JP2020164922A - Hardening method - Google Patents

Abstract

To provide a technology for enhancing the possibility of suppressing influence of thermal expansion even when a coolant mainly composed of water is used.SOLUTION: A hardening method for cooling a target material of hardening includes: a primary cooling step for cooling the target material with a coolant and stopping cooling before the temperature of the surface of the target material reaches the initiation temperature of martensite transformation or lower; a soaking step for soaking the surface and inside of the target material; and a secondary cooling step for cooling the target material with a coolant mainly composed of water until martensite transformation of at least the surface of the target material.SELECTED DRAWING: Figure 1

Description

The present invention relates to a quenching method.

Conventionally, there is known a quenching method in which an object to be hardened is immersed in a coolant and cooled to a temperature equal to or lower than the martensitic transformation temperature. In such a quenching technique, a technique of using water or quenching oil as a cooling agent is known, and as a technique of using the quenching oil, for example, Patent Document 1 can be mentioned.

Japanese Patent Application Laid-Open No. 6-2030

A temperature difference occurs between the surface where cooling is initially started when the object to be treated comes into contact with the coolant and the inside which does not come into direct contact with the coolant. Since thermal expansion occurs when the object to be processed is at a high temperature, the entire object to be processed expands when the inside of the object to be processed is at a high temperature.

Water-based coolants have a faster cooling rate than hardened oils. Therefore, when a water-based coolant is used, the temperature drops below the martensitic transformation start temperature earlier than when the quenching oil is used as the coolant. In the process of quenching, the surface of the object to be treated cools before the inside, so the surface of the object to be treated transforms into martensite before the inside. When the martensitic transformation occurs, the surface of the object to be treated becomes hard, so that the object to be treated is maintained in a state of thermal expansion even if the inside is subsequently cooled. Conventionally, when quenching is performed using a coolant containing water as the main component, the surface of the object to be treated becomes hard while the inside of the object to be treated is thermally expanded, and the effect of thermal expansion is large (due to elongation). If there is, it was thought that the object to be treated would be cured in a state of (large elongation). As a result, it was considered difficult to suppress the influence of thermal expansion by using a coolant containing water as a main component.
The present invention has been made in view of the above problems, and an object of the present invention is to increase the possibility of suppressing the influence of thermal expansion even when a coolant containing water as a main component is used.

In order to achieve the above object, the quenching method for cooling the object to be hardened is to cool the object to be processed with a coolant so that the surface of the object to be hardened is at a temperature equal to or lower than the start temperature of martensitic transformation. A primary cooling step of stopping cooling before the cooling occurs, a soaking step of equalizing the surface and the inside of the object to be treated, and at least water is mainly used until the surface of the object to be treated is transformed into martensitic transformation. It is configured to include a secondary cooling step of cooling the object to be treated with a cooling agent as a component.

That is, in the configuration in which quenching is performed with a coolant containing water as a main component in the secondary cooling step, the surface of the object to be treated is cooled by performing the primary cooling before the secondary cooling. The inside is also cooled accordingly. In this state, if the temperature falls below the martensitic transformation start temperature, the surface of the object to be treated will harden. Therefore, the primary cooling should be stopped before the surface becomes below the martensitic transformation start temperature, and the object to be treated should be stopped after the stop. The surface and the inside are homogenized.

As a result, the heat inside the object to be processed is transferred to the surface, and the inside is cooled. By this cooling, the temperature inside the object to be processed can be lowered as compared with the configuration in which the surface is cooled to the martensitic transformation start temperature or lower in the primary cooling stage. Therefore, the degree of thermal expansion can be suppressed. Then, after the temperature inside the object to be treated has dropped, the surface of the object to be treated can be cured by cooling until the surface of the object to be treated undergoes martensitic transformation, so that the degree of thermal expansion is suppressed. it can. As a result, the possibility of suppressing the influence of thermal expansion can be increased.

