JPH0650429A - Piston ring of titanium alloy and its manufacture - Google Patents

Abstract

PURPOSE:To provide a piston ring which is more lightweight than the conventional piston ring made of steel, excellent in the antiseize property, and has the strength to withstand the higher output and higher speed, and its manufacturing method. CONSTITUTION:In a piston ring made of titanium alloy, the piston ring body is made of titanium alloy, has the fiber structure in the circumferential direction of the piston ring, and a surface-hardened layer composed of the non-molten oxygen-rich layer at least on a sliding surface with the cylinder wall. After the wires of titanium alloy are bent in the ring shape, the oxygen-rich layer can be formed by heating the wires in the atmosphere where at least oxygen is present at the temperature of 550-1050 deg.C.

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.

[0002]

2. Description of the Related Art Conventionally, a piston ring for an internal combustion engine is a cast iron ring whose surface is hard-Cr-plated, but it is difficult to manufacture a piston ring with a thin axial direction, and the piston ring has a relatively large cross-sectional area. Therefore, there is a problem that the inertia becomes large and the fluttering phenomenon is likely to occur. In recent years, internal combustion engines have been made into wire rods by hot working and cold working after melting, and then bent into a ring shape after tempering, in response to the demand for high output, high speed, and measures against exhaust gas. The applied steel piston ring is becoming the mainstream. As ring materials made of these steels, in addition to Si-Cr steel, 1
There are 3Cr type and 17Cr type stainless steels and the like, and those subjected to surface treatment such as hard Cr plating treatment or nitriding treatment are used on the surface of these rings.

[0003]

As described above, the steel piston ring makes it possible to reduce the axial width of the piston ring, the contact area with the cylinder wall is reduced, and the friction loss is reduced. Further, there is an advantage that the weight of the ring itself can be reduced, which cannot be obtained by the conventional cast iron piston ring. Recently, however, the demand for higher output has increased, and a material for the piston ring capable of coping with higher speed rotation has been demanded. In order to follow high-speed rotation, it is necessary to further reduce the weight of the piston ring.With conventional steel piston rings, if it is made thinner than this, the strength will be insufficient and important functions of the internal combustion engine will be impaired. There was a problem.
In order to solve the above problems, a piston ring using titanium or titanium alloy having a small specific gravity (Japanese Patent Application Laid-Open No. 2-129)
No. 467) and constituent members of automobile engine parts (Japanese Patent Laid-Open No. 1-1119682).

Of these, Japanese Patent Application Laid-Open No. 2-129467
A piston ring body comprising a piston ring body made of steel, a titanium or titanium alloy layer adhered to the outer peripheral surface side, and a titanium nitride layer formed at least on the outer peripheral surface side. However, since the body of the piston ring uses tool steel or martensitic stainless steel to secure spring characteristics, the effect of weight reduction is small, rather the outer peripheral surface side of the clad titanium or titanium alloy layer. It is intended to form a relatively thick titanium nitride layer having a thickness of 50 μm or more. On the other hand, in the member disclosed in JP-A-1-119682, the surface layer of pure titanium or titanium alloy is heated to a melting temperature or higher, and oxygen is absorbed and solid-solved in the melted portion to form a surface-hardened layer which is a molten oxygen-enriched layer. Is formed.

However, when the surface layer of a thin ring-shaped outer peripheral portion such as a piston ring is heated above a high melting temperature of about 1700 ° C., the piston ring is deformed due to thermal influence or contraction at the time of solidification, and a resolidification structure. However, there is a drawback that the toughness is lowered by the formation of. An object of the present invention is to provide a novel piston ring which is lighter in weight than conventional steel piston rings and has strength enough to withstand high output and high speed, and a manufacturing method thereof.

[0006]

SUMMARY OF THE INVENTION The inventor has focused on titanium or titanium alloys having a specific gravity of about 60% that of steel, because there is a limit to reducing the weight of conventional steel piston rings. I considered using it as a main body. By the way, there are problems in characteristics required of the piston ring itself as factors that hinder the practical use of the piston ring made of titanium or titanium alloy, and manufacturing problems that hinder the processing of the piston ring. The shortage of titanium or titanium alloy with respect to the properties required for piston rings is as follows: (1) The strength level is low, and the heat resistance and wear resistance are insufficient. (2) The seizure with the sliding mating metal easily occurs. Further, as a method of processing into a piston ring, (a) cutting out from a bar material, (b) cutting a pipe into slices, (c)
There are punching of plate material and wire cutting. But,
The methods (a) and (c) significantly impair the yield, and in the methods (a) and (b), the fiber structure is in the axial direction of the ring, and in the method (c), the fiber structure is in a fixed direction with respect to the ring surface. As a result, it was found that the strength and toughness of the titanium alloy are further reduced.

