JP2010100881A - Sliding component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sliding component which has excellent wear resistance and is suitably used as the gear, pulley, shaft or the like of automobiles and industrial machinery. <P>SOLUTION: There is provided the sliding component subjected to carburizing or carbonitriding, wherein in the surface layer part in the range from the surface of a sliding face to a depth of 10 μm, the average particle diameter of cementite particles is ≤0.6 μm, the number density of the cementite particles in the cross-section in the vertical direction to the sliding face is ≥1 piece/μm<SP>2</SP>, also, the Vickers hardness in a depth of 10 μm from the surface of the sliding face satisfies ≥700, and further, the surface roughness of the sliding face satisfies Rz: ≤4.0 μm and Rpk/Rk: <1.0; wherein, Rz represents the maximum height roughness prescribed in JIS B 0601 (2001), and further, Rpk and Rk represent the projecting crest height and the level difference of core parts prescribed in JIS B 0671-2 (2002), respectively. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sliding component as a power transmission component having excellent wear resistance, and more particularly to a carburized or carbonitrided sliding component.

  Conventionally, parts such as gears, pulleys, and shafts in automobiles and industrial machines are quenched by carburizing or carbonitriding JIS standard SCr420, SCM420, SNCM420 and other mechanical structural alloy steels (hereinafter, carburized and quenched). Is called “carburizing and quenching”, and carbonitriding and quenching is called “carbonitriding and quenching”), followed by tempering at a temperature of 200 ° C. or less and, if necessary, shot peening treatment Thus, it has been carried out to ensure characteristics required for each component such as surface fatigue strength, bending fatigue strength, and wear resistance.

  However, in recent years, in order to cope with improvement in fuel consumption of automobiles and higher output of engines, parts have become smaller and lighter, and accordingly, the load on the parts has been remarkably increased. For this reason, the industry demands that the sliding parts for power transmission have particularly excellent wear resistance.

  In addition, as a measure to improve the wear resistance of parts that have been carburized or carbonitrided and quenched so far, the surface roughness of the parts is reduced, the hardness of the surface of the parts is increased, and incomplete quenching is performed. It is known to prevent tissue generation.

  However, simply taking the measures as described above cannot prevent the wear resistance from being lowered when the load on the parts is remarkably increased, and cannot meet the above-mentioned demand from the industry.

  Therefore, for example, in Patent Document 1, the chemical components are defined, and “after carburizing under a condition where the carbon potential is 1.2% by weight or more, it is cooled to a temperature range of A1 temperature or lower and subjected to a reheating treatment. A technique relating to “a carburized member characterized by the above” is disclosed.

  Further, Patent Document 2 contains a specific amount of component elements, carbon concentration from the surface to a depth of 0.3 mm, maximum diameter of precipitated carbide, average diameter, area ratio of precipitated carbide, residual austenite amount and normal temperature. A technique relating to “a rolling element of a continuously variable transmission” that defines the hardness of the motor is disclosed.

  Furthermore, Patent Document 3 discloses that the maximum height Ry of the roughness curve of the contact surface is 1 to 3 μm, and Rpk / between the attenuation peak height Rpk of the load curve obtained from the roughness curve and the maximum height Ry. A technique relating to a “mechanical part” characterized by having a contact surface satisfying the relationship of Ry ≦ 0.1 is disclosed.

JP-A-11-117059 Japanese Patent Laid-Open No. 11-199983 WO97 / 19279

  The “carburized member” disclosed in Patent Document 1 is regulated to adjust the average particle size and amount of cementite dispersed by adjusting the surface C concentration during carburizing and then cooling and reheating. However, no consideration is given to the surface roughness of the member and its shape characteristics. However, the wear resistance varies depending not only on the surface layer structure of the member but also on the characteristics of hardness, surface roughness and its shape. For this reason, the technique proposed in Patent Document 1 that merely defines the average particle diameter of cementite and the amount of dispersion thereof may not ensure sufficient wear resistance. Moreover, in Patent Document 1, no consideration has been given to improving the wear resistance when the friction coefficient is rapidly reduced, such as at the time of starting the part.

  The “rolling element of a continuously variable transmission” disclosed in Patent Document 2 is also a sliding component for power transmission. As described above, the wear resistance includes not only the structure and hardness of the member surface layer but also the surface. Roughness and its shape characteristics also affect. For this reason, in the technique proposed in Patent Document 2 in which consideration is not given to the surface roughness and its shape, there is a case where excellent wear resistance cannot be ensured. Further, even in this Patent Document 2, no consideration has been given to improving the wear resistance in the case where the coefficient of friction rapidly decreases, such as at the time of starting the part.

  The “cam follower roller” disclosed as one embodiment of the “mechanical part” proposed in Patent Document 3 is also a power transmission part. However, the wear resistance includes the surface roughness of the member and the shape thereof. Not only the characteristics, but also the hardness and texture of the surface layer are affected. For this reason, the technique proposed in Patent Document 3 in which consideration is not given to the structure and hardness of the surface layer of the member may not ensure excellent wear resistance. Further, in the case of Patent Document 3 as well, no consideration has been given to improving the wear resistance in the case where the friction coefficient rapidly decreases, such as at the time of starting the part.

