Ferritic nitrocarburized track pins for track chain assemblies for machines

Abstract

A track pin (80, 180) for a track chain assembly (16) is provided, the track pin including a body (120, 220) made of a steel alloy. The steel alloy has a composition including iron, nitride-forming elements, carbide-forming elements, and silicon. The composition of the steel alloy includes at least 0.5 wt% silicon. The body (120, 220) includes a composite layer (130, 230) on its outer surface (125, 225). The composite layer (130, 230) includes at least one of an Fe 2‑3 (C,N) microstructure and an Fe4N microstructure formed therein by ferritic nitrocarburizing.

Description

Technical Field

[0001] The present disclosure generally relates to a track chain assembly for a tracked machine, and more particularly, to a track pin in a track chain assembly for a machine. Background Art

[0002] Tracked machines are widely used in construction, mining, forestry, and other similar industries. The undercarriage of such tracked machines utilizes track assemblies instead of wheels to provide ground-engaging propulsion. Such track assemblies may be preferred in environments where there are problems generating sufficient traction, such as those commonly encountered in the industries mentioned above. Specifically, instead of relying on wheels to roll across the working surface, a tracked machine utilizes one or more track assemblies, the one or more track assemblies including an endless loop of interconnected track links that define an outer surface supporting ground-engaging track shoes, and an inner surface that travels around one or more rotatable track-engaging elements (e.g., such as drive sprockets, idlers, tensioners, and rollers).

[0003] Typical track chain assembly designs include track pins fixedly or rotatably connected to a pair of chain links, and bushings positioned rotatably between the links and around the track pins. Such track chain assemblies can operate in extremely adverse environments where track joints may be exposed to various abrasive mixtures of water, dirt, sand, rock, or other minerals or chemical elements. The bearing interface between the track pin and the bushing can experience high contact stresses, which leads to galling failures. Galling is the primary failure mode of track chain assemblies and can limit the life of track chain assemblies in many applications.

[0004] Track bushings are typically made of carbon steel or low steel alloys that are directly hardened or carburized and hardened. When used in combination with this type of track bushing, the hardness of any bare steel or carburized pin is limited by the hardening ability of the carbon in the steel. The surface microstructure of a directly hardened or carburized track pin may be similar to that of the steel bushing; this similarity is believed to limit performance.

[0005] To address galling failures, it is known to coat the pins with one of several types of hard coatings, such as by using physical vapor deposition (PVD) or chemical vapor deposition (CVD). These coatings are deposited on the surface of the substrate material, and they can create a new structure that is completely different from the structure of the bushing. These coatings can improve galling resistance. Unfortunately, the deposition cost of these coatings is high and adhesion can be a problem.

[0006] Another way to solve the galling problem is to increase the surface contact area between the contacting components, thereby reducing the contact stress and the tendency to gall. This option is not advisable because increasing the size of the track pin would result in a disproportionate increase in system cost, since all other related components would also have to scale and increase in size accordingly.

[0007] Nitriding is an existing heat treatment method that can produce a very hard thin shell on the surface of a nitrided alloy. However, nitriding requires a high processing temperature (above 500 °C), which causes most steels to lose their strength. This results in a hard shell being formed over a much softer substrate, which may not have the strength to support the expected working loads of the track chain assembly, including shear and fatigue loads in large track-type machines, especially large track-type tractors.

[0008] U.S. Patent No. 10,272,960, titled "Nitrided Track Pin for Track Chain Assembly of Machine," relates to a track pin for a track chain assembly, the track pin including a body made of a steel alloy. The steel alloy has a composition containing iron, nitride-forming elements, and silicon. The composition of the steel alloy contains at least 0.5 wt% silicon. The body includes an outer nitrided surface.

[0009] There is a continuing need in the art for additional solutions for track chain assemblies. For example, there is a continuing need for track pins for track chain assemblies that should not only be strong enough to support their expected working loads but also extremely durable to provide an extended service life for the track chain assembly.

[0010] It should be appreciated that this background description is created by the inventors to assist the reader and is not considered to indicate that any of the noted problems are themselves known in the art. Although the described principles may alleviate problems inherent in other systems in some respects and embodiments, it should be appreciated that the scope of the protected innovation is defined by the appended claims, rather than by the ability of any disclosed feature to solve any specific problem mentioned herein. Summary of the Invention

[0011] In one embodiment, the present disclosure describes a track pin for a track chain assembly. The track pin includes a body made of a steel alloy. The steel alloy has a composition containing iron, nitride-forming elements, carbide-forming elements, and silicon. The composition of the steel alloy contains at least 0.5 wt% silicon. The body includes a composite layer on its outer surface. The composite layer contains at least one of Fe(C,N) microstructure and Fe4N microstructure formed therein by ferritic nitrocarburizing. The composite layer contains at least 1 wt% carbon measured 0.003 mm below the outer surface of the composite layer. 2-3 (C,N) microstructure and Fe4N microstructure. The composite layer contains at least 1 wt% carbon measured 0.003 mm below the outer surface of the composite layer.

[0012] In another embodiment, a track pin for a track chain assembly includes a body made of a steel alloy. The steel alloy has a composition comprising iron, nitride-forming elements, carbide-forming elements, and silicon. The composition of the steel alloy includes between 0.5 wt% and 4 wt% silicon. The body includes a composite layer on its outer surface. The composite layer includes at least one of Fe 2-3 (C,N) microstructure and Fe4N microstructure formed therein by ferritic nitrocarburizing. The composite layer has an elastic modulus of at least 190 GPa.

[0013] In yet another embodiment, a track chain assembly is described that includes a track pin and a bushing. The track pin defines a longitudinal axis. The track pin includes a body made of a steel alloy. The steel alloy has a composition comprising iron, nitride-forming elements, carbide-forming elements, and silicon. The composition of the steel alloy includes at least 0.5 wt% silicon. The body includes a composite layer on its outer surface. The composite layer includes at least one of Fe 2-3 (C,N) microstructure and Fe4N microstructure formed therein by ferritic nitrocarburizing. The composite layer includes at least 1 wt% carbon as measured 0.003 mm below the outer surface of the composite layer.

