CN111334656A

CN111334656A - Method for thermal processing with a gradient temperature profile

Info

Publication number: CN111334656A
Application number: CN201910490066.6A
Authority: CN
Inventors: H·李; D·J·威尔逊; 王良; G·A·德格雷斯
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2018-12-19
Filing date: 2019-06-05
Publication date: 2020-06-26
Anticipated expiration: 2039-06-05
Also published as: US20200199704A1; CN111334656B; DE102019115659A1

Abstract

The invention provides a method for performing heat treatment by using a gradient temperature profile. The present invention relates to a method for heat treating a crankshaft or other workpiece of a vehicle propulsion system, the method comprising heating at least a portion of the crankshaft to form a graduated temperature profile. The temperature profile has a temperature that gradually decreases from the surface to the core of the crankshaft. The temperature profile includes a midpoint temperature at a midpoint between the surface and an innermost portion of the core that is at least 50% of the surface temperature measured on a celsius scale. The surface temperature is within the transition range of the crankshaft material. The method also includes quenching the surface of the crankshaft journal. The material of the crankshaft is preferably a carbon steel alloy having a DI of less than 1.7 and having greater than 0.3 wt% carbon.

Description

Method for thermal processing with a gradient temperature profile

Technical Field

The present disclosure relates to a system and method for heat treating a crankshaft of a vehicle propulsion system.

Background

The crankshaft of the engine converts the reciprocating linear movement of the piston into rotational movement about a longitudinal axis to provide torque to propel a vehicle (such as, but not limited to, a train, a boat, an airplane, or an automobile). The crankshaft is an important part of the engine and is the starting point for engine design.

The crankshaft includes at least one crankpin bearing journal offset from the longitudinal axis, to which the reciprocating piston is attached by a connecting rod. The force applied to the crankshaft from the piston through the offset connection between the piston and the crankshaft generates a torque in the crankshaft that rotates the crankshaft about a longitudinal axis, which is the axis of rotation. The crankshaft further includes at least one main bearing journal disposed concentrically about the longitudinal axis. The crankshaft is secured to the engine block at the main bearing journals. The bearings are disposed around the main bearing journals between the crankshaft and the engine block.

The crankshaft pin and main bearing journal surfaces are typically hardened to enable handling of loads and wear. One method of hardening is inductively heating and then quenching to harden the crankshaft journal surface. With induction heating/hardening, a high-frequency alternating current is used to induce eddy currents in the surface region of the workpiece to be hardened. These eddy currents cause joule heating that causes the workpiece to heat rapidly to a certain temperature. Hardening is then achieved by rapid quenching.

Induction hardening of crankshafts has created problems in the past. One problem is that when induction hardening increases hardness and strength, residual stress is generated with volume growth of phase transformation due to hardening. When these residual stress components are combined with the working stresses, they pose an adverse risk of promoting premature fatigue failure in the underlying surface between the hardened surface layer and the unhardened core. Residual stresses are the result of temperature changes in the heating and cooling of the object and volume changes in the hardening due to specific volume differences between the original and new phases formed in the steel. If the underlying surface material is subjected to significant stress, the material may develop cracks that can propagate and cause failure of the crankshaft.

Conventional attempts to alleviate or reduce residual tensile stresses caused by induction hardening have included preheating and/or post-hardening (e.g., high temperature) tempering the entire crankshaft in an oven or furnace. However, these conventional methods have many challenges, including cost, time, and marginally effective results.

Disclosure of Invention

The present disclosure provides a method of hardening that utilizes induction heating to produce a gradual temperature profile within a workpiece prior to quenching. This gradual profile results in a more evenly distributed tensile stress across the workpiece rather than concentrating the tensile stress near the underlying surface between the hardened surface and the unhardened core.

In one form, which may be combined with or separate from other forms disclosed herein, a method for heat treating a crankshaft of a vehicle propulsion system is provided. The crankshaft is preferably formed of a crankshaft steel alloy. The method includes heating at least a portion of a crankshaft to form a temperature profile having a surface temperature at a surface of the crankshaft. The temperature profile of the crankshaft has a temperature that gradually becomes lower from the surface of the crankshaft to the core. The temperature profile includes a midpoint temperature at a midpoint between the surface and the innermost portion of the core. The midpoint temperature is at least 50% of the surface temperature as measured on the celsius scale. The surface temperature is within the transformation range of the crankshaft steel alloy. The method also includes quenching the surface of the crankshaft.