  The present invention has been made in view of the above situation, and provides a sliding component having excellent wear resistance, and in particular, a sliding component which has been subjected to carburizing or carbonitriding and has excellent wear resistance. With the goal.

  As already mentioned, it is only necessary to take conventional measures such as reducing the surface roughness of the component, increasing the hardness of the component surface layer, and preventing the formation of an incompletely quenched structure. If the load increases significantly, a decrease in wear resistance cannot be avoided.

  Therefore, the present inventors have investigated focusing on controlling the surface layer portion, in particular, controlling the surface roughness and the dispersion of cementite, in order to improve the wear resistance when the load on the part is significantly increased.・ Research was repeated, and further detailed examinations were made on the conditions attached to it.

  As a result, the following findings (a) to (d) were obtained.

  (A) The power transmission component is composed of a drive component and a driven component, and a speed difference may occur between the two components. In the steady state, this speed difference changes constant or continuously, and the adhesive contact where the true contact between the contact surfaces is broken by shearing force, or the high hardness roughness protrusion between the contact surfaces is low hardness Abrasive wear that scrapes off the surface is the main. On the other hand, for example, when a speed difference is instantaneously generated from a stopped state, such as when a part is started, the friction on the contact surface instantaneously changes from a static friction state to a dynamic friction state. In this case, since the value of the dynamic friction coefficient is smaller than that of the static friction coefficient, the friction coefficient rapidly decreases, and as a result, vibration is generated with the difference between the static friction force and the dynamic friction force as an excitation force. Although this vibration is attenuated in a relatively short time, repeated wear causes fatigue wear on the contact surface.

  (B) The surface roughness affects “adhesion wear” and “abrasive wear”. In order to suppress these wears, it is effective to reduce the maximum roughness value, for example, Rz which is the “maximum height roughness” defined in JIS B 0601 (2001). In addition, the ratio of Rpk, which is the “projection peak height” defined in JIS B 0671-2 (2002), and Rk, which is the “level difference between the core portions”, that is, [Rpk / Rk] It is effective to make the value of less than 1.0.

  (C) However, when the surface roughness is reduced, the coefficient of static friction is increased, and therefore, vibration that is generated when a speed difference is instantaneously generated is likely to occur.

  (D) Even when the surface roughness is reduced, the generation of vibration described in (c) above may be suppressed by dispersing cementite having a specific size in the surface layer. This is thought to be because the frequency of direct contact between the steels can be reduced.

  Below, the specific content of the investigation and research that led to obtaining the above findings (a) to (d) will be described.

(A) Adhesive wear and abrasive wear:
The inventors first investigated the effect of surface roughness on wear resistance by the following method.

  That is, steel having the chemical composition shown in Table 1 was melted in a 150 kg vacuum melting furnace and then cast to produce an ingot.

  The above ingot was held at 1250 ° C. for 8 hours, then allowed to cool in the air and once cooled to room temperature. Next, it was reheated to 1250 ° C. and held for 30 minutes, and hot forged at a finishing temperature of 1000 ° C. or higher to obtain a round bar having a diameter of 45 mm. In addition, after completion | finish of hot forging, it stood to cool in air | atmosphere and cooled to room temperature.

  The round bar thus obtained was subjected to normalization which was kept at 925 ° C. for 1 hour, then allowed to cool in the air and cooled to room temperature.

  From the R / 2 part (R: radius) of the round bar having a diameter of 45 mm after normalization, a block test piece for block-on-ring test having a shape shown in FIG. The block-on-ring test and the shape of the test piece are those defined by ASTM-G77-98. (A) and (b) in FIG. 1 are a front view and a side view of a block test piece, respectively.

  The block test piece for the block on-ring test (hereinafter referred to as “block test piece”) is carburized in the heat pattern shown in FIG. 2 or FIG. It was quenched and tempered at 170 ° C. for 2 hours. Note that “Cp” in FIGS. 2 and 3 means a carbon potential.

  Various surface treatments such as grinding, shot peening, and polishing were applied to the test portion of the block test piece carburized and quenched and tempered as described above to change the surface roughness.

  Table 2 shows the details of the surface processing conditions together with the heat treatment pattern as “processing conditions”.

  Here, “longitudinal grinding” in Table 2 means grinding in the longitudinal direction of the test piece, that is, the length of 15.75 mm in FIG. 1, while “lateral grinding” is perpendicular to the longitudinal direction. It means grinding in the direction, that is, the direction of 6.35 mm in FIG. In addition, grinding was implemented using the grindstone with a particle size of 80-500.

  Further, “paper polishing” means wet polishing in a random polishing direction in the order of # 500 and # 800 SiC polishing papers.

  “Specular polishing” means wet polishing in random polishing directions in the order of # 500, # 800, # 1000, # 1500 and # 2000 SiC polishing paper, and further polishing direction with alumina abrasive grains having a particle diameter of 50 μm Means buffing and finishing as random.

