KR20170118904A - Sliding component and sliding structure - Google Patents

Abstract

A sliding part excellent in wear resistance is provided. And, a sliding structure provided with this sliding part is provided. The steel sheet according to any one of claims 1 to 3, wherein the steel sheet comprises, by mass%, 0.7 to 1.6% of C, 0.5 to 3.0% of Si, 0.1 to 3.0% of Mn, 0.05% or less of P, 0.01 to 0.12% of S, 0.3 to 1.5% 0.5 to 1.7%, V: 0 to 0.70%, Cu: 0.1 to 1.0%, Al: 0.10 to 0.70%, and Nb: 0 to 1.0% in one or two of Mo, 0.30%, balance Fe and impurities, and has a hardness of 52HRC or more and less than 58HRC. The sliding part is configured to slide with the sliding surface of the mating part under an environment in which lubricating oil intervenes on the sliding surface of the sliding part.

Description

[0001] SLIDING COMPONENT AND SLIDING STRUCTURE [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sliding part used in various sliding environments, such as an oil ring or a cam lobe fitted into an internal combustion engine. In addition, the present invention relates to a sliding structure such as an internal combustion engine in which these sliding parts are assembled.

BACKGROUND ART [0002] Conventionally, sliding parts constituting sliding structures such as oil rings, cam lobes, tappets, piston fins, cylinder liners, mission gears, thrust plates and vanes constituting components of an internal combustion engine are made of SUJ2 or SKD11 Has been used. SKD11 is a steel grade that can attain a high hardness of 60 HRC or more by quenching tempering and is also excellent in abrasion resistance because it is rich in carbides in the structure. A press mold has been proposed in which a sliding property (self-lubricating property) of a material is imparted by improving the composition of the material, and the wear resistance is improved (Patent Document 1).

Japanese Patent Application Laid-Open No. 2007-002333

The press die of Patent Document 1 has excellent wear resistance due to the manifestation of its self-lubricating properties. However, the application of the material of the press die of Patent Document 1 to the component parts of the internal combustion engine has not been considered.

An object of the present invention is to provide a sliding part having excellent abrasion resistance. And, there is provided a sliding structure provided with this sliding part.

The present invention relates to a ferritic stainless steel comprising, by mass%, 0.7 to 1.6% of C, 0.5 to 3.0% of Si, 0.1 to 3.0% of Mn, 0.05% or less of P, 0.01 to 0.12% of S, 0.3 to 1.5% : 0.5 to 1.7%, V: 0 to 0.70%, Cu: 0.1 to 1.0%, Al: 0.10 to 0.70%, one or both of Mo and W: (Mo + Nb: 0 to 0.30%, balance Fe and impurities, and has a hardness of 52 HRC or more and less than 58 HRC.

Further, the present invention is a sliding structure, wherein the sliding part of the present invention is configured to slide with a sliding surface of a mating part under an environment in which lubricating oil exists on the sliding surface of the sliding part.

According to the present invention, wear resistance of a sliding part can be improved.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a view showing an example of a relationship between a hardness and a fatigue strength of a sliding part of the present invention and a comparative example. FIG.
Fig. 2 is a diagram showing an example of the results of the friction coefficient measured by the ball-on-disc test of the sliding parts of the present invention and the comparative example.
Fig. 3 is a diagram showing an example of the relationship between the fatigue strength of the sliding parts of the present invention and the comparative example and the sliding distance when the friction coefficient measured by the ball-on-disk test reaches 0.20.

(Mode for carrying out the invention)

Most sliding parts constituting various sliding structures slide on the sliding surfaces of the mating parts under an environment in which lubricating oil is present on the sliding surfaces as represented by the components of internal combustion engines such as oil rings and cam lobes, . Under these circumstances, it has been found that the sliding parts of the present invention exhibit the self-lubricating properties effectively, and the wear resistance of the sliding parts is improved. Hereinafter, constituent requirements of the present invention will be described.

