JP6587570B2 - Piston ring wire for internal combustion engine and piston ring for internal combustion engine - Google Patents

Description

  The present invention relates to a piston ring wire for an internal combustion engine with improved scuffing resistance while ensuring sufficient wear resistance on a sliding surface, and to a piston ring for an internal combustion engine molded therefrom.

  Piston rings used in internal combustion engines, particularly automobile engines, have been changed from cast iron to steel piston rings obtained by processing wires such as steel flat wires into a ring shape. Against this background, there is a need to reduce the ring thickness and increase mechanical strength in order to meet the demands for reducing the weight, fuel consumption, speed, and output of internal combustion engines, greatly reducing the ring manufacturing process. The effect is also a major reason for the transition.

  The transition to the steel piston ring precedes the top ring and oil ring in the high load region, and the material is Si-Cr steel or 11-17 mass% Cr martensitic stainless steel. Piston rings with chrome plating or nitriding treatment are also frequently used. On the other hand, since the second ring plays an auxiliary role of the top ring and the oil ring, the material is not required to be expensive stainless steel, and is often used in a material state that is not subjected to surface treatment. However, although steel piston rings have better strength, fatigue resistance, and wear resistance than cast iron piston rings, inferior scuffing resistance is one factor that prevents the second ring from becoming steel.

  In response to this problem, the applicant added a proper amount of S to a low alloy steel based on 0.3 to 0.8% by mass C, and added Ca in combination to this, so that scuffing resistance was improved. Has been proposed (see Patent Document 1). In this example, sulfide (sulfide) such as MnS is present in the steel, so that S forms an in situ sulfide film on the friction surface due to frictional heat generation, which improves the lubrication performance. In addition, the MnS in steel becomes a source of stress concentration with the base material during cutting or grinding, and has the effect of reducing cutting energy, thus making it possible to achieve both scuffing resistance and workability. .

  However, Patent Document 1 improves the scuffing resistance on the entire peripheral surface of the piston ring by forming a self-lubricating sulfide, particularly MnS, in the steel, while this sulfide is easily processed by hot working. Because of the characteristic of spreading, shape control is not easy. Further, since MnS is a soft inclusion, the contribution to the wear resistance required as a piston ring material is not high.

  Patent Document 1 includes a piston ring material that includes at least one of Ti and Zr and satisfies a specific relational expression with S to improve both scuffing resistance and wear resistance. Has also been proposed (see Patent Document 2).

  In Patent Document 2, by adding S to a low alloy steel based on 0.3 to 0.8% by mass C, simultaneously adding Ti or Zr having a higher sulfide forming ability than Mn, As a result of the formation of Ti or Zr sulfide or carbon sulfide with little form change due to hot working, good wear resistance and scuffing resistance are simultaneously achieved (paragraph 0007).

  On the other hand, when the ring groove of the piston on which the piston ring is mounted is an Al alloy, or when the piston ring itself is an alloy containing Al, there is a possibility that Al adheres to the surface of the piston ring (patent) Reference 3). When Al adhesion occurs on the piston ring, it is assumed that the gas sealability is lost.

JP 2001-329345 A (Claim 1, Claim 2, paragraphs 0014, 0035) International Publication No. 2009/119388 pamphlet (Claim 1, paragraphs 0019-0027, FIG. 5, FIG. 6) JP2003-113941A (paragraph 0004)

  From the above, in order to suppress the scuffing due to the adhesion of Al on the piston ring surface, it is required to increase the resistance to scuffing (scuffing resistance).

  From the above background, the present invention proposes a piston ring wire for an internal combustion engine and a piston ring for an internal combustion engine capable of suppressing Al adhesion by aiming to improve scuffing resistance from Patent Document 2. .

