System and method for improving fatigue life of iron-based camshaft

Abstract

A method of casting a camshaft comprising iron includes determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft. The method includes casting the camshaft, including cooling the camshaft in a chiller based on a cooling rate profile. The method includes imparting the camshaft with a microstructure that includes carbide, ledeburite, pearlite, ausferrite, or a combination thereof.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 353,743, filed on June 20, 2022, the contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates generally to the field of camshafts used in internal combustion engine systems, fuel systems, and the like. background

[0003] An internal combustion engine includes at least one cylinder that receives fuel and air and burns the fuel to generate mechanical energy. The mechanical energy is collected via a piston that translates within the cylinder. An intake valve opens to allow the cylinder to be filled with air, and an exhaust valve opens to allow combustion gases to exit. The opening and closing of the valves is controlled by one or more camshafts. In some applications, the camshaft may experience rolling contact fatigue (RCF), which is a wear mechanism that occurs when the camshaft is subjected to rolling stresses. Overview

[0004] Embodiments described herein generally relate to systems and methods for providing improved fatigue (eg, rolling contact fatigue) life of iron-based camshafts.

[0005] At least one aspect of the present disclosure relates to a method of casting a camshaft comprising iron. The method includes determining a cooling rate profile based on the chemical composition of the camshaft and a target bearing life of the camshaft. The method also includes casting the camshaft, including cooling the camshaft in a chiller based on the cooling rate profile. The method still further includes imparting a microstructure comprising carbides and pearlite to the camshaft.

[0006] In some embodiments, the method includes isothermally quenching the camshaft to homogenize the pearlite. In some embodiments, the cooling rate profile includes a cooling rate that varies with time. In some embodiments, the cooling rate profile includes a cooling rate that is constant over time. In some embodiments, the cooling rate profile is also determined based on the geometry of the chiller, the size of the chiller, the wall thickness of the chiller, the mass of the camshaft, the thickness of the camshaft, the size of the camshaft, the target hardness of the camshaft, or a combination thereof. In some embodiments, cooling the camshaft reduces the amount of graphite nodules in the microstructure of the camshaft. In some embodiments, casting the camshaft also includes pouring molten iron into a mold before cooling the camshaft so that the cooled camshaft contains chilled ductile iron. In some embodiments, imparting a microstructure to the camshaft includes achieving the microstructure based on the chemical composition of the camshaft and cooling the camshaft according to the cooling rate profile.

[0007] At least one aspect of the present disclosure relates to a method of casting a camshaft comprising iron. The method includes determining a cooling rate profile based on the chemical composition of the camshaft and a target bearing life of the camshaft. The method includes casting the camshaft, including cooling the camshaft in a chiller based on the cooling rate profile. The method also includes imparting a microstructure to the camshaft including carbides and ledeburite. The method still further includes austempering the camshaft to treat the microstructure.

[0008] In some embodiments, the cooling rate profile includes a cooling rate that varies with time. In some embodiments, austempering the camshaft homogenizes the microstructure. In some embodiments, the microstructure also includes pearlite, and austempering the camshaft converts the pearlite into ausferrite. In some embodiments, cooling the camshaft includes treating the camshaft in a chiller at different temperatures over different time periods. In some embodiments, cooling the camshaft is also based on the wall thickness of the chiller. In some embodiments, casting the camshaft also includes pouring molten iron into a mold before cooling the camshaft. In some embodiments, imparting a microstructure to the camshaft includes achieving the microstructure based on the chemical composition of the camshaft and the cooling rate profile.

[0009] At least one aspect of the present disclosure relates to a method of casting a camshaft comprising iron. The method includes determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft. The method includes casting the camshaft, including cooling the camshaft in a chiller based on the cooling rate profile. The method also includes austempering the camshaft to impart a microstructure of the camshaft including carbides and ausferrite.

[0010] In some embodiments, the method still further comprises imparting to the camshaft a microstructure comprising carbides and pearlite. In some embodiments, austempering the camshaft homogenizes the pearlite in the microstructure to form ausferrite.

[0011] Those skilled in the art will appreciate that the summary is illustrative only and is not intended to be limiting in any way. Other aspects, inventive features and advantages of the apparatus and / or process described herein, as limited only by the claims, will become apparent in the detailed description set forth herein and in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The details of one or more embodiments are described in the accompanying drawings and the following description. Other features, aspects and advantages of the present disclosure will become apparent from the specification, drawings and claims, in which:

[0013] Figure 1 A schematic diagram of a casting system according to an embodiment is illustrated.

[0014] Figure 2 A casting system according to an embodiment is illustrated.

[0015] Figure 3 is a flow chart illustrating an exemplary method of casting a camshaft comprising iron.

[0016] Figure 4 is a photomicrograph of the microstructure of a chilled ductile iron sample according to an embodiment.

[0017] Figure 5 The microstructure of a chilled, austempered ductile iron sample is shown in accordance with an embodiment.

[0018] Fig. 6A is a table comparing the RCF life of differently chilled ductile iron samples according to an embodiment.

[0019] Figure 6B Comparison of implementation plans Fig. 6A A graph of the RCF life of differently chilled ductile iron samples is shown in FIG.

[0020] Figure 7 A graph showing cooling curves for different chiller wall thicknesses according to an embodiment.

[0021] Fig. 8A is a table comparing the RCF life of differently chilled ductile iron samples according to an embodiment.

[0022] Figure 8B Comparison of implementation plans Fig. 8A A graph of the RCF life of differently chilled ductile iron samples is shown in FIG.

[0023] Fig. 9A is a table comparing the RCF lives of chilled ductile iron and 1080 steel samples according to an embodiment.

[0024] Fig. 9B Comparison of implementation plans Fig. 9A A graph showing the RCF life of cast iron and 1080 steel samples.

