JP4757685B2 - piston ring - Google Patents

Description

  The present invention relates to a piston ring used in an internal combustion engine, and more particularly to a second pressure ring used in a diesel engine for an internal combustion engine.

In recent years, engine development has been made mainly in consideration of environmental problems (CO ₂ reduction) regarding prevention of global warming. Diesel engines have higher thermal efficiency than gasoline engines. However, since heat load and pressure load are large, improvement in durability is required. Even in such a diesel engine, improvement in fuel efficiency is required by reducing friction, and further development of environmentally friendly engines such as reduction of unburned particulate matter (particulate) due to combustion is promoted as a problem unique to diesel engines. ing.

  A piston of a diesel engine is usually equipped with three piston rings, a first pressure ring and a second pressure ring as pressure rings, and an oil ring. For the first pressure ring exposed to a harsh environment, a steel material such as SUS440, which is martensitic stainless steel, is used, and for the second pressure ring with less heat and pressure load, 9-13 mass of Cr is used. % Steel material is used.

  As a conventional piston ring, for example, in Patent Document 1 below, C: 0.5 to 1.0 mass%, Mn: 1.0 mass for the purpose of improving wear resistance, high temperature strength, and heat sagability. %, Ni: 2% by mass or less, Cr: 11-13% by mass, Mo: 0.4-1.5% by mass, V: 1.5% by mass or less, a piston ring made of a steel material has been proposed . In Patent Document 2 below, for the purpose of improving wear resistance, scuffing resistance, heat resistance, and fatigue resistance, C: 0.55 to 1.40 mass% and Cr: 12.0 to 19.0. A piston ring having a soft nitrided layer on the outer surface of a piston ring made of a steel material containing mass% has been proposed. In Patent Document 3 below, C: 0.8 to 1.1 mass%, Cr: 9 to 11 mass%, Mo: 0.6 to 1... Are intended to improve wear resistance and scuffing resistance. A piston ring having a nitride layer on the outer surface of a piston ring made of a steel material containing 5% by mass and V: 0.1 to 0.5% by mass has been proposed.

The piston ring is required to improve the characteristics as proposed in each of the above-mentioned patent documents, but the realization of cost reduction is also an important technical problem. For example, in Patent Document 4 below, C: 0.59 to 0.76 mass%, Si: 0.15 to 0.35 is used as a low-cost second pressure ring that can be used in a gasoline engine and suppress aluminum adhesion. A piston ring made of a steel material containing mass% and Mn: 0.6 mass% or less has been proposed, and a piston ring subjected to chemical conversion treatment has been proposed.
JP 58-45357 A JP-A-57-203848 JP 60-155647 A JP 2000-34543 A

  The inventor has developed a low-cost and good-characteristic piston ring that is preferably used in a diesel engine for internal combustion engines with a high thermal load. However, the conventional piston rings described in the above-mentioned patent documents are not always satisfactory. Could not get the result.

  For example, although the piston ring described in Patent Document 4 can be used for a gasoline engine, a diesel engine with a large heat load has a problem of causing sag due to heat, and further subjected to chemical conversion treatment. However, the heat resistance of the piston material (Al alloy) is not sufficient. And when this piston ring is used as it is on a piston for a diesel engine, wear occurs, or an aluminum alloy piston material (ring groove material) sticks to the lower surface of the piston ring, and so-called aluminum adhesion occurs. It sometimes occurred.

  Further, the piston rings described in Patent Documents 1 to 3 contain a large amount of Cr and cope with the high combustion pressure of a diesel engine by performing heat treatment such as quenching and tempering and surface treatment such as nitriding. These piston rings correspond mainly by forming a hard surface treatment layer on the outer peripheral sliding surface, but if the nitride layer is not formed on the upper and lower surfaces other than the sliding surface, the piston ring is made of an aluminum alloy. There was a problem that it was not possible to prevent wear and adhesion of aluminum. Patent Document 3 includes, in mass%, Cr: 9 to 11%, C: 0.8 to 1.1%, Mn: 0.6 to 1.5%, V: 0.1 to 0.5%. The composition discloses the hard surface treatment on the outer peripheral sliding surface. However, there is no disclosure about the nitride layer thickness, deformation prevention, and aluminum adhesion prevention. In Patent Document 2, a soft nitriding layer is formed in a high Cr material (Cr: 12 to 19% by mass), which is a combination of composition and nitriding. The depth of the nitride layer is also widely disclosed, but importance is attached to wear resistance, and there is no disclosure about prevention of deformation and prevention of aluminum adhesion. When the soft nitriding layer is formed to have a thickness of 30 μm or more, there is a problem that a dimensional change before and after the treatment is large and a high hardness compound layer called a white layer is formed on the outermost surface. For this reason, after nitriding, it is particularly necessary to perform grinding or chemical removal to remove the white layer, and cost reduction is difficult.

