JPH11106874A - Piston ring material excellent in scuffing resistance and workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston ring material not only having excellent drawability and rollability in a wire rod producing process, but also having extremely excellent bendability even in the case relatively high hardness after heat treatment is set and moreover excellent in characteristics as a piston ring. SOLUTION: This material has the compsn. contg., by weight, 0.2 to 1.2% C, 5.0 to 25.0% Cr, and the balance Fe with impurities, and has the structure in which the content of M7 C3 type carbides is regulated to <=4.0% by area. Preferably, it may contain <=0.25% Si, <=0.30% Mn, one or more kinds among Mo, W, V and Nb by 0.3 to 2.5%, <=4.0% Cu, <=2.0% Ni and <=1.5% Al.

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 for an internal combustion engine.

[0002]

2. Description of the Related Art In recent years, various improvements have been made to internal combustion engines such as low fuel consumption, high performance, light weight, and purification of exhaust gas. Above all, with respect to the piston ring, which is the sliding part of the internal combustion engine, the characteristics such as fatigue characteristics, wear resistance and scuffing resistance have been improved due to the lightening of the engine and the thinning of the piston ring accompanying the high rotation speed. Cast iron piston rings, which have been strongly demanded and conventionally used, are changing to steel piston rings having excellent strength, fatigue characteristics, and the like. At present, steel piston rings are JIS
Si-Cr steel equivalent to SWOSC-V or 12-
Materials based on martensitic stainless steel containing 21% Cr (hereinafter referred to as high Cr martensitic stainless steel) are mainly used.

[0003] Normally, a piston ring made of Si-Cr steel is used by applying a Cr plating treatment to the surface thereof.
The abrasion resistance required for its use is insufficient. Furthermore, when applied to a high-load internal combustion engine, a problem arises in that the ring base material is exposed due to peeling of the plated portion, and as a result, scuffing readily occurs with the inner wall of the cylinder. In addition, the Cr plating process
There are various problems related to the waste liquid generated after the treatment, such as an adverse effect on the environment and an increase in waste liquid treatment cost in recent years.

On the other hand, most of the above-mentioned piston rings made of high Cr martensitic stainless steel are used after nitriding the surface. This nitrided layer is
In addition to having higher wear resistance than the r-plated layer, the nitriding treatment is a treatment that utilizes diffusion, so there is no problem of peeling off the treated layer. Have. Further, the nitriding treatment is an advantageous treatment method as compared with the Cr plating treatment because the treatment cost is low and the influence on the environment is small. In addition, high Cr martensitic stainless steel has higher heat resistance of the material itself than Si-Cr steel even in the case where Cr plating must be performed for its application.
Since it has excellent wear resistance and corrosion resistance, it can be used as a piston ring material for Cr plating.

[0005] As described above, the conventional piston ring, which has been mainly applied to a high-load internal-combustion engine that emphasizes relatively performance, has recently been used to reduce fuel consumption, improve performance, reduce weight, and purify exhaust gas of an internal-combustion engine. Due to the demand for higher performance, the range of use is not limited to high-load internal combustion engines, but is gradually expanding.

[0006]

In the process of manufacturing a high-Cr martensitic stainless steel as a piston ring material, usually, a material formed into a flat wire or a deformed wire is once heated to 900 to 1100 ° C. and quenched and quenched. After that, tempering is performed at a relatively high temperature. The high-Cr martensitic stainless steel material after the heat treatment is to be formed into a predetermined ring shape. In order to enhance the bending workability (curling property) involved in forming into this ring shape, its hardness is increased. The hardness must be adjusted to a low value of 35 to 45 HRC with respect to the hardness of the Si-Cr steel after the heat treatment of 45 to 55 HRC.

As is essential, if the characteristics such as wear resistance, scuffing resistance and fatigue strength of the piston ring are emphasized, the higher the heat treatment hardness, the better. However, in the case of high Cr martensitic stainless steel with a large amount of residual carbides, if the heat treatment hardness is high, there is a problem that it breaks during bending. There was a problem that it had to be adjusted.

