JP2000290725A - Induction hardening method and induction hardening device - Google Patents

Abstract

(57) [Abstract] [Object] To suppress the heating temperature and heating time during quenching even when the work 10 is a hard quenched material made of a high Cr alloy subjected to spheroidizing treatment. To avoid a decrease in efficiency due to normalizing heat treatment before quenching. After heating a surface portion of a workpiece by high-frequency induction heating to a temperature equal to or higher than a transformation point by a heating means, the cooling of the surface layer is controlled by a cooling means to obtain a structure suitable for quenching. Subsequently, the surface layer is induction-heated at a high frequency to a quenching temperature by the heating means 40 and rapidly cooled by the cooling means 50 to obtain a quenched structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction quenching method and an induction quenching apparatus suitable for induction quenching of hard-hardened materials such as high-Cr alloys that have been subjected to spheroidization.

[0002]

2. Description of the Related Art Induction quenching is used to harden the surface layer of a workpiece in a limited manner. In this induction quenching, the surface layer of the work is heated to an austenitizing temperature or higher in a short time, and thus the hardenability is greatly affected by the structure of the material. Generally, in the case of the same heating time, the austenitizing temperature shifts to a higher temperature side as the structure of the material changes to martensite, sorbite, pearlite, and spherical carbide. Further, the austenitizing temperature shifts to a higher temperature side as the crystal grain size is smaller.

In addition, in castings such as FC and FCD, pearlite in the raw material also affects the austenitizing temperature, and the smaller the amount of pearlite, the more the austenitizing temperature tends to shift to a higher temperature side.

[0004] In addition, high Cr such as SCM material and SUS material
In the alloy, Cr carbide precipitates, and since the precipitate is more difficult to dissolve in austenite than cementite precipitated in carbon steel, the austenitizing temperature is further increased.

[0005] The shift of the austenitizing temperature to the high temperature side means that if the heating time for quenching is the same, the heating temperature must be increased, and quenching is performed at the same temperature. This means that sufficient heating time must be ensured. Otherwise, uniform austenitization is not performed during heating, resulting in incomplete quenching, which impairs hardness and other quenching quality.

By the way, recently, for the purpose of improving machinability (cold workability in drawing or cold forging, etc.),
The number of products that soften the material and perform induction hardening after processing has increased. Generally, in order to soften the material, heat treatment is performed to maintain the temperature just below the transformation point, called spheroidizing annealing, and then gradually cool to spheroidize the carbide. The structure is unsuitable for quenching, and in order to obtain a good quenched structure, it is necessary to raise the heating temperature during quenching considerably compared to a normal structure or to secure a sufficient heating time.

[0007] Particularly, in a high Cr alloy such as an SCM material or a SUS material, the hardenability is inferior because the Cr carbide has a spheroidized structure.

FIG. 1 shows the TTT of a 50Cr-50Mo alloy.
FIG. A is an annealed material, the annealing condition is 85
Furnace cooling at 0 ° C. × 20 minutes−540 ° C. × 61000 seconds.
N is the normalizing material, the normalizing condition is 850 ° C x 20 minutes-
Furnace cooling at 650 ° C. × 1500 seconds. H is a tempered material, the tempering condition is 850 ° C x 20 minutes-water cooling-710 ° C
X 4 hours-air cooling. S is a spheroidized annealing material. The annealing condition is 850 ° C. × 30 minutes−745 ° C. × 7 hours—slow cooling—720 ° C. × 15 hours—slow cooling.

The austenitizing temperature increases as the heating rate increases. Therefore, in induction hardening in which the surface layer of the work is heated for a short time, an essentially high heating temperature is required. Above all, the spheroidized annealing material S, which is a spheroidal carbide structure, does not sufficiently austenite unless the temperature is raised particularly high.

