JP7320780B2 - machine parts - Google Patents

Description

The present invention relates to mechanical parts. More specifically, the present invention relates to steel mechanical components.

Conventionally, carbon (C) and nitrogen (N), which are interstitial elements, are penetrated and diffused into the surface of machine parts made of steel to strengthen the surface solid solution (carburizing treatment, nitriding) processing) is widely known.

A method described in Japanese Patent Application Laid-Open No. 2002-323051 (Patent Document 1) is known as a surface treatment of mechanical parts using boron. In the surface treatment method described in Patent Document 1, a boride layer is formed on the surface of the mechanical component (the raceway surface of the outer ring of the rolling bearing). The boride layer is made of iron boride (Fe ₂ B, FeB).

JP-A-2002-323051

However, iron boride is brittle. Therefore, in the outer ring of the rolling bearing described in Patent Document 1, the boride layer causes brittle fracture.

The present invention has been made in view of the problems of the prior art as described above. More specifically, the present invention provides a mechanical component and a method of manufacturing the mechanical component that can improve the hardness of the surface while suppressing the occurrence of brittle fracture on the surface.

A mechanical component according to one aspect of the present invention is made of steel. A diffusion layer in which boron (B) is solid-dissolved is formed on the surface of the mechanical component. The concentration of boron in the diffusion layer is higher than the concentration of boron inside the mechanical component.

In the mechanical part, the steel contains 0.95 mass percent or more and 1.1 mass percent or less carbon, 0.3 mass percent or less silicon, 0.5 mass percent or less manganese, and 1.4 mass percent It may contain more than 1.6% by mass of manganese and less than 1.6% by mass.

In the above mechanical component, the concentration of boron on the surface may be 0.1% by mass or more and less than 8% by mass.

In the mechanical component described above, the surface hardness may be 800 Hv or more and 1200 Hv or less. In the above mechanical component, the diffusion layer may have a thickness of 0.01 mm or more and 0.3 mm or less.

According to the mechanical component and the method for manufacturing the mechanical component according to one aspect of the present invention, it is possible to improve the hardness of the surface while suppressing the occurrence of brittle fracture on the surface of the mechanical component.

4 is a top view of the outer ring 10; FIG. FIG. 2 is a cross-sectional view along II-II in FIG. 1; FIG. 3 is an enlarged view in region III of FIG. 2; 4A to 4C are process diagrams showing a method of manufacturing the outer ring 10; It is a cross-sectional SEM image of a test piece. It is an EPMA analysis result of a test piece. 4 is a graph showing the relationship between the distance from the interface between the Fe ₂ B layer and the diffusion layer 11 and the hardness of the test piece. 4 is a graph showing the relationship between boron concentration and hardness in the diffusion layer 11. FIG.

Details of embodiments of the present invention will be described with reference to the drawings. In the drawings below, the same or corresponding parts are denoted by the same reference numerals, and duplicate descriptions will not be repeated in principle.

(Configuration of mechanical parts according to the embodiment)
The configuration of the mechanical component according to the embodiment will be described below.

A mechanical component according to the embodiment is, for example, an outer ring 10 of a rolling bearing. The mechanical component according to the embodiment is not limited to this. For example, the mechanical component according to the embodiment may be an inner ring or rolling element of a rolling bearing. Below, the outer ring 10 will be described as an example of the mechanical component according to the embodiment.

FIG. 1 is a top view of the outer ring 10. FIG. FIG. 2 is a cross-sectional view along II-II in FIG. As shown in FIGS. 1 and 2, the outer ring 10 has a top surface 10a, a bottom surface 10b, an inner peripheral surface 10c, and an outer peripheral surface 10d. The upper surface 10a, the bottom surface 10b, the inner peripheral surface 10c, and the outer peripheral surface 10d form the surface of the outer ring 10. As shown in FIG.

The upper surface 10a and the bottom surface 10b form end surfaces of the outer ring 10 in the direction along the central axis 10e. The bottom surface 10b is the opposite surface of the top surface 10a. The inner peripheral surface 10 c forms a raceway surface of the outer ring 10 . The inner peripheral surface 10c continues to the top surface 10a and the bottom surface 10b. The outer peripheral surface 10d continues to the top surface 10a and the bottom surface 10b.

Outer ring 10 is made of steel. The steel forming the outer ring 10 is hardened by quenching. The steel constituting the outer ring 10 includes, for example, 0.95 mass percent or more and 1.1 mass percent or less carbon, 0.01 mass percent or more and 0.3 mass percent or less silicon (Si), and 0.01 mass percent or more. It contains manganese (Mn) of 0.5 mass percent or less and chromium (Cr) of 1.4 mass percent or more and 1.6 mass percent or less. However, the composition of the steel forming the outer ring 10 is not limited to this.

FIG. 3 is an enlarged view in region III of FIG. A diffusion layer 11 is formed on the surface of the outer ring 10 . Boron is solid-dissolved in the diffusion layer 11 . The concentration of boron in the diffusion layer 11 is higher than the concentration of boron inside the outer ring 10 . Since the diffusion layer 11 is formed on the surface of the outer ring 10, no compounds of boron and iron (eg, Fe ₂ B, FeB) are present on the surface of the outer ring 10 .

