Heat treatment method and heat treatment apparatus

Abstract

To provide a heat treatment method and a heat treatment apparatus capable of effectively suppressing deflection deformation of a steel wire during a heat treatment and obtaining the steel wire having relatively high straightness after the heat treatment.SOLUTION: A heat treatment method according to the present invention is a method for performing a heat treatment on a steel wire SW, the method including a twisting step of, during cooling of the steel wire SW after heating of the steel wire SW, applying a rotational force in a twisting direction around an axial direction to the steel wire SW under application of a tensile force in the axial direction to the steel wire SW to cause twisting deformation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heat treatment method and a heat treatment apparatus used for heat treatment such as quenching or tempering of steel wire. [Background technology]

[0002] For example, in order to satisfy required properties, extrusion pins of dies used in resin injection molding and metal die casting may use steel wire made of alloy tool steel or other materials with enhanced wear resistance, impact resistance, heat resistance, etc. In order to further increase the hardness of such steel wire and prevent it from bending when used as an extrusion pin, etc., it is effective to quench and temper the steel wire.

[0003] On the other hand, plastic processing (twist processing) is known, in which a workpiece such as a bar or plate is twisted on an axis to deform it, thereby producing machine parts, decorative objects, etc. For example, Patent Document 1 discloses a method for twisting a workpiece using two opposing rotating shafts, a workpiece heating device, and a control device for controlling each of the rotating shafts and the heating device, with the aim of reducing the load torque of torsional deformation and performing twisting with good phase positioning accuracy. The twisting method includes the following steps: a first synchronous rotation step in which the two rotating shafts hold both ends of the workpiece and rotate the two rotating shafts synchronously; a heating step in which the workpiece is heated by the heating device while rotating the two rotating shafts synchronously; a twisting step in which, after a predetermined heating time has elapsed since the start of heating in the heating step, a difference is set in the rotational speeds of the two rotating shafts to apply a twisting action to the workpiece; a second synchronous rotation step in which the two rotating shafts are rotated synchronously after the twisting step is completed; a heating stop step in which heating by the heating device is stopped during the second synchronous rotation step; and a release step in which the synchronous rotation of the two rotating shafts is stopped after heating by the heating device is stopped. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-11367 Summary of the Invention [Problem to be solved by the invention]

[0005] When subjecting a steel wire to heat treatment such as quenching or tempering, it may be necessary to heat the steel wire to a relatively high temperature depending on the material of the steel wire. However, when the steel wire is heated to a high temperature, the steel wire may undergo deformation such that it bends significantly into a bow due to thermal expansion during the heat treatment. In this case, there is a problem that the straightness of the steel wire after the heat treatment decreases.

[0006] In order to suppress the bending deformation of a steel wire during heat treatment, it is considered effective to perform the heat treatment while applying a tensile force in the axial direction to the steel wire. However, the tensile force needs to be large enough not to cause breakage of the steel wire, and the bending deformation of the steel wire could not be sufficiently suppressed by applying only a tensile force small enough not to cause breakage.

[0007] The present invention addresses the above-mentioned problems, and has as its object to provide a heat treatment method and heat treatment device that can effectively suppress the bending deformation of a steel wire during heat treatment and can obtain a steel wire with a relatively high straightness after heat treatment. [Means for solving the problem]

[0008] The heat treatment method of the present invention is a method for heat treating a steel wire, and includes a twisting step in which, during cooling after heating the steel wire, a torsional rotational force is applied to the steel wire around the axial direction while an axial tensile force is applied to the steel wire, thereby causing torsional deformation.

[0009] The twisting step is preferably carried out while maintaining the temperature of the steel wire.

[0010] The heat treatment method preferably includes a high-temperature-side cooling step of cooling the steel wire after heating, before the twisting step, and a low-temperature-side cooling step of further cooling the steel wire to a temperature lower than that in the high-temperature-side cooling step, after the twisting step.

[0011] In the high-temperature-side cooling step, the steel wire is preferably naturally cooled.

[0012] In the low-temperature side cooling step, it is preferable to perform forced cooling of the steel wire using a refrigerant.

