Chain

Abstract

chain comprising several pairs of outer links, each connected by two pins, and several pairs of inner links, each connected by two sockets alternately connected to each other, the pins being loosely fitted in the sockets, at least one of the pin, bushing, inner link and outer link is a chain component of a power transmission chain for industrial use, wherein the chain component comprises the following: a steel base material; and a chromium nitride layer formed on an outer side of the steel base material and containing iron in a wt.% of 1 or more and 45 or less, wherein the chromium nitride layer of the chain component has an iron concentration distribution that gradually decreases from a surface of the steel base material outwards, and wherein the chromium nitride layer of the chain component has a chromium and nitrogen concentration distribution that gradually decreases from an outer side to a surface of the steel base material.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present invention relates to a chain comprising chain components. These chain components are chain parts such as pins, bushings, chain links, and rollers, which constitute power transmission chains for industrial use, such as roller chains and toothed chains, which are used, for example, as automotive timing chains. 2. State of the art

[0002] It is known that a chromium nitride layer formed on a metal surface improves the metal's wear and corrosion resistance. The deposition of chromium nitride layers is therefore widely used in practice to extend the service life of machine parts, metal molds, tools, and the like.

[0003] Chromium nitride layers are generally formed by physical vapor deposition (PVD) processes, such as ion plating or sputtering. In the former, nitrogen gas is introduced into a vacuum chamber while a base material is bombarded with vaporized and ionized chromium. In the latter, a high voltage is applied between a target and a substrate to generate a glow discharge, causing argon ions from the plasma to collide with the target surface and eject chromium atoms, which are then deposited onto the substrate.

[0004] One problem with chromium nitride coatings formed by a PVD process was that, when used as a surface treatment coating for highly stressed sliding components of a chain, the coating would easily peel off the metal base material, such as steel, and it was difficult to make the coating adhere to the surface of the base material and bond with it in such a way that it would hardly peel off.

[0005] PVD also results in the occasional formation of droplets on the surface. When droplets are present, surface roughness increases, and cracks begin to form from the droplets, reducing wear resistance. Although droplets can be removed by polishing, openings remain where the droplets were. When a load is applied, these openings enlarge and merge, preventing any improvement in wear resistance.

[0006] Due to the cracks and deterioration of wear resistance that occur in PVD processes, the layer thickness could not be increased to extend the service life.

[0007] Another problem was that if the material being processed was porous, it was difficult to form a layer on the inner surfaces of the pores.

[0008] An example of the machine parts mentioned above are pins used in the timing chains of vehicle engines. Examples of timing chains include roller chains, bushing chains, toothed chains, and the like.

[0009] A roller chain has rollers attached to cylindrical bushings, which are pressed at both ends into bushing openings of a pair of inner plates, whereas pins fitting into the bushings are pressed at both ends into pin openings of a pair of outer plates located on both outer sides of the pair of inner plates. Bushing chains do not have rollers.

[0010] In conventional timing chains, the steel base material of the pins would undergo a chrome plating treatment to improve the wear resistance of the bushings and pins.

[0011] However, timing chains used with a lot of old engine oil inside the vehicle's engine compartment were prone to wear on pins and bushings, which is why their lifespan tended to be short.

[0012] Furthermore, soot produced during the engine's combustion process, which mixed with the engine oil, posed a risk of increasing the coefficient of friction of the pins and bushings or accelerating wear despite the coating, as lubricating oil containing soot could penetrate between components such as pins and bushings of the timing chain, which runs at high speed under high load, and the soot, being a hard substance, could damage the coating between the pins and bushings.

[0013] Accordingly, a surface treatment was desired that would improve the wear resistance of chains.

[0014] Japanese patent application JP H11-29848A discloses a method for forming chromium nitride layers as a solution to the problems associated with the deposition of chromium nitride layers on metal surfaces, namely layer separation due to temperature stress over time (heat history) and poor adhesion to the base material. After chromium plating of the surface of a metal material, the chromium-plated surface is cleaned and activated by heating the metal material in a reactive gas containing halogen compounds or halogens, prior to nitriding the chromium-plated surface by applying heat in a nitriding atmosphere.

[0015] DE 20 2006 020 978 U1, DE 10 2012 016 027 A1, WO 2014 / 019 699 A1, DE 10 2013 222 244 A1, DE 10 2004 012 463 A1, DE 602 13 779 T2, DE 698 38 575 T2, US 2012 / 0 325 673 A1 and WO 2012 / 151 603 A1 represent further relevant prior art for the present application. SUMMARY OF THE INVENTION

[0016] The process for forming chromium nitride layers according to Japanese patent application no. JP H11-29848A involves a highly complex process. This process includes industrial chromium plating on a base material such as steel, followed by a special chromium coating, such as a highly corrosion-resistant, crack-free chromium coating, a macroporous chromium coating, or an amorphous chromium coating containing 2% to 4% carbon, as well as halogen pretreatment prior to the nitriding step. As shown in working examples 1 to 3 of Japanese patent application no. JP H11-29848A, the resulting chromium nitride layer has a Vickers hardness of 1700 to 2000 HV. The difference in hardness between the chromium nitride layer and the soft base material is so great that the adhesion is not sufficient to maintain wear resistance over a long period of time.

