JPH06145911A - Piston ring material - Google Patents

Abstract

PURPOSE:To provide a piston ring material having resistance to seizing, wear and corrosion and enhancing the performance of a piston ring or making the piston ring usable even in the case of use of alcoholic fuel. CONSTITUTION:A basic compsn. consisting of, by weight, 0.6-1.3% C, <=1.5% Si, <=1.5% Mn, >20.0-25.0% Cr, 0.5-5.0% Cu and the balance Fe with inevitable impurities is imparted to a piston ring material. The compsn. may contain Mo and/or W added so as to satisfy Mo+1/2W<=2.5% or may further contain V and/or Nb added so as to satisfy V+1/2Nb=0.05-1.5% and >=0.5%, in total, of <=2.5% Ni and/or <=7% Co may be substd. for part of Fe in the compsn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston ring material used in an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, cast iron has been used as a material for piston rings, but with the recent demand for engine efficiency, high load, and lighter weight, the use of steel piston rings has expanded. There is. Since this piston ring made of steel allows the piston to be made thinner, it meets the demand for weight reduction and is manufactured by ring processing of the flat wire, so the manufacturing process is significantly simplified compared to cast iron rings. There is an advantage that can be realized. From such a background, steel piston ring materials are disclosed in, for example, Japanese Patent Publication No. 61-22131, Japanese Patent Publication No. 57-8302, Japanese Patent Publication No. 58-46542, Japanese Patent Publication No. 61-21302, and Japanese Patent Application Laid-Open No. 1-208435. Many materials have been proposed. Japanese Patent Laid-Open No. 1-201441 discloses a high Cr content material.
Is characterized by the addition of
It is intended to improve scuff resistance and wear resistance. However, the addition of Al tends to produce non-metallic inclusions, which may cause damage during use.

At present, among the steel piston rings for automobile engines, particularly those requiring severe working conditions, Si-Cr steel (JIS SWOSC-V), SKD61, 13 are used.
Cr, 17Cr system martensitic stainless steel and the like are used. These materials are used with a hardness of HRC 38 to 45 due to the requirement of ring workability, and the outer peripheral part of the ring that slides with the cylinder is hard Cr plated or hardened to improve wear resistance and seizure resistance. For composite plating containing hard particles, or high Cr-based material, nitriding treatment is mainly performed. At present, 17Cr type stainless steel (SUS440B class) + nitriding material is positioned as the highest performance piston ring.

[0004]

By the way, in addition to the high performance of engines in recent years, in addition to the use of low-grade fuel, introduction of combustion gas into the engine for exhaust gas regulations, alcohol fuel,
The use of new fuels such as natural gas-based fuels has been studied and some test runs have been conducted. In these internal combustion engines, oil deterioration is accelerated due to factors such as running out of oil due to speed increase, increase of moisture generated after combustion, increase of corrosiveness due to sulfur oxides and carboxylic acids, and deterioration of lubricity of piston ring and cylinder. Therefore, there is a demand for a piston ring material that is superior in seizure resistance or scuff resistance (hereinafter simply referred to as seizure resistance) and corrosion resistance to the conventionally proposed materials. The object of the present invention is to eliminate the risk of breakage during use due to the addition of Al as a stainless steel piston ring material, and to improve seizure resistance and particularly corrosion resistance to carboxylic acid at the same time as compared with conventional materials. To provide a ring material.

[0005]

DISCLOSURE OF THE INVENTION The present inventors have examined the influence of various elements that simultaneously enhance seizure resistance and corrosion resistance on stainless steel for piston rings, using four types of gray cast iron as mating materials for piston rings. As a result, when the content of Cr exceeds 20% (high Cr), Cu in the steel containing Cr carbide or carbides such as Mo, W, V and Nb is further contained.
However, they have found that it is more effective in improving the seizure resistance and particularly the corrosion resistance to carboxylic acids, and have completed the present invention.

