JPH05172248A - Piston ring and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a piston ring and its manufacturing method, fatigue strength is large satisfactorily and which has at the whose periphery a hardened ceramic layer due to ion plating process. CONSTITUTION:At the periphery of a parent metal 1 to a piston ring, a hardened ceramic layer 3 is formed by ion plating process followed by a gas nitrization process to form a nitride layer 2 at the side faces and the inside circumference, while the peripheral surface is left out of nitride layer and provided with hardened ceramic layer solely.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston ring used in an internal combustion engine, a compressor, etc. and a method for manufacturing the piston ring.

[0002]

2. Description of the Related Art Conventionally, as a piston ring for an internal combustion engine, a compressor, etc., a spheroidal graphite cast iron base material having a hard chrome plating applied on its outer peripheral surface has been widely used.
As a piston ring with excellent wear resistance, SUS440
A martensitic stainless base material typified by B or DINX90 material subjected to gas nitriding treatment is put to practical use. Since the nitrogen diffusion layer is formed on the entire circumference of the gas nitriding ring, wear resistance is improved not only on the outer peripheral surface in contact with the cylinder wall but also on the upper and lower side surfaces in contact with the piston groove. It has the advantage of significantly improved durability.

Recently, physical vapor deposition (Physical Vapor) is applied to the outer peripheral surface in order to further extend the life of the piston ring.
Deposition: PVD) treatment, especially the application of hard ceramic coatings such as chromium nitride (CrN) and titanium nitride (TiN) by the ion plating method has been increasing. These hard ceramic coatings have a hardness of HmV 1,500
Due to the above, there are drawbacks that they are weaker in impact and less in toughness than metals. Moreover, from the viewpoint of improving durability, there is a demand for the coating thickness of the ceramic coating layer to be 20 μm or more, and the adhesion and fatigue strength of the coating film to the base material due to the thickening become a problem. In particular, the chromium nitride coating is likely to be thickened, and has recently attracted attention as a coating for piston rings, and those having a coating of 20 μm or more have been put into practical use.

In the ion plating, an object to be processed, which is rotatably held in a vacuum container, is heated to about 400 ° C. by a heater, and a crucible provided below the metal plating contains metal chromium or titanium as a vapor deposition material. Argon gas radiated from the HCD gun provided on the side wall of the container and nitrogen gas introduced from the gas introduction pipe provided on the wall, which is vaporized by the plasma beam, are introduced into the container, for example, 3 × 10 ^-2 torr.
Then, a nitride layer made of TiN or CrN is formed.
By changing the amount of nitrogen gas during ion plating, the nitride layer coating by ion plating has a structure in which each phase of Cr, Cr ₂ N, and CrN coexists in the case of chromium. In terms of Cr ₂ N and CrN
A composition consisting of has been put to practical use.

By the way, in the piston ring, it is necessary to prevent side wear from the viewpoint of function, and when ion plating is applied to the outer peripheral surface, conventionally, the piston ring base material of high chromium stainless steel is nitrided, After that, it is general to perform ion plating.

However, in such a method, the toughness of the thickened layer composed of Cr ₂ N and CrN phases is insufficient, so that the ion plating layer is cracked and the crack is rapidly propagated to the nitride layer. Therefore, there is a drawback that the fatigue strength is significantly reduced.

[0007]

SUMMARY OF THE INVENTION The present invention has eliminated the above-mentioned drawbacks of the conventional method of manufacturing a piston ring having nitrided layers on both sides and a hardened ceramic coating layer by ion plating on the outer peripheral surface. An object of the present invention is to provide a piston ring having sufficient fatigue resistance and a method for manufacturing the piston ring.

[0008]

In order to solve the above-mentioned problems, a piston ring according to the present invention has a nitride layer only on both side surfaces and an inner peripheral surface of a martensitic stainless piston ring, and has an ionic surface on an outer peripheral surface. It is characterized by having a hardened ceramic coating layer by plating.

One of the manufacturing methods is to form a hardened ceramic coating layer by ion plating only on the outer peripheral surface of a martensitic stainless steel piston ring base material, and then perform gas nitriding (GN) treatment on both side surfaces and A feature is that a nitride layer is formed on the inner peripheral surface.

Another of the manufacturing methods is to form a nitriding prevention layer such as nickel or water glass on the outer peripheral surface of a martensitic stainless steel piston ring base material, and then leave it in nitrogen gas to nitride the surface. A gas nitriding treatment for forming a layer is performed, the nitriding prevention layer on the outer peripheral surface is thereafter removed, and a hard ceramic coating layer is formed on the outer peripheral surface by ion plating.

[0011]

According to the first manufacturing method, the hardened ceramic coating layer is formed only on the outer peripheral surface of the piston ring base material by ion plating, and then the gas nitriding treatment is performed. Since the hardened ceramic coating has already been applied, the nitriding layer is formed only on both side surfaces other than the outer peripheral surface and the inner peripheral surface without contacting the nitrogen gas atmosphere during the nitriding treatment.

According to the second manufacturing method, since the nitriding prevention layer is formed on the outer peripheral surface of the piston ring base material and the gas nitriding treatment is performed, the nitride layer is not formed on the outer peripheral surface of the ring.
The nitride layer is formed only on both side surfaces and the inner peripheral surface. afterwards,
The nitriding prevention layer on the outer peripheral surface is removed, and the hard ceramic layer is formed on the outer peripheral surface by ion plating.Therefore, a nitride layer is not formed on the outer peripheral surface and only the hard ceramic layer is formed, and the hard ceramic layer is cracked. Even if it enters, it hardly propagates to the base material and the fatigue strength is significantly improved.