  The present invention has been made in order to solve the above-mentioned problems, and its purpose is to be used as a second pressure ring of a heavy-duty diesel engine and to be excellent in wear resistance at low cost and to prevent aluminum adhesion. An object of the present invention is to provide an inexpensive and inexpensive piston ring.

  The piston ring of the present invention for solving the above problems is a second pressure ring used in a diesel engine for an internal combustion engine, and is Cr: 9.0% or more and 11.0% or less and C: 0.0. It is made of a steel material containing 45% or more and 0.55% or less, and a nitride diffusion layer having a hardness of 700 Hv 0.05 or more is formed on the upper surface, lower surface, outer peripheral surface, and inner peripheral surface at a depth of 2 μm or more and 25 μm or less. It is characterized by being.

  According to this invention, it becomes easy to form a nitrided diffusion layer by using a piston ring made of a steel material containing Cr: 9.0% to 11.0% and C: 0.45% to 0.55%. . Furthermore, a nitrided diffusion layer having a hardness of 700 Hv0.05 or more is formed on the upper surface, lower surface, outer peripheral surface, and inner peripheral surface of the piston ring with a thin depth of 2 μm or more and 25 μm or less. No white layer is formed or only a small amount is formed. Therefore, it is not necessary to remove a white layer that is hard, fragile, and highly attackable by the opponent, and there is no need for grinding after nitriding, so a significant cost reduction can be achieved. Further, the piston ring of the present invention is a piston ring having a small dimensional difference before and after nitriding because the nitrided diffusion layer is thinned to 2 μm or more and 25 μm or less.

  In the piston ring of the present invention, it is preferable that the nitrided diffusion layer is formed with a depth of 5 μm or more and 20 μm or less. According to the present invention, the nitrided diffusion layer having a hardness of 700 Hv 0.05 or more formed on the upper surface, the lower surface, the outer peripheral surface, and the inner peripheral surface of the piston ring is uniformly formed without unevenness, and the influence of the white layer is further suppressed as much as possible. A highly reliable piston ring can be provided.

  According to the piston ring of the present invention, as a second pressure ring of a heavy-duty internal combustion engine diesel engine, it is possible to provide a low-cost piston ring that has excellent sliding characteristics, can prevent aluminum adhesion, and is inexpensive. it can. Since the present invention is made of a steel material having the above composition, the nitrided diffusion layer in the above range can be uniformly formed without unevenness while suppressing the generation of a white layer. As a result, grinding after nitriding is unnecessary, and a significant cost reduction can be achieved.

  Hereinafter, the piston ring of the present invention will be described with reference to the drawings. In addition, the piston ring of this invention is not limited only to the form shown to the following description and drawing. Moreover, in this application, "%" when showing a component means the mass%.

  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 AA in FIG. A piston ring 10 according to the present invention is attached to a ring groove formed on the outer surface of a piston and slides in contact with the inner surface of the cylinder, and as shown in FIG. It is made from steel. The piston ring 10 has a substantially rectangular cross section including an outer peripheral surface a, an upper surface b, a lower surface c (hereinafter, simply referred to as “upper and lower surfaces b, c”), and an inner peripheral surface d. Since the piston ring 10 of the present invention exhibits the function as the second pressure ring, it is preferable that the outer peripheral surface has a shape such as a taper, a taper undercut, or a taper inner cut. A nitride diffusion layer having a hardness of 700 Hv 0.05 or more is formed at a depth D of 2 μm or more and 25 μm or less on the outer peripheral surface a, upper and lower surfaces b, c, and inner peripheral surface d.