[0014] The bushing includes an inner surface defining a cylindrical bore. The bushing is coaxially positioned around the track pin such that the track pin extends through the cylindrical bore of the bushing. The bushing is rotatable relative to the track pin about the longitudinal axis. The inner surface of the bushing is made of a bushing material. The bushing material is different from the steel alloy of the body of the track pin.

[0015] Additional and alternative aspects and features of the disclosed principles will be appreciated from the following detailed description and the drawings. It should be understood that the principles related to the track pins and track chain assemblies disclosed herein can be implemented in other and different embodiments and can be modified in various aspects. Accordingly, it should be understood that the foregoing general description and the following detailed description are merely exemplary and explanatory and do not limit the scope of the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic side elevational view of one embodiment of a track-type machine including a chassis constructed in accordance with the principles of the present disclosure.

[0017] Figure 2 A fragmentary perspective view of a portion of one embodiment of a track chain assembly constructed in accordance with the principles of the present disclosure.

[0018] Figure 3 For Figure 2 A perspective view of a cross-section of a track pin joint assembly of a track chain assembly.

[0019] Figure 4 A longitudinal cross-sectional view of an embodiment of a track pin assembly constructed in accordance with the principles of the present disclosure.

[0020] It should be understood that the figures are not necessarily to scale and that the disclosed embodiments are sometimes shown diagrammatically and in partial views. In some cases, details that are not necessary for understanding the present disclosure or that obscure other details may have been omitted. Of course, it should be understood that the present disclosure is not limited to the particular embodiments shown herein. Detailed Description

[0021] The present disclosure provides embodiments of track pins for a track chain assembly of a track-type machine, the track pins having undergone a nitriding process in the form of ferritic nitrocarburizing (also referred to herein as "FNC"). Examples of track-type machines include machines for construction, mining, forestry, and other similar industries. In some embodiments, the machine may be a bulldozer, loader, excavator, or any other on-road or off-road vehicle having a track-type chassis. The chassis may include a track chain assembly adapted to engage the ground or other surface to propel the track-type machine.

[0022] An embodiment of a track pin constructed in accordance with the principles of the present disclosure may include a body made of a steel alloy that includes a temper-resistant nitriding alloy that can maintain sufficient core strength for its intended application even after undergoing a nitriding technique in the form of a ferritic nitrocarburizing process. Examples of suitable alloys include those described in U.S. Patent No. 5,131,965 and U.S. Patent Application Publication No. US 2017 / 0130304, both of which are incorporated herein by reference in their entirety. By nitriding the body of the track pin via a suitable FNC process, the outer surface of the body will become a very hard shell and the core of the body will sufficiently retain its strength. The nitriding process produces a hardened metal-matrix shell, referred to herein as a compound layer (also referred to by those skilled in the art as a "white layer"). The compound layer may be structurally significantly different from the surface microstructure of a track bushing that mates with the nitrided track pin. In embodiments, the combination of the core strength, surface hardness, and dissimilar microstructure (relative to the mating bushing) of the nitrided track pin, relative to the same non-nitrided track pin, may contribute to providing a robust track chain assembly with excellent anti-seizure properties and sufficient strength for an extended service life.

[0023] Turning now to the figures, Figure 1 An exemplary embodiment of a machine 10 having a track-type chassis 12 is shown. Machine 10 may also be referred to herein as a track-type machine. In other embodiments, machine 10 may be any suitable machine having a track-type chassis, such as a bulldozer, loader, excavator, or any other on-road or off-road vehicle.

[0024] Machine 10 includes a frame 14 having a first track chain assembly 16 disposed on its first side 18 and a second track chain assembly (not shown) disposed on its second side 19. The second side 19 is in a relation opposite to the first side 18. The track assemblies together are adapted to engage the ground or other surface to propel the machine 10.

[0025] It should be appreciated that the track assemblies of the machine 10 can be similar and can additionally represent mirror images of each other. Thus, only the first track chain assembly 16 will be described herein. It is understood that the description of the first track chain assembly 16 can also apply to the second track chain assembly.

[0026] The first track chain assembly 16 extends around a plurality of rolling elements such as a drive sprocket 20, a front idler 22, a rear idler 24, and a plurality of track rollers 26. The track chain assembly 16 includes a plurality of ground-engaging track shoes 28 for engaging the ground or other surface and propelling the machine 10.

[0027] During typical operation of the chassis 12, the drive sprocket 20 is driven in a forward rotational direction FR to drive the track chain assembly 16 and thus the machine 10 in a forward direction F, and is driven in a reverse rotational direction RR to drive the track chain assembly 16 and thus the machine 10 in a reverse direction R. The drive sprocket 20 of the chassis 12 can be operated independently to turn the machine 10.

[0028] Although the machine 10 is shown in the context of a tracked machine, it should be appreciated that the present disclosure is not so limited and that a variety of other machines having tracks are also contemplated in this context. For example, in other embodiments, the track chain assembly 16 can be included in a conveyor system as a track for transmitting torque between rotating elements, or included in any other application known to those skilled in the art.

[0029] Now referring Figure 2 , the first track chain assembly 16, only a portion of which is shown, includes a plurality of track pin joint assemblies 42. Each track pin joint assembly 42 includes a pin assembly 44, an inner link 46, an outer link 48, and a track shoe 28 connected to the inner link 46 and the outer link 48 via any suitable technique known to those skilled in the art (see Figure 3 ), for example, connected by a plurality of fasteners 49 as shown in Figure 3 .

[0030] Referring Figure 2, a plurality of track pin joint assemblies 42 are mechanically coupled to adjacent track pin joint assemblies 42 such that when a suitable number of these track pin joint assemblies 42 are connected together, a track chain assembly 16 is formed. The first track chain assembly 16 has a predetermined length for a given application, and its opposite ends can be connected together to form a closed loop. The closed loop is formed by mechanically coupling the opposite ends together to provide an inner chain 56 of a series of inner linkages 46 and an outer chain 58 of a series of outer linkages 48 that are coupled together via a plurality of pin assemblies 44, respectively. In embodiments, as known to those skilled in the art, suitable master link assemblies can be used to facilitate the connection of the track pin joint assemblies 42 to form a closed loop. The inner linkages 46 and the outer linkages 48 can be made of any suitable material, such as metal.

