Quenching method

Abstract

The present invention provides a quenching method capable of reducing a cooling speed difference in the vertical direction without requiring a deep cooling tank. This quenching method cools an object to be processed placed on a support table, and comprises: a descending control step for controlling the support table so that the support table descends into a coolant which is accumulated in a cooling tank in a non-flowing state and in which the maximum value of the surface heat transfer coefficient in the boiling stage is 6000 W / m2 * K or more; during the period of forming a vapor film of the coolant around the object to be treated by using the heat of the object to be treated, the immersion of the object to be treated is completed and the support table is stopped; and a state maintaining step for maintaining a state in which the coolant does not flow and a state in which the support table does not move so that a relative flow velocity is not imparted between the object to be processed and the coolant, after stopping the lowering of the support table and at least before martensite transformation occurs on the surface of the object to be processed.

Description

Technical Field

[0001] This invention relates to a quenching method. Background Technology

[0002] Previously, techniques were known for controlling the relative velocity between the workpiece and the coolant surrounding it during quenching using water, which has high cooling performance. For example, Patent Document 1 discloses a structure that cools the entire surface from the boiling stage without forming a vapor film stage by immersing the workpiece in a refrigerant with an average flow rate of 1.0 m / s or higher.

[0003] Patent Document 2 discloses a structure in which, during quenching by moving the workpiece into the interior of a water-based coolant, the relative velocity between the workpiece and the coolant is slower than the movement speed of the workpiece, until at least the workpiece undergoes a martensitic phase transformation. Patent Document 3 discloses a quenching method in which a metal component is immersed in heat treatment oil for quenching, wherein the metal component descends in the heat treatment oil, stops at the vapor film stage (the initial oil-submerged portion), and then rises.

[0004] In addition, Patent Document 4 discloses a structure that, in order to suppress the influence of vapor film on the quenching result, immerses the object to be quenched in a state of suspension on a rod, thereby actively peeling the vapor film off the object to be quenched.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2002-97520

[0006] Patent Document 2: International Publication No. 2020-203226

[0007] Patent Document 3: Japanese Patent Application Publication No. 2021-147626

[0008] Patent Document 4: Japanese Patent Application Publication No. 2023-153496

[0009] When performing quenching that requires a certain internal hardness or depth of hardened layer, the workpiece needs to be rapidly cooled to increase the internal cooling rate. Therefore, various coolants with high cooling performance are used. However, if the cooling rate varies across different parts of the workpiece when using a high-performance coolant, residual deformation may occur after quenching.

[0010] For example, in the technology disclosed in Patent Document 1, by providing a high flow rate to the coolant, the entire surface is cooled from the boiling stage without forming a vapor film. However, in Patent Document 1, the suction mechanism for imparting a flow rate to the water is operated before the cooling of the processed article ends. Therefore, even after transitioning from the vapor film stage to the boiling stage, a flow rate is imparted to the coolant before the cooling ends. Furthermore, in the technology disclosed in Patent Document 1, a top-to-bottom flow rate is imparted to the processed article. In this case, the coolant remains in the lower part of the processed article, resulting in a low relative flow rate, while in the upper part of the processed article, the coolant is stirred, increasing the relative flow rate. Therefore, the upper part of the processed article is cooled at a high speed compared to the lower part. Consequently, a difference in cooling rate occurs between the upper and lower parts of the processed article until the martensitic transformation, causing deformation of the processed article after quenching.

[0011] On the other hand, according to the technology disclosed in Patent Document 2, the relative velocity between the workpiece and the coolant is slower than the moving speed of the workpiece, thus the cooling speed in the vertical direction of the workpiece is homogenized. However, in Patent Document 2, the workpiece is lowered until a martensitic transformation occurs, and the coolant flows downwards, thereby making the relative velocity between the workpiece and the coolant slower than the moving speed of the workpiece. Therefore, in order to maintain a slow relative velocity before the martensitic transformation, the workpiece needs to move downwards more deeply, requiring a deeper cooling tank.

[0012] Furthermore, in Patent Document 3, the metal component needs to be lowered and then raised within a cooling tank, with quenching completed during this upward movement. Therefore, a relative flow rate exists between the workpiece and the coolant until the martensitic transformation occurs, causing deformation of the workpiece after quenching. Additionally, a very deep cooling tank is required, with a descent depth of 100–700 m.

[0013] Furthermore, Patent Document 4 does not disclose the idea of ​​actively utilizing the vapor film by keeping the quenched object in an unstable state to quickly peel off the vapor film.

[0014] The present invention was made in view of the above-mentioned problems, and its purpose is to reduce the difference in cooling rate in the vertical direction without the need for a deep cooling tank, thereby reducing heat treatment deformation. Summary of the Invention

[0015] One embodiment of the quenching method involves cooling a workpiece placed on a support platform, comprising: a descent control step, controlling the support platform such that the maximum surface heat transfer coefficient of the workpiece in the boiling stage, which is in a non-flowing state within the cooling tank, is 6000 W / m. 2The process involves the following steps: First, the coolant descends to a temperature of K or higher. During this process, the heat of the workpiece is used to form a vapor film of the coolant around the workpiece, during which the impregnation of the workpiece is completed and the support platform stops. Second, a state maintenance step is performed whereby, after the descent of the support platform stops, the coolant is kept in a state of non-flow and the support platform is kept in a state of non-movement, at least until a martensitic phase transformation occurs on the surface of the workpiece, so that no relative flow velocity is imparted between the workpiece and the coolant.

[0016] The maximum surface heat transfer coefficient during the boiling stage is 6000 W / m. 2 Coolants with a K-level temperature range have extremely high cooling performance. Therefore, when cooling begins in the boiling stage using such a coolant, the cooling rate is very high, increasing the cooling speed within the workpiece and ensuring the internal hardness and depth of the hardened layer. On the other hand, when the coolant flows in one direction around the workpiece, the relative velocity to the coolant is high on the upstream side of the flow, while on the downstream side, the coolant tends to stagnate, resulting in a lower relative velocity. Consequently, the cooling rate on the upstream side is faster than on the downstream side, and this difference in cooling rate becomes significant, especially with coolants possessing extremely high cooling performance. As a result, the quenched workpiece may deform.

[0017] Therefore, to prevent coolant displacement due to coolant flow, the workpiece is immersed in coolant stored in a non-flowing state within a cooling tank, and the support platform is stopped. This maintains a state where no relative flow velocity is imparted between the workpiece and the coolant, at least until a martensitic transformation occurs on the surface of the workpiece. In this structure, no relative velocity is generated between the workpiece and the surrounding coolant after the descent of the workpiece stops. Therefore, the possibility of cooling rate differences occurring at each part of the workpiece can be reduced, the possibility of uneven quenching can be reduced, and heat treatment deformation can be minimized.

[0018] Furthermore, by maintaining a state where no relative flow velocity is imparted between the workpiece and the coolant, at least before the martensitic transformation occurs on the surface of the workpiece, it is possible to reduce the difference in expansion accompanying the martensitic transformation on the upstream and downstream sides of the workpiece when a relative flow velocity is imparted, thereby reducing deformation in the quenched workpiece. It is important to quench the workpiece within the stagnant coolant to prevent differences in the relative flow velocity between each part of the workpiece and the surrounding coolant. However, if the coolant is not allowed to flow, a relative flow velocity will inevitably be generated between the workpiece and the coolant during the process of immersing the workpiece in the liquid coolant. Therefore, the immersion of the workpiece is completed and stopped while it is covered by a vapor film. According to this structure, the immersion process with a stagnant coolant that generates a relative flow velocity can be completed during the slow-cooling vapor film stage, thus minimizing the influence of the relative flow velocity during the immersion process. Additionally, a very deep cooling tank is not required. Attached Figure Description

[0019] Figure 1A This diagram schematically illustrates the apparatus for performing the quenching method. Figure 1B This is a diagram showing the state during quenching.

[0020] Figure 2 This is a flowchart illustrating the heat treatment process.

[0021] Figure 3 It is a diagram used to illustrate the itinerary.

[0022] Figure 4 This is a graph showing the surface heat transfer coefficient of the coolant.

[0023] Figure 5 It is a diagram used to illustrate the effect.

[0024] Figure 6 This is a graph showing the temperature change and martensite fraction of the treated material according to Example 1.

[0025] Figure 7 This is a graph showing the amount of deformation of the treated object according to Example 1.

[0026] Figure 8 This is a graph showing the temperature change and martensite fraction of the treated material according to Comparative Example 1.

[0027] Figure 9 This is a graph showing the amount of deformation of the treated object according to Comparative Example 1.

[0028] Figure 10 The graph shows the deformation, elongation, and internal hardness of the treated objects according to Example 1 and Comparative Example 1.

[0029] Figure 11 This is a graph showing the hardness of the treated objects according to Example 1 and Comparative Example 2.

[0030] Figure 12 This is a graph showing the temperature change and martensite fraction of the treated material according to Example 2.

[0031] Figure 13 This is a graph showing the amount of deformation of the treated object according to Example 2.

[0032] Figure 14 This is a graph showing the temperature change and martensite fraction of the treated material according to Example 3.

[0033] Figure 15 This is a graph showing the amount of deformation of the treated object according to Example 3.

[0034] Figure 16 The graph shows the deformation, elongation, and internal hardness of the treated objects according to Examples 2 and 3.

[0035] Figure 17 This is a diagram illustrating an embodiment in which the object to be processed, S, is placed at multiple different positions in the vertical direction.

[0036] Figure 18A , Figure 18B This is a diagram showing the structure of the gear ring, which is the object being processed. Figure 18C , Figure 18D This is a diagram showing the structure of the drive shaft that serves as the object being processed.

[0037] Figure 19 This is a diagram showing an example of a support platform when impregnating a gear ring.

[0038] Figure 20 This is a schematic diagram illustrating the period during which the vapor film is maintained in the case of an impregnated drive shaft, section by section.

[0039] Figure 21 This is a diagram showing the state after impregnation is completed when the drive shaft is the object being processed.

[0040] Figure 22 This is a diagram illustrating an embodiment in which a drive shaft serving as the object to be processed is mounted at multiple different positions in the vertical direction of a support platform.

[0041] Figure 23 This is a diagram showing an example of a support platform when the drive shaft is immersed.

[0042] Figure 24 This is a diagram showing the state of the insertion part and the connecting part 211c for inserting a drive shaft, viewed from the direction of the central axis Ax of the drive shaft.

[0043] Explanation of reference numerals in the attached figures:

[0044] 10 Cooling tank, 20 Moving device, 21 Support platform, 22 Support unit Detailed Implementation

[0045] Hereinafter, embodiments of the present invention will be described in the following order: (1) Structure of the apparatus for performing the quenching method; (2) Heat treatment process; (3) Examples; (4) Other embodiments.

[0046] (1) Structure of the apparatus for performing the quenching method:

[0047] Figure 1A This is a diagram schematically illustrating an apparatus for implementing a quenching method according to one embodiment of the present invention. Figure 1A The main parts of the device are shown, and various structures can be used as mechanisms for driving each part, as well as the shapes of each part. Figure 1A The apparatus shown includes a cooling tank 10 with a hollow cuboid portion. In this embodiment, a coolant W is pre-stored in the cooling tank 10. In this embodiment, the coolant W is a liquid that maintains a vapor film around the workpiece S after it has been impregnated as a quenching material, at least until the impregnation of the workpiece S is complete. Specific examples of this coolant W will be described later.

[0048] In this embodiment, the apparatus for performing the quenching method includes a moving device 20 for raising and lowering the workpiece S. The moving device 20 has a support platform 21 and a support portion 22, on which the workpiece S is placed. The support portion 22 has a portion extending in the vertical direction, the lower end of which is connected to the support platform 21. A motor M is connected to the support portion 22, and by using a mechanism (not shown) to convert the rotational force of the motor M into the vertical movement of the support portion 22, the support platform 21 can be moved vertically.

[0049] The structure used to move the support 22 vertically can be of various types, and the drive source for the motor M can be of various energy sources. Alternatively, the support 22 can also move vertically using various mechanisms such as electric, hydraulic, or pneumatic drives. The type of motor M is not limited; it can also be a linear motor, etc.

[0050] In this embodiment, the motor M can change the lifting speed of the support platform 21 on which the object to be processed S is placed. By the control signal output from the control device to the motor M, the lifting speed and the lowering speed of the support platform 21 can be specified.

[0051] Furthermore, the number and placement (or orientation) of the processed items S placed on the support platform 21 can be varied. For example, a tray can be installed on the support platform 21, and a plurality of processed items S can be arranged in the tray. In this specification, the case where there is only one processed item S will be described as an example. Of course, the support platform 21, support section 22, etc., can also have various features. For example, the support platform 21 can also be formed in a grid or lattice shape to facilitate the lowering of the support platform 21.