[0010]

In the case of a hard-hardened material that is not suitable for induction hardening, such as a high Cr alloy that has been subjected to spheroidizing treatment, the heating temperature during quenching is increased considerably from the normal structure or the heating time is increased. It is necessary to secure enough. However, prolonging the heating time causes a quenching pattern to collapse or lowers productivity.

In addition, depending on the shape and quenching specification of the product, there are many cases in which the heating temperature during quenching cannot be increased and the heating time cannot be extended. That is, when the heating temperature is increased, distortion or cracks occur depending on the product,
If the heating time is extended, the quenching depth will be too deep,
Depending on the hardening specification, the specification may not be satisfied.

In such a case, conventionally, heat treatment is performed before quenching to change the material structure to a normalized structure or the like that is easy to quench. In addition, the quenching temperature is set to be relatively high with some risk in mind.

[0013] However, in order to change the material structure from a material viewpoint, a diffusion time is required. For this reason, even if heating is performed for a short time in the order of several tens of seconds at the longest, such as high-frequency induction heating, the material structure cannot be changed. For this reason, a long-time batch process is required, and the efficiency of the quenching operation is significantly reduced.

When the quenching temperature is set higher, there is a possibility that distortion or cracks may occur depending on the product.

In order to increase the work efficiency in the moving quenching, the surface layer of the work is preheated by high-frequency induction heating before quenching heating. However, the heating temperature is low, and furthermore, after the preheating, Since the cooling control is not performed, the hardenability has not been improved.

The present invention has been made in view of the above-mentioned circumstances, and it is possible to efficiently form hardened materials such as high chromium alloys which have been subjected to spheroidization without causing distortion and cracking. An object of the present invention is to provide an induction hardening method and an induction hardening device capable of performing induction hardening.

[0017]

Means for Solving the Problems To achieve the above object, an induction hardening method according to the present invention comprises the steps of: The temperature is raised to the transformation point by induction heating, and only the surface layer is changed to a structure suitable for quenching by the temperature rise and the subsequent cooling control, followed by quenching the surface layer. .

Further, the induction hardening apparatus according to the present invention includes a heating means for changing the structure for induction heating the surface layer of the work before quenching above the transformation point, and a surface layer of the work heated above the transformation point. Cooling means for changing the structure by controlling the cooling rate of the part to change to a structure suitable for quenching, and quenching for induction heating the surface layer of the work changed to a structure suitable for quenching to the quench temperature And a quenching cooling means for rapidly cooling the surface layer of the work heated to the quenching temperature to form a quenched structure.

In the case of carrying out the moving quenching, in particular, a work transfer means for transferring a long work in the axial direction, and a surface layer portion of the long work which is provided in the work transfer path and has a part above the transformation point in the axial direction. A heating means for changing the structure for high-frequency induction heating, and a heating means provided downstream of the heating means for forcibly cooling the surface layer part of the work in a part of the axial direction to a structure suitable for quenching. A cooling means for changing the structure to be changed; a quenching heating means provided on the downstream side of the cooling means for high-frequency induction heating the surface layer of the workpiece to a quenching temperature for a part in the axial direction; A quenching cooling means provided on the downstream side of heating of the means and quenching the surface layer portion of the work in a part of the axial direction to form a quenched structure.

In high-frequency induction heating, it is difficult to change the structure of the entire material to a structure suitable for quenching. However, the portion hardened by high-frequency induction heating is the surface layer of the work, and if only the surface layer of the work is used, the structure can be changed to a structure suitable for quenching even by high-frequency induction heating.

Therefore, in the induction quenching method and the induction quenching apparatus according to the present invention, the surface layer to be quenched is changed into a structure suitable for quenching in a short period of time. Even hard-hardened materials such as Cr alloys are efficiently induction hardened without distortion or cracking.

As a structure suitable for quenching, a normalized structure is preferable. This organization transformation point, in particular obtained by a cooling to heating of the _three or more points A, A ₁ following subsequent thereto.
Some martensite structures are also suitable for quenching.