[0017] If the surface treatment process of the Japanese patent application with disclosure number JP H11 - 29 848 A were applied to chain components, such as pins and the like of timing chains, there would be the problems of a complex manufacturing process, high manufacturing costs and a wear resistance that cannot be advantageously maintained over a long period of time.

[0018] The present invention was made with such circumstances in mind, and it is an object of the invention to provide a chain with a chain component that has a simple surface treatment structure and can maintain advantageous wear resistance over a long period of time. The chain incorporating this chain component is intended to maintain advantageous resistance to wear-induced elongation.

[0019] The present invention relates to a chain according to claim 1, claim 4, or claim 6, wherein the chain comprises a chain component. The chain component according to the present invention is a chain component of a power transmission chain for industrial use and comprises a steel base material and a chromium nitride layer formed on an outer side of the steel base material, containing iron in a wt.% of 1% or more and 45% or less.

[0020] The chain according to the present invention is formed by several pairs of outer links, each connected by two pins, and several pairs of inner links, each connected by two bushings that are alternately connected to one another, the pins being loosely mounted in the bushings. At least one of the pin, bushing, inner link, and outer link is the chain component described above.

[0021] The chain according to the present invention is formed by several pairs of outer links, each connected by two pins, and several pairs of inner links, each connected by two bushings, each bushing having a roller mounted thereon, which are alternately connected to one another, the pins being loosely mounted in the bushings. At least one of the pin, bushing, inner link, outer link, and roller is the chain component described above.

[0022] The chain according to the present invention is a chain formed from the following: several inner links, each having a pair of V-shaped toothed links at one end in a direction along the short side, and a pair of front and rear pin openings, wherein the inner links are pivotably connected by pins inserted into the pin openings and arranged in a width direction of the chain such that one toothed link of each inner link overlaps the other toothed link of another adjacent inner link; and guide links arranged on both outer sides in the width direction, through which the pins are firmly inserted. At least one of the pin, the inner link, and the guide link is the chain component described above.

[0023] The chain component according to the present invention has a chromium nitride layer formed on the outer side of the steel base material. The chain component has a simple surface treatment structure and can easily be manufactured more cost-effectively with fewer process steps.

[0024] Chromium nitride has a low coefficient of friction and high strength, so the chain component formed with the chromium nitride layer exhibits low aggressiveness towards counterparts and is hardly damaged by fine soot particles or similar substances that have a high hardness.

[0025] Due to its low coefficient of friction, the chromium nitride layer generates minimal frictional heat. Since chromium nitride has a high oxidation induction temperature and exhibits minimal oxidation even at high temperatures, the wear resistance of the chain component is advantageously maintained.

[0026] Since the chromium nitride coating contains iron, it exhibits advantageous adhesion to the steel base material. The iron content is at least 1 wt.%, but no more than 45 wt.%, thus maintaining the wear resistance of the chain component over a long period.

[0027] The chromium nitride layer exhibits low aggressiveness towards counterparts and is hardly damaged by tiny soot particles or the like, which have a high hardness, thus increasing the degree of freedom when adjusting the gap area of ​​sliding parts.

[0028] The chain of the present invention exhibits advantageous resistance to wear-induced elongation, since it includes the chain component which exhibits the effects described above. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a perspective view showing part of an example of a roller chain; Fig. Figure 2 is a perspective view showing part of an example of a toothed chain; Fig. Figure 3 is a graphical representation showing the composition distribution of Fe, Cr and N in a cross-section of a pen from Working Example 1, which was determined by line analysis using an electron probe micro-analyzer (EPMA) device; Fig. Figure 4 is a graphical representation showing the test results on the amount of wear on pins and bushings in which the pins are fitted, of a roller chain using the pins from working example 1 and of a roller chain using the pins from comparison example 1 after a predetermined operating time of the chain; Fig. Figure 5 is an optical microscope image of the surface of the pen according to working example 1; Fig.Figure 6 is an optical microscope image of the surface of the pen according to comparative example 2; Fig. Figure 7 is a graphical representation showing the relationship between the Fe content in the chromium nitride layer and the ratio of wear-induced elongation; Fig. Figure 8 is a graphical representation showing the relationship between the thickness of the chromium nitride layer and the ratio of wear-induced elongation; Fig. 9A is a view of a socket chain; Fig. 9B is a cross-sectional view showing the spaces between a pin and a socket of a socket chain; Fig. Figure 10 is a graphical representation showing the amount of wear, plotted against time, of pins and bushings when the spacing and surface layer are different; and Fig.11A to 11D are optical microscope images of the surfaces when old motor oil was used, whereby Fig. 11A and Fig. 11C those of conventional examples are and Fig. 11B and Fig. 11D those of the present invention. DESCRIPTION OF PREFERRED EXECUTION FORMS

[0029] A chain component according to the present invention comprises a steel base material and a chromium nitride layer formed on an outer side of the steel base material.