[0052] In this embodiment, the workpiece S is a component that has undergone carburizing treatment. The carburizing treatment can be performed by... Figure 1A The carburizing process, not shown in the diagram, can be performed using any type of furnace that heats the workpiece S, allowing the carbon surrounding the workpiece S to carburize it. The furnace structure is not limited; it can be a structure that simultaneously carburizes and transports the workpiece S within the furnace, or it can be carburized from a fixed position within the furnace and then removed. The carburizing method is also not limited; it can be gas carburizing, liquid carburizing, solid carburizing, vacuum carburizing (vacuum gas carburizing), plasma carburizing, and various other methods. In short, the workpiece S, after carburizing, is placed on the support platform 21 and quenched.

[0053] (2) Heat treatment process:

[0054] Next, the heat treatment processes (carburizing and quenching) for the workpiece S will be explained. Figure 2 This is a flowchart illustrating the heat treatment process according to this embodiment. In the heat treatment process, the workpiece S to be heat treated is placed in a carburizing apparatus (step S100). Next, carburizing treatment is performed (step S105). The conditions for carburizing treatment are determined based on the intended use of the workpiece S, etc. For example, a predetermined carbonaceous material (gas, etc.) is introduced into the carburizing apparatus in which the workpiece S is placed, and the workpiece S is heated to a target temperature at a predetermined heating rate. Furthermore, if the workpiece S reaches the target temperature, the target temperature is maintained for a predetermined period of time.

[0055] Next, the carburized workpiece S is placed on the moving device 20 (step S110). That is, the carburized workpiece S is placed on the support platform 21. Furthermore, in this embodiment, the cooling tank 10 does not have a device for flowing the coolant W inside, so the coolant W is in a state where it does not flow in the cooling tank 10.

[0056] Next, the descent speed Ve of the workpiece is set to a predetermined speed (step S115). That is, a control signal is output to the motor M, and as a result, the descent speed Ve of the support platform 21 becomes the predetermined speed, and the support platform 21 begins to descend. The predetermined speed is set to complete the impregnation of the workpiece S during the period when a vapor film of coolant W is formed around the workpiece S using the heat of the workpiece S.

[0057] The state in which the upper end of the object S is below the liquid level of the coolant W is considered the completed immersion state. In this embodiment, as... Figure 3 As shown, the stroke ST is determined by a predetermined distance Lg below the surface Sw of the coolant W, where the upper end Es of the workpiece S is below the surface Sw. That is, the stroke ST is set such that the distance Lg between the upper end Es of the workpiece S and the surface Sw of the coolant W is greater than 0. Furthermore, the distance Lg does not need to be excessive; it can be the minimum required length. Specifically, the distance Lg only needs to be set such that the workpiece S is not exposed to the outside of the coolant W, and when the workpiece S stops descending and is cooled at a distance Lg from the surface Sw, a vapor film can be stably generated, and the coolant W covers the workpiece S even during the boiling phase after the vapor film disappears. Specifically, the distance Lg can be set to the maximum fluctuation length (height) + 30 mm, etc. The distance Lg can also be set to less than 1 times the total height of the workpiece S, or 1 / 2, etc.

[0058] The descent speed Ve can be set to complete the immersion of the workpiece S during the period when a vapor film of coolant W is formed around the workpiece S. This setting can be determined based on the height H of the workpiece S, the characteristics of the coolant W, etc. Specifically, in this embodiment, descent continues until the distance (Lg+H) from the liquid surface Sw of the coolant W to the lower end of the workpiece S at the descent stop position of the support platform 21 matches the stroke ST. Furthermore, the descent speed Ve is set to be faster than (stroke ST / vapor film maintenance period T around the workpiece S). When set to such a speed, the immersion of the workpiece S can be completed before the vapor film disappears.

[0059] If the vapor film maintenance period T is the same for the first and last parts of the workpiece S, then the difference between the timing of vapor film disappearance at the first and last parts of the workpiece S is the same as the difference in timing between the two parts. Therefore, in order to minimize the difference in the timing of vapor film disappearance at the first and last parts of the workpiece S, it is preferable to move the support platform 21 as high as possible during the vapor film maintenance period T after the first part is immersed.

[0060] Therefore, (stroke ST / vapor film maintenance period T of the workpiece S) is the lower limit of the descent rate Ve, and the descent rate Ve is set to be greater than ST / T. For example, when using a cylindrical workpiece S with a height of 36 mm made of carburized SCM420, and immersed in 20% water-soluble coolant with a stroke ST of 520 mm, a descent rate Ve of 400 mm / s can be used.

[0061] Furthermore, the vapor film maintenance period T is the period during which the vapor film forms. In this embodiment, the vapor film maintenance period T is the period from the moment the first part of the workpiece S is immersed until the vapor film around that part disappears and boiling begins. The vapor film is formed by the heat transfer from the workpiece S to the coolant W, causing the coolant W to vaporize. The vaporized coolant W exists between the surface of the workpiece S and the liquid coolant W.

[0062] The state in which a vapor film exists around the workpiece S means that a vapor film exists on the entire outer surface of the workpiece S. Furthermore, in this embodiment, it is assumed that the state in which a vapor film exists around the workpiece S means that a vapor film exists on the entire outer surface of the workpiece S, but the possibility of the vapor film partially or temporarily disappearing on the outer surface of the workpiece S is not excluded. That is, even if a state of temporary absence of vapor occurs on a very small portion of the outer surface of the workpiece S, if the state of partial disappearance of vapor does not continue, it can be considered that a vapor film exists.

[0063] When the vapor film of coolant W is in contact with the outer surface of the workpiece S, the surface heat transfer coefficient (heat transfer per unit area per unit temperature difference) is smaller compared to when the liquid of coolant W is in contact with the outer surface. Therefore, the vapor film maintenance period T is the period during which the change in surface heat transfer coefficient per unit temperature between coolant W and workpiece S is below a predetermined value while workpiece S is immersed in coolant W. Furthermore, the surface heat transfer coefficient is defined in JIS Z 8000-5:2014 "Quantities and Units - Part 5: Thermodynamics" as surface heat transfer coefficient α = Q / (A(Tw-Ta)). Where Q is the amount of heat transferred (W), and A is the heat transfer area (m²). 2 Tw is the surface temperature of the object being processed (K), and Ta is the temperature of the coolant (K).

[0064] Figure 4 This is a graph showing the surface heat transfer coefficient of coolant W. Figure 4In the diagram, the horizontal axis represents temperature (surface temperature of the workpiece S - coolant temperature: °C), and the vertical axis represents the surface heat transfer coefficient, which is shown for each of the plurality of coolants W. Furthermore, the temperature of the coolant W can be set to various temperatures, and the surface heat transfer coefficient varies depending on the temperature of the coolant W. Therefore, the difference between the surface temperature of the workpiece S and the temperature of the coolant W is used as the temperature on the horizontal axis. Additionally, solid lines represent water-soluble coolants with 10% dissolved polymers in water, dashed lines (shown with dots) represent water-soluble coolants with 20% dissolved polymers in water, dashed lines represent hot oil, dashed lines (shown with lines) represent cold oil, and double-dashed lines represent water. Figure 4 In this system, water-soluble coolant and water are kept at 25°C, cold oil at 80°C, and hot oil at 100°C. Furthermore, in... Figure 4 In the figure, multiple points on the curve represent the values ​​of temperature and surface heat transfer coefficient. Furthermore, the surface heat transfer coefficient of coolant W is a coefficient calculated from the cooling curve obtained according to the cooling performance test method in JIS K2242:2012 "Heat Treatment Oils".

[0065] A water-soluble coolant is a coolant W in which a water-soluble substance is dissolved in water. It is a polymer-based water-soluble coolant containing polymers such as polyalkylene glycols, polyvinyl alcohol, polyethylene glycol, sodium polyacrylate, and polyvinylpyrrolidone. It can also be a polymer-based water-soluble coolant containing at least one of these polymers. The coolant W in this embodiment is a water-soluble coolant with polyalkylene glycol as its main component. The concentration of the polymer is, for example, 5–30 vol%, 10–30 vol%, or 10–20 vol%. For example, Daphne Plastic Quench DQ (registered trademark) manufactured by Idemitsu Kosan Co., Ltd.

[0066] Examples of hot and cold oils include quenching oils made by adding various additives to mineral oil. For example, a hot oil is Glorious Decomposition Quenching Oil S (registered trademark) produced by Nippon Yushu Co., Ltd., which uses low-sulfur refined mineral oil as a base oil and adds additives. For a cold oil, an example is DaphneMaster Quench A (registered trademark) produced by Idemitsu Kosan Co., Ltd., which uses paraffinic mineral oil as a base oil and adds additives.

[0067] according to Figure 4It is known that when the workpiece S is impregnated with a material at a higher temperature than the A1 phase transformation line of the steel phase diagram and becomes austenitic, a vapor film is formed. For example, in a 10% water-soluble coolant, the surface heat transfer coefficient is approximately constant at temperatures t1 to t2. This constant surface heat transfer coefficient is smaller than the surface heat transfer coefficient over most of the temperature range below t1. Thus, the state where the surface heat transfer coefficient is approximately constant means that, by forming a vapor film around the workpiece S, heat is difficult to transfer from the workpiece S to the coolant W compared to the case where the area around the workpiece S is liquid. That is, in the temperature range where the surface heat transfer coefficient is approximately constant, the workpiece S and the coolant W exchange heat via a gaseous vapor film, and therefore, the surface heat transfer coefficient is smaller compared to the state where heat exchange occurs with the liquid coolant W.

[0068] Furthermore, in temperature zones where the surface heat transfer coefficient is approximately constant, such as Figure 4 As shown, preferably, the surface heat transfer coefficient is 2000 W / m. 2 Below K. More preferably, the surface heat transfer coefficient is 1300 W / m. 2 Below K. Furthermore, in a temperature range where the surface heat transfer coefficient is approximately constant, the variation range of the surface heat transfer coefficient is 1080–1164 W / m in a water-soluble coolant containing 10% dissolved polymer compounds. 2 K, in a water-soluble coolant containing 20% ​​dissolved polymer compounds, is 1245–1285 W / m 2 ·K. Additionally, in hot oil it is 640W / m 2 K, roughly constant, is 500–680 W / m in cold oil. 2 K, in water, is 800–1000 W / m 2 K. Thus, the temperature range within which the surface heat transfer coefficient can be approximately constant is 200 W / m. 2 · Around K, preferably 100W / m 2 K or less, preferably 70W / m 2 · Below K, 40W / m 2 Coolant W below K.

[0069] When observing Figure 4 By considering the surface heat transfer coefficient of the coolant W, it is possible to determine whether a vapor film forms around the workpiece S when it is immersed in the coolant. For example, when the workpiece S, which has undergone carburizing at a target temperature of approximately 850°C, is immersed in a 10% water-soluble coolant, cooling begins and a vapor film forms, but it remains intact until the temperature of the workpiece S reaches t1. When the workpiece S reaches temperature t1, the vapor film disappears, and the workpiece S is then surrounded by liquid coolant W.

[0070] As described above, the surface heat transfer coefficient is relatively small and does not change much during the formation of the vapor film. That is, the change in the surface heat transfer coefficient relative to the temperature decrease during the process of the workpiece S being immersed in the coolant W is below a predetermined value. For example, it can be assumed that the change in surface heat transfer coefficient per 10°C is 100 W / m. 2 Examples below K. Of course, this given value is just an example; the change in surface heat transfer coefficient per 10°C could also be 80 W / m. 2 · Below K, 50W / m 2 · Below K, 20W / m 2 Values ​​below K, etc.

[0071] The state where the change in surface heat transfer coefficient relative to the temperature decrease is below a predetermined value is maintained between the temperature t2 and temperature t1 after the initial formation of the vapor film following impregnation. If the temperature becomes lower than t1, the change in surface heat transfer coefficient relative to the temperature decrease increases sharply, exceeding the predetermined value. Therefore, the vapor film maintenance period T is the period from when the change in surface heat transfer coefficient relative to the temperature decrease first falls below the predetermined value until it exceeds the predetermined value. This vapor film maintenance period T is determined, for example, through experiments or simulations.

[0072] As described above, preferably, the surface heat transfer coefficient remains approximately constant during the vapor film stage, but becomes larger when the vapor film maintenance period T ends and the process transitions to the boiling stage. In this invention, a maximum surface heat transfer coefficient of 6000 W / m is used during the boiling stage. 2 A coolant W of K or higher is used, enabling rapid cooling of the workpiece S, increasing the internal cooling rate of the workpiece S, and ensuring the internal hardness and depth of the hardened layer. Specifically, in the vapor film stage, due to the surface heat transfer coefficient of 2000 W / m... 2 Below K, the heat transfer from the processed material S to the coolant W is suppressed compared to the boiling stage. On the other hand, the maximum surface heat transfer coefficient during the boiling stage is 6000 W / m. 2 At temperatures above K, the surface heat transfer coefficient varies by at least 4000 W / m during the vapor film and boiling phases. 2 K. Therefore, if the process is moved to the boiling stage, a large amount of heat can be transferred from the processed material S to the coolant W. Furthermore, Figure 4 The hot oil shown is excluded from this invention.