As a method for solving this problem, Japanese Patent Laid-Open Publication No.
Japanese Patent Application Laid-Open No. 166665/1988 and Japanese Patent Application Laid-Open No. 63-140066 discloses a low alloy type piston ring material. These methods reduce the alloy content of Cr to 2.0 to 9.0% and can improve the breakage resistance, but on the other hand, the scuffing resistance is extremely reduced. For this reason, the component systems proposed above have not been practically used widely because of problems in the characteristics as piston rings.

[0009] In addition, high Cr martensitic stainless steel has greater work hardening than Si-Cr steel, so that it is not possible to increase the working ratio until finishing to a flat wire or a deformed wire. Therefore, a number of annealing steps are required during the drawing process or the rolling process, and as a result, there is a problem in that the cost for manufacturing the wire is increased.

Therefore, the present invention has been made in view of the above-mentioned matters,
By improving the drawability and rolling workability in the warm or cold during wire production without impairing the required characteristics as a piston ring, the production cost is reduced, and breakage during ring molding is also reduced. It is an object of the present invention to provide a piston ring material capable of performing the following.

[0011]

Means for Solving the Problems First, the inventor of the present invention carries out a detailed study on the factors affecting the drawing and rolling workability of a linear piston ring material after hot rolling in warm and cold. Was. Furthermore, the factors affecting the properties of the bending workability after heat treatment of the above materials and the scuffing resistance and wear resistance, which are the most important as piston rings, were studied in detail. As a result, the above properties are greatly affected by the form of carbides present in the structure of the piston ring material.
The present inventor has found out an optimum carbide state to have extremely good workability even during wire production and after heat treatment without lowering the required characteristics of the piston ring. Further, it has been found that adjusting the amounts of C and Cr as elements contained in the piston ring material is effective in further achieving the above-mentioned properties and in achieving an optimum carbide state. The invention has been reached.

That is, the piston ring material of the present invention comprises:
By weight%, C: 0.2 to 1.2%, Cr: 5.0 to 2
The content of M ₇ C ₃ -type carbide, which is 5.0%, the balance being Fe and impurities and present in the structure is 4.0 in area%.
%, Excellent scuffing resistance and workability are achieved. With the piston ring material of the present invention, excellent scuffing resistance and workability can be achieved even with a low Cr martensitic piston ring material having a Cr content of 5.0% or more and less than 12.0%. Is possible.

[0013] In addition to the above means, the piston ring material according to the present invention is characterized in that the content of Si is 0.25% or less by weight,
Is adjusted to 0.30% or less, or one or two or more of Mo, W, V, and Nb are adjusted to a total of 0.3 to 2.5% to obtain the characteristics required for the piston ring material. Can be further improved, with Cu being 4.0% or less, and Ni being 2.% or less.
It is also possible to adjust Al to 0% or less, or Al to 1.5% or less.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The piston ring material of the present invention has improved bendability after heat treatment in addition to workability in the production of a wire rod, and has a lower alloy strength than a conventional material. It has scuffing properties. The most important feature of the present invention lies in that, as means for achieving these excellent characteristics of the present invention, the content of C and Cr in steel and the state of carbide in the structure are properly adjusted. Hereinafter, the above-mentioned constituent elements forming the basis of the present invention will be described in detail.

C is an important element of the present invention which not only enhances scuffing resistance and wear resistance by forming carbides, but also contributes to improvement in strength and fatigue properties by being partially dissolved in the matrix. One. In order to obtain these effects, C must be at least 0.2%, but if it exceeds 1.2%, the workability in warm or cold during wire production and the bending workability after heat treatment are reduced. . Therefore, in the present invention, the content of C is limited to 0.2 to 1.2%.

Similarly to C, Cr, which is one of the important elements constituting the present invention, combines with C to form a carbide, thereby contributing to the improvement of scuffing resistance and wear resistance, and a part of the base. And acts as a secondary hardening element during tempering, thereby contributing to the improvement of heat resistance of the piston ring. In addition, since fine nitrides are formed in the nitrided layer by the nitriding treatment, it is possible to further improve the scuffing resistance and the wear resistance of the piston ring. In order to obtain the above effect, at least 5.0% of Cr is required.
A content exceeding 5.0% causes an increase or increase in the amount or particle size of carbides, and lowers workability. Therefore, the content of Cr of the present invention is set to 5.0 to 25.0%.