[0030] The chromium nitride layer contains at least 1 wt% but not more than 45 wt% Fe. The lower limit of the Fe content should preferably be 5 wt%, and more preferably 8 wt%. The upper limit should preferably be 32 wt%.

[0031] The layer should preferably have an Fe distribution, with the Fe concentration gradually decreasing from the surface of the steel base element towards the outside.

[0032] The Cr and N content should preferably decrease gradually from the outer side towards the surface of the steel base material.

[0033] The chromium nitride layer should preferably contain at least 1 wt.% but not more than 45 wt.% Fe, 45 wt.% or more and 90 wt.% or less Cr, and 5 wt.% or more and 25 wt.% or less N, based on a total amount of 100 wt.%.

[0034] The lower limit of the iron content should preferably be 1 wt.%, more preferably 5 wt.%, and even more preferably 8 wt.%. The upper limit should preferably be 45 wt.% and more preferably 32 wt.%.

[0035] The lower limit of the Cr content should preferably be 48 wt.% and more preferably 51 wt.%. The upper limit should preferably be 77 wt.% and more preferably 67 wt.%.

[0036] The lower limit of the nitrogen content should preferably be 9 wt.% and more preferably 13 wt.%.

[0037] The Fe content values ​​are those determined by qualitative / quantitative analysis using an EPMA. The Cr and N content values ​​are those determined by qualitative / quantitative analysis using an EPMA and corrected by considering the values ​​of reference samples of chromium nitride.

[0038] The chromium nitride layer should preferably have a thickness of 2 µm or more and 30 µm or less. In this range, the surface roughness is low, cracking is minimal, and wear resistance is advantageous, resulting in beneficial resistance to wear-induced elongation of the chain and the chain component mounted therein.

[0039] An intermediate layer can be provided between the chromium nitride layer and the steel base material to increase the adhesion of the chromium nitride layer to the steel base material.

[0040] Examples of the interlayer include Cr, CrB, CrB2, CrC, Cr2N, Cr2O3, CrSi2, CrNi, CrB-O, CrB2-O, (V, Cr)C, (Cr, Zr)N, CrBN, CrB2+Ni, (Cr, Mn)C, (Cr, Mo)N, (V, Cr)B, (Cr, Fe)C, (Cr,W)N, (Cr,Mn)B, (Cr,Co)C, (Cr,Cu)N, (Cr,Fe)B, (Cr,Ni)C, (Cr,V)N, (Cr,Co)B, (Cr,Cu)C, (Cr,Ni)B, (Cr,Zn)C, (Cr,Cu)B, (Cr,Zr)C, (Cr,Zn)B, (Cr,Nb)C, (Cr,Zr)B, (Cr,Mo) C, (Cr,Nb)B, (Cr,Hf)C, (Cr,Mo)B, (Cr,Ta)C, (Cr,Hf)B, (Cr,W)C, (Cr,Ta)B, (Cr,W)B and the like.

[0041] The chromium nitride layer on the chain component according to the present invention is formed on the outer side of the steel base material as follows: the steel base material and a treatment agent containing chromium powder, aluminum oxide (hereinafter referred to as aluminum oxide), and ammonium halide are placed in a heating furnace, and the temperature of the furnace is raised to a target value. After the temperature has been maintained for a predetermined time, the heating furnace is slowly cooled. The treatment agent may contain a compound from which the element contained in the aforementioned intermediate layer originates.

[0042] In the following, a chain component according to the present invention is described, wherein the component consists of pins of a roller chain which is used as a timing chain or the like of a vehicle engine.

[0043] Fig.Figure 1 is a perspective view showing part of an example of a roller chain 1.

[0044] The roller chain 1 has bushings 3 which are pressed into bushing openings 2a of a pair of inner plates 2 at both ends, and pins 6 which are fitted into the bushings 3 and pressed into pin openings 5a of a pair of outer plates 5 which are arranged on both outer sides of the pair of inner plates 2. Rollers 4 are attached to the bushings 3.

[0045] The chromium nitride layer described above is provided on the outer side of pins 6.

[0046] The following describes the method for manufacturing the pins 6 as an example of a chain component according to the present invention.

[0047] Wire rod made of structural steel, chromium-molybdenum steel (SCM) or high-carbon chromium bearing steel (SUJ) and the like are used as the steel base material of the pins 6.

[0048] The chromium nitride layer is formed on the surface of the steel base material of the pins 6 by diffusion coating of Cr and N.

[0049] The process known as the "powder bed" process can be used for the Cr diffusion coating process.