  “Shot peening” uses a round cut wire with a hardness of 800 Vickers hardness and a particle size of 0.8 mm. “Particle shot peening” means a hardness of 800 and Vickers hardness. It means that shot peening was performed at a projection pressure of 0.4 MPa using a round cut wire having a particle size of 0.25 mm.

  The surface roughness of the block test piece surface-treated as described above was measured under the following conditions in accordance with the method defined in JIS B 0601 (2001) and JIS B 0671-2 (2002).

Measurement direction: specimen longitudinal direction,
-Evaluation length: 3.0 mm,
Cut-off value: 0.8mm
Measurement items: Rz, Rpk, Rk and Rvk.

  Table 2 shows the Rz, Rpk, Rk and Rvk measured in this way together with the value of [Rpk / Rk]. Rz represents the “maximum height roughness” defined in JIS B 0601 (2001), and Rpk, Rk, and Rvk are “protrusion peaks” defined in JIS B 0671-2 (2002), respectively. "Part height", "Level difference of core part", and "Projection valley depth".

  Moreover, the Vickers hardness in the depth of 10 micrometers from the surface of the block test piece surface-treated as mentioned above was investigated as follows.

  That is, the peak depth of compressive residual stress due to shot peening is often within 50 μm from the surface. Therefore, the increase in hardness due to shot peening is considered to occur within 50 μm from the surface, and for the purpose of observing the hardness of the surface layer in more detail than usual, the block test piece at the position corresponding to the sliding portion After cutting the central portion, it was embedded in a resin at an angle of 15 ° with respect to the cross section perpendicular to the longitudinal direction and mirror-polished. At this time, since the surface is apparently enlarged in the depth direction, the hardness at 5 points was measured at a position of 40 μm from the surface. The above position corresponds to a 10 μm position in the vertical direction. A Vickers hardness tester was used for the hardness measurement, and the Vickers hardness (hereinafter also referred to as “Hv hardness”) was measured with a test force of 1.961 N. And the arithmetic average value of these 5 points | pieces of hardness was calculated | required.

  Table 2 also shows the Vickers hardness at the depth of 10 μm thus determined. In Table 2, the hardness is expressed as “surface hardness”.

  Furthermore, the block-on-ring test was performed under the conditions shown in Table 3 using the surface-treated block test piece and the block-on-ring test ring test piece having the shape shown in FIG. 4 (hereinafter referred to as “ring test piece”). And the wear resistance was investigated.

  FIG. 5 shows a schematic diagram of the block-on-ring test.

  The number of tests was two for each treatment condition, and the wear width of the block test piece after the test was measured with an optical microscope. In addition, as shown in FIG. 6, the measurement location was made into the both ends and the center of the wear trace about each test piece, and the wear width of 6 places in total was arithmetically averaged for each treatment condition, and this was made into the wear width.

  In addition, a ring test piece is cut out in parallel to the forging axis by machining from the center part of the round bar having a diameter of 45 mm after normalization described above, and using a gas carburizing furnace, the heat pattern shown in FIG. After carburizing, it was quenched in oil having an oil temperature of 80 ° C., and further tempered at 170 ° C. for 2 hours. Then, it grind | polished for 2 to 3 minutes with the grinding | polishing speed | rate of 2000 m / min using the grindstone of the particle size 80, and finished the surface roughness to 0.15-0.30 micrometer by Rq. “Rq” represents “square square root roughness” defined in JIS B 0601 (2001).

  Table 4 shows the measurement results of the wear width. Table 4 also shows the Vickers hardness at a depth of 10 μm of the block test piece shown in Table 2 and the values of Rz and [Rpk / Rk] of the surface roughness. In Table 4, the hardness is expressed as “surface hardness”.

  First, when comparing the Vickers hardness and the wear width at a depth of 10 μm, the processing condition h where the Vickers hardness is 580 having a value lower than 700, and the processing conditions e and 830 and 910 having a Vickers hardness exceeding 800 are It can be seen that the wear width of f is a remarkably large value exceeding 2 mm.

  The surface roughness Rz of the processing condition h is 1.93 μm, and the wear width is 1.14 mm, which is about the same as 1.95 μm of the small processing condition a. This is probably because the Vickers hardness at a depth of 10 μm is lower than 700.

  Therefore, the relationship between the wear width and Rz for the remaining six conditions excluding the processing condition h is shown in FIG. Note that the reference numerals in FIG. 7 represent “processing conditions”.

  From FIG. 7, it is recognized that the wear width increases as Rz increases, and that the wear width does not reach 2 mm when Rz is 2.0 μm or less. Therefore, in the case of the processing conditions e and f, the wear width is remarkably large even though the Vickers hardness at a depth of 10 μm is a high value exceeding 800, and the Rz is 6.99 μm and 4. This is considered to be a large value exceeding 4.0 μm, which is 82 μm.

  However, even in the case of processing conditions a to d and g in which Rz is 4.0 μm or less in FIG. 7, the wear width varied from 1.14 to 1.72 mm.