In another form, which may be combined with or separate from other forms disclosed herein, a method for forming a crankshaft of a vehicle propulsion system is provided. The method includes forming a crankshaft, preferably from a crankshaft steel alloy, and forming a circular bearing journal surface around the crankshaft. The method also includes applying a series of induction heating pulses to the crankshaft until the crankshaft has a gradual temperature profile extending perpendicularly from the circular bearing journal surface to an innermost portion of a core of the crankshaft. The ramp temperature profile includes a surface temperature at the surface of the circular bearing journal that is within the transformation range of the crankshaft steel alloy. The ramp temperature profile also includes a midpoint temperature at a midpoint between the circular bearing journal surface and the innermost portion of the wick. The midpoint temperature is at least 50% of the surface temperature. The method includes quenching the circular bearing journal surface to a temperature below the transition temperature to harden the circular bearing surface.

In yet another form, which may be combined with or separate from the other forms disclosed herein, a method of induction hardening a workpiece is provided. The method includes providing a workpiece formed of a workpiece material and having an outer surface. The method also includes applying a series of induction heating pulses to the workpiece until the workpiece has a gradual temperature profile extending perpendicularly from an outer surface of the workpiece to an inner portion of the workpiece. The graded temperature profile includes a surface temperature at the outer surface, wherein the surface temperature is within a transition range of the workpiece material. The gradual temperature profile includes a midpoint temperature at a midpoint between the outer surface and the inner component. The midpoint temperature is at least 50% of the surface temperature. The method also includes quenching the outer surface to a temperature below the transition temperature to harden the outer surface.

Additional features may be provided, including but not limited to the following: wherein heating the portion of the crankshaft comprises induction heating the portion of the crankshaft; wherein the temperature profile comprises a 25 th percentile temperature at a 25 th percentile located midway between the midpoint and the surface, the 25 th percentile temperature being within 10% of the surface temperature; wherein the temperature profile comprises a 75 th percentile temperature at a 75 th percentile located midway between the midpoint and the innermost portion of the core, the 75 th percentile temperature being at least 50% of the surface temperature; the midpoint temperature is at least 70% of the surface temperature; wherein the midpoint temperature is in the range of 70% to 80% of the surface temperature; wherein the 75 th percentile temperature is in the range of 60% to 70% of the surface temperature; wherein the crankshaft surface is located on a circular bearing journal surface of the crankshaft and the temperature profile extends along a radius of the bearing journal surface to an innermost portion of a core of the crankshaft; providing a crankshaft material as a steel having an ideal critical Diameter (DI) of less than 1.70; the steel is a carbon steel having at least 0.3 wt.% carbon; wherein heating the portion of the crankshaft comprises applying a plurality of induced magnetic field pulses to the crankshaft; wherein the heating crankshaft includes: application has a viscosity of 2.0J/C mm²To 2.5J/C*mm²A first induced pulse having an intensity in the range of 2.0J/C mm is applied²To 2.5J/C mm²Applying a second inductive pulse having an intensity in the range of 2.0J/C mm²To 2.5J/C mm²And a third sense pulse of an intensity within a range of (a) and a pause is made between the application of each of the first, second and third sense pulses; applying a first induction pulse in a first period; applying a second sense pulse for a second period; applying a third sense pulse during a third period; each of the first period, the second period, and the third period is in a range of 8 seconds to 12 seconds; wherein inductively heating the crankshaft comprises applying an alternating current to the coil conductor; and wherein discontinuing comprises discontinuing between application of each of the first sense pulse, the second sense pulse, and the third sense pulse a discontinuing period of between 1 second and 3 seconds.

Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.

Drawings

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1 is a partial side view of a portion of a crankshaft having induction heating coils disposed about an outer bearing journal surface according to the principles of the present disclosure;

FIG. 2 is a graph illustrating an exemplary temperature profile used in a method of induction hardening a crankshaft journal, according to the principles of the present disclosure;

FIG. 3 is a diagram illustrating another exemplary temperature profile used in a method of induction hardening a crankshaft journal, according to the principles of the present disclosure; and is

FIG. 4 is a graph illustrating martensite formation as a function of depth during a method of induction hardening of a crankshaft journal, according to principles of the present disclosure.