[0073] Furthermore, in this embodiment, the impregnation of the workpiece S needs to be completed within the vapor film maintenance period T, and the support platform 21 needs to be stopped. Therefore, it is preferable that the vapor film maintenance period T is not too short, and that a vapor film forms within a certain period. Specifically, it is preferable that the boiling start temperature at which the vapor film formed around the workpiece S disappears and begins to boil is below 600°C. Furthermore, this boiling start temperature is also related to... Figure 4 Similarly, the temperature on the horizontal axis is evaluated based on the surface temperature of the workpiece S minus the coolant temperature. For example, with a coolant temperature of 25°C, a boiling start temperature of 600°C means that the workpiece S transitions to the boiling stage when its surface temperature is 625°C.

[0074] When using a coolant W with a boiling start temperature of 600°C or lower, and starting impregnation at a surface temperature of approximately 800°C for the workpiece S, the vapor film is maintained until cooling to approximately 175°C. Therefore, even without moving the workpiece S at excessively high speeds, impregnation of the workpiece S can be completed within the vapor film maintenance period T. Furthermore, even when the workpiece S has a long vertical length, and when it is placed at multiple different positions along the vertical direction of the support platform, impregnation of the workpiece S can still be completed within the vapor film maintenance period T.

[0075] If the boiling start temperature is below 600°C, the impregnation of the workpiece S can be completed within the vapor film maintenance period T. Examples of such coolants W include... Figure 4 The examples shown are 10% water-soluble coolant (boiling point 492°C), 20% water-soluble coolant (boiling point 545°C), cold oil (boiling point 540°C), and hot oil (boiling point 560°C). Furthermore, when using coolant W with a boiling point 600°C or lower, Figure 4 The water shown has been drained.

[0076] Furthermore, in this embodiment, rapid cooling cannot be performed if the period of maintaining the vapor film is too long; therefore, it is preferable that the boiling start temperature is not too low. Thus, for example, given that the martensitic phase transformation temperature of the base material is around 420°C, the boiling start temperature is preferably 450°C or higher.

[0077] Furthermore, in order to rapidly cool the workpiece S using coolant W during the boiling stage, it is preferable to rapidly cool it immediately after transitioning from the vapor film stage to the boiling stage. For example, it is preferable that the rate of increase in the surface heat transfer coefficient per unit temperature decrease after the vapor film formed around the workpiece disappears and boiling begins is 100 W / m. 2 ·K 2 above.

[0078] More specifically, by transitioning from the vapor film stage to the boiling stage, the boiling stage transfers heat from the surface of the workpiece S to the coolant W more efficiently than the vapor film stage. Therefore, the surface heat transfer coefficient increases sharply immediately after transitioning to the boiling stage. This degree can be evaluated by the rate of increase in the surface heat transfer coefficient per unit temperature decrease during the temperature reduction process. Furthermore, if this rate of increase is 100 W / m... 2 ·K 2 The above methods enable rapid cooling at a sufficient rate during the boiling stage.

[0079] If the rate of increase in the surface heat transfer coefficient per unit temperature decrease is 100 W / m 2 ·K 2 The above method can rapidly cool the processed material S during the boiling stage, but examples of such a coolant W include... Figure 4 The 10% water-soluble coolant shown has a rise rate of 121 W / m. 2 ·K 2 ), 20% water-soluble coolant (rise rate 170W / m) 2 ·K 2 ), cold oil (rise rate 144W / m) 2 ·K 2 Furthermore, when using a rise rate of 100W / m 2 ·K 2 In the case of the above coolant W, Figure 4 The water and hot oil shown were removed.

[0080] In addition, Figure 4 The results show that in 10% water-soluble coolant, 20% water-soluble coolant, and cold oil, the rate of increase in the surface heat transfer coefficient per unit temperature decrease after transitioning from the vapor film stage to the boiling stage is 100 W / m. 2 ·K 2 As described above, by increasing at this rate, the surface heat transfer coefficient becomes 6000 W / m. 2 K and above. Therefore, these coolants W rapidly cool the treated material S during the boiling stage, and the surface heat transfer coefficient is 6000 W / m. 2 The state above K is maintained until the martensitic phase transformation is fully completed (e.g., until the temperature drops below 300°C). Therefore, the workpiece S can be cooled efficiently.

[0081] return Figure 4The flowchart shown is explained below. In step S115, when the descent speed Ve is set to a predetermined speed, it is determined whether the depth of the lower end of the object being processed S has reached the stroke ST (step S120). That is, it is determined whether the distance from the liquid surface Sw of the coolant W to the lower end of the object being processed S is consistent with the stroke ST. This determination can be achieved through various structures, for example, it can be based on the detection results of various sensors, the drive time of the motor M, etc.

[0082] As described above, in this embodiment, the descent speed Ve is set to a predetermined speed in step S115, and in step S120, the material is lowered until the depth of the lower end of the workpiece S reaches the stroke ST. Therefore, through steps S115 and S120, the workpiece S can be lowered into the coolant W accumulated in the cooling tank 10, and the impregnation of the workpiece is completed during the period when a vapor film of coolant W is formed around the workpiece S using the heat of the workpiece S. As in this embodiment, if the impregnation process of immersing the workpiece S in coolant W that is not flowing in the cooling tank 10 is performed, a relative flow velocity will inevitably be generated between the workpiece S and the coolant. Therefore, in this embodiment, the impregnation process that generates a relative flow velocity is completed during the vapor film stage when the cooling rate is slow. As a result, the influence of the relative flow velocity in the impregnation process can be reduced, that is, the difference in cooling rate between the upstream and downstream sides of the workpiece S with a relative flow velocity can be minimized.

[0083] In step S120, when it is determined that the depth of the lower end of the workpiece S has reached the stroke ST, the motor M stops the descent of the support platform 21 (step S125). That is, the control device outputs a predetermined control signal to the motor M, stopping the operation of the motor M, thereby stopping the descent of the support platform 21. In this embodiment, the coolant W does not flow in the cooling tank 10. Moreover, in this embodiment, the cooling tank 10 does not have a mechanism for moving the coolant W by applying external force using a propeller, pump, or the like. Therefore, if the descent of the support platform 21 is stopped, a state is achieved where no relative flow velocity is imparted between the workpiece S and the coolant W surrounding the workpiece S.

[0084] Therefore, if the descent of the support platform 21 stops, the environment becomes extremely stable, with no factors, other than natural convection, causing the coolant W to flow around the workpiece S. Thus, according to this embodiment, there are no factors promoting the cooling of the workpiece S, and the cooling rate of the workpiece S does not vary from place to place. As a result, the workpiece S is not cooled unevenly, and the possibility of uneven quenching is reduced.

[0085] In step S125, with the descent of the support platform 21 stopped, the vapor film disappears after the vapor film maintenance period T. The vapor film disappears from the vicinity of the workpiece S, and rapid cooling begins when the workpiece S comes into contact with the liquid coolant W. When rapid cooling begins, the temperature of the workpiece S reaches the martensitic transformation initiation temperature Ms, and the martensitic transformation begins from the surface of the workpiece S.

[0086] In this embodiment, the predetermined period is defined as the time during which the martensite fraction of the surface of the workpiece S changes to a predetermined value. This predetermined period can be defined, for example, by the length of time elapsed since the start of impregnation. The martensite fraction P is expressed by the following formula:

[0087] P(t) = 1 - exp(-b(Ms-t))

[0088] t: temperature

[0089] Ms: Martensitic phase transformation onset temperature

[0090] b: A constant determined by the material and carbon concentration (e.g., in SCM420, b = 0.143 in the base material and b = 0.01 in the case of surface carbon concentration of 0.8 (mass%) after carburizing).

[0091] In this embodiment, when the martensite fraction on the surface of the workpiece S becomes a predetermined value, the surface of the workpiece S is considered to have undergone a martensitic transformation. Since a higher martensite fraction results in a harder workpiece S and makes deformation more difficult, the condition of the martensite fraction becoming a predetermined value can be considered a condition used to suppress the magnitude of deformation to below an allowable level. For example, various values ​​such as 21%, 28%, 50%, and 61% can be defined as predetermined values ​​based on the allowable magnitude of deformation. Furthermore, the period during which the martensite fraction reaches this predetermined value, i.e., the predetermined period, can be predetermined through experiments or simulations. In this embodiment, in step S130, it is determined whether the predetermined period has elapsed. If the predetermined period has elapsed, it is considered that the surface of the workpiece S has undergone a martensitic transformation and has been sufficiently quenched. Furthermore, the determination of whether the predetermined period has elapsed can be made by measuring the elapsed time from the start of immersion using a timing device (not shown).

[0092] The cooling tank 10 of this embodiment does not have a mechanism for moving the coolant W by applying external force such as a propeller or pump. Therefore, after the support platform 21 stops, the coolant W will not flow due to external force during the period before the predetermined period is determined to have elapsed in step S130. That is, the coolant W remains in a state where it does not move due to external force during the period before the martensitic phase transformation occurs on the surface of the workpiece S. Therefore, the possibility that the cooling rate of the surface of the workpiece S will become uneven due to the flow of coolant W is very small. Furthermore, if the cooling tank 10 has a mechanism for moving the coolant W, the coolant W can be moved after the predetermined period is determined to have elapsed in step S130 to promote cooling.

[0093] In step S135, it is determined whether the processed object S has reached a predetermined temperature. That is, the temperature at which the processed object S is removed from the coolant W is predetermined. The determination of whether the predetermined temperature has been reached can be implemented using various structures, for example, based on the detection results of various sensors, the measurement of time length, etc.

[0094] In step S135, when it is determined that the workpiece S has reached the specified temperature, the workpiece is raised (step S140). That is, the moving device 20 is controlled to raise the support platform 21. Thus, the state of the workpiece S immersed in the coolant W ends, and the heat treatment process ends. Of course, this cooling process is just one example; subsequent heat treatments such as tempering, annealing, and high-frequency heating can also be performed.

[0095] Here, set as Figure 2 The effect of completing the impregnation during the vapor film maintenance period T, with the coolant W in a non-flowing state as shown, and stopping the support platform 21, will be explained. Figure 4 This diagram illustrates the effects of the various technical concepts employed in this embodiment. Figure 5 In the middle, the technical concept of each element is shown on the left.

[0096] Specifically, if the surface heat transfer coefficient of the boiling stage is 6000 W / m 2 Coolant W with a K or higher temperature, after transferring to the boiling stage, can cause a large amount of heat to move from the workpiece S to the coolant W, increasing the cooling rate inside the workpiece S and improving its internal hardenability. Figure 5 In the diagram, the circles representing the hardenability column indicate the surface heat transfer coefficient as it increases with use, which is 6000 W / m. 2 The hardenability is improved by using coolant with a K or higher K content.

[0097] On the other hand, the surface heat transfer coefficient during the boiling stage is 6000 W / m 2Coolant W with a temperature of K or higher has very high cooling performance, therefore, the workpiece S is prone to deformation. Specifically, when the coolant W flows in one direction around the workpiece S, the relative velocity between the workpiece S and the coolant W is high on the upstream side of the coolant W flow, making the coolant W easily agitated. Conversely, on the downstream side of the coolant W flow, the coolant W tends to stagnate, resulting in a lower relative velocity. Therefore, the cooling rate on the upstream side is faster than on the downstream side, and the difference in cooling rate between different parts of the workpiece S becomes significant. As a result, the quenched workpiece S will deform. Figure 5 In the diagram, the × in the column indicating heat treatment deformation represents the situation where deformation is likely to occur when using a coolant W with high cooling performance.