[0031] It should be recognized that in this instance, the terms "inner" and "outer" with respect to the linkages 46, 48 of each track pin joint assembly 42 are used only as descriptors of the directions shown in the drawings. Other terms such as "left" and "right" or "first" and "second" can also be used interchangeably. It should be understood that these terms are merely convenient labels applied to different views and are not intended to be limiting in any way.

[0032] The inner linkages 46 and the outer linkages 48 are mirror images of each other. Thus, it should be understood that a description of one linkage 46 generally also applies to the other. The inner linkages 46 and the outer linkages 48 each include a body 60 having a first end 62, a second end 64, an outer wall 66, and an inner wall 68. The outer wall 66 and the inner wall 68 extend between the first end 62 and the second end 64 along a body axis BA. The first end 62 and the second end 64 define a first pin passage 70 and a second pin passage 72, respectively. Each of the first pin passage 70 and the second pin passage 72 extends transversely between the outer wall 66 and the inner wall 68.

[0033] The illustrated inner linkages 46 and outer linkages 48 include offset linkages. The first ends 62 of the inner linkages 46 and the outer linkages 48 include inwardly offset ends, while the second ends 64 of the inner linkages 46 and the outer linkages 48 include outwardly offset ends. In the illustrated embodiment, the outer wall 66 of the body 60 defines a first offset recess 74 at the first end 62 of the body 60, while the inner wall 68 of the body 60 defines a second offset recess 76 at the second end 64 of the body 60. The inwardly offset ends 62 of the inner linkages 46 and the outer linkages 48 of each track pin joint assembly 42 can be rotatably mounted relative to the track pins 80 of its pin assembly 44. The outwardly offset ends 64 of the inner linkages 46' and the outer linkages 48' of each track pin joint assembly 42' can be fixedly coupled to the track pins 80 of the pin assembly 44 of an adjacent track pin joint assembly 42. In other embodiments, as will be recognized by those skilled in the art, the linkages 46, 48 of the track chain assembly 16 can have different configurations.

[0034] Reference Figure 3 , according to one of several possible embodiments of the present disclosure, the pin assembly 44 is illustrated. The illustrated pin assembly 44 includes a track pin 80, a bushing 82, a pair of thrust rings 86, 87, and a pair of seal assemblies 89, 90.

[0035] The track pin 80 defines a longitudinal axis LA. The track pin 80 extends through a first pin passage 70 of the inner link 46 and the outer link 48 of the track pin joint assembly 42 and is at least partially positioned in a second pin passage 72 of the inner link 46' and the outer link 48' of an adjacent track pin joint assembly 42'. The bushing 82 is coaxially positioned around the track pin 80 and is rotatable relative to the track pin 80 about the longitudinal axis LA. As shown, the inwardly offset ends 62 of the inner link 46 and the outer link 48 are fixedly connected to the bushing 82, which can be at least partially positioned in the first pin passage 70 of the inwardly offset ends 62 of the inner link 46 and the outer link 48. Similarly, the outwardly offset ends 64 of the inner link 46' and the outer link 48' of the adjacent track pin joint assembly 42' are fixed to the track pin 80, which can be at least partially positioned within the second pin passage 72 of the inwardly offset ends 62 of the inner link 46' and the outer link 48' of the adjacent track pin joint assembly 42'.

[0036] For example, the bushing 82 and the track pin 80 can be fixed to the respective inner links 46, 46' and outer links 48, 48' by a press fit. Specifically, the bushing 82 can be press-fitted into the first pin passage 70 of the inwardly offset ends 62 of the inner link 46 and the outer link 48, while the track pin 80 can be press-fitted into the second pin passage 72 of the outwardly offset ends 64 of the inner link 46' and the outer link 48' of an adjacent track pin joint assembly 42'. In other embodiments, any suitable technique for securing the components together can be used, such as by using welding, snap rings, or other mechanisms known in the art.

[0037] Thus, when the track pin joint assembly 42 rotates, the inwardly offset end 62 mounted to the bushing 82 can pivot relative to the outwardly offset end 64 mounted to the track pin 80. To facilitate such rotation, in an embodiment, a lubricant can be deposited between the bushing 82 and the track pin 80.

[0038] In the illustrated embodiment, the track pin 80 includes an outer outer surface 101 and an inner outer surface 102 that define a cylindrical hole 104 that extends through and is concentrically disposed about the longitudinal axis LA. The track pin 80 defines a cross bore 106 that extends inwardly from its outer outer surface 101 to the hole 104 in a direction perpendicular to the central longitudinal axis LA to distribute lubricant stored in the central hole of the pin.

[0039] One or more plugs (not shown) may be positioned in the holes 104 of the track pin 90 to form a fluid reservoir 110 in its hole 104. In use, the fluid disposed within the fluid reservoir 110 is in fluid communication with the transverse hole 106 and advances through the transverse hole to the outer outer surface 101 of the track pin 90. Once disposed on the outer outer surface 101, the fluid facilitates rotation of the bushing 82 relative to the track pin 80 about the longitudinal axis LA. The seal assemblies 89, 90 help retain the fluid within the fluid reservoir 110, sealingly engaging the inner link 46' and the bushing 82 and the outer link 48' and the bushing 82 respectively, while also helping to prevent debris (e.g., sand, dust, etc.) from entering between the bushing 82 and the track pin 80.

[0040] In an embodiment of a track pin constructed in accordance with the principles of the present disclosure, the track pin 80 includes a body 120 made of a steel alloy having a composition comprising iron, nitride-forming elements, and carbide-forming elements. The body 120 includes an outer nitrided surface 125 and a compound layer 130 produced via a suitable FNC treatment technique.