1A is a diagram schematically showing an apparatus for performing a quenching method, and FIGS. 1B to 1D are diagrams schematically showing a quenching process. 2A to 2C are diagrams schematically showing the quenching process, and FIG. 2D is a diagram schematically showing an apparatus for carrying out the quenching method. 3A to 3D are diagrams schematically showing the quenching process. It is a flowchart which shows the heat treatment process. It is a flowchart which shows the heat treatment process. It is a figure which shows the comparative example and the Example. It is a figure which shows the hardness of the object to be processed. It is a figure which shows the temperature change of the object to be processed, and the martensite fraction. It is a figure which shows the relationship between a martensite fraction and a strain amount. It is a figure which shows the transition of the growth amount in a comparative example and an Example. 11A and 11B are diagrams showing the temperature change of the object to be treated and the microstructure transformation point for each temperature. FIG. 12A is a flowchart showing the heat treatment process, and FIG. 12B is a diagram showing the effect of auxiliary cooling.

Here, embodiments of the present invention will be described in the following order.
(1) Configuration of the device that implements the quenching method:
(2) Heat treatment process:
(3) Example:
(4) Other embodiments:

(1) Configuration of the device that implements the quenching method:
FIG. 1A is a diagram schematically showing an apparatus for carrying out the quenching method according to the embodiment of the present invention. FIG. 1A shows the main part of the device, and various configurations can be adopted as the mechanism for driving each part, the shape of each part, and the like. The device shown in FIG. 1A includes a cooling tank 10 formed by opening one surface of a hollow rectangular parallelepiped. In the present embodiment, the coolant W is accumulated in advance in the cooling tank 10. In this embodiment, the coolant W is water. The coolant W may be a coolant containing water as a main component, and the coolant may be, for example, an aqueous solution in which various materials are dissolved in water.

In the present embodiment, the device that implements the quenching method is provided with a moving device 20 that raises and lowers the object S to be processed. The moving device 20 includes a support base 21 and a support portion 22, and the object S to be processed is placed on the support base 21. The support base 21 is supported by a support portion 22 extending in the height direction of the cooling tank 10. A drive source such as a motor (not shown) is connected to the support portion 22, and the support base 21 can be moved up and down by an elevating mechanism (not shown). Of course, a drive source such as a motor may be driven by various energies, and various energies such as electric, hydraulic drive, and atmospheric pressure drive can be used. Further, the power transmission mechanism is not limited to a motor or the like, and may be a linear motor or the like (the same applies hereinafter). Further, various configurations can be adopted for raising and lowering the object S to be processed.

In the present embodiment, the drive source can change the ascending / descending speed of the support 21 on which the object S to be processed is placed, and by changing the control signal for the drive source, the ascending speed of the support 21 and the support 21 You can specify the descending speed of. The support portion 22 extends in the vertical direction from the bottom surface of the cooling tank 10 toward the opening side. Therefore, the lower part of the support portion 22 is immersed in the coolant W in the cooling tank 10, and the support base 21 is moved up and down to immerse the object S on the support base 21 in the coolant W. Further, the object S to be processed in the coolant W can be taken out to the outside.

The number and placement (orientation) of the objects to be processed S placed on the support base 21 may be in various modes. For example, a pallet may be attached to the support base 21, and a plurality of objects S to be processed may be arranged in the pallet. In this specification, the case where the object to be processed S is one will be described as an example. Of course, the support base 21 and the support portion 22 may have various characteristics. For example, the support base 21 is formed in a mesh or a grid pattern so that the support base 21 can be easily lowered. You may be.

In the cooling tank 10, a flow device 30 for flowing the coolant W is provided. The flow device 30 includes a shaft 31 and a propeller 32. That is, in the cooling tank 10, a shaft 31 extending along the side surface is provided in the vicinity of the side surface thereof. The shaft 31 is rotatable about a line in a direction parallel to the vertical direction. A propeller 32 is connected to the shaft 31, and the propeller 32 is rotated by a drive source such as a motor (not shown).

In the present embodiment, the drive source can induce a flow in the vertical direction by rotating the propeller 32, and in the present embodiment, a flow in the vertical direction is induced. When the propeller 32 induces a flow upward in the vertical direction, the flow is dispersed in the horizontal direction near the liquid surface.

