JPH04341515A - Method for correcting strain caused by local quenching - Google Patents

Abstract

PURPOSE:To effectively correct strain at an inner diameter part by preheating the inner diameter part before regularly heating the local part to be quenched in order to solve the problem on accuracy of the parts caused by the strain in the inner diameter part in the case of quenching the parts having the inner diameter part, e.g. ring-like parts. CONSTITUTION:In the method where the local part of a steel-made work W having the inner diameter part is heated with high frequency and quenched while correcting the strain by inserting a mandrel 31 into the inner diameter part, after preheating the work so that surface temp. of the insert part in the mandrel becomes at 300-600 deg.C, the regular heating is executed and quenching is executed after inserting the mandrel.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting distortion in a steel part having a hollow inner surface (hereinafter referred to as the inner diameter section) which occurs when locally hardening the steel component.

0002

2. Description of the Related Art When a part having an inner diameter, such as a ring-shaped part, is hardened, distortion occurs in the inner diameter and this distortion sometimes poses a problem in terms of the accuracy of the part. Therefore, it was necessary to correct and reduce the distortion in the inner diameter portion during hardening. Therefore, as a prior art, for example, published technical report 84-159
A method called plug hardening as shown in No. 01 was used. This plug hardening is performed on ring-shaped parts with a hardness of 850~
It is heated to 950° C., and a mold called a plug, which is a strain correction member whose outer shape matches the inner diameter portion, is inserted into the expanded inner diameter portion. When the product undergoes shrinkage due to cooling for quenching, this method corrects the distortion by shrinking the inner diameter part by wrapping it around a plug, so to speak. This method can be applied not only to cases where the inner diameter part is cylindrical, but also to cases where the inner diameter part has a spline or a tapered shape by matching the outer shape of the plug to the shape.

0003

[Problems to be Solved by the Invention] However, this method of correcting distortion in the inner diameter part, called plug hardening, requires heating the entire product by furnace heating or high-frequency heating in order to expand the inner diameter part and press fit the plug. Since heating is required, it cannot be applied when hardening only a local part of the product, such as the end face of the boss or the outer periphery. In other words, since the entire product is heated, hardening occurs in areas other than the desired areas, so hardening does not occur only in localized areas. In addition, if you try to harden while straightening the strain by heating only the local area, even if the local area is heated to a temperature suitable for hardening, the temperature of the inner diameter part where you want to straighten the strain will rise only slightly. do not have. Therefore, the yield point of the material has not been lowered, so even if a plug was inserted in this state to correct the strain, plastic deformation would be difficult and the effect would be small.

[0004] Therefore, the present invention sets the inner diameter portion into which the strain correction member is inserted to a temperature range in which the lower limit is such that the yield point is lowered and sufficient strain correction can be performed, and the upper limit is such that the metal structure is not hardened, that is, the metal structure does not change to austenite. The object of the present invention is to effectively correct distortion in the inner diameter during local hardening by preheating and then performing main heating to raise the temperature of the local area to be hardened to a temperature suitable for hardening.

[0005]

[Means for Solving the Problems] The means of the present invention for solving such problems is to heat a locally hardened portion of a steel component having an inner diameter portion with high frequency, and then insert a strain correction member into the inner diameter portion. In the strain correction method for local quenching, in which the locally quenched part is quenched while correcting the strain that occurs in the inner diameter part during quenching, the surface temperature of the inner diameter part is 300 to 600°C.
A first step of pre-heating so that it becomes , a second step of locally main heating only the locally quenched part to the austenitizing temperature, and a third step of inserting a strain correction member into the inner diameter part,
The method is characterized by comprising a fourth step of hardening the locally hardened portion. In this case, in order to prevent the area to be hardened from spreading due to the diffusion of heat after the local main heating in the second step, the fourth step is carried out immediately after the end of the second step. is desirable.

[0006] The main heating time is determined experimentally depending on the size and shape of the product, the size and location of locally hardened parts, etc., but it is usually 1 to 3 seconds for products used industrially. desirable. This is because if it is too short, the temperature will not rise to the quenching temperature sufficiently, and if it is too long, the high temperature area will spread due to heat diffusion, and there is a risk that quenching will occur in areas other than the desired areas. The cooling time for the fourth step, quenching, is also determined experimentally, but is preferably 5 to 15 seconds. If it is too short, it may not be cooled enough and may not be cooked properly. There is no particular problem in terms of quality if the length is long, but if only a local part is hardened, cooling for about 15 seconds is sufficient, and longer cooling times will reduce productivity.