The piston ring wire for an internal combustion engine according to the first aspect of the present invention is, in mass%, C: 0.50 to 0.70%, Si: 1.30 to 1.50%, Mn: 0.70 to 0.00. 90%, S: 0.20 to 0.30%, Ni: 0.50 to 0.70%, Cr: 0.55 to 0.75%, Cu: 0.30 to 0.50%, Al: 0 .30 to 0.50%, Zr: 0.30 to 0.50%, the balance consisting of Fe and inevitable impurities,
The total number of at least one of Zr sulfide and Zr carbosulfide having an equivalent circle diameter of 50 μm or less and a maximum diameter of 0.1 μm or more present in a metal surface structure parallel to the length direction is the metal surface. The number density per tissue area is 1000 / mm 2 or more.

A piston ring for an internal combustion engine according to a second aspect of the present invention has the same composition and the same mass ratio as the piston ring wire according to the first aspect, and has an equivalent circular diameter existing in a metal surface structure parallel to the circumferential direction. The total number of at least one of Zr sulfide and Zr carbosulfide having a maximum diameter of 0.1 μm or more is 1000 pieces / mm 2 or more in terms of the number density per area of the metal surface structure. It is characterized by that.

  According to the present invention, by providing the requirements described in the claims as described later, high scuffing resistance exceeding Patent Document 2 can be obtained, so that sufficient wear resistance on the sliding surface is ensured. The piston ring for an internal combustion engine with improved scuffing resistance can be provided.

Zr confirmed in a region of a constant area (viewing area) in the metal surface structure parallel to the length (circumferential length) direction that becomes the sliding surface with the counterpart material for each test piece (sample Nos. 1 to 6). It is a graph showing the magnitude | size (micrometer) of circle equivalent diameters, such as sulfide, and the total number of Zr sulfides. (A) to (f) are sample Nos. It is the photograph of the microstructure which imaged 1-6 with the optical microscope. It is the graph which showed the abrasion width of the sliding direction with the other party material which arose in each test piece (sample No. 1-4, 6) as a result of the abrasion resistance test. The measurement result of the load (surface pressure) when seizure occurs between each specimen (sample No. 1-6) and the counterpart material (AC8A) by the scuffing resistance test when the hardness is 40 HRC is shown. It is a graph. Shows the measurement results of load (surface pressure) when seizure occurs between each specimen (sample No. 1-6) and counterpart material (AC8A) by scuffing resistance test when hardness is 50 HRC It is a graph. It is the model (outline) figure which showed the mode of the reciprocating friction wear test. It is the model (outline) figure which showed the mode of the high pressure friction wear test.

  The piston ring wire of the present invention (Claim 1) is a linear material before bending into a finished piston ring, and the “length direction” in Claim 1 is the length direction of the piston ring wire itself (material axis). Direction). The piston ring is a product after the piston ring wire is bent into an annular shape, and the “circumferential direction” in claim 2 refers to the length direction of the piston ring wire. “At least one of Zr sulfide and Zr carbosulfide” includes both Zr sulfide and Zr carbosulfide in addition to Zr sulfide only and Zr carbosulfide only. Say that. Hereinafter, “at least one of Zr sulfide and Zr carbon sulfide” is referred to as Zr sulfide or the like.

  As described in Patent Document 2, C contributes to the improvement of strength and fatigue characteristics by forming carbides in the alloy to increase scuffing resistance and wear resistance, and partly forming a solid solution in the base. It is an important element. In order to exhibit these performances, 0.3 mass% (hereinafter simply referred to as%) or more of C is required. However, if it exceeds 0.8%, the workability to the steel flat wire and the workability to the ring may be difficult, and based on the fact that the particularly preferable range is 0.4 to 0.7% (patent document) 2) In the present invention, C is set to 0.50 to 0.70%. 0.50 to 0.70 means 0.50 or more and 0.70 or less. Hereinafter, the same applies to other elements.