  Therefore, Rpk (projection peak height), Rk (core level difference) and Rvk (projection valley depth) which are geometric parameters of roughness defined in JIS B 0671-2 (2002) Paying attention, we investigated the relationship with wear width.

  “Rpk”, “Rk” and “Rvk” defined in the above JIS B 0671-2 (2002) are “initial wear height” and “effective load” in the surface roughness load curve in the load moving direction, respectively. Rpk and Rk are considered to be involved in the contact between the test pieces, corresponding to the expression expressing the “roughness” and “oil sump depth” separately.

  That is, “Rpk” corresponding to the initial wear height represents a particularly high protrusion in the roughness curve, and thus has a great influence on “direct contact”. Further, “Rk” corresponding to the effective load roughness represents a roughness distribution intermediate between “Rvk” and “Rpk”, and a specific region of “Rk” affects “direct contact”. However, since “Rpk” is a projection having a particularly high height in the roughness curve, it may be worn at the initial stage of contact or sliding, and the wear powder may wear the mating surface or its own surface. For this reason, it is desirable that “Rpk” is small. Further, since “Rk” is directly involved in only about half of the region, it is preferable that the value is large.

  As “Rpk” is larger than “Rk”, the contact becomes more severe, and the mating material is worn away, the surface of the mating material is roughened, and further, the generated wear powder self-wears, or the surface becomes rough. Since it is considered that the material is worn away from the mating member, it is considered preferable that the value of [Rpk / Rk], which is the ratio of the two roughnesses, is smaller.

  Therefore, the relationship between the wear width and the value of [Rpk / Rk] for the processing conditions a to d and g is shown in FIG. Note that the reference numerals in FIG. 8 represent “processing conditions”.

  FIG. 8 shows that when the value of [Rpk / Rk] is less than 1.0, the wear width is suppressed to 1.5 mm or less.

  That is, from Table 4 and FIG. 7 and FIG. 8, in addition to setting the Vickers hardness at a depth of 10 μm to 700 or more, the surface roughness is set to Rz of 4.0 μm or less, and [Rpk / It can be seen that if the value of Rk] is less than 1.0, the wear width can be suppressed to 1.5 mm or less, and good wear resistance can be ensured.

(B) Fatigue wear:
In a power transmission component, when a speed difference occurs instantaneously from a stopped state, such as when the component is started, the friction on the contact surface instantaneously changes from a static friction state to a dynamic friction state. At this time, since the value of the dynamic friction coefficient is smaller than that of the static friction coefficient, the friction coefficient rapidly decreases, and as a result, vibration is generated with the difference between the static friction force and the dynamic friction force as an excitation force. This vibration is attenuated in a relatively short time, but if this is repeated, a crack may be generated at the contact surface, and this crack is connected by an increase in the number of repetitions, and the sliding surface is peeled off. It is thought that fatigue wear occurs. Therefore, it is necessary to suppress the generation of this crack in order to reduce fatigue wear.

  Therefore, in order to clarify the conditions for suppressing the above cracks, the present inventors have a specimen having a surface hardness and a surface roughness capable of increasing the wear resistance at a constant sliding speed, that is, The Vickers hardness at a depth of 10 μm from the surface of the sliding surface is 700 or more, the surface roughness is Rz is 4.0 μm or less, and the value of [Rpk / Rk] is less than 1.0. Investigation and research were repeated using the adjusted specimen.

  Specifically, the block having the shape shown in FIG. 1 is parallel to the forging axis by machining from the R / 2 portion (R: radius) of the round bar having a diameter of 45 mm after normalization described in (A) above. Cut out the test piece and use a gas carburizing furnace to carburize with the heat pattern shown in FIG. 2 and then quench in oil with an oil temperature of 80 ° C., or perform high-concentration carburization with the heat pattern shown in FIGS. Furthermore, after reheating treatment, it was quenched in oil having an oil temperature of 80 ° C. to change the structure of the surface layer portion. In any case, after oil quenching, tempering was performed at 170 ° C. for 2 hours.

  In addition, “Cp” in FIGS. 9 to 11 means a carbon potential, and after carrying out high-concentration carburization, nitrogen cooling is performed, the temperature is once cooled to 600 ° C., held at 600 ° C. for 15 minutes, and then heated again. Reheating treatment was performed at 870 ° C., 850 ° C., or 830 ° C. in an atmosphere having a carbon potential of 1.0%.

  Subsequently, the surface roughness of the block test piece subjected to the above tempering was subjected to grinding and polishing to change the surface roughness.

  Table 5 shows the details of the surface processing conditions together with the heat treatment pattern as “processing conditions”.

  Here, “longitudinal grinding” in Table 5 means grinding in the longitudinal direction of the test piece, that is, the length of 15.75 mm in FIG. 1, while “lateral grinding” is the direction perpendicular to the longitudinal direction. That is, it means grinding in the direction of 6.35 mm in FIG. In addition, grinding was implemented using the grindstone with a particle size of 80-500.