  In the piston ring 10 of the present invention, the outer peripheral surface a is a surface that faces and slides against the inner peripheral surface of the cylinder, and the upper surface b and the lower surface c are formed on the piston outer peripheral surface when the piston reciprocates in the cylinder. This is the surface that hits the wall surface of the piston ring groove. The upper surface b and the lower surface c are required to be compatible with an aluminum alloy that is a material of the piston ring groove in order to contact the piston ring groove when the piston ring 10 is mounted on the piston and slides in the cylinder. . Further, the inner peripheral surface d is a surface facing the bottom surface of the ring groove. Since the piston ring of the present invention is preferably used as a second pressure ring for a piston for a diesel engine, the nitrided diffusion layer 12 has an upper surface b and a lower surface c in consideration of at least wear resistance and aluminum adhesion. It is necessary to be provided in. In the case where the nitrided diffusion layer 12 is formed only on the upper surface b and the lower surface c, it is necessary to mask the other surface, which makes the manufacturing complicated and increases the cost. Therefore, in the present invention, the nitrided diffusion layer 12 is preferably formed on the outer peripheral surface a and the inner peripheral surface d as well as the upper and lower surfaces b and c.

  First, the nitride diffusion layer will be described. In the piston ring of the present invention, a nitride diffusion layer 12 having a depth D of 2 μm or more and 25 μm or less is formed. The nitrided diffusion layer 12 needs to be formed on at least the upper and lower surfaces b and c of the peripheral surface of the piston ring 10, but is preferably formed on the entire peripheral surface including the outer peripheral surface a and the inner peripheral surface d. It is preferable.

  By making the depth D of the nitrided diffusion layer 12 as thin as 2 μm or more and 25 μm or less, changes in ring dimensions and roughness before and after nitriding can be reduced, and generation of a white layer is suppressed as much as possible. Yes. Therefore, after forming the nitrided diffusion layer 12, there is no need to perform processing for removing the white layer, and the number of processing steps can be reduced by omitting the grinding step. As a result, the obtained piston ring can realize cost reduction, and the effect is extremely great.

  If the depth D of the nitrided diffusion layer 12 is less than 2 μm, uneven nitridation is likely to occur, and uniform characteristics may not be maintained on each surface. When the depth D of the nitrided diffusion layer 12 exceeds 25 μm, the ring dimension changes to an unacceptable level, so that there is a problem that grinding for adjusting the dimension is required and the number of processing steps increases. Further, since the white layer is also remarkably generated, it is necessary to simultaneously perform a grinding process for removing the white layer, and there is a problem that the number of processing steps increases.

  The depth D of the nitrided diffusion layer 12 is more preferably 5 μm or more and 20 μm or less, and particularly preferably 5 μm or more and 15 μm or less. When the depth D of the nitrided diffusion layer 12 is 5 μm or more, uneven nitridation does not occur even if the accuracy of the nitriding conditions is not increased, which is more preferable from the viewpoint of manufacturing. The depth D of the nitrided diffusion layer 12 is 20 μm or less. In this case, it is preferable from the viewpoint that the amount of change in the ring dimension becomes smaller (the same applies to the case of 15 μm or less).

  The depth D of the nitrided diffusion layer 12 is more preferably in the above range on the entire circumferential surface. However, in the present invention, the upper and lower surfaces b and c are preferentially secured to ensure the characteristics on the upper and lower surfaces b and c. The outer peripheral surface a and the inner peripheral surface d may not be uniform, and a difference may be generated in the above thickness. In addition, since the second pressure ring is usually tapered as shown in FIG. 1B, the outer peripheral sliding portion e indicated by reference numeral e of the outer peripheral surface a contacts the inner surface of the cylinder. Slide. At the time of product shipment, the outer peripheral sliding portion e is shipped by light polishing or lapping so that the outer peripheral sliding portion e has a conformability. Therefore, the depth of the nitrided diffusion layer 12 in the outer peripheral sliding portion e is usually the outer periphery. It is thinner than the depth of the part other than the sliding part e.

  The hardness of the nitrided diffusion layer 12 formed with the depth D within the above range is 700 Hv 0.05 or more, and the nitrided diffusion layer 12 having such a hardness is a viewpoint of the wear resistance and scuff resistance of the piston ring 10. To preferred. Note that the upper limit of the hardness of the nitrided diffusion layer 12 is usually about 1000 to 1100 Hv 0.05 in relation to the following component composition. In the piston ring used as the second pressure ring, a nitride diffusion layer 12 of 700 Hv 0.05 or more is provided on the upper and lower surfaces b and c, and is provided on the entire peripheral surface including the outer peripheral surface a and the inner peripheral surface d. It is more preferable from the viewpoint of manufacturing.