A plate-shaped member having a plane parallel to the vertical direction is provided in the cooling tank 10, the uppermost portion of the plate-shaped member exists at a position deeper than the liquid surface, and the lowermost portion of the plate-shaped member is a cooling tank. It exists at a position shallower than the bottom of 10. Further, the wide surfaces of the plate-shaped members are arranged so as to face each other. Therefore, the flow induced in the coolant W circulates in opposite directions on the front and back surfaces of the plate-shaped member. Therefore, when the flow induced by the propeller 32 is dispersed in the horizontal direction near the liquid surface, it further flows downward in the vertical direction near the center of the cooling tank 10. Then, when the flow downward in the vertical direction near the center of the cooling tank 10 reaches the vicinity of the bottom surface, it flows to the side surface side again and circulates to the propeller 32 side. As a result, a flow as shown by the broken line arrow in FIG. 1A is formed. That is, in the cooling tank 10, a circulating flow that flows downward in the vertical direction near the center and flows upward in the vertical direction near the side surface of the cooling tank 10 is formed. Here, as long as the circulating flow can be formed, a member other than the plate-shaped member, for example, an annular member may be arranged.

The drive source that rotates the shaft 31 can change the rotation speed of the shaft 31, and by changing the control signal for the drive source, the flow velocity of the circulating flow in the cooling tank 10 can be specified. In the present embodiment, when the object S to be processed is immersed, the flow velocity of the downward flow Fd at the portion in contact with the side surface of the object S to be processed can be controlled. That is, when the flow velocity is specified by the control instruction to the drive source, the flow velocity of the flow Fd below the coolant W at the portion in contact with the side surface of the object S to be processed is configured to be the specified flow velocity.

In the present embodiment, the object to be treated S is a part after carburizing. The carburizing treatment may be carried out by a carburizing treatment apparatus (not shown in FIG. 1A), and the object S to be processed is heated by a furnace of various modes, and the carbon existing around the object S to be processed is removed from the object S to be processed. It would be good if it could be carburized. Of course, the configuration of the furnace is not limited, and the object to be processed S may be transported while carburizing in the furnace, or the object to be processed S existing at a fixed position in the furnace is carburized. It may be taken out afterwards. The mode of carburizing is not limited, and carburizing may be performed in various modes such as gas carburizing, liquid carburizing, solid carburizing, vacuum carburizing (vacuum gas carburizing), and plasma carburizing. In any case, the object S to be processed after carburizing may be set on the support base 21 and quenching may be performed.

(2) Heat treatment process:
Next, the heat treatment step (carburizing treatment and quenching treatment) for the object S to be treated will be described. 4 and 5 are flowcharts showing the heat treatment steps according to the present embodiment. In the heat treatment step, the object to be heat-treated S is set in the carburizing treatment device (step S100). Next, carburizing treatment is performed (step S105). The conditions of the carburizing treatment are determined based on the purpose of use of the object S to be treated and the like. For example, a predetermined carbon-containing material (gas or the like) is introduced into the carburizing apparatus in which the object to be processed S is set, and the object to be processed S is heated to a target temperature at a predetermined heating rate. Then, when the object S to be processed reaches the target temperature, it is maintained at the target temperature for a predetermined period.

Next, the object S to be carburized is set in the moving device 20 (step S110). That is, the object S to be carburized is placed on the support base 21. In the present embodiment, the synchronized state described later is realized in the primary cooling step and the secondary cooling step. In order to realize the synchronized state, the flow velocity Vq is first set to the synchronized speed (step S115). That is, a control signal is output to the drive source that rotates the shaft 31, and the rotation of the propeller 32 is started. At this time, the flow velocity of the flow Fd below the coolant W at the portion in contact with the side surface of the object S to be processed is set to be the synchro velocity. Here, the synchro speed is a predetermined speed, and the details will be described later.

Next, the descending speed Ve of the object to be processed is set to the synchro speed (step S120). That is, a control signal is output to the drive source that moves the support base 21, and as a result, the descending speed Ve of the support base 21 becomes the synchro speed, which is the same value as the flow velocity of the flow Fd below the coolant W. The synchro speed is preset as a speed value at which the descending speed Ve for lowering the support base 21 and the flow velocity of the lower flow Fd of the coolant W at the portion in contact with the side surface of the object S to be processed are synchronized.

That is, in the present embodiment, the moving device 20 can control the descending speed of the support 21, and the rotation of the propeller 32 causes the flow velocity of the lower flow Fd of the coolant W at the portion in contact with the side surface of the object S to be processed. Take advantage of the controllability to match both speeds. As a result, when the object S to be treated comes into contact with the liquid surface of the coolant W and immersion is started, the relative velocity between the object S to be treated and the coolant W inside the liquid surface of the coolant W becomes 0. ..