[0025] Fig.10 A casting system according to an embodiment is illustrated.

[0026] Fig.11 Shown is a graph of temperature versus time for various locations of a casting system according to an embodiment.

[0027] Fig.12 Shown is a graph of temperature versus time for various locations of a casting system according to an embodiment.

[0028] Fig.13A is a photomicrograph of a chilled ductile iron sample subjected to spallation surface analysis according to an embodiment.

[0029] Fig. 13B is a photomicrograph of a chilled ductile iron sample subjected to spalling surface analysis according to an embodiment.

[0030] Fig. 13C is a photomicrograph of a chilled ductile iron sample subjected to spalling surface analysis according to an embodiment.

[0031] Fig.14 According to the embodiment, Figure 13A-13C A graph of the volume fraction of graphite and a graph of the average diameter of graphite in differently chilled ductile iron samples are shown in FIG.

[0032] Fig.15 According to the embodiment, Figure 13A-13C Graphs of subsurface cracking area and RCF life for differently chilled ductile iron samples are shown in FIG.

[0033] Fig.16A is a graph of hardness through depth versus depth for different chilled ductile iron samples according to an embodiment.

[0034] Fig. 16B is a plot of the depth hardness versus depth for three different improved CDI samples.

[0035] Fig.17A is a comparison of different chilled ductile iron samples according to an embodiment of the invention. Figure 17B-17E A diagram of the area fractions of different phases is shown in FIG.

[0036] Fig. 17B is a graph of the area fraction of carbides in differently chilled ductile iron samples according to an embodiment.

[0037] Fig. 17C is a graph of the area fraction of dendrites in different chilled ductile iron samples according to an embodiment.

[0038] Fig.17D is a graph of the area fraction of rod-shaped grown ledeburite in different chilled ductile iron samples according to an embodiment.

[0039] Fig.17E is a graph of the area fraction of lamellar-grown ledeburite in different chilled ductile iron samples according to an embodiment.

[0040] Fig.18 is a photomicrograph of the microstructure of a chilled ductile iron sample according to an embodiment.

[0041] It will be appreciated that for illustrative purposes, some or all of the drawings are schematic representations. The drawings are provided for the purpose of illustrating one or more embodiments, with the express understanding that these drawings will not be used to limit the scope or meaning of the claims. Details

[0042] The following is a more detailed description of various concepts related to methods, apparatuses, and systems for improving fatigue life of iron-based camshafts and implementations of these methods, apparatuses, and systems. The various concepts introduced above and discussed in more detail below can be implemented in any of a variety of ways, as the concepts described are not limited to any particular implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

[0043] I. Overview Internal combustion engines include camshafts that may experience rolling contact fatigue (RCF). Rolling contact fatigue may be caused by camshaft and follower spalling, Hertzian contact stresses and / or subsurface initiation. Steel is commonly used as a material for camshafts due to its hardness. However, camshafts made of steel (e.g., steel-based camshafts) may be more expensive than camshafts made of iron (e.g., iron-based camshafts).

[0044] Embodiments described herein relate to a method of casting a camshaft comprising iron. The method includes determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft. The method includes casting the camshaft, including cooling the camshaft in a chiller based on the cooling rate profile. The method includes imparting a microstructure to the camshaft including carbides and pearlite.

[0045] Embodiments described herein relate to a method of casting a camshaft comprising iron. The method includes determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft. The method includes casting the camshaft, including cooling the camshaft in a chiller based on the cooling rate profile. The method includes imparting a microstructure to the camshaft including carbides and ledeburite. The method includes austempering the camshaft to treat the microstructure.

[0046] Embodiments described herein relate to a method of casting a camshaft comprising iron. The method includes determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft. The method includes casting the camshaft, including cooling the camshaft in a chiller based on the cooling rate profile. The method includes austempering the camshaft to impart a microstructure of the camshaft comprising carbides and ausferrite.

[0047] The methods described herein provide an iron-based camshaft having improved rolling contact fatigue life compared to a steel-based camshaft or a conventional iron-based camshaft.The improved iron-based camshaft may be less expensive than a steel-based camshaft.

[0048] II. Exemplary Method of Casting a Camshaft Figure 1 A schematic diagram of a casting system 100 is illustrated. Figure 2 The casting system 100 is illustrated. The casting system 100 includes one or more castings 105 (e.g., chilled ductile iron castings, chilled austempered ductile iron castings, etc.). The composition of one or more castings 105 includes iron (Fe). One or more castings 105 may include carbon (C), chromium (Cr), copper (Cu), molybdenum (Mo) and / or nickel (Ni). For low alloy white cast iron, one or more castings 105 may include less than 5wt% of chromium, copper, molybdenum and nickel. For high alloy white cast iron, one or more castings 105 may include greater than 5wt% of chromium, copper, molybdenum and nickel.

[0049] The casting system 100 includes one or more chills 110. The one or more chills 110 surround the one or more castings 105. Each of the one or more chills 110 has a wall thickness 115. According to various embodiments, each of the one or more chills 110 can have a wall thickness 115 between 2 mm and 15 mm (e.g., 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 9.5 mm, 10 mm, 10.5 mm, 11 mm, 11.5 mm, 12 mm, 12.5 mm, 13 mm, 13.5 mm, 14 mm, 14.5 mm, or 15 mm).

[0050] The one or more chillers 110 may include a first chiller having a first wall thickness and a second chiller having a second wall thickness. The first wall thickness may be greater than the second wall thickness. The first chiller may provide a greater cooling rate than the second chiller. The one or more chillers 110 cool the one or more castings 105. For example, the one or more chillers 110 may cool the one or more castings 105 based on the chemical composition of the one or more castings 105. The one or more chillers 110 may cool the one or more castings 105 based on the target bearing life of the one or more castings 105. Each of the one or more chillers 110 has a cavity. Each of the one or more chillers 110 may have a geometry that produces a camshaft lobe.