As a result of further studies on the above-mentioned characteristic problems and manufacturing problems, forward titanium is inadequate in terms of strength and heat resistance, so that the piston ring body is limited to titanium alloy. It was found that if the piston ring is formed into a ring shape by bending after being processed into a wire material, and the fiber structure is made to coincide with the circumferential direction, constant strength and uniform spring characteristics can be obtained. In addition, after bending into a ring shape, it is heated to 550 to 105 in an atmosphere containing oxygen.
A non-melting oxygen-enriched layer is formed on the surface only by heating and holding at a temperature of 0 ° C, which not only significantly increases the wear resistance and seizure resistance of the sliding part, but also forms on the surface other than the sliding part. It was found that the oxygen-enriched layer thus formed was also effective in strengthening the piston ring body.

Here, the non-molten oxygen-enriched layer of the present invention is
In the above-mentioned JP-A-1-119682, the surface-hardened layer heats the surface layer to a melting temperature or higher and absorbs oxygen in the melted portion to form a solid solution, whereas in the atmosphere where oxygen is present, the temperature is much lower than the melting temperature. An oxygen-enriched layer (also referred to as α case) obtained only by heating and holding it in the above. The present invention simultaneously solves the characteristic problem and the manufacturing problem required for the piston ring itself.

That is, in the first aspect of the present invention, the piston ring body is made of a titanium alloy, has a fiber structure in the circumferential direction of the piston ring, and at least the sliding surface with the cylinder wall is enriched with non-melting oxygen. A piston ring made of a titanium alloy, which has a surface-hardened layer made of a layer, wherein the piston ring body is made of a titanium alloy and has a fiber structure in the circumferential direction of the piston ring, and at least a cylinder. A titanium alloy piston ring having a composite surface hardening layer including a non-melting oxygen-enriched layer on a sliding surface with a wall, the third invention is that after bending a titanium alloy wire material into a ring shape. , A titanium alloy piston, characterized by forming an oxygen-enriched layer on the surface by heating at a temperature of 550 to 1050 ° C. in an atmosphere containing at least oxygen. The fourth invention is a method of manufacturing a ring, in which the titanium alloy wire material is bent into a ring shape, and then subjected to solution treatment and aging to harden the piston ring body, and at the same time, an oxygen-enriched layer is formed on the surface portion. This is a method for manufacturing a titanium alloy piston ring.

[0010]

The titanium alloy used for the piston ring body of the present invention may be an α-type alloy, an α + β-type alloy or a β-type alloy as long as it is a titanium-based alloy other than pure titanium having low strength. be able to. Further, among these, α + β type alloys and β type alloys can be strengthened by combining solution treatment and aging treatment, but they may be used as they are in wire processing or in an annealed state. The titanium alloy piston ring of the present invention is limited to a piston ring that has a metal flow in the circumferential direction, that is, has a fiber structure, that is, is bent after being processed into a wire rod. The reason is that, as described above, the strength and toughness are insufficient in the fiber structure of the ring taken from the rod, pipe or plate. In the titanium alloy piston ring of the present invention, the fiber structure itself has a ring shape and follows the shape of the ring, so that sufficient strength and toughness are ensured against bending stress from the outside.

Further, since the titanium alloy piston ring of the present invention is apt to seize with the sliding metal to be mated, a surface hardened layer consisting of a non-melted oxygen enriched layer is formed on at least the sliding surface with the cylinder. It is mandatory. This surface hardened layer not only enhances the wear resistance of the piston ring itself, but can also significantly suppress seizure with the mating metal on the cylinder side, but if necessary, hard Cr plating, porous Cr plating, composite Plating, Cr spraying, M
The effect is further enhanced by using a composite surface-hardened layer in which various surface treatments such as thermal spraying and nitriding treatment are appropriately used in combination. Further, the surface treatment is not limited to only the sliding surface with the cylinder wall, and since it also has the effect of compensating for the lack of strength of the titanium alloy that is the base material of the piston ring, other surface portions may also have the above-mentioned properties. A surface hardened layer may be formed.