Specifically, since the object S to be processed is mounted on the support 21 of the moving device 20, the movable direction of the object S to be processed coincides with the movable direction of the support 21. Therefore, the moving direction of the object S to be processed is a direction directed vertically downward. On the other hand, the direction in which the coolant W flows at the portion in contact with the side surface of the object S to be treated is also parallel to the vertical direction in almost the entire height direction and is directed downward vertically. Therefore, the moving direction of the object S to be processed coincides with the direction of the flow of the coolant W in contact with the object S to be processed.

Further, in the present embodiment, the descending speed Ve of the support base 21 and the flow velocity Vq of the flow Fd below the coolant W at the portion in contact with the side surface of the object S are both synchronized velocities. There is. Therefore, the relative velocity between the object S to be treated and the coolant W inside the liquid level of the coolant is 0. In this embodiment, this state is referred to as a synchronized state. The descending speed Ve may be any speed, but the shorter the period from the start of immersion of the object S to the coolant to the completion of immersion, the more time difference the object S to be treated comes into contact with the coolant. The temperature difference becomes small and distortion is unlikely to occur. Therefore, the descending speed Ve is preferably as fast as possible, and can be, for example, a speed of 100 mm / s to 1500 mm / s.

In the synchronized state as described above, the relative speed between the object to be processed S and the coolant W is 0, and the moving speed of the object to be processed S is the descending speed Ve. Since the descending speed Ve is larger than 0 in this state, it can be said that the relative velocity between the object S to be processed and the coolant W is slower than the moving speed (descending velocity Ve) of the object to be processed. Since it is difficult to strictly control or measure the direction of the flow velocity, there may be an error in the direction and velocity of the flow, and the direction and velocity of the flow are not the measurement results but the control target amount. Is also good.

When the synchronized state is realized in steps S115 and S120, the object to be processed S is immersed. That is, in the present embodiment, from before the immersion of the object S to be started (before the object S comes into contact with the liquid surface of the coolant W), the object S is in the same direction as the moving direction and is to be processed. A flow at the same speed as the moving speed of the object S is formed in the coolant W. Therefore, in the present embodiment, the object S to be treated is already in the synchronized state at the stage of contacting the liquid surface of the coolant W.

FIG. 1B is a diagram schematically showing a state before the object S to be immersed is immersed. When the synchronized state is realized, the object S to be treated gradually approaches the liquid surface of the coolant W in a state where the flow velocity Vq and the descending speed Ve are synchronized as shown in FIG. 1B. When the object S to be treated descends in the synchronized state and reaches the liquid level of the coolant W as shown in FIG. 1C, the heat of the object S to be processed in the portion in contact with the coolant W is transferred to the coolant W. The object S to be processed is cooled. As shown in FIG. 1C, the state in which the object S to be treated reaches the liquid level of the coolant W is the state in which immersion is started. After the start of immersion, the movement by the moving device 20 is continued, and when the vertically upper surface of the object S to be treated reaches the liquid level of the coolant W as shown in FIG. 1D, the entire object S to be processed becomes the coolant W. It will be in a soaked state. The state in which the entire object S to be treated is immersed in the coolant W is the state in which the immersion is completed.

In the present embodiment, the synchronized state is continued even after the immersion is started and the immersion is completed (for example, the state shown in FIG. 2A). In the synchronized state, as shown in FIGS. 1B to 1D, the object S to be treated descends downward in the vertical direction, while the liquid level Sw of the coolant W does not move in the vertical direction (into the liquid level). Excluding the rise in the liquid level by the volume of the contained object S). Therefore, in FIG. 1C and the like, the relative velocity between the object S to be treated and the liquid level Sw of the coolant W is not zero. On the other hand, after the start of immersion, the coolant W flows downward in the vertical direction inside the liquid level Sw. Therefore, after the state shown in FIG. 1C, in the synchronized state, the relative velocity between the object S to be treated and the coolant W inside the liquid level Sw of the coolant W is 0.

