JP4267588B2 - piston ring - Google Patents

Description

  The present invention relates to a piston ring, and more particularly to a piston ring having excellent wear and fatigue strength.

  For internal combustion engines, high output and low fuel consumption are constantly demanded, and the load on the components continues to increase. Piston rings are no exception, and there is a demand for improvements in wear resistance and durability so that they can withstand the increased load accompanying higher output and lower fuel consumption of internal combustion engines.

  For example, a pressure piston ring used as a piston ring (hereinafter simply referred to as “piston ring”) has excellent wear resistance and durability by nitriding the base material to form a nitrided layer on the surface. Although a piston ring can be obtained, further wear resistance, durability, and the like have been increased to the extent that they cannot be satisfied only by forming the nitride layer on the base material.

For this reason, attempts have been made to further improve the wear resistance, durability, etc. of the piston ring by forming a hard chromium plating film at a desired location of the base material whose surface has been nitrided. For example, Patent Document 1 discloses a method of obtaining a piston ring having excellent scuffing properties by performing nitriding treatment on the entire surface except the outer peripheral surface of a base material, and further applying a hard chromium plating film or the like to the outer peripheral surface. Are listed. Patent Document 2 does not have a nitride layer formed on the base material, but a hard chromium plating film having a laminated structure is provided on the outer peripheral sliding surface of the base material to provide wear resistance, seizure resistance and fatigue strength. A piston ring with improved performance is described.
Japanese Examined Patent Publication No. 6-1064 JP 2002-106716 A

  In both of the piston ring obtained by the method described in Patent Document 1 and the piston ring described in Patent Document 2, a hard chromium plating film is formed directly on the outer peripheral surface of the base material. There is still room for improvement in the wear resistance of the outer peripheral sliding surface. For example, it is possible to further improve the wear resistance of the outer peripheral sliding surface by forming a nitride layer on the outer peripheral surface of the base material and forming a hard chromium plating film on the nitride layer.

  Piston rings with a nitrided layer may be chipped in the corner due to the brittleness of the nitrided layer, so the corners that are connected to the upper and lower surfaces in the thickness direction of the outer peripheral surface are curved or chamfered to prevent chipping. Often it is a surface. However, in a piston ring having such a curved surface or chamfered surface, it is difficult to improve fatigue strength even if a hard chromium plating film is formed on the nitride layer, and it is difficult to suppress breakage caused by the curved surface or chamfered surface. There is.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a piston ring excellent in wear resistance and fatigue strength, which is preferably used as a compression ring.

The piston ring of the present invention for solving the above problems is a steel base material in which a nitride layer is formed on each of an outer peripheral sliding surface, an inner peripheral surface, and an upper and lower surface in the thickness direction, which form part of the outer peripheral surface. When, the a said piston ring having a hard chromium plating film covering the outer peripheral surface of the steel base material, wherein of the outer peripheral surface, a curved surface in the corner portion continuous with said top and bottom surfaces from the outer peripheral sliding surface or chamfered with the surface is formed, with the outer circumferential sliding surface nitride layer formed on said upper and lower surfaces formed by being nitrided layer is separated apart only the curved or chamfered surface, the outer peripheral sliding There Vickers hardness of nitrided layer formed on a surface within the range of 400～900HV0.05, the width L of the corner portion in which the nitride layer is not formed is 50 to 400 [mu] m, consisting of the width L steel corners Wherein the hard chromium plating film on Le made base material is formed directly.

  According to the present invention, a nitride layer having a Vickers hardness in the range of 400 to 900 HV0.05 is formed on the outer peripheral surface of the steel base material, and a hard chromium plating film is formed on the nitride layer. In addition, the wear resistance of the outer peripheral sliding surface can be improved. In addition, since the nitride layer formed on the outer peripheral surface of the steel base material and the nitride layer formed on the upper and lower surfaces in the thickness direction are separated by a curved surface or chamfered surface, the curved surface or chamfered surface is separated. On the surface, a brittle nitride layer is not formed on the steel base material, and a hard chromium plating film is directly formed. As a result, relatively high toughness can be easily secured on the curved surface or chamfered surface, so that breakage that easily occurs on the curved surface or chamfered surface can be suppressed, and the piston has excellent wear resistance and fatigue strength. A ring is provided.