The titanium alloy constituting the piston ring body is hot-worked and then cold-worked or warm-worked and cold-worked to form a wire material having an irregular cross section, which is bent and formed into a ring shape. . The formed ring is heated and held at a temperature of 550 to 1050 ° C. in an atmosphere containing oxygen to form an oxygen-enriched layer on the surface of the titanium alloy. The atmosphere in which oxygen is present may be not only atmospheric air, but also a mixed gas of oxygen and nitrogen, or may be decompressed or in a vacuum of about 10 −3 Torr with very little oxygen. If the heating temperature is lower than 550 ° C, oxygen cannot be solid-dissolved and diffused in the base of the titanium alloy. Conversely, if it exceeds 1050 ° C, not only the crystal grains of the titanium alloy body become coarser but the toughness is impaired. The excessively solid-solved oxygen-enriched layer becomes brittle, and when it is used as a piston ring, chipping and cracking easily occur. Therefore, the temperature range for heating in an atmosphere containing oxygen is limited to 550 to 1050 ° C.

For example, Ti-6 which is a typical titanium alloy
When an Al-4V alloy wire is bent into a ring shape and then heated in the atmosphere for 1 hour, the depth of the oxygen-enriched layer is 800 ° C and 20
It can be used as a piston ring after removing the oxide film formed on the outermost surface layer. Further, the α + β type and β type titanium alloys are more effective if they are used by strengthening the piston ring body by solution treatment and aging and forming an oxygen enriched layer on the surface portion. In this case, after bending into a ring shape, the solution heat treatment is heated and rapidly cooled in an atmosphere in which oxygen is present to form the oxygen-enriched layer, and the subsequent treatment for forming the oxygen-enriched layer is omitted. can do.

[0014]

EXAMPLES Examples to which the present invention is applied will be described in detail below. (Example 1) Ti-5Al-2.5Sn which is an α type titanium alloy
The alloy was made into a rectangular wire rod with a cross section of 2.0 mm x 3.5 mm, and then the wire rod was made into an inner and outer diameter with a three-point roll, and the outer diameter was 50.
After being continuously molded to have a size of mm, the ring was cut to obtain 60 rings. Of these, 20 are 780 ℃ × 1 hour in the atmosphere, other
Forty of them were heated in the atmosphere at 840 ℃ for 1 hour. Also,
Twenty of the 40 pieces were subjected to gas soft nitriding treatment for 6 hours in an ammonia decomposition gas atmosphere at 580 ° C. after thinly grinding and removing the oxide film on the circumferential portion.

After carrying out the above-mentioned surface hardening treatment, the cross-section hardness was measured. As a result, the hardness of the base metal of each treated material is HV318.
The surface hardness of 780 ℃ heating material is ~ HV52 on average for ~ 330.
7. The depth of the surface hardened layer of HV450 or higher was about 25 μm.
The surface hardness of the 840 ° C. heating material was HV519 on average, and the depth of the surface hardened layer of HV450 or higher was about 30 μm or more. Further, the average surface hardness of the material subjected to the soft nitriding treatment after the oxygen enrichment treatment was HV1250.

(Embodiment 2) Ti-6Al-4V alloy, which is an α + β type titanium alloy, is used as a rectangular wire rod having a cross section of 2.0 mm × 3.5 mm, and the wire rod is a cylinder made of heat-resistant steel and the edges are the inner and outer diameters. Spirally wound closely and continuously molded to an outer diameter of 50 mm. Next, the solution was placed in a vacuum heat treatment furnace at 920 ° C. in a restrained state in which it was tightly wound around a cylinder of heat-resistant steel, the holding time was set to 1 hour, leaking, and immediately subjected to solution treatment by water cooling. The degree of vacuum during heating and holding in the vacuum heat treatment is 10
Adjusted to minus squared Torr.

After the solution treatment, the spirally wound wire rod was axially cut into individual rings. Next, the individual rings were arranged on a steel flat plate, and the same steel flat plate was placed on the ring and placed in a heating furnace at 538 ° C. for aging treatment for 4 hours. After the solution treatment and aging treatment, the cross section was corroded with an aqueous solution of hydrofluoric acid 0.5 cc against 100 cc of water, and a white layer enriched with oxygen was observed under an optical microscope. Is recognized and its depth is 65
It was μ. Furthermore, when the hardness was measured, the hardness of the base material was HV397 and the surface hardness was HV532 on average.

(Embodiment 3) By forming a non-melting oxygen-enriched layer on the surface of titanium alloy, which is one of the features of the present invention, the effect of seizure with the sliding mating metal is confirmed. Therefore, the following fabby test was performed. In this Fabry test, a test piece having a diameter of 6.5 mm and a length of 40 mm was rotated at 300 rpm, and a mating material was prepared on the test piece 2
The V-block is clamped and the clamping load is gradually applied, while the seizure is detected by the torque fluctuation of the pin provided on the upper part of the test piece, and the load at this time is measured. In this test, FC25, which is a cylinder material of the engine, was used as a counterpart material, and a wet method in which lubricating oil was dropped was used during the test. The load was 8 kgf / sec. It has been confirmed from experience so far that this test method is a test method that can faithfully simulate the degree of seizure in the actual test of the piston ring.