In this way, when the movement of the object S to be processed inside the coolant W and the movement of the coolant W in contact with the object S are synchronized, the object S is in contact with the object S to be processed and the object S is to be processed. The coolant W to which heat has been transferred moves together with the object S to be processed and stays around the object S to be processed. Therefore, in the object S in contact with the coolant W, rapid cooling is started by the coolant W, but if the synchronized state is maintained, the coolant W in contact with the coolant S gradually warms up. Cooling is not promoted.

That is, when the coolant W around the object S to be processed moves to another place by stirring or the like, the coolant W that has become hot around the object S to be processed is replaced with the coolant W that has a low temperature. However, in the synchronized state, the coolant W that has become hot in contact with the object S to be treated is not easily replaced by the low temperature coolant, and cooling is not promoted. When the synchronized state is maintained, the cooling rate of the portion that first reaches the liquid level of the coolant W and starts cooling first gradually slows down. On the other hand, the cooling rate of the portion that later reaches the liquid level of the coolant W and starts cooling is faster than the cooling rate of the portion where cooling is started earlier. Therefore, when the synchronized state is maintained, the temperature difference generated on the surface of the object to be processed S gradually becomes smaller, and the occurrence of strain on the object to be processed S can be suppressed.

In the present embodiment, by realizing the synchronized state as described above, the primary cooling step is performed so that distortion does not occur in the object S to be processed, but in the primary cooling step, the synchronized state is performed. May be omitted. For example, in a state where the flow is not induced by the flow device 30 (Vq = 0), the object to be processed is lowered in step S115, and after the immersion is completed, the object S to be processed has a predetermined height in the coolant. The descent may be stopped in step S120 when the height is reached.

In any case, when the object S to be processed is in contact with the coolant W, the object S to be processed is in a state of being primary cooled. In the present embodiment, in the primary cooling, cooling is stopped before the surface of the object to be treated S reaches a temperature equal to or lower than the martensitic transformation start temperature. Therefore, it is determined whether or not a predetermined period has elapsed since the object S to be treated came into contact with the coolant W (step S125). The predetermined period in step S125 is the period after the object S to be treated comes into contact with the coolant W, and the period is predetermined so that the surface of the object S to be treated does not undergo martensitic transformation. That is, the object S to be processed is raised by the moving device 20 in the subsequent step S130, but the surface of the object S to be processed is martensitic transformed at the stage when the object S to be processed is pulled up from the coolant W by the increase. It suffices if the default period is set so that there is no such thing.

As described above, in the present embodiment, the determination for preventing the surface of the object to be treated from becoming below the martensitic transformation start temperature is made based on the predetermined period. However, the determination may be made in various ways. For example, it may be detected by a sensor (not shown) or the like that the surface of the object to be treated reaches a specific temperature higher than the martensitic transformation start temperature (for example, immediately above the martensitic transformation start temperature), and the support 21 is initially set. When the support base 21 is lowered from the position at the lowering speed Ve, even if it is determined whether or not the predetermined period has elapsed by measuring the time for the object S to move from the initial position to the position in contact with the coolant W. good. Further, it may be determined whether or not the predetermined period has elapsed by measuring the time after the object S to be processed has stopped.

In step S125, when it is determined that the predetermined period has elapsed since the object S to be processed comes into contact with the coolant W, the object to be processed is raised (step S130). That is, a control signal is output to the drive source that moves the support base 21, and as a result, the support base 21 rises. The ascending speed Ve may be any speed, but the ascending is performed so that the surface of the object to be treated is not martensitic transformed at the stage when the object S to be processed is pulled up by the ascending. Here, too, the ascending speed Ve can be, for example, a speed of 100 mm / s to 1500 mm / s.

In step S130, when the object S to be processed starts to rise at the ascending speed Ve, the object S to be processed gradually approaches the liquid level of the coolant W, and the object S to be processed is eventually pulled up above the liquid level. In the present embodiment, when the object S to be treated is pulled up and reaches a predetermined height above the coolant W, the rise is stopped (step S135). The default height is predetermined as long as the entire object S to be treated is at a height outside the liquid level of the coolant W. FIG. 2B is a diagram showing a state in which the ascent of the object to be processed S is stopped. In the present embodiment, when the object S to be treated reaches the outside of the coolant W, the cooling by the coolant is stopped, so steps S115 to S130 are the primary cooling steps.