  While Si has a function as a deoxidizer, it affects the temper softening behavior of steel, which plays an important role especially in low alloy steels, prevents temper softening, and increases Si heat resistance by 0.1% or more. Need. However, excessive addition may decrease the cold workability, and based on the fact that a particularly preferable range is 1.0 to 1.5% (Patent Document 2), Si is 1.30 to 1 in the present invention. Set to 50%.

  Mn is also an element necessary as a deoxidizing agent like Si, and 0.1% or more of Mn is required to obtain the effect. However, excessive addition may impair hot workability, and based on the fact that a particularly preferable range is 0.5 to 1.0% (Patent Document 2), Mn is 0.70 to 0 in the present invention. Set to 90%.

  S combines with Zr when added to form Zr sulfides and carbon sulfides in the structure, thereby exhibiting self-lubricating properties and improving scuffing resistance, and also effective in improving machinability. In order to obtain these effects, 0.01% or more of S is required. However, excessive addition may deteriorate corrosion resistance and toughness during cold working, and may also reduce hot workability. Based on the preferable range of 0.1 to 0.3% (Patent Document) 2) In the present invention, S was set to 0.20 to 0.30%.

  Ni serves to improve the toughness of the piston ring when subjected to an impact load in use, and 0.05% or more of Ni is required to obtain this effect. However, excessive addition may lead to a decrease in workability in the annealed state, and based on the fact that a particularly preferable range is 0.5 to 1.0% (Patent Document 2), in the present invention, Ni is set to be 0.00. It was set to 50 to 0.70%.

  Cr partly combines with C to form carbides to increase wear resistance, and partly dissolves in the base to increase corrosion resistance, and also increases resistance to temper softening. It is necessary to obtain sufficient heat treatment hardness by ensuring improvement and hardenability. In order to obtain these effects, 0.1% or more of Cr is required. However, excessive addition lowers the thermal conductivity. As a result, the temperature of the contact surface is increased by sliding, and the scuffing resistance is impaired. In addition, an increase in the amount of carbide and an increase in the size of the carbide may be caused, and the workability may be extremely reduced. Based on the fact that the particularly preferable range is 0.4 to 1.0% (Patent Document 2), this In the invention, Cr is set to 0.55 to 0.75%.

  Cu functions to improve corrosion resistance while improving toughness during cold working. In order to obtain this effect, it is preferable to add 0.1% or more of Cu. However, excessive addition increases the amount of retained austenite, leading to a decrease in tempering hardness, and may also decrease hot workability, based on the preferable range of 0.2 to 0.6% ( In Patent Document 2), in the present invention, Cu is set to 0.30 to 0.50%.

  Al, as well as Si and Mn, is effective as a deoxidizing element and has the effect of increasing the nitriding hardness. In order to obtain this effect, 0.1% or more of Al is preferably added. However, excessive addition may cause a significant decrease in toughness and ductility due to the formation of AlN, and based on the fact that a particularly preferred range is 0.2 to 0.5% (Patent Document 2), Al is used in the present invention. It was set to 0.30 to 0.50%.

  Zr combines with S in the molten steel to crystallize as a sulfide, and after forming a stable carbide at a higher temperature, a part of the Zr also crystallizes as a carbon sulfide that is substituted or bonded to S. This Zr sulfide or Zr carbon sulfide contains not only effective self-lubricating agent but also hard inclusions because it contains S having lubricity inside, so it has high wear resistance like carbide. Also contribute. Further, as compared with MnS, it is difficult to extend by hot working, so that shape control is not difficult.

  Furthermore, since the above Zr sulfides and the like are very stable, the shape hardly changes even if a tempering heat treatment is performed, and the structure control is easy. In order to obtain these effects, 0.05% or more of Zr is required. However, excessive addition not only saturates the above effects, but also causes a large amount of oxides and nitrides to remain in the steel, which causes a significant deterioration in corrosion resistance and toughness. In addition, the toughness and ductility may be reduced, and based on the fact that the particularly preferable range is 0.2 to 0.8% (Patent Document 2), Zr is 0.30 to 0.50% in the present invention. Set to.