[0050] In particular, the pin 6 and a treatment agent comprising chromium powder, aluminum oxide, and ammonium halide are placed, for example, in an aluminum oxide crucible, which is then placed in a heating oven, such as an electric oven. The treatment agent should preferably contain 60 to 67 wt.% chromium powder, 30 to 37 wt.% aluminum oxide, and 0.2 to 3 wt.% ammonium halide, based on a total amount of 100 wt.%.

[0051] Examples of ammonium halides include ammonium chloride, ammonium bromide, ammonium iodide, ammonium fluoride, and the like. One type, two, or more types of ammonium halide are selected according to the target layer structure.

[0052] The atmosphere is replaced with an inert gas such as Ar or N2 before the temperature is increased.

[0053] The temperature is then raised to a specific level.

[0054] During heating, a preset flow rate of NH3 and / or N2 can be introduced according to the thickness, layer configuration and total layer thickness of the target chromium nitride layer.

[0055] The oven is cooled down after the temperature has been maintained for a predetermined period.

[0056] If the target layer has not yet formed, the oven is heated again to the predetermined temperature while NH3 and / or N2 are introduced, and after holding the temperature for a preset time, it is cooled.

[0057] The composition ratio of the treatment agent, the treatment temperature and the holding time are determined taking into account the composition of the steel base material and the thickness, layer configuration, total layer thickness and / or the like of the target chromium nitride layer.

[0058] Nitriding of the surface or CrC layer of the steel base material is an example of a process for forming a chromium nitride layer.

[0059] According to this method for forming a chromium nitride layer, a chromium nitride layer can be easily and cost-effectively formed on the outer surface of the steel base material in just a few process steps. Cr, C, and Fe exhibit concentration gradients, resulting in advantageous adhesion between the chromium nitride layer and the steel base material.

[0060] The chain component obtained through the manufacturing process described above exhibits advantageous wear resistance due to its outer chromium nitride layer, which has a high oxidation induction temperature and shows minimal oxidation even at high temperatures. Furthermore, the favorable adhesion between the chromium nitride layer and the steel base material ensures excellent resistance to wear-induced elongation over a long period.

[0061] While the example described above involved the formation of the chromium nitride layer on pin 6, the target is not limited to the pin. The chromium nitride layer can be formed on the surface of at least one of the inner tab 2, the bushing 3, the roller 4, and the outer tab 5.

[0062] The chain 1, which comprises the chain component according to the present invention, maintains an advantageous resistance to wear-induced elongation over a long period of time.

[0063] The chain according to the present invention can be a bushing chain that does not have rollers.

[0064] The chain according to the present invention can be a toothed chain.

[0065] Fig. Figure 2 is a perspective view showing part of an example of a toothed chain 10.

[0066] The toothed chain 10 is formed from several inner links 11, each having a pair of V-shaped toothed links 11a at one end in the direction of the short side, and guide links 13 arranged on both outer sides in a width direction of the toothed chain 10, through which pins are firmly inserted. The inner links 11 are pivotably connected to one another by pins 12, which are inserted into pin openings and arranged in the width direction such that one toothed link 11a of each inner link 11 overlaps the other toothed link 11a of another adjacent inner link 11.

[0067] The toothed chain 10 includes the chromium nitride layer on the surface of at least one of the chain components, including the inner plates 11, the pins 12 and the guide plates 13. Examples

[0068] The present invention is described below in more specific terms based on working examples. Working example 1

[0069] A SUJ2 rolled wire, cut to a predetermined length and cross-section, was used as the processed material from Work Example 1 to obtain a pin-6 material like the steel base material.

[0070] A treatment agent containing Cr powder, aluminum oxide, and NH4Cl, each in amounts within the ranges specified above, was placed in an aluminum oxide crucible containing pin 6, and the aluminum oxide crucible was placed in a heating furnace. After exchange with an inert gas, the furnace was heated to the preset temperature while a suitable flow rate of an additive gas (NH3 and N2) was introduced. The temperature was held for a period of time to form a chromium nitride layer on the outer side of pin 6. The heating power was then switched off, and the furnace was slowly cooled.

[0071] Thus, a pin 6 was obtained with a chromium nitride layer formed on the outer side of the steel base material.

[0072] The chromium nitride layer contained 13 wt% Fe, 74 wt% Cr and 13 wt% N and had a thickness of 13 µm.

[0073] Fig.Figure 3 is a graphical representation showing the composition distribution of Fe, Cr, and N in a cross-section of pin 6 from Working Example 1, determined by line analysis using an EPMA. The horizontal axis represents the length in the thickness direction, and the vertical axis represents the detection intensity of each component. The measurement conditions were as follows. Acceleration voltage: 15kV Sampling current: 50nA Beam diameter: 1 µm

[0074] Fig. Figure 3 indicates that the Fe content gradually increases, while the Cr and N content gradually decreases from the outer side towards the surface of the base material of the pin 6.