  In addition, “mirror polishing” is performed by wet polishing in a random polishing direction in the order of # 500, # 800, # 1000, # 1500 and # 2000 SiC polishing paper, and further polishing with alumina abrasive grains having a particle diameter of 50 μm. The direction means buffing and finishing as random.

  The surface roughness of the block test piece surface-treated as described above was measured under the following conditions in accordance with the method defined in JIS B 0601 (2001) and JIS B 0671-2 (2002).

Measurement direction: specimen longitudinal direction,
-Evaluation length: 3.0 mm,
Cut-off value: 0.8mm
Measurement items: Rz, Rpk and Rk.

  Table 5 also shows the values of Rz and [Rpk / Rk] thus measured. Rz represents the “maximum height roughness” defined in JIS B 0601 (2001), and Rpk and Rk are respectively “projection peak heights” defined in JIS B 0671-2 (2002). ”And“ level difference of the core part ”.

  Further, the structure of the surface layer portion of the block test piece surface-treated as described above and the Vickers hardness at a depth of 10 μm from the surface were examined as follows.

  That is, as already described in the section (A), after cutting the central portion of the block test piece corresponding to the sliding portion, it is embedded in the resin at an angle of 15 ° with respect to the cross section perpendicular to the longitudinal direction. And mirror polished. At this time, since the surface is apparently enlarged in the depth direction, the hardness at 5 points was measured at a position of 40 μm from the surface. The above position corresponds to a 10 μm position in the vertical direction. For hardness measurement, a Vickers hardness tester was used, and the Hv hardness was measured with a test force of 1.961 N. And the arithmetic average value of these 5 points | pieces of hardness was calculated | required.

Next, the surface of which the hardness of the block test piece is measured is corroded with picral, and using a scanning electron microscope (hereinafter referred to as “SEM”), the vertical direction so as to include the outermost layer of the test piece is included. The area from the surface corresponding to the 10 μm position to the 40 μm position was photographed at four fields of view at a magnification of 10,000 times, and the structure of the surface layer portion was examined. The size of each visual field is 10.6 μm × 13 μm. Also, the distribution of cementite particles was investigated from image processing of SEM images, and the average particle diameter and the number of cementite particles per 1 μm ² area, that is, the number density, were calculated.

  “Particle diameter” refers to “equivalent diameter”, and the above average particle diameter and number density were calculated using data of cementite particles having an equivalent diameter of 0.1 μm or more.

  Table 5 also shows the Vickers hardness at a depth of 10 μm determined as described above. In Table 5, the above hardness was expressed as “surface hardness”.

  Table 6 shows the structure of the surface layer part, the average particle diameter and the number density of the cementite particles.

  Further, as described above in the case of the item (A), the surface-processed block is assumed that the cause of the crack is that the contact surface generates a vibration having a difference between the static frictional force and the dynamic frictional force. The test piece and the ring test piece already described in the section (A), that is, the center part of a round bar having a diameter of 45 mm after normalization, are cut out in parallel to the forging axis by machining, and using a gas carburizing furnace, Carburized with the heat pattern shown in FIG. 2 and then quenched in oil at an oil temperature of 80 ° C., further tempered at 170 ° C. for 2 hours, and then polished at a polishing rate of 2000 m / min using a grindstone with a particle size of 80 Using a ring test piece polished in the circumferential direction for 2 to 3 minutes and finished with a surface roughness of Rq 0.15 to 0.30 μm, a block-on-ring test was conducted to determine the maximum static friction coefficient and dynamic friction coefficient And further, crack initiation Free were investigated.

  The maximum static friction coefficient and the dynamic friction coefficient were measured by pressing the block test piece against the ring test piece with a load of 1000 N, and then rotating the ring test piece at a sliding speed of 0.1 m / s. At this time, an automatic transmission oil having a temperature of 90 ° C. was used as the lubricating oil.

  Since a speed difference is suddenly generated on the contact surface from the stationary state, as shown in FIG. 12, the friction coefficient is instantaneously increased at the beginning of the slip, and thereafter, the friction coefficient is decreased to shift to the dynamic friction state. Thus, although the friction coefficient changes with the change of the sliding speed, in the above-described block-on-ring test, the peak value at the beginning of sliding is set as the maximum static friction coefficient, and the average friction coefficient for 10 to 15 seconds after the start of rotation is set as the dynamic friction coefficient. . Moreover, after repeating this test 2000 times for each test piece, the sliding part of the block test piece was observed with an optical microscope at a magnification of 500 times to confirm the presence or absence of cracking.

  Table 5 also shows the maximum static friction coefficient, dynamic friction coefficient, and crack initiation investigation results obtained as described above.

  From Table 5, it can be seen that cracks are not generated when the ratio between the maximum static friction coefficient and the dynamic friction coefficient is 2 or less. In any case of the treatment conditions A to L, the surface hardness and surface roughness conditions shown in the item (A), that is, a surface hardness of 700 or more at a depth of 10 μm from the surface of the sliding surface is 10 μm. Rz is 4.0 μm or less, and the surface roughness of [Rpk / Rk] is less than 1.0 is satisfied. Therefore, it is considered that the cracks are generated under the processing conditions A to F, while the cracks are not generated in the processing conditions G to L because of the difference in the dispersion form of the cementite particles depending on the heat treatment pattern.

