JP2002348639A - Steel for piston ring suitable for ion plating treatment superior in fatigue strength and heat settling resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel for a piston ring which has superior thermal settling resistance of the piston ring main body when ion plated, superior abrasion resistance after nitrided, and consequently has high fatigue strength. SOLUTION: The steel for the piston ring superior in the high fatigue strength and thermal settling resistance and suitable for ion plating treatment includes, by weight ratio, 0.70-1.00% C, 2.00% or less Si, 1.00% or less Mn, 7.00-11.00% Cr, 0.50-1.50% Mo, 0.10-0.50% V, and the balance Fe with unavoidable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel for a piston ring used in an internal combustion engine, and particularly to a fatigue strength suitable for being subjected to an ion plating treatment for improving performance such as abrasion resistance. And a steel for piston rings having excellent heat set resistance.

[0002]

2. Description of the Related Art In the past, cast iron was mainly used as a material for a piston ring for an internal combustion engine, but in order to increase the output and the rotation speed of the internal combustion engine, a thinner and lighter piston ring is required. Steel materials such as Si-Cr steel and martensitic stainless steel, which can obtain higher strength than cast iron, have come to be used. However, these piston ring steels do not have sufficient sliding characteristics such as wear resistance and seizure resistance, and are therefore used after being subjected to surface treatment on the outer peripheral surface. Usually, hard Cr plating is used for Si-Cr steel and nitriding treatment is mainly used for martensitic stainless steel. However, for engines that require more sliding characteristics, ceramic coating by ion plating on the outer peripheral surface is used. Piston rings that have been used have also been used. Chromium nitride and titanium nitride coatings are often used for ceramic coatings.

[0003]

The steel for the piston ring is formed by quenching and tempering a flat or deformed wire material to adjust the heat treatment hardness to about 380 to 550 HV. This is because of the subsequent bending work to form the shape of the piston ring. If the hardness is low, the deformation of the cross section of the wire becomes a problem during bending, and if the hardness is high, the bending becomes difficult. is there. In addition, the outer periphery of the piston ring with ion plating is subjected to ion plating, and the upper and lower surfaces of the piston ring are required to have wear resistance due to sliding with the piston ring groove.
Generally, a nitriding treatment is performed.

[0004] During the ion plating process,
The material is heated to a temperature of 200-600C. And
The higher the coating temperature, the better the adhesion and productivity. Therefore, considering only this treatment, it is desirable to coat at as high a temperature as possible. However, steel materials with low high-temperature strength and low tempering softening resistance are softened by ion plating and cause heat settling, so that there is a problem that a predetermined tension cannot be obtained, and low Cr (8 to 13% Cr) It is difficult to apply martensitic stainless steel to ion plating steel. Further, the wear resistance of the upper and lower surfaces of the low Cr martensitic stainless steel after nitriding was not sufficient.

Therefore, as a steel for a piston ring to be subjected to ion plating, a high Cr (for example, 17% Cr) martensitic stainless steel excellent in high-temperature strength and nitriding characteristics is used.

[0006] However, 17% Cr stainless steel has no problem of heat set during ion plating and wear resistance of upper and lower surfaces, but has a durability of the piston ring in a high-load diesel engine, particularly an engine with an exhaust brake. Is insufficient. That is, when the exhaust brake is actuated, a sudden load is applied to the piston ring, and phenomena such as fluttering occur. If this phenomenon is frequently repeated for a long period of time, the piston ring becomes fatigued and has a problem in durability.

It is presumed that this is due to large primary carbides that are present in large numbers in high Cr martensitic stainless steels. When this primary carbide is present, the workability is reduced. Therefore, during bending, the hardness must be lowered, and it is difficult to increase the hardness. Also, the presence of primary carbides has a great adverse effect on fatigue strength. As described above, the adverse effect on the fatigue strength due to the presence of the primary carbides is large, and as a result, it is considered that the above-described insufficient durability occurs.

[0008] A plurality of patent applications have already been filed for piston ring steel having excellent wear resistance, and some of the steels that have been applied have been used in practice and have been effective. However, the actual application of surface hardening treatment by ion plating to piston rings is still new from the late 1980's (for example, see the description of automotive piston rings issued by Sankaido Co., Ltd., page 132).

