CN111334656B

CN111334656B - Method for heat treatment using a gradual temperature profile

Info

Publication number: CN111334656B
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: 2023-05-16
Anticipated expiration: 2039-06-05
Also published as: CN111334656A; US20200199704A1; DE102019115659A1

Abstract

The invention provides a method for heat treatment by utilizing a gradual temperature characteristic diagram. A method for heat treating a crankshaft or other workpiece of a vehicle propulsion system includes heating at least a portion of the crankshaft to form a map of a ramped temperature. 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, the midpoint temperature being 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 further 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 heat treatment using a gradual 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 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, boat, aircraft, or automobile). The crankshaft is an important part of the engine and is the starting point for the engine design.

The crankshaft comprises 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 fixed to the engine block at the main bearing journals. Bearings are disposed about the main bearing journals between the crankshaft and the engine block.

Crankpin and main bearing journal surfaces are typically hardened to enable handling of loads and wear. One method of hardening is to inductively heat and then quench to harden the crankshaft journal surface. With induction heating/hardening, a high-frequency alternating current is used to induce eddy currents in the surface area of the workpiece to be hardened. These eddy currents cause joule heating that causes the workpiece to heat up 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 a volume increase accompanying a phase change due to hardening. When these residual stress components are combined with the working stresses, they pose an adverse risk of promoting the initiation of 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 phase and the new phase formed in the steel. If the underlying surface material is subjected to significant stresses, the material may develop cracks that can propagate and lead to failure of the crankshaft.

Conventional attempts to mitigate or reduce residual tensile stresses caused by induction hardening include 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 create a gradual temperature profile within a workpiece prior to quenching. This graded 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 from 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 decreases from the surface of the crankshaft to the core. The temperature profile includes a midpoint temperature at a midpoint between the surface and an innermost portion of the core. The midpoint temperature is at least 50% of the surface temperature as measured on a celsius scale. The surface temperature is within the transformation range of the crankshaft steel alloy. The method also includes quenching a 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 the crankshaft, preferably from a crankshaft steel alloy, and forming a circular bearing journal surface about the crankshaft. The method further 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 circular bearing journal surface that is within the transformation range of the crankshaft steel alloy. The gradual 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 other forms disclosed herein, a method of induction hardening a workpiece is provided. The method includes providing a workpiece formed from a workpiece material and having an outer surface. The method further 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 further includes quenching the outer surface to a temperature below the transition temperature to harden the outer surface.

Can provideAdditional features include, but are not limited to, the following: wherein the portion that heats the crankshaft comprises a portion that inductively heats the crankshaft; wherein the temperature profile includes a 25 th percentile temperature at a 25 th percentile point midway between the midpoint and the surface, the 25 th percentile temperature being within 10% of the surface temperature; wherein the temperature profile includes a 75 th percentile temperature at a 75 th percentile point intermediate 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 the crankshaft material as steel having a desired 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 induction magnetic field pulses to the crankshaft; wherein heating the crankshaft comprises: applying a composition having a thickness of 2.0J/C mm ² To 2.5J/C mm ² Applying a first induced pulse having an intensity in the range of 2.0J/C mm ² To 2.5J/C mm ² A second induction pulse having an intensity in the range of 2.0J/C mm is applied ² To 2.5J/C mm ² A third sense pulse of an intensity within the range of (a), and discontinuing between application of each of the first sense pulse, the second sense pulse, and the third sense pulse; applying a first sense pulse over a first period; applying a second sense pulse in a second period; applying a third sense pulse in 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 includes applying an alternating current to the coil conductor; and wherein ceasing comprises ceasing a period of discontinuation between 1 second and 3 seconds between application of each of the first sense pulse, the second sense pulse, and the third sense pulse.

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 in accordance with the principles of the present disclosure;

FIG. 2 is a diagram illustrating an exemplary temperature profile for use in a method of induction hardening a crankshaft journal in accordance with the principles of the present disclosure;

FIG. 3 is a diagram illustrating another exemplary temperature profile for use in a method of induction hardening a crankshaft journal in accordance with the principles of the present disclosure; and is also provided with

FIG. 4 is a graph showing martensite formation as a function of depth during an induction hardening method of a crankshaft journal in accordance with the 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. For convenience and clarity only, directional terms, such as top, bottom, left, right, up, over, under, rear, front, interior, and exterior, may be used with respect to the drawings. 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 numbers correspond to like or similar components throughout the several figures, FIG. 1 is a partial side view of a portion of a crankshaft 100, the 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 through 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, 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 collar 108 is heated by the induction heating coil 102 to ultimately 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 through the crankshaft 100 in the pin journal 108, which in turn generates heat within the pin journal 108.

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

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

Referring to fig. 2, a diagram 200 illustrates an exemplary induction heating profile 202 in accordance with 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 diagram 200, 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 upon heating to the surface temperature S.

The temperature profile 202 includes a temperature that gradually decreases 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 the 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 along the longitudinal axis L at a distance of 10425mm from the surface. 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 a celsius scale.

Referring to fig. 2, data points corresponding to points on the temperature profile curve 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 a 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 described 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 the 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 variations 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 up to 10%, or even in some cases by up to 30%. For example, different materials may be used for crankshaft 100 or other workpieces, which will cause the temperature profile to be different from the precise temperature profile 202 shown in fig. 2 and table 1.