The method of quenching may be moving quenching for quenching a part of the work or non-moving quenching for quenching the whole work at once. In the case of moving quenching, particularly efficient quenching work becomes possible. The cooling means for changing the structure can be omitted, but in that case, heat is dissipated, and the cooling time becomes longer. By providing the cooling means for changing the structure, work efficiency is particularly improved, and productivity is increased. In the case of non-moving quenching, the heating means and the cooling means for quenching can also serve as the heating means and the cooling means for changing the structure, respectively.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a configuration diagram of the induction hardening apparatus according to the embodiment of the present invention.

The induction hardening apparatus according to the embodiment of the present invention is used for performing the induction hardening method according to the present invention. Specifically, it is used for moving and quenching a long work 10 such as a rail. The long work 10 is, for example, an SCM
It is made of a high Cr alloy such as a material or a SUS material. This high Cr
After workability is improved by spheroidizing, the alloy is repeatedly drawn and soft-annealed to obtain a long workpiece 1 having a predetermined shape.
The surface layer is hardened by induction hardening.

The induction hardening device used for hardening the surface layer includes a transport means (not shown) for transporting the long work 10 in the axial direction, and a structure changing mechanism provided on the transfer path of the long work 10. Heating means 20, cooling means 30 for tissue change provided downstream of heating means 20, cooling means 3
0, a heating means 40 for quenching provided further downstream of
And a cooling means 50 for quenching provided further downstream of the heating means 40.

The heating means 20 and 40 are both long workpieces 1.
0 is a high-frequency induction heating coil surrounding a part in the axial direction. The former heating means 20, that is, the heating means for changing the structure, heats the surface layer of the long work 10 to a temperature higher than the transformation point by high-frequency induction heating. The latter heating means 40, that is, a heating means for quenching, heats the surface layer of the long workpiece 10 by high frequency induction to a temperature higher than the austenitizing temperature.

The cooling means 30 and 50 are both long workpieces 1.
0 is an annular jacket surrounding a part in the axial direction. The former cooling means 30, i.e., the cooling means for the tissue changes, the cooling liquid to the surface of the elongated workpiece 10, by blowing a coolant such as cooling air, the surface layer portion heated above _three points A below the transformation point Cool down to a normalized structure suitable for quenching. The latter cooling means 50, that is, the cooling means for quenching, quenches the surface layer heated to a quenching temperature higher than the austenitizing temperature, thereby rapidly cooling the surface layer to form a quenched structure. .

The long workpiece 10 made of a high Cr alloy that has been subjected to spheroidizing treatment is a hard-to-harden material, and is easily deformed by induction hardening. For this reason, it is difficult to secure the quenching temperature,
When the quenching temperature is insufficient, the quenching quality is not ensured. When the quenching temperature is increased, the quenching quality is ensured, but significant distortion occurs. Therefore, conventionally, a batch type normalizing heat treatment was performed before quenching to ensure both quenching quality and distortion prevention, but it was unavoidable that the working efficiency was significantly reduced.

[0030] However, using a high-frequency hardening device, provided by carrying out the induction hardening method according to the present invention, the surface portion of the elongated workpiece 10 is heated in a short time more than _three points A by the heating means 20 after, by being cooled in a short time to less than ₁ point a by the cooling means 30, a normalizing tissue its surface layer portion suitable for hardening in a short time. Therefore, in the subsequent heating to the quenching temperature by the heating means 40,
Since the austenitizing temperature decreases and the heating temperature can be reduced, the cooling means 5 can be used even when the quenching quality is ensured.
The occurrence of distortion after quenching by 0 is prevented.

That is, according to the induction quenching method and the induction quenching apparatus of the present invention, first, high quenching quality is secured without increasing the heating temperature. Second, by not increasing the heating temperature, an increase in quenching depth is avoided. Third,
By not increasing the heating temperature, the occurrence of distortion is prevented. Fourth, a batch type normalizing heat treatment before quenching becomes unnecessary, and even if not, the processing time can be shortened by relaxing the conditions, thereby improving productivity.