That is, the first aspect of the present invention is, in terms of weight%, C 0.6 to 1.3%, Si 1.5% or less, Mn 1.5% or less, Cr.
A piston ring material comprising more than 20.0% and not more than 25.0%, Cu 0.5 to 5.0%, the balance Fe and unavoidable impurities. And Mo or W one or two
2.5% or less at + 1 / 2W, and V and Nb
1 or 2 of V + 1 / 2Nb of 0.05 to 1.5% is added to the piston ring material, and the fourth invention is a part of Fe of each invention, in which Ni of 2.5% or less and Ni of 7% or less are used. It is a piston ring material in which 1 or 2 types of Co (however, Ni + Co is 0.5% or more) are replaced by equal amounts.

[0007]

The reasons for limiting the components of the present invention will be described below. C combines with elements such as Cr, Mo, W, V, and Nb to form carbides, which contributes to the improvement of wear resistance and seizure resistance, and part of which forms a solid solution in the matrix. Strengthen. In the case of the steel piston ring material of the present invention, these effects must be added in an amount of 0.6% or more in connection with the high Cr content, but if it exceeds 1.3%, excessive carbides are formed. Therefore, the workability of the ring material and the formability of the ring itself are deteriorated. Therefore, C is limited to 0.6 to 1.3%.

Si is an element added for the purpose of deoxidizing during refining of steel, and is an element effective for improving corrosion resistance, hardenability and strength. However, if a large amount is contained, cold workability is impaired, so the content is limited to 1.5% or less. Mn is added for the purpose of desulfurization during refining of steel, but if it exceeds 1.5, it impairs hot workability, so it is limited to 1.5% or less.

As described above, Cr forms a carbide (M ₂₃ C ₆ type and M ₇ C ₃ type) by combining with C to improve wear resistance and seizure resistance, and further, partly in the matrix. Solid solution improves corrosion resistance, oxidation resistance, and heat resistance. Further, in the nitriding treatment which is particularly effective as one of the surface treatments of the piston ring, a hard nitriding layer is formed, wear resistance,
Greatly improves seizure resistance. In order to exert these effects and sufficiently achieve the above object, it is necessary to add more than 20%, but if the conventional amount exceeds 20%, the toughness decreases, so that the problem of deterioration of workability such as curling into a ring occurs. was there. However, it has been found that this problem can be solved by warm curling or the like, and if it exceeds 20%, the area ratio of carbides becomes high, and the seizure resistance becomes particularly good when co-added with Cu. However, if it exceeds 25%, the workability is also impaired, so the range of Cr exceeds 20.0% and 25.0%.
Limited to not more than%.

Mo and W combine with C to form carbides themselves, and also form a solid solution in Cr carbides,
This strengthens this, further increases the softening resistance in tempering, and when nitriding is performed, it contributes to the formation of a nitrided layer and improves wear resistance and seizure resistance. Furthermore, Mo is
It has the effect of improving sulfuric acid corrosion resistance. But Mo
Addition of more than 2.5% at +1/2 W increases the amount of hard carbides, causes fatigue strength to decrease, and is an expensive element.
Limited to 2.5% or less at o + 1 / 2W.

Both V and Nb have a grain refining effect and contribute not only to improving the toughness of the piston ring, but they also form carbides themselves as in Mo and W, and in Cr carbides. By solid-dissolving it and strengthening it, wear resistance and seizure resistance are improved. Further, both elements improve sulfuric acid corrosion resistance and carboxylic acid corrosion resistance. In order to obtain these effects, at least 0.05% or more of V + 1 / 2Nb must be used for one or two of V and Nb. However, if added excessively, MC type carbides are excessively formed and the toughness is deteriorated, so the upper limit of the amount of V + 1 / 2Nb was set to 1.5%.