[0009] Piston rings subjected to ion plating have been applied only to some limited engines even today. And, among the steels for piston rings that have been identified so far, including the steels for piston rings that have been identified in the patent application publication, it is still insufficient to determine which steels are suitable for ion plating. I don't know.

Japanese Patent Application Laid-Open No. H11-294584 is an example of an invention made to improve the thermal settability which becomes a problem when performing an ion plating process. According to the present invention, in order to improve heat setting, an appropriate amount of Mo and Cr effective for improving heat resistance is added, and M
In order to prevent the effect of improving the heat resistance of o and Cr from being reduced, the amount of C added is reduced to 0.35 to 0.45% as compared with conventional piston ring steel. is there.

However, according to the present invention, the amount of carbon is reduced as compared with other steels for piston rings in order to improve the heat setting and to suppress the formation of carbides of Mo and Cr which are heat resistance improving elements. I have. Therefore, as a natural result, there is a problem that the carbide in the steel is small and the wear resistance after the nitriding treatment cannot be said to be sufficiently excellent.

In view of the above-mentioned problems, the present invention provides a piston ring steel having both excellent heat settability of a piston ring body at the time of ion plating and abrasion resistance after nitriding treatment and high fatigue strength. The purpose is to do.

[0013]

According to the first aspect of the present invention, there is provided a steel for a piston ring which is used by applying a ceramic coating by ion plating, wherein C: 0.70 to 1.00% by weight, : 2.00% or less, M
n: 1.00% or less, Cr: 7.01 to 11.00%,
Mo: 0.50 to 1.50%, V: 0.10 to 0.50
%, With the balance being Fe and unavoidable impurities. The piston ring steel is excellent in fatigue strength and heat resistance suitable for ion plating.

What should be noted in the present invention is that a component system capable of solving the problem in the case of ion plating has been newly proposed and clarified. In other words, many inventions for steels for piston rings have been applied for patents, but applications up to the early 1980s, before ion plating was actually applied to piston rings, were processed by ion plating. It is an invention that does not take into account the problems arising from the above, and is completely useless when referred to.

[0015] Also, with respect to the applications filed thereafter, there are very few inventions in which the component system suitable for the ion plating process is clarified. It is merely an invention that features the method itself.

The ceramic coating referred to in the present invention.
Is, for example, TiN, TiC, TiCN, ZrN,
CrN, Cr₂Selected from N, TaN, TiAlN
A film formed from one or more components.
Point to. Also, for example, a coating of chromium nitride
CrN, Cr ₂N and Cr are mixed
There is a film consisting of the following components.

Next, the reasons for limiting the ranges of the respective chemical components of the steel for piston rings of the present invention will be described. C: 0.70 to 1.00% C partially contributes to the improvement of hardness and fatigue strength by forming a solid solution in the matrix, and also generates carbides to enhance wear resistance. To achieve these effects, C must be at least 0.7
0%, preferably 0.80% or more is required.
However, if it is contained in a large amount, the primary carbides generated during solidification become coarse and cause a reduction in fatigue strength. Therefore, the upper limit was made 1.00%. Preferably 0.9
It is better to be 0% or less.

Si: 2.00% or less Si is added for the purpose of deoxidation at the time of refining steel, and also forms a solid solution in the matrix and contributes to improvement in hardness and fatigue strength.
However, if added in a large amount, the cold workability is impaired, so the content is limited to 2.00% or less. To improve hardness and fatigue strength, it is preferable to add 0.25% or more.

Mn: 1.00% or less Mn is added to deoxidize the steel at the time of refining and fix S in the steel. However, if added in a large amount, the cold workability is impaired. Limited to the following. For deoxidation and fixing of S in steel, it is preferable to add 0.30% or more.

Cr: 7.01 to 11.00% Cr is an indispensable element for improving wear resistance because it combines with C to form carbides and has the effect of increasing the hardness of the nitrided layer. . To obtain these effects, Cr must be at least 7.00% or more. However,
If contained in a large amount, the primary carbides generated during solidification become coarse and cause a reduction in fatigue strength. Therefore, the upper limit was set to 11.00%.