(1) A sliding component according to the present invention comprises, by mass%, 0.7 to 1.6% of C, 0.5 to 3.0% of Si, 0.1 to 3.0% of Mn, 0.05% 0.5 to 1.7%, V: 0 to 0.70%, Cu: 0.1 to 1.0%, and at least one of Al and Al in the relation of (Mo + 1 / 2W) : 0.10 to 0.70%, Nb: 0 to 0.30%, and the balance of Fe and impurities.

In particular, the feature of the sliding component of the present invention is the " addition of S and Cu in a cavity ", which contributes greatly to the development of the self-lubricating property. Conventionally, S and Cu are elements that inhibit the hot workability of a steel material and are elements that are not actively added in most steel materials. The action and effect of the composition of the sliding part of the present invention will be described below.

C: 0.7 to 1.6 mass% (hereinafter simply referred to as "%")

C is an element that is employed in the base to impart strength to the sliding part. In addition, it is an element that forms carbide to increase abrasion resistance and resistance to sliding of a sliding part. However, if C is excessively large, the amount of C employed in the matrix increases and the machinability in the finish of the shape of the sliding part deteriorates. In addition, coarse carbides are produced, and the dimensional change of the heat treatment at the time of quenching becomes large. Therefore, C is set to 0.7 to 1.6%. It is preferably 0.9% or more. Further, it is preferably 1.3% or less. It is more preferably 1.1% or less.

Si: 0.5 to 3.0%

Si is an element that improves the high-temperature softening characteristics of the sliding part. However, if Si is excessively large, the formation of delta ferrite in the structure becomes remarkable, which hinders the maintenance of the hardness of the sliding parts. Therefore, Si is set to 0.5 to 3.0%. It is preferably 0.9% or more. Further, it is preferably not more than 2.0%. More preferably, it is 1.5% or less. More preferably, it is 1.1% or less.

Mn: 0.1 to 3.0%

Mn is an element that enhances quenching. However, if it is excessively large, the machinability deteriorates. Therefore, Mn is set to 0.1 to 3.0%. It is preferably at least 0.3%. More preferably, it is 0.4% or more. Further, it is preferably 1.0% or less. More preferably, it is 0.6% or less.

· P: not more than 0.05%

P is an element that inevitably contains, even if it is not normally added. It is an element that hinders the toughness of the sliding part. Therefore, it should be 0.05% or less. Preferably 0.03% or less. More preferably 0.02% or less.

S: 0.01 to 0.12%

S is an element contributing to improvement of the self-lubricating property of the sliding part of the present invention together with Cu described later. The present inventor investigated the phenomenon occurring on the sliding surface when the sliding component having the component composition of Patent Document 1 was used in an environment in which lubricating oil was present on the sliding surface. As a result, when the sliding surfaces of the sliding part and the mating part come into contact with each other with a surface pressure that is high enough to cause the sintering, the organic component in the lubricating oil adsorbed on the sliding surface of the sliding part is dehydrogenated, Graphite and the like. Among these diamonds and graphites, the " graphite intercalation compound " having a structure sandwiched between sulfuric acid ions or sulfuric acid molecules periodically improves the self lubrication characteristics of the sliding parts and lowers the friction coefficient between the sliding surfaces of the sliding parts I found that I could keep it.

Then, S in the sliding parts is oxidized on the sliding surface in use to generate sulfate ions. Then, the produced sulfate ions are sandwiched between the graphite layers to promote the formation of the above-described graphite intercalation compound. Alternatively, the generated sulfate ions combine with the hydrogen ions generated by the dehydrogenation of the lubricating oil to become sulfuric acid molecules, which are sandwiched between the graphite layers, thereby promoting the formation of the above-described graphite intercalation compounds. As a result, the surface interval of the graphite in the C-axis direction is widened to suppress the ingot transformation of the graphite into the diamond in the state of the nano level, and the lubricity is improved by increasing the degree of freedom of sliding. However, when S in the sliding parts becomes excessive, excessive sulfuric acid ions are formed on the sliding surface to such an extent that they are not sandwiched between the graphite layers. Further, this excessive sulfate ion promotes damage to the sliding surface, which hinders the development of self-lubricating properties. Therefore, S is set to 0.01 to 0.12%. It is preferably 0.03% or more. More preferably, it is 0.04% or more. More preferably, it is 0.05% or more. Further, it is preferably 0.09% or less. More preferably, it is 0.08% or less.