  In the piston ring of the present invention, the nitride layer formed on the inner peripheral surface of the steel base material and the upper and lower surfaces in the thickness direction includes a first nitride layer having a Vickers hardness of less than 700 HV0.05, Preferably, the second nitride layer covers the first nitride layer, and the second nitride layer has a Vickers hardness greater than the Vickers hardness of the first nitride layer.

  According to the present invention, the nitride layer having the first nitride layer and the second nitride layer is formed on the inner peripheral surface of the steel base material and the upper and lower surfaces in the thickness direction. Not only the wear resistance but also the wear resistance on the inner peripheral surface and the wear resistance in the thickness direction can be excellent, and the fatigue strength can also be excellent.

  In the piston ring of the present invention, the hard chrome plating film preferably has a laminated structure, and the Vickers hardness of the hard chrome plating film is preferably in the range of 900 to 1200 HV0.05.

  According to this invention, since the hard chromium plating film has a laminated structure and the Vickers hardness of the hard chromium plating film is within the above range, the wear resistance and fatigue strength can be further improved.

  According to the piston ring of the present invention, the wear resistance of the outer peripheral sliding surface can be improved. In addition, since relatively high toughness can be easily ensured by a curved surface or chamfered surface extending from the outer peripheral sliding surface to the upper and lower surfaces, it is possible to suppress breakage that easily occurs on the curved surface or chamfered surface. As a result, according to the present invention, a piston ring that easily improves wear resistance and fatigue strength is provided, so that it becomes easy to achieve high output and low fuel consumption of the internal combustion engine.

  Hereinafter, the piston ring of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing an example of a piston ring of the present invention. 1A is a schematic plan view, and FIG. 1B is a cross-sectional view taken along the line I-I ′ of FIG. The piston ring of the present invention is not limited to the following embodiment.

  As shown in FIGS. 1A and 1B, the piston ring 10 of the present invention is an annular member having one abutment portion 1, and an outer peripheral sliding surface e that forms a part of the outer peripheral surface a. A steel base material 11 in which nitride layers (12, 13) are respectively formed on an inner peripheral surface d, and an upper surface b and a lower surface c (hereinafter simply referred to as “upper and lower surfaces b, c”) in the thickness direction; And a hard chromium plating film 14 covering the outer peripheral surface a of the steel base material 11.

  The steel base material 11 is made of, for example, martensitic stainless steel (SUS440 material, SUS410 material, or a material obtained by adding Co to SUS440 material) or a steel material containing 10% by weight of chromium. Is desirable.

  The nitride layer 12 formed on the outer peripheral sliding surface e forming part of the outer peripheral surface a of the steel base material 11 has a Vickers hardness in the range of 400 to 900 HV0.05. When the Vickers hardness of the nitride layer 12 is less than 400 HV0.05, the wear resistance of the outer peripheral sliding surface e of the piston ring 10 is lowered. On the other hand, even if the Vickers hardness of the nitrided layer 12 exceeds 900 HV0.05, the sliding characteristics of the piston ring are not changed, resulting in excessive quality. The Vickers hardness of the nitride layer 12 is more preferably in the range of 400 to 700 HV0.05.

  On the other hand, the nitride layer 13 formed on the inner peripheral surface d and the upper and lower surfaces b, c of the steel base material 11 includes a first nitride layer 13a having a Vickers hardness of less than 700 HV0.05, and the first nitride layer 13a. And a second nitride layer 13b covering the substrate. The Vickers hardness of the second nitride layer 13b is larger than the Vickers hardness of the first nitride layer 13a. From the viewpoint of improving the wear resistance of the inner peripheral surface d and the upper and lower surfaces b and c of the piston ring 10, the Vickers hardness of the second nitride layer 13b is preferably in the range of 700 to 1200 HV0.05. More preferably, it is in the range of 750-1100HV0.05. If the Vickers hardness of the second nitride layer 13b exceeds 1200 HV0.05, it is not preferable because the aggressiveness to the aluminum alloy as the piston material is increased.