[0013] The low-temperature side cooling step is preferably performed while rotating the steel wire around its axial direction.

[0014] In the heat treatment method, a tensile force in the axial direction is applied to the steel wire before the twisting step, and the tensile force applied to the steel wire can be increased in the twisting step.

[0015] When quenching the steel wire, the twisting step can be carried out during cooling after heating during quenching of the steel wire.

[0016] In this case, the steel wire can be tempered following the quenching.

[0017] The heat treatment device of this invention is an apparatus used to apply heat treatment to steel wire, and is equipped with a holding section that holds the steel wire, a forward / backward drive mechanism that can apply an axial tensile force to the steel wire held in the holding section, a rotation drive mechanism that can apply a rotational force in at least the torsional direction around the axial direction to the steel wire held in the holding section, thereby causing torsional deformation, and a heating section that heats the steel wire.

[0018] The heat treatment device preferably includes a cooling unit that performs forced cooling of the steel wire using a refrigerant.

[0019] The rotation drive mechanism is preferably configured to be capable of rotating each end of the steel wire held by the holding portion in the same direction around the axial direction.

[0020] The rotary drive mechanism preferably includes two rotary drive parts connected to the holder parts that hold the steel wire at each end.

[0021] The advance / retract drive mechanism preferably includes a plurality of advance / retract drive parts each having a different magnitude of tensile force that can be applied to the steel wire held by the holding part. [Effects of the Invention]

[0022] According to the heat treatment method or heat treatment device of the present invention, it is possible to effectively suppress the bending deformation of the steel wire during the heat treatment, and to obtain a steel wire having a relatively high straightness after the heat treatment. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a partial cross-sectional view schematically showing a heat treatment apparatus according to an embodiment of the present invention. [Figure 2] 2 is a block diagram showing a control unit, a storage unit, a display unit, and an input unit that can be provided in the heat treatment apparatus of FIG. 1. FIG. [Figure 3] FIG. 2 is a schematic diagram showing an example of a method for producing a steel wire to be heat treated using the heat treatment apparatus of FIG. [Figure 4] 1 is a graph showing an example of a change in temperature of a steel wire over time in a heat treatment method according to an embodiment of the present invention. [Figure 5] 1 is a graph showing the change in temperature of a steel wire over time during heat treatment in an example. DETAILED DESCRIPTION OF THE INVENTION

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. A heat treatment method according to one embodiment of the present invention includes a twisting step during cooling of a steel wire after heating, in which a rotational force in a torsional direction about the axial direction is applied to the steel wire under the action of a tensile force in the axial direction, thereby causing torsional deformation.

[0025] In the twisting process, a tensile force is applied to the steel wire to cause torsional deformation. The bending deformation of the steel wire due to thermal expansion is corrected to a straight shape by torsional deformation around the axial direction, suppressing the bending deformation. This allows the steel wire to be heat-treated while suppressing bending deformation, even when the tensile force applied to the steel wire is large enough not to cause breakage when heated to a relatively high temperature. As a result, a steel wire with high straightness can be obtained after the heat treatment. This heat treatment method can be carried out, for example, using a heat treatment device 1 as shown in FIG. 1.

[0026] (heat treatment equipment) 1 includes holding units 2a and 2b that hold a steel wire SW as a workpiece, an advance / retract drive mechanism 3 that can apply a tensile force in the axial direction (the left-right direction in FIG. 1) to the steel wire SW held by the holding units 2a and 2b, a rotation drive mechanism 4 that can apply a rotational force in at least the torsional direction around the axial direction to the steel wire SW held by the holding units 2a and 2b to cause torsional deformation, and a heating unit 5 that heats the steel wire SW. Note that the holding units 2a and 2b can preferably be two collet chucks or the like that grip and hold the ends Ea and Eb of the steel wire SW, as in the illustrated embodiment.

[0027] Here, the advance / retreat drive mechanism 3 and the rotation drive mechanism 4 are each capable of applying at least a tensile force and a rotational force in the torsional direction to the steel wire SW.