[0041] In an embodiment, the body 120 of the track pin 80 is made of a steel alloy that includes a temper-resistant nitriding alloy that can maintain sufficient core strength even after high-temperature tempering for its intended application. In an embodiment, the body 120 of the track pin 80 is made of a steel alloy that contains iron, nitride-forming elements, carbide-forming elements, and silicon. In an embodiment, the composition of the steel alloy contains at least 0.5 wt% silicon. In an embodiment, the composition of the steel alloy contains between 0.5 wt% and 4 wt% silicon. In an embodiment, the body 120 of the track pin 80 may be made of a steel alloy as described in U.S. Patent No. 5,131,965 or U.S. Patent Application Publication No. US 2017 / 0130304, the patents and application publications of which are hereby incorporated by reference in their entirety.

[0042] The body 120 includes a compound layer 130 on the outer outer surface 101, which is produced by subjecting the body 120 to a suitable FNC treatment. In an embodiment, the compound layer 130 contains at least one of Fe 2-3 (C,N) microstructure and Fe4N microstructure formed therein by FNC treatment. In an embodiment, the compound layer 130 contains both Fe 2-3 (C,N) microstructure and Fe4N microstructure formed therein by FNC treatment.

[0043] In an embodiment, the body 120 of the track pin 80 can be made of any suitable steel alloy configured to produce a compound layer 130 after undergoing a nitriding process such as a suitable FNC treatment. For example, in an embodiment, the steel alloy has a composition comprising iron, nitride-forming elements, carbide-forming elements, and silicon. In an embodiment, the composition of the steel alloy comprises at least 0.5 wt% of silicon. In an embodiment, the composition of the steel alloy comprises between 0.5 wt% and 4 wt% of silicon, between 0.5 wt% and 2 wt% of silicon in other embodiments, and between 1 wt% and 3 wt% of silicon in still other embodiments. In an embodiment, the composition of the steel alloy comprises a combination of at least one nitride-forming element, at least one carbide-forming element, and silicon sufficient to provide the desired core hardness to the body 120 of the track pin 80 without adding significant amounts of other expensive alloying elements such as Ni, Mo, and Ti. In an embodiment, the steel alloy has a composition comprising iron, carbon, nitride-forming elements, and at least 0.5 wt% of silicon. In an embodiment, the composition of the steel alloy comprises between 0.2 wt% and 0.4 wt% of carbon. In an embodiment, the composition of the steel alloy comprises between 0.5 wt% and 1.6 wt% of manganese. In an embodiment, the composition of the steel alloy comprises at most 2.5 wt% of chromium, at most 0.3 wt% of vanadium, and at most 0.3 wt% of aluminum.

[0044] In an embodiment, the steel alloy making up the body 120 can have a chemical composition within the ranges listed in Table I:

[0045]

[0046]

[0047] The presence of carbon in the composition of the steel alloy making up the body 120 of the track pin 80 can contribute to the achievable hardness level and the hardening depth of the steel and can contribute to providing a sufficient response to nitriding via a suitable FNC treatment. In an embodiment, the composition of the steel alloy making up the body 120 of the track pin 80 comprises at least 0.20 wt% or more of carbon. In an embodiment, the composition of the steel alloy making up the body 120 of the track pin 80 comprises between 0.24 wt% and 0.34 wt% of carbon.

[0048] The presence of manganese in the composition of the steel alloy making up the body 120 of the track pin 80 can contribute to hardenability and can contribute to providing sufficient core hardness for the intended application of the track pin 80. In an embodiment, the composition of the steel alloy making up the body 120 of the track pin 80 comprises at least 0.5 wt% or more of manganese. To maintain uniformity of response to heat treatment, lower amounts of manganese between 0.5 wt% and 1.5 wt%, and between 1.0 wt% and 1.3 wt% in still other embodiments, can be used.

[0049] The presence of chromium in the composition of the steel alloy that makes up the body 120 of the track pin 80 can contribute to the hardenability and nitride formation of the body 120, thus enhancing the nitride response. In an embodiment, the composition of the steel alloy that makes up the body 120 of the track pin 80 contains at least 0.4 wt% or more of chromium. In an embodiment, a narrower range of chromium of 0.9 wt% to 1.2 wt% can be used.

[0050] The presence of aluminum in the composition of the steel alloy that makes up the body 120 of the track pin 80 can contribute to hardenability and nitride formation. In an embodiment, the composition of the steel alloy that makes up the body 120 of the track pin 80 contains at least 0.07 wt% or more of aluminum. To help avoid case brittleness, the composition of the steel alloy that makes up the body 120 of the track pin 80 contains aluminum in the range of between 0.07 wt% and 1.0 wt% in some embodiments and in the range of between 0.07 wt% and 0.3 wt% in still other embodiments.

[0051] In an embodiment, the composition of the steel alloy that makes up the body 120 of the track pin 80 contains at least 0.03 wt% or more of vanadium to help enhance case and core hardness. To reduce cost, the composition of the steel alloy that makes up the body 120 of the track pin 80 contains vanadium in the range of between 0.03 wt% and 0.3 wt% in some embodiments, in the range of between 0.05 wt% and 0.1 wt% in still other embodiments, and in the range of between 0.1 wt% and 0.2 wt% in yet other embodiments. Thus, in an embodiment, the steel alloy that makes up the body 120 can have a chemical composition in the following ranges: carbon between 0.2 wt% and 0.4 wt%, manganese between 0.5 wt% and 1.6 wt%, silicon between 0.5 wt% and 2.0 wt%, chromium between 0.4 wt% and 1.5 wt%, vanadium between 0.03 wt% and 0.3 wt%, aluminum between 0.07 wt% and 0.3 wt%, with the balance being iron. It should be understood that the "balance" of iron can include residual amounts of elements, such as impurities, which may be present in small amounts within commercially acceptable allowable amounts.

[0052] In an embodiment, the composition of the steel alloy of the body 120 forming the track pin 80 includes nickel and molybdenum in amounts each of 1.0 wt% or less. In an embodiment, nickel and / or molybdenum may be added in an amount sufficient to improve the toughness and / or hardenability of the steel alloy, depending on the size and geometry of the track pin 80. In an embodiment, the composition of the steel alloy of the body 120 forming the track pin 80 includes a combined amount of nickel and molybdenum of 1.0 wt% or less. To further reduce cost, the composition of the steel alloy of the body 120 forming the track pin 80 includes nickel and molybdenum in amounts each of 0.1 wt% or less in some embodiments and each of 0.01 wt% or less in still other embodiments. In an embodiment, except for trace impurities, the composition of the steel alloy of the body 120 forming the track pin 80 is substantially free of nickel and molybdenum.