  A chamfered surface 15c is formed in the outer peripheral surface a of the steel base material 11 in a region extending from the outer peripheral sliding surface e to the upper and lower surfaces b and c, as shown in FIG. The nitride layer 12 formed on the outer peripheral sliding surface e and the nitride layer 13 formed on the upper and lower surfaces b and c are separated with the chamfered surface 15c therebetween. Therefore, in the region 15s where the nitride layers 12 and 13 are not formed, the base material of the steel base material 11 is formed with a width L in the circumferential direction of the piston ring. Each region 15 s can be formed intermittently in the circumferential direction of the steel base material 11, but is preferably formed over the entire length of the steel base material 11 in the circumferential direction. In addition, the width L of the region 15s is usually preferably in the range of 50 to 400 μm, and more preferably in the range of 150 to 300 μm. As described above, since the brittle nitride layer is not formed in the region extending from the outer peripheral sliding surface e to the upper and lower surfaces b and c, the corner portion has toughness and breakage hardly occurs. Yes. In FIG. 1, a region continuous from the outer peripheral sliding surface e to the upper and lower surfaces b and c is indicated by a chamfered surface 15 c, but the region may have a gently convex curved shape on the outside.

  The hard chromium plating film 14 preferably has a Vickers hardness in the range of 900 to 1200 HV0.05, and the structure may be a single layer structure or a laminated structure of two or more layers. In any case, the hard chromium plating film 14 is preferably a porous plating film because it is desirable that the hard chromium plating film 14 be a film with high oil retention. The thickness of the hard chrome plating film 14 is preferably in the range of about 100 to 200 μm, and more preferably in the range of about 120 to 180 μm. When the thickness of the hard chrome plating film 14 is less than 100 μm, the wear resistance of the outer peripheral sliding surface e of the piston ring 10 tends to be low. On the other hand, when the thickness exceeds 200 μm, there is no change in the quality, but rather the quality becomes excessive and the cost increases.

  The hard chrome plating film 14 covers the outer peripheral surface a of the steel base material 11 as described above. Therefore, in each region 15 s where the nitride layers 12 and 13 are separated from each other, the hard chromium plating film 14 is directly formed on the base material of the steel base material 11.

  In the piston ring 10 having the above-described structure, the nitride layer 12 is formed on the outer peripheral surface a of the steel base material 11, and the hard chromium plating film 14 is formed so as to cover the nitride layer 12, so that the hard chromium After the plating film 14 is worn away, the nitride layer 12 becomes the outer peripheral sliding surface e. Therefore, the piston ring 10 of the present invention can maintain the wear resistance even after the hard chromium plating film 14 is worn away. Further, the piston ring 10 of the present invention has the nitrided layer 13 formed on the inner peripheral surface d and the upper and lower surfaces b, c of the steel base material 11 and has the chamfered surfaces 15c described above. Wear due to sliding with the cylinder body is also suppressed.

  Furthermore, since the hard chromium plating film 14 is directly formed on the steel base material 11 in the region 15s where the brittle nitride layer is not formed, it is possible to easily ensure relatively high toughness in the region 15s. it can. As a result, the fatigue strength of the piston ring 10 can be improved, and breakage from the region that is the chamfered surface 15c can be suppressed.

  The piston ring 10 of the present invention can be manufactured, for example, as follows.

  First, a steel base material 11 made of martensite stainless steel or the like is prepared, and is formed into a piston ring shape by performing known machining. A nitride layer 13 is formed on the entire piston ring material in which the cross-sectional shape of the steel base material 11 after machining is substantially rectangular. This nitriding treatment can be performed by, for example, a gas nitriding method, a salt bath nitriding method, or the like.

  Although the nitriding conditions vary depending on the nitriding method to be applied, the thickness of the first nitride layer 13a is in the range of 30 to 100 μm, the thickness of the second nitride layer 13b is in the range of 50 to 150 μm, Conditions (treatment time, temperature, etc.) are set arbitrarily so that the total thickness of the first nitride layer 13a and the second nitride layer 13b is in the range of 80 to 250 μm. If the total thickness of the nitride layer 13 is less than 80 μm, the wear resistance of the inner peripheral surface d of the piston ring finally obtained and the wear resistance of the upper and lower surfaces b, c in the thickness direction are likely to be lowered. . Further, even if the total thickness of the nitride layer 13 exceeds 250 μm, there is no merit in terms of quality, but rather the cost is increased. The total thickness of the nitride layer 13 is more preferably in the range of 120 to 200 μm.

  When nitriding is performed by a gas nitriding method or a salt bath nitriding method, a brittle compound layer is generated on the surface of the steel base material 11, and this compound layer can be removed by chemical polishing or the like, for example. .