When the object S to be treated is present outside the coolant W as described above, the object S to be treated is in a state of being thermalized. That is, since the surface of the object S to be treated is in contact with the coolant W in the primary cooling step, it is directly cooled by the coolant, but since the inside of the object S to be processed is not in contact with the coolant W, the cooling rate Is slow and the internal temperature is higher than the surface temperature. Therefore, in the heat equalization step, the internal heat is dissipated to the surroundings through the surface. Therefore, the heat inside is transferred to the surface, so that the surface and the inside of the object S to be treated are equalized.

In the present embodiment, it is determined whether or not the thermalization step is completed depending on the time. Therefore, it is determined whether or not the predetermined period has elapsed (step S140). The predetermined period in step S140 may be set so as to decrease the temperature inside the object to be processed S to a target temperature or lower due to thermalization, and the period is predetermined. The period may be measured by various methods. For example, the period may be the period after the lowermost portion of the object S reaches the liquid level of the coolant W, or the increase of the object S to be processed. It may be a period after the start of the operation, or a period after the rise of the object S to be processed has stopped, and various configurations can be adopted.

As described above, the temperature inside the object S to be processed is set during the period from when the object S to be processed is drawn above the liquid level of the coolant W in step S130 until it is determined that the predetermined period has elapsed. Steps S130 to S140 are thermalization steps because the temperature is below the target temperature. When such thermalization is performed, the temperature inside the object to be processed S becomes higher than that in the configuration in which the object S to be processed at the quenching temperature is cooled by the coolant until it becomes lower than the martensitic transformation start temperature. Quenching can be started in a lowered state. Therefore, quenching can be started in a state where deformation of the object to be processed S due to thermal expansion is suppressed.

In the present embodiment, in steps S200 to S230, a secondary cooling step for quenching is executed. Specifically, first, the flow velocity Vq is set to the synchro velocity (step S200). That is, a control signal is output to the drive source that rotates the shaft 31, and the rotation of the propeller 32 is started. At this time, the flow velocity of the flow Fd below the coolant W at the portion in contact with the side surface of the object S to be processed is set to be the synchro velocity. Here, the synchro speed is a predetermined speed, and the details will be described later. If the flow velocity Vq in step S200 is the same as the flow velocity Vq in step S115, step S200 can be omitted.

Next, the descending speed Ve of the object to be processed is set to the synchro speed (step S205). That is, a control signal is output to the drive source that moves the support base 21, and as a result, the descending speed Ve of the support base 21 becomes the synchro speed, which is the same value as the flow velocity of the flow Fd below the coolant W. The synchro speed is preset as a speed value at which the descending speed Ve for lowering the support base 21 and the flow velocity of the lower flow Fd of the coolant W at the portion in contact with the side surface of the object S to be processed are synchronized.

That is, in the present embodiment, the moving device 20 can control the descending speed of the support 21, and the rotation of the propeller 32 causes the flow velocity of the lower flow Fd of the coolant W at the portion in contact with the side surface of the object S to be processed. Take advantage of the controllability to match both speeds. As a result, when the object S to be treated comes into contact with the liquid surface of the coolant W and immersion is started, the relative velocity between the object S to be treated and the coolant W inside the liquid surface of the coolant W becomes 0. ..

Specifically, since the object S to be processed is mounted on the support 21 of the moving device 20, the movable direction of the object S to be processed coincides with the movable direction of the support 21. Therefore, the moving direction of the object S to be processed is a direction directed vertically downward. On the other hand, the direction in which the coolant W flows at the portion in contact with the side surface of the object S to be treated is also parallel to the vertical direction in almost the entire height direction and is directed downward vertically. Therefore, the moving direction of the object S to be processed coincides with the direction of the flow of the coolant W in contact with the object S to be processed.

Further, in the present embodiment, the descending speed Ve of the support base 21 and the flow velocity Vq of the flow Fd below the coolant W at the portion in contact with the side surface of the object S are both synchronized velocities. There is. Therefore, the relative velocity between the object S to be treated and the coolant W inside the liquid level of the coolant is 0. In this embodiment, this state is referred to as a synchronized state. The descending speed Ve may be any speed, but the shorter the period from the start of immersion of the object S to the coolant to the completion of immersion, the more time difference the object S to be treated comes into contact with the coolant. The temperature difference becomes small and distortion is unlikely to occur. Therefore, the descending speed Ve is preferably as fast as possible, and can be, for example, a speed of 100 mm / s to 1500 mm / s.