[0028] In this embodiment, the rotation drive mechanism 4 includes, for example, one rotation drive unit 4a such as a motor connected to a holding unit 2a that holds one end Ea of the steel wire SW so as to be able to rotate the steel wire SW, and the other rotation drive unit 4b such as a servo motor connected to a holding unit 2b that holds the other end Eb of the steel wire SW so as to be able to rotate the steel wire SW. The rotation drive units 4a and 4b may be pneumatic, hydraulic, or electric rotary actuators other than motors.

[0029] The two rotational drive units 4a, 4b can be configured to rotate at least in the same direction in synchronization with each other around the axial direction of the steel wire SW. When the two rotational drive units 4a, 4b are rotated in the same direction, the entire steel wire SW, including its ends Ea, Eb, can be rotated in that direction. The rotational drive mechanism 4 can also be provided with a brake or braking unit 4c that can fix one end Ea of the steel wire SW so that it does not rotate. By fixing one end Ea of the steel wire SW with the braking unit 4c and rotating the other end Eb of the steel wire SW with the other rotational drive unit 4b, a torsional rotational force can be applied to the steel wire SW.

[0030] In addition to or instead of providing the braking unit 4c, the two rotational drive units 4a, 4b may be rotatable in opposite directions. Rotating the two rotational drive units 4a, 4b in opposite directions promotes the opposite rotation of the ends Ea, Eb of the steel wire SW, thereby applying a torsional torque to the steel wire SW. Although two rotational drive units 4a, 4b are provided in this example, only one rotational drive unit may be provided (not shown). Even with a single rotational drive unit, it is possible to apply a torsional torque to the steel wire by making one end of the steel wire rotatable by the rotational drive unit and fixing the other end so that it does not rotate. Furthermore, by making the other end of the steel wire rotatable and rotating one end by the rotational drive unit, the entire steel wire can be rotated in one direction around the axial direction by the single rotational drive unit.

[0031] As the advance / retract drive mechanism 3, various mechanisms can be employed as long as they can apply a tensile force to the steel wire SW held by the holding portions 2a and 2b.

[0032] In this embodiment, as an example, the other rotation drive unit 4b is fixed in the axial direction, while one rotation drive unit 4a, together with the brake unit 4c, can be moved axially together with a movable unit 4d, such as a base or casing, on which they are placed, by the advance / retract drive mechanism 3. In this case, by using the advance / retract drive mechanism 3 to move the movable unit 4d connected to the rod of the advance / retract drive mechanism 3, together with one rotation drive unit 4a and the brake unit 4c, in a direction away from the other rotation drive unit 4b, the holding units 2a, 2b to which each rotation drive unit 4a is connected are displaced in directions away from each other, and an axial tensile force can be applied to the steel wire SW held at each end Ea, Eb by the holding units 2a, 2b.

[0033] The illustrated advance / retract drive mechanism 3 includes advance / retract drive units 3a and 3b. The advance / retract drive units 3a and 3b can be, for example, a cylinder such as an air cylinder, a ball screw, or other pneumatic, hydraulic, or electric linear actuators. If the advance / retract drive mechanism 3 is provided with at least one advance / retract drive unit 3a or 3b, a tensile force can be applied to the steel wire SW by transmitting the driving force from the advance / retract drive mechanism 3 as described above.

[0034] On the other hand, from the viewpoint of realizing more precise control of the magnitude of the tensile force applied to the steel wire SW, it is desirable to provide two or more, for example, two advance / retract drive units 3a and 3b. In this case, it is preferable that the two advance / retract drive units 3a and 3b have different magnitudes of tensile force that can be applied to the steel wire SW held by the holding units 2a and 2b (for example, a relatively large advance / retract drive unit 3a and a small advance / retract drive unit 3b). By selectively using or combining the two advance / retract drive units 3a and 3b, it becomes possible to precisely adjust the tensile force applied to the steel wire SW.

[0035] The heating unit 5 included in the heat treatment device 1 is capable of heating the steel wire SW. The illustrated heating unit 5 is not limited to this, but includes, for example, disk electrodes 5a, 5b attached to the back surface of each of the holders 2a, 2b, opposite the steel wire SW side, coaxially with the rotation axis of the steel wire SW and rotatable together with the holders 2a, 2b, conductive brushes 5c, 5d in contact with the disk electrodes 5a, 5b, and a heating power source 5e, such as an AC power source, electrically connected to the conductive brushes 5c, 5d by conductors. In the heating unit 5, the steel wire SW can be electrically heated by passing a current from the heating power source 5e through the conductive brushes 5c, 5d and the disk electrodes 5a, 5b to the steel wire SW.