[0053] In an embodiment, the composition of the steel alloy of the body 120 forming the track pin 80 includes titanium and niobium in amounts each sufficient to help reduce grain coarsening during hot working. When molybdenum and / or vanadium are added, titanium and niobium form carbonitrides with nitrogen and carbon in the steel and also effectively enhance the core hardness and surface hardness. In an embodiment, the composition of the steel alloy of the body 120 forming the track pin 80 includes 0.05 wt% of titanium, 0.01 wt% or less in other embodiments, and a combined amount of titanium and niobium of 0.01 wt% or less in still other embodiments.

[0054] In an embodiment, the composition of the steel alloy of the body 120 forming the track pin 80 includes phosphorus in an amount of 0.03 wt% or less, which may be present in the steel as an impurity. To help avoid deterioration of toughness or corrosion resistance, in still other embodiments, the composition of the steel alloy of the body 120 forming the track pin 80 includes phosphorus in an amount of 0.01 wt% or less.

[0055] In an embodiment, the composition of the steel alloy of the body 120 forming the track pin 80 includes the balance of iron. In an embodiment, the composition of the steel alloy of the body 120 forming the track pin 80 includes iron in an amount of at least 80 wt%, at least 85 wt% in other embodiments, and at least 90 wt% in still other embodiments.

[0056] In other embodiments, the steel alloy of the body 120 forming the track pin 80 may have a chemical composition within the ranges listed in Table II:

[0057]

[0058]

[0059] In some such embodiments, the composition of the steel alloy that makes up the body 120 of the track pin 80 includes: carbon between 0.26 wt% and 0.37 wt%, manganese between 0.5 wt% and 1.0 wt%, silicon between 1.0 wt% and 3.0 wt%, chromium between 1.5 wt% and 2.5 wt%, molybdenum between 0.3 wt% and 1.0 wt%, vanadium between 0.05 wt% and 0.2 wt%, titanium between 0.03 wt% and 0.1 wt%, aluminum between 0.01 wt% and 0.03 wt%, phosphorus less than 0.025 wt%, sulfur less than 0.025 wt%, nitrogen between 0.005 wt% and 0.013 wt%, with the balance being iron.

[0060] In an embodiment, the track pin 80 can be made using any suitable technique, such as by forging or rolling to form the desired shape. The formed track pin can be hardened by heating to a temperature of about 870 °C (1600 °F) for about one hour and then quenched in water or oil to complete the transformation of the ferrite and pearlite microstructure to martensite. After tempering to precipitate and agglomerate carbide particles and thereby provide improved toughness, the formed track pin can be machined (e.g., to provide the cylindrical hole 104 and the transverse hole 106) to the desired final dimensions and then nitrided.

[0061] Nitriding is a thermochemical process by which the surface of the outer surface 101 of the track pin 80 is enriched with nitrogen to form alloy nitrides and form a compound layer 130. In an embodiment, the track pin 80 can be subjected to any suitable nitriding technique during the manufacture of the track pin 80, such as a suitable FNC treatment.

[0062] In an embodiment, any suitable FNC treatment can be used to treat the track pin 80 for nitriding of the track pin 80. FNC can diffuse nitrogen and carbon into the surface of the ferrous material at a temperature within the ferrite phase field. The FNC treatment process is essentially diffusive and introduces both nitrogen and carbon into the outer surface 101 of the body 120 when the steel is in the ferrite phase in terms of temperature. In an embodiment, any suitable FNC treatment technique can be used, as would be understood by those skilled in the art, including gaseous, salt bath, ion (plasma), furnace, and fluidized bed FNC treatment techniques known to those skilled in the art. Ferritic nitrocarburizing typically results in the compound layer 130 containing varying amounts of Fe 2-3 (C,N) microstructure and Fe4N microstructure, as well as cementite and various carbides and nitrides. In an embodiment, the FNC treatment can form a diffusion layer adjacent to the compound layer 130 and deeper within the body 120, which can contain nitrogen in solid solution and precipitate as metal nitrides (M x N).

[0063] By nitriding the body 120 of the track pin 80 using a suitable FNC process, the outer outer surface 101 of the track pin 80 will become the outer nitrided surface 125 of the body, such that the body 120 has a very hard nitrided case and the core of the body sufficiently retains its strength. The nitriding process produces a hardened metal-matrix case in the form of a compound layer 130, commonly referred to as the "white layer". The compound layer 130 can be structurally significantly different from the surface microstructure of the core 135 of the body 120 of the track pin 80 (and also from the material structure of the bushing 82 that mates with the nitrided track pin 80). The hardness and different microstructure of the compound layer 130 can improve anti-seizure properties and can improve the corrosion resistance of the track pin 80. In an embodiment, the compound layer 130 or white layer provides anti-seizure properties, while the core 135 of the body 120 retains sufficient strength after nitriding the track pin 80 by undergoing the FNC process, such that the track pin 80 functionally behaves as if it were larger than its actual size. In an embodiment, the compound layer 130 or white layer can be at least three microns thick, and in other embodiments can be at least five microns thick.

[0064] In an embodiment, the compound layer 130 comprises Fe 2-3 (C,N) microstructure and at least one of Fe4N microstructure. In an embodiment, the compound layer 130 comprises Fe 2-3 (C,N) microstructure and both Fe4N microstructure.

[0065] In an embodiment, the compound layer 130 has a modulus of elasticity of at least 190 GPa. In an embodiment, the outer nitride surface 125 of the track pin 80 has at least R c 50, in other embodiments at least R c 55, in still other embodiments at least R c 55 and in yet other embodiments at least R c 65 surface hardness. In an embodiment, the compound layer 130 has a hardness of at least 9 GPa, in yet other embodiments at least 10 GPa.