[0075] The results above confirmed that a chromium nitride layer formed on the outer surface of the steel base material, with Cr and N partially scattered on the surface of the pin 6 material. Due to this scattering, Cr and N exhibit concentration gradients. The layer also displays an Fe concentration distribution, with the Fe content gradually decreasing from the surface of the steel base material towards the outer surface. These concentration gradients of Fe, Cr, and N indicate good adhesion between the pin 6 base material and the chromium nitride layer. Comparative example 1

[0076] The pins, as a comparative example 1, were obtained by a conventional powder bed process, whereby a CrC layer of 15 µm thickness was formed on a steel base material. Comparative example 2

[0077] The pins, as a comparative example 2, were obtained by a conventional PVD process, whereby a chromium nitride layer of 6 µm thickness was formed on a steel base material.

[0078] Roller chains were assembled using the pins 6 from working example 1, the pins from comparison example 1 and the pins from comparison example 2.

[0079] The resistance to wear-related elongation of each roller chain was evaluated.

[0080] A car was indeed driven 5,000 km, 10,000 km and 15,000 km in the city using SAE 5W-30 engine oil, and the old engine oil was collected after each trip.

[0081] Using each motor oil, each roller chain, which featured pins from Working Example 1, Comparison Example 1, and Comparison Example 2, was tested under severe conditions, running at high speed for 100 hours. The results are shown in Table 1. Table 1 shows the wear-related elongation in percent (ratio of wear-related elongation) from Working Example 1 and Comparison Example 2 relative to that of the roller chain from Comparison Example 1 as 100. [Table 1] Table 1 (%) Distance traveled (km) Working example 1 Comparative example 1 Comparative example 2 5.000 80 100 118 10.000 70 100 146 15.000 63 100 182

[0082] Table 1 shows that working example 1 exhibited better resistance to wear-induced elongation than comparison example 1, which in turn exhibited better resistance to wear-induced elongation than comparison example 2. Specifically, it is evident that the roller chain 1 from working example 1, which has a chromium nitride layer containing more than 0 wt.% but not more than 55 wt.% Fe on the outer side of the steel base material, exhibits advantageous resistance to wear-induced elongation. With increasing mileage (as the engine oil ages), the effect of the chromium nitride layer on improving resistance to wear-induced elongation increases.

[0083] Fig.Figure 4 is a graphical representation showing the results of the investigation on the wear amount on pins and bushings in which the pins are mounted, of a roller chain using the pins 6 from working example 1 and of a roller chain using the pins from comparison example 1 after a predetermined operating time of the chain.

[0084] Fig. Figure 4 shows that the wear on pins and bushings is reduced when using the roller chain with the pins 6 from Working Example 1, compared to using the roller chain with the pins from Comparative Example 1. Wear on the bushings is particularly reduced. This is because the chromium nitride layer on the pins 6 from Working Example 1 exhibits low corrosiveness to the sliding mating parts (bushings).

[0085] Fig.Figure 5 is an optical microscope image showing the surface of the pen 6 from working example 1. Fig. Figure 6 is an optical microscope image showing the surface of the pen from comparison example 2.

[0086] While on the surface of the pen 6 from working example 1, as in Fig. As shown in Figure 5, no droplets are present, whereas a large number of droplets are present on the surface of the pen from Comparison Example 2. It is evident that the pen from Comparison Example 2 has a higher surface roughness and, due to the cracks that will originate from the droplets, will exhibit lower wear resistance.

[0087] Next, the results of the evaluation test for resistance to wear-induced elongation are described. The test was performed on the roller chain using old motor oil with varying iron content in the chromium nitride coating.

[0088] Similar to Working Example 1, pencils 6 were produced from Working Examples 2 to 6 and pencils from Comparative Example 3, each with the elemental composition as shown in Table 2 below. Table 2 also shows Working Example 1 and Comparative Example 1.

[0089] The Fe content values ​​for the elements in Table 2 are those determined by qualitative / quantitative analysis using an EPMA. The Cr and N content values ​​are those determined by qualitative / quantitative analysis using an EPMA and corrected in light of the values ​​of reference chromium nitride samples. [Table 2] Table 2 (%) Working example 2 Working example 3 Working example 4 Working example 1 Working example 5 Working example 6 Comparative example 1 Comparative example 3 Cr 90 77 67 74 51 45 30 N 9 18 25 13 17 5 15 Fe 1 5 8 13 32 55 60 Total 100 100 100 100 100 105 105 ratio of wear-related elongation 80 67 60 59 60 98 100 122

[0090] A car was indeed driven 10,000 km in the city using SAE 0W-20 engine oil, and the old engine oil was collected and used in the test.

[0091] Using this motor oil, the roller chains, each containing the pins from Work Examples 1 to 6, Comparison Example 1, and Comparison Example 3, were tested under severe conditions, running at high speed for 150 hours. The results are shown in Table 2. Table 2 shows the wear-related elongation in percent (ratio of wear-related elongation) of the various work examples and Comparison Example 3 relative to that of the roller chain from Comparison Example 1 as 100.