Actually, as shown in Table 6, in the case of the processing conditions G to L in which no crack was observed, the average particle diameter of the cementite particles was 0.6 μm or less and the number density was 1 particle / μm ² or more. is there. On the other hand, in the case of treatment conditions A to F in which no cracks were observed, there was no cementite particles in the structure of the surface layer part (treatment conditions A to C). .62 to 0.64 μm, and the number density is as small as 0.26 to 0.31 / μm ² (processing conditions D to F).

From this, the Vickers hardness at a depth of 10 μm from the surface of the sliding surface is 700 or more, the surface roughness is Rz of 2 μm or less, and the value of [Rpk / Rk] is less than 1.0, and By controlling the number of cementite particles with an average particle diameter of 0.6 μm or less on the surface layer to 1 particle / μm ² or more in number density, in addition to suppressing adhesion wear and abrasive wear, fatigue wear due to rapid slip can be suppressed. I understand that I can do it.

  The present invention has been completed based on the above findings, and the gist of the present invention resides in the following sliding parts.

“Carburized or carbonitrided sliding parts, in the surface layer part from the surface of the sliding surface to a depth of 10 μm,
Vickers hardness at a depth of 10 μm from the surface of the sliding surface: 700 or more,
Average particle diameter of cementite particles: 0.6 μm or less,
The number density of cementite particles in the cross section perpendicular to the sliding surface satisfies: 1 / μm ² or more, and the surface roughness of the sliding surface is
Rz: 4.0 μm or less,
Rpk / Rk: less than 1.0,
A sliding part characterized by satisfying
Rz represents the “maximum height roughness” defined in JIS B 0601 (2001), and Rpk and Rk are respectively “projection peak heights” defined in JIS B 0671-2 (2002). ”And“ level difference of the core part ”. ]

  Since the sliding component of the present invention has excellent wear resistance, it is suitable for use as a gear, pulley, shaft, or the like, which is a sliding component for power transmission in automobiles and industrial machines.

  Hereinafter, each requirement of the present invention will be described.

<1> Surface hardness (Vickers hardness at a depth of 10 μm from the surface of the sliding surface):
As described in the section “(A) Adhesive wear and abrasive wear”, when the Vickers hardness at a depth of 10 μm from the surface is less than 700, extremely large wear occurs. For this reason, when the load concerning components increases remarkably, it cannot use as a gear, a pulley, a shaft, etc. which are sliding components for power transmission.

  Therefore, in the surface layer portion from the surface of the sliding surface to a depth of 10 μm, it was defined that the Vickers hardness at a depth of 10 μm from the surface was 700 or more.

  The Vickers hardness at a depth of 10 μm from the surface is preferably 730 or more. In addition, since said Vickers hardness is so high that it is high, an upper limit is not prescribed | regulated in particular.

<2> Surface roughness:
As described in the section “(A) Adhesive wear and abrasive wear”, even if the “surface hardness” rule of <1> is satisfied, a large wear occurs when Rz exceeds 4.0 μm. . For this reason, when the load concerning components increases remarkably, it cannot use as a gear, a pulley, a shaft, etc. which are sliding components for power transmission.

  Similarly, even if the value of [Rpk / Rk] exceeds 1.0, the amount of wear increases. Therefore, if the load on the product is significantly increased, the gear that is a sliding component for power transmission is used. Cannot be used as pulleys, shafts, etc.

  Therefore, it was defined that the surface roughness of the sliding surface satisfies Rz: 4.0 μm or less and [Rpk / Rk]: less than 1.0.

  The Rz is preferably 2.0 μm or less. If Rz is smaller than 0.30 μm, the risk of seizure during sliding increases. Therefore, Rz is desirably 0.30 μm or more.

  The value of [Rpk / Rk] is preferably 0.80 or less. If [Rpk / Rk] is smaller than 0.20, the risk of seizure during sliding increases. Therefore, the value of [Rpk / Rk] is desirably 0.20 or more.

<3> Cementite particles:
As described in the section “(B) Fatigue wear”, cementite particles are present in the surface layer up to the region corresponding to the 10 μm position in the vertical direction, and the average particle diameter is 0.6 μm or less, and When the number density is 1 piece / μm ² or more, since no cracks are generated, fatigue wear can be prevented. On the other hand, if the cementite particles are not present in the structure of the surface layer portion or if they are present, the average particle diameter is large, and if the number density is small, cracks occur and fatigue wear occurs. End up.

Therefore, in the surface layer portion from the surface of the sliding surface to a depth of 10 μm, the average particle diameter of the cementite particles is 0.6 μm or less, and the number density of the cementite particles in the cross section perpendicular to the sliding surface is 1 It was defined that the number of particles / μm ² or more.

  The upper limit of the average particle size of the cementite particles is preferably 0.5 μm.

The number density of the cementite is preferably 1.5 / μm ² or more.