Mo: 0.50 to 1.50% Mo has the effect of improving the tempering softening resistance and is an element indispensable for improving the heat setting during ion plating. In addition, it forms carbide similarly to Cr, increases the hardness of the nitrided layer during nitriding, and improves the wear resistance. In order to obtain these effects, the content needs to be 0.50% or more. However, if it exceeds 1.50%, the effect is saturated and the hot workability is impaired.
And

V: 0.10 to 0.50% V has the effect of improving the tempering softening resistance as in the case of Mo, and is effective in improving the heat setting during ion plating. In addition, it forms carbide similarly to Cr and Mo, increases the hardness of the nitrided layer during the nitriding treatment, and improves the wear resistance. In order to obtain these effects, the content must be 0.10% or more. However, if it exceeds 0.50%, the effect is saturated and the hot workability is impaired.
And

Next, the operation of the present invention will be described. In the present invention, the above-mentioned prior application (JP-A-11-2945)
No. 84, hereinafter referred to as prior application. Unlike the case (1), the amount of C is increased as compared with the prior application to increase the amount of carbide precipitated. When the amount of C is simply increased, giant carbides precipitate and the deterioration of the fatigue characteristics is unavoidable.
Prevention is achieved by adding an appropriate amount of V. In addition, Cr, Mo, V
By adding the amount, the hardness of the nitrided layer generated by the nitriding treatment is improved, and the wear resistance of the nitrided layer is improved.

Therefore, as a result of these component adjustments, a huge 1
Precipitation of secondary carbides is extremely small, resulting in a structure in which many fine carbides are precipitated, and a hard nitrided layer can be formed on the surface by nitriding. In addition, since the carbide of this steel is fine, it is possible to prevent the adverse effect of the carbide on the fatigue characteristics, and it is possible to obtain excellent performance in both wear resistance and fatigue strength.

Further, in the present invention, an appropriate amount of Mo, V which is effective for improving the tempering softening resistance is added. As a result, 200 to 600
Even when exposed to a high temperature of ℃, the decrease in hardness is small and heat set can be minimized.

Next, as in the second aspect of the present invention,
It is more desirable to adjust the components of the steel described in (1) so as to satisfy the condition of 36C + 3Cr + 8Mo + 2V ≦ 70. By adjusting so as to satisfy this equation, the formation of coarse primary carbides is almost suppressed, and excellent fatigue strength can be secured.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The effects of the present invention will be described below with reference to embodiments. Table 1 shows the chemical components of the steel used in the examples.

[0028]

[Table 1]

Of the steels shown in Table 1, Steels Nos. 1 to 7 are steels of the present invention. Steels Nos. 8 to 10 are comparative steels having some components outside the scope of the present invention. The 11 to 13 steels are martensitic stainless steels, which are conventional steels. Conventional steel 11
Steels No. to No. 13 are steels which have been used for piston rings after nitriding, and among them, steel No. 13 has been used for piston rings even when subjected to ion plating.

The test materials shown in Table 1 were prepared by the method described below. That is, first, it melt | dissolved using the 30 kg VIM melter, and produced the 120-mm steel ingot. Next, after hot forging to obtain a rod-shaped material of φ15 mm,
Hardening was performed at 0 to 1070 ° C and tempering at 550 to 650 ° C, and the hardness was adjusted to 400 to 450 HV. In Table 1,
In addition to the chemical components, the values of 36C + 3Cr + 8Mo + 2V and the area ratio of carbide of 5 μm or more after heat treatment are shown.

As is clear from Table 1, the steels of the present invention, the comparative steels, and the conventional steels having a low C content of 10 to 12
Nine steels with a small amount of r have few large primary carbides, and all have an area ratio of 0.5% or less. Further, among the steels of the present invention, all of the test steels except for the six steels having a value of 36C + 3Cr + 8Mo + 2V of 70 or less are as small as 0.3% or less. Further, although not described in Table 1, the steel of the present invention has a higher C content than 10 to 12 steel, and
Compared with steel 0-12, it was observed that fine carbides were precipitated in a large amount and almost uniformly.

On the other hand, 8 steel having a high C content and a high Cr content,
Thirteen steels with a large amount of r show an extremely large amount of giant carbide in an area ratio of 2% or more. from this result,
To reduce giant carbides, it is necessary to keep the amounts of C and Cr within an appropriate range.
It turns out that it is effective to set the value of 3Cr + 8Mo + 2V to 70 or less.