In the above embodiment, the cooling means 30 is used for the purpose of shortening the cooling time for changing the structure and shortening the line length. However, the cooling means 30 may be omitted. In that case, cooling for changing the structure is allowed to cool. An after-cooling jacket can be arranged downstream of the cooling means 50 for quenching.

Although the above embodiment is a moving quenching apparatus, a non-moving quenching apparatus as shown in FIG. 3 is also possible depending on the type of work.

In the induction hardening apparatus shown in FIG. 3, there is a so-called turntable type conveying means for conveying a work in a radial manner for conveying the work in a circumferential shape. That is, the first heating station 20 ′ for changing the organization and the second heating station 3
0 ', a structure changing cooling station 40', and a quenching heating / cooling station 50 'are provided.

First, the work carried into the first heating station 20 'for changing the organization has a surface layer of A of the whole work.
High frequency induction heating over ₃ transformation points. When the heating is completed, the structure is moved from the first heating station for changing tissue 20 'to the second heating station for changing tissue 30'. Furthermore, is moved to organizational changes for cooling station 40 ', the surface portion of the entire workpiece is cooled below the A ₁ transformation point. As a result, the surface layer of the entire work has a normalized structure suitable for quenching.

When the heating and cooling for changing the structure are completed,
The work is moved to the quenching heating / cooling station 50 ', and after the surface of the entire work is induction-heated to a temperature higher than the quenching temperature, the work is cooled and the surface of the work is hardened.

In the case of such an induction hardening apparatus as well, the first induction hardening method according to the present invention is carried out, so that the first
High quenching quality is assured. Second, an increase in quenching depth is avoided. Third, the occurrence of distortion is prevented. 4th
In addition, although heat treatment is performed before quenching, the heat treatment is limited to the surface layer, so that the time is short and the productivity is improved.

[0038]

EXAMPLES Next, examples of the present invention will be described, and are compared with conventional examples and comparative examples.

The surface portion of the high Cr alloy (martensitic stainless steel) which has been subjected to the spheroidizing treatment and the subsequent normalizing treatment is heat-treated by high-frequency induction heating in three types of patterns A to C shown in FIG. did. FIG. 5 shows the results of examining the hardness distribution of the surface layer after each heat treatment.

Pattern A is a conventional example in which low-temperature preheating is performed before quenching to shorten the heating time during quenching. The heating temperature during quenching is suppressed to a relatively low temperature that does not cause distortion. The heating time is set short enough to avoid increasing the quenching depth. Quenching was performed following low-temperature preheating. However, since the preheating temperature was lower than the A ₁ transformation point and the structure was not changed, the surface hardness after quenching was about 500 in Vickers hardness Hv, and Rockwell hardness ( about in H _R C) 5
0.

The pattern B has a preheating temperature of A₁More than the transformation point
It is the comparative example which raised. Set the preheating temperature to A ₁Higher than the transformation point
However, the cooling temperature is A₁Above the transformation point and high
And cooling is not adequately controlled.
The surface hardness after entering is about 600 in Vickers hardness Hv,
Cowell hardness (H_RC) is about 56.

On the other hand, the pattern C has a preheating temperature of A
Increase the cooling temperature in cooling following preheating to _three or more points
It is an example of the present invention controlled to _one transformation point or less. The heating temperature at the time of quenching is relatively low, the same as the conventional example and the comparative example,
The heating time also despite being limited, the surface hardness after quenching is about 680 in Vickers hardness Hv, as high as about 59 Rockwell hardness (H _R C). This is because a normalized structure suitable for quenching was formed in the surface layer by the pre-heat treatment.

