JP5060054B2 - Induction hardening method - Google Patents

Description

  The present invention relates to an induction hardening method, and more particularly to an induction hardening method applied to a long workpiece made of an Fe-based alloy extending along an axis.

  As a technique for subjecting a long rod-shaped workpiece, for example, induction hardening to a drive shaft that constitutes a traveling engine of an automobile, single shot quenching that performs quenching processing on the entire long workpiece at once, Moving quenching is exemplified in which a part of the work is surrounded by a high-frequency heating coil, and the part to be heat-treated is sequentially changed by transferring the long work in the axial direction. In any of the quenching methods, the long workpiece is cooled by the coolant after being heated by the high-frequency heating coil.

  Here, in the single shot quenching, the long workpiece is clamped from both bottom sides and is further urged to rotate (see, for example, Patent Document 1). The long workpiece is heated in this state, and then cooled while the rotation is continued. Thereby, quenching is performed on the long workpiece. When the long workpiece is distorted during the cooling, the rotating portion comes into contact with the correction roller disposed in proximity to the long workpiece. This contact corrects the distortion of the long workpiece.

JP-A-4-141523

  However, it is difficult to say that the distortion is sufficiently suppressed with the straightening roller alone, and cold strain removal processing is usually performed after the quenching process. Moreover, since a long workpiece may be cracked by this processing, a magnetic flaw inspection is performed to confirm the presence or absence of the crack. From the above, the number of processes is increased, and for this reason, it is not easy to improve the production efficiency of long workpieces.

  The present invention has been made in order to solve the above-described problems, and can suppress the occurrence of distortion in a long workpiece. For this reason, it is possible to omit strain removal processing and magnetic flaw detection inspection. It aims to provide a simple induction hardening method.

In order to achieve the above object, the present invention performs high-frequency induction heating while rotating a long workpiece made of an Fe-based alloy, and when distortion occurs in the long workpiece, a correction roller is brought into contact with the distortion correction. In the induction hardening method of quenching while performing
A heating step of performing the high-frequency induction heating to a first temperature range where austenite is generated while rotating the long workpiece at a first rotational speed;
The first workpiece is cooled to a second temperature range not higher than the pearlite precipitation end temperature but higher than the martensite precipitation start temperature while rotating the long workpiece at a second rotation speed that is higher than the first rotation speed. A cooling process;
After the temperature of the long workpiece has reached the second temperature range, the cooling is continued while the long workpiece is rotated at a third rotational speed that is smaller than the second rotational speed. A cooling process;
It is characterized by having.

  The Fe-based alloy that is the material of the long workpiece has a structure in which strain is easily removed in a temperature range up to the pearlite precipitation end temperature (Pf temperature). Therefore, after the heating process is completed, the rotation of the long workpiece is cooled to the maximum, and when the distortion occurs, the distortion generated in the long workpiece is efficiently brought into contact with the correction roller when the distortion occurs. Can be removed. This is because the frequency of contact of the long workpiece with the straightening roller increases.

  For this reason, according to the present invention, there is almost no distortion in the long workpiece after the second cooling step. Therefore, it is possible to omit the cold strain removing process, and inevitably, it is possible to omit the magnetic flaw inspection for confirming whether or not a crack has occurred by the cold strain removing process. By omitting these steps, the production efficiency of long workpieces is improved.

  In addition, since the metal structure is substantially uniform over the entire long workpiece, the various characteristics are also substantially uniform throughout.

  The first cooling step for maximizing the rotation speed of the long work is continued until the long work reaches a predetermined temperature range (second temperature range). Specifically, the temperature range is from the Pf temperature or lower to the martensite precipitation start temperature (Ms temperature), and the temperature just above the Ms temperature is particularly preferable.

  In addition, when changing the rotation speed of the correction roller, the actual rotation speed gradually increases or decreases due to inertia. Therefore, immediately after the start of the first cooling process, the rotational speed is increasing, and immediately after the second cooling process is started, the rotational speed is decreasing.

  It is preferable that at least one of the correction rollers is set so as to be rotatable without following the rotation of the other correction rollers, so-called rotation-free. In this case, there is an advantage that the configuration is simplified and distortion correction is possible even if another correction roller is constrained for some reason.