[0036] The heat treatment device 1 may further include a cooling unit 6 that performs forced cooling of the steel wire SW using a refrigerant. In the illustrated example, the cooling unit 6 is an air-cooling cooling unit that uses air as the refrigerant. This cooling unit 6 is provided with a refrigerant injection nozzle 6a positioned close to the steel wire SW, with its central axis oriented parallel to the axial direction. The refrigerant injection nozzle 6a has multiple injection ports (not shown) formed on the steel wire SW side. Air is supplied as a refrigerant to the refrigerant injection nozzle 6a from a blower 6b, such as an electric blower, and the air can be injected toward the steel wire SW from the injection ports. This allows forced cooling of the steel wire SW. The cooling unit may also use a gas other than air or a liquid such as water as the refrigerant.

[0037] Additionally, a temperature sensor 7 capable of measuring the temperature of the surface of the steel wire SW can be provided in the heat treatment device 1. The temperature sensor 7 is preferably a non-contact type, more specifically a radiation thermometer.

[0038] The heat treatment apparatus 1 may include a control unit such as a control panel that controls its operation. As shown in FIG. 2, the control unit may be connected to the heating unit 5, cooling unit 6, temperature sensor 7, and other sensors. If necessary, the forward / backward drive mechanism 3 and rotation drive mechanism 4 may be connected to the control unit. The control unit may also be connected to an input unit, such as an operation panel used by the user to input information, and a display unit used to convey information to the user. At least a portion of the input unit and the display unit may be a touch panel. The control unit may also be connected to a storage unit, such as a hard disk drive (HDD) or flash memory, that stores information or data. The control unit often includes a processor, random access memory (RAM), read-only memory (ROM), and the like, and controls the operation of the heat treatment apparatus 1 based on a program recorded in the ROM or storage unit.

[0039] Incidentally, the steel wire SW to be subjected to heat treatment may be obtained by cutting a long steel wire to a predetermined length before the heat treatment. If the long steel wire SW is not cut to a predetermined length in advance and is subjected to heat treatment such as quenching, the long steel wire tends to bend more greatly during the heat treatment. In this case, for example, a wire rod straightening cutting device 11 as shown in Figure 3 can be used.

[0040] In Fig. 3, a steel wire coil SWC in which a long steel wire SWL is wound in a coil shape is provided around a reel 21. The wire rod straightening and cutting device 11 illustrated in Fig. 3 straightens the long steel wire SWL unwound from the steel wire coil SWC on the reel 21 into a straight shape and then cuts it, and a wire rod straightening unit 12 is provided downstream of the reel 21 in the feeding direction of the long steel wire SWL, and a wire rod cutting unit 13 is provided further downstream thereof.

[0041] In the wire rod straightening section 12, a number of pinch rolls 12b and withdrawal rolls 12c are arranged in series in the feed direction of the long steel wire SWL within a roll stand 12a. The pinch rolls 12b and withdrawal rolls 12c sandwich the long steel wire SWL from both sides. The wire rod cutting section 13 has a cutter 13a that cuts the long steel wire SWL into a steel wire SW. As shown by the solid arrows in Figure 3, the long steel wire SWL unwound from the steel wire coil SWC is passed between the pinch rolls 12b, whereby the long steel wire SWL is straightened into a straight shape. Then, the cutter 13a is moved as shown by the hollow arrow in Figure 3 with respect to the long steel wire SWL fed by the withdrawal roll 12c, to cut the long steel wire SWL to a predetermined length, thereby obtaining a steel wire SW.

[0042] Depending on the straightening of the long steel wire SWL in the wire rod straightening unit 12 and the cutting of the long steel wire SWL in the wire rod cutting unit 13, the steel wire SW obtained after cutting may be prone to bow-shaped bending deformation when heated by heat treatment such as quenching. Even in such cases, by subjecting the steel wire SW to the heat treatment according to the present invention, bending deformation can be effectively suppressed, and a steel wire SW with high straightness can be obtained after the heat treatment.