In the synchronized state as described above, the relative speed between the object to be processed S and the coolant W is 0, and the moving speed of the object to be processed S is the descending speed Ve. Since the descending speed Ve is larger than 0 in this state, it can be said that the relative velocity between the object S to be processed and the coolant W is slower than the moving speed (descending velocity Ve) of the object to be processed. Since it is difficult to strictly control or measure the direction of the flow velocity, there may be an error in the direction and velocity of the flow, and the direction and velocity of the flow are not the measurement results but the control target amount. Is also good.

When the synchronized state is realized in steps S200 and S205, the object to be processed S is immersed. That is, in the present embodiment, from before the immersion of the object S to be started (before the object S comes into contact with the liquid surface of the coolant W), the object S is in the same direction as the moving direction and is to be processed. A flow at the same speed as the moving speed of the object S is formed in the coolant W. Therefore, in the present embodiment, the object S to be treated is already in the synchronized state at the stage of contacting the liquid surface of the coolant W.

The synchronized state in the secondary cooling step is also similar to that in the primary cooling step, and FIGS. 1B to 1D and 2A are the same as in the primary cooling step. That is, FIG. 1B is a diagram schematically showing a state before the object S to be immersed is immersed. When the synchronized state is realized, the object S to be treated gradually approaches the liquid surface of the coolant W in a state where the flow velocity Vq and the descending speed Ve are synchronized as shown in FIG. 1B. When the object S to be treated descends in the synchronized state and reaches the liquid level of the coolant W as shown in FIG. 1C, the heat of the object S to be processed in the portion in contact with the coolant W is transferred to the coolant W. The object S to be processed is cooled. As shown in FIG. 1C, the state in which the object S to be treated reaches the liquid level of the coolant W is the state in which immersion is started. After the start of immersion, the movement by the moving device 20 is continued, and when the vertically upper surface of the object S to be treated reaches the liquid level of the coolant W as shown in FIG. 1D, the entire object S to be processed becomes the coolant W. It will be in a soaked state. The state in which the entire object S to be treated is immersed in the coolant W is the state in which the immersion is completed.

In the secondary cooling step, the synchro state is continued even after the immersion is started and the immersion is completed (for example, the state shown in FIG. 2A). The state of cooling in the synchronized state is the same as in the primary cooling step, and if the synchronized state is maintained, the cooling rate of the part that first reaches the liquid level of the coolant W and starts cooling first gradually increases. It will be late. On the other hand, the cooling rate of the portion that later reaches the liquid level of the coolant W and starts cooling is faster than the cooling rate of the portion where cooling is started earlier. Therefore, when the synchronized state is maintained, the temperature difference generated on the surface of the object to be processed S gradually becomes smaller, and the occurrence of strain on the object to be processed S can be suppressed.

Then, when the surface of the object to be treated S undergoes martensitic transformation while the temperature difference on the surface of the object to be processed S is suppressed and the occurrence of strain on the object to be processed S is suppressed, the surface of the object to be processed S becomes hard. After that, the object to be processed S is less likely to be deformed. Therefore, since the synchronized state is maintained, quenching can be completed in a state in which the occurrence of strain is suppressed. Therefore, when the secondary cooling step including the synchronized state is performed after the heat equalization as in the present embodiment, the workpiece S is baked in a state in which both deformation of the object to be processed S due to thermal expansion and occurrence of strain are suppressed. Can be put in.

In the present embodiment, in order to complete the quenching in the synchronized state as described above, it is considered that the surface of the object to be treated S has undergone martensitic transformation when a predetermined period has elapsed after the start of immersion. Therefore, when the immersion of the object to be processed S is started in steps S200 and S205, it is determined whether or not a predetermined period has elapsed since the object to be processed S came into contact with the coolant W (step S210). The predetermined period is a period from when the object S to be treated comes into contact with the coolant W until the surface of the object S to be treated undergoes martensitic transformation, and is predetermined. The predetermined period may be determined by various methods, and in the present embodiment, it is determined as a period until the martensite fraction on the surface of the object S to be treated reaches the predetermined ratio. That is, when the ratio of martensite formed on the surface of the object S to be treated is equal to or greater than the threshold value, it is considered that the surface of the object S to be treated has undergone martensitic transformation.