[0092] Fig. Figure 7 is a graphical representation showing the relationship between the iron content in the chromium nitride layer and the ratio of wear-induced elongation. The horizontal axis represents the iron content (wt%) and the vertical axis represents the ratio of wear-induced elongation (%).

[0093] Table 2 and Fig.Figure 7 shows that the roller chains of 1 different working examples, which have a chromium nitride layer containing more than 0 wt.% but not more than 55 wt.% Fe, exhibit advantageous resistance to wear-induced elongation.

[0094] The lower limit of the iron content should preferably be 1 wt.%, more preferably 5 wt.%, and even more preferably 8 wt.%. The upper limit should preferably be 45 wt.% and more preferably 32 wt.%.

[0095] The lower limit of the Cr content should preferably be 48 wt.% and more preferably 51 wt.%. The upper limit should preferably be 77 wt.% and more preferably 67 wt.%.

[0096] The lower limit of the nitrogen content should preferably be 9 wt.% and more preferably 13 wt.%.

[0097] The results of the evaluation test for resistance to wear-induced elongation, which was carried out using old motor oil with different thicknesses of the chromium nitride layer on the roller chain, are now described.

[0098] A car was indeed driven 10,000 km in the city using SAE 0W-30 engine oil, and the old engine oil was collected and used in the test.

[0099] Using this motor oil, the roller chains, each containing pins from different work samples with varying thicknesses of the chromium nitride layer, were tested under harsh conditions, running at high speed for 180 hours.

[0100] Fig.Figure 8 is a graphical representation showing the relationship between the thickness of the chromium nitride layer and the ratio of wear-induced elongation. The horizontal axis represents the layer thickness (µm), and the vertical axis represents the percentage of resistance to wear-induced elongation (%) relative to that of the roller chain from comparison example 1 as 100.

[0101] Fig. Figure 8 shows that resistance to wear-induced elongation is advantageous when the thickness of the chromium nitride layer is 2 µm or more and 30 µm or less. If the layer thickness is greater than 30 µm, cracks form and impair the resistance to wear-induced elongation.

[0102] As demonstrated above, it was confirmed that the chromium nitride layer of the pins 6 according to working examples of the present invention did not exhibit droplets, so that it would hardly peel off, the layer would show low aggressiveness towards the counterparts, and since the layer thickness could be in the range of 2 µm to 30 µm, the roller chain 1 would have advantageous resistance to wear-induced elongation, which would be advantageously maintained over a long period of time.

[0103] Next, the results of the test, which was conducted using old engine oil on the [unclear text], will be described. Fig. 9A and Fig. The bushing chain 20 shown in 9B was carried out.

[0104] In general, the gap CL between the pin 6 and the inner circumference of the bushing 3 is designed to be small for better wear resistance in order to reduce surface pressure on bearing parts when tensile stress is applied.

[0105] However, an excessively small gap CL leads to poorer twistability and flexibility of the entire chain, poorer mountability in the engine, and lower strength due to the load applied by the chain itself.

[0106] An excessively small gap (CL) also allows soot or similar substances to accumulate more easily in the engine oil. The coefficient of friction increases due to the damage caused by soot or similar substances to the surfaces of the pins and the inner circumference of the bushings, which can lead to heat generation, increased resistance, and wear.

[0107] Accordingly, the gap CL is strictly designed to be within a very small area, according to the purpose and the operating environment, taking into account the relationship between the surface pressure on bearing parts when tensile stress is applied, and other influences.

[0108] According to the present invention, by applying the chromium nitride layer to the surface with low friction and high hardness, the space CL can be increased, which increases the surface pressure on the bearing parts without loss of wear resistance.

[0109] Since the chromium nitride layer exhibits low aggressiveness towards mating surfaces and suffers little damage from tiny, hard soot particles, the gap CL can be reduced to allow soot or similar substances to accumulate more easily with a lower possibility of damage from the soot on the surfaces of the pins and the inner circumference of the bushings, which in turn reduces the possibilities of heat generation and increased resistance or wear caused by an increased coefficient of friction.

[0110] This increases the degree of freedom when setting the gap CL and thus makes it possible to deal flexibly with different purposes and changes in the usage environment.

[0111] In particular, it was confirmed that the chain could be used without problems with the gap CL between the pins 6 and sockets 3 in the range of 30 µm to 120 µm.

[0112] It was also confirmed that the chain could be used without problems at 60 ≥ CL / N ≥ 2.8, where N is the thickness of the chromium nitride layer, and that the gap CL could be produced to a sufficient size even when the layer thickness was small.

[0113] Fig. Figure 10 shows changes in wear-related elongation plotted against time of a chain with a conventional chromium plating treatment on the surface of the pins 6 and the chain with the chromium nitride layer of the present invention when using old motor oil.