  The sliding component according to the present invention may be any material as long as it can be carburized or carbonitrided. Preferred materials include, for example, mass% and C: 0.13 to 0.13. 0.35%, Si: 0.05-0.80%, Mn: 0.35-1.50%, P: 0.020% or less, S: 0.005-0.035%, Cr: 0.00. 50 to 2.5%, Al: 0.020 to 0.040%, N: 0.0030 to 0.0250%, and if necessary, [a] Cu: 0.30% or less, Ni: 0.30% or less, [b] Mo: 0.50% or less, Nb: 0.080% or less, including one or more elements selected from the two groups, with the balance being Fe and impurities, Steel having an O (oxygen) content of 0.0020% or less.

  Hereinafter, the configuration, operation, and effects of the present invention will be described more specifically by way of examples. However, the present invention is not limited by the following examples, and appropriate modifications are made within a range that can meet the gist. It is also possible to implement them, and they are all included in the technical scope of the present invention.

  Steels 1 to 7 having chemical compositions shown in Table 7 were melted in a 30 kg vacuum melting furnace, and then cast to produce an ingot.

  The above ingot was held at 1250 ° C. for 8 hours, then allowed to cool in the air and once cooled to room temperature. Next, it was reheated to 1250 ° C. and held for 30 minutes, and hot forged with a finishing temperature of 1000 ° C. or higher to obtain a round bar with a diameter of 25 mm. In addition, after completion | finish of hot forging, it stood to cool in air | atmosphere and cooled to room temperature.

  The round bar thus obtained was subjected to normalization which was kept at 925 ° C. for 1 hour, then allowed to cool in the air and cooled to room temperature.

  From the R / 2 part (R: radius) of a round bar having a diameter of 45 mm after normalization, a block test piece having the shape shown in FIG. 1 was cut out parallel to the forging axis by machining.

  Using the gas carburizing furnace, the block test piece is carburized at a high concentration in the heat pattern shown in FIG. 10 or FIG. 11, and further reheated and then quenched in oil at an oil temperature of 80 ° C., or Then, using a gas carburizing furnace, high-concentration carburizing with the heat pattern shown in FIG. 13 is performed, and after reheating treatment and nitriding, quenching is performed in oil at an oil temperature of 80 ° C. Time tempering was performed.

  In addition, “Cp” in FIG. 13 also means carbon potential. After high-concentration carburization, nitrogen cooling is performed, the temperature is once cooled to 600 ° C., held at 600 ° C. for 15 minutes, and then heated again, and the temperature is 830 ° C. Then, reheating treatment was performed in an atmosphere having a carbon potential of 1.0% and a nitrogen gas flow rate of 15 L / min.

  Subsequently, the surface roughness of the block test piece subjected to the above tempering was subjected to grinding and polishing to change the surface roughness.

  Table 8 shows the details of the test steel, heat treatment pattern and surface processing conditions.

  Here, “longitudinal grinding” in Table 8 means grinding in the longitudinal direction of the test piece, that is, the length of 15.75 mm in FIG. In addition, grinding was implemented using the grindstone with a particle size of 80-500.

  In addition, “mirror polishing” means # 500, # 800, # 1000, # 1500, and # 2000 SiC abrasive paper in the order of wet polishing in a random polishing direction, and further with alumina abrasive grains having a particle diameter of 50 μm. The polishing direction means buffing and finishing as random.

  The surface roughness of the block test piece surface-treated as described above was measured under the following conditions in accordance with the method defined in JIS B 0601 (2001) and JIS B 0671-2 (2002).

Measurement direction: specimen longitudinal direction,
-Evaluation length: 3.0 mm,
Cut-off value: 0.8mm
Measurement items: Rz, Rpk and Rk.

  Table 8 shows the values of Rz and [Rpk / Rk] thus measured. As described above, Rz represents “maximum height roughness” defined in JIS B 0601 (2001), and Rpk and Rk are respectively defined in JIS B 0671-2 (2002). In addition, “projection peak height” and “level difference of core portion” are represented.

  Further, the structure of the surface layer portion of the block test piece surface-treated as described above and the Vickers hardness at a depth of 10 μm from the surface were examined as follows.

  That is, after cutting the central part of the block test piece corresponding to the sliding part, it was embedded in a resin at an angle of 15 ° with respect to the cross section perpendicular to the longitudinal direction and mirror-polished. At this time, since the surface is apparently enlarged in the depth direction, the hardness at 5 points was measured at a position of 40 μm from the surface. The above position corresponds to a 10 μm position in the vertical direction. For hardness measurement, a Vickers hardness tester was used, and the Hv hardness was measured with a test force of 1.961 N. And the arithmetic average value of these 5 points | pieces of hardness was calculated | required.

Next, the surface on which the hardness of the block test piece is measured is corroded with picral, and using the SEM, the surface from the surface corresponding to the 10 μm position in the vertical direction to the position of 40 μm is included so as to include the outermost layer of the test piece. The field was photographed with 4 fields of view at a magnification of 10,000 times. The size of each visual field is 10.6 μm × 13 μm. Next, the distribution of cementite particles was investigated from image processing of SEM images, and the average particle diameter and the number of cementite particles per area of 1 μm ² , that is, the number density, were calculated.