[0098] Therefore, in order to prevent the coolant W from being stirred or stagnated due to the flow of the coolant, after the workpiece S is immersed in the coolant W accumulated in the cooling tank 10 in a non-flowing state and the support platform 21 is stopped, a state in which no relative flow velocity is imposed between the workpiece S and the coolant W is maintained before the martensitic transformation occurs on the surface of the workpiece S. Therefore, in this embodiment, after transitioning to the boiling stage, a situation in which one part of the workpiece S is cooled while the other part is inhibited from cooling will not occur. Therefore, the cooling rate of each part of the workpiece S is unlikely to be different, and as a result, the amount of deformation of each part of the workpiece S is unlikely to be different. Furthermore, by maintaining a state in which no relative flow velocity is imposed between the workpiece S and the coolant W at least before the martensitic transformation occurs on the surface of the workpiece S, the difference in expansion of the upstream and downstream sides of the workpiece S accompanying the martensitic transformation caused by the imposed relative flow velocity can be reduced, thereby reducing the deformation of the workpiece S after quenching. Furthermore, in this embodiment, the immersion process is performed to complete immersion during the vapor film stage of the coolant W, and the support table is stopped. When the workpiece S is immersed in stagnant coolant W, a relative flow velocity is generated between the workpiece S and the coolant W. However, in this embodiment, the immersion process is completed during the vapor film stage, where the cooling rate is slow. Therefore, the influence of the relative flow velocity generated around the workpiece S during immersion is smaller; that is, the difference in cooling rate between the upstream and downstream sides of the workpiece S in terms of relative flow velocity can be minimized. As a result, the amount of deformation at each part of the workpiece S is less likely to vary. Figure 5 In this case, using circles within the columns representing heat treatment deformation to indicate the amount of deformation at each location makes it difficult to produce differences.

[0099] However, when transitioning to the boiling stage, if the coolant W is not allowed to flow before the martensitic phase transformation occurs on the surface of the workpiece S, the cooling rate inside the workpiece S is slower compared to the case where the coolant W flows around the workpiece S. Therefore, sometimes the desired internal hardness and hardened layer depth cannot be obtained from the workpiece S, and the internal hardenability of the workpiece is reduced. Figure 5 In the figure, the hardenability is represented by the × symbol in the column of hardenability, indicating that the hardenability decreases as coolant W is not allowed to flow before the martensitic phase transformation occurs on the surface of the workpiece.

[0100] Furthermore, the decrease in hardenability can be prevented by using alloys with improved hardenability (Cr, Mo, Mn, Ni, B, Si, V) as the material to be processed, S. However, since Mo, Ni, V, etc., are expensive, this leads to increased costs. Therefore, the decrease in hardenability can be translated as an increase in material costs. However, in this embodiment, since the surface heat transfer coefficient of the boiling stage is 6000 W / m... 2 Coolant W with high hardenability above K will not cause hardenability issues due to the inability to flow coolant W.

[0101] Furthermore, if the rate of increase of the surface heat transfer coefficient during the boiling stage is 100 W / m 2 ·K 2 The coolant W described above can be rapidly cooled at a sufficient rate during the boiling stage, with a surface heat transfer coefficient of 6000 W / m during the boiling stage. 2 Similarly, for coolants W above K, the internal cooling rate of the processed object S increases, and the internal hardenability of the processed object S improves. Figure 5 In the diagram, the circles representing the hardenability column indicate that the rate of increase in hardenability with the surface heat transfer coefficient during the boiling stage is 100 W / m. 2 ·K 2 The above-mentioned coolant W is increased.

[0102] In addition, the surface heat transfer coefficient increases by 100 W / m during the boiling stage. 2 ·K 2 The coolant W has high cooling performance; therefore, if a difference in the degree of cooling occurs in each part of the processed material S, the surface heat transfer coefficient during the boiling stage is 6000 W / m. 2 Coolants with a K content or higher are also prone to deformation. Figure 5In the previous example, the "×" in the column indicating heat treatment deformation indicates that deformation is more likely to occur when using a coolant W with high cooling performance. However, in this embodiment, before the surface of the workpiece S undergoes a martensitic phase transformation, a state in which no relative flow velocity is imparted between the workpiece S and the coolant W is maintained. Furthermore, the impregnation is completed during the vapor film stage of the coolant W, and the impregnation action is performed to stop the support table. Therefore, as described above, heat treatment deformation is less likely to occur.

[0103] Furthermore, in order to complete the impregnation during the vapor film stage, the upper surface of the workpiece S needs to reach below the liquid surface during the vapor film maintenance period T, requiring the support platform 21 to descend at a high speed. Moreover, the faster the support platform 21 moves, the larger the structure of the equipment used to drive it needs to be, requiring equipment with durability to withstand repeated quenching processes in the production process. For example, in the device for lowering the support platform 21, there are inevitably constraints such as an upper limit to the load capacity and an upper limit to the descent speed, requiring excessive costs to increase these limits. Additionally, if there is an upper limit to the descent speed of the support platform 21, the height of the workpiece S needs to be limited so that impregnation can be completed below that descent speed. Therefore, the number of workpieces S arranged vertically and placed on the support platform 21 is limited. Figure 5 In the process, the × column of productivity is used to indicate that as the support platform 21 is lowered at high speed, the design of the equipment becomes difficult. In addition, the height of the processed object S and the number of it arranged in the height direction are constrained.

[0104] As described above, if impregnation is completed during the vapor film stage, it is difficult to improve productivity. However, in this embodiment, productivity is not reduced by using a coolant W with a boiling start temperature of 600°C or lower. That is, if a coolant W with a boiling start temperature of 600°C or lower is used, for example, if impregnation begins when the surface temperature of the workpiece S is around 800°C, the vapor film is maintained until it cools to around 175°C. Thus, if the boiling start temperature is below 600°C, sufficient time can be ensured for completing impregnation during the vapor film stage. Therefore, even without moving the workpiece S at excessively high speeds, impregnation of the workpiece S can be completed within the vapor film maintenance period T. Figure 5 In the diagram, the circles in the productive column indicate that by using coolant W with a boiling start temperature below 600°C, sufficient time can be ensured to complete the impregnation during the vapor film stage.

[0105] Thus, if a coolant W with a boiling start temperature below 600°C is used, a sufficiently long vapor film maintenance period T can be obtained. However, if the vapor film maintenance period T is longer, time is required from the start of impregnation of the workpiece S until the start of rapid cooling. That is, if the transition temperature to the boiling stage is low, the internal cooling rate of the workpiece S becomes insufficient, leading to poor quenching (deterioration of internal hardness and hardened layer depth). Figure 5 In the column for hardenability, the × indicates that the hardenability decreases as coolant W with a boiling start temperature below 600°C is used.

[0106] As mentioned above, it is difficult to increase the cooling rate when using a coolant W with a boiling start temperature below 600°C. However, in this embodiment, a surface heat transfer coefficient of 6000 W / m during the boiling stage is used. 2 • Coolant K or higher, or a surface heat transfer coefficient rising at a rate of 100 W / m during the boiling phase. 2 ·K 2 The coolant W increases the internal cooling rate of the workpiece S, thus preventing a decrease in hardenability as described above.

[0107] As described above, the disadvantages arising from the use of the various technical concepts in this embodiment are compensated for by the advantages of other technical concepts. Therefore, according to this embodiment, a quenching method can be provided that does not require a deep cooling tank, reduces the difference in cooling rates in the vertical direction, and makes deformation less likely.

[0108] (3) Example:

[0109] Next, the quenching process in the aforementioned heat treatment steps will be described. Here, an example is shown where a cylindrical shaft (36 mm in diameter and 148 mm in length) formed using an SCM420 is used as the workpiece S, and is quenched without rolling while supported on a support table 21 with the shaft's axial direction horizontal. This will be explained through... Figure 5 The sample obtained by quenching the workpiece S in the heat treatment process shown is called Example 1. It will be processed by passing the coolant W in the cooling tank 10 through... Figure 3 The sample subjected to quenching in the heat treatment process shown is referred to as Comparative Example 1.

[0110] In the heat treatment process of Comparative Example 1, the coolant W in the cooling tank 10 flows in a constant direction around the workpiece S. This structure can be achieved, for example, by providing a flow section such as a propeller inside the cooling tank 10 to allow the coolant W to flow using external force, thereby causing the coolant W circulating inside the cooling tank 10 to flow in a constant direction around the workpiece S. That is, in Comparative Example 1, quenching is performed with the coolant W flowing around the workpiece S in a direction parallel and the same as the downward direction of the support platform 21. Furthermore, the flow velocity Vq of the coolant W is set to be the same as the downward velocity Ve. Therefore, during the descent of the support platform 21, the relative velocity between the workpiece S and the coolant W is 0, but when the support platform 21 stops, the coolant W has a downward relative velocity Ve (=Vq) relative to the workpiece S.

[0111] The stroke ST in both Example 1 and Comparative Example 1 was 520 mm. Furthermore, the coolant W in both Example 1 and Comparative Example 1 was a 20% water-soluble coolant. The internal temperature of the workpiece S when initially immersed in the coolant W was 850°C. A 1 mm surface carburizing treatment was performed on the workpiece S with a surface carbon concentration of 0.8 (mass%). The descent speed Ve was 400 mm / s in both Example 1 and Comparative Example 1, but the flow rate Vq of the coolant W was 0 mm / s in Example 1 and 400 mm / s downwards in Comparative Example 1. In both Example 1 and Comparative Example 1, the temperature of the coolant W was room temperature (e.g., 25°C).

[0112] Figure 3 This is a graph showing the temperature change and martensite fraction of the treated material S, as in Example 1. Furthermore, the horizontal axis represents time logarithmically, the left vertical axis represents temperature, and the right vertical axis represents the martensite fraction. Figure 6 In this graph, the temperature and martensite fraction of the treated material S are shown as they change over each elapsed time since the material S comes into contact with the coolant W. Figure 6 In the diagram, the surface temperature and martensite fraction of the lowermost axially central portion of the workpiece S are represented by solid lines. Conversely, the surface temperature and martensite fraction of the uppermost axially central portion of the workpiece S are represented by dashed lines. Furthermore, in this embodiment, the martensite fraction of the uppermost surface of the workpiece S overlaps with that of the lowermost surface, thus resulting in a state where only solid lines are visible. Moreover, the temperature and martensite fraction of the interior (center) of the workpiece S are represented by double-dashed lines.

[0113] Figure 6 This represents the time variation of the deformation amount in Example 1. Figure 7In the diagram, the horizontal axis represents time logarithmically, and the vertical axis represents the amount of deformation. The amount of deformation (bending) indicates the degree to which the cylindrical shaft of the workpiece S bends in the vertical direction, representing the distance between the uppermost and lowermost parts of the cylindrical shaft in the vertical direction. Furthermore, positive and negative values ​​indicate whether the center or end of the cylindrical shaft is above. A positive value indicates that the center of the cylindrical shaft is higher than the end (upward convexity), and a negative value indicates that the center of the cylindrical shaft is lower than the end (downward convexity).

[0114] When the impregnation of the workpiece S begins, it reflects the deviation in the timing of the impregnation start between the upper and lower parts of the workpiece S, such as... Figure 7 As shown, a temperature difference is created between the bottommost and topmost surfaces of the workpiece S. In this state, the workpiece S gradually cools over time as the temperature difference between the bottommost and topmost surfaces gradually increases.

[0115] However, in Example 1, since the impregnation is completed while the workpiece S is covered by the vapor film and the support platform 21 stops, the temperature difference between the lowermost and uppermost surfaces of the workpiece S does not increase. Specifically, if the workpiece S is impregnated in the coolant W of this embodiment, a vapor film forms around the impregnated portion. Therefore, during the period from the start of impregnation until time te after the vapor film maintenance period T, heat exchange between the workpiece S and the coolant W occurs via the vapor film. Therefore, the cooling rate after the start of impregnation is relatively slow, approximately 100°C / second. Figure 6 It can be seen that in Example 1, during the period from the start of immersion to time ts, the temperature difference between the lowermost and uppermost surfaces of the treated object S remains approximately constant.

[0116] In the processed object S, deformation occurs reflecting the temperature difference. As shown in Example 1, when the lower part of the processed object S is colder than the upper part, the upper part of the processed object S expands more thermally than the lower part, thus the upper part becomes longer and the lower part becomes shorter axially. As a result, the deformation of the processed object S is positive (convex upward). In Example 1, as... Figure 6 As shown, positive deformation occurs from the very beginning of impregnation, and the amount of deformation gradually increases.

[0117] After impregnation begins, the support stage 21 stops during the vapor film maintenance period T. Figure 7 At time ts (1.3 seconds after the start of immersion), the support platform 21 stops. In this embodiment, the cooling tank 10 does not have a mechanism for flowing the coolant W, and the coolant W does not flow. Therefore, after the support platform 21 stops at time ts, the position of the coolant W around the processed object S hardly changes.

[0118] Therefore, no relative flow velocity is generated around the workpiece S and between the workpiece S and the coolant W, and the possibility of a difference in cooling rate above and below the workpiece due to the difference in relative flow velocity between the workpiece S and the coolant W is low. As a result, from the start of immersion to time te, as... Figure 6 As shown, the deformation increases roughly uniformly.