Detailed Description

Reference will now be made in detail to several examples of the present disclosure that are illustrated in the accompanying drawings. Wherever possible, the same or similar reference numbers are used in the drawings and the description to refer to the same or like parts or steps. The figures are in simplified form and are not drawn to precise scale. Directional terms, such as top, bottom, left, right, upper, on, above, below, behind, front, inside, and outside, may be used with respect to the drawings for convenience and clarity only. These and similar directional terms should not be construed to limit the scope of the present disclosure in any way.

Referring now to the drawings, in which like reference numerals correspond to like or similar components throughout the several figures, FIG. 1 is a partial side view of a portion of a crankshaft 100 having an induction heating coil 102 disposed about an outer surface 104 of a pin journal 108 of the crankshaft 100. In this example, the outer surface 104 of the pin journal 108 of the crankshaft 100 is a circular bearing journal surface of the crankshaft 100. Crankshaft 100 includes a pair of counterweights 106 connected by pin journals 108. The outer surface 104 of the pin journal 108 transitions into the counterweight 106 via a fillet or chamfer 110. While the exemplary crankshaft 100 of fig. 1 is included on a single pin journal 108, it should be appreciated that the crankshaft may include any number of additional pin bearing journals, main bearing journals, and counterweights, without limitation, as desired for the particular engine for which it is designed.

According to an exemplary aspect of the present disclosure, the outer surface 104 of the pin journal 108 is heated by the induction heating coil 102 to eventually harden the surface 104. The induction heating coil 102 may have any desired configuration. The induction heating coil 102 may be energized by a suitable high frequency ac power source, which causes a high density ac power to be induced to flow in the pin journals 108 through the crankshaft 100, which in turn generates heat within the pin journals 108.

The present disclosure provides a method for heat treating the surface 104 of the pin journal 108 that can be applied to any surface of the crankshaft 100 to reduce stresses that may otherwise result from induction hardening.

In an exemplary aspect of the present disclosure, induction heating is performed on the crankshaft 100 to provide a gradually decreasing temperature profile extending inwardly from the surface 104.

Referring to fig. 2, a diagram 200 illustrates an exemplary induction heating profile 202 according to the present disclosure. The horizontal axis 204 of the graph 200 corresponds to depth (in millimeters) from the surface 104, while the vertical axis 206 corresponds to material temperature (in degrees celsius). In the example shown in graph 200, the surface temperature S of surface 104 reaches approximately 920 degrees Celsius, which is within the transformation range of the steel alloy of crankshaft 100. In other words, the steel alloy at the surface 104 becomes austenitized when heated to the surface temperature S.

The temperature profile 202 includes progressively lower temperatures from the crankshaft outer surface 104 (at 0mm along the axis 204) to the innermost portion 112 of the core of the crankshaft 100. The temperature profile 202 extends vertically along a radius of the bearing journal surface 104 to the innermost portion 112 of the pin journal 108 of the crankshaft 100.

In this example, the crankshaft 100 is solid and the innermost portion 112 of the core of the crankshaft 100 is positioned along the longitudinal axis L (also the rotational axis of the crankshaft 100). In this case, the innermost portion 112 of the solid core is positioned 25mm from the surface 104along the longitudinal axis L. In other examples, the crankshaft 100 may be hollow, and in such cases, the innermost portion 112 of the core may be located on an inner surface of the crankshaft 100 that is offset from its axis of rotation.

The temperature profile 202 includes a midpoint temperature M at a midpoint 208 between the crankshaft outer surface 104 and the innermost portion 112 of the core. The temperature profile 202 has a temperature that gradually decreases from the surface 104 toward the innermost portion 112 of the core. Since the variation in the profile 202 is gradual along the profile 202, the midpoint temperature M is at least 50% of the surface temperature S.

As used herein, the percentage of temperature is measured relative to the celsius scale. Thus, for example, the midpoint temperature M is at least 50% of the surface temperature S when measured using the celsius scale.