[0114] The elongation of the chain with the chromium nitride layer of the present invention was undoubtedly reduced regardless of the gap CL.

[0115] Even when the gap CL was large, the elongation of the chain with the chromium nitride layer of the present invention was more or less the same as that of the chain with the conventional chromium plating treatment when the gap CL was small, which confirmed that the degree of freedom in adjusting the gap CL was increased.

[0116] Fig. Figures 11A to 11D show illustrations of the surface conditions of the pen with the conventional chromium plating treatment and of the pen with the chromium nitride layer of the present invention.

[0117] Fig. 11A and Fig.Figure 11B shows scratched surface conditions of the pin with the conventional chrome plating treatment and of the pin with the chromium nitride coating of the present invention when old motor oil was used. Fig. 11C and Fig. Figure 11D shows the surface conditions of the pins with the conventional chromium plating treatment and of the pin with the chromium nitride layer of the present invention when a Vickers hardness test was performed.

[0118] How to explain the scratching conditions in Fig. 11A and Fig. As can be seen in Figure 11B, the pen with the chromium nitride layer of the present invention showed hardly any scratches due to the low coefficient of friction and the high hardness, whereas the pen with the conventional chromium treatment showed many scratches.

[0119] As from Fig. 11C and Fig.As can be seen in Figure 11D, the pen with the chromium nitride layer of the present invention showed no cracks due to its high hardness, whereas the pen with the conventional chromium plating treatment showed cracks around the indentation.

[0120] As described above, the chain component according to the present invention is a chain component of a power transmission chain for industrial use and is characterized in that it comprises a steel base material and a chromium nitride layer formed on an outer side of the steel base material and contains at least 1 wt.% but not more than 45 wt.% iron.

[0121] According to the present invention, the chromium nitride layer is formed on the outer side of the steel base material. The chain component has a simple surface treatment structure and can be easily and cost-effectively manufactured with fewer process steps.

[0122] Chromium nitride has a low coefficient of friction, meaning that chain components coated with a chromium nitride layer exhibit low aggressiveness towards mating parts. The chromium nitride layer generates little heat due to sliding friction. Furthermore, chromium nitride has a high oxidation induction temperature and exhibits minimal oxidation even at high temperatures, thus advantageously maintaining the wear resistance of the chain component.

[0123] Since the chromium nitride coating contains iron, it exhibits good adhesion to the steel base material. Furthermore, because the iron content is at least 1 wt.% but no more than 45 wt.%, the wear resistance of the chain component is maintained over a long period.

[0124] The chain component according to the present invention is further characterized in that the chromium nitride layer has an iron concentration distribution, wherein the iron concentration gradually decreases from a surface of the steel base material to an outer side.

[0125] According to the present invention, adhesion to the steel base material is even more advantageous.

[0126] The chain component according to the present invention is further characterized in that the chromium nitride layer has a chromium and nitrogen concentration distribution that gradually decreases from an outer side towards the surface of the steel base material.

[0127] According to the present invention, adhesion to the steel base material is even more advantageous.

[0128] The chain component according to the present invention is further characterized in that the iron content is 1 wt.% or more and 45 wt.% or less.

[0129] According to the present invention, the wear resistance is even better.

[0130] The chain component according to the present invention is further characterized in that the chromium nitride layer contains at least 1 wt.% but not more than 45 wt.% iron, 45 wt.% or more and 90 wt.% or less chromium, and 5 wt.% or more and 25 wt.% or less nitrogen, based on a total amount of 100 wt.%.

[0131] According to the present invention, the wear resistance is maintained more advantageously and the adhesion to the steel base material is even better.

[0132] The chain component according to the present invention is further characterized in that the chromium nitride layer has a thickness of 2 µm or more and 30 µm or less.

[0133] According to the present invention, the surface roughness is low, cracks hardly form, and the wear resistance is advantageous.

[0134] The chain according to the present invention is formed of several pairs of outer links, each connected by two pins, and several pairs of inner links, each connected by two bushings that are alternately connected to each other, the pins being loosely inserted into the bushings, and is characterized in that at least one of the pin, bushing, inner link and outer link is one of the chain components described above.

[0135] The bushing chain of the present invention exhibits advantageous resistance to wear-induced elongation.

[0136] The chain according to the present invention is formed of several pairs of outer links, each connected by two pins, and several pairs of inner links, each connected by two bushings, each having a roller attached thereto, which are alternately connected to one another, the pins being loosely mounted in the bushings, and is characterized in that at least one of the pin, bushing, inner link, outer link and roller is one of the chain components described above.

[0137] The roller chain of the present invention exhibits advantageous resistance to wear-induced elongation.

[0138] The chain according to the present invention is further characterized in that at least one of the pin and bushing is one of the chain components described above and that the gap between the pin and the bushing is 30 µm to 120 µm.

[0139] The chain of the present invention exhibits advantageous resistance to wear-induced elongation and can flexibly cope with various purposes and changes in the usage environment.