[0007]

[Operation] According to the present invention, a steel part having an inner diameter portion is preheated so that the surface temperature of the inner diameter portion is 300 to 600°C, and then the locally hardened portion to be hardened is heated to a temperature suitable for hardening. That is, main heating is performed locally to the austenitizing temperature, a strain correction member is inserted into the inner diameter portion, and the locally hardened portion is hardened. Therefore, when the strain correction member is inserted, the yield point of the inner diameter portion is lowered by preheating, and strain correction can be effectively performed.

[0008] Furthermore, since the temperature of the locally hardened portion that has been main heated is high and the temperature of the inner diameter portion that has been preheated is low, the high temperature portion expands due to thermal diffusion from the locally hardened portion. Therefore,
In order to keep the part to be quenched in the desired location, it is necessary to restrict heat diffusion from the high-temperature parts to provide appropriate temperature distribution in each part of the product. In the present invention, by performing the steps in the order of preheating and then main heating, it is possible to shorten the time from the end of main heating to quenching, or to perform quenching immediately. Therefore, since thermal diffusion can be suppressed to a minimum, each part of the product can have a desired temperature distribution, that is, the inner diameter part has a temperature suitable for strain correction, and the locally hardened part has a temperature suitable for hardening.

[0009]

EXAMPLES The present invention will be explained in detail based on examples below. FIG. 1 is a schematic cross-sectional view showing an example of a local hardening apparatus for carrying out the method of the present invention. An embodiment using a component called a clutch hub having a spline on its inner diameter will be described. This apparatus consists of a saddle 1 that supports the entire apparatus, a workpiece support means 2, a distortion correction means 3, a rotation/stopping means 4, and a hardening means 5. The configuration will be explained in order below.

The saddle 1 is raised and lowered by a drive device (not shown). The work supporting means 2 consists of a work holder 21 and a work holder 23. The workpiece holder 21 is attached to the saddle 1 and is rotatable around a central axis. Further, the workpiece holder 21 has a protrusion 22, and by fitting the protrusion 22 into the protrusion 22 in accordance with the phase of the inner diameter spline of the workpiece W, the workpiece W is positioned at a predetermined position and in a predetermined attitude. The workpiece holder 23 is slidably attached through the side surface of the saddle 1, and fixes the workpiece W in the forward position and does not fix it in the backward position.

The distortion correction means 3 includes a mandrel 31, a phase determining section 32, a rod 33, and a drive cylinder 34. The mandrel 31 is a distortion correcting member, and its outer shape is manufactured to match the shape of the inner diameter spline (not shown) of the workpiece W.
It is inserted into and removed from the inner diameter portion of the work W by a drive cylinder 34 via a rod 33 connected to a mandrel 31 . The drive cylinder 34 is attached to the saddle 1. Further, a phase determining part 32 is provided at the tip of the mandrel 31, and guides the mandrel 31 so that it fits into the inner diameter spline of the work W by matching the phases of the mandrel 31 and the inner diameter spline.

The rotation/stopping means 4 is a means for rotating or stopping the mandrel 31 and the workpiece holder 21, and includes a brake 41, a clutch 42, a shaft 43, a rod sprocket 44, and a workpiece holder sprocket 45.
, an upper chain 46, a lower chain 47, an upper shaft sprocket 48, and a lower shaft sprocket 49.

The brake 41 stops the rotation of the rod 33, which is rotatable around the central axis, when activated. From a drive device (not shown), a shaft 43, an upper sprocket for the shaft 48,
Power is transmitted to the rod sprocket 44 and the workpiece holder sprocket 45 via the shaft lower sprocket 49, upper chain 46, and lower chain 47. Since the workpiece holder sprocket 45 is connected to the central axis of the workpiece holder 21 passing through the saddle 1, the workpiece holder 21 also rotates as the workpiece holder sprocket 45 rotates. On the other hand, the rod sprocket 44 is not fixed to the rod, and the rod sprocket 44 is not fixed to the rod.
4 rotates, the rod 33 does not rotate, but the clutch 4
By connecting 2, the power of the rod sprocket 44 is transmitted to the rod 33, and the rod 33 also rotates.

The quenching means 5 is composed of a quenching coil 51 and an injection hole (not shown) provided in the quenching coil 51 for quenching cooling water. The hardened coil 51 is fixed in position separately from the saddle 1, and even if the saddle 1 goes up and down, the hardened coil 51 remains fixed.
does not move, and therefore its relative position with respect to the saddle 1 changes. When the saddle 1 is raised, the hardening coil 51 faces the boss end face 61, which is the locally hardened portion of the workpiece W. The quenching cooling water injection hole communicates with a cooling water source (not shown), and the workpiece W
Cooling water is injected toward the boss end face 61.