Referring to fig. 2, data points corresponding to points on the temperature profile 202 are shown in table 1 below.

Table 1: temperature profile 202 as a function of distance from surface 104。

Table 1 shows data points of the temperature profile 202 as a function of distance (in millimeters) from the surface 104. The third column also shows the percentile of the depth along which each temperature and depth data point falls. Thus, for example, at 0.25mm from the surface, the temperature profile 202 has a temperature of 920 degrees celsius, and this is 1 percentile away from the surface 104 (in this example, along the longitudinal axis L of the crankshaft 100) toward the innermost portion 112 of the core.

As mentioned above, the midpoint temperature M is at least 50% of the surface temperature S. The midpoint 208 is located at the 50 th percentile of depth or midway between the surface 104 and the innermost portion 112 of the core. In this particular example, the midpoint temperature M is 712 degrees Celsius and the surface temperature S is 920 degrees Celsius. Thus, in this example, the midpoint temperature M is greater than 70% of the surface temperature S; and more specifically, the midpoint temperature is about 77% of the surface temperature S. However, it should be understood that the temperature profile 202 may have some variation without falling outside the spirit and scope of the present disclosure. For example, in some cases, the midpoint temperature M may be in the range of 70% to 80% of the surface temperature S. Similarly, other temperatures in table 1 may vary, for example, by as much as 10%, or even in some cases by as much as 30%. For example, different materials may be used for the crankshaft 100 or other workpiece, which would result in a temperature profile that is different from the precise temperature profile 202 shown in FIG. 2 and Table 1.

As can be seen from graph 200 and from Table 1, temperature profile 202 includes a 25 th percentile temperature T at a 25 th percentile 210 midway between midpoint 208 and outer surface 104₂₅. In this case, the 25 th percentile temperature T₂₅Within 10% of the surface temperature S. More specifically, in this case, the 25 th percentile temperature T₂₅Is 858 degrees celsius. The surface temperature S is 920 degrees Celsius, and thus, the 25 th percentile temperature T₂₅Greater than 93% but less than 94% of the surface temperature S.

In addition, as can be seen from graph 200 and table 1, the temperatureThe signature graph 202 includes a 75 th percentile temperature T at a 75 th percentile 212 midway between the midpoint 208 and the innermost portion 112 of the core₇₅. In this case, the 75 th percentile temperature T₇₅Is at least 50% of the surface temperature S. More specifically, in this case, the 75 th percentile temperature T₇₅At 593 degrees celsius. The surface temperature S is 920 degrees Celsius, and thus, the 75 th percentile temperature T₇₅Between 60% and 70% of the surface temperature S.

Some materials are more suitable than others for providing a graded temperature profile 202 that reduces stress. In this example, the crankshaft 100 is preferably formed from steel (such as carbon steel having greater than 0.3 wt.% carbon). The steel may have an ideal critical Diameter (DI) of less than 1.70. In other variations, a steel having an ideal critical Diameter (DI) of less than 3.0 may be provided. Some examples of materials that may be used for crankshaft 100 include 1541 steel, 1545 steel, 1440 steel, 1040 steel, and microalloys (such as 1538MV steel or 44MnSiVS6 steel).

During the induction hardening process, the surface temperature S is raised to a temperature at or above the AC3 temperature of the crankpin journal surface material. The AC3 temperature may correspond to the temperature at which the ferrite to austenite transformation is completed during heating. The temperature profile 202 has progressively lower temperatures along the profile 202, and at the innermost portion 112 of the core, the temperature profile 202 has a temperature below the austenitizing temperature. However, not only the surface 104 and the portion of the crankshaft 100 immediately below the surface 104 are heated to a temperature above the austenitizing temperature. Thus, residual tensile stress is generated within the crankshaft 100, rather than merely being present at the surface 104 and abutting compressive stress near the surface. Thus, the method of the present disclosure provides for deep heating of the crankshaft 100 during the induction hardening process itself. The resulting surface 104 may have a hardness of at least 50 HRC.