  The cooling time in the first cooling step is set according to the size, mass, and hardness of the long workpiece. For example, when the long workpiece has a cylindrical shape, the cooling time is set longer as the diameter increases.

  In addition, the rotation speed at the time of a heating process and the rotation speed at the time of a 2nd cooling process, ie, a 1st rotation speed, and a 3rd rotation speed can be set equal.

  According to the present invention, in a temperature range where a tissue capable of easily removing strain is formed on a long workpiece, the rotation speed of the long workpiece is maximized and brought into contact with the correction roller. I try to correct distortion. Accordingly, it is possible to suppress the occurrence of distortion in the long workpiece, thereby eliminating the need to perform cold strain removal processing and magnetic flaw detection, thereby improving the production efficiency of the long workpiece.

  Preferred embodiments of the induction hardening method according to the present invention will be described below in detail with reference to the accompanying drawings.

  The induction hardening method according to the present embodiment is broadly divided into a heating process, a first cooling process, and a second cooling process. That is, the long workpiece is heated in the heating process, and then cooled in the first cooling process and the second cooling process performed continuously thereafter.

  FIG. 1 is a side view of a quenching treatment apparatus 10 for performing the heating process, the first cooling process, and the second cooling process, and FIGS. 2 and 3 are cross-sectional views taken along line II-II in FIG. It is a figure and an upper arrow important part top view. The quenching apparatus 10 includes a correction mechanism 12, rotary chucks 14a and 14b constituting a clamp mechanism, a high-frequency heating coil 16, and a moving cooling jacket (not shown).

  The correction mechanism 12 has a first bearing 20a to a fourth bearing 20d erected on the pedestal 18. The first bearing 20a and the second bearing 20b support the first rotating shaft 22a, while the third bearing. The second rotary shaft 22b is pivotally supported by 20c and the fourth bearing 20d. Of course, the first rotating shaft 22a and the second rotating shaft 22b are rotatable independently of each other.

  As shown in FIG. 1, a first correction roller 24a and a second correction roller 24b are positioned and fixed to the first rotation shaft 22a, and a first correction roller 24a and a second correction roller are fixed to the second rotation shaft 22b. The third correction roller 24c and the fourth correction roller 24d are positioned and fixed at positions that do not interfere with 24b. The side peripheral walls of the first correction roller 24a to the fourth correction roller 24d are separated from the side peripheral wall of the long workpiece LW by a predetermined distance.

  The rotary chucks 14a and 14b constituting the clamp mechanism can be separated from and approached to the bottom surfaces of the long workpiece LW, in other words, can be opened and closed. When the rotary chucks 14a and 14b are closed, both of them hold the long workpiece LW from both bottom surfaces, thereby clamping the long workpiece LW.

  Further, the rotary chucks 14a and 14b can be rotated by appropriately setting the number of rotations under the action of a rotation control motor (not shown). The rotation speed is controlled by setting a rotation biasing force by the rotation control motor.

  The high-frequency heating coil 16 is positioned at substantially the end of the long work LW and curved along the upper half circumference of the long work LW, and both ends of the arch parts 26a and 26b are connected to each other. It has the straight part 28a, 28b provided so that it might bridge. The arch portions 26a and 26b are provided with arm portions 30a and 30b, one end of which is supported by a lifting mechanism (not shown), and the arm portions 30a and 30b are lifted and lowered under the action of the lifting mechanism. Thus, the high-frequency heating coil 16 approaches the position surrounding the upper half circumference of the long workpiece LW, while rotating so as to be separated from the upper half circumference.

  Here, the long workpiece LW is not particularly limited as long as the dimension in the height direction (axial direction) is equal to or larger than the diameter dimension of the bottom surface, the width dimension, and the depth dimension. An example is a drive shaft.

  The induction hardening method according to the present embodiment is performed as follows.

  First, a long work LW such as a drive shaft is clamped from both bottom surfaces by closing the rotary chucks 14a and 14b. Thereafter, the lifting mechanism is energized to lower the arm portions 30a and 30b of the high-frequency heating coil 16, and finally the high-frequency heating coil 16 surrounds the upper half of the long work LW as shown in FIG. To do.