  Next, with respect to the steel base material 11 on which the nitrided layer is formed, the corners on the upper and lower surfaces of the outer peripheral surface a are chamfered or curved by grinding or the like, and the steel base material 11 as the base material of the nitrided layer is formed. Are locally exposed to form the respective regions 15s shown in FIG. Next, the nitride layer formed on the outer peripheral surface a of the steel base material 11 is polished in the thickness direction to leave the nitride layer 12 having a Vickers hardness in the range of 400 to 900 HV0.05.

  Thereafter, a hard chromium plating film 14 is formed on the outer peripheral surface a of the steel base material on which the nitride layer 12 remains, as shown in FIG. The hard chromium plating film 14 can be formed by various known or known methods, for example. If the hard chromium plating film 14 is formed by the manufacturing method described in Patent Document 2, a hard chromium plating film having a laminated structure with high oil retention and excellent wear resistance and seizure resistance can be obtained. As described above, the piston ring 10 shown in FIG. 1 is obtained.

  As described above, according to the piston ring of the present invention, the wear resistance of the outer peripheral sliding surface can be improved. In addition, since relatively high toughness can be easily ensured by a curved surface or chamfered surface extending from the outer peripheral sliding surface to the upper and lower surfaces, it is possible to suppress breakage that easily occurs on the curved surface or chamfered surface. As a result, according to the present invention, a piston ring that easily improves wear resistance and fatigue strength is provided, so that it becomes easy to achieve high output and low fuel consumption of the internal combustion engine.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

Example 1
As a steel base material for forming a piston ring, in mass%, Cr: 10.05%, C: 0.51%, Si: 0.20%, Mn: 0.31%, P: 0.02 %, S: Using a material having a composition of 0.02% (hereinafter referred to as A material), cutting and grinding were performed so as to obtain a piston ring shape. Next, the steel base material 11 processed into a piston ring shape was gas-nitrided to form a nitrided layer 13. The nitriding treatment at this time is performed under the condition that the first nitrided layer 13a is formed by holding at 590 ° C. for 6 hours in the ammonia decomposition gas atmosphere and the second nitrided layer 13b is formed by holding at 540 ° C. for 2 hours. It was. By such nitriding treatment, a nitride layer 13 having a total thickness of 150 μm composed of a first nitride layer 13 a having a thickness of 50 μm and a second nitride layer 13 b having a thickness of 100 μm was formed on the steel base material 11.

  Next, the steel base material 11 after the nitriding treatment is subjected to chemical polishing to remove the compound layer formed on the nitrided layer 13, and then corners connected from the outer peripheral sliding surface e to the upper and lower surfaces b and c. A portion of the nitrided layer 13 was removed by polishing, and a chamfered surface 15c was formed so that the steel base material 11 was exposed to a width L of about 150 μm. At that time, the nitride layer 12 on the outer peripheral sliding surface e was polished together until the thickness became 35 μm. Next, a hard chrome plating film 14 having a laminated structure was formed so as to cover the outer peripheral surface a including the outer peripheral sliding surface e. The hard chromium plating film 14 having a laminated structure was formed by an electroplating method using a known chromium fluoride solution and repeatedly performing a positive electric step and a reverse electric step so as to obtain a plating thickness of 10 μm per layer. Thus, a hard chromium plating film 14 having a laminated structure of 15 layers was formed with a thickness of about 150 μm. Furthermore, as a finish, lapping was performed to adjust the properties of the outer peripheral sliding surface.

  In the piston ring 10 thus manufactured, the nitrided layer 12 formed on the outer peripheral sliding surface e has a Vickers hardness of 900 HV0.05 in the vicinity of the outer peripheral surface, and the first nitridation formed on the steel base material. The layer 13a has a Vickers hardness of 582HV0.05 on the base material side from the position of the second nitride layer 13b where the Vickers hardness is 700HV0.05, and is formed so as to cover the first nitride layer 13a. Layer 13b had a Vickers hardness of 1200 HV0.05 at the highest hardness. Moreover, the hard chromium plating film 14 formed on the outer peripheral surface a so as to cover the outer peripheral sliding surface e had a Vickers hardness of 1200 HV0.05. The Vickers hardness is measured by using a micro Vickers hardness meter to form a cross section as shown in FIG. 1 (b) and applying a weight of 0. 0 to each nitride layer 12, 13a, 13b and hard chrome plating film 14 appearing in the cross section. The measurement was performed by pressing a 05 kg (50 g) diamond indenter.