[0015] How to carry out the strain correction method for local hardening of the present invention using the local hardening apparatus configured as described above will be explained below. It is divided into process and quenching process. First, the phase matching process will be explained. This process is for aligning the inner diameter spline of the workpiece W with the phase of the mandrel before inserting the mandrel in the next hardening process.

First, the workpiece W is placed on the workpiece pedestal 21 with the inner diameter spline aligned with the phase of the protrusion 22 . The rod 33 and the mandrel 31 are lowered by a driving cylinder 34 to a position where a phase determining part 32 attached to the tip of the mandrel 31 and which matches the phases of the inner diameter spline of the work W and the mandrel 31 partially meshes with the inner diameter spline of the work W. At this point, the rod 33 is not connected to the rod sprocket 44 and can rotate freely, so the brake 41 is activated to keep it stationary. When the workpiece holder 21 is slowly rotated, the phasing part 32 at the tip of the mandrel 31 and the internal spline of the workpiece W match in phase, and the rod 33 begins to rotate overcoming the resistance force of the brake 41. When the rod 33 starts rotating, the rotation of the workpiece pedestal 21 is stopped. Release the brake 41 on the rod 33 and remove the clutch 4 attached to the rod 33.
2 to the rod sprocket 44, and the rod 33
is driven by the rod sprocket 44 so that it can rotate. The mandrel 31 is detached from the work W by raising the rod 33 by the drive cylinder 34, but the rod 33 is connected to a rod sprocket 44 via a clutch 42, and is further connected to an upper chain 46, a lower chain 47, a shaft 43, and a shaft. The mandrel 31 rotates synchronously with the workpiece holder 2 through the upper sprocket 48 for the shaft, the lower sprocket 49 for the shaft, and the sprocket 45 for the workpiece holder, and even if the workpiece W rotates, the mandrel 31 also rotates synchronously. Therefore, work W
The splines and the mandrel 31 are never out of phase.

Next, the hardening process will be explained. First, when the saddle 1 is raised, the workpiece W is raised together with the saddle 1, so that the distance between the boss end face 61, which is the locally hardened part of the workpiece W, and the hardened coil 51, which does not move, is a specified amount (1.0 mm).
Stop saddle 1 at the position. FIG. 1 shows this state. When the workpiece holder 21 is rotated, the mandrel 3
1 also rotates in sync. At this point, it is still Mandrel 3.
1 is not inserted into the inner diameter of the workpiece W. Quenched coil 5
When a low-voltage high-frequency current is supplied to 1 and the work W is preheated until the surface temperature of the inner diameter portion reaches 520° C., the inner diameter portion expands. Thereafter, a high-voltage, high-frequency current is supplied to the hardening coil 51 to perform main heating for 1.5 seconds. Because it heats up rapidly in a short period of time, the temperature rises only in the vicinity of the local area that you want to harden. During main heating, the rod 33 is lowered by the drive cylinder 34,
Insert the mandrel 31 into the inner diameter portion of the workpiece W. Immediately after the main heating is completed, cooling water is injected toward the boss end face for 10 seconds from an injection hole (not shown) provided in the quenching coil 51 for quenching. After the quenching is completed, the saddle 1 is lowered. Work holder 23 slidably attached to saddle 1
moves forward and fixes the workpiece W. FIG. 2 shows this state. The rod 33 is raised and the mandrel 31 is detached from the workpiece W. The work holder 23 is moved back and the work W is taken out from the work holder 21.

The local hardening apparatus of the embodiment can carry out the strain straightening method of the present invention by carrying out such a series of work hardening and straightening steps. Table 1 shows an example of the processing conditions under which the method of the present invention was carried out. When such processing conditions are used, the boss end face temperature measuring section 63 and the inner diameter temperature measuring section 64 shown in FIG. Figure 4 shows the temperature history of the boss end face and inner diameter part of the work W measured at t = 5 mm.
become that way. In addition, as a comparative example, one in which only main heating was performed without preheating was also carried out. The temperature history is shown in FIG.

[0019]

[Table 1]

After locally hardening the boss end face under the conditions shown in Table 1,
The large diameter of the internal spline at the inner diameter of the workpiece was measured. In the clutch hub of this example, since it was necessary to locally harden the boss end face 61 on both the upper and lower sides, the series of workpiece hardening and straightening steps was carried out once, and then the workpieces W were replaced from top to bottom and carried out again. The measurement locations for the large diameter of the internal spline are a, shown in Figure 6.
b, c, and the inner spline large diameter is the dimension of the part represented by D (d1 = 2 mm, d2 =
8mm, d3=8mm, d4=2mm). The measurement results are shown in FIG. 7, and as a result of implementing the present invention, it can be seen that the large diameter inner spline has a smaller amount of deformation from the dimension before quenching than that of the comparative example, and the strain correction effect is large.

