JPH11279647A - Method for tempering cylindrical work - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make heat treatment equipment compact. SOLUTION: At the time of heating the part to be hardened of a work up to a temperature not lower than the Ac3 point and then cooling it, cooling is controlled so that cooling is discontinued at a temperature not higher than the Mf point of the work and not lower than tempering temperature, and thereafter the hardened part is tempered by the retained heat of the work. It is desirable that the work consists of a track bushing or a track pin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for tempering a hollow or solid cylindrical work (for example, a track bushing or a pin).

[0002]

2. Description of the Related Art When a cylindrical work such as a crawler bushing or a pin is subjected to furnace heating or induction heating to form a quenched portion in the cylindrical work, the furnace is heated or induced to improve the toughness of the quenched portion. Reheating is performed by heating to temper the hardened portion of the cylindrical work. A conventional heat cycle of quenching and tempering is, for example, as shown in FIG. 2 in the case of furnace heating, in which a work is heated to a quenching temperature of _three or more Ac, held for about 5 minutes, and then rapidly cooled to room temperature. By quenching the work by
Then, it is reheated to the tempering temperature to temper the hardened portion of the cylindrical work. Here, the hardened portion of the cylindrical work includes the following. 1. In the case of a solid cylindrical work such as a crawler pin 1-1. A quenched structure forming part obtained by heating the entire work by furnace heating and obtaining the quenching performance of the steel. 1-2. The workpiece is heated by induction heating, and the quenched structure forming part obtained by the penetration depth at that frequency or the quenching performance of steel (for the parts other than the quenched structure forming part, the as-rolled structure, or the base texture structure before induction heating) Is). 2. In the case of a hollow cylindrical work such as a crawler bushing 2-1. A quenched structure forming part with uniform hardness of the work section obtained by quenching the entire work thickness by induction heating from the outer peripheral surface of the work. 2-2. An outer peripheral surface obtained by forming an induction hardened portion from the outer peripheral surface and the inner peripheral surface toward the center of the thickness, and forming a tempered portion without performing tempering on the bushing thick core between the induction hardened portions. Structure forming part on the side and inner peripheral side. (A method for obtaining this quenched structure is disclosed in Japanese Patent Application Laid-Open No. Sho 59-77979 and Japanese Patent Application No. 7-299.
997 and JP-A-1-75629. )

[0003]

However, any of the conventional methods (1-1, 1-2, 2-1 and 2-2) for tempering a cylindrical work has the following problems. . For the tempering treatment, a heat treatment facility for tempering such as a furnace or induction heating is required. Therefore, when the quenching equipment and the tempering equipment are combined, the entire heat treatment equipment becomes long, and it is necessary to maintain and update the heat treatment equipment for tempering. Therefore, there is a problem that a sufficient site for the heat treatment equipment is required, and a cost for maintenance and renewal is required, and the facility operation rate is reduced due to the maintenance and renewal work.
An object of the present invention is to provide a method of tempering a cylindrical workpiece that can make the heat treatment equipment compact.

[0004]

The present invention for achieving the above object is as follows. (1) When the part to be quenched is heated to a temperature of ₃ or more Ac and then cooled, the cooling should be stopped at a temperature below the M _f (martensite finish) point of the work and higher than the tempering temperature. A method of tempering a cylindrical workpiece in which the cooling is controlled and then the quenched part is tempered by the heat held by the workpiece. (2) The method for tempering a cylindrical work according to (1), wherein the work comprises a bushing or a pin for a crawler belt.