In addition to adjusting the content of the above elements, the most important means for obtaining the effects of the present invention is to control the amount of M ₇ C ₃ type carbide present in the structure to 4.0% by area%. % Or less.

As described above, the workability and scuffing resistance required for the piston ring material depend on the Cr-based carbide. However, the present inventor has determined that the degree of this effect depends on the type of the Cr-based residual carbide. It has been found that the difference is greatly related to the difference between the particle size and the distribution state. That is, the scuffing resistance and workability of the piston ring material differ greatly depending on the type of these Cr-based residual carbides, and the present inventor has found an optimum carbide state for improving these characteristics. Hereinafter, carbide present in the structure of the piston ring material will be described in detail.

As the Cr-based carbides present in the piston ring material, two types of carbides, M ₇ C ₃ type and M ₂₃ C ₆ type, are well known. However, M ₇ C ₃ type carbides are formed as coarse primary carbides at the time of solidification, and are relatively stable even at high temperatures, so that it is difficult to adjust the shape by hot working temperature and heat treatment temperature. is there. On the other hand, among the same Cr-based carbides, M ₂₃ C ₆ -type carbides are characterized in that their particle size and distribution can be easily adjusted by hot working temperature and heat treatment conditions.

Therefore, in a material in which a large amount of M ₇ C ₃ type carbide is present, it is caused by a microscopic difference in the structure after quenching and tempering, that is, due to the existence of a dense part and a sparse part in the amount of carbide. Phenomenon such as generation of microscopic scuffing from a portion where the amount of carbide is sparse occurs, and as a result, scuffing resistance is reduced. Further, if coarse M ₇ C ₃ type carbides are unevenly distributed in the structure, not only will the scuffing resistance extremely decrease, but also the workability will extremely decrease.

In other words, if the M ₇ C ₃ type is in a carbide state in which it does not become extremely dominant, the carbide after quenching and tempering becomes fine, and the distribution state can be made extremely uniform. In addition, it is possible to make it difficult to reduce the scuffing resistance due to the uneven distribution of carbides as described above. In addition, the fact that the amount of coarse primary carbides is small and that the carbides after quenching and tempering are fine means that even if it is a high alloy material that has relatively difficult workability, In addition, it is possible to improve the workability in the cold state and the bending workability after the heat treatment, and therefore, it is also possible to improve the production efficiency and reduce the production cost.

For the above reasons, the present inventor has found that the reduction of M ₇ C ₃ type carbide is most effective in improving various properties of the piston ring material. As a specific adjustment requirement, the amount of M ₇ C ₃ type carbide present in the structure is set to 4.0% in area%.
It is very important to adjust the following: Preferably,
2.5% or less. In addition, the area% referred to in the present invention is:
It is a ratio of the total cross-sectional area of the M ₇ C ₃ type carbide to the cross-sectional area.

FIG. 1 shows an example of an M ₇ C ₃ type carbide present in the structure of a piston ring material whose hardness has been adjusted by tempering after quenching. It is a microstructure photograph and its schematic diagram which corroded M ₇ C ₃ type carbides to white and M ₂₃ C ₆ type carbides to black using a reagent and observed with a light microscope at × 2000. FIG. 1 (a)
Has an area ratio of M ₇ C ₃ type carbide of 2.2% and satisfies the carbide state of the present invention. In other words, the predominant carbide in this structure is M ₂₃ C ₆
Mold, which is a carbide state effective for obtaining the characteristics of the present invention. On the other hand, in FIG. 1B, the area ratio of the M ₇ C ₃ type carbide is 6.3%, and as shown in the figure, it is recognized that the M ₇ C ₃ type carbide is extremely unevenly distributed. . That is,
This is a carbide state which is difficult to obtain the characteristics of the present invention.