  In the present invention, Zr existing in the metal surface structure parallel to the length (peripheral length) direction of the piston ring wire (or piston ring product) having this composition after setting the mass ratio of each element as described above. By adjusting the distribution of sulfides, etc., we have reached the stage where we can show the basis for improving scuffing resistance while ensuring sufficient wear resistance on the sliding surface of the piston ring wire as follows: did. Specifically, in the present invention, among the above Zr sulfides, etc., the Zr sulfide having a size of “equivalent circle diameter of 50 μm or less” is limited (attention), and the number density of the size is further reduced. By adjusting, it became possible to improve wear resistance and scuffing resistance on the sliding surface.

  Among Zr sulfides, Zr sulfides with an equivalent circle diameter of 50 μm or less are fine, so they can be distributed over the entire surface of the metal surface structure (matrix) and distributed almost evenly. It is. Therefore, the wear resistance and scuffing resistance characteristics of individual Zr sulfides can be imparted to the entire base of the above metal surface structure, resulting in excellent wear resistance on the piston ring itself. And scuffing resistance are imparted.

  As a result, it is also possible to suppress the variation of both excellent wear resistance and scuffing resistance between individual metal surface structures or between piston rings as individual products. It is possible to give both stable characteristics to each piston ring itself. The “equivalent circle diameter of 50 μm or less” such as Zr sulfide existing in the metal surface structure is preferably “the maximum equivalent circle diameter is 50 μm or less” from the viewpoint of improving the uniformity of Zr sulfide. It is.

From the above points, in the above metal surface structure, if the number of Zr sulfides having an equivalent circle diameter of 50 μm or less is increased, the individual Zr sulfides are densely and evenly distributed over the entire surface of the metal surface structure. Since it will disperse | distribute, it can be said that said effect is exhibited more reliably. Based on this viewpoint and the following test results, specifically, the number of Zr sulfides having an equivalent circle diameter of 50 μm or less is “1000 pieces / mm ² or more” in terms of the number density per area of the metal surface structure described above. By doing so, it is possible to obtain scuffing resistance as high as exceeding Patent Document 2 while ensuring sufficient wear resistance on the sliding surface. The number density per area of Zr sulfide or the like of 50 μm or less is preferably “1500 pieces / mm ² or more”.

  The metal surface structure for measuring the number density of Zr sulfide or the like is the piston ring wire or the “surface” of the piston ring. In this case, specifically, the piston ring wire or the “outermost surface” of the piston ring is polished and the “new surface” at a position of 0.5 mm or more from the outermost surface toward the inside is provided. This new surface is taken as a “test surface”, and this test surface is observed with an optical microscope with a magnification of 1000 times and the microstructure is photographed. Then, by processing the photographed microstructure, the equivalent circle diameter and number density of Zr sulfide and the like confirmed in the image can be obtained. At this time, Zr sulfide having a maximum diameter of less than 0.1 μm in the Zr sulfide confirmed in the above image is excluded from the measurement target. The above image processing can be performed using existing image processing software.

  In this example, test pieces corresponding to the piston ring wires (or piston rings) of the present invention and comparative examples were produced. The abrasion resistance test and scuffing resistance test in Patent Document 2 were carried out for each of the prepared test specimens, and the abrasion resistance and scuffing resistance of the test specimens were evaluated.

  First, sample No. obtained by casting a molten metal adjusted to a composition having a plurality of mass ratios as a material of a test piece corresponding to a piston ring wire (or piston ring). 1-6 ingots were prepared. Sample No. Compositions and mass ratios of 1 to 6 are as shown in Table 1 below (the balance is Fe and inevitable impurities). Only 2 satisfies the range of the composition of the present invention and the ratio of each element. Sample No. 1 and 3 to 6 are comparative examples of the present invention.