Ni: 0.3 to 1.5%

Ni is an element that contributes to maintaining the hardness of sliding parts by quenching and Ni-Al intermetallic compound precipitates by bonding with Al to be described later in the quenching and tempering process. However, if Ni is excessively large, the machinability in machining into the shape of the sliding part deteriorates in the annealing state before quenching tempering. Therefore, Ni is set to 0.3 to 1.5%. It is preferably 0.4% or more. Further, it is preferably 1.0% or less. More preferably, it is 0.8% or less. More preferably, it is 0.6% or less.

Cr: 7.0 to 13.0%

Cr is an element that enhances the quan- tity of the base. Further, it is an element that forms a carbide with the above-mentioned C to increase wear resistance and anti-seizure property of the sliding part. However, the increase of the carbide deteriorates the machinability. Therefore, Cr is set to 7.0 to 13.0%. Preferably, it is at least 7.5%. More preferably, it is at least 8.0%. Further, it is preferably not more than 11.0%. More preferably, it is 10.0% or less. More preferably, it is 9.0% or less.

· One or two kinds of Mo and W: 0.5 to 1.7% in the relation of (Mo + 1 / 2W)

Mo and W are elements that form fine carbides in the structure after quenching and impart fatigue strength to the sliding parts. However, if it is too large, it causes deterioration of machinability and toughness. Mo and W may be added singly or in combination. The addition amount at this time can be defined together with the relational expression (Mo + 1 / 2W) in that W is an atomic weight of about twice that of Mo. In the present invention, the value of (Mo + 1 / 2W) is made 0.5 to 1.7%. It is preferably 0.7% or more. More preferably, it is 0.9% or more. More preferably, it is 1.0% or more. Further, it is preferably 1.5% or less. More preferably, it is 1.3% or less. More preferably, it is 1.2% or less.

V: 0 to 0.70%

V can be included for improvement of quenchability. However, since V forms a hard VC carbide, the excessive V content inhibits machinability. Therefore, in the present invention, the content of V is 0.70% or less. And preferably 0.50% or less. More preferably, it is 0.30% or less. More preferably, it is 0.20% or less.

Cu: 0.1 to 1.0%

Cu, together with the aforementioned S, is an element contributing to improvement of the self-lubricating property of the sliding part of the present invention. That is, Cu is an element showing a catalytic action for producing the above-mentioned "graphite intercalation compound". Cu can precipitate an extremely small amount on the sliding surface of the sliding part after quenching tempering. The Cu precipitated on the sliding surface has a function of promoting the formation of the aforementioned " graphite intercalation compound ". However, if Cu is contained in excess, the hot workability of the workpiece is deteriorated due to heat and brittleness. Therefore, Cu is set to 0.1 to 1.0%. It is preferably at least 0.2%. More preferably, it is 0.3% or more. Further, it is preferably 0.8% or less. More preferably, it is 0.6% or less. More preferably, it is 0.5% or less.

Al: 0.10 to 0.70%

Al is an element contributing to the maintenance of the hardness of the sliding part by bonding with Ni to form a Ni-Al intermetallic compound. However, if Al is excessively large, the formation of delta ferrite in the structure becomes significant, which hinders maintenance of the hardness of the sliding parts. Therefore, Al is set to 0.10 to 0.70%. It is preferably at least 0.15%. More preferably, it is 0.25% or more. Further, it is preferably 0.50% or less. More preferably, it is 0.45% or less.

Nb: 0 to 0.30%

Nb, like V, can be included for the purpose of improving the quenchability. However, the presence of excess Nb inhibits machinability. Therefore, in the present invention, the content of Nb is 0.30% or less. Preferably not more than 0.20%. More preferably 0.15% or less. In addition, a preferable content for obtaining the above effect is 0.03% or more. More preferably, it is 0.05% or more. More preferably, it is 0.07% or more.