Next, the results of evaluating the heat set resistance, the fatigue strength, and the wear resistance after ion plating will be described. When the ion plating process is performed, the temperature rises to a maximum of about 600 ° C. during the process, and the material is softened during the process, which becomes a problem due to heat sink. Therefore, the evaluation of the heat settability was performed by measuring the degree of change in the hardness of the material by heating and holding at a temperature of 600 ° C., which is equivalent to the maximum temperature rising during the treatment, for one hour.

Since it is necessary to consider the effect of temperature rise due to the ion plating process on the fatigue characteristics, a rod-shaped material having a diameter of 15 mm is heated to 600 ° C. and held for 1 hour as in the evaluation of the heat-resistant set resistance. by processing the specimen geometry was, by a rotating bending fatigue test Ono-type, was assessed by determining the fatigue limit of ¹⁰⁷ rotation.

Further, the piston rings subjected to the ion plating process are used after nitriding the upper and lower surfaces of the product, so that it is necessary to ensure excellent wear resistance after the nitriding process. Therefore, φ after quenching and tempering
A test piece for each evaluation was collected from a 15 mm material, and the temperature was 570 ° C.
A gas nitriding treatment of × 6 h was performed. Then, to remove the brittle compound layer formed on the outermost surface, the surface of the test piece was
Abrasion resistance was evaluated by polishing 30 μm, measuring the hardness of the outermost surface of the nitride layer, and performing a wear test.

The abrasion test was performed using a high-temperature wet-type abrasion tester with a friction speed of 0.5 m / s, lubrication conditions of motor oil # 30, dropping of 0.15 cc / min, and a contact load of 49.
0N, the contact time was 4 hours, the material of the mating material was gray cast iron (FC250), and the temperature of the mating material was 180 ° C. Table 2 shows the test results.

[0037]

[Table 2]

As is clear from Table 2, the comparative steel 8
Steel has a large amount of C and Cr, and the value of the above equation is as large as 83.6. Therefore, the steel has a large amount of large carbides and is inferior in fatigue limit. Nine steels
Since the amount of Cr, which is a carbide forming element, is small, the wear resistance is extremely poor. Steel No. 10 has a small amount of C and a small amount of V, and therefore has a small amount of carbides and has a slightly inferior wear resistance.

Further, among the conventional steels, the steels 11 and 12 which have been used after being subjected to nitriding treatment have a remarkably inferior heat resistance and are hardly resistant.
The material is greatly softened by heating at 600 ° C., so that the fatigue strength is low and the wear resistance is slightly inferior due to the small amount of the carbide-forming elements Mo and V. 13 steel which has been conventionally used for ion plating has no problem with heat resistance, but has a large amount of Cr and the value of the above equation is as large as 90.9. Since the carbides are present in a large amount at an area ratio of 2.8%, the fatigue strength is poor.

On the other hand, the steels 1 to 7 of the present invention are:
It was confirmed that even after the heat treatment at 600 ° C. for 1 hour, the decrease in hardness was small, and excellent results were obtained in the fatigue strength, the hardness after nitriding, and the wear resistance test results.

Next, in order to confirm whether the expected effects were obtained when the piston ring was actually manufactured using the steel of the present invention, the piston ring was actually manufactured and the performance was evaluated. That is, the piston ring material used as the test material is a 2 ton steel ingot having substantially the same composition as the invention steel 4 and the conventional steel 13 used in the above embodiment, and is subjected to spheroidizing annealing after hot rolling. Further, it is finished to a wire shape for a piston ring by cold working, quenched and tempered, and has a hardness of 400 to 4
Prepared by adjusting to 50 HV.

Further, in order to manufacture a piston ring from this material, the above wire rod is formed into a ring, gas nitriding is performed, a nitride layer of about 100 μm is formed on the entire circumference of the piston ring, and then the compound layer on the outer circumference is removed. Then, a piston ring for performance evaluation was manufactured by forming a chromium nitride film on the sliding surface by ion plating. In addition,
The steel 4 of the present invention and the conventional steel 13 did not have a problem that a predetermined tension could not be obtained due to heat sink.