[0051] Figure 3 A flow chart of an exemplary process 300 (e.g., method, procedure, etc.) for casting a camshaft containing iron (e.g., an iron-based camshaft, an iron-based camshaft lobe, etc.) is illustrated. The camshaft may be an engine camshaft or a fuel system camshaft. The camshaft may include chilled ductile iron (CDI) or chilled austempered ductile iron (CADI). Chilled ductile iron is formed by chilling or cooling molten iron. Chilled austempered ductile iron is formed by chilling molten iron to produce chilled ductile iron, and then austempering the chilled ductile iron to produce chilled austempered ductile iron. Process 300 may be used to form a camshaft, a camshaft lobe, a roller, or other vehicle components.

[0052] The process 300 begins at 305 by determining a cooling rate profile based on the chemical composition of the camshaft (e.g., the camshaft lobe) and the target bearing life of the camshaft. The cooling rate profile includes the cooling rate of the camshaft. The cooling rate can remain constant or vary over time. The cooling rate profile can be determined based on the geometry or size of one or more chillers 110, the wall thickness 115 of one or more chillers 110, the mass of the camshaft, the thickness of the camshaft, the size of the camshaft, and / or the target hardness of the camshaft. The cooling rate profile can be determined by the target microstructure of the camshaft.

[0053] For a given chemical composition of the camshaft, the cooling rate can vary. The camshaft can have a chemical composition similar to or the same as one or more castings 105. Each camshaft lobe can have a chemical composition similar to or the same as one or more castings 105. For example, the composition of the camshaft or each camshaft lobe includes iron. The composition of the camshaft or each camshaft lobe can include carbon, chromium, copper, molybdenum and / or nickel. For low alloy white cast iron, the camshaft can contain less than 5 wt% chromium, copper, molybdenum and nickel. For high alloy white cast iron, the camshaft can contain greater than 5 wt% chromium, copper, molybdenum and nickel.

[0054] The target bearing life of the camshaft includes the length of time the camshaft is expected to operate based on predetermined operating conditions or target operating conditions. Determining the cooling rate profile may include running a simulation based on desired or target properties of the camshaft. For example, the target properties of the camshaft may include a target bearing life of the camshaft. The simulation may be calibrated based on the properties and chemical composition of the camshaft.

[0055] The process 300 continues at 310 with casting a camshaft. Casting the camshaft includes cooling the camshaft in a chiller based on a cooling rate profile. For example, cooling the camshaft in a chiller based on the cooling rate profile may include cooling the camshaft in one or more chillers 110 based on the cooling rate profile. Casting the camshaft may include pouring molten iron having a chemical composition similar or identical to the one or more castings 105 into a mold to form the camshaft.

[0056] The molten iron may be cooled according to a cooling rate profile. For example, the molten iron may be cooled at a first temperature for a first time period. The molten iron may be cooled at a second temperature for a second time period. The molten iron may be cooled at a third temperature for a third time period. The cooling rate profile may include different temperatures and different time periods. For example, the cooling rate profile may include a first temperature, a second temperature, and a third temperature and a first time period, a second time period, and a third time period. The cooling rate profile may include additional temperatures and additional time periods. The cooling rate profile may include a series of temperature changes over time. Cooling the camshaft may reduce the presence of graphite nodules in the microstructure of the camshaft.

[0057] Process 300 continues to 315, imparting a camshaft microstructure. The microstructure (e.g., primary microstructure) includes phases including carbides, pearlite, and graphite, wherein the amount of each phase is measured by volume fraction or area fraction. The camshaft may include less than 1% (e.g., 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.95%, etc.) of graphite. The camshaft may include at least 50% (e.g., 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc.) of carbides. The camshaft may include an average of 50%-60% carbides. The camshaft may locally (e.g., a volume of the camshaft less than the entire volume of the camshaft) contain 70% carbides, while the remaining volume of the camshaft may contain pearlite (e.g., 49%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, etc.).

[0058] In some embodiments, reference Figure 17A-17E, the microstructure of the camshaft includes various combinations of carbides, dendrites (including primary austenite and / or spheroidal pearlite), graphite and / or ledeburite (including lamellar growth ledeburite and / or rod-shaped growth ledeburite) in various volume fractions / area fractions. In some embodiments, the camshaft contains at least 15% (by area fraction) (e.g., 15%, 20%, 25%, 30%, 35%, 40%, 45%, etc.) of lamellar growth ledeburite. In some embodiments, the camshaft contains at least 25% of lamellar growth ledeburite. In some embodiments, the camshaft contains less than 35% (by area fraction) (e.g., 30%, 25%, 20%, 15%, 10%, 5%, etc.) of carbides. In some embodiments, the camshaft contains less than 25% (e.g., 20%, 15%, 10%, 5%, etc.) of carbides. In some embodiments, the camshaft comprises less than 40% (by area fraction) (e.g., 35%, 30%, 25%, 20%, 15%, 10%, 5%, etc.) dendrites. In some embodiments, the camshaft comprises less than 30% (e.g., 25%, 20%, 15%, 10%, 5%, etc.) dendrites. In some embodiments, the camshaft comprises less than 0.05% (by volume fraction) (e.g., 0.04%, 0.035%, 0.03%, 0.025%, 0.02%, 0.015%, etc.) graphite. In some embodiments, the camshaft contains at least 25% lamellar growth ledeburite, less than 25% carbides, less than 30% dendrites, and less than 0.05% graphite, such as for an improved CDI sample with chromium cast in a chiller with a wall thickness of 5 mm (denoted by "I-C2") and an improved CDI sample without chromium cast in a chiller with a wall thickness of 10 mm (denoted by "B-C4"). In some embodiments, the I-C2 sample and the B-C4 sample exhibit a higher RCF life than the sample with a smaller wall thickness and without chromium (e.g., the sample denoted by "B-C1" as described below).