According to the present invention described above, for example, a low alloy material having a Cr content of 5.0% or more and less than 12.0%, which has good workability but does not satisfy the required characteristics for scuffing resistance. It is also possible to improve the scuffing resistance without sacrificing workability,
This is an excellent means to achieve both excellent workability and scuffing resistance as a piston ring material.

Hereinafter, the reasons for the limitation and the effects of the elements other than those described above which are preferable for constituting the piston ring material of the present invention will be described.

Si is an element which improves the bending workability after heat treatment in addition to the workability at the time of manufacturing a wire, which is one of the objects of the present invention. That is, the present inventor has found that an appropriate amount of Si contained in steel has a great effect on achieving the above-mentioned object of the present invention. In particular, the content of Si is 0.25%.
It was ascertained that the effect became remarkable below.

On the other hand, Si is an element remaining in the steel as a deoxidizing element in the refining process, and has a Cr content of 2.0 to typified by JP-A-61-59066.
In low to medium Cr martensitic stainless steels of 9.0%, at least 0.3% or more is required as an element for improving oxidation resistance and heat resistance. However, it is not necessary to attach importance to the oxidation resistance, because the actual piston rings are used in lubricating oil, and because they are used after being subjected to some surface treatment such as nitriding or Cr plating. It's gone.

In addition, the present inventor has conducted detailed studies on the effect of Si added for the purpose of improving the heat set resistance. That is, the conventional Si
The addition of is significantly expressing the effect by delaying agglomeration of carbides precipitated by the tempering in a material that has been tempered at a low temperature. That is, it is considered that most of the precipitated carbides are aggregated at 550 to 650 ° C.
In a martensitic piston ring material generally subjected to a tempering treatment, the effect of other additional elements contributing to secondary hardening is greater, and no remarkable effect is observed for Si. He gained the knowledge.

It should be noted that with the recent progress in steelmaking technology, Si
Even if the amount of the deoxidizing agent is reduced, it is possible to sufficiently reduce oxide non-metallic inclusions. For the above reasons, the Si of the present invention
Is 0.25% or less as a content that improves the bending workability after heat treatment in addition to the workability at the time of manufacturing a wire.
A desirable range of Si is 0.05 to 0.20%.

As described above, according to the present invention in which the Si content is appropriately adjusted, the workability in manufacturing a wire and the bending workability after a heat treatment can be further improved. In particular, that the bendability after heat treatment is improved by the present invention,
The heat treatment hardness can be adjusted to be higher than conventional piston ring materials, so the scuffing and wear resistance of the piston ring, which has been compromised to some extent to improve bending workability, is exhibited at a higher level. What you can do is possible.

Mn is one of the elements necessary for refining steel as a deoxidizing agent or a desulfurizing agent. JP-A-61-590 mentioned above.
According to No. 66, to improve strength and hardness,
It states that a minimum content of 0.5% is required. However, when Mn contains more than 0.30%,
It was confirmed that the workability in the annealed state was deteriorated even though the influence of the reduction of the Si amount was not so large. Therefore, the content of Mn of the present invention is limited to 0.30% or less.

Mo, W, V and Nb not only combine with C to form a hard carbide, but also partially form Cr.
Since Cr forms a solid solution in carbide, Cr carbide itself is an element that is strengthened to improve wear resistance. Also, when tempering,
Since it contributes as a secondary hardening element, it is also effective in improving the heat resistance of the piston ring. However, excessive addition leads to an increase in hard carbide, which not only significantly increases the wear amount of the cylinder, but also causes a reduction in workability. Therefore, the present invention provides Mo, W, V, Nb
And one or two or more of the above to a total of 0.3 to 2.5%.

Cu forms Fe, without forming carbides or nitrides.
By forming a fine solid solution in the matrix, it contributes to strengthening of the matrix and improvement of heat-resistant set resistance, and therefore can be added as necessary. However, if the content exceeds 4.0%, the hot workability is extremely reduced, so the upper limit is set to 4.0%.
0% or less. Therefore, in the present invention, the desirable Cu content for obtaining the above effect is 0.5 to 3.0%.

Although Ni need not always be added,
When a shocking stress is applied during use as a piston ring, it can be added as needed for the purpose of improving toughness. However, if added in excess of 2.0%, the workability in the annealed state is significantly reduced.
%.