In one exemplary induction heating method, the induction heating process includes applying a series of induction heating field pulses through the coil 102 into the crankpin pin journal 108 of the crankshaft 100. For example, the induction heating method may include: applying a first induction pulse in a first period; stopping; applying a second sense pulse for a second period: inStopping; and a third sense pulse is applied during a third period. In one example, at 2.0J/C mm²To 2.5J/C mm²(such as 2.25J/C mm)²) Each induction heating pulse is applied. Each of the first period, the second period, and the third period lasts for a duration in the range of 8 seconds to 12 seconds, such as about 10 seconds, so that the application of the field pulse is continuously performed in each of the first period, the second period, and the third period before the suspension. By way of example, the pause between each cycle of induction field application may be in the range of 1 to 3 seconds or about 2 seconds. In one exemplary aspect, pulsing may be accomplished by periodically turning the alternating current in an induction coil in the tool on and off and/or cycling the strength of the induction field generated by the induction coil.

The pulsing of the induction field application allows for deep heating of the crankshaft material using the gradient temperature profile 202. However, it should be understood that the temperature profile 202 may be formed in any suitable manner, such as by a single application of a high intensity induction field.

After heating the crankpin journal 108 to form the gradual temperature profile 202, the methods herein include quenching the outer surface 104 to a temperature substantially below the transition temperature to harden the outer surface 104. The quenching is shallow and rapid to rapidly cool the outer surface 104. For example, a polymer quencher in aqueous solution may be applied to the outer surface 104.

Referring now to fig. 3, a diagram 300 illustrates an alternative exemplary induction heating profile 302 according to the present disclosure. The induction heating profile 302 may be used with the methods described above in place of the profile 202. By way of example, the induction heating profile 302 may be implemented using similar induction heating pulses as described above. The horizontal axis 304 of the graph 300 corresponds to depth (in millimeters) from the surface 104, while the vertical axis 306 corresponds to material temperature (in degrees celsius). In the example shown in graph 300, surface temperature S' reaches approximately 850 degrees celsius, which is within the transformation range of the steel alloy of crankshaft 100. In other words, the material at the surface 104 becomes austenitized when heated to the surface temperature S'.

The temperature profile 302 includes a midpoint temperature M' at a midpoint 308 between the crankshaft outer surface 104 and the innermost portion 112 of the core. The temperature profile 302 has a temperature that gradually decreases from the surface 104 toward the innermost portion 112 of the core. The midpoint temperature M 'is at least 50% of the surface temperature S'.

Referring to fig. 3, data points corresponding to points on the temperature profile curve 302 are shown in table 2 below.

Table 2: temperature profile 302 as a function of distance from surface 104。

Table 2 shows data points of the temperature profile 302 as a function of distance (in millimeters) from the surface 104. The third column also shows the percentile of the depth along which each temperature and depth data point falls. Thus, for example, at 5mm from the surface, the temperature profile 302 has a temperature of 850 degrees celsius, and this is the 20 th percentile located away from the surface 104 (in this example, located along the longitudinal axis L of the crankshaft 100) toward the innermost portion 112 of the core.

As mentioned above, the midpoint temperature M 'is at least 50% of the surface temperature S'. The midpoint 308 is located at the 50 th percentile of depth or midway between the surface 104 and the innermost portion 112 of the core. In this particular example, the midpoint temperature M 'is about 658 deg.C and the surface temperature S' is 850 deg.C. Thus, in this example, the midpoint temperature M' is greater than 70% of the surface temperature S; in this case, it is about 77%. However, it should be understood that the temperature profile 302 may have some variation without falling outside the spirit and scope of the present disclosure. In some cases, the midpoint temperature M 'may be in the range of 70% to 80% of the surface temperature S'. Similarly, other temperatures in table 2 may vary, for example, by as much as 10% or even as much as 30%. For example, different materials may be used for the crankshaft 100 or other workpiece, which would result in a temperature profile that is different from the precise temperature profile 302 shown in FIG. 3 and by Table 2.

As can be seen from the graph 300 and Table 2, the temperature characteristicsThe profile 302 includes a 25 th percentile temperature T at a 25 th percentile 310 midway between the midpoint 308 and the outer surface 104₂₅'. In this case, the 25 th percentile temperature T₂₅'within 10% of the surface temperature S'. More specifically, in this case, the 25 th percentile temperature T₂₅' is 825 degrees Celsius. The surface temperature S' is 850 degrees Celsius, and thus, the 25 th percentile temperature T₂₅' greater than 97% of the surface temperature S ', but less than 98% of the surface temperature S '.