[0059] Imparting a camshaft microstructure may include achieving a microstructure of a given chemical composition of the camshaft by processing (e.g., cooling). For example, the manner in which the camshaft is cooled and the chemical composition of the camshaft may determine the microstructure of the camshaft. The microstructure may determine the RCF life or fatigue life of the camshaft (e.g., iron-based camshaft fatigue life, iron-based rolling contact fatigue life, rolling contact fatigue life, etc.).

[0060] According to various embodiments, the target bearing life of the camshaft corresponds to at least 2×10 6 Lifetime hours L 10 (For example, L 10 Life span, B 10lifespan). 10 A minimum expected life or bearing life associated with 90% reliability may be included. For example, a target bearing life for a camshaft may correspond to 2.35 × 10 6 Lifetime hours L 10 The target bearing life of the camshaft can correspond to at least 3×10 7 Lifetime hours L 10 For example, the target bearing life for a camshaft may correspond to 3.076 × 10 7 Lifetime hours L 10 .

[0061] According to various embodiments, the target bearing life of the camshaft can correspond to at least 3×10 7 Lifetime hours L 50 (For example, L 50 Life span, B 50 lifespan). 50 The life can include mean life or bearing life associated with 50% reliability. For example, a target bearing life for a camshaft may correspond to 3.6 × 10 7 Lifetime hours L 50 The target bearing life of the camshaft can correspond to at least 2×10 8 Lifetime hours L 50 For example, the target bearing life for a camshaft may correspond to 2.59 × 10 8 Lifetime hours L 50 .

[0062] In some embodiments, process 300 continues to 320, austempering the camshaft. Austempering the camshaft homogenizes the pearlite contained in the microstructure of the camshaft. Austempering can improve the RCF life of the chilled ductile iron. Austempering can convert pearlite into ausferrite. Austempering can harden the camshaft and reduce the hardness variation between different phases of the camshaft. Austempering can improve the wear resistance and fatigue properties of the camshaft. The austempering process can also harden the chilled ductile iron. The austempering process can also refine and homogenize the microstructure of the chilled ductile iron, thereby producing chilled austempered ductile iron.

[0063] Figure 4A micrograph 400 of the microstructure of chilled ductile iron is illustrated. The microstructure of the chilled ductile iron includes carbides 405 and pearlite 410. The carbides 405 are represented by dark phases and the pearlite 410 is represented by light phases. The microstructure of the chilled ductile iron may include graphite nodules 415. The graphite nodules 415 may be associated with a failure mode (e.g., cracking) of the camshaft. A camshaft or camshaft lobe may be made of such chilled ductile iron. The camshaft or camshaft lobe may have a microstructure including carbides 405 and pearlite 410. A camshaft or camshaft lobe made of chilled ductile iron may have an improved RCF compared to a camshaft or camshaft lobe made of chilled iron or austempered iron. A camshaft or camshaft lobe made of chilled ductile iron may have a similar RCF compared to a camshaft or camshaft lobe made of steel. Camshafts or camshaft lobes made from chilled ductile iron can provide wear resistance.

[0064] Figure 5 The microstructure of a chilled austempered ductile iron is illustrated. A camshaft or camshaft lobe may be made of such a chilled austempered ductile iron. The camshaft or camshaft lobe may have a microstructure including carbides 405 and pearlite 410. A camshaft or camshaft lobe made of chilled austempered ductile iron may have an improved RCF compared to a camshaft or camshaft lobe made of chilled iron or austempered iron. A camshaft or camshaft lobe made of chilled austempered ductile iron may have a similar RCF compared to a camshaft or camshaft lobe made of steel. A camshaft or camshaft lobe made of chilled austempered ductile iron may provide wear resistance.

[0065] Fig. 6A A table 600 comparing RCF life of differently chilled ductile iron samples is illustrated. The differently chilled ductile iron samples include a baseline CDI, an improved CDI without chromium cast in a chiller with a wall thickness of 2.5 mm (denoted by "2.5 No Cr"), and an improved CDI without chromium cast in a chiller with a wall thickness of 5 mm (denoted by "5 No Cr"). Testing was performed at 3.9 GPa using smooth ball bearings. The CDI samples may correspond to camshaft lobes.

[0066] The target bearing life for the baseline CDI may correspond to 3.3 × 10 5 Lifetime hours L 10 The target bearing life for the baseline CDI may correspond to 1.4 × 10 7 Lifetime hours L 50The target bearing life of a chromium-free CDI cast in a chiller with a wall thickness of 2.5 mm can correspond to 2.35 × 10 6 Lifetime hours L 10 The target bearing life of a chromium-free CDI cast in a chiller with a wall thickness of 2.5 mm can correspond to 3.6 × 10 7 Lifetime hours L 50 The target bearing life of a chromium-free CDI cast in a chiller with a wall thickness of 5 mm can correspond to 3.076 × 10 7 Lifetime hours L 10 The target bearing life of a chromium-free CDI cast in a chiller with a wall thickness of 5 mm can correspond to 2.59 × 10 8 Lifetime hours L 50 .

[0067] Figure 6B A graph 650 comparing the RCF lives of differently chilled ductile iron samples is illustrated. Graph 650 includes the differently chilled ductile iron samples illustrated in table 600. The differently chilled ductile iron samples include a baseline CDI, an improved CDI without chromium cast in a chiller with a wall thickness of 2.5 mm (denoted by "2.5 Cr-free" or "B-C1" as described below), and an improved CDI without chromium cast in a chiller with a wall thickness of 5 mm (denoted by "5 Cr-free" or "B-C2" as described below). The RCF lives of the differently chilled ductile iron samples are plotted as a Weibull distribution using maximum likelihood estimation.