  Then, the rotary chucks 14a and 14b are rotated under the action of the rotation control motor, thereby rotating the long workpiece LW. The rotational speed may be, for example, 100 to 200 rpm.

  In this state, the high frequency heating coil 16 is energized to start the heating process, and the long work LW is heated to about 900 to 950 ° C. by electromagnetic induction heating. That is, the heating process of the induction hardening process is started. With this electromagnetic induction heating, austenite transformation occurs in the metal structure of the long workpiece LW, which is an Fe-based alloy.

  After a predetermined time has elapsed, energization of the high-frequency heating coil 16 is stopped, and the heating jacket is rotated to be separated from the long work LW, while the rotation speed of the rotary chucks 14a and 14b is increased. What is necessary is just to set the final rotation speed of rotary chuck | zipper 14a, 14b to 240-300 rpm, for example.

  Further, immediately after the heating jacket is separated from the long work LW, the long work LW is surrounded by the moving cooling jacket.

  The moving cooling jacket has a semi-cylindrical shape and surrounds a part of the upper half circumference of the long workpiece LW along the longitudinal direction and is displaced along the longitudinal direction of the long workpiece LW. Further, an injector for ejecting a coolant to the long workpiece LW is installed on the inner peripheral wall.

  That is, the long workpiece LW is cooled by the coolant sprayed from the inner peripheral wall of the moving cooling jacket, and the first cooling process is started accordingly. When the moving cooling jacket is displaced along the longitudinal direction of the long work LW, the entire long work LW is cooled.

  In this cooling process, ferrite and pearlite are precipitated from the metal structure of the long workpiece LW (Fe-based alloy). Until the pearlite deposition is cooled to the pearlite deposition finish temperature (Pf temperature), the long work LW is caused by the change in the metal structure of the long work LW accompanying the precipitation of ferrite and pearlite. A part of the bulge may bulge and cause distortion. In this case, the part where the distortion has occurred contacts any one of the first correction roller 24a to the fourth correction roller 24d at a rate of 0.83 to 5 times / minute, and thereby the distortion of the long workpiece LW is corrected. . Of course, during this time, ejection of the coolant from the moving cooling jacket is continued.

  In the temperature range from the austenite generation temperature to the Pf temperature, the long workpiece LW forms a structure in which strain is easily removed. For this reason, in the first cooling step, the distortion of the long workpiece LW is efficiently removed by bringing the long workpiece LW into contact with the first correction roller 24a to the fourth correction roller 24d while maximizing the rotation speed of the long workpiece LW. Can do.

  That is, in the present embodiment, the long workpiece LW is rotated at a rotational speed exceeding the rotational speed at the time of high-frequency heating, and cooling is performed in this state, whereby the first straightening roller 24a to the fourth straightening roller 24d. The contact frequency of the long workpiece LW is increased. Thereby, the distortion correction effect with respect to the long workpiece | work LW improves.

  In addition, in this case, the metal structure of the long workpiece LW is substantially uniform throughout the entire structure, so that various characteristics can be equalized.

  In the maintenance of the number of rotations of the rotating chucks 14a and 14b, and in the first cooling step, the temperature of the long workpiece LW is a predetermined temperature range in which large distortion is hardly generated in the long workpiece LW, specifically, The process is continued until the temperature becomes lower than the Pf temperature. However, when the first cooling step is performed until the temperature reaches the martensite deposition start temperature (Ms temperature) or lower, martensite is precipitated, and so-called burning cracks may occur. In order to avoid this, the final temperature of the first cooling step is higher than the Ms temperature.

  In short, the temperature range of the long workpiece LW when the first cooling step is completed is from the Pf temperature or lower to the Ms temperature higher. It is preferable that the final temperature is just above the Ms temperature. This is because the dimensional accuracy of the long workpiece LW is improved in this case.

  Here, the Pf temperature and the Ms temperature are obtained in advance by a continuous transformation curve (CCT curve) before performing the first cooling step. If the material of the long workpiece LW is, for example, S40CM, the CCT curve shown in FIG. 4 may be referred to. Note that Fs and Ps in FIG. 4 represent a ferrite precipitation start temperature at which ferrite precipitation starts and a pearlite precipitation start temperature at which pearlite precipitation starts, respectively.