Al enters N and Al during the nitriding process.
The formation of N increases the hardness of the nitrided layer and contributes to the improvement of the wear resistance of the piston ring, so that it can be added as necessary. However, when the content exceeds 1.5%, not only the workability and the fatigue properties are extremely lowered, but also the hard AlN precipitated by nitriding becomes extremely large, and the wear of the cylinder is significantly increased. Therefore, the upper limit of the amount of Al to be added is 1.5% or less, preferably 0.2 to 0.6%.

The piston ring material of the present invention may further include, as necessary, Ti, Mg, which increases the hardness of the nitrided layer, and Co, which is effective for improving the corrosion resistance, in addition to the elements described above. It is possible to

[0037]

EXAMPLES The effects of the present invention will be described below with reference to examples. First, a 30 kg steel ingot adjusted to a predetermined composition by high frequency induction melting in the atmosphere was produced. Next, through hot working, the above-mentioned steel ingot was converted into a linear material having a diameter of 8 mm.
Annealed. Table 1 shows the composition of the obtained annealed material.

[0038]

[Table 1]

Next, a part of the obtained annealed material was processed into a tensile test piece shape having a parallel portion length of 40 mm and a parallel portion diameter of 6 mm, and a tensile test was conducted for the purpose of evaluating the wire drawing and rolling workability. Was. At the same time, the hardness was also measured. The remaining annealed material had a diameter of 5.5 at room temperature.
The wire is drawn until it becomes a wire rod of mm.
After quenching at 0 ° C., the hardness was adjusted by tempering. In addition,
The hardness after the adjustment is no. Nos. 1 to 10 of the present invention material and The comparative materials 21 and 22 have 48 to 50 HRC, and the other inventive materials and comparative materials have 38 to 40 HRC.
And, from these heat-treated materials whose hardness has been adjusted, 3 mm
A bending test piece having a cross section of × 3 mm was prepared, and a bending test was performed as an evaluation of bending workability.

Subsequently, regarding the material of the present invention and the comparative material,
In order to confirm the superiority or inferiority of the properties of the nitrided layer formed on the surface, test specimens for evaluation were collected from the above-mentioned heat-treated material, and after the heat treatment, the nitriding treatment usually performed on a piston ring processed into a predetermined shape was performed. Assuming, a gas nitriding treatment at 520 ° C. × 10 hours was performed. Then, in order to remove the brittle nitride layer formed on the outermost surface, the surface of the test piece was polished for 10 minutes.
After removing 15 μm, hardness measurement of the outermost surface of the nitride layer and anti-scuffing test were performed.

The scuffing resistance test was carried out under the following conditions by using an ultra-high pressure friction and wear tester, and evaluated by the seizure load. FIGS. 2 and 3 show the outline of the tester test piece. Friction speed: 8 m / s Friction surface pressure: Initial pressure: 20 kgf / cm ² , rising by 10 kgf / cm ² every 3 minutes Lubricating oil: Motor oil # 30, oil temperature 80 ° C,
400ml / min. From the center of the stator holder. Lubrication detection at .... Detection by load cell and dynamic strain meter Counterpart material: JIS gray cast iron (FC250) Table 2 shows the test results.

[0042]

[Table 2]

From Table 2, it can be seen that the material of the present invention has a larger drawing value after annealing than the comparative material having the same Cr content and has extremely good cold workability. Also, it can be seen that the material of the present invention shows a higher value of the deflection amount after the heat treatment than the comparative material. In other words, according to the material of the present invention, even if the hardness after the heat treatment is adjusted to a high value, breakage during bending is hard to occur, so that the scuffing resistance and the wear resistance can be improved by adjusting the high hardness. It is advantageous.

Next, the evaluation results of the characteristics after the nitriding treatment, that is, the characteristics required for the piston ring itself actually used will be described. The hardness of the surface nitrided layer of the material of the present invention is almost equal to that of the conventional material, and sufficient wear resistance as a piston ring can be achieved. Furthermore, it is understood that the material of the present invention has a high scuff surface pressure value by a scuffing test, and has extremely good scuffing resistance as a piston ring.