The concentration of boron in diffusion layer 11 on the surface of outer ring 10 is preferably 0.1% by mass or more and less than 8% by mass. The solid solubility limit of boron in steel is 8% by mass.

The diffusion layer 11 has a thickness TH. The thickness TH is preferably 0.01 mm or more and 0.3 mm or less. When the hardness is measured from the surface of the outer ring 10 toward the inside of the outer ring 10, the hardness gradually decreases from the surface of the outer ring 10 toward the inside of the outer ring 10, and finally reaches a constant value. The distance from the surface of the outer ring 10 until the hardness becomes constant is the thickness TH of the diffusion layer 11 .

The surface hardness of the outer ring 10 is preferably 800 Hv or more and 1200 Hv or less. The hardness of the surface of the outer ring 10 is measured according to the Vickers hardness test method specified in the JIS standard (JIS Z 2244:2009).

(Manufacturing method of machine part according to embodiment)
A method for manufacturing a mechanical component according to the embodiment will be described below. Note that, similarly to the above, the method of manufacturing the outer ring 10 will be described as an example of the method of manufacturing the mechanical component according to the embodiment.

4A to 4D are process diagrams showing a method of manufacturing the outer ring 10. FIG. As shown in FIG. 4, the method for manufacturing a mechanical component (the method for manufacturing the outer ring 10) according to the embodiment includes a preparation step S1, a immersion step S2, a quenching step S3, a tempering step S4, and a post and a processing step S5.

In the preparation step S1, a ring-shaped (annular) member to be processed is prepared. The member to be processed is made of steel. This steel is the same steel as the steel forming the outer ring 10 .

In the immersion step S2, a diffusion layer 11 is formed on the surface of the member to be processed. The diffusion layer 11 is formed using a spark plasma sintering (SPS) method. In the spark plasma sintering method, first, the member to be processed is placed in a jig while the surface of the member to be processed is in contact with the powder containing boron.

The powder containing boron is made of, for example, boron carbide ( _B4C ). The jig is made of graphite. The atmosphere inside the jig is a vacuum. The degree of vacuum in the jig is preferably 10 Pa or less.

In the discharge plasma sintering method, secondly, the member to be processed whose surface is in contact with the powder containing boron is heated while being pressurized. The pressure applied at this time is, for example, 11 MPa.

Incidentally, although the diffusion layer 11 is formed on the surface of the member to be processed as described above, a compound of boron and iron is also formed on the surface of the member to be processed.

In the quenching step S3, the member to be processed is quenched. The quenching step S3 has a heating and holding step S31 and a cooling step S32. The heating and holding step S31 is performed by holding the member to be processed at a predetermined holding temperature for a predetermined time. This predetermined holding temperature is a temperature equal to or higher than the _A1 transformation point of the steel forming the member to be processed. A part of the ferrite phase contained in the steel constituting the member to be processed is transformed into the austenite phase by the heating and holding step S31.

In the cooling step S32, the member to be processed is cooled from the predetermined heating temperature to a temperature below the _MS point of the steel forming the member to be processed. In the cooling step S32, a martensite phase is generated from the austenite phase generated in the heating and holding step S31, and the workpiece is hardened by quenching.

In the tempering step S4, the member to be processed is tempered. The tempering step S4 is performed by holding the member to be processed at a predetermined temperature for a predetermined time. This predetermined temperature is a temperature below the _A1 transformation point of the steel that constitutes the member to be processed.

In the post-processing step S5, post-processing is performed on the member to be processed. In the post-processing step S5, for example, cleaning of the member to be processed and machining such as grinding and polishing of the surface of the member to be processed are performed. In the post-treatment step S5, the compound of boron and iron formed on the surface of the member to be processed in the immersion step S2 is removed, and the diffusion layer 11 is exposed on the surface of the member to be processed. As described above, the mechanical component (outer ring 10) according to the embodiment is manufactured.

(Effects of mechanical parts according to the embodiment)
The effects of the mechanical component according to the embodiment will be described below.

As described above, in the mechanical component according to the embodiment, the diffusion layer 11 in which boron is solid-dissolved is formed on the surface. From another point of view, no compound of boron and iron is present on the surface of the mechanical component according to the embodiment. A compound of boron and iron is brittle and causes brittle fracture, but in the mechanical component according to the embodiment, since there is no compound of boron and iron on the surface, the occurrence of brittle fracture can be suppressed. .

The surface of the mechanical component according to the embodiment is solid-solution-strengthened by solid-solution of boron. Further, due to solid solution of boron, hardenability of the mechanical component according to the embodiment is improved on the surface. As described above, according to the mechanical component according to the embodiment, it is possible to improve the hardness of the surface while suppressing the occurrence of brittle fracture on the surface.

(Example)
Examples of the mechanical component according to the embodiment will be described below.

<Test piece>
A member having a diameter of 19 mm and a thickness of 5 mm was prepared as a test piece. The steel comprising this specimen contained 1.0 weight percent carbon, 0.26 weight percent silicon, 0.41 weight percent manganese, and 1.39 weight percent chromium, as shown in Table 1. are doing.