As described above, according to the present invention, high quenching quality can be ensured even when the quenching temperature is suppressed to a relatively low temperature when the work is a hardly quenched material, and the quenching temperature can be reduced to a relatively low temperature. The suppression prevents the work from being distorted or cracked. Also,
Since there is no need to extend the heating time, an increase in the quenching depth is avoided. Further, since a structure suitable for quenching is formed only in the surface layer of the work, the time required for forming the structure is short, and the formation can be performed by moving quenching. For this reason, the efficiency of quenching work is high, and it becomes possible to omit the batch type normalizing heat treatment and shorten the time,
High productivity is ensured.

In Example C of the present invention shown in FIG. 4, since the work after preheating is allowed to cool, the cooling time is long, but by performing the cooling control here, the cooling time can be shortened.

It should be noted that the present invention relates to a high Cr
Suitable for induction quenching of hard-hardened materials such as alloys, but it is also applicable to other materials, for example, induction hardening of carbon steel and the like. Induction hardening can be performed efficiently.

[0046]

As described above, in the induction hardening method and the induction hardening apparatus according to the present invention, before the surface layer portion of the work is induction hardened, the surface layer portion is subjected to high-frequency induction heating and subsequent heating. A structure suitable for quenching is obtained by cooling control. For this reason, the heating temperature in the induction hardening can be reduced, and distortion and cracking of the work can be prevented. Also,
Even when the quenching temperature is lowered, excellent quenching quality is ensured. Further, since it is not necessary to extend the heating time, an increase in the quenching depth is avoided. Furthermore, the quenching time is short,
Heating and cooling before quenching are performed in a relatively short time.
High productivity can be ensured by omitting the normalizing heat treatment and alleviating the conditions. Accordingly, high quality quenched products are efficiently and economically produced.

[Brief description of the drawings]

FIG. 1 is a TTA diagram of a 50Cr-50Mo alloy.

FIG. 2 is a configuration diagram of an induction hardening device according to an embodiment of the present invention.

FIG. 3 is a configuration diagram of an induction hardening apparatus according to another embodiment of the present invention.

FIG. 4 is a diagram showing heating patterns in a conventional example, a comparative example, and an example of the present invention.

FIG. 5 is a diagram showing hardness distributions in a conventional example, a comparative example, and an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Work 20 Heating means for changing the structure 20 'First heating station for changing the structure 30 Cooling means for changing the structure 30' Second heating station for changing the structure 40 Heating means for quenching 40 'Cooling station for changing the structure 50 Burning Cooling means for loading 50 'Heating / cooling station for quenching 70 Loading / unloading station

Claims (3)

[Claims] 1. Before the surface layer of a work is hardened by high-frequency induction heating to a limited extent, the surface layer is heated to a temperature equal to or higher than the transformation point by high-frequency induction heating. An induction hardening method characterized in that only the surface layer is changed to a structure suitable for quenching, and thereafter the surface layer is hardened. 2. A heating means for structurally changing the surface layer of the work before quenching by high frequency induction heating to a temperature higher than the transformation point, and controlling the cooling rate of the surface layer of the work heated to the transformation point or higher. A cooling means for changing the structure to a structure suitable for quenching, a heating means for quenching for heating the surface layer of the work changed to a quenching temperature to a quenching temperature, and a quenching temperature. An induction quenching apparatus, comprising: a cooling means for quenching a surface layer portion of the heated work to rapidly form a quenched structure. 3. A work transfer means for transferring a long work in the axial direction, and a structure changing means provided in the work transfer path for inducing high-frequency induction heating of a surface layer portion of the long work to a portion above the transformation point at a temperature higher than a transformation point. A heating means, and a cooling means for changing the structure which is provided on the downstream side of the heating of the heating means and forcibly cools the surface layer portion of the workpiece in a part of the axial direction to change the structure to a structure suitable for quenching. And a heating means for quenching, which is provided downstream of the cooling means and heats the surface layer portion of the workpiece by high-frequency induction to a quenching temperature for a part of the workpiece in the axial direction, and is provided downstream of heating of the heating means. And a quenching means for quenching the surface layer portion of the workpiece in an axial direction to form a quenched structure.