(Example 2)
The Vickers hardness of the nitride layer 12 formed on the outer peripheral sliding surface e is 800 HV0.05, and the Vickers hardness of the hard chromium plating film 14 formed so as to cover the outer peripheral sliding surface e is 900 HV0.05. A piston ring of Example 2 was produced in the same manner as Example 1 except that. The nitride layer 12 having a Vickers hardness of 800 HV0.05 formed on the outer peripheral sliding surface e is formed by polishing the nitride layer of Example 1, and is formed so as to cover the outer peripheral sliding surface e. The hard chromium plating film 14 having a Vickers hardness of 900 HV0.05 was formed by adjusting the current density and the plating bath temperature.

(Example 3)
The Vickers hardness of the nitride layer 12 formed on the outer peripheral sliding surface e is 400 HV0.05, and the Vickers hardness of the hard chromium plating film 14 formed so as to cover the outer peripheral sliding surface e is 1000 HV0.05. A piston ring of Example 3 was produced in the same manner as Example 1 except that. The nitride layer 12 having a Vickers hardness of 400 HV0.05 formed on the outer peripheral sliding surface e is formed by polishing the nitride layer of Example 1, and is formed so as to cover the outer peripheral sliding surface e. The hard chromium plating film 14 having a Vickers hardness of 1000 HV0.05 was formed by adjusting the current density and the plating bath temperature.

(Example 4)
As a steel base material for forming the piston ring, in mass%, Cr: 17.85%, Co: 4%, Mo: 1.16%, C: 0.89%, Si: 0.32%, Except for using a material (hereinafter referred to as B material) having a composition of Mn: 0.35%, V: 0.12%, P: 0.02%, S: 0.02% Thus, the piston ring of Example 4 was produced. In the piston ring 10 thus manufactured, the nitride layer 12 formed on the outer peripheral sliding surface e has a Vickers hardness of 900HV0.05, and the first nitride layer 13a formed on the steel base material is the first nitride layer 13a. The Vickers hardness on the 10 μm base material side is 586 HV0.05 from the position of the Vickers hardness 700 HV0.05 of the second nitride layer 13 b, and the second nitride layer 13 b formed so as to cover the first nitride layer 13 a is Vickers The hardness was 700HV0.05. Moreover, the hard chromium plating film 14 formed on the outer peripheral surface a so as to cover the outer peripheral sliding surface e had a Vickers hardness of 1200 HV0.05.

(Example 5)
B material is used as a steel base material for forming the piston ring, and the Vickers hardness of the nitride layer 12 formed on the outer peripheral sliding surface e is set to 800 HV0.05 to cover the outer peripheral sliding surface e. A piston ring of Example 5 was produced in the same manner as in Example 4 except that the Vickers hardness of the hard chrome plating film 14 used was 900 HV0.05. The nitride layer 12 having a Vickers hardness of 800 HV0.05 formed on the outer peripheral sliding surface e is formed by polishing the nitride layer of Example 4, and is formed so as to cover the outer peripheral sliding surface e. The hard chromium plating film 14 having a Vickers hardness of 900 HV0.05 was formed by adjusting the current density and the plating bath temperature.

(Example 6)
B material is used as a steel base material for forming the piston ring, and the Vickers hardness of the nitride layer 12 formed on the outer peripheral sliding surface e is set to 400 HV0.05 so as to cover the outer peripheral sliding surface e. A piston ring of Example 6 was produced in the same manner as in Example 4 except that the Vickers hardness of the hard chrome plating film 14 was changed to 1000 HV0.05. The nitride layer 12 having a Vickers hardness of 400 HV0.05 formed on the outer peripheral sliding surface e is formed by polishing the nitride layer of Example 4, and is formed so as to cover the outer peripheral sliding surface e. The hard chromium plating film 14 having a Vickers hardness of 1000 HV0.05 was formed by adjusting the current density and the plating bath temperature.

(Comparative Example 1)
A material different from that of Example 1 only in that the outer peripheral corner portion of the piston ring material is formed, and heat treatment similar to that of Example 1 is performed, and only the outer peripheral sliding surface e is polished to thicken the nitride layer 13. A chamfered surface 15c was formed so as to leave a thickness of about 150 μm. Other than that was carried out similarly to Example 1, and produced the piston ring of the comparative example 1. FIG. As in Example 1, the nitride layer 12 formed on the outer peripheral sliding surface e has a Vickers hardness of 900 HV0.05, and the first nitride layer 13a formed on the steel base material is the second. The Vickers hardness on the 10 μm base material side from the position of the Vickers hardness 700HV0.05 of the nitride layer 13b is 577HV0.05, and the second nitride layer 13b formed so as to cover the first nitride layer 13a is Vickers hardness. The hardness was 1100HV0.05 in the hardest part. The hard chromium plating film 14 formed so as to cover the outer peripheral sliding surface e had a Vickers hardness of 1200 HV0.05.