  Table 8 also shows the Vickers hardness, the average particle diameter of cementite particles, and the number density at a depth of 10 μm determined as described above. In Table 8, the hardness is expressed as “surface hardness”.

  Also, the above-mentioned surface-treated block test piece and the ring test piece already described, that is, the steel having the chemical composition shown in Table 1 are machined from the center of a round bar having a diameter of 45 mm after normalization. Cut out parallel to the wrought axis, carburized with a gas carburizing furnace, and then carburized in the heat pattern shown in FIG. 2 and then quenched in oil at an oil temperature of 80 ° C., and further tempered at 170 ° C. for 2 hours, Using a ring test piece, which was polished in a circumferential direction at a polishing rate of 2000 m / min for 2 to 3 minutes using a grindstone with a grain size of 80 and finished to a surface roughness of 0.15 to 0.30 μm with Rq An on-ring test was conducted to investigate sliding wear.

  The number of tests was one for each test number, and the wear width of the block test piece after the test was measured with an optical microscope. In addition, as already described, the measurement points are the both ends and the center of the wear mark for each test piece (see FIG. 6), and for each test number, the wear width at the three locations is arithmetically averaged to be the wear width. . Note that the target of the wear width in the present invention is within 1.5 mm.

  Furthermore, fatigue wear resistance was also evaluated. That is, after pressing the block test piece against the ring test piece with a load of 1000 N, sliding it for 5 seconds at a sliding speed of 0.1 m / s, unloading it, and stopping the rotation of the ring test piece for each test number. Repeated 4000 times. Thereafter, the sliding part of the block test piece was observed with an optical microscope at a magnification of 500 times to investigate the presence or absence of a crack. As a lubricating oil, an automatic transmission oil having a temperature of 90 ° C. was used.

  Table 8 also shows the results of investigation on the wear width and the presence or absence of cracks.

  As is apparent from Table 8, if the conditions specified in the present invention are satisfied, the wear width is within 1.5 mm in the sliding wear test in the block-on-ring test, and no crack is generated in the fatigue wear test. It is clear that the wear resistance is excellent.

  Since the sliding component of the present invention has excellent wear resistance, it is suitable for use as a gear, pulley, shaft, or the like, which is a sliding component for power transmission in automobiles and industrial machines.

It is a figure which shows the shape of the block test piece for a block on ring test, (A) is a front view, (B) is a side view. It is a figure explaining the heat pattern of "carburization hardening" in "carburization hardening-tempering." Note that “Cp” in FIG. 2 means carbon potential. It is a figure explaining the heat pattern of another "carburization hardening" in "Carburizing quenching-tempering." Note that “Cp” in FIG. 3 means a carbon potential. It is a figure which shows the shape of the ring test piece for a block on ring test. It is a figure which illustrates a block on ring test typically. It is a figure explaining the location which measured the abrasion width of the block test piece after a block on ring test with the optical microscope. It is a figure which arranges and shows the relation between wear width and Rz about processing conditions ag in Table 2 and Table 4. FIG. It is a figure which arrange | positions and shows the relationship between a wear width and the value of [Rpk / Rk] about the process conditions ad and g in Table 2 and Table 4. FIG. It is a figure explaining the heat pattern of "high concentration carburizing reheating quenching" in "high concentration carburizing reheating quenching-tempering." In addition, “Cp” in FIG. 9 means a carbon potential. It is a figure explaining the heat pattern of another "high concentration carburizing reheating quenching" in "high concentration carburizing reheating quenching-tempering." Note that “Cp” in FIG. 10 means a carbon potential. It is a figure explaining the heat pattern of another "high concentration carburizing reheating quenching" in "high concentration carburizing reheating quenching-tempering". Note that “Cp” in FIG. 11 means a carbon potential. It is a figure explaining the fluctuation | variation of the friction coefficient in the case of evaluation of the fatigue wear property by the block on-ring test performed in the Example, and the definition of the "maximum static friction coefficient" and the "dynamic friction coefficient". It is a figure explaining the heat pattern of "high concentration carburizing reheating nitriding quenching" in "high concentration carburizing reheating nitriding quenching-tempering". Note that “Cp” in FIG. 13 means a carbon potential.

Claims (1)

Carburized or carbonitrided sliding parts, in the surface layer portion from the surface of the sliding surface to a depth of 10 μm,
Vickers hardness at a depth of 10 μm from the surface of the sliding surface: 700 or more,
Average particle diameter of cementite particles: 0.6 μm or less,
The number density of cementite particles in the cross section perpendicular to the sliding surface satisfies: 1 / μm ² or more, and the surface roughness of the sliding surface is
Rz: 4.0 μm or less,
Rpk / Rk: less than 1.0,
A sliding part characterized by satisfying
Rz represents the “maximum height roughness” defined in JIS B 0601 (2001), and Rpk and Rk are respectively “projection peak heights” defined in JIS B 0671-2 (2002). ”And“ level difference of the core part ”.

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