  If the cooling time in the first cooling step is excessively short, the long workpiece LW remains heated, so that the long workpiece LW enters a so-called heat return state, and the hardness decreases. On the other hand, if it is excessively long, the processing efficiency is lowered. For this reason, the cooling time in the first cooling step is set within a range in which the hardness of the long workpiece LW does not decrease and the processing efficiency does not decrease.

  The cooling time is appropriately set according to the diameter, mass, and hardness of the long workpiece LW. In other words, the cooling time is not uniquely determined, but may be set to 10 to 20 seconds, for example, when the long work LW is a cylindrical body having a diameter of about 20 cm made of S40CM.

  After finishing the first cooling step, cooling of the long workpiece LW is continued by continuing to eject the coolant from the moving cooling jacket while lowering the rotational speed of the rotary chucks 14a, 14b and the long workpiece LW. (Second cooling step). Note that the ejection of the cooling liquid may be stopped, or the cooling liquid may be ejected at a lower temperature than in the first cooling step.

  The number of rotations in the second cooling process can be made equal to the number of rotations in the heating process, for example. That is, for example, when the heating process is performed at 100 rpm, it may be set to 100 rpm, and when the heating process is performed at 150 rpm, it may be set to 150 rpm. Preferably, the number of rotations in the heating process and in the second cooling process is 180 rpm. Thereby, it can also suppress that the elongate workpiece | work LW deform | transforms with a martensitic transformation.

  When the predetermined time elapses and the cooling is finished, all the steps of the induction hardening process are finished. FIG. 5 shows the relationship between the passage of time and the number of rotations in each of the above steps. FIG. 5 shows an example in which the number of rotations in the heating process and the second cooling process is 180 rpm, and the number of rotations in the first cooling process is 250 rpm.

  The long workpiece LW obtained in this way has almost no distortion, and therefore it is not necessary to perform cold distortion removal processing for removing the distortion. Inevitably, it is not necessary to perform a magnetic flaw inspection for confirming whether or not the long workpiece LW is cracked by the cold strain removing process. For this reason, the processing efficiency of the long work LW is improved, and eventually the production efficiency of the long work LW is improved.

  In the above-described embodiment, the CCT curve of the S40CM material is referred to. However, if the CCT curve corresponding to the material of the long workpiece LW is referred to, the Pf temperature and the material other than S40CM are also referred to. Ms temperature etc. can be determined. That is, the material of the long workpiece LW is not particularly limited as long as it is an Fe-based alloy.

  Further, the long workpiece LW is not limited to a cylindrical body having a spherical bottom surface, and may be a polygonal column having a polygonal bottom surface. Further, there is no need for both bottom surfaces to have the same shape.

It is a side view of the hardening processing apparatus for enforcing the induction hardening method which concerns on this Embodiment. It is the II-II sectional view taken on the line of FIG. It is an upper arrow important part top view of the hardening processing apparatus of FIG. It is a CCT curve of S40CM material. It is a graph which shows the rotation speed in each process of an induction hardening method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Quenching processing apparatus 12 ... Straightening mechanism 14a, 14b ... Rotary chuck 16 ... High frequency heating coil 22a, 22b ... Rotary shaft 24a-24d ... Straightening roller LW ... Long work

Claims (2)

In the induction hardening method in which high-frequency induction heating is performed while rotating a long workpiece made of an Fe-based alloy, and when the distortion occurs in the long workpiece, the correction roller is brought into contact with the correction roller to perform hardening while performing distortion correction.
A heating step of performing the high-frequency induction heating to a first temperature range where austenite is generated while rotating the long workpiece at a first rotational speed;
The first workpiece is cooled to a second temperature range not higher than the pearlite precipitation end temperature but higher than the martensite precipitation start temperature while rotating the long workpiece at a second rotation speed that is higher than the first rotation speed. A cooling process;
After the temperature of the long workpiece has reached the second temperature range, the cooling is continued while the long workpiece is rotated at a third rotational speed that is smaller than the second rotational speed. A cooling process;
Induction hardening method characterized by having. 2. The induction hardening method according to claim 1, wherein the first rotational speed and the third rotational speed are made equal.

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