[0119] In this embodiment, the vapor film disappears at time te after time ts. Furthermore, in the shaft of this embodiment, the lowest axial end of the processed object S is cooled first, reaching [temperature value missing]. Figure 7 When the temperature in the shaft reaches 545°C (the surface temperature of the workpiece S is 570°C), it transitions to the boiling stage. In the shaft of this embodiment, when a portion of the workpiece S around it transitions to the boiling stage, the vapor film around the shaft peels off and transitions to the boiling stage, triggering this transition. Therefore, in Figure 4 In the example shown, the vapor film is peeled off at a stage where the surface temperature of the uppermost part of the processed object S is 710°C and the surface temperature of the lowermost part is 680°C.

[0120] When the vapor film disappears, the liquid coolant W comes into contact with the surface of the object being treated, S. The surface heat transfer coefficient of the liquid coolant W is greater than that of the vapor film coolant W; therefore, cooling proceeds rapidly after time te. After time te, as... Figure 6 As shown, the temperature difference is temporarily observable between the bottom and top of the processed object S. However, after the processed object S is rapidly cooled, as... Figure 6 As shown, the cooling rate slows down near time tb, thus the temperature difference between the bottom and top parts gradually diminishes. Therefore, starting near time tb, the degree of thermal expansion of the top part of the processed object S becomes close to that of the bottom part, as... Figure 6 As shown, after time tb, the deformation gradually decreases.

[0121] Furthermore, the temperature on the surface of the workpiece S reaches the martensitic transformation initiation temperature of that surface (at... Figure 7 Before time tm (denoted as Ms point of the carburized layer), the temperature difference between the bottom and top parts of the treated material S is roughly eliminated, and the deformation converges to a minimum value (around 9 μm) after time tb. As mentioned above, in Figure 6 , Figure 6In Example 1, the descent of the workpiece S is stopped during the formation of a vapor film around it, and the coolant W remains stationary. Therefore, the coolant W does not flow around the workpiece S, either during the formation of the vapor film or after the vapor film disappears and rapid cooling begins. Consequently, no relative flow velocity is generated between the workpiece S and the coolant W, and the possibility of a difference in cooling rate due to a difference in relative flow velocity occurring at different locations within the workpiece S is low. Therefore, partial cooling does not occur within the workpiece S, and a temperature difference is unlikely to occur within the workpiece S. Consequently, deformation of the workpiece S is unlikely.

[0122] When the surface of the workpiece S is below the martensitic transformation initiation temperature, martensite gradually forms on the surface of the workpiece S. For example... Figure 7 As shown, no difference was found in the change of the martensite fraction on the surface over time at the bottom and top of the workpiece S. Therefore, the amount of deformation remaining in the workpiece S after quenching is very small.

[0123] Figure 6 This is a graph showing the temperature change and martensite fraction of the treated material S, which serves as Comparative Example 1. Furthermore, the horizontal axis represents time logarithmically, the left vertical axis represents temperature, and the right vertical axis represents the martensite fraction. Figure 8 In this graph, the temperature and martensite fraction of the treated material S are shown as they change over each elapsed time since the material S comes into contact with the coolant W. Figure 8 In the diagram, a solid line represents the temperature and martensite fraction of the lowest surface of the workpiece S. A single-dotted line represents the temperature and martensite fraction of the highest surface of the workpiece S, and a double-dotted line represents the temperature and martensite fraction of the interior (center) of the workpiece S.

[0124] Figure 8 The time variation of deformation in Comparative Example 1 is shown. Figure 9 In the diagram, the horizontal axis represents time logarithmically, and the vertical axis represents the amount of deformation. The definition of deformation is... Figure 9 The definitions in Example 1 shown are the same.

[0125] When the impregnation of the workpiece S begins, it reflects the deviation in the timing of the impregnation start between the upper and lower parts of the workpiece S, such as... Figure 7As shown, a slight temperature difference is created between the lowermost and uppermost surfaces of the workpiece S. However, in Comparative Example 1, since the coolant W flows downward at the same speed as the falling speed of the workpiece S, the temperature difference is smaller than in Example 1. Specifically, when the support platform 21 moves the workpiece S downward, the magnitude and direction of the falling speed Ve and the flow velocity Vq of the coolant W are the same. Therefore, the coolant W moves downward together with the workpiece S, resulting in a state where it is difficult to generate a relative flow velocity between the workpiece S and the coolant W.

[0126] like Figure 8 As shown, in Comparative Example 1, cooling was performed during the vapor film maintenance period T, with the temperatures of the bottom and top parts of the workpiece being similar. Furthermore, in Comparative Example 1, heat exchange between the workpiece S and the coolant W during the vapor film maintenance period T also occurred via the vapor film. Therefore, the cooling rate after the start of impregnation was relatively slow, approximately 100°C / second.

[0127] In the workpiece S, deformation reflecting the temperature difference occurred. Therefore, in Comparative Example 1, it was observed that the lower part of the workpiece S was colder than the upper part, and the amount of deformation became positive (convex upward) immediately after the impregnation began. Furthermore, in Comparative Example 1, the temperature difference between the upper and lower parts of the workpiece S was smaller than in Example 1 immediately after the impregnation began; therefore, the amount of deformation after the impregnation began was smaller than in Example 1. Additionally, in Comparative Example 1, since the temperature difference between the upper and lower parts of the workpiece S was approximately constant, the amount of deformation hardly changed before time ts.

[0128] In Comparative Example 1, the support stage 21 also stopped during the vapor film maintenance period T. Figure 8 In Comparative Example 1, the support platform 21 stops at time ts (1.3 seconds after the start of immersion). However, in Comparative Example 1, the coolant W descends at a downward velocity Vq around the workpiece S. Therefore, when the support platform 21 stops at time ts, the coolant W around the workpiece S flows downward. Consequently, in the axial central portion of the workpiece S, upstream of the flow of coolant W (the upper part of the workpiece S), the coolant W is agitated, resulting in a higher relative flow velocity between the workpiece S and the coolant W; downstream (the lower part of the workpiece S), the coolant W stagnates and becomes in a state of lower relative flow velocity.

[0129] Under these conditions, cooling is promoted around the upper periphery of the workpiece S, while cooling is suppressed around the lower periphery of the workpiece S.

[0130] Thus, in the comparative example, after the support platform 21 stops at time ts, the upper part of the processed object S cools down more easily than the lower part. (Refer to...) Figure 8It can be seen that the surface temperature of the upper part of the object S decreases earlier than the surface temperature of the lower part. In this case, as time passes, the degree of thermal expansion of the lower part of the object S compared to the upper part increases, such as... Figure 8 As shown, after time ts, the deformation changes from positive to negative.

[0131] In Comparative Example 1, the vapor film also disappeared at time te. However, during the rapid cooling phase immediately following the disappearance of the vapor film, the surface temperature of the upper part was lower than that of the lower part, and the upper part was more conducive to cooling than the lower part. Therefore, after time te, the negative deformation increased sharply.

[0132] After the processed material S is rapidly cooled, as... Figure 9 As shown, the cooling rate slows down near time tb, therefore, in Comparative Example 1, the temperature difference generated between the upper and lower parts gradually disappears. Therefore, as... Figure 8 As shown, the absolute value of the deformation gradually decreases after time tb. However, in Comparative Example 1, because the flow of coolant W promotes cooling of the upper part, the temperature difference between the upper and lower parts is difficult to eliminate even when the cooling rate slows down near time tb. In this comparative example, as... Figure 9 As shown, even at the moment tm when the martensitic phase transformation begins (Ms point of the carburized layer) on the surface of the workpiece S is reached, there is a temperature difference between the bottom and top parts of the workpiece S.

[0133] Thus, in Comparative Example 1, at the stage of reaching the martensitic transformation initiation temperature, a temperature difference exists between the lowermost and uppermost parts of the workpiece S, and the temperature of the upper part of the workpiece S is consistently lower than that of the lower part from time te to time tm. Therefore, if we consider the surface temperature of the workpiece S, it is assumed that the lower part of the workpiece S has a greater degree of thermal expansion than the upper part, and bulges downward. However, in the comparative example, as... Figure 8 As shown, the deformation of the processed object S becomes positive at time tr, bulging upwards.

[0134] This is believed to be because the outermost layer of the treated material S reaches the martensitic transformation initiation temperature earlier than the slightly deeper layers, resulting in volume expansion through the martensitic transformation. That is, in Figure 9 In this study, the portion slightly deeper than the surface layer is considered the surface of the workpiece S. This portion slightly deeper than the surface layer is labeled as "surface martensite" and the martensite fraction is shown. However, in the actual surface layer of the workpiece S, the martensitic phase transformation can begin earlier.

[0135] As described above, if a temperature difference is generated on the surface or outer layer of the workpiece S, the timing of the initiation of the martensitic phase transformation differs in each part of the workpiece S. The result is as follows: Figure 8As shown, the amount of deformation of the treated object S becomes a value different from the value predicted only from the surface of the treated object S, and changes in a very complex way over time.

[0136] Furthermore, in the upper part of the workpiece S, the surface, which is slightly deeper than the surface layer, reaches the martensitic transformation initiation temperature at time tm, and the martensite fraction increases after time tm. At time tm, there is a temperature difference between the upper and lower surfaces of the workpiece S. Since the lower part reaches the martensitic transformation initiation temperature later, the martensite fraction in the lower part increases later than that in the upper part.

[0137] Therefore, as the temporal variation of volumetric expansion due to martensitic phase transformation differs between the upper and lower parts of the treated material S, the difference in the degree of volumetric expansion in each part of the treated material S becomes the cause of deformation. Figure 9 In Comparative Example 1 shown, the deformation amount after quenching was 22 μm due to variations caused by various factors. As described above, in Comparative Example 1, the deformation amount was larger than in the embodiment where the coolant W did not flow after the support platform 21 was stopped due to the complex variations in deformation amount.

[0138] As above Figure 9 As explained, in Example 1, the descent of the support platform 21 is stopped during the vapor film maintenance period T, and a state in which no relative flow velocity is imparted between the workpiece S and the coolant W is maintained, at least until the martensitic transformation occurs on the surface of the workpiece S. Therefore, even if some temperature difference is generated at each part of the workpiece S during the vapor film disappearance phase, this temperature difference is eliminated or substantially eliminated when the martensitic transformation initiation temperature is reached. Therefore, the martensite formation rate at each part of the workpiece S is unlikely to vary, thus minimizing deformation.

[0139] exist Figure 6 The diagram shows the deformation (bending amount) (μm), elongation (μm), and internal hardness (Hv) of the treated object S as described above in Example 1 and Comparative Example 1. The deformation (bending amount) is similar to that described above. Figure 10 , Figure 7 The definitions are the same. Elongation is the difference between the axial length of the workpiece S after quenching and the axial length of the workpiece S at room temperature without heat treatment. Internal hardness is the Vickers hardness at the center of the workpiece S.

[0140] In the examples above, comparing Example 1 and Comparative Example 1, although the internal hardness was the same, the deformation was 9 μm and 22 μm upwards, respectively, and the elongation was 131 μm and 150 μm, respectively. Therefore, the deformation and elongation of Example 1 were smaller. As mentioned above, during the quenching of Example 1, the coolant W did not flow due to external force. Therefore, compared with Comparative Example 1, where the coolant W flowed and the cooling rate of each part of the processed object S was uneven, the deformation and elongation of Example 1 were smaller.

[0141] like Figure 9 As shown, if the liquid exists in a temperature range where the change in surface heat transfer coefficient relative to the temperature drop after impregnation is below a predetermined value, then due to the existence of a vapor film maintenance period T, impregnation can be completed within this vapor film maintenance period T, and quenching with minimal heat treatment deformation and high surface hardness can be achieved by stopping the temperature drop. However, if the maximum surface heat transfer coefficient during the boiling stage is 6000 W / m... 2 Coolant W of K or higher can increase the internal hardness and the depth of the hardened layer in the same material being treated, thus increasing the effective hardening depth, compared to the use of hot oil. Figure 4 This is a graph showing the hardness of Example 1, which uses a 20% water-soluble coolant and sets the descent speed Ve to 400 mm / s for quenching, and Comparative Example 2, which uses hot oil and sets the descent speed Ve to 400 mm / s for immersion and then stops, with the relative velocity between the workpiece S and the surrounding coolant W being 400 mm / s. Figure 11 In the graph shown, the horizontal axis represents the distance from the center, and the vertical axis represents Vickers hardness. Furthermore, the center is the cylindrical axis of the workpiece S being treated; distances from this cylindrical axis towards the bottom are represented by negative values, and distances from the cylindrical axis towards the top are represented by positive values. Figure 11 In the diagram, the Vickers hardness of Example 1 is represented by a solid line, and the Vickers hardness of Comparative Example 2 is represented by a dashed line. Additionally, a dashed line indicating 513 HV, the Vickers hardness used as an indicator of effective hardening depth, is also marked.