[0013]

[Examples] A SUS 440B stainless steel 85 mm diameter x 2 mm height x 3.1 mm radial direction rectangular cross-section with a BF-shaped outer periphery of a piston ring base material was prepared, and the following three types of surface treatment were applied to the specimen. Created. (1) According to the present invention, a chrome nitride film having a thickness of 40 μm is formed on the outer peripheral surface of a test piece by ion plating, and then gas nitriding (GN) is performed at a nitriding treatment temperature of 520 ° C. to 570 ° C. I did. The depth of the gas nitriding layer is 50 μm. There is no change in the composition of the chromium nitride film at the above gas nitriding temperature.

(2) As is generally done conventionally,
First, gas nitriding was performed on the base material to form a nitride layer having a depth of 50 μm on both side surfaces, the outer circumference and the inner circumference, and thereafter, a chromium nitride film having a thickness of 15 μm was formed on the outer circumference by ion plating. (3) A 40 μm thick chromium nitride film was formed on the outer periphery by the same method as (2).

FIG. 1 (a) shows a cross section of a piston ring specimen manufactured by the method of the above (1), that is, the method of the present invention, and FIG. 1 (b) shows the above (2) and (3). The cross section of the specimen produced by the method is shown. In the cross section of (b), the nitride layer 2 is formed on both side surfaces and the inner and outer circumferences of the base material 1, and the chromium nitride coating 3 is formed on the nitride layer on the outer circumference. On the other hand, in the cross section of (a), the nitride layer 2 is formed only on both side surfaces and the inner circumference of the base material 1, and the nitride layer 2 is not formed under the chromium nitride coating film 3 on the outer circumference.

A fatigue test was conducted on the above three types of piston ring test pieces. In the test method, as shown in FIG. 2, one end of the abutment of the piston ring is fixed, and the other end is vibrated in the closing direction to repeatedly generate tensile stress on the outer periphery of the ring as shown in FIG. In this case, the maximum stress occurs at a position 180 ° from the abutment. Therefore, the amplitude changes with stress. Stress when the piston ring is closed to the nominal diameter
f ₂ is about 33 kg / mm ² in this case. If a certain stress is applied from f ₂ and the number of repetitions of 10 ⁷ is cleared, f ₂
+ A certain stress becomes the fatigue limit stress.

FIG. 4 shows the results of fatigue tests conducted on the above three types of piston ring specimens. The curve (1) connecting the points indicated by Δ in the figure is the fatigue curve for the specimen (1), and the fatigue limit stress is f ₂ +35 kg / mm ² . The curve (2) connecting the points indicated by □ and the curve (3) connecting the points indicated by ○ in the figure are for the specimens (2) and (3), respectively, and their fatigue limit stress is f ₂ +25 kg. / Mm ² and f ₂ + 19kg /
mm ² , which is the fatigue limit stress of (1) f ₂ +35 kg /
Remarkably lower than mm ² . Specimen of (1), that is, P
By performing gas nitriding treatment after VD treatment, a nitride layer is not formed on the outer peripheral surface, and only a chromium nitride film is formed.
The specimen with a nitride layer formed only on the other surface does not have a nitride layer on the outer peripheral surface, so the fatigue limit stress is f ₂ +
35kg / mm ^2, which is a sufficient level.

As a method of forming a hard ceramic coating film of chromium nitride or the like by PVD treatment without forming a nitride layer on the outer peripheral surface of the piston ring, the above-mentioned outer peripheral surface is subjected to PVD treatment and then gas nitriding treatment. In addition to the above method, nickel strike plating on the outer circumference of the ring
5 μm, a nitriding prevention layer is formed on the outer periphery and gas nitriding treatment is performed, a nitriding layer is formed on both side surfaces and an inner peripheral surface, and then the nitriding prevention layer is removed by lapping and PVD such as ion plating. A method of forming a hard ceramic coating film by treatment can also be adopted. As the nitriding prevention layer, a water glass layer may be formed in addition to nickel strike plating.

[0019]

As described above, according to the present invention, since the nitride layer is not formed on the outer periphery but the ion plating layer is formed, a piston ring having sufficient fatigue strength can be obtained.

[Brief description of drawings]

FIG. 1 (a) shows a cross section of a piston ring test piece according to the present invention, and FIG. 1 (b) shows a cross section of a piston ring test piece having a nitride layer and an ion plating film formed on the outer periphery by a conventional method. FIG.

FIG. 2 is an explanatory diagram illustrating a fatigue test method for the piston ring test piece.

FIG. 3 is a graph showing how the stress varies with time during the fatigue test.

FIG. 4 is a curve diagram showing comparison of fatigue test results between a piston ring test piece according to the present invention and a test piece obtained by performing nitriding and ion plating treatment by a conventional method.

[Explanation of symbols]

 1 Piston ring base material 2 Nitride layer 3 Ion plating layer coating

Claims (3)

[Claims] 1. A piston ring comprising a martensitic stainless steel piston ring having a nitride layer only on both side surfaces and an inner peripheral surface thereof, and having a hard ceramic coating layer formed by ion plating on an outer peripheral surface thereof. 2. A hard ceramic coating layer is formed by ion plating only on the outer peripheral surface of a martensitic stainless steel piston ring base material, and then gas nitriding is performed to form nitride layers on both side surfaces and inner peripheral surfaces. The method for manufacturing a piston ring according to claim 1, wherein 3. A martensitic stainless steel piston ring base material is formed with a nitriding prevention layer of nickel, water glass or the like on the outer peripheral surface thereof, and then gas nitriding treatment is performed, after which the nitriding prevention layer on the outer peripheral surface is removed to form an outer periphery. The method for producing a piston ring according to claim 1, wherein a hard ceramic coating layer is formed on the surface by ion plating.