  Sample No. 1 is sample No. 1. 2 is 0.08% lower (about 67%) than the sample No. Unlike sample 2, sample no. 3 is a sample No. 3. 2 in that the mass ratio of Zr is twice that of Sample No. 2 and different. Sample No. No. 4 indicates that the mass ratio of Zr is Sample No. It is 2.275 times of 1. Sample No. Although the mass ratios of the main constituent elements 1, 5, and 6 are the same, they are different in terms of “distribution of Zr sulfides” due to differences in “manufacturing (casting) conditions”. However, a difference appears in the results shown in FIGS. Sample No. In Nos. 5 and 6, the solidification rate of the molten metal at the time of casting was measured as Sample No. It is slower than 1. Thereby, in the state of the test piece, the sample No. The size (equivalent circle diameter) of Zr sulfide and the like in Examples 5 and 6 is the sample No. It is larger than that of 1.

In the wear resistance test, an annealed material obtained by hot working on the above ingot was quenched, and then a cylindrical test piece of φ8 mm × 20 mmL was prepared from the heat treated material produced by tempering so that the hardness was 40 HRC. The test piece was prepared and subjected to an abrasion resistance test based on the following conditions. As a test piece, Sample No. A plurality of test pieces are produced every 1 to 6, and the maximum value, the minimum value, and the average value of the plurality of test pieces are taken. FIG. 6 shows a schematic diagram of the reciprocating frictional wear test.
Load: 490N
Speed: 0.25m / s
Mating material: JIS gray cast iron (FC250)
Number of sliding times: 500 times Lubricating oil: Turbine oil # 100 (lubricating: room temperature)
Test piece hardness: 40 HRC

Further, as a scuffing resistance test, a high-pressure friction and wear tester was used, and a high-pressure friction and wear test was performed based on the following conditions. At this time, after quenching the annealed material obtained by hot working on the above ingot as a test piece, 5 mm square × 10 mm L from the heat treated material produced by tempering so that the hardness becomes 40 HRC or 50 HRC. A prismatic test piece was prepared, and the test piece was subjected to a scuffing resistance test based on the following conditions. FIG. 7 shows a schematic diagram of the high-pressure frictional wear test.
Friction speed: 2 m / s
Frictional surface pressure: Initial 15 kgf / cm ² , rising by 5 kgf / cm ² every minute Lubricating oil: Turbine oil # 100 (lubricating: room temperature), lubricating only for the first minute Partner material: JIS aluminum alloy casting (AC8A)
Test piece hardness: 40 HRC, 50 HRC

In FIG. 1, for each test piece 1 (sample Nos. 1 to 6), a fixed area (viewing area: visual field area) in the metal surface structure parallel to the length (peripheral length) direction serving as a sliding surface with the counterpart material 2 described above. 22494μm ²⁾ of the circle equivalent diameter of Zr sulfides confirmed in a region size as the ([mu] m), representing the total number of such Zr sulfides. The measuring procedure for the equivalent circle diameter and the total number of Zr sulfides, etc. at this time was in accordance with the procedure described in the above item. The right vertical axis represents the equivalent circle diameter (μm) of Zr sulfide and the like, and the left vertical axis represents the number of Zr sulfide and the like per visual field area. 2 (a) to (f) show sample Nos. It is the photograph of the microstructure which imaged 1-6 with the optical microscope.

  3 shows the wear width in the sliding direction of the mating member 2 generated in each test piece (Sample Nos. 1 to 4 and 6) as a result of the wear resistance test. Here, Sample No. The result of 5 is not displayed.

  From FIG. No. 2 (invention) has the smallest wear width and averages about 2.08 mm. The average value of 1 and 4 is about 2.2 mm. It can be seen that the average values of 3 and 6 are about 2.16 mm and 2.15 mm, respectively. Sample No. Although the average value of 2.08 mm of 2 is about 0.34 larger than the average value of 1.74 mm of the result of FIG. 5 in Patent Document 2 showing the test results under the same conditions (about 20% increase), FIG. Sample No. with the smallest value and small variation from specimen to specimen. 2 is the best result.