[0068] Figure 7 Graph 700 illustrates cooling curves for different chiller wall thicknesses. The cooling curves may represent cooling rate profiles. The 2.5 mm curve represents a sample or casting cooled by a chiller having a wall thickness of 2.5 mm. The 5 mm curve represents a sample or casting cooled by a chiller having a wall thickness of 5 mm. The 7.5 mm curve represents a sample or casting cooled by a chiller having a wall thickness of 7.5 mm. The 10 mm curve represents a sample or casting cooled by a chiller having a wall thickness of 10 mm.

[0069] The cooling rate varies with the solidification time. The cooling rate profile may include different cooling rates or varying cooling rates. The cooling rate profile may include a constant or time-varying cooling rate. The cooling rate profile may be determined based on the geometry or size of one or more chillers 110, the wall thickness 115 of one or more chillers 110, the mass of the camshaft, the thickness of the camshaft, the size of the camshaft, and / or the target hardness of the camshaft. The cooling rate profile may be determined by the target microstructure of the camshaft. The cooling rate may vary for a given chemical composition of the sample.

[0070] Fig. 8A Table 800 comparing the RCF life of ductile iron samples of different chilling is illustrated. The ductile iron samples of different chilling include a baseline CDI, an improved CDI without chromium cast in a chiller with a wall thickness of 2.5 mm (represented by "B-C1"), an improved CDI without chromium cast in a chiller with a wall thickness of 5 mm (represented by "B-C2"), and an improved CDI containing chromium cast in a chiller with a wall thickness of 5 mm (represented by "I-C2"). In some embodiments, the amount of chromium in the I-C2 sample has a range of 0.5 wt% to 1 wt%. Tests were performed at 3.6 GPa using smooth ball bearings. The CDI samples may correspond to camshaft lobes.

[0071] The target bearing life for the baseline CDI may correspond to 3.3 × 10 5 Lifespan hours B 10 The target bearing life for the baseline CDI may correspond to 1.4 × 10 7 Lifespan hours B 50 The target bearing life for a chromium-free CDI (“B-C1”) cast in a chiller with a wall thickness of 2.5 mm can correspond to 2.35×10 6 Lifespan hours B 10 The target bearing life of a chromium-free CDI cast in a chiller with a wall thickness of 2.5 mm can correspond to 3.6 × 10 7 Lifespan hours B 50 The target bearing life for a chromium-free CDI (“B-C2”) cast in a chiller with a wall thickness of 5 mm can correspond to 3.07×10 7 Lifespan hours B 10 The target bearing life of a chromium-free CDI cast in a chiller with a wall thickness of 5 mm can correspond to 2.59 × 10 8 Lifespan hours B 50The target bearing life for a chromium-containing CDI (“I-C2”) cast in a chiller with a wall thickness of 5 mm can correspond to 1.48×10 8 Lifespan hours B 10 The target bearing life of a chromium-containing CDI cast in a chiller with a wall thickness of 5 mm can correspond to 5.13 × 10 8 Lifespan hours B 50 .

[0072] Figure 8B A graph 850 comparing the RCF life of ductile iron samples of different chills is illustrated. Graph 850 includes the ductile iron samples of different chills illustrated in table 800. The ductile iron samples of different chills include a baseline CDI, an improved CDI without chromium cast in a chiller with a wall thickness of 2.5 mm ("B-C1"), an improved CDI without chromium cast in a chiller with a wall thickness of 5 mm ("B-C2"), and an improved CDI with chromium cast in a chiller with a wall thickness of 5 mm ("I-C2"). The RCF life of the ductile iron samples of different chills is plotted with a Weibull distribution using maximum likelihood estimation.

[0073] Fig. 9A Table 900 comparing RCF life of chilled ductile iron and 1080 steel samples is illustrated. The chilled ductile iron samples may include an improved CDI (denoted by "B-C4") without chromium cast in a chiller with a wall thickness of 10 mm. The 1080 steel is denoted by "IH 1080". The tests were conducted at 3.6 GPa using a rough ball bearing. The samples may correspond to camshaft lobes.

[0074] The target bearing life of cast iron can correspond to 7.97×10 of a rough ball bearing. 6 Lifespan hours B 10 The target bearing life for cast iron may correspond to 3×10 of a rough ball bearing. 7 Lifespan hours B 50 The target bearing life of 1080 steel can correspond to 1.52×10 7 Lifespan hours B 10 The target bearing life for cast iron may correspond to 5.0 × 10 7 Lifespan hours B 50 .

[0075] Fig. 9B A graph 950 comparing the RCF lives of cast iron and 1080 steel samples is illustrated. Graph 950 includes the cast iron and 1080 steel samples illustrated in table 900. The RCF lives of the cast iron and 1080 steel samples were plotted as a Weibull distribution using least squares estimation.

[0076] Fig.10 The casting system 100 according to the embodiment is illustrated. The casting system 100 may include one or more risers 1005. For example, the casting system 100 includes a first riser (riser 1), a second riser (riser 2), a third riser (riser 3) and a fourth riser (riser 4). The casting system 100 may include a sprue well 1010. The casting system 100 may include one or more cavities. For example, the casting system 100 includes a first cavity (cavity 1), a second cavity (cavity 2), a third cavity (cavity 3) and a fourth cavity (cavity 4). The first cavity has a wall thickness of 2.5 mm. The second cavity has a wall thickness of 5 mm. The third cavity has a wall thickness of 7.5 mm. The fourth cavity has a wall thickness of 10 mm.