[0142] As shown in the figure, the Vickers hardness of Comparative Example 2 is lower than that of Example 1 over the entire region from the surface to the interior of the workpiece S. Therefore, it can be said that the effective hardening depth of Comparative Example 2 is shallower than that of Example 1. Thus, when quenching workpiece S of the same material, if a water-soluble coolant is used as the coolant W, a workpiece S with a deeper effective hardening depth can be obtained compared to using hot oil.

[0143] (4) Other implementation methods:

[0144] The above-described embodiment is an example for implementing the present invention, and various other embodiments may also be adopted. For example, the workpiece S is not limited to a shaft; various items such as gears and building components may also be used as workpieces. Furthermore, various postures can be adopted as the posture of the workpiece S during quenching. Any structure can be adopted as long as the workpiece S is fixed to a part such as the support platform 21 for lowering the workpiece S, and the workpiece S remains stationary within the coolant W that does not flow as the support platform 21 lowers. Moreover, in order to stabilize the generation of the vapor film, the gas pressure in the gas environment of the cooling tank 10 can be adjusted. Specifically, the higher the gas pressure in the gas environment of the cooling tank 10, the more stable the vapor film; the lower the gas pressure, the less stable the vapor film. Therefore, the gas pressure can be increased to a predetermined value or higher before the workpiece's descent is complete, and the gas pressure can be reduced to a predetermined value after the workpiece's descent stops.

[0145] Quenching is simply a heat treatment that involves heating metal to a specified temperature and then rapidly cooling it. Various materials can be considered as the material being treated. For example, it is not limited to quenching carburized steel as described in the above embodiment; it can also involve preparing carbon-containing steel in advance, heating it, and then rapidly quenching it. Furthermore, the material being treated can also be a carburized or nitrided material, or a nitrided material.

[0146] Furthermore, any material that can be quenched can be treated, regardless of its material composition. For example, various steel materials, general rolled steel, carbon steel, alloy steel, carburizing steel, tool steel, spring steel, bearing steel, hot-rolled steel plates, cold-rolled steel plates, and carbon steel castings can all be treated. In addition, steel materials defined in JIS, SAE, DIN, and other material standards, such as JIS S35C, JIS S45C, JIS SCM440, JIS SCM420, JIS SCM415, JIS SCR440, JIS SCR420, MSB20, DEG, and AG20, can also be treated. Furthermore, materials that have undergone carburizing, carburizing and nitriding, or nitriding treatments can also be treated.

[0147] In the descent control process, as long as the support platform can be controlled to descend into the coolant accumulated in the cooling tank in a non-flowing state, the impregnation of the workpiece is completed and the support platform stops during the period when a vapor film of coolant forms around the workpiece due to the heat of the workpiece. That is, the descent control process only needs to complete the impregnation and stop the support platform before the vapor film disappears. The cooling tank only needs to be able to accumulate coolant W in a non-flowing state; its shape and capacity are arbitrary. Furthermore, a device for applying external force to make the coolant W flow may or may not be provided. If provided, after the martensitic phase transformation occurs on the surface of the workpiece, by making the coolant W flow, cooling can be achieved as early as possible, and the workpiece can be removed.

[0148] The coolant W can be any material capable of forming a vapor film around the workpiece S. That is, the coolant W can be any liquid that, through the formation of a vapor film, results in a heat transfer between the workpiece S and the coolant W that is less than that of a boiling state. Typically, such a coolant W can be a liquid exhibiting a flat temperature band (where the change in temperature per unit unit is below a predetermined value) between the workpiece and the coolant W after immersion, as shown in a curve of surface heat transfer coefficient versus temperature. For example, besides the water-soluble coolant mentioned above, various coolants W can be used, including aqueous solutions containing various materials dissolved in water, and quenching oils.

[0149] Furthermore, when transitioning from the vapor film stage to the boiling stage, heat moves from the workpiece to the coolant; however, for proper quenching, faster heat movement is preferable in the boiling stage. The extent of this heat movement can be evaluated by the surface heat transfer coefficient, and for proper quenching in the boiling stage, the maximum value of the surface heat transfer coefficient is preferably 6000 W / m. 2 Above K. The surface heat transfer coefficient is the amount of heat transferred per unit area and per unit temperature from the workpiece to the coolant. Therefore, the higher the surface heat transfer coefficient, the more efficient the rapid cooling process. Furthermore, it is known that the maximum surface heat transfer coefficient during the boiling stage is 6000 W / m². 2 At K and above, without allowing the coolant around the workpiece to flow, the cooling rate inside the workpiece S increases, enabling martensitic phase transformation and quenching that increases internal hardness and the depth of the hardened layer. Of course, a high surface heat transfer coefficient is preferable, and a maximum value of 7000 W / m is more preferable. 2 K and above, 8000W / m 2 K and above.

[0150] The support platform used to lower the workpiece can have various structures. For example, as shown in the above embodiment, it can be a support platform for placing the workpiece, a support platform having a support portion for supporting the workpiece, an insertion portion for inserting the workpiece, etc., or it can be a basket-shaped support platform for using coolant W. In addition, it can be a support platform that can fix the workpiece by various fixing members, or it can adopt various other structures.

[0151] A vapor film is a film of vapor formed by the movement of heat from the workpiece to the coolant W. In other words, the state in which vapor is in direct contact with the workpiece, forming a layer of vapor covering it, is the state in which a vapor film is formed. The vapor film only needs to prevent direct contact between the workpiece and the liquid coolant W. The state in which a vapor film is formed is assumed to be one where vapor exists on the entire outer surface of the workpiece, but the outer surface of the workpiece is not in contact with the liquid coolant W. However, it is also permissible to allow the outer surface of the workpiece to partially contact the liquid coolant W without affecting deformation.

[0152] Immersion is simply a process of immersing the object to be treated in coolant W. That is, immersion is considered complete when the object changes from a state where coolant W is absent around it to a state where the entire object is immersed in coolant W. Immersion is completed when the uppermost part of the object is below the surface of coolant W, but to complete immersion in a state where a vapor film is formed, the support platform does not need to be lowered too deeply. For example, the support platform only needs to be lowered to a depth so that the uppermost part of the object is not exposed above the surface of coolant W due to changes in the liquid level.

[0153] The support platform only needs to be stopped in a state where there is no relative flow velocity between the workpiece and the surrounding coolant W. That is, within the non-flowing coolant W, the workpiece is stationary due to the stationary support platform; apart from natural convection, any state where no relative flow velocity is generated is acceptable.

[0154] The state-maintaining process is a process that, after the descent of the support platform has stopped, and at least before the martensitic transformation occurs on the surface of the workpiece, maintains a state in which the coolant does not flow and the support platform does not move in order to prevent a relative flow velocity from being imposed between the workpiece and the coolant W. In other words, after impregnation, the workpiece is kept stationary within the coolant W until the martensitic transformation occurs on the surface of the workpiece.

[0155] Furthermore, the workpiece is preferably supported on the support table in a point contact or line contact manner. Even if point contact or line contact is identified, as long as it is supported or held in multiple (e.g., more than 3) positions and thus fixed to the support table, it is possible to achieve a state in which no relative flow velocity is imparted between the workpiece and the coolant W.

[0156] Furthermore, from the start of impregnation until at least before the martensitic transformation occurs on the surface of the workpiece, a state in which no relative flow velocity is imposed between the workpiece and the coolant W is maintained. This state of imposing a relative flow velocity can be achieved using a mechanism other than a device for lowering the support platform of the workpiece, such as a mechanism for circulating the coolant W. If no flow of coolant W based on this mechanism is performed before the martensitic transformation occurs on the surface of the workpiece, the state in which no relative flow velocity is imposed between the workpiece and the coolant W is maintained.

[0157] That is, in the descent control process and the state maintenance process, the coolant W does not flow through the mechanism used to make the coolant W flow; if minor movements such as natural convection are not considered as flow, it is in a non-flowing state. Thus, during the period before the martensitic phase transformation occurs on the surface of the workpiece, no force is applied to the coolant W from the outside for the purpose of moving it; in this sense, the coolant W does not circulate within the cooling tank. However, the coolant W may move due to external forces not intended for movement. For example, the coolant W may acquire a flow rate greater than 0 as the workpiece descends, or the coolant W may move due to natural convection. Such movement is not included in the movement of the coolant W caused by external forces.

[0158] After the martensitic phase transformation occurs on the surface of the workpiece, the coolant W can be moved by external force. When the coolant W moves, the cooling rate may differ between the upper and lower parts of the workpiece.

[0159] Therefore, if the coolant W flows around the workpiece while the support platform is stationary, differences in the cooling rate of the workpiece may cause deformation. However, after the entire surface of the workpiece undergoes a martensitic transformation, the workpiece hardens, making deformation difficult. Therefore, even if the coolant W moves due to external force after the entire surface of the workpiece undergoes a martensitic transformation, deformation will not occur, or the deformation will be small. Therefore, moving the coolant W after the martensitic transformation can promote cooling, complete the cooling of the workpiece earlier, and remove it from the coolant W.

[0160] Furthermore, whether a martensitic phase transformation has occurred on the surface of the workpiece can be determined by various methods, such as by the time elapsed after the workpiece begins to be impregnated. This time elapsed period can be determined, for example, by the martensite fraction or by the temperature of the surface of the workpiece. For example, a baseline of 21%, 28%, 50%, 61%, etc., for the martensite fraction can be set, and the period up to the statistically significant baseline value can be determined.

[0161] Figure 11 , Figure 12 Indicates that will be with Figure 13 , Figure 6 Example 2, in which the same shaft is immersed in coolant W and the coolant W is allowed to flow after the martensite fraction reaches 21%. Figure 7 , Figure 12 The notation method of curve graphs in China and Figure 13 , Figure 6 Same. Figure 7 , Figure 12 In Example 2 shown, the coolant W is a 20% water-soluble coolant, and the temperature is room temperature (e.g., 25°C). The descending speed of the support stage 21 is 400 mm / s. Furthermore, before the martensite content reaches 21%, the flow rate Vq of the coolant W is 0 mm / s, and after the martensite content reaches 21%, the downward flow rate Vq of the coolant W is 200 mm / s. The stroke ST is 520 mm, and the internal temperature of the workpiece S at the start of immersion in the coolant W is 850°C. A 3 mm surface carburizing treatment is performed on the workpiece S with a surface carbon concentration of 0.8 (mass%).

[0162] exist Figure 13 , Figure 12 In Example 2 shown, the actions before the martensite fraction reaches 21% are roughly the same as... Figure 13 , Figure 6 The same applies to Example 1 shown. Therefore, before the martensite fraction reaches 21%, the progression of surface temperature and martensite fraction is... Figure 7 , Figure 6 The embodiment shown is the same. At time tm, when the surface temperature of the workpiece S reaches the martensitic phase transformation initiation temperature (at Figure 7 At point tm (marked as Ms point of the carburized layer), the martensitic phase transformation occurs. After time tm, as... Figure 12 The surface martensite (top) and (bottom) are shown, and the surface martensite fraction increases.

[0163] When the martensite fraction reaches 21% at time tw, coolant W begins to flow. In this embodiment, the downward flow velocity is 200 mm / s. When this flow velocity is generated around the workpiece S, after time tw, the temperature of the upper part of the workpiece S is lower than that of the lower part. In addition, after time tw, the martensite fraction of the upper part of the workpiece S increases earlier than that of the lower part. After time tw, the difference in temperature (difference in the degree of thermal expansion) and the difference in the magnitude of the martensite fraction (difference in the degree of expansion with the martensitic phase transformation) between the upper and lower parts of the workpiece S are reflected, such as Figure 12 As shown, after time tw, the deformation varies but eventually converges to a constant value. In this example, because the flow of coolant W begins when the martensite fraction is relatively low, deformation occurs due to the difference in expansion caused by the martensitic phase transformation. The martensitic phase transformation takes place while maintaining this deformation, thus... Figure 13 , Figure 6 Compared to the case where the coolant is not flowing, the deformation is larger, with a final deformation value of about 23 μm. If the coolant W is allowed to flow under the condition of deformation, the temperature of the processed object S can be reduced earlier than when it is not flowing, so that the processed object S can be removed from the cooling tank 10 earlier.

[0164] Figure 7 , Figure 14 Indicates that will be with Figure 15 , Figure 6 Example 3, in which the same shaft is immersed in coolant W and the coolant W is allowed to flow after the martensite fraction reaches 61%. Figure 7 , Figure 14 The notation method of curve graphs in China and Figure 15 , Figure 6 same. Figure 7 , Figure 14 The illustrated embodiment 3, except for the timing of the start of the flow of coolant W caused by the flow section, is similar to... Figure 15 , Figure 12 The same as Example 2 shown.