  The nitriding diffusion layer 12 can be formed by a nitriding method such as gas nitriding, ion nitriding, salt bath nitriding, or sulfur nitriding. Any of these nitriding methods can be applied, but salt bath soft nitriding capable of rapid nitriding is desirable. The control of the depth D of the nitrided diffusion layer 12 when using each method can be easily controlled by the processing temperature and the nitriding time.

  Next, the composition of the piston ring will be described. The piston ring of the present invention is formed of a steel material (also referred to as a steel material) containing Cr: 9.0% to 11.0% and C: 0.45% to 0.55% by mass.

  C (carbon) is an element that is important for imparting hardness and strength, and is an element that improves wear resistance by forming fine hard Cr carbide. When it is preferably used as a second pressure ring for a diesel engine as in the present invention, the C content is preferably 0.45% or more and 0.55% or less. By setting the C content within the above range, various mechanical properties can be satisfied, and excessive generation of primary carbide can be suppressed. If the C content is less than 0.45%, mechanical properties such as hardness and strength may not be satisfied. On the other hand, if the C content exceeds 0.55%, precipitation of plate-like primary carbides appears, and the aggressiveness against the inner circumferential surface of the cylinder, which is the counterpart material, is increased, which may increase wear.

  Cr (chromium) is an element that improves the heat resistance and corrosion resistance by solid solution in the matrix, and partly forms carbides to improve seizure resistance and wear resistance. When it is preferably used as a second pressure ring for a diesel engine as in the present invention, the Cr content is preferably in the range of 9.0% to 11.0%. By setting the Cr content within the above range, sag due to heat can be prevented, and the nitrided diffusion layer after nitriding can be easily controlled within the above range with a uniform depth. When the Cr content is less than 9.0%, there is a problem that Cr nitride after the nitriding treatment is not sufficiently formed due to the balance with the carbon amount, and the depth of the nitrided diffusion layer is likely to be uneven. Further, when the Cr content exceeds 11.0%, the formation of Cr nitride becomes excessive, it is difficult to control the depth of the nitrided diffusion layer within the above range, and the white layer (hard compound layer) ) Is also easy to generate.

  As long as the piston ring of the present invention is a steel material containing at least Cr and C within the above range and the balance being iron and inevitable impurities, the piston ring may contain other elements according to any purpose. Examples of such elements include the following Si and Mn, but other elements such as Mo, Ni, and V can be added to further improve wear resistance, corrosion resistance, heat resistance, and the like.

  Si (silicon) is added as a deoxidizer and is an element effective for preventing sag due to heat in the same manner as Cr, and the preferred content is 0.1% or more and 0.3% or less. It is. If the Si content is less than 0.1%, the above-mentioned effects cannot be achieved. If the Si content exceeds 0.3%, the cold workability during ring molding is impaired and the toughness is likely to be lowered.

  Mn (manganese) is added as a deoxidizing agent in the same manner as Si, and is an element effective for increasing the strength. The preferred content is 0.2% or more and 0.4% or less. The Even if the Mn content is less than 0.2%, it is effective as a deoxidizing agent. However, in order to improve the strength, the lower limit is preferably 0.2%, and the Mn content exceeds 0.4%. In some cases, the hot workability and the cold workability during ring molding may be impaired, and the upper limit is preferably set to 0.4%.

  Since the piston ring of the present invention has at least C and Cr in the above range, it has the strength required as a second pressure ring for a diesel engine, and a nitriding diffusion layer is generated evenly during nitriding. And rapid generation can be prevented, and the hardness of the nitrided diffusion layer 12 can be 700 Hv 0.05 or more. When the hardness of the nitrided diffusion layer 12 is less than 700 Hv 0.05, the wear resistance may be reduced and the wear amount may be increased. The hardness adjustment of the nitriding diffusion layer 12 depends on the components contained in the steel material, but can be adjusted to some extent by the condition control of the nitriding method. For example, in the salt bath nitriding method, the hardness of the nitriding diffusion layer 12 can be adjusted by controlling the composition, processing temperature, processing time, and the like of the salt bath. Further, in the case of the gas nitriding method, the hardness of the nitriding diffusion layer 12 can be adjusted by controlling the components of the gas atmosphere, the processing time, the processing temperature, and the like.

  If the depth D of the nitrided diffusion layer 12 is within the above range as in the present invention, the change in the ring dimension after nitriding is small, and grinding such as lapping after nitriding can be omitted. The range of Si, Mn, and the like having a composition other than Cr and C is preferably within the above range. With the above composition, there is an advantage that the nitrided diffusion layer 12 can be formed uniformly and stably, and the hardness of the nitrided diffusion layer 12 can be maintained at a stable hardness of 700 Hv 0.05 or more.