[0066] In an embodiment, the core hardness of the body 120 of the track pin 80 can be measured at 0.5 mm below the outer nitrided surface 125. In an embodiment, measured at 0.5 mm below the outer nitrided surface 125, the body 120 of the track pin 80 has at least R c 40, in other embodiments at least R c 42, in still other embodiments at least R c 45 core hardness. It should be understood that the hardness measurement values can include the average of at least three measurements.

[0067] In an embodiment, the composite layer 130 contains a greater weight percentage of nitrogen and carbon than is present in the steel alloy from which the body 120 is made. In an embodiment, the composite layer 130 contains at least 1 wt% carbon and at least 1 wt% nitrogen as measured at 0.003 mm below the outer surface of the composite layer.

[0068] In an embodiment, as determined by glow discharge optical emission spectroscopy (GDOES), the composite layer 130 has the following composition. In an embodiment, the composite layer 130 contains at least 1 wt% of carbon. In an embodiment, the composite layer 130 contains at least 1 wt% carbon as measured at 0.003 mm below the outer surface of the composite layer, and in other embodiments at least 2 wt% carbon as measured at 0.003 mm below the outer surface of the composite layer. In an embodiment, the composite layer 130 contains between 1 wt% and 8 wt% of carbon. In an embodiment, the composite layer 130 contains at least 1 wt% of nitrogen. In an embodiment, the composite layer 130 contains between 1 wt% and 16 wt% of nitrogen. In an embodiment, the composite layer 130 contains at least 0.5 wt% of silicon. In an embodiment, the composite layer 130 contains between 0.5 wt% and 2 wt% of silicon. In an embodiment, the composite layer 130 contains at most 0.3 wt% of vanadium. In an embodiment, the composite layer 130 contains at least 0.2 wt% of chromium. In an embodiment, the composite layer 130 contains between 0.2 wt% and 2.5 wt% of chromium. In an embodiment, the composite layer 130 contains at least 0.2 wt% of manganese. In an embodiment, the composite layer 130 contains between 0.2 wt% and 1.2 wt% of manganese. In an embodiment, the composite layer 130 contains at most 1.0 wt% of molybdenum.

[0069] In an embodiment, as determined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), the composite layer 130 has the following composition. In an embodiment, the composite layer 130 contains carbon in an amount of at least 7 wt%. In an embodiment, the composite layer 130 contains carbon in an amount between 7 wt% and 13 wt%. In an embodiment, the composite layer 130 contains nitrogen in an amount of at least 1 wt%. In an embodiment, the composite layer 130 contains nitrogen in an amount between 1 wt% and 6 wt%. In an embodiment, the composite layer 130 contains silicon in an amount of at least 0.5 wt%. In an embodiment, the composite layer 130 contains silicon in an amount between 0.5 wt% and 2 wt%. In an embodiment, the composite layer 130 contains vanadium in an amount of at most 0.3 wt%. In an embodiment, the composite layer 130 contains chromium in an amount of at least 0.2 wt%. In an embodiment, the composite layer 130 contains chromium in an amount between 0.2 wt% and 2 wt%. In an embodiment, the composite layer 130 contains manganese in an amount of at least 0.2 wt%. In an embodiment, the composite layer 130 contains manganese in an amount between 0.2 wt% and 1.2 wt%. In an embodiment, the composite layer 130 contains molybdenum in an amount of at most 1.0 wt%.

[0070] In an embodiment, after alloying the steel according to the principles of the present disclosure, the steel can be hot deformed by forging or hot rolling and rough machining. The steel alloy is quenched and tempered to a specific core hardness and then finish machined to form the track pin 80. Subsequently, the track pin 80 is nitrided via a suitable FNC treatment technique. Any suitable nitriding technique known to those skilled in the art can be used to nitride the track pin 80, such as gas nitriding, salt bath nitriding, and plasma nitriding. The track pin 80 can then be lapped or lightly ground to conform to the predetermined specifications of the track pin 80.

[0071] The thickness and phase constitution of the resulting composite layer 130 can be selected and the process can be modified for the specific properties required for the intended application of the track pin 80. It should be noted that while the composite layer 130 is shown in Figure 3 as being present only at the outer outer surface 101 of the track pin 80, this is for illustrative purposes only. It is understood that the composite layer 130 can be present at any site on the track pin 80 where the nitriding process is carried out.

[0072] Reference Figure 3, the bushing 82 includes a generally cylindrical outer surface 141 and an inner surface 142 that defines a passageway in the form of a cylindrical bore 144 therethrough. The bushing 82 is coaxially positioned about the track pin 80 such that the track pin 80 extends through the cylindrical bore 144 of the bushing 82. The bushing 82 is rotatable relative to the track pin 80 about a longitudinal axis LA. Separately, a first axial end face 147 and a second axial end face 148 of the bushing 82 are respectively disposed adjacent to the second ends 64 of the inner link 46' and the outer link 48' of the adjacent track pin joint assembly 42'.

[0073] The outer surface 141 of the bushing 82 is configured to engage a drive sprocket 20 that drives the first track chain assembly 16. When the bushing 82 engages the drive sprocket 20, the bushing is rotatable relative to the track pin 80 about the longitudinal axis LA, thereby reducing wear on the bushing 82 caused by the interaction between the bushing 82 and the drive sprocket 20.

[0074] In an embodiment, the bushing 82 includes a case-hardened surface 150 that includes the inner surface 142 (and, in the embodiment, the outer surface 141). In the illustrated embodiment, the case-hardened surface 150 is in contact with the nitrided outer surface 125 of the track pin 80. In an embodiment, the case-hardened surface 150 of the bushing 82 can be produced by any suitable technique, such as by one of direct hardening and carburizing, for example.