In this example, the surface temperature of the inner diameter part during preheating was 520°C, the main heating time was 1.5 seconds, and the cooling water injection time was 10 seconds.
Even when the hardening was carried out at 0° C. for 1 to 3 seconds or 5 to 15 seconds, local hardening with good strain correction was possible as in this example.

As is clear from the above explanation, in the strain straightening method for local hardening of the embodiment, the yield point of the material is lowered by preheating the inner diameter part, so the inner diameter part during local hardening is distortion can be effectively corrected. Further, since the preheating temperature of the inner diameter portion is lower than the austenitizing temperature and the hardening is performed immediately after the main heating of the local portion to be hardened, only the vicinity of the desired local portion is hardened. Furthermore, since the mandrel is inserted after the inner diameter of the workpiece has expanded, the press-fitting load is small.
There are fewer defects such as cracks on the inner diameter of the workpiece when inserting the mandrel.

Although this embodiment has been explained using a ring-shaped part called a clutch hub, which has a spline on the inner diameter part, parts having an inner diameter part of various shapes such as a cylindrical inner diameter part without a spline or a tapered inner diameter part can also be used. It is obvious that this method can also be applied by matching the shape of the mandrel, which is the strain correction member, to the shape of the inner diameter portion. In addition, in this example, preheating of the inner diameter part was performed by lowering the voltage applied to the high-frequency coil for main heating of the locally hardened part, but the voltage was constant and the frequency was lowered during the preheating stage to heat the inside. However, in the main heating, the skin effect of electromagnetic induction may be strengthened by increasing the frequency to heat only the local area to be hardened. Furthermore, it is also possible to preheat it in another heating furnace and then set it in the main local hardening device and immediately perform the main heating and hardening. In addition, although this embodiment has been described with a product in which the boss end face is a locally hardened part, the locally hardened part is not limited to the boss end face, but can also be applied to the outer periphery of a ring-shaped part. It is clear that the correction will be sufficient.

[0024]

Effects of the Invention The strain straightening method for local hardening of the present invention preheats the inner diameter portion to 300 to 600°C, then main heats the locally hardened portion, inserts the strain straightening member, and hardens the local hardened portion. Even when only quenching is performed, the temperature of the inner diameter portion is sufficiently raised and the yield point is lowered, so strain correction can be performed effectively.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing a state in which a workpiece W is being heated in an embodiment of a local hardening apparatus that implements the strain correction method for local hardening of the present invention.

[Fig. 2] In the local hardening apparatus that implements the strain correction method for local hardening of the present invention, the saddle 1 is lowered and the work holder 23 is
FIG.

FIG. 3 is a schematic diagram showing temperature measurement sites on the end face and inner diameter portion of the product.

FIG. 4 is a graph showing the temperature history of the end surface temperature and the temperature of the inner diameter portion of a product in which the present invention is implemented.

FIG. 5 is a graph showing the temperature history of the end surface temperature and the temperature of the inner diameter portion of the product subjected to the method of the comparative example.

FIG. 6 is a schematic diagram showing the dimensional measurement positions of a product in which the present invention was implemented and a product in which the method of a comparative example was implemented.

FIG. 7 is a graph showing the dimensional measurement results of a product in which the present invention was implemented and a product in which the method of a comparative example was implemented.

[Explanation of symbols]

1...Saddle 2...Work support means 21...Work holder 22...Protrusion 23...Work holder 3...Distortion correction means 31...Mandrel (distortion correction member) 32...
Phase determining part 33... Rod 34... Drive cylinder 4... Rotating/stopping means 41... Brake 42... Clutch 43... Shaft 44... Sprocket for rod 45... For receiving workpiece Sprocket 46...
Upper chain 47... Lower chain 48... Upper sprocket for shaft 49...
Lower sprocket for shaft 5... Hardening means 51... Hardened coil W... Workpiece (steel part with hollow inner surface) 61... Boss end face (locally hardened part) 62... Inner diameter part (hollow ) 63...Boss end surface temperature measurement part 64...Inner diameter temperature measurement part

Claims (1)

[Claims] Claim 1: After high-frequency heating of a locally hardened portion of a steel component having a hollow inner surface, a strain correction member is inserted into the inner surface, and the locally hardened portion is hardened while correcting the strain generated on the inner surface during hardening. In the strain straightening method for local hardening, the first step is preheating so that the surface temperature of the inner surface becomes 300 to 600°C, and the second step is local main heating of only the locally hardened portion to the austenitizing temperature. A strain correction method for local hardening, comprising the following steps: a third step of inserting a strain correction member into the inner surface, and a fourth step of hardening a locally hardened portion.