In the above methods (1) and (2) for tempering a cylindrical work, by controlling the cooling conditions during quenching and cooling, the pulling heat after quenching (the work is held at the time when the cooling is stopped). Is used to temper the quenched part, so there is no need to install a heat treatment facility for tempering such as a furnace or induction heating, and both conventional quenching and tempering facilities were required. The heat treatment equipment can be made more compact as compared with. Further, since the pulling heat after quenching is used for tempering, energy can be saved as compared with the conventional case of cooling down to room temperature in quenching cooling and then heating up to the tempering temperature. In addition, since the pulling heat after quenching is used for tempering, compared to the conventional case of quenching cooling to lowering to room temperature and then heating to the tempering temperature, heat treatment equipment for tempering such as furnace or induction heating. Need not be used, and tempering is performed in the quenching step, so that the number of steps can be reduced and the heat treatment time can be shortened.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a method for tempering a cylindrical workpiece according to the present invention is to control the cooling conditions at the time of quenching and cooling by utilizing the pulling heat after quenching. It is a method of tempering the forming part. Examples of the cylindrical work include a crawler track bushing and a crawler track pin. However, it is not limited to crawler bushings or crawler pins.

At the time of quenching, the portion of the workpiece to be quenched is heated to a temperature of ₃ or more Ac (hardening temperature) by furnace heating or induction heating (the structure is thereby austenitized). It is held for a predetermined time (for example, about 5 minutes), and then cooled (quenched) (this converts the structure to martensite).
At the time of this quenching cooling, the cooling is controlled so that the cooling is stopped at a temperature lower than the M _f (martensite finish) point of the work and higher than the tempering temperature. Thereafter, the quenched part is tempered by leaving the work for a certain period of time with the heat held by the work.

[0008] The method will be described for each method of hardening a cylindrical work described in the description of the conventional method. 1-1, 1-2,
When performing quenching heating and cooling, such as 2-1 once, stop cooling immediately after cooling quenching forming portion of the workpiece directly below M _f point by controlled cooling conditions after quenching heating, M _f point The quenched part is tempered by leaving the quenched part at a temperature directly below for a certain period of time. 2-2
When the quenching heating and cooling steps as described above are performed twice each, the quenched part obtained by the quenching heating and cooling in the first step is tempered in the same manner as described above, and then the second step. The quenched part obtained by quenching heating and cooling is also tempered by the above method.

In the quenching cooling and subsequent tempering, even if there is a portion exceeding the _Mf point immediately after the cooling is stopped, the work is substantially uniformly tempered as follows. That is, as shown in FIG.
If the outer surface temperature of the pin 1) for track has ceased cooled when it is less than M _f point, the temperature T ₁ of the core portion may be the above M _f point reference ((a in FIG. 3)). However, after X seconds, the temperature gradient immediately after stopping the cooling becomes uniform. The reasons are as follows: (1) The core is cooled to the _Mf point or lower by cooling the core in the low-temperature part of the surface. (2) The temperature distribution is made uniform by recuperating a portion of the core whose surface has been cooled at a high temperature. (See (b) of FIG. 3). In this case, when the temperature T ₁ of the core portion and falls T ₂ is a temperature below M _f point after X seconds, if kept (T ₁ -T ₂₎ / X a certain level, the core portion Also burns. Of (b) subsequent 3, the core portion naturally cooled from T ₂ also surface is also tempered substantially uniformly.

When the temperature of the workpiece becomes just below the _Mf point during quenching and cooling, the cooling is stopped and tempering is performed using the heat held by the workpiece. Therefore, heat treatment for tempering such as furnace or induction heating. Eliminates the need for equipment, makes it smaller than when heat treatment equipment for tempering is required, reduces the number of work processes and shortens the work time compared to when the temperature is lowered to room temperature and then tempered. Is done.

[0011]

EXAMPLES The method of the present invention was applied to track pins and track bushings to test the effect of tempering. The chemical compositions of the crawler pin and the crawler bushing used were as follows. 1) Crawler pin (obtained by adding boron to SAE1035) C: 0.32 to 0.38 Si: 0.15 to 0.35 Mn: 0.60 to 0.90 P: 0.030 or less S: 0 0.030 or less Cu: 0.30 or less Sn:-Ni: 0.20 or less Cr: 0.20 or less Al: 0.015 to 0.070 Mo:-Ti: 0.010 to 0.040 B: 0.0005 2) Track bushing (SAE1040 to which manganese and boron are added) C: 0.39 to 0.42 Si: 0.15 to 0.35 Mn: 1.00 to 1.20 P: 0 0.025 or less S: 0.025 or less Cu: 0.30 or less Sn:-Ni: 0.20 or less Cr: 0.20 or less Al: 0.015 to 0.070 Mo:-Ti: 0.015 to 0. 050 B: 0.0005 to 0.0030