[0043] The steel wire SW may be any steel wire rod and may be of various types or compositions. Examples of the material for the steel wire SW include high-speed tool steel, particularly SKH such as SKH51 and other molybdenum-based high-speed tool steels, and stainless steel such as SUS440C. This embodiment is suitable for use with steel wire SW having a wire diameter of 2 mm to 5 mm, but is not limited to wire diameters within this range.

[0044] (Heat treatment method) The following is a detailed description of an example of a heat treatment method that can be performed using the above-described heat treatment apparatus 1. Here, an example will be described in which the temperature of the steel wire SW is changed over time to sequentially quench and temper the steel wire SW as shown in Fig. 4, but Fig. 4 is merely an example and is not limited thereto.

[0045] First, the steel wire SW that has been straightened and cut using a wire rod straightening and cutting device 11 as shown in Fig. 3 is transported to the heat treatment device 1 using a transport device or the like (not shown), and set in the heat treatment device 1. Specifically, one end Ea of the steel wire SW is held by one holding part 2a of the heat treatment device 1, and the other end Eb of the steel wire SW is held by the other holding part 2b, resulting in the configuration shown in Fig. 1.

[0046] At this time, a tensile force of 0.01 MPa to 0.60 MPa may be applied to the steel wire SW using the advance / retract drive mechanism 3. This makes it difficult for the wire to slacken during thermal expansion, i.e., it can accommodate expansion during heating and contraction during cooling. A tensile force of this magnitude can be applied throughout the heating step S1, high-temperature step S2, and high-temperature-side cooling step S3, which will be described below.

[0047] Then, in the heating step S1 of quenching shown in Fig. 4, an electric current is passed through the steel wire SW from the heating power source 5e of the heating unit 5 via the conductive brushes 5c, 5d and the disk electrodes 5a, 5b. By this electrical heating, the temperature of the steel wire SW gradually increases and the steel wire SW is heated as shown in Fig. 4.

[0048] In the region where the temperature of the steel wire SW is close to the maximum quenching temperature Tqmax, the temperature of the steel wire SW can be maintained or gradually heated or cooled as shown in Fig. 4 as a high-temperature quenching step S2. Although it depends on the material of the steel wire SW and other conditions and circumstances, for example, the maximum quenching temperature Tqmax may be set to a temperature within the range of 1050°C to 1200°C, and the time for maintaining at the maximum temperature Tqmax or slowly heating or cooling at that temperature may be set to 10 to 40 seconds.

[0049] In the heating step S1, the steel wire SW may be preheated from the start of heating to a temperature of, for example, 880° C. to 900° C. at a relatively fast rate. In this case, the steel wire SW can be held at the above temperature (880° C. to 900° C.) for 10 to 25 seconds, and then heated to the above maximum temperature Tqmax at a slower rate than during preheating.

[0050] Thereafter, the steel wire SW is cooled. At this time, during the cooling, a twisting step S4 can be performed in which a rotational force in the torsional direction around the axial direction is applied to the steel wire SW while a tensile force in the axial direction is applied to the steel wire SW to cause torsional deformation. If a tensile force has been applied to the steel wire SW in advance, the tensile force can be increased. The tensile force applied to the steel wire SW in the twisting step S4 is preferably 4.90 MPa to 9.80 MPa. After the twisting step S4 is completed, the tensile force can be reduced to approximately the same magnitude as before the twisting step S4.

[0051] As described above, the advance / retract drive mechanism 3 is used to apply a tensile force to the steel wire SW, and the rotation drive mechanism 4 is used to apply a rotational force in the torsional direction. In the heat treatment device 1 of the embodiment shown in Fig. 1, the advance / retract drive units 3a and / or 3b drive the movable unit 4d together with one rotation drive unit 4a and the brake unit 4c so that the movable unit 4d moves away from the other rotation drive unit 4b, thereby applying or increasing a tensile force to the steel wire SW. Furthermore, when the brake unit 4c fixes the rotational movement of one end Ea of the steel wire SW while the other rotation drive unit 4b rotates the other end Eb of the steel wire SW around the axial direction, a rotational force in the torsional direction acts on the steel wire SW, causing torsional deformation.