Ti-13V-11Cr-3A, which is a β-type titanium alloy
The alloy was hot worked into a material having a diameter of 8 mm, the first group was left as it was, and the second group was roughly worked into a predetermined shape, followed by solution treatment and aging in the atmosphere. Then, the first group was cut to a diameter of 6.5 mm so as to completely remove the oxygen-enriched layer formed on the surface during the heat treatment, and used as a comparative material. In the second group, only the outermost oxide film formed during the heat treatment was removed by grinding to obtain the material of the present invention.

Furthermore, as a conventional material, 0.87% C-0.47% Si-, which is the most excellent seizure resistance and wear resistance among steel rings currently used for nitriding treatment.
0.43% Mn-17.12% Cr-1.20% Mo-0.30% V-Fe steel (17C
(r steel) was rough-processed into a prescribed shape, then tempered and tempered to HRC40 for finish processing. Then, 540
Gas nitriding treatment was performed at 20 ° C. for 20 hours. Further, a brittle nitride was formed on the outermost surface of the nitrogen diffusion layer by the gas nitriding treatment, and thus this was removed by grinding. The Fabry test was conducted according to the above procedure, and the respective measurement results are summarized by an index when the load when the sample subjected to the nitriding treatment on the conventional material is 100 is seized, and evaluated as seizure property and shown in Table 1. .

[0021]

[Table 1]

From Table 1, sample No. 1 obtained by adding an oxygen-enriched layer to the titanium alloy of the present invention is a conventional sample.
It can be seen that seizure resistance is almost equal to that of sample No. 3 obtained by subjecting Cr steel to nitriding treatment. On the other hand, it can be seen that seizure occurs extremely easily in the sample No. 2 which is not subjected to the surface hardening treatment as the comparative sample.

Example 4 Annealed 6Al-4V
A reduced tensile test piece was taken in the radial direction from a 65 mm round bar of Ti alloy. On the other hand, using a 4.8 mm round wire sample taken from the middle of warm drawing in Example 2, this was annealed at 704 ° C. for 2 hours, and then a reduced tensile test piece having the same size as the above was prepared. did. The former tensile test piece represents a piston ring machined from a bar material, and the latter tensile test piece represents a piston ring having a fiber structure in the circumferential direction, which is the present invention, to evaluate the mechanical properties. A tensile test was conducted at room temperature, and the results are shown in Table 2.

[0024]

[Table 2]

As shown in Table 2, the radial characteristics of the round bar are lower in tensile strength, elongation and drawing than the characteristics of the wire. As described above, even when the same titanium alloy is compared, it can be seen that the piston ring having the fiber structure in the circumferential direction of the present invention is superior.

[0026]

Since the titanium alloy piston ring according to the present invention has a fiber structure in the circumferential direction of the piston ring, it has sufficient strength and toughness against external bending stress applied in the transverse direction of the ring. The titanium alloy piston ring according to the present invention has a surface-hardened layer provided with an oxygen-enriched layer at a low temperature without melting the surface portion at least on the sliding surface with respect to the cylinder wall. It has almost the same seizure resistance as a stainless steel piston ring of the same series that has undergone nitriding. Further, according to the production method of the present invention, after the bending process into a ring shape, the oxygen-enriched layer generated during the solution treatment which is performed as necessary can be used as it is, and the production efficiency can be improved. Further, since the titanium alloy piston ring is about 60% of the weight of the conventional 17Cr stainless steel piston ring, it can cope with high output and high speed of the internal combustion engine.

Claims (4)

[Claims] 1. A piston ring body is made of a titanium alloy, has a fiber structure in the circumferential direction of the piston ring, and has a surface hardening layer made of a non-melting oxygen enriched layer on at least a sliding surface with a cylinder wall. Titanium alloy piston ring characterized by 2. A composite surface hardening layer having a piston ring main body made of a titanium alloy, having a fiber structure in the circumferential direction of the piston ring, and including a non-melting oxygen-enriched layer on at least a sliding surface with a cylinder wall. A titanium alloy piston ring characterized by having. 3. After bending a titanium alloy wire material into a ring shape, it is heated to 550 to 105 in an atmosphere containing at least oxygen.
A method for producing a piston ring made of titanium alloy, which comprises heating to a temperature of 0 ° C. to form an oxygen-enriched layer on the surface. 4. A titanium alloy wire material is bent into a ring shape, and then subjected to solution heat treatment / aging to harden the piston ring body and simultaneously form an oxygen-enriched layer on the surface portion. Manufacturing method of titanium alloy piston ring.