Further, as can be seen from the graph 300 and table 2, the temperature profile 302 includes a 75 th percentile temperature T at a 75 th percentile 312 midway between the midpoint 308 and the innermost portion 112 of the core₇₅'. In this case, the 75 th percentile temperature T₇₅'is at least 50% of the surface temperature S'.

Referring now to fig. 4, a graph 400 illustrates the proportion of the martensite phase after quenching as a function of the depth from the surface 104 of the crankpin journal 108 to the innermost portion 112 of the core. Curve 402 represents martensite phase data points, with depth (in millimeters) shown on horizontal axis 404 and the percentage of martensite shown along vertical axis 406. Figure 4 shows martensite formed after the first application of the temperature profile 302 shown in figure 3 and then quenching. 100% martensite is observed at the surface 104, while 0% martensite is observed at the innermost portion 112 of the core. The graph 400 shows that the martensite gradually decreases along the depth, rather than rapidly vanishing near the surface 104, which results in a more uniform distribution of stress, which in turn results in a less likely occurrence of cracking under the application loading.

While the method described herein is applied to the crank pin 108 of the crankshaft 100, it should be understood that the method may be applied to any other workpiece where hardening without cracking is desired.

The description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims.

Claims

1. A method for heat treating a crankshaft of a vehicle propulsion system, the crankshaft formed of a crankshaft material and having an outer surface, the method comprising:

heating at least a portion of the crankshaft to form a temperature profile having a surface temperature at the outer surface, the temperature profile including progressively lower temperatures from the outer surface to a core of the crankshaft, the temperature profile including a midpoint temperature at a midpoint between the outer surface and an innermost portion of the core, the midpoint temperature being at least 50% of the surface temperature measured on a scale of degrees Celsius, the surface temperature being within a transition range of the crankshaft material; and subsequently quenching the outer surface of the crankshaft.

2. The method of claim 1, wherein heating the portion of the crankshaft comprises induction heating the portion of the crankshaft.

3. The method according to any of the preceding claims, wherein the temperature profile comprises a 25 th percentile temperature at a 25 th percentile located midway between the midpoint and the outer surface, the 25 th percentile temperature being within 10% of the surface temperature measured on the celsius scale, wherein the temperature profile comprises a 75 th percentile temperature at a 75 th percentile located midway between the midpoint and the innermost portion of the core, the 75 th percentile temperature being at least 50% of the surface temperature measured on the celsius scale, the midpoint temperature being at least 70% of the surface temperature measured on the celsius scale.

4. A method according to claim 3, wherein the 75 th percentile temperature is within a range of 60% to 70% of the surface temperature measured on the celsius scale.

5. The method according to any of the preceding claims, wherein the midpoint temperature is in the range of 70% to 80% of the surface temperature measured on the celsius scale.

6. The method of any of the preceding claims, wherein the outer surface is a circular bearing journal surface of the crankshaft and the temperature profile extends along a radius of the bearing journal surface to the innermost portion of the core, the method further comprising providing the crankshaft material as a steel having an ideal critical Diameter (DI) of less than 1.70.

7. The method of claim 6, further comprising providing the steel as a carbon steel having at least 0.3 wt.% carbon.

8. The method of any of the preceding claims, wherein heating the portion of the crankshaft comprises applying a plurality of induction field pulses to the crankshaft.

9. The method of any preceding claim, wherein heating the portion of the crankshaft comprises: applying the first time period to the substrate with a thickness of 2.0J/C mm²To 2.5J/C mm²A first induction pulse having an intensity in the range of 2.0J/C mm is applied for a second period²To 2.5J/C mm²A second induction pulse having an intensity in the range of 2.0J/C mm, and is applied during a third period²To 2.5J/C mm²A third induction pulse of an intensity in a range of (a), each of the first period, the second period, and the third period being in a range of 8 seconds to 12 seconds; and pausing between said applying of each of the first sense pulse, the second sense pulse and the third sense pulse.

10. The method of any of the preceding claims, wherein inductively heating the portion of the crankshaft comprises applying an alternating current to a coil conductor.