  4 and 5 show the measurement results of the load (surface pressure) when seizure occurs between each test piece 1 (sample Nos. 1 to 6) and the counterpart material 2 (AC8A) by the scuffing resistance test. Show. 4 shows the case where the hardness is 40 HRC, and FIG. 5 shows the case where the hardness is 50 HRC. In FIG. The measurement of 5 is not carried out.

From FIG. 4, in the case of 40HRC, the sample No. 2 (invention) has an average value of about 125 kgf / cm ² (≈12.3 MPa (N / mm ² )), which is the largest. In the case of 40HRC, the sample No. The average value of 2 indicates the sample No. Sample No. 1 larger than the average value of 1 and 6. It is about 5 kgf / cm ² (≈0.49 MPa (N / mm ² )) larger than the average value of 3 and 4. On the other hand, as can be seen from FIG. The average value of 3 and 4 is the sample No. 2 is smaller than the average value of 140 kgf / cm ² (≈13.7 MPa (N / mm ² )) by 15 kgf / cm ² (≈1.47 MPa (N / mm ² )). It is smaller than the average value of 1.

Further, according to FIG. In comparison with the average value of 2, sample no. The average values of 1 and 6 are low and about 100 kgf / cm ² (≈9.81 MPa (N / mm ² )), whereas the sample No. The average value of 3 and 4 is about 120 kgf / cm ² (≈11.8 MPa (N / mm ² )). 3 and 4 are sample Nos. It seems that the result is equivalent to 2. However, according to FIG. The average value of 3 and 4 is the sample No. Since it is lower than the average value of No. 1, the sample No. 3 and 4 are sample Nos. It is hard to say that the performance equivalent to 2 can be demonstrated.

Sample No. for 50HRC The average value of 140 kgf / cm ² (≈13.7 MPa (N / mm ² )) is equal to the average value 85.1 of the result of FIG. 6 (black bar) in Patent Document 2 showing the test results under equivalent conditions. This shows a size of about 1.65 times. It can be said that No. 2 exhibits high scuffing resistance by about 65% from the specimen of Patent Document 2.

  Furthermore, according to FIG. Since 1 and 6 have a large variation between the minimum value and the maximum value, there is a factor that is considered that the performance stability of each test piece is low or the certainty of the performance is lacking. According to FIG. 3 and 4 have a large variation between the minimum value and the maximum value. Therefore, it is considered that the performance stability or reliability of each test piece is low. In contrast, sample no. 2 is similar to the result of FIG. 3 from both the results of FIG. 4 and FIG. In comparison with 1, 3-6, it can be said that the stability or the certainty of the performance of each test piece is high.

  From these results, sample no. Samples No. 1-6 It can be said that 2 shows the composition which can acquire scuffing resistance higher than patent document 2 irrespective of the difference in hardness.

Therefore, sample No. 1 which exhibited scuffing resistance much higher than the specimen of Patent Document 2. As shown in FIG. 1, the circle equivalent diameter of the Zr sulfide 2 is about 13 μm at the maximum and the average value is about 3 μm. The number of Zr sulfides or the like per visual field area is about 40/22494 μm ² . 40 pieces / 22494μm ² = 40 pieces /0.022494mm ² = 1778 pieces / mm ^2.

On the other hand, sample No. The equivalent circle diameter of 1 Zr sulfide, etc. is about 14 μm at maximum, the average value is about 3 μm, and the number of Zr sulfide, etc. per visual field area is about 27/22494 μm ² = about 1200.3 / mm ² It is. Sample No. The maximum equivalent circle diameter of Zr sulfide 3 is about 9 μm, the average value is about 4 μm, and the number of Zr sulfides per visual field area is about 22/22494 μm ² = 978.0 pieces / mm ² It is. Sample No. The maximum equivalent circle diameter of Zr sulfide 4 is about 10 μm, the average value is about 6 μm, and the number of Zr sulfides per field area is about 26/22494 μm ² = 1155.9 / mm ² It is.