[0165] When the martensite fraction reaches 61% at time tw, coolant W begins to flow. As a result, after time tw, the temperature of the upper part of the processed material S is lower than the temperature of the lower part. Furthermore, after time tw, the martensite fraction in the upper part of the processed material S increases earlier than in the lower part. After time tw, the difference in temperature (difference in the degree of thermal expansion) and the difference in the magnitude of the martensite fraction (difference in the degree of expansion with the martensitic phase transformation) between the upper and lower parts of the processed material S are reflected in, as... Figure 13As shown, after time tw, the deformation amount changes but eventually converges to a constant value. In this example, the final deformation amount is approximately 18 μm. Furthermore, after time tw when the surface martensite fraction reaches 61%, it is also possible to obtain a result where, even with coolant W flowing, the degree of deformation remains unchanged compared to the case where it does not flow. Therefore, in this embodiment, as long as the martensite fraction reaches 61%, coolant W can be flowed without worsening the deformation. Therefore, compared to the case where it does not flow, the temperature of the workpiece S can be lowered earlier, allowing the workpiece S to be removed from the cooling tank 10 earlier.

[0166] exist Figure 15 The diagram shows the deformation (bending amount) (μm), elongation (μm), and internal hardness (Hv) of the treated object S as described in Examples 2 and 3. The deformation (bending amount) is similar to that described above. Figure 16 , Figure 7 The definitions are the same. Elongation and internal hardness are the same as... Figure 9 The definitions are the same. Comparing Examples 2 and 3, although the internal hardness and elongation are equal, the deformation amounts are 23 μm and 18 μm upward convexity, respectively. As mentioned above, Example 2 has a larger deformation amount than Example 3 because the coolant W flows before the martensite phase transformation is fully completed due to the low martensite fraction.

[0167] Furthermore, multiple items S can be placed on the support table 21. Alternatively, items S can be placed at multiple different positions in the vertical direction of the support table 21. Figure 10 This embodiment illustrates a case where the workpiece S is placed at multiple different positions in the vertical direction of the support platform 21. In this embodiment, the structure other than the support platform 21 and the workpiece S placed on the support platform 21 can be implemented using the same structure as in the embodiment described above.

[0168] exist Figure 17 In this design, multiple objects S to be processed can be placed at two different locations in the vertical direction on the support platform 21. Specifically, three objects S are placed on the lower layer of the support platform 21, and three objects S are placed on the upper layer. However, objects S can also be placed in the depth direction shown in the attached drawing. The objects S placed on the lower layer are referred to as the lowermost objects S, and the objects S placed on the upper layer are referred to as the uppermost objects S. Alternatively, objects S can be placed in three or more layers in the vertical direction.

[0169] In this embodiment, the state where the uppermost end Eu of the treated material S is below the liquid level Sw of the coolant W indicates that the impregnation is complete. In this embodiment, as... Figure 17As shown, the stroke ST is determined by a predetermined distance Lg between the uppermost end Eu of the treated object S and the liquid surface Sw of the coolant W. That is, the stroke ST is set such that the distance Lg between the uppermost end Eu of the treated object S and the liquid surface Sw of the coolant W is greater than 0. Furthermore, the distance Lg does not need to be too large; it can be the minimum required length. In other words, the distance Lg only needs to be set in such a way that the treated object S does not protrude outside the coolant W, and when the descent of the treated object S stops and it is cooled at a distance Lg from the liquid surface Sw, a vapor film can be stably generated, and the coolant W covers the treated object S even during the boiling phase after the vapor film disappears. Specifically, the distance Lg can be set to the maximum fluctuation length (height) + 30 mm, etc. The distance Lg can also be set to less than 1 times the total height of the treated object S, or 1 / 2, etc.

[0170] The descent speed Ve can be set to complete the immersion of the uppermost part of the uppermost workpiece S during the period when a vapor film of coolant W is formed around the lowermost workpiece S. It can be set based on the height H from the lower end El of the lowermost workpiece S to the upper end Eu of the uppermost workpiece S, the characteristics of the coolant W, etc. Specifically, in this embodiment, descent continues until the distance (Lg+H) from the liquid surface Sw of the coolant W to the descent stop position of the support platform 21 at the lower end El of the lowermost workpiece S matches the stroke ST. Furthermore, the descent speed Ve is set to be faster than (stroke ST / vapor film maintenance period T around the lowermost workpiece S).

[0171] When set to this speed, the impregnation of all processed materials S can be completed before the vapor film disappears. The support platform 21 is lowered at a descending speed Ve, and stops when the distance from the liquid surface Sw matches the stroke ST. According to the above structure, during the period when the vapor film forms on the bottommost processed material S, the impregnation of the uppermost part (upper end Eu) of the topmost processed material S can be completed, and the support platform 21 can be stopped. Moreover, at least until the martensitic phase transformation occurs on the surface of all processed materials S, a state in which no relative flow velocity is imparted between the processed materials S and the coolant W is maintained.

[0172] According to this structure, during the period when the bottommost workpiece S is covered by a vapor film, the movement of the workpiece S, which is placed across multiple layers in the vertical direction, is stopped. Furthermore, the coolant W around the workpiece S does not flow, at least until a martensitic transformation occurs on the surface of all the workpieces S. Therefore, there are no factors that impart a relative flow rate between the workpiece S and the coolant W around all the workpieces S being processed, and no factors that partially promote the cooling of the workpiece S. Therefore, the possibility of a difference in cooling rate occurring at each part of all the workpieces S being processed can be reduced, thereby reducing the possibility of uneven quenching. In addition, multiple workpieces S can be quenched at once.

[0173] In the above embodiment, the vapor film maintenance period T is the period from the time the first part of the workpiece S is impregnated until the vapor film around that part disappears and boiling begins. This vapor film maintenance period T is defined assuming that boiling occurs first around the first part of the workpiece S being impregnated, and this assumption holds true in many components.

[0174] Furthermore, if the ease of peeling off the vapor film varies at each part of the workpiece S, the easier-to-peel part can be made the lower end of the workpiece S during impregnation, thus making this assumption valid. For example, if the workpiece S contains parts of various shapes, and there are pointed parts, the vapor film is easier to peel off from the pointed parts compared to the non-pointed parts. In this case, the workpiece S can be placed on the support table 21 so that the pointed part is the lower end. In addition, if there are multiple pointed parts in the workpiece S, the pointed parts may sometimes also be located at the lower end by setting an orientation that is easy to place relative to the support table 21.

[0175] Figure 17 , Figure 18A An embodiment of a workpiece S having multiple pointed portions is shown. In this embodiment, the workpiece S is a toothed ring Gr. The toothed ring Gr is a ring-shaped component. Figure 18B This indicates the state of the gear ring Gr as observed along the central axis Ax of the ring. Figure 18A This is a cross-sectional view showing the ring cut along a plane containing its central axis Ax. Teeth that mesh with other gears are formed on the outer periphery of the gear ring Gr. Figure 18B In the diagram, the toothed areas are indicated by dashed lines. The front ends of the toothed portions of the gear ring Gr are sharper than the front ends of the other portions.

[0176] Therefore, as Figure 18A , Figure 18AAs shown, if the gear ring Gr is placed on the support table 21 with the central axis Ax in a horizontal direction, the toothed portion exists at the lower end. Therefore, in this configuration, the vapor film maintenance period T can be considered as the period from the first part of the workpiece S to be impregnated until the vapor film around that part disappears and boiling begins.

[0177] Figure 18B It means immersion. Figure 19 , Figure 18A The diagram shows an example of the support platform 210 for the gear ring Gr. The support platform 210 is a platform capable of supporting the gear ring Gr across three layers in the vertical direction. Figure 18B In the middle, used with Figure 19 The same cross section represents the gear ring Gr, and indicates the state in which the support platform 210 is cut off in that cross section.

[0178] The support table 210 has a mounting portion 210a for mounting the gear ring Gr. The mounting portion 210a can be mounted on the support table 210 at three different locations in the vertical direction. Recesses are formed at multiple locations on the mounting portion 210a, allowing the inner circumferential surface of the gear ring Gr to be positioned by hanging it in each recess. With the inner circumferential surface of the gear ring Gr hanging in each recess, the mounting portion 210a is provided on the support table 210. Of course, the workpiece S can also be mounted in the depth direction shown in the figure.

[0179] In this case, as well as Figure 18B As shown, the stroke ST is determined by a predetermined distance Lg below the surface of the coolant W, where the uppermost end Eu of the uppermost processed material S is lower than the surface of the coolant W, Sw. The descent continues until the distance (Lg+H) from the surface of the coolant W, Sw to the lowermost end El of the lowermost processed material S at the descent stop position of the support platform 210, matches the stroke ST. Furthermore, the descent speed Ve is set to be faster than (stroke ST / vapor film maintenance period T around the lowermost processed material S).

[0180] When the speed is set to this level, the entire workpiece S can be impregnated before the vapor film disappears. The support platform 210 is lowered at a descending speed Ve, and stops when the distance from the liquid surface Sw matches the stroke ST. According to the above structure, the impregnation of the uppermost part (upper end Eu) of the uppermost workpiece S can be completed while the lowermost workpiece S has a vapor film, and the support platform 210 can be stopped. Moreover, at least until the surface of all workpieces S undergoes a martensitic phase transformation, a state in which no relative flow velocity is imparted between the workpiece S and the coolant W is maintained.

[0181] According to this structure, during the period when the lowest layer of workpiece S is covered by a vapor film, the movement of the workpiece S, which is placed across multiple layers in the vertical direction, is stopped. Furthermore, the coolant W around the workpiece S does not flow, at least until a martensitic transformation occurs on the surface of all the workpieces S. Therefore, there are no factors that impart a relative flow rate between the workpiece S and the coolant W around all the workpieces S being processed, and no factors that partially promote the cooling of the workpiece S. Therefore, the possibility of a cooling rate difference occurring at each part of all the workpieces S being processed can be reduced, thereby reducing the possibility of uneven quenching. In addition, multiple workpieces S can be quenched at once.

[0182] Furthermore, in cases where the vapor film maintenance period T is shorter, especially if the area around the part that was first impregnated is different from the part that was first impregnated, the vapor film can be maintained for a shorter period. Figure 19 , Figure 18C This embodiment illustrates a workpiece S with a locally pointed portion. In this embodiment, the workpiece S is a drive shaft Sd. The drive shaft Sd is a generally cylindrical component. Figure 18D This indicates the state of the drive shaft Sd as viewed from a direction perpendicular to the central axis Ax. Figure 18C This is a cross-sectional view showing the state when cut by a plane containing the central axis Ax of the ring. In the drive shaft Sd, a pinion portion Gp and a spline portion Sp are formed in the circumferential direction centered on the central axis Ax. The pinion portion Gp has teeth that mesh with other gears, and the spline portion Sp has teeth that mesh with other components.

[0183] exist Figure 18D In this embodiment, detailed information about the pinion portion Gp and the teeth formed in the spline portion Sp is omitted. In this embodiment, the teeth formed in the spline portion Sp have a lower tooth height and less pointed tooth tips compared to the teeth formed in the pinion portion Gp. Therefore, in the drive shaft Sd of this embodiment, the area around the tooth tips of the spline portion Sp is most susceptible to vapor film peeling. Furthermore, in the context of… Figure 18C , Figure 18C With the drive shaft Sd mounted on the support platform 21 in the shown configuration, the pinion gear Gp transitions to the boiling stage first, compared to the lower end where impregnation begins first. In this case, the vapor film maintenance period T is considered to be the period from the start of impregnation of the workpiece S until the point where the surrounding vapor film disappears and boiling begins.

[0184] Figure 18D This is a schematic diagram illustrating the period during which the vapor film is maintained in the case of an impregnated drive shaft Sd, section by section. Figure 20 In the middle, in order to and Figure 20 , Figure 18CWith the same orientation, i.e., the spline portion Sp is located lower than the pinion portion Gp and impregnated with the central shaft Ax facing up and down, the period for maintaining the vapor film is shown for each portion. Furthermore, in Figure 18D In the figure, the periods Tl, Ts, and Tg for maintaining the vapor film are shown along the time axis t.

[0185] exist Figure 20 In this example, it is assumed that the support platform 21 carrying the drive shaft Sd descends, and the impregnation of the lower end El begins at time tls. Next, it is assumed that the impregnation of part Ps begins at time tss, and the impregnation of part Pg begins at time tgs. After impregnation begins, a vapor film forms around each part. In this example, the vapor film formed around the lower end El disappears at time tle, and after time tle, the area around the lower end El transitions to the boiling stage. Similarly, the vapor film formed around part Ps disappears at time tse, and after time tse, the area around part Ps transitions to the boiling stage. Furthermore, the vapor film formed around part Pg disappears at time tge, and after time tge, the area around part Pg transitions to the boiling stage.