<Conditions of immersion treatment>
When performing the discharge plasma sintering method on the test piece, powder of borocarbon was used as the powder containing boron. The pressure applied to the test piece during the discharge plasma sintering method was 11 MPa. The degree of vacuum in the jig containing the test piece was set to 10 Pa or less. Heating in the spark plasma sintering method was performed at 850° C. for 6 hours.

<Quenching and tempering conditions>
The heating and holding step S31 for the test piece was performed by holding at 790° C. for 0.5 hours. The cooling step S32 for the test piece was performed by oil cooling. The tempering step S4 for the test piece was performed by air cooling after holding at 180°C for 2 hours. Table 2 shows the immersion treatment conditions and the quenching/tempering conditions described above.

<Results of structure observation and elemental analysis>
FIG. 5 is a cross-sectional SEM image of the test piece. FIG. 6 is the EPMA analysis result of the test piece. In FIG. 6, the horizontal axis is the distance from the surface of the test piece (unit: mm), and the vertical axis is the concentration of boron (unit: mass percent). As shown in FIG. 5, a layer composed of a compound of boron and iron and a diffusion layer 11 were formed on the surface of the test piece by performing the boron immersion step S2. The layer composed of a compound of boron and iron included a layer of FeB on the side of the specimen near the surface, and a layer of Fe ₂ B immediately below it. The diffusion layer 11 was formed directly under the Fe ₂ B layer.

As shown in FIG. 6, by EPMA (Electron Probe Micro Analyzer), boron could be detected to a depth of about 0.07 mm from the interface between the Fe ₂ B layer and the diffusion layer 11 . At a position 0.07 mm or more away from the interface between the Fe ₂ B layer and the diffusion layer 11, boron could not be detected _by EPMA. It is considered that the diffusion is to a position further away from the interface with the diffusion layer 11 .

<Hardness test results>
FIG. 7 is a graph showing the relationship between the distance from the interface between the Fe ₂ B layer and the diffusion layer 11 and the hardness of the test piece. In FIG. 7, the horizontal axis is the distance (unit: mm) from the interface between the Fe ₂ B layer and the diffusion layer 11, and the vertical axis is the hardness (unit: Hv) of the test piece. As shown in FIG. 7, the hardness of the diffusion layer 11 reached 1200 Hv at the interface with the Fe ₂ B layer. At a position at a distance of 0.3 mm or more from the interface between the Fe ₂ B layer and the diffusion layer 11, the hardness was constant at about 750 Hv. From this, it is considered that boron diffuses to a depth of about 0.3 mm from the interface between the Fe ₂ B layer and the diffusion layer 11, although it cannot be detected by EPMA.

FIG. 8 is a graph showing the relationship between boron concentration and hardness in the diffusion layer 11. As shown in FIG. In FIG. 8 , the horizontal axis represents the boron concentration (unit: mass percent) in the diffusion layer 11 and the vertical axis represents the hardness (unit: Hv) of the diffusion layer 11 . As shown in FIG. 8, the hardness of the diffusion layer 11 increased as the boron concentration in the diffusion layer 11 increased. Specifically, by setting the boron concentration in the diffusion layer 11 to 0.1% by mass or more, the hardness of the diffusion layer 11 is 800 Hv or more, and the boron concentration in the diffusion layer 11 is about 1.4% by mass. By percentage, the hardness of the diffusion layer 11 was 1200Hv.

Although the embodiment of the present invention has been described as above, it is also possible to modify the above-described embodiment in various ways. Also, the scope of the present invention is not limited to the embodiments described above. The scope of the present invention is indicated by the scope of claims, and is intended to include all changes within the meaning and scope of equivalence to the scope of claims.

The above embodiments are particularly advantageously applied to steel machine parts and methods for manufacturing steel machine parts.

10 outer ring, 10a upper surface, 10b bottom surface, 10c inner peripheral surface, 10d outer peripheral surface, 10e center shaft, 11 diffusion layer, S1 preparation step, S2 immersion step, S3 quenching step, S4 tempering step, S5 post-treatment step, S31 heating and holding step, S32 cooling step, TH thickness.

Claims (5)

Machine parts made of steel,
A diffusion layer in which boron is solid-dissolved is formed on the surface of the mechanical component,
In the diffusion layer, boron is dissolved in the steel and does not form a compound with iron,
A mechanical component, wherein the concentration of boron in the diffusion layer is higher than the concentration of boron in the interior of the mechanical component. The steel comprises 0.95 to 1.1 weight percent carbon, 0.3 weight percent or less silicon, 0.5 weight percent or less manganese, and 1.4 weight percent to 1.6 weight percent. 10. The mechanical component of claim 1, containing less than 10% of chromium. 3. The mechanical component according to claim 1, wherein the concentration of boron on the surface is 0.1% by mass or more and less than 8% by mass. The mechanical component according to any one of claims 1 to 3, wherein the surface has a hardness of 800 Hv or more and 1200 Hv or less. The mechanical component according to any one of claims 1 to 4, wherein the diffusion layer has a thickness of 0.01 mm or more and 0.3 mm or less.