The self-lubrication properties of the sliding parts of the present invention are exerted by using the above composition of compositions by using " alteration behavior due to friction " of the lubricating oil interposed on the sliding surfaces. Therefore, it is sufficient that the lubricating oil according to the present invention is lubricated with a lubricating oil, for example, a hydrocarbon-based lubricant, between the lubricating oil and the lubricating lubricant, ) Can be selected.

(2) The sliding part of the present invention has a hardness of 52 HRC or more and less than 58 HRC.

In general, it has been considered that lowering the hardness of a sliding part leads to a decrease in wear resistance of the sliding part. Therefore, the conventional sliding parts have been adjusted to hardness of 60HRC or more. However, the sliding part of the present invention has a fatigue strength higher than that of the conventional SKD11 due to the above-described composition of the components. Further, the value of the fatigue strength is improved remarkably by lowering the hardness of the sliding part moderately. That is, as shown in Fig. 1, the conventional SKD11 (x in Fig. 1) had a fatigue strength of about 560 MPa when adjusted to 60 HRC, which is the hardness of a general sliding part. Then, the value of the fatigue strength does not rise to about 600 MPa even if the hardness is lowered. On the other hand, in the case of the material composition of the composition according to the present invention (circle in Fig. 1), the value of the fatigue strength shows a high fatigue strength of about 630 MPa when the hardness is reduced to 58 HRC. Thereafter, the high fatigue strength is maintained at a low hardness region thereafter.

In the sliding component according to the present invention having the above-described composition, the coefficient of friction during use is effectively reduced along with the increase in the value of the fatigue strength of the sliding component, so that the self- (See FIG. 3). The present invention aims at a sliding component having a fatigue strength exceeding 600 MPa, which is difficult to attain in the conventional SKD11, as the fatigue strength stably achieving this synergistically improved self-lubricating property. Preferably greater than 630 MPa. The hardness of the sliding part of the present invention is set to be less than 58 HRC as a range in which the fatigue strength exceeding 600 MPa can be easily achieved. Preferably not more than 57 HRC.

However, when the sliding part of the present invention is used, it is not a coincidence to lower the hardness of the sliding part of the present invention, assuming that the relative part has a high hardness. For example, when SUJ2, which is a bearing steel of JIS grade steel, is used for a relative part, its hardness is usually adjusted to 60 to 62 HRC, which is higher than that of the sliding part of the present invention. SUJ2 is a "high carbon chrome bearing steel material" which is standardized by JIS-G-4805, and its composition is as follows, in mass%.

The steel sheet according to any one of the above items (1) to (3), wherein the steel sheet contains 0.95 to 1.10% of C, 0.15 to 0.35% of Si, 0.50% or less of Mn, 0.025% or less of P,

And, when the sliding part of the present invention is an oil ring or a cam lobe, the sliding surface thereof slides with the sliding surface of the mating part in an " intermittent " In this contact form, when the hardness of the sliding part of the present invention is significantly lower than that of the counterpart, the Hertz stress to be applied is increased. Then, when this Hertz stress exceeds the fatigue strength of the sliding part, fine plastic deformation occurs on the sliding surface. Then, the wear of the sliding part is caused to cause wear, and the friction coefficient between the sliding surfaces increases, thereby hindering the self-lubricating property of the present invention. Therefore, the lower limit of the hardness of the sliding part of the present invention is 52 HRC. The lower limit is preferably 53 HRC. More preferably, it is 54 HRC. More preferably, it is 55HRC.

Under these conditions, for example, a metal material such as SUJ2 can be used as a material of a relative part, and a mechanism of a sliding structure having a long lifetime, which achieves both suppression of adhesion (adhesion) damage and improvement in fatigue life Can be obtained.

Example

Each of the sliding parts 1 and 2 having the composition of the samples Nos. 1 and 2 in Table 1 was prepared. Sample No. 2 is SKD11.