1) The dimensions of the crawler pin were as follows. Outer diameter: 38.0 mm Total length: 212.0 mm 2) The dimensions of the crawler bushing were as follows. Outer diameter: 59.0 mm Inner diameter: 38.7 mm Total length: 145.5 mm

The heat cycle was as follows. 1) Heat cycle of crawler belt pin Quenching temperature: 850 ° C (furnace heating; more than induction heating) _Ms point (start temperature of martensitic transformation): 400 ° C _Mf point (95% martensite) : 210 ° C Tempering temperature: 170 ° C Tempering holding time of the conventional method: 1.0 h 2) Heat cycle of crawler bushing Hardening temperature: 825 ° C (for furnace heating, higher for induction heating) _Ms point (Start temperature of martensite transformation): 365 ° C. M _f point (95% martensite): 180 ° C. Tempering temperature: 160 ° C. Tempering holding time of conventional method: 1.0 h

The test results were as follows. 1) Crawler track pin A bending test was performed on the track track pin tempered by the method of the present invention and a track pin pin tempered by a conventional heat cycle (a cycle of lowering to room temperature and then reheating to the tempering temperature). As a result, the breaking load (load up to breakage due to bending) and the deflection (the amount of deformation up to breakage) were equivalent to each other. 2) Crawler track bushing A crush test is performed on the track track bushing tempered by the method of the embodiment of the present invention and a crawler track bushing tempered by a conventional heat cycle (a cycle in which the temperature is lowered to room temperature and then reheated to the tempering temperature). When the test was performed, the breaking load (the load until the cylinder was compressed to break) and the deflection (the amount of deformation until the break was broken) were equal to each other.

[0015]

According to the method for tempering a cylindrical work according to the first and second aspects, by controlling the cooling conditions during quenching and cooling, the pulling heat after quenching (the work is held at the time when the cooling is stopped). Since the quenching part is tempered using heat, there is no need to provide a furnace or heat treatment equipment for tempering such as induction heating, and both conventional quenching equipment and tempering equipment were required. In comparison, heat treatment equipment can be made more compact. Further, since the pulling heat after quenching is used for the heating of the tempering, energy can be saved as compared with the case where the temperature is once lowered to room temperature in the conventional quenching cooling and then heated to the tempering temperature. In addition, since the pulling heat after quenching is used to heat the tempering, compared to the conventional case of quenching and cooling to lowering to room temperature and then heating to the tempering temperature, it is more suitable for tempering such as furnace or induction heating. Since it is not necessary to use heat treatment equipment and tempering is performed in the quenching step, the number of steps can be reduced and the heat treatment time can be shortened.

[Brief description of the drawings]

FIG. 1 is a heat cycle diagram of a method for tempering a cylindrical workpiece according to an embodiment of the present invention.

FIG. 2 is a heat cycle diagram of a conventional cylindrical work tempering method.

FIG. 3 is a temperature distribution diagram immediately after cooling is stopped and after X seconds.

[Explanation of symbols]

1 Crawler pin M _f Martensite finish temperature

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiroyuki Takeno 5-9, Yonbancho, Chiyoda-ku, Tokyo Topy Industries, Ltd.

Claims (2)

[Claims] When heating a portion of a workpiece to be quenched to a temperature of not less than Ac ₃ points and then cooling it, the cooling is stopped so that the cooling is stopped at a temperature of not more than the M _f point of the workpiece and not less than the tempering temperature. A method of tempering a cylindrical workpiece that controls and then tempers the quenched part with the heat held by the workpiece. 2. The method for tempering a cylindrical workpiece according to claim 1, wherein said workpiece comprises a track bushing or a pin.