[0012] Ni and Co do not form carbides with both elements, and they form a solid solution in the matrix, and have the effect of enhancing the sulfuric acid corrosion resistance. Especially in the case of a piston ring for nitriding,
Since Ni and Co themselves do not form a nitride, the action remains in the nitride layer. To obtain this effect, at least 0.5% of Ni + Co of one or two of Ni and Co is required. However, when Ni exceeds 2.5%, it becomes difficult to obtain a predetermined hardness in heat treatment, and when Co exceeds 7% in this composition system, hot workability and cold workability are deteriorated. 2.5% or less, Co is 7%
Limited to:

Cu is an important element that not only improves the seizure resistance but also enhances the corrosion resistance to carboxylic acid in the steel of the present invention containing Cr in an amount of more than 20%. Cu does not form carbides or nitrides, and Cu
It was found that the fine dispersion of the solid solution significantly improves the seizure resistance between the piston ring and the cylinder. Further, as described above, since the Cu-containing steel has remarkably high corrosion resistance to carboxylic acid, it can be used as a piston ring having higher corrosion resistance than conventional materials against corrosive atmosphere such as combustion gas of alcohol fuel. can do. In order to obtain the above effect, Cu needs to be 0.5% or more, but if it exceeds 5.0%, hot workability deteriorates, so the range of Cu is limited to 0.5 to 5.0%. As mentioned above,
Conventionally, high Cr (> 20%) content steel has been considered to be unsuitable in view of a decrease in workability such as curling, although it can be expected to improve seizure resistance and corrosion resistance to some extent. The present inventors have made the present invention by discovering that by combining the high Cr content and the addition of Cu, the seizure resistance is greatly improved, and particularly the corrosion resistance to carboxylic acid is remarkably improved. The deterioration of workability due to high Cr can be avoided by warm curling or the like.

[0014]

The present invention will be described in detail below with reference to examples. Table 1 shows the chemical composition of the test materials. Of these, No.
Nos. 1 to 12 are materials of the present invention, Nos. 21 to 27 are conventional materials, and Nos. 28 and 29 are comparative materials. Among the conventional materials, Nos. 21 and 22 are SKD61 and 13Cr-based materials that are currently used as top rings for gasoline engines, respectively, and No. 23 is currently used under particularly severe usage conditions.
The Cr type piston rings, No. 24 and No. 25, are steels and No. 26, 2 disclosed in the above-mentioned JP-A-1-208435.
7 is an example of the steel disclosed in the above-mentioned JP-A-1-201441. The test material was manufactured by the steps of melting, forging, and annealing, and then quenched and tempered to obtain a hardness of HR.
Prepared to C40-43. Then, gas nitriding treatment was performed at 540 ° C. for 20 hours. Since a brittle nitride is formed on the outermost surface of the nitride diffusion layer by the gas nitriding treatment, this was removed by polishing to obtain a test material.

[0015]

[Table 1]

[0016]

[Table 2]

Table 2 shows the results of the seizure test and abrasion test of each test material and the results of the corrosion test with 10% sulfuric acid and carboxylic acid (5% acetic acid + 5% formic acid). An ultrahigh pressure abrasion tester was used for the two tests. The outline of the test piece part is shown in FIGS. The test conditions in the seizure test are as follows, and the pressure at which seizure occurred was evaluated. Friction speed ・ ・ ・ 8m / s Friction surface pressure ・ ・ ・ Initial pressure 20kgf / cm ² , gradually increasing by 10kgf / cm ² every 3 minutes Lubricating oil ・ ・ ・ Motor oil # 30, temperature 80 ℃, stator 400ml / min lubrication from the center of the holder Seizure detection: Detected by load cell and dynamic strain gauge (detects abnormal frictional force during seizure) Counterpart material: JIS gray cast iron type 4 (FC25)

The wear test was carried out under the following conditions to measure the wear amount (dimension) of the test piece. Friction speed ・ ・ ・ 3m / s Friction surface pressure ・ ・ ・ 80kgf / cm ² Lubricating oil ・ ・ ・ Motor oil # 30, temperature 80 ℃, 400ml / min lubrication from the center of the stator holder Friction distance ・ ・ ・ 50km・ ・ ・ ・ JIS gray cast iron type 4 (FC25) For the corrosion resistance test, 10mmφ × 20mmL gas-nitrided sample (outermost surface removal), 10% sulfuric acid, 40 ° C, 40% corrosion loss and 5% acetic acid 5 % Formic acid + water, corrosion loss at 60 ° C. for 40 hours were obtained.