[0052] In the twisting step S4, a tensile force is applied to the steel wire SW to cause a twisting deformation in the steel wire SW, and the twisting deformation is repeated at a small pitch in the axial direction to suppress bow-like bending deformation due to the weight of the steel wire SW during thermal expansion, etc. In this way, the steel wire SW is prevented from bow-like bending deformation during heat treatment, and therefore has a high degree of straightness after heat treatment.

[0053] The number of twisting rotations of the steel wire SW in the twisting step S4 may be, for example, 40 to 60 rotations. The twisting step S4 can be performed when the steel wire SW reaches a temperature Tqhld within the range of 500°C to 600°C during cooling, and it is preferable to maintain the temperature of the steel wire SW at that temperature Tqhld during the twisting step S4. If the temperature at which the steel wire SW is torsionally deformed is higher than 600°C, work hardening will not occur, and torsional deformation may occur locally, resulting in the risk of the steel wire SW breaking. On the other hand, if the temperature is lowered below 400°C, there is a concern that the steel wire SW may break due to brittle fracture. Furthermore, by maintaining the temperature while the steel wire SW is torsionally deforming, breakage during twisting can be prevented and the deformation can be dispersed at a uniform pitch over the entire length of the workpiece. Note that during this temperature maintenance, a temperature fluctuation of approximately ±10°C from the above-mentioned maintenance temperature Tqhld is permitted. Even if the temperature fluctuates slightly within this range, it can be considered that the temperature is maintained.

[0054] As described above, when the twisting step S4 is performed during the cooling of the steel wire SW, a high-temperature-side cooling step S3 for cooling the steel wire SW after heating in the heating step S1 and the high-temperature step S2 can be performed before the twisting step S4. In addition, after the twisting step S4, a low-temperature-side cooling step S5 for further cooling the steel wire SW, which is at a lower temperature than that in the high-temperature-side cooling step S3, can be performed.

[0055] In the high-temperature side cooling step S3 before the twisting step S4, the steel wire SW can be cooled by natural cooling to the above temperature in the twisting step S4. Natural cooling means that the steel wire SW is left as it is without performing any cooling operation after the heating operation is stopped.

[0056] On the other hand, in the low-temperature side cooling step S5 after the twisting step S4, it is preferable to forcibly cool the steel wire SW by using the cooling unit 6 to inject a coolant such as air from the coolant injection nozzle 6a toward the steel wire SW. This ensures quenching quality and straightness. The forcible cooling may be performed from the start of the low-temperature side cooling step S5, or may be performed midway through the low-temperature side cooling step S5. The forcible cooling time may be, for example, 120 to 300 seconds.

[0057] Furthermore, the low-temperature-side cooling step S5 is preferably performed while rotating the steel wire SW around its axis, for example, by rotating one end Ea and the other end Eb of the steel wire SW in the same direction around its axis using two rotation drive units 4a, 4b. By rotating the steel wire SW in this manner, the entire surface of the steel wire SW can be uniformly cooled even with the refrigerant from multiple injection ports (not shown) of the refrigerant injection nozzle 6, which is arranged with its central axis parallel to the axial direction of the steel wire SW.

[0058] After the low-temperature side cooling step S5, when the temperature of the steel wire SW has decreased to normal temperature or room temperature, quenching of the steel wire SW is completed.

[0059] Subsequently, the steel wire SW can be tempered. The tempering may include a heating step S6 in which the steel wire SW is heated using the heating unit 5 until the temperature of the steel wire SW reaches the maximum tempering temperature Ttmax, a temperature holding step S7 in which the temperature of the steel wire SW is held at the maximum temperature Ttmax, and a cooling step S8 in which the steel wire SW is cooled by forced cooling using the cooling unit 6 or by natural cooling. The tempering cooling step S8 may be performed while the steel wire SW is rotated using the rotary drive mechanism 4.

