxidation and peeling occur, and the oxidation resistance is reduced.

[0026]

As described above, according to the present invention, 800 ° C.
Even under such a high-temperature use environment, a usable high-temperature member can be manufactured stably at low cost, and the industrially significant effect is achieved. Further, according to the present invention, there is also an effect that the service life of the high temperature member can be extended.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G046 MA06 MB03 MB08 MB09 MC01 4K028 BA03 BA12

Claims (6)

[Claims] 1. A high temperature member having a surface treatment layer on a surface layer of a base material made of a metal material, wherein the surface treatment layer is Hv1000.
A high-temperature member excellent in oxidation resistance and wear resistance, characterized in that it is a chromium carbide layer having a thickness of 1 to 30 µm and a thickness of 1 to 30 µm. 2. The high-temperature member according to claim 1, wherein the chromium carbide layer is a layer made of Cr ₇ C ₃ or a layer in which Cr ₇ C ₃ and Cr ₂₃ C ₆ are mixed. . 3. A method for producing a high-temperature member having a surface treatment layer on a surface layer of a base material made of a low-carbon metal material having a carbon content of 0.40 mass% or less. A first step of forming a carburized layer on the surface layer of the base material, and then the low-carbon metal material base material having the carburized layer formed on the surface layer in the first step includes chromium maintained at 850 ° C or higher. Immerse in a molten salt bath, and apply a hardness Hv100 to the surface layer of the low carbon metal base material.
A second step of forming a chromium carbide layer having a thickness of 1 to 30 μm having a thickness of 0 to 1800 and a second step of sequentially forming the chromium carbide layer. 4. The method according to claim 3, wherein the thickness of the carburized layer is 50 to 500 μm. 5. A method for producing a high-temperature member having a surface treatment layer on a surface layer of a metal material base material containing more than 0.40% by mass of carbon, wherein the metal material base material is heated to 850 ° C. Immerse in the molten salt bath containing chromium held above, and on the surface,
A method for producing a high-temperature member excellent in oxidation resistance and wear resistance, comprising forming a chromium carbide layer having a hardness Hv of 1000 to 1800 and a thickness of 1 to 30 μm. 6. The method according to claim 3, wherein the chromium carbide layer is a layer made of Cr ₇ C ₃ or a layer in which Cr ₇ C ₃ and Cr ₂₃ C ₆ are mixed. A method for producing the high-temperature member according to the above.