The performance evaluation of the manufactured piston ring is as follows.
It was performed by evaluating the fatigue resistance characteristics by a fatigue test. As shown in Fig. 1, the test method
One end of the joint was fixed by the fixing member 2 and the amplitude member 3 at the other end was caused to oscillate to repeatedly generate stress. In this case, the maximum stress occurs at a position 180 ° from the joint. Since the piston ring is actually used with the nominal diameter closed, the test was performed with the apex closed and the average stress at 180 ° from the apex was 500M.
Carried out in such a manner that the Pa, was determined the fatigue limit of after performing 10 ⁷ times. Table 3 shows the results.

[0044]

[Table 3]

Table 3 shows the values of the amplitude stress having an average of 500 MPa (α value of 500 ± αMPa).
Table 3 shows that the piston ring using the steel of the present invention has better fatigue strength than the conventional steel 13 in which giant carbide is precipitated. It was confirmed that good fatigue strength was obtained without the problem of sag.

Next, invention steel 1, invention steel 4, comparative steel 10,
Conventional steel 13 was finished to the final processing into a top ring, and an actual machine test using an engine was performed. The specifications of the top ring are as follows: After providing a nitrided layer on each base material of the invention steel, comparative steel, and conventional steel, the ion plating film (C
rN, film thickness 28 μm, hardness 1752 HV), nominal diameter 95 mm × width 2.5 mm × thickness 3.35 mm
It is. Test conditions are water-cooled 4-cylinder, displacement 2800cc
The engine was operated at 400 rpm × 400 hours. Table 4 shows the results.

[0047]

[Table 4]

According to the above engine evaluation, the invention steel No.
1 and No. No. 4 shows the wear of the upper and lower surfaces of the ring was lower than that of the conventional steel No. 4.
It was almost equivalent to 13. The wear amount of the ring groove is the same as that of the conventional steel No. As compared with No. 13, good results were obtained.

[0049]

According to the present invention, unlike the prior application, Cr, Mo,
It has been found that a large amount of giant carbide does not precipitate even when about 0.8% of C is contained by optimizing the amount of V. By adding an appropriate amount of Mo and V which are carbide forming elements, fatigue characteristics are adversely affected. It is possible to obtain a structure in which fine carbides necessary for improving the wear resistance without causing a large amount of precipitates compared to the steel described in the earlier application. As a result, excellent characteristics can be obtained in both fatigue characteristics and wear resistance.

Further, even when heated to 600 ° C., which is the maximum heating temperature at the time of the ion plating process, the hardness does not greatly decrease and the heat resistance is excellent. Therefore, extremely excellent wear resistance is required on the outer peripheral surface, and it is a steel for a piston ring which is very suitable for manufacturing a piston ring in which ion plating is indispensable. As described above, according to the present invention, it is possible to provide a piston ring steel having excellent heat settability of the piston ring body at the time of ion plating and abrasion resistance after nitriding treatment, and having high fatigue strength. .

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method for evaluating fatigue characteristics of a piston ring.

[Explanation of symbols]

 1. . . Piston ring, 2. . . 2. fixing members, . . Amplitude material,

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) // C23C 14/16 C23C 14/16 A (72) Inventor Masahiro Oka Wanowari 1 Arao-cho, Tokai City, Aichi Prefecture Address Aichi Steel Co., Ltd. (72) Inventor Shigeo Inoue 1-37 Hokutocho, Kashiwazaki-shi, Niigata Prefecture RIKEN Kashiwazaki Office (72) Inventor Junya Takahashi 1-37, Hokutocho, Kashiwazaki-shi, Niigata Co., Ltd. F-term in the Kashiwazaki Plant of RIKEN (reference) 3J044 AA01 AA02 BA01 BB20 BB28 BB31 DA09 4K029 AA02 BA58 BC02 BD04 CA03

Claims (2)

[Claims] 1. A steel for a piston ring, which is used by applying a ceramic coating by ion plating, in a weight ratio of C: 0.70 to 1.00%, Si:
2.00% or less, Mn: 1.00% or less, Cr: 7.0
0 to 11.00%, Mo: 0.50 to 1.50%, V:
0.10 to 0.50%, with the balance being Fe and unavoidable impurities, suitable for ion plating and having excellent fatigue strength and heat set resistance. 2. The method according to claim 1, wherein 36C + 3Cr + 8.
Mo + 2V ≦ 70, piston ring steel excellent in fatigue strength and heat resistance suitable for ion plating treatment.