[0075] In an embodiment, the inner surface 142 of the bushing 82 is made of a bushing material. In an embodiment, the bushing material is different from the steel alloy that makes up the body 120 of the track pin 80. In the illustrated embodiment, the entire bushing 82 is made of the bushing material. In an embodiment, the bushing material can be any suitable material, such as a suitable steel, including, for example, SAE 15B21, SAE 15B26, or SAE 1060. The composite layer 130 of the track pin 80 can be structurally different from the surface microstructure of the inner surface 142 of the bushing 82 such that this dissimilar microstructure (relative to the mating bushing 82) can contribute to good anti-galling resistance relative to the same track pin without nitriding to extend the service life of the track pin 80.

[0076] In other embodiments, one or more different bushings may be used in the track pin joint assembly 42. For example, in an embodiment, the outer surface 141 of the bushing 82 may define a lobed surface, as shown and described in U.S. Patent Application Publication No. 2010 / 0139993, "Lobed Bushing For Track Assembly and Track-Type Machine Using Same", which is incorporated herein by reference in its entirety. In still other embodiments, the bushing 82 may have different shapes and configurations known in the art. In still other embodiments, the track pin joint assembly 42 may include an inner bushing and an outer bushing having configurations known in the art.

[0077] The components of the track pin joint assembly 42 may define a plurality of annular seal cavities 152, 153 concentrically disposed about the longitudinal axis LA of the track pin 80. Each seal cavity 152, 153 may be adapted to receive therein one of the seal assemblies 89, 90, which are adapted to sealingly engage the relatively rotatable components of the track pin joint assembly 42. In other embodiments of the track pin joint assembly, other components (e.g., the bushing 82) may define suitable seal cavities.

[0078] The thrust rings 86, 87 may be adapted to limit the axial loads applied to the seal assemblies 89, 90, respectively. The seal assemblies 89, 90 are positioned radially outwardly from the thrust rings 86, 87 and provide a running seal between the outer link 48 and the inner link 46 and the bushing 82 to retain lubricant within the fluid reservoir 110.

[0079] In some embodiments, a track chain assembly in accordance with the principles of the present disclosure may include other components and have different arrangements. For example, in other embodiments, the track chain assembly may include a pin barrel assembly having sleeve bearings and other components, as shown and described in U.S. Patent Application Publication No. 2006 / 0284485, which is incorporated herein by reference in its entirety. Additionally, it is contemplated that a variety of track link designs may be used with the track pin assembly constructed in accordance with the principles of the present disclosure. For example, in an embodiment, the inner link and the outer link may include offset links having an S-shape, the configuration of which is different from Figure 2 and 3 the configuration shown therein, or may include straight links known to those skilled in the art.

[0080] Reference Figure 4, One of several possible embodiments according to the following principles of the present disclosure illustrates a track pin barrel assembly 175. The illustrated track pin barrel assembly 175 includes a track pin 180; a bushing 182; a first thrust ring 186 and a second thrust ring 187; a plurality of seal assemblies 189, 190, 191, 192; a first bearing member 194 and a second bearing member 195; and a first collar 197 and a second collar 198. The track pin barrel assembly 175 is arranged with the bushing 182 disposed between the first bearing member 194 and the second bearing member 195, and the bearing members are respectively disposed between the first collar 197 and the bushing 182 and between the second collar 198 and the bushing 182.

[0081] The track pin 180 defines a longitudinal axis LA. The bushing 182 and the first bearing member 194 and the second bearing member 195 are rotatably positioned about the track pin 180 such that the bushing 182 and the first bearing member 194 and the second bearing member 195 can rotate independently relative to the track pin 180 about the longitudinal axis LA. The first collar 197 and the second collar 198 are respectively positioned at the ends of the track pin 180 and press-fitted with the track pin 180 such that the first collar 197 and the second collar 198 are rotationally coupled with the track pin 180.

[0082] The first thrust ring 186 is disposed between the first collar 197 and the first bearing member 194 and is adapted to transmit an axial load therebetween. The second thrust ring 187 is similarly disposed between the second collar 198 and the second bearing member 196 and is adapted to transmit an axial load therebetween.

[0083] The components of the track pin barrel assembly 175 may define a plurality of annular seal grooves or cavities concentrically disposed about the longitudinal axis LA of the track pin 180. Each seal cavity may be adapted to receive one of the seal assemblies 189, 190, 191, 192 therein, and the seal assemblies are used to sealingly engage the relatively rotatable components of the track pin barrel assembly 175.

[0084] The illustrated track pin barrel assembly 175 includes four seal assemblies 189, 190, 191, 192. A pair of seal assemblies 189, 190 are respectively disposed between the bushing 182 and the first bearing member 194 and between the bushing 182 and the second bearing member 195. Another pair of seal assemblies 191, 192 are respectively disposed between the first bearing member 194 and the second bearing member 195 and between the first collar 197 and the second collar 198. The first collar 197 and the second collar 198 can be positioned relative to the ends of the track pin 180 such that the seal assemblies 189, 190, 191, 192 of the track pin barrel assembly 175 are compressively engaged between the corresponding adjacent components to sealingly contact the seal surfaces of the adjacent members, so as to form a seal that is impermeable to flowing fluid therebetween.

[0085] The illustrated track pin 180 includes a body 220 made of a steel alloy. In an embodiment, the steel alloy has a composition that includes iron and nitride forming elements. The body 220 is cylindrical with a solid interior and includes an outer nitrided surface 225 that is part of a composite layer 230 formed by nitriding the track pin 180 via a suitable FNC process. In an embodiment, the body 220 includes a solid interior such that the body 220 is substantially devoid of internal passages designed to act as fluid reservoirs for lubricant. By omitting an internal fluid reservoir within the track pin 180, in some embodiments, the diameter of the track pin can be reduced such that the volume of use required for the track pin 180 can be reduced relative to a similar track pin that includes a fluid reservoir defined therein. The spacing savings achievable with such embodiments can be used to reduce the overall size of the track pin barrel assembly 175 (and help achieve cost savings) and / or increase the size of associated components.