[0140] The chain according to the present invention is a chain made of several inner plates, each having a pair of V-shaped toothed plates at one end in a direction of the short side, the inner plates being pivotably connected to one another by pins inserted into the pin openings and arranged in a width direction of the chain such that one toothed plate of each inner plate overlaps the other toothed plate of another inner, adjacent plate, and guide plates arranged on both outer sides in the width direction by which the pins are firmly inserted, and is characterized in that at least one of the pin, the inner plate and the guide plate is one of the chain components described above.

[0141] The toothed chain of the present invention exhibits advantageous resistance to wear-induced elongation.

[0142] The chain according to the present invention is further characterized in that at least one of the pin and the inner tab is one of the chain components described above, and that there is a gap between the pin and the inner tab in the range of 30 µm to 120 µm.

[0143] The chain of the present invention exhibits advantageous resistance to wear-induced elongation and can flexibly cope with various purposes and changes in the usage environment.

[0144] It is understood that the embodiments disclosed herein are given for illustrative and non-limiting purposes. The scope of the present invention is not defined by the above description and is intended to include content equivalent to the claims and any modifications made within the scope of the claims.

[0145] The chain component of the present invention is not limited, for example, to components of the roller chain, bushing chain, and toothed chain described above. The chain component can also be applied to components of power transmission chains for industrial uses different from timing chains.

Claims

[1] Chain comprising several pairs of outer links, each connected by two pins, and several pairs of inner links, each connected by two sockets alternately connected to each other, the pins being loosely fitted in the sockets, at least one of the pin, bushing, inner link and outer link is a chain component of a power transmission chain for industrial use, wherein the chain component comprises the following: a steel base material; and a chromium nitride layer formed on an outer side of the steel base material and containing iron in a wt.% of 1 or more and 45 or less, wherein the chromium nitride layer of the chain component has an iron concentration distribution that gradually decreases from a surface of the steel base material outwards, and wherein the chromium nitride layer of the chain component has a chromium and nitrogen concentration distribution that gradually decreases from an outer side to a surface of the steel base material. [2] Chain according to claim 1, wherein the chromium nitride layer of the chain component contains: 45 wt.% or more and 90 wt.% or less chromium, and 5 wt.% or more and 25 wt.% or less nitrogen, based on a total amount of 100 wt.%. [3] Chain according to one of claims 1 to 2, wherein the chromium nitride layer of the chain component has a thickness of 2 µm or more and 30 µm or less. [4] Chain comprising several pairs of outer links, each connected by two pins, and several pairs of inner links, each connected by two bushings, each bushing having a roller attached thereto, the bushings being alternately connected to each other, the pins being loosely fitted in the bushings, at least one of the pin, bushing, inner link, outer link and roller is a chain component of a power transmission chain for industrial use, wherein the chain component comprises the following: a steel base material; and a chromium nitride layer formed on an outer side of the steel base material and containing iron in a wt.% of 1 or more and 45 or less, wherein the chromium nitride layer of the chain component has an iron concentration distribution that gradually decreases from a surface of the steel base material outwards, and wherein the chromium nitride layer of the chain component has a chromium and nitrogen concentration distribution that gradually decreases from an outer side to a surface of the steel base material. [5] Chain according to any one of claims 1 to 4, wherein at least one of the pin and bushing is a chain component of a power transmission chain for industrial use, the chain component comprising: a steel base material; and a chromium nitride layer formed on an outer side of the steel base material, containing iron in a wt.% of 1 or more and 45 or less; and The gap between the pin and the socket is 30 µm to 120 µm. [6] Chain comprising: several inner links, each having a pair of V-shaped toothed links at one end in a direction of the short side, and a pair of front and rear pin openings, the inner links being pivotably connected to one another by pins inserted into the pin openings and arranged in a width direction of the chain such that one toothed link of each inner link overlaps the other toothed link of another adjacent inner link; and guide links arranged on both outer sides in the width direction, through which the pins are firmly inserted, at least one of the pin, the inner tab and the guide tab is a chain component of a power transmission chain for industrial use, wherein the chain component comprises the following: a steel base material; and a chromium nitride layer formed on an outer side of the steel base material and containing iron in a wt.% of 1 or more and 45 or less, wherein the chromium nitride layer of the chain component has an iron concentration distribution that gradually decreases from a surface of the steel base material outwards, and wherein the chromium nitride layer of the chain component has a chromium and nitrogen concentration distribution that gradually decreases from an outer side to a surface of the steel base material. [7] Chain according to claim 6, wherein at least one of the pin and the inner link is a chain component of a power transmission chain for industrial use, the chain component comprising: a steel base material; and a chromium nitride layer formed on an outer side of the steel base material, containing iron in a wt.% of 1 or more and 45 or less; and The gap between the pins and the pin openings in the inner tabs in sliding contact with the pins is 30 µm to 120 µm.

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