As can be seen from the graph 200 and from table 1, the temperature profile 202 includes a 25 th percentile temperature T at a 25 th percentile point 210 midway between the midpoint 208 and the outer surface 104 ₂₅ . In this case, the 25 th percentile temperature T ₂₅ Within 10% of the surface temperature S. More specifically, in this case, the 25 th percentile temperature T ₂₅ Is 858 degrees celsius. The surface temperature S is 920 degrees Celsius, and thus, the 25 th percentile temperature T ₂₅ Greater than 93% of the surface temperature S but less than 94% of the surface temperature S.

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

Some materials are more suitable than others for providing a reduced stress ramp temperature profile 202. In this example, the crankshaft 100 is preferably formed of steel (such as carbon steel having greater than 0.3 wt.% carbon). The steel may have a desired critical Diameter (DI) of less than 1.70. In other variations, steels having a desired 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 a temperature at which transformation of ferrite to austenite is completed during heating. The temperature profile 202 has a temperature that gradually decreases along the profile 202, and at the innermost portion 112 of the core, the temperature profile 202 has a temperature that is 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 stresses are generated within crankshaft 100, rather than merely being present at surface 104 and abutting compressive stresses 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 journal 108 of the crankshaft 100. For example, the induction heating method may include: applying a first sense pulse over a first period; stopping; applying a second sense pulse in a second period: stopping; and applying a third sense pulse in a third period. In one example, at 2.0J/C mm ² To 2.5J/C mm ² (such as 2.25J/C. Times.mm) ² ) Each induction heating pulse is applied at an intensity of (2). Each of the first, second, and third periods lasts for a duration in the range of 8 seconds to 12 seconds (such as about 10 seconds) such that the application of the field pulse is performed continuously in each of the first, second, and third periods before the suspension. By way of example, the discontinuance between each cycle of the 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 switching on and off alternating current in an induction coil in the tool 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 gradual temperature profile 202. However, it should be appreciated 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 crankpin journal 108 to form graded temperature profile 202, the methods herein include quenching outer surface 104 to a temperature substantially below the transition temperature to harden outer surface 104. Quenching is shallow and rapid to rapidly cool the outer surface 104. For example, a polymer quenching agent in an 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 in accordance with the present disclosure. The induction heating profile 302 may be used in place of the profile 202 with the methods described above. 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 diagram 300, the 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 upon heating 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 the 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 away from the surface 104 toward the innermost portion 112 of the core (in this example, disposed along the longitudinal axis L of the crankshaft 100).

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 the 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 ℃ and the surface temperature S' is 850 ℃. Thus, in this example, the midpoint temperature M' is greater than 70% of the surface temperature S; in this case, about 77%. However, it should be understood that the temperature profile 302 may have some variations 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, the other temperatures in table 2 may vary, for example, by up to 10% or even up to 30%. For example, different materials may be used for crankshaft 100 or other workpieces, which will cause the temperature profile to differ from the precise temperature profile 302 shown in FIG. 3 and by Table 2.

As can be seen from graph 300 and table 2, the temperature profile 302 includes a 25 th percentile temperature T at a 25 th percentile point 310 midway between the midpoint 308 and the outer surface 104 ₂₅ '. In this case, the 25 th percentile temperature T ₂₅ 'within 10% of the surface temperature S'. More specifically, in this case, the 25 th percentile temperature T ₂₅ ' is 825 degrees celsius. The surface temperature S' is 850 degrees Celsius, and thus, the 25 th percentile temperature T ₂₅ ' is greater than 97% of the surface temperature S ' but less than 98% of the surface temperature S '.

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

Referring now to FIG. 4, a graph 400 shows the proportion of the martensite phase after quenching as a function of 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 a horizontal axis 404 and percent martensite shown along a vertical axis 406. Fig. 4 shows martensite formed after the first application of the temperature profile 302 shown in fig. 3 and then quenching. 100% martensite was observed at the surface 104, while 0% martensite was observed at the innermost portion 112 of the core. The graph 400 shows that martensite gradually decreases in depth rather than rapidly vanishing near the surface 104, which results in a more uniform distribution of stress and thus less likelihood of cracking under application loading.

While the method described herein applies to the crankpin 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 studying 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 from 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 a progressively lower temperature 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 in a range of 70% to 80% of the surface temperature measured on a celsius scale, the surface temperature being in a transition range of the crankshaft material; and subsequently quenching the outer surface of the crankshaft;

wherein the temperature profile comprises a 25 th percentile temperature at a 25 th percentile point of an intermediate position between the midpoint and the outer surface, the 25 th percentile temperature being greater than 93% and less than 94% of the surface temperature, wherein the temperature profile comprises a 75 th percentile temperature at a 75 th percentile point of an intermediate position between the midpoint and the innermost portion of the core, the 75 th percentile temperature being in a range of 60% to 70% of the surface temperature measured on the celsius scale;

wherein the crankshaft comprises at least one crankpin journal that is offset from the longitudinal axis, during the induction hardening process, the surface temperature increases to a temperature at or above the AC3 temperature of the crankpin journal surface material, the AC3 temperature corresponding to a temperature at which ferrite to austenite transformation is completed during heating;

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 steel having a desired critical Diameter (DI) of less than 1.70; providing the steel as a carbon steel having at least 0.3 wt% carbon;

wherein heating the portion of the crankshaft comprises: applied in a first period with a torque of 2.0J/mm ² To 2.5J/mm ² A first induction pulse having an intensity in the range of 2.0J/mm is applied in a second period ² To 2.5J/mm ² A second induction pulse having an intensity in the range of 2.0J/mm is applied in a third period ² To 2.5J/mm ² A third sense pulse of an intensity in a range of 8 seconds to 12 seconds for each of the first period, the second period, and the third period; and ceasing between said applying of each of the first sense pulse, the second sense pulse and the third sense pulse.