[0060] Generally, tempering may need to be performed multiple times, but in this embodiment, although the reason is not necessarily clear, by performing the twisting step S4 during quenching, the steel wire SW may have the desired properties with a single tempering. In this embodiment, tempering may be performed multiple times, and in this case, the properties of the steel wire SW are expected to be further improved.

[0061] Straightness is measured by placing a steel wire SW on a surface plate, rolling it, and inserting plates of different thicknesses called feeler gauges to measure the gap between the surface plate and the wire. For example, the thickness of the gap is measured at 60mm intervals over a total length of 2m, and the variation in the measured gap thickness is used to check for any bending. [Example]

[0062] Next, a prototype heat treatment apparatus of the present invention was fabricated, and the heat treatment method of the present invention was experimentally carried out using the prototype apparatus, which will be described below. However, the description here is for illustrative purposes only and is not intended to be limiting.

[0063] Example 1 A long steel wire made of SKH51 was straightened and cut using a wire straightening and cutting device as shown in Figure 3, to obtain a steel wire approximately 2 m long. In addition, a heat treatment device as shown in Figure 1 was prototyped, and using this, the above steel wire was quenched and tempered using the temperature changes shown in Figure 5.

[0064] In the quenching process, first, an electric current was supplied to the steel wire from the heating power supply in the heating section of the heat treatment device, and the steel wire was electrically heated. Here, as preheating, the steel wire was heated to 880°C in 10 to 30 seconds and held at that temperature for 10 to 20 seconds. This was followed by main heating, where the temperature of the steel wire was raised to 1200°C in 25 seconds, and then slowly cooled to 1150°C over 30 seconds. During this time, the steel wire bent under its own weight in the high-temperature range, and the center position in the axial direction sagged downward by several centimeters, forming a large bow-like curve.

[0065] Next, the temperature of the steel wire was lowered to 510°C by natural air cooling as high-temperature side cooling. Then, while maintaining that temperature, a rotational force in the torsional direction was applied to the steel wire while a tensile force of 4.90 MPa to 9.80 MPa was applied to the steel wire, causing torsional deformation. The number of torsional rotations was changed depending on the wire diameter of the steel wire; more specifically, it was 40 rotations for a steel wire with a wire diameter of 3.2 mm and 60 rotations for a steel wire with a wire diameter of 2.2 mm. As a result, the steel wire underwent torsional deformation at a fine pitch in the axial direction over its entire length, and the large deflection deformation described above was almost completely eliminated.

[0066] Thereafter, as a low-temperature side cooling step, the two rotary drive units were synchronized to rotate each end of the steel wire in the same direction around the axial direction, while the steel wire was forcedly cooled by air using the cooling unit. This completed the quenching.

[0067] Subsequently, after the above quenching was completed, tempering was carried out continuously. In tempering, the steel wire was heated to a temperature of 620°C over 30 to 60 seconds using a heating section, and held at that temperature for approximately 30 seconds. After that, while rotating each end of the steel wire in the same direction, the steel wire was forcedly cooled by air cooling using a cooling section. In this way, the temperature of the steel wire was lowered to room temperature, and tempering was completed.

[0068] Example 2 The same conditions and methods as in Example 1 were used until the end of tempering, except that the preheating, main heating and high-temperature side cooling were carried out while applying a tensile force of 0.01 MPa to 0.60 MPa to the steel wire.

[0069] (Comparative Example 1) The tempering was carried out under the same conditions and by the same method as in Example 1, except that the temperature of the steel wire was lowered to 510°C and, while maintaining that temperature, a rotational force in the torsional direction was applied to the steel wire without applying a tensile force of 0.01 MPa to 0.60 MPa to cause torsional deformation.

[0070] In the full-length feeler gauge measurements (gap thickness measurements) of the steel wires after tempering in Examples 1 and 2, the thicknesses at both ends (the ends Ea and Eb in FIG. 1) were 0.03 to 0.04 mm, but were 0.03 mm at the center (between the ends: between the ends Ea and Eb in FIG. 1). On the other hand, in Comparative Example 1, the thicknesses at both ends (the ends Ea and Eb in FIG. 1) exceeded 0.04 mm, and were 0.03 mm at the center (between the ends: between the ends Ea and Eb in FIG. 1).