  Next, a manufacturing example of the piston ring 10 of the present invention will be described. First, a steel wire containing the above-mentioned components is prepared, the steel wire is wound into a ring shape, cut, and further subjected to cutting and grinding to form, for example, a piston ring shape as shown in FIG. The obtained piston ring material is subjected to nitriding treatment to form a nitrided diffusion layer 12. This nitriding treatment can be performed by, for example, a salt bath nitriding method, a gas nitriding method, or the like.

  The nitriding conditions vary depending on the nitriding method to be applied, but conditions (processing time, temperature, etc.) that allow the depth D of the nitriding diffusion layer 12 to be within the above range are arbitrarily set. In the present invention, since the depth D of the nitrided diffusion layer 12 is within the above range, the ring size after the nitriding treatment does not change greatly, and the white layer (the N concentration formed on the surface of the nitrided diffusion layer is high, brittle and hard). As a result, there is a remarkable manufacturing effect that a grinding process such as a lapping process for adjusting the ring dimension and removing the white layer is unnecessary.

  Since the hardness of the nitrided diffusion layer 12 depends on the component composition of the steel material, the hardness of 700 Hv0.05 or more can be imparted to the nitrided diffusion layer 12 by using the steel material having the above component composition. As described above, for example, the piston ring 10 having the form shown in FIG. 1 is obtained. Note that a PVD film or a composite plating film may be applied on the outer peripheral sliding surface on the nitride diffusion layer 12 to further improve the wear resistance.

  As described above, according to the piston ring of the present invention, it is possible to provide a low-cost and good characteristic piston ring as the second pressure ring of the diesel engine for an internal combustion engine having a large load. In particular, since it is made of a steel material having the above composition, a nitrided diffusion layer in the above range can be formed uniformly without unevenness in a state in which the formation of a white layer is suppressed. As a result, grinding after nitriding is unnecessary, and a significant cost reduction can be achieved.

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

Example 1
As a steel wire 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”), winding, cutting, and grinding are performed so that the piston ring shape of the second pressure ring shape shown in FIG. 1 is obtained. It was. Next, the piston ring material 11 processed into a piston ring shape was subjected to salt bath soft nitriding (tuftride treatment) to form a nitrided diffusion layer 12. The soft nitriding treatment at this time was performed under the condition that the nitrided diffusion layer 12 was formed by holding a commonly used salt bath and holding at 580 ° C. for 5 minutes. Such nitriding treatment is performed on five samples, and after nitriding the piston ring 10 of Example 1 in which the depth D of the nitriding diffusion layer 12 of each sample falls between 2 to 10 μm, the white layers on the upper and lower surfaces are not removed. It was prepared.

  The hardness of the nitrided diffusion layer 12 of the piston ring 10 thus manufactured was in the range of 900 Hv0.05 to 1100 Hv0.05 for each sample. For the Vickers hardness, a micro Vickers hardness meter is used to form a cross section as shown in FIG. 1B, and a diamond indenter having a weight of 0.05 kg (50 g) is pressed against the nitrided diffusion layer 12 appearing in the cross section. Measured.

(Example 2)
A piston ring of Example 2 was obtained in the same manner as in Example 1 except that the nitrided diffusion layer 12 was formed by holding at 580 ° C. for 10 minutes. Also in this piston ring, nitriding treatment was performed on five samples. The depth D of the nitrided diffusion layer 12 of each sample was between 13 and 16 μm, and the hardness of the nitrided diffusion layer 12 was in the range of 900 Hv0.05 to 1100 Hv0.05 for each sample. The obtained sample was cut and the nitride layer on the lower surface side of the piston ring was confirmed. FIG. 2A is a photomicrograph (400 times) showing the cross-sectional form of the nitrided diffusion layer.

(Example 3)
A piston ring of Example 3 was obtained in the same manner as in Example 1 except that the nitrided diffusion layer 12 was formed by holding at 580 ° C. for 15 minutes. Also in this piston ring, nitriding treatment was performed on five samples. The depth D of the nitrided diffusion layer 12 of each sample was between 18 and 25 μm, and the hardness of the nitrided diffusion layer 12 was in the range of 900 Hv0.05 to 1100 Hv0.05 for each sample. A slight white layer was observed on the surface of the nitrided diffusion layer, but it was in a range where there was no problem.