(Comparative Example 2)
Except for using A material as the steel base material for forming the piston ring and setting the Vickers hardness of the nitride layer 12 formed on the outer peripheral sliding surface e to 360 HV0.05, the same as in Example 1. The piston ring of Comparative Example 2 was produced. The nitride layer 12 having a Vickers hardness of 360 HV0.05 formed on the outer peripheral sliding surface e was formed by polishing the nitride layer of Example 1.

(Evaluation: Fatigue strength test)
The fatigue strength of each piston ring of Examples 1 to 6 and Comparative Examples 1 and 2 was measured using a ring solid fatigue tester 20 (hereinafter referred to as tester 20) schematically shown in FIG. First, one end of the piston ring 10 on the side of the mating portion 1 is fixed to the support base 21 of the testing machine 20, and the other end is fixed to the lever arm 22. Next, the eccentric cam 23 is rotated to reciprocate the power transmission rod 24 in the direction indicated by the arrow A in FIG. As the power transmission rod 24 reciprocates, the lever arm 22 connected to the power transmission rod 24 reciprocates in the direction indicated by arrow B in FIG. Changes. Each of the examples and comparative examples was tested until the piston ring 10 was broken under the same test conditions, and withstands a number of repetitions of 1 × 10 ⁷ times from the SN curve (stress-repetition number curve) at this time. The stress obtained was determined as fatigue strength (fatigue limit). In addition, the code | symbol 25 in FIG. 2 is a guide for controlling the direction of the reciprocating motion of the power transmission rod 24. FIG.

  The results are shown in Table 1. The results in Table 1 are obtained by comparing the fatigue strength obtained in Examples 1 to 6 and Comparative Example 2 with the results of Comparative Example 1 with the fatigue strength obtained in Comparative Example 1 as the fatigue strength index 100. did. As is apparent from Table 1, the piston rings of Examples 1 to 6 according to the present invention had a high fatigue strength index and had excellent fatigue strength.

It is a schematic diagram which shows an example of the piston ring of this invention, (a) is a schematic plan view, (b) It is a schematic cross section. It is the schematic which shows the ring substance type fatigue testing machine used for the measurement of fatigue strength.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Piston ring 1 Joint part 11 Steel base material 12, 13 Nitride layer 13a 1st nitride layer 13b 2nd nitride layer 14 Hard chromium plating film 15c Chamfering surface 15s Area | region where the nitride layer is not formed L width a outer peripheral surface b Upper surface c Lower surface d Inner peripheral surface e Outer peripheral sliding surface

Claims (3)

A steel base material in which a nitride layer is formed on each of the outer peripheral sliding surface, the inner peripheral surface, and the upper and lower surfaces in the thickness direction, which form part of the outer peripheral surface, and a hard material that covers the outer peripheral surface of the steel base material A piston ring having a chromium plating film,
Of the outer peripheral surface, a curved surface or a chamfered surface is formed at a corner portion extending from the outer peripheral sliding surface to the upper and lower surfaces, and a nitrided layer formed on the outer peripheral sliding surface and the upper and lower surfaces are formed. Separated from the nitride layer being separated only by the curved surface or chamfered surface ,
The Vickers hardness of the nitride layer formed on the outer peripheral sliding surface is in the range of 400 to 900 HV0.05,
A width L of the corner portion where the nitride layer is not formed is 50 to 400 μm, and the hard chromium plating film is directly formed on a steel base material of the corner portion having the width L. Piston ring to do.
  The nitride layer formed on the inner peripheral surface of the steel base material and the upper and lower surfaces in the thickness direction includes a first nitride layer having a Vickers hardness of less than 700 HV0.05, and a second nitride layer covering the first nitride layer 2. The piston ring according to claim 1, wherein the second nitride layer has a Vickers hardness larger than that of the first nitride layer. The piston ring according to claim 1 or 2, wherein the hard chrome plating film has a laminated structure, and the Vickers hardness of the hard chrome plating film is in a range of 900 to 1200 HV0.05.

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