[0077] Fig.11 A graph 1100 of temperature versus time at various locations of the casting system 100 is shown. One or more thermocouples may be located at various locations of the casting system 100. The temperature of a thermocouple located in the gate well 1010 is plotted at various points in time. The temperature of a thermocouple located in the first riser is plotted at various points in time. The temperature of a thermocouple located in the second riser is plotted at various points in time. The temperature of a thermocouple located in the fourth riser is plotted at various points in time.

[0078] Fig.12 A graph 1200 of temperature versus time at various locations of the casting system 100 is shown. The temperature of a thermocouple located at the bottom of a first chamber is plotted at various points in time. The temperature of a thermocouple located at the top of a second chamber is plotted at various points in time. The temperature of a thermocouple located at the bottom of a third chamber is plotted at various points in time. The temperature of a thermocouple located at the top of a fourth chamber is plotted at various points in time.

[0079] Figure 13A-Figure 18 Various test results and analyses are presented in relation to improved CDI samples including B-C1, B-C2, I-C2 and B-C4, which were obtained by Figure 7 For example, the B-C1 sample was cooled according to the cooling curve corresponding to a chiller with a wall thickness of 2.5 mm; the B-C2 and I-C2 samples were cooled according to the cooling curve corresponding to a chiller with a wall thickness of 5 mm; and the B-C4 sample was cooled according to the cooling curve corresponding to a chiller with a wall thickness of 10 mm.

[0080] Figure 13A-13C Three-dimensional micrographs of three improved CDI samples, each subjected to exfoliation surface analysis, are shown. For example, micrographs may be obtained by X-ray microscopy (XRM). Fig.13ACorresponding to the improved CDI sample without chromium cast in a chiller with a wall thickness of 2.5 mm ("B-C1"), Fig. 13B corresponds to the improved CDI sample without chromium cast in a chiller with a wall thickness of 5 mm ("B-C2"), and Fig. 13C Corresponds to the chromium-containing improved CDI sample ("I-C2") cast in a chiller with a wall thickness of 5 mm. Analysis and comparison based on characteristics Figure 13A-13C The improved CDI sample shown in FIG. 5 includes the size and volume fraction of graphite nodules (eg, graphite) near the spalling, the area of ​​subsurface cracking caused by the spalling, and the RCF life.

[0081] Fig.14 A graph 1400 showing the variation in volume fraction (in %) of graphite nodules between different improved CDI samples including B-C1, B-C2, and I-C2, and a graph 1450 showing the variation in average diameter of graphite nodules between different samples near the exfoliation produced during the exfoliation surface analysis. Figure 13A-13C The volume fraction and average diameter of graphite spheres were calculated from the CT images of the graphite spheres. It should be noted that due to the limitation of the scanning resolution of the CT images, the graphite spheres with submicron size were Fig.14 1450 shown in FIG.

[0082] As shown in graph 1450, all three samples include graphite nodules having substantially similar or identical average sizes near the spalling. For example, the average diameter of the graphite nodules varies from about 0.007 mm (or 7 μm) to about 0.01 mm (or 10 μm) between the different samples. As shown in graph 1400, the volume fraction of graphite nodules in the B-C1 sample is significantly higher than that of the B-C2 sample, which has a similar volume fraction to the I-C2 sample. For example, the difference in the volume fraction of graphite nodules between the B-C1 sample and the B-C2 sample is about 0.2%, while the difference in the volume fraction of graphite nodules between the B-C2 sample and the I-C2 sample is about 0.025%, wherein both the B-C2 sample and the I-C2 sample include less than 0.05% graphite nodules.

[0083] In addition, the changes in the volume fraction of graphite nodules between the B-C1 sample, the B-C2 sample, and the I-C2 sample are generally opposite to the changes in the RCF life of the same samples, e.g. Fig. 8A and Figure 8B For example, the B-C1 sample with the highest volume fraction of graphite nodules has the shortest RCF life (e.g., B 10 life), while the I-C2 sample with the lowest volume fraction of graphite nodules has the longest RCF life (e.g., B 10 life).

[0084] Fig.15 A graph 1500 showing the variation of subsurface cracking area between different improved CDI samples including B-C1, B-C2 and I-C2, and a graph 1550 showing the variation of RCF life between different samples are shown. As shown in graph 1500, the B-C2 sample exhibits a lower subsurface cracking area than the B-C1 sample, which does not contain chromium and is cast in a chiller with a different wall thickness. In addition, the I-C2 sample containing chromium cast in a chiller with the same wall thickness as the B-C2 sample exhibits a lower subsurface cracking area than the B-C2 sample. As shown in graph 1550, the variation of RCF life between the three different samples exhibits a trend opposite to that of graph 1500. For example, the I-C2 sample with the lowest subsurface cracking area has the highest RCF life, and the B-C1 sample with the highest subsurface cracking area has the lowest RCF life (see also Fig. 8A and Figure 8B ).

[0085] Fig.16A A graph 1600 comparing the hardness (e.g., Vickers hardness or HV) versus depth of three different improved CDI samples including B-C1, B-C2, and B-C4, all of which are chromium-free and cast in a chiller with different wall thicknesses as described in detail above, is shown. The data points of graph 1600 were obtained by conducting a hardness test (e.g., Vickers hardness test) under an applied load of HV 500 gf according to ASTM Standard E92. The average hardness (in HV) was measured from the surface (i.e., 0 mm depth) to a depth of 2 mm (in the finished camshaft).

[0086] Fig. 16B A graph 1650 comparing the hardness (e.g., HV) versus depth of three different improved CDI samples including B-C1, B-C2, and B-C4 is shown. Similar to graph 1600, the average hardness in graph 1650 is measured from the surface (i.e., 0 mm depth) to a depth of 2 mm (in the finished camshaft). However, unlike graph 1600, the data points of graph 1650 are obtained by conducting a hardness test under an applied load of HV 100 gf in accordance with ASTM Standard E92. Fig.16A and Fig. 16B The error bars shown in each correspond to the 95% confidence interval (CI).