[0186] In this example, the vapor film surrounding part Pg disappears first. In this case, the vapor film maintenance period T is the period from the start of impregnation of the workpiece S until the part Pg where the surrounding vapor film disappears and boiling begins, i.e., the period Tsd from time tls to time tge. In this case, during the descent control process, the support stage 21 is controlled within the period Tsd to complete the impregnation of the workpiece S and stop the support stage 21. Figure 20 This diagram shows the state after impregnation is completed when the drive shaft Sd is used as the workpiece S. Figure 21 The image shows the state in which the workpiece S is placed on the support table 21 with the spline portion Sp positioned lower than the pinion portion Gp.

[0187] In this example, such as Figure 21 As shown, the stroke ST is determined by a predetermined distance Lg below the upper end Eu of the workpiece S and the liquid surface Sw of the coolant W. This distance Lg can also be set to the same as in the example above. The descent speed Ve can be set to complete the immersion of the workpiece S during the period when a vapor film of coolant W is formed around the pinion Gp, and can be set according to the height H from the lower end El of the workpiece S to the upper end Eu of the workpiece S, the characteristics of the coolant W, etc.

[0188] Specifically, in this embodiment, the descent continues until the distance (Lg+H) from the liquid surface Sw of the coolant W to the lower end El of the workpiece S at the descent stop position of the support platform 21 matches the stroke ST. Furthermore, the stroke STp is defined as the distance from the liquid surface Sw to the lower end Ep of the pinion Gp, where the vapor film first peels off, and the period Tg is defined as the time from when the lower end Ep of the pinion Gp is ​​immersed until the area around the lower end Ep transitions to the boiling stage (see reference). Figure 21 When ), the descent rate Ve is set to be faster than STp / Tg.

[0189] If this speed is set, then from the moment the lower end Ep of the pinion Gp is ​​immersed, the lower end Ep of the pinion Gp will reach the depth of the stroke STp faster than during the period Tg. Therefore, as Figure 19 As shown, when the condition that the vapor film first disappears at location Pg is met, impregnation can be completed while maintaining a vapor film around the workpiece S, and the support table 21 can be stopped. Furthermore, at least until a martensitic transformation occurs on the surface of the workpiece S, a state in which no relative flow velocity is imparted between the workpiece S and the coolant W is maintained. According to this structure, the possibility of cooling rate differences occurring at each location of the workpiece S can be reduced, thereby reducing the possibility of uneven quenching.

[0190] also, Figure 20 , Figure 18C The drive shaft Sd, which serves as the object being processed S, is asymmetrical in the vertical direction. Therefore, as shown... Figure 18D Therefore, the travel distance STp differs depending on whether the spline portion Sp is oriented lower than the pinion portion Gp, or vice versa, i.e., the spline portion Sp is oriented higher than the pinion portion Gp. Specifically, when the spline portion Sp is oriented higher than the pinion portion Gp, the lower end of the pinion portion Gp becomes more... Figure 21 The state shown is a deeper position. Therefore, the stroke STp up to the lower end of the pinion Gp becomes deeper. In this state, the lower limit of the descent speed Ve, STp / Tg, becomes larger, requiring faster control.

[0191] Therefore, in a workpiece S that is asymmetrical in the vertical direction, it is preferable to place it on the support platform 21 with the part of the workpiece S in which the vapor film around it disappears first and begins to boil facing upwards in the vertical direction. According to this structure, compared with the case where the workpiece S is placed on the support platform 21 in a state of opposite orientation in the vertical direction, it is not necessary to make the descent speed Ve too fast, thus increasing the design freedom of the device for lowering the support platform 21.

[0192] Furthermore, the object S to be processed can also be placed in a plurality of different positions in the vertical direction of the support platform 21. Figure 21 An embodiment is shown in which the drive shaft Sd, serving as the object to be processed S, is placed at multiple different positions in the vertical direction of the support platform 21. Figure 22 In the support platform 21, a plurality of objects S to be processed can be placed at two different locations in the vertical direction. The number of objects S to be processed arranged in the vertical and horizontal directions can be arbitrary, or the objects S to be processed can be placed in the depth direction shown in the figure.

[0193] In this embodiment, the state where the uppermost end Eu of the treated material S is below the liquid level Sw of the coolant W indicates that the impregnation is complete. In this embodiment, as... Figure 22 As shown, the stroke ST is determined by a predetermined distance Lg, where the uppermost end Eu of the uppermost workpiece S is below the surface Sw of the coolant W. This distance Lg can also be set to the same as in the example above. The descent speed Ve can be set to complete the immersion of the uppermost workpiece S during the period when a vapor film of coolant W is formed around the pinion Gp of the lowermost drive shaft Sd. It can be set according to the height from the lower end Ep of the pinion Gp of the lowermost drive shaft Sd to the upper end Eu of the uppermost workpiece S, the characteristics of the coolant W, etc.

[0194] Specifically, in this embodiment, the descent continues until the distance (Lg+H) from the liquid surface Sw of the coolant W to the lower end El of the lowest layer of the processed material S at the descent stop position of the support platform 21 matches the stroke ST. Furthermore, the stroke STp is defined as the distance from the liquid surface Sw to the lower end Ep of the pinion Gp, where the vapor film first peels off in the drive shaft Sd. The period Tg is defined as the time from when the lower end Ep of the pinion Gp is ​​immersed until the area around the lower end Ep transitions to the boiling stage (refer to...). Figure 22 When ), the descent rate Ve is set to be faster than STp / Tg.

[0195] If the speed is set to this level, the impregnation of all the workpieces S can be completed before the vapor film on the bottom layer disappears. The support platform 21 is lowered at a descending speed Ve, and stops when the distance from the liquid surface Sw matches the stroke ST. According to the above structure, the impregnation of the uppermost part (upper end Eu) of the uppermost workpiece S can be completed while a vapor film is formed on the bottom layer of workpiece S, and the support platform 21 can then be stopped. Furthermore, at least until a martensitic phase transformation occurs on the surface of all the workpieces S, a state in which no relative flow velocity is imparted between the workpiece S and the coolant W is maintained.

[0196] According to this structure, during the period when the lowest layer of workpiece S is covered by a vapor film, the movement of the workpiece S, which is placed across multiple layers in the vertical direction, is stopped. Furthermore, the coolant W around the workpiece S does not flow, at least until a martensitic transformation occurs on the surface of all the workpieces. Therefore, there are no factors that impart a relative flow rate between the workpiece S and the coolant W around all the workpieces S being processed, and no factors that partially promote the cooling of the workpiece S. Therefore, the possibility of a cooling rate difference occurring at each part of all the workpieces S being processed can be reduced, thereby reducing the possibility of uneven quenching. In addition, multiple workpieces S can be quenched at once.

[0197] Figure 20 It means immersion. Figure 23 , Figure 18C The diagram shows an example of a support platform 211 for drive shaft Sd. The support platform 211 is a platform capable of supporting a plurality of drive shafts Sd across two layers in the vertical direction. Figure 18D In the middle, used with Figure 23 The same cross section represents the drive shaft Sd, and indicates the state in which the support platform 211 is cut off in that cross section.

[0198] The support platform 211 has insertion portions 211a and 211b for inserting the drive shaft Sd. The insertion portions 211a and 211b are members having an inner circumferential surface slightly larger than the outer circumference at multiple locations (three locations in this embodiment) on the outer periphery of the drive shaft Sd. These insertion portions 211a and 211b hold the drive shaft Sd in a vertically upright position when inserted into the splined side of the drive shaft Sd.

[0199] In this embodiment, insertion portions 211a and 211b are formed at two different locations in the vertical direction relative to a drive shaft Sd. Furthermore, in this embodiment, insertion portion 211a is connected to connecting portion 211c, which extends in a predetermined direction and connects to a portion extending vertically from another connecting portion 211c or support platform 211. Insertion portion 211b is connected to connecting portion 211d, which connects to a portion extending in a predetermined direction and extending vertically from another connecting portion 211d or support platform 211.

[0200] Insertion parts 211a and 211b can be inserted into and hold the drive shaft Sd, and connecting parts 211c and 211d can support the insertion parts 211a and 211b. Figure 18D The diagram shows the state of the insertion part 211a and the connecting part 211c for inserting a drive shaft Sd, viewed from the central axis Ax direction of the drive shaft Sd. (See diagram for reference.) Figure 24As shown, the connecting portion 211c extends in three directions from the center of the drive shaft Sd, and each portion has an insertion portion 211a. The connecting portion 211c is connected to other connecting portions 211c in portions not shown.

[0201] exist Figure 24 In the illustrated embodiment, the descent continues until the distance (Lg+H) from the liquid surface Sw of the coolant W to the lower end El of the lowest layer of the processed material S at the descent stop position of the support platform 21 matches the stroke ST. Furthermore, the stroke STp is defined as the distance from the liquid surface Sw to the lower end Ep of the pinion Gp, where the vapor film first peels off in the drive shaft Sd. The period Tg is defined as the time from when the lower end Ep of the pinion Gp is ​​immersed until the area around the lower end Ep transitions to the boiling stage (refer to...). Figure 23 Figure 20 When ), the descent rate Ve is set to be faster than STp / Tg.

[0202] If the speed is set to this level, the impregnation of all the workpieces S can be completed before the vapor film on the bottommost workpiece S disappears. The support platform 211 is lowered at a descending speed Ve, and stops when the distance from the liquid surface Sw matches the stroke ST. According to this structure, the impregnation of the uppermost part (upper end Eu) of the uppermost workpiece S can be completed while a vapor film is formed on the bottommost workpiece S, and the support platform 211 can then be stopped. Furthermore, at least until a martensitic transformation occurs on the surface of all the workpieces S, a state in which no relative flow velocity is imparted between the workpieces S and the coolant W is maintained. According to this structure, the possibility of a cooling rate difference occurring at each part of the workpiece S can be reduced, thereby reducing the possibility of uneven quenching. Additionally, multiple workpieces S can be quenched at once.

Claims

1. A quenching method for cooling a workpiece placed on a support table. in, include: The descent control process controls the support platform to ensure that the surface heat transfer coefficient of the material accumulating in the cooling tank in a non-flowing state during the boiling phase reaches a maximum of 6000 W / m. 2 The coolant, which is above K, descends, and during the process of forming a vapor film of the coolant around the workpiece using the heat of the workpiece, the impregnation of the workpiece is completed and the support platform stops. as well as The state maintenance process, after stopping the descent of the support platform, maintains the state in which the coolant does not flow and the support platform does not move, at least before the martensitic phase transformation occurs on the surface of the workpiece, so as not to impart a relative flow velocity between the workpiece and the coolant.

2. The quenching method according to claim 1, wherein, The boiling start temperature at which the vapor film formed by the coolant around the object being treated disappears and begins to boil is below 600°C.

3. The quenching method according to claim 2, wherein, The boiling start temperature is above 450°C, at which the vapor film formed by the coolant around the work being treated disappears and begins to boil.

4. The quenching method according to claim 1, wherein, The rate of increase in the surface heat transfer coefficient per unit temperature decrease after the vapor film formed by the coolant around the workpiece disappears and begins to boil is 100 W / m. 2 ·K 2 above.

5. The quenching method according to claim 1, wherein, The coolant is a water-soluble coolant containing a polymer compound dissolved in water.

6. The quenching method according to claim 5, wherein, The polymeric compound includes at least one of polyalkylene glycol, polyvinyl alcohol, polyethylene glycol, sodium polyacrylate, and polyvinylpyrrolidone. The coolant is a water-soluble coolant in which 5% to 30% of the polymer compound is dissolved in water.

7. The quenching method according to claim 1, wherein, The period during which the vapor film forms is from the time the first part of the workpiece is immersed until the vapor film around that part disappears and boiling begins.

8. The quenching method according to claim 1, wherein, The period during which the vapor film forms is from the time the treated material begins to be impregnated until the point where the surrounding vapor film disappears and boiling begins.

9. The quenching method according to claim 1, wherein, The period during which the vapor film is formed is from the time the surface heat transfer coefficient between the coolant and the treated object first falls below a predetermined value during the process of the treated object being immersed in the coolant and its temperature decreasing, until it exceeds the predetermined value.

10. The quenching method according to claim 1, wherein, The descent speed of the object being processed in the descent control process is faster than the distance from the surface of the coolant to the lower end of the object at the descent stop position / the period during which the vapor film is formed.

11. The quenching method according to claim 1, wherein, When the martensite fraction on the surface of the workpiece becomes a predetermined value, it is considered that a martensitic phase transformation has occurred on the surface of the workpiece.

12. The quenching method according to claim 1, wherein, If a predetermined period has elapsed since the start of impregnation of the workpiece, it is considered that a martensitic phase transformation has occurred on the surface of the workpiece.

13. The quenching method according to claim 1, wherein, The state in which no relative flow velocity is imparted between the processed object and the coolant is a state in which the coolant is not moved by external force and the support platform is not moved.

Images