The following can be seen from Table 2. The piston ring material of the present invention has a higher seizure-occurring surface pressure than either the conventional material or the comparative material due to the combined effect of high Cr (> 20%) and addition of Cu, and corrosion in sulfuric acid and carboxylic acid. The weight loss is small. In other words, the conventional material No. 27 has a high Cr content and is approximately the same as the comparative material No. 28 except for the fact that it contains Al. Performance. In contrast, high Cr-containing Cu
The material of the present invention is 10 to 30 kgf / cm ² higher in the surface pressure at which seizure occurs, the sulfuric acid corrosion weight loss is reduced to about 75% or less, and the carboxylic acid corrosion weight loss is reduced to about 16% or less, respectively. There is. Further, Comparative Example No. 29 containing 2.7% Cu has a low Cr content of 17.5%, and therefore has a seizure-occurring surface pressure as low as No. 27 and No. 28, which are high Cr materials. In addition, compared with the two (No. 27, 28), this No. 29 decreased to about 87% and about 45% in sulfuric acid corrosion weight loss and carboxylic acid corrosion weight loss, respectively, but this reduction degree is Remarkably lower than invention materials. From this, it is understood that high seizure resistance and corrosion resistance can be obtained only when the combination of high Cr (> 20%) and Cu addition is achieved. At first glance, the wear amount seems to be inversely proportional to the surface pressure at which seizure occurs, and it is understood that the material of the present invention is as good as or better than the comparative material and the conventional material.

[0020]

As described above, the piston ring material of the present invention combines the high Cr content and the addition of Cu to prevent the risk of breakage during use without adding Al. It is a piston ring material that has significantly improved seizure resistance and corrosion resistance compared to conventional products, and can sufficiently cope with the recent increase in internal combustion engine load and changes in various fuels.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an ultrahigh pressure wear test device.

FIG. 2 is a sectional view taken along the line AA of FIG.

[Explanation of symbols]

 1 Test piece (5.0mm square x 10L) 2 Disc (Mating material ... FC25) 3 Stator holder 4 Rotor 5 Test piece holder 6 Lubricating oil inlet 7 Load cell 8 Dynamic strain gauge P Friction pressure

Claims (4)

[Claims] 1. By weight%, C 0.6 to 1.3%, Si 1.5% or less, Mn 1.5% or less, Cr 20.0% to 25.0% or less, Cu 0.
A piston ring material characterized by being composed of 5 to 5.0%, the balance Fe and inevitable impurities. 2. By weight%, C 0.6-1.3%, Si 1.5% or less, Mn 1.5% or less, Cr 20.0% to 25.0% or less, one or two kinds of Mo and W 2.5% at Mo + 1 / 2W. Below, Cu 0.5
~ 5.0%, balance Fe and unavoidable impurities, piston ring material. 3. By weight%, C 0.6 to 1.3%, Si 1.5% or less, Mn 1.5% or less, Cr 20.0% to 25.0% or less, one or two kinds of Mo and W 2.5% at Mo + 1 / 2W. Below, V and Nb
1 or 2 of V + 1/2 Nb 0.05 ~ 1.5%, Cu 0.5
~ 5.0%, balance Fe and unavoidable impurities, piston ring material. 4. The Fe according to claim 1, wherein a part of Fe is replaced by 2.5% or less of Ni and one or two kinds of Co of 7% or less (however, Ni + Co is 0.5% or more) in equal amounts. The piston ring material described in Crab.