In particular, the material No. Regarding 1 to 10, despite the fact that the Cr content is less than 12% and the piston ring material is a relatively low alloy, by adjusting the M ₇ C ₃ type carbide to an appropriate amount, a comparison of the same component system was made. Material No. 2
It can be seen that the scuffing resistance is greatly improved as compared with Nos. 1 and 22. Thus, the present invention provides the above-mentioned “Cr: 5.
It can be seen that it is also effective in improving the characteristics of "0% or more and less than 12.0% piston ring material".

The comparative material No. 25 and 26 show that despite the fact that the amount of M ₇ C ₃ type carbide in the tissue exceeds the present invention,
Good scuffing resistance. This is considered to be due to the inclusion of a large amount of M ₇ C ₃ -type carbide, which far exceeds the provisions of the present invention, and an extreme increase in the particle size. However, as described above, an extreme increase in the M ₇ C ₃ type carbide significantly reduces the workability of the material, so that the comparative material no. 25, 26
Is inferior in the amount of deflection.

To improve only the scuffing resistance of the material, the comparative material No. Like 25, 26,
It is only necessary to increase or increase the amount and particle size of carbides in the structure, but then, the workability as a piston ring material is too low, and it is implemented in the current piston ring production Cold bending becomes impossible.

Further, the comparative material No. Also for 23 and 24, the bending workability is deteriorated due to the increase in the amount of carbide, and it is understood that the carbide adjustment of the present invention is effective for achieving both workability and scuffing resistance.

In addition, the comparative material No. In Nos. 21 and 22, although the C and Cr contents of the present invention are satisfied, the amount of M ₇ C ₃ type carbide contained therein exceeds the present invention, so that a sufficient amount of carbide is adjusted to improve the scuffing resistance. Is difficult.

[0050]

According to the present invention, not only have excellent characteristics as a piston ring, but also excellent drawability and rolling workability in the wire rod manufacturing process and a relatively high hardness after heat treatment. Even when the length is set, since extremely excellent bending workability can be achieved, a piston ring material excellent in various properties can be supplied at low cost. Therefore, such as improving production efficiency and reducing production costs,
Its industrial utility is extremely high.

[Brief description of the drawings]

FIG. 1 is a metal microstructure photograph showing an example of carbide present in the structure of a piston ring material and a schematic diagram thereof.

FIG. 2 is a cross-sectional view of a test piece in an ultrahigh pressure friction and wear tester.

FIG. 3 is a sectional view taken along the line AA of FIG. 1;

[Explanation of symbols]

1. 1. test piece (5 mm square x 10 L); Disk (Material ...
FC250), 3. 3. stator holder, Rotor,
5. 5. Test piece holder, 6. lubrication oil inlet, Load cell, 8. Dynamic strain gauge, P: friction pressure

Claims (8)

[Claims] (1) C: 0.2 to 1.2% by weight,
r: 5.0 to 25.0%, the balance being Fe and impurities, and the content of M ₇ C ₃ type carbide present in the structure is 4.0% or less in area%. Piston ring material with excellent scuffing resistance and workability. 2. Cr: 5.0% or more by weight%.
2. The piston ring material excellent in scuffing resistance and workability according to claim 1, wherein the piston ring material is less than 0%. 3. The piston ring material having excellent scuffing resistance and workability according to claim 1, wherein the content of Si is 0.25% or less by weight. 4. The piston ring material having excellent scuffing resistance and workability according to claim 1, wherein Mn is not more than 0.30% by weight%. 5. The anti-scuffing property according to claim 1, wherein the content is one or more of Mo, W, V, and Nb: 0.3 to 2.5% by weight%. Piston ring material with excellent workability and workability. 6. The piston ring material excellent in scuffing resistance and workability according to claim 1, wherein Cu: 4.0% or less by weight%. 7. The piston ring material having excellent scuffing resistance and workability according to claim 1, wherein Ni is not more than 2.0% by weight. 8. The piston ring material excellent in scuffing resistance and workability according to claim 1, wherein Al is not more than 1.5% by weight.