[0086] In an embodiment, the body 220 of the track pin 180 can be made of any suitable steel alloy discussed herein in connection with Figure 3 the track pin 80. For example, in an embodiment, the steel alloy making up the body 220 of the track pin 180 has a composition that includes iron, nitride forming elements, carbide forming elements, and silicon, and the steel alloy includes between 0.5 wt% and 4 wt% silicon. In an embodiment, the composition of the steel alloy making up the body 220 of the track pin 180 has a composition that includes between 0.5 wt% and 1.6 wt% manganese and between 0.2 wt% and 0.4 wt% carbon. Figure 4 The track pin 180 of Figure 3 can be similar in other respects to the track pin 80 of

[0087] Industrial applicability

[0088] From the foregoing discussion, the industrial utility of the embodiments of the track chain assembly and track pin described herein will be readily understood. At least one embodiment of the disclosed track pin can be used in a track chain assembly. At least one embodiment of the disclosed track pin can be used in the undercarriage of a track-type machine. One exemplary embodiment discloses a track pin having a nitrided body, where the body is made of a temper-resistant nitriding alloy and the body has been treated using ferritic nitrocarburizing (FNC) technology.

[0089] Compared to track pins made of similar materials but not subjected to nitriding in the form of the FNC technique, embodiments of track pins constructed in accordance with the principles of the present disclosure may exhibit excellent shear strength, fatigue strength, and anti-seizure properties. Embodiments of track pins constructed in accordance with the principles of the present disclosure may have improved anti-seizure properties such that sleeve bearings may be omitted from a track joint assembly including the track pin, thereby eliminating components and additional machining operations associated therewith. Embodiments of track pins constructed in accordance with the principles of the present disclosure may exhibit increased surface hardness, wear resistance, resistance to certain types of corrosion, and compressive surface stress, which will improve the fatigue resistance of the track pin as compared to track pins made of similar materials but not subjected to nitriding in the form of the FNC technique.

[0090] Embodiments of track pins and track chain assemblies in accordance with the principles of the present disclosure may find potential applications in any machine such as a track-type tractor employing a track-type chassis. Additionally, the present disclosure may be applicable to track chain assemblies where components are subject to significant wear. Such machines may include, but are not limited to, bulldozers, loaders, excavators, or any other on-road or off-road vehicle or stationary machine employing a track assembly as described herein.

[0091] It should be understood that the foregoing description provides examples of the disclosed systems and techniques. However, it is contemplated that other embodiments of the present disclosure may differ in detail from the foregoing examples. All references to the present disclosure or its examples are intended to refer to the specific examples being discussed at that time and are not intended to imply any limitation on the scope of the present disclosure more generally. All distinctions and disparaging language regarding certain features are intended to indicate that these features of interest are not preferred, but unless otherwise specified, these features are not entirely excluded from the scope of the present disclosure.

[0092] Unless otherwise indicated herein, the recitation of ranges of values herein is merely intended to be a shorthand method of referring separately to each individual value falling within the range, and each individual value is incorporated into the specification as if it were recited herein separately. All methods described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. A track pin (80, 180) for a track chain assembly (16), the track pin (80, 180) comprising: A body (120, 220) made of a steel alloy having a composition comprising iron, nitride-forming elements, carbide-forming elements, and silicon, the composition of the steel alloy comprising at least 0.5 wt% silicon; Wherein the bodies (120, 220) include a composite layer (130, 230) on their outer surfaces (125, 225), and the composite layer (130, 230) contains both Fe(C,N) microstructure and Fe4N microstructure formed therein by fer nitrocarburizing, and the composite layer (130, 230) contains at least 1 wt% carbon measured at 0.003 mm below the outer surface (125, 225) of the composite layer (130, 230), and wherein the composite layer (130, 230) has a hardness of at least 9 GPa and an elastic modulus of at least 190 GPa. 2-3 (C,N) microstructure and Fe4N microstructure, the composite layer (130, 230) contains at least 1 wt% carbon measured at 0.003 mm below the outer surface (125, 225) of the composite layer (130, 230), and wherein the composite layer (130, 230) has a hardness of at least 9 GPa and an elastic modulus of at least 190 GPa.

2. The track pin (80, 180) according to claim 1, wherein the composition of the steel alloy comprises: Carbon between 0.2 wt% and 0.4 wt%, Manganese between 0.5 wt% and 1.6 wt%, Silicon between 0.5 wt% and 4 wt%, Chromium up to 2.5 wt%, Vanadium up to 0.3 wt%, and Aluminum up to 0.3 wt%.

3. The track pin (80, 180) according to claim 1, wherein the composition of the steel alloy comprises: Carbon between 0.2 wt% and 0.4 wt%, Manganese between 0.5 wt% and 1.6 wt%, Silicon between 0.5 wt% and 2.0 wt%, Chromium between 0.4 wt% and 1.5 wt%, Vanadium between 0.03 wt% and 0.3 wt%, Aluminum between 0.07 wt% and 0.3 wt%, and The balance being iron.

4. The track pin (80, 180) according to claim 1, wherein the body (120, 220) of the track pin (80, 180) has a core hardness of at least R c 40 measured 0.5 mm below the composite layer (130, 230).

5. The track pin (80, 180) according to claim 1, wherein the composite layer (130, 230) comprises at least 0.5 wt% silicon.

6. The track pin (80, 180) according to claim 1 or claim 5, wherein the composite layer (130, 230) comprises at least 1 wt% nitrogen.

7. The track pin (80, 180) according to claim 6, wherein the composite layer (130, 230) comprises nitrogen and carbon in respective first weight amounts, and wherein the steel alloy of the body (120, 220) comprises nitrogen and carbon in respective second weight amounts, the respective first amount of each of nitrogen and carbon being greater than the respective second amount.

8. A track chain assembly (16) comprising: A track pin (80, 180) according to any one of claims 1 to 7, the track pin (80, 180) defining a longitudinal axis (LA); A bushing (82, 182) including an inner surface (142) defining a cylindrical bore (144), the bushing (82, 182) being coaxially positioned around the track pin (80, 180) such that the track pin (80, 180) extends through the cylindrical bore (144) of the bushing (82, 182), the bushing (82, 182) being rotatable relative to the track pin (80, 180) about the longitudinal axis (LA), wherein the inner surface (142) of the bushing (82, 182) is made of a bushing material different from the steel alloy of the body (120, 220) of the track pin (80, 180).

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