[0087] As shown in both Figures 1600 and 1650, the hardness relative to the measured depth (e.g., depth hardness) is arranged from lowest to highest in the following order: B-C4 sample, B-C2 sample, and B-C1 sample. Specifically, the B-C4 sample has an average hardness of a minimum of 700 HV measured from the surface to the maximum depth (e.g., 2 mm), with no measured values ​​less than 600 HV. In contrast, when subjected to the same hardness test and the same applied load, the I-C2 sample (not shown in Figures 1600 and 1650) has an average hardness of a minimum of 600 HV, with no measured values ​​less than 550 HV.

[0088] The surface hardness (e.g., in Rockwell Hardness C scale or HRC) of the B-C4 sample and the I-C2 sample was also compared. The surface hardness was measured by performing a hardness test (e.g., Rockwell hardness test) according to ASTM Standard E18. Specifically, the surface hardness of the B-C4 sample was a minimum of 57 HRC, and the surface hardness of the I-C2 sample was a minimum of 55 HRC.

[0089] Fig.17A A graph 1700 is shown comparing the area fractions (in %) of various microstructural phases (e.g., phases) present in different improved CDI samples including B-C1, B-C2, I-C2, and B-C4 after performing exfoliation surface analysis. Each of the samples includes at least four different phases, such as a primary carbide phase (e.g., carbide; "C") 1702; a dendrite phase (e.g., dendrite; "D") 1704, which includes a primary austenite phase (e.g., austenite) and / or a spherical pearlite phase (e.g., pearlite); a rod-shaped growth ledeburite phase (e.g., rod-shaped growth ledeburite; "R") 1706; and a lamellar growth ledeburite phase (e.g., lamellar growth ledeburite; "L") 1708.

[0090] As shown, as the chiller wall thickness increases, the amount (i.e., area fraction) of the primary carbide phase 1702 generally decreases, and the amount of the lamellar growth ledeburite phase 1708 generally increases. For example, the I-C2 sample (with a 5 mm chiller wall thickness) includes less than 25% of the primary carbide phase 1702 but more than 25% of the lamellar growth ledeburite phase 1708, while the B-C4 sample (with a 10 mm chiller wall thickness) includes less than 15% of the primary carbide phase 1702 and more than 40% of the lamellar growth ledeburite phase 1708.

[0091] In addition, Figure 8A-B and Figure 9A-9B, the decrease in the amount of the primary carbide phase 1702 and the increase in the amount of the lamellar growth ledeburite phase 1708 indicate a sample with a relatively high RCF life. For example, the B-C2 sample, the I-C2 sample, and the B-C4 sample each include less primary carbide phase 1702 (e.g., less than 30%, such as less than 30%) compared to the B-C1 sample having the lowest RCF life. Fig.17A ) and a more layered growth ledeburite phase 1708 (e.g., greater than 15%, such as Fig.17A ).

[0092] In some embodiments, the I-C2 sample and the B-C4 sample have similar amounts of dendrite phase 1704, such as between 25% and 30%. In some embodiments, both the I-C2 sample and the B-C4 sample also include graphite nodules, although the amount (e.g., volume fraction) of graphite nodules in each sample is relatively lower than that in the example of FIG. Fig.17A For example, for the I-C2 sample and the B-C4 sample, the amount of graphite nodules is less than 0.05% and less than 0.03%, respectively.

[0093] Figure 17B-17E A series of graphs are shown, each comparing the area fraction of each microstructural phase described in graph 1700 for the B-C1 sample, the B-C2 sample, the I-C2 sample, and the B-C4 sample. For example, Fig. 17B Graph 1720 compares the area fractions of the primary carbide phase 1702; Fig. 17C Graph 1740 compares the area fraction of the dendrite phase 1704; Fig.17D Graph 1760 compares the area fraction of rod-like growth ledeburite phase 1706; and Fig.17E Graph 1780 compares the area fraction of the layered growth ledeburite phase 1708. Fig. 17B and Fig.17E As shown in FIG. 1 , the amount of the lamellar growth ledeburite phase 1708 generally varies inversely with the amount of the primary carbide phase 1702 in the sample. In addition, the amount of the lamellar growth ledeburite phase 1708 generally varies in a similar trend among the samples, i.e., samples (e.g., I-C2 and B-C4) having a larger amount of the lamellar growth ledeburite phase 1708 exhibit a longer RCF life.

[0094] Fig.181800 is a micrograph showing the microstructural phase of the B-C1 sample after undergoing the exfoliation surface analysis provided herein. As shown, the sample includes a surface 1810 and an exfoliation 1820 below the surface 1810. The sample includes a primary carbide phase 1830 near the exfoliation 1820, a primary austenite (e.g., dendrite) phase 1840, a lamellar growth ledeburite phase 1850, and a rod-shaped growth ledeburite phase 1860. Figure 17A-17E and Fig.18 The presence and relative amounts of the different phases described in Figure 7 The cooling curves presented in are generated by the manner in which the various samples were cooled, and can be further correlated to one or more material properties of the samples presented herein, such as hardness (both deep and surface hardness).

[0095] III. Configuration of the Exemplary Embodiments Although this specification contains many specific implementation details, these should not be interpreted as limitations on the scope of the content that can be claimed, but should be interpreted as descriptions of features that are unique to specific implementations. Certain features described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. On the contrary, the various features described in the context of a single implementation can also be implemented individually or in any suitable sub-combination in multiple implementations. Moreover, although features can be described as working in certain combinations and even initially claimed as such, one or more features from the claimed combination can be deleted from the combination in some cases, and the claimed combination can involve a sub-combination or a deformation of the sub-combination.