(Comparative Example 1)
Using the same piston ring material as in Example 1, the nitrided diffusion layer 12 was formed by holding at 580 ° C. for 60 minutes. In the same manner as in Example 1, after the nitriding treatment, a piston ring of Comparative Example 1 was obtained without removing the upper and lower white layers. Also in this piston ring, nitriding treatment was performed on five samples. The obtained sample was cut and the nitride layer on the lower surface side of the piston ring was confirmed. The depth D of the nitrided diffusion layer 12 was considerably deep as 40 to 50 μm, and a thick white layer (4 to 7 μm) was observed on the surface as shown in the micrograph (400 times) in FIG. The hardness of the nitrided diffusion layer 12 was in the range of 950 Hv0.05 to 1100 Hv0.05 for each sample.

(Comparative Example 2)
After performing the same treatment as in Comparative Example 1, the white layer was removed with a chemical, and only the upper and lower surfaces were polished to remove the white layer.

(Dimensional accuracy)
Regarding the dimensional accuracy, the accuracy of the outer peripheral surfaces of Example 1, Example 2 and Example 3 subjected to the thin nitriding treatment (close the abutment, make the abutment and the 180 degree direction vertical, and the outer shape in a 90 degree perpendicular direction. When the ratio U) corresponding to the vertical and horizontal directions was set to 100 (ratio) in comparison example 1 with respect to that before the processing, 30 in example 1, 50 in example 2, and 60 in example 3. The compound layer white layer thickness by nitriding treatment was 0.2 to 0.5 μm in Example 1, 0.6 to 1.3 μm in Example 2, and 1.6 to 2.3 μm in Example 3. It was. At these thicknesses, it is not necessary to remove the white layer. In Comparative Example 1, a 4 to 7 μm white layer is formed, and it is necessary to remove the white layer.

(Appearance comparison)
The appearance of the piston ring obtained in Example 1 and the piston ring obtained in Comparative Example 2 were compared. Since the piston ring obtained in Example 1 is not subjected to grinding after forming the nitrided diffusion layer, as shown in the upper micrograph (10 times) in FIG. The grinding marks formed during processing of the base material before nitriding showed a slight appearance. On the other hand, since the piston ring obtained in Comparative Example 2 is ground after the nitrided diffusion layer is formed, as shown in the lower micrograph (10 ×) in FIG. Was presenting. Such comparison makes it possible to clearly distinguish the piston ring of the present invention from the conventional ground piston ring in terms of appearance.

It is a schematic diagram which shows an example of the piston ring of this invention, (a) is a schematic plan view, (b) is typical AA sectional drawing of Fig.1 (a). 2 is a photomicrograph of a cross-sectional form of a nitrided diffusion layer obtained in Example 2 and Comparative Example 1. It is the microscope picture result of the external appearance comparison of the piston ring obtained in Example 1, and the piston ring obtained in Comparative Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Piston ring 1 Joint part 11 Steel material 12 Nitride diffused layer D Depth of nitrided diffused layer a Outer peripheral surface b Upper surface c Lower surface d Inner peripheral surface e Outer peripheral sliding part

Claims (2)

A second pressure ring used in a diesel engine for an internal combustion engine, wherein Cr: 9.0% to 11.0%, C: 0.45% to 0.55% , Si: 0.1 in mass% % 0.3% or less, and Mn: made 0.2% to 0.4% or less is steel, the upper surface, a lower surface, an outer peripheral surface, the inner peripheral surface, Chi lifting a hardness of more than 700Hv0.05, A piston ring , wherein a nitrided diffusion layer is formed with a depth of 2 μm or more and 10 μm or less, and a white layer is formed with a thickness of 0.2 μm or more and 0.5 μm or less on the surface of the nitrided diffusion layer . Cr: 9.0% to 11.0%, C: 0.45% to 0.55%, Si: 0.1% to 0.3%, and Mn: 0.2% or more in mass% A steel material having a composition of 0.4% or less is processed into a piston ring shape and subjected to salt bath soft nitriding on the upper surface, lower surface, outer peripheral surface, and inner peripheral surface, and a hardness of 700 Hv 0.05 or higher at a depth of 2 μm to 10 μm. And a white layer having a thickness of 0.2 μm or more and 0.5 μm or less is formed on the surface of the nitrided diffusion layer.

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