  From the above results, Sample No. It can be said that it is appropriate to specify a range for the mass ratio of the main alloy as the raw material of the piston ring or the original piston ring wire rod based on the mass ratio of 2. Here, Sample No. Assuming that the mass ratio of 2 is the best, or is a numerical value showing high scuffing resistance, a result comparable to the central numerical value within the error range is obtained up to at least about 0.1% before and after the numerical value. What you get is empirical.

  To summarize this, it is concluded that the mass ratio of the main alloy as described in the first paragraph of claims 1 and 2 is one condition for obtaining high scuffing resistance exceeding Patent Document 2. Attached. In addition, by adding the requirements described in the second paragraphs of claims 1 and 2, it can be said that an effect of high scuffing resistance exceeding that of Patent Document 2 can be obtained with certainty.

The requirement described in the second paragraph is “the total number of Zr sulfides etc. having a circle-equivalent diameter of 50 μm or less existing in the metal surface structure parallel to the length direction (circumferential length direction) per area of the metal surface structure. The number density is 1000 / mm ² or more. If attention is paid only to this requirement, the sample No. Sample numbers other than 2 1 and 4 also meet this requirement. However, as described above, the sample No. Nos. 1 and 4 may have low stability or certainty of performance for each test piece. 1, 4 should be excluded. Eventually, sample no. Only 2 can have high scuffing resistance exceeding Patent Document 2 while having high performance stability for each test piece. The preferred total number of Zr sulfides etc. is the sample No. If the result of 2 is noted, it can be said that it is 1500 / mm ² or more.

  By increasing the scuffing resistance of the piston ring wire that is the test piece 1, it is possible to suppress the adhesion of Al and to improve the wear resistance.

From the results of FIG. 3 to FIG. 5, the requirement that the mass ratio of the main alloy be within a certain range and the total number of at least one of Zr sulfide and Zr carbonitride having an equivalent circle diameter of 50 μm or less are metal surfaces. By providing the requirement of 1000 pieces / mm ² or more per area of tissue, it can be said that high scuffing resistance exceeding Patent Document 2 can be obtained while having high performance stability for each test piece. . As a result, it can be said that scuffing due to the adhesion of Al can be suppressed and the Al adhesion resistance can be improved.

1 ... Test piece,
2 ...
3 …… Turbine oil.

Claims (2)

In mass%, C: 0.50 to 0.70%, Si: 1.30 to 1.50%, Mn: 0.70 to 0.90%, S: 0.20 to 0.30%, Ni: 0.50-0.70%, Cr: 0.55-0.75%, Cu: 0.30-0.50%, Al: 0.30-0.50%, Zr: 0.30-0. 50%, the balance consists of Fe and inevitable impurities,
The total number of at least one of Zr sulfide and Zr carbosulfide having an equivalent circle diameter of 50 μm or less and a maximum diameter of 0.1 μm or more present in a metal surface structure parallel to the length direction is the metal surface. A piston ring wire for an internal combustion engine, wherein the number density per area of tissue is 1000 pieces / mm 2 or more. In mass%, C: 0.50 to 0.70%, Si: 1.30 to 1.50%, Mn: 0.70 to 0.90%, S: 0.20 to 0.30%, Ni: 0.50-0.70%, Cr: 0.55-0.75%, Cu: 0.30-0.50%, Al: 0.30-0.50%, Zr: 0.30-0. 50%, the balance consists of Fe and inevitable impurities,
The total number of at least one of Zr sulfide and Zr carbosulfide having an equivalent circle diameter of 50 μm or less and a maximum diameter of 0.1 μm or more existing in the metal surface structure parallel to the circumferential direction is the metal surface. A piston ring for an internal combustion engine, wherein the number density per area of tissue is 1000 pieces / mm 2 or more.