[0096] As utilized herein, the term "substantially" and similar terms are intended to have a broad meaning consistent with common and accepted usage by those of ordinary skill in the art to which the subject matter of the present disclosure belongs. Those skilled in the art who review the present disclosure should understand that these terms are intended to allow description of certain features described and claimed without limiting the scope of these features to the precise numerical ranges provided. Therefore, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations to the subject matter described and claimed are considered to be within the scope of the present invention as described in the appended claims.

[0097] As used herein, the terms "coupled," "connected," and the like mean the joining of two components to one another, directly or indirectly. Such joining may be fixed (e.g., permanent) or movable (e.g., removable or releasable). Such joining may be achieved by the two components, or the two components and any additional intermediate components, being integrally formed as a single unitary body with one another, or by the two components, or the two components and any additional intermediate components, being attached to one another.

[0098] As used herein, the terms "fluid coupling," "fluid communication," and similar terms mean that two components or objects have a path formed between the two components or objects through which a fluid (e.g., exhaust, water, air, gaseous reductant, gaseous ammonia, etc.) can flow, with or without intervening components or objects. Examples of fluid couplings or configurations for achieving fluid communication may include tubes, channels, or any other suitable components for achieving the flow of a fluid from one component or object to another component or object.

[0099] It is important to note that the construction and arrangement of the systems shown in the various exemplary embodiments are illustrative and non-restrictive in nature. All changes and modifications within the spirit and / or scope of the described embodiments need to be protected. It should be understood that some features may not be necessary, and embodiments lacking various features may be considered to be within the scope of the present application, which is defined by the appended claims. When the language "a portion" is used, the item may include a portion and / or the entire item unless explicitly stated to the contrary.

[0100] In addition, the term "or" is used in its inclusive sense (rather than in its exclusive sense), such that when used, for example, to connect a list of elements, the term "or" means one, some, or all of the elements in the list. Unless explicitly stated otherwise, connective language such as the phrase "at least one of X, Y, and Z" is understood in the context to generally convey that an item, term, etc. can be X; Y; Z; X and Y; X and Z; Y and Z; or X, Y, and Z (i.e., any combination of X, Y, and Z). Therefore, unless otherwise specified, such connective language is generally not intended to imply that certain embodiments require that at least one X, at least one Y, and at least one Z are each present.

[0101] In addition, the term "or" is used in its inclusive sense (rather than in its exclusive sense), such that when used, for example, to connect a list of elements, the term "or" means one, some, or all of the elements in the list. Unless explicitly stated otherwise, connective language such as the phrase "at least one of X, Y, and Z" is understood in the context to generally convey that an item, term, etc. can be X; Y; Z; X and Y; X and Z; Y and Z; or X, Y, and Z (i.e., any combination of X, Y, and Z). Therefore, unless otherwise specified, such connective language is generally not intended to imply that certain embodiments require that at least one X, at least one Y, and at least one Z are each present.

Claims

1. A method of casting a camshaft comprising iron, comprising: determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft; Casting the camshaft includes cooling the camshaft in a chiller based on the cooling rate profile; and The camshaft is imparted with a microstructure comprising carbides and pearlite. 2 . The method of claim 1 , further comprising isothermally quenching the camshaft to homogenize the pearlite. The method of claim 1 , wherein the cooling rate profile comprises a cooling rate that varies over time. The method of claim 1 , wherein the cooling rate profile comprises a cooling rate that is constant over time.

5. The method of claim 1 , wherein the cooling rate profile is further determined based on the geometry of the chiller, the size of the chiller, the wall thickness of the chiller, the mass of the camshaft, the thickness of the camshaft, the size of the camshaft, the target hardness of the camshaft, or a combination thereof.

6. The method of claim 1, wherein cooling the camshaft reduces an amount of graphite nodules in a microstructure of the camshaft.

7. The method of claim 1, wherein casting the camshaft further comprises pouring molten iron into a mold prior to cooling the camshaft such that the cooled camshaft comprises chilled ductile iron. 8 . The method of claim 1 , wherein imparting the microstructure to the camshaft comprises achieving the microstructure based on a chemical composition of the camshaft and cooling the camshaft according to the cooling rate profile.

9. A method of casting a camshaft comprising iron, comprising: determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft; casting the camshaft includes cooling the camshaft in a chiller based on the cooling rate profile; imparting to the camshaft a microstructure comprising carbides and ledeburite; and The camshaft is austempered to treat the microstructure.

10. The method of claim 9, wherein the cooling rate profile comprises a cooling rate that varies with time.

11. The method of claim 9, wherein imparting the microstructure to the camshaft produces a first amount of carbides and a second amount of ledeburite, the second amount being greater than the first amount.

12. The method of claim 9, wherein austempering the camshaft homogenizes the microstructure.

13. The method of claim 12, wherein austempering the camshaft transforms pearlite in the microstructure to ausferrite.

14. The method of claim 9, wherein cooling the camshaft comprises subjecting the camshaft to different temperatures in the chiller for different time periods.

15. The method of claim 9, wherein cooling the camshaft is further based on a wall thickness of the chiller.

16. The method of claim 9, wherein casting the camshaft further comprises pouring molten iron into a mold prior to cooling the camshaft.

17. The method of claim 9, wherein imparting the microstructure to the camshaft comprises achieving the microstructure based on a chemical composition of the camshaft and the cooling rate profile.

18. A method of casting a camshaft comprising iron, comprising: determining a cooling rate profile based on a chemical composition of the camshaft and a target bearing life of the camshaft; casting the camshaft includes cooling the camshaft in a chiller based on the cooling rate profile; as well as The camshaft is austempered to impart to the camshaft a microstructure comprising carbides and ausferrite.

19. The method of claim 18, further comprising imparting to the camshaft a microstructure comprising carbides and pearlite.

20. The method of claim 19, wherein austempering the camshaft homogenizes pearlite in the microstructure to form the ausferrite.

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