Next, with respect to each of the sliding parts 1 and 2, the three pieces of the target hardness A: 50HRC, B: 55HRC, and C: 60HRC were prepared. At this time, the actual hardness of each of the sliding parts is 50.4 HRC for the sliding parts 1-A, 56.2 HRC for 1-B, 62.0 HRC for 1-C, 50.0 HRC for 2-A, 55.8 HRC for 2-B, C was 61.0 HRC. The sliding part 2-C having the target hardness SKD11 of 60 HRC corresponds to a conventional sliding part. Then, the fatigue strength of these sliding parts was measured. In the method of measuring the fatigue strength, each of the sliding parts is processed into a rotary bending fatigue test piece and subjected to an Ogoshi rotary bending fatigue test. The surface stress of the test piece was adjusted by adjusting the secondary moment of inertia determined from the shape of the test piece and the weight of the weight hanging at the center of the parallel portion of the test piece. The stress amplitude was set under the condition that the stresses in the tensile and compressive directions (in the amplitude ratio-1) were the same in one revolution of the test piece. The rotation speed of the test piece was set to 50 Hz (3,000 rpm). Then, the stress when the rotational bending fatigue test piece reached the fracture was regarded as the fatigue strength. The results are shown in Fig.

Then, a ball-on-disk test was conducted on each of the sliding parts to evaluate the self-lubricating characteristics of each sliding part. The test conditions are as follows. Then, the change of the friction coefficient was continuously measured until the sliding distance reached 100 m. The results are shown in Fig.

Device: CSM Manufacturing Friction Abrasion Tester

Specimen:

· Disc (sliding part): 20 mm diameter × 5 mm thickness

· Ball (relative parts): SUJ2 (diameter 6mm, hardness 62HRC)

Ball load: 10N

Number of disk rotations: 500 rpm

Sliding radius: 3.3 mm

Sliding distance: 100m

Oil content (coating amount): 0.1 μ

Oil (lubricating oil):

· Base oil: Commercial paraffin oil

Formic acid: Addition amount 2.9 x 10 ^-4 ppm

From Fig. 2, the friction coefficients of the sliding parts 2-A, 2-B, and 2-C, which are component compositions that do not exhibit the self-lubricating property, increase and the frictional coefficient values exceeding 0.30 are measured. In the sliding parts 2-B and 2-C, the sliding occurred before the sliding distance reached 100 m, and the friction coefficient rapidly increased.

On the other hand, the sliding parts 1-A, 1-B, and 1-C, which are component compositions that exhibit self-lubricating properties, did not occur in the sliding distance of 100 m. The values of the friction coefficient between the sliding parts 1-A and 1-B were maintained at 0.30 or less. The sliding part 1-B of the present invention in which the hardness is adjusted to "less than 58HRC and less than 58HRC" in addition to the component composition that exhibits the above-mentioned self-lubrication property has a self-lubricating property synergistically improved, And the value was 0.20 or less.

Fig. 3 shows the relationship between the fatigue strength of each sliding part and the sliding distance when the friction coefficient measured above reaches 0.20. Here, the value of the friction coefficient of " 0.20 " is an index of the friction coefficient when the sliding part exhibits a synergistic self-lubricating property under the test conditions of this embodiment, as described above. 3, the sliding part 1-B of the present invention has a fatigue strength exceeding 600 MPa. Further, even when the sliding distance reached 100 m, a low friction coefficient of 0.20 or less was maintained (in FIG. 3, it is shown at the position of "100 m" for convenience). The sliding part 1-B of the present invention is improved in self-lubrication characteristics (the coefficient of friction is small) and improved in its self-lubricating property as compared with the sliding parts 1-A and 1-C, Respectively.

Claims (2)

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet comprises, by mass%, 0.7 to 1.6% of C, 0.5 to 3.0% of Si, 0.1 to 3.0% of Mn, 0.05% or less of P, 0.01 to 0.12% of S, 0.3 to 1.5% 0.5 to 1.7%, V: 0 to 0.70%, Cu: 0.1 to 1.0%, Al: 0.10 to 0.70%, and Nb: 0 to 1.0% in one or two of Mo, 0.30%, balance Fe and impurities, and has a hardness of 52 HRC or more and less than 58 HRC. The sliding structure according to claim 1, wherein the sliding part is configured to slide with the sliding surface of the mating part under an environment in which lubricating oil is present on the sliding surface of the sliding part.

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