[0071] Therefore, it was confirmed that in Examples 1 and 2, steel wires having relatively high straightness were obtained compared to Comparative Example 1. In Example 1, the tube bent under its own weight in the high temperature range, and the middle position in the axial direction drooped downward by several centimeters, resulting in a large bow-like curve, but this tendency was not observed in Example 2. [Explanation of symbols]

[0072] 1. Heat treatment equipment 2a, 2b holding part 3. Advance / retreat drive mechanism 3a, 3b Advance / retreat drive unit 4 Rotation drive mechanism 4a, 4b Rotation drive unit 4c Braking part 4d moving parts 5 Heating section 5a, 5b Disk electrodes 5c, 5d Conductive Brush 5e Heating power supply 6 Cooling section 6a Refrigerant injection nozzle 6b blower 7 Temperature Sensor 11 Wire straightening and cutting device 12 Wire straightening section 12a Roll Stand 12b Pinch Roll 12c Drawer Roll 13 Wire cutting section 13a Cutter 21 reels SW steel wire Ea One end Eb other end S1 Hardening heating process S2 High temperature quenching process S3 High temperature side cooling process of quenching S4 Twisting process of quenching S5 Low temperature cooling process of quenching S6 Tempering heating process S7 Tempering temperature holding process S8 Tempering cooling process SWC Steel Wire Coil SWL Long steel wire Tqmax Maximum quenching temperature Tqhld holding temperature Ttmax Maximum tempering temperature

Claims

1. A method for heat treating a steel wire, comprising: A heat treatment method including a twisting step in which, during cooling of a steel wire after heating, a rotational force in a torsional direction around the axial direction is applied to the steel wire while an axial tensile force is applied to the steel wire, thereby causing torsional deformation.

2. The heat treatment method according to claim 1 , wherein the twisting step is performed while maintaining the temperature of the steel wire.

3. 3. The heat treatment method according to claim 1, further comprising: a high-temperature-side cooling step of cooling the steel wire after the heating, before the twisting step; and a low-temperature-side cooling step of further cooling the steel wire to a temperature lower than that in the high-temperature-side cooling step, after the twisting step.

4. The heat treatment method according to claim 3 , wherein the high-temperature-side cooling step comprises natural cooling of the steel wire.

5. The heat treatment method according to claim 3 , wherein the low-temperature side cooling step comprises forced cooling of the steel wire using a refrigerant.

6. The heat treatment method according to claim 3 , wherein the low-temperature side cooling step is performed while rotating the steel wire around its axial direction.

7. The heat treatment method according to claim 1 or 2, wherein an axial tensile force is applied to the steel wire before the twisting step, and the tensile force applied to the steel wire is increased in the twisting step.

8. 3. The heat treatment method according to claim 1, wherein the twisting step is carried out during cooling after heating during quenching of the steel wire.

9. The heat treatment method according to claim 8, wherein the quenching is followed by tempering the steel wire.

10. An apparatus used to apply heat treatment to steel wire, a holding portion that holds the steel wire; a forward / backward driving mechanism capable of applying a tensile force in an axial direction to the steel wire held by the holding portion; a rotation drive mechanism that applies a rotational force in at least a torsional direction around the axial direction to the steel wire held by the holding portion, thereby causing torsional deformation; a heating section for heating the steel wire; A heat treatment device comprising:

11. The heat treatment device according to claim 10, further comprising a cooling unit that performs forced cooling of the steel wire using a refrigerant.

12. The heat treatment device according to claim 10 or 11, wherein the rotary drive mechanism is capable of rotating each end of the steel wire held by the holding portion in the same direction around the axial direction.

13. 12. The heat treatment apparatus according to claim 10, wherein the rotary drive mechanism includes two rotary drive parts connected to the holder parts that hold the steel wire at each end.

14. 12. The heat treatment apparatus according to claim 10, wherein the advance / retract drive mechanism includes a plurality of advance / retract drive parts each having a different magnitude of tensile force that can be applied to the steel wire held by the holding part.

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