The martensite fraction may be determined by the degree of strain allowed in the object S to be processed. For example, a configuration in which the period until the martensite fraction on the surface of the object to be processed reaches 28% is the default period. It can be adopted. According to this configuration, the strain generated in the object S to be processed can be reduced to almost the limit (details will be described later). Here, the martensite fraction P (t) is
P (T) = 1-exp (-b (Ms-T))
T: Temperature Ms: Martensitic transformation start temperature b: A constant specified by the material and carbon concentration (for example, in SCM420, the base material was carburized to a surface carbon concentration of b = 0.143, 0.8 (mass%)). In some cases, b = 0.01)
It is expressed by.

In any case, in step S210, whether or not the surface of the object to be treated S has undergone martensitic transformation is specified based on a predetermined period. When determining whether or not a predetermined period has elapsed since the object S to be treated comes into contact with the coolant W, the start of the period may be specified by various methods. For example, it may be detected by a sensor (not shown) or the like that the object S is in contact with the coolant W, or when the support base 21 lowers the support base 21 from the initial position at a lowering speed Ve, it is covered from the initial position. The time required for the processed object S to move to the position where it comes into contact with the coolant W may be measured.

In step S210, when it is determined that the predetermined period has elapsed since the object S in contact with the coolant W, the flow velocity Vq is set to the quenching speed (step S215), and the descending speed Ve of the object to be processed becomes 0. It is set (step S220). That is, in the present embodiment, the synchronized state is maintained for a predetermined period after the object S is in contact with the coolant W, and after the predetermined period, the lowering of the support 21 in the mobile device 20 is stopped and the synchronized state is maintained. It is stopped (state shown in FIG. 2C). As a result, the circulation of the coolant W around the object S to be treated is promoted, and the outflow of heat from the object S to be treated to the coolant W is promoted. Therefore, cooling is performed at a higher speed.

The quenching speed, which is the flow velocity Vq set in step S215, may be predetermined as the flow velocity when the coolant W promotes heat exchange after the synchro state is stopped. To this extent, it may be the same as or different from the sync speed. If the quenching rate is the same as the sync rate, step S215 can be omitted. In step S220, the descending speed Ve is set to 0 in order to stop the synchronized state, but of course, other values may be used. For example, if the support base 21 is raised little by little so that the workpiece S exits the coolant W as the quenching is completed, it is necessary to raise the workpiece S after the quenching is completed. The period can be shortened.

In any case, when the synchronized state is stopped by steps S215 and S220, it waits until the quenching is completed (step S225). The end of quenching may be determined by various conditions, and for example, a configuration or the like subject to the passage of a predetermined time can be adopted.

When it is determined in step S225 that quenching has been completed, the object to be processed is raised (step S230). That is, the moving device 20 is controlled and the support base 21 is raised. As a result, the state in which the object to be treated S is immersed in the coolant W ends, and the heat treatment step ends. Of course, this cooling step is an example, and after that, heat treatment such as tempering, annealing, and high frequency heating may be performed.

In the present embodiment, the descent speed Ve of the support base 21 is constant from before the start of dipping to the completion of quenching after the completion of dipping, but of course, the descent speed Ve and the like are variable. Is also good. For example, in the period from the start of immersion to the completion of immersion, the descending speed is set to end the period from the start of immersion to the completion of immersion at an early stage, and the descending speed is changed continuously or stepwise after the start of immersion or the completion of immersion. It may be configured to be allowed. That is, a configuration may be adopted in which the control from the start of immersion to the completion of immersion and the control after the completion of immersion are controlled separately. That is, the relative speed between the object S to be processed and the coolant W may be controlled at various speeds as long as the state of being slower than the moving speed of the object S to be processed is maintained.

(3) Example:
Next, the characteristics of the object to be treated S when quenching is performed by the above-mentioned heat treatment step will be described. In FIG. 6, a columnar shaft (diameter 36 mm, shaft length 148 mm) formed by using the SCM 20 is placed on a support 21 in a state where the axial direction is perpendicular to the vertical direction, and quenching is performed. It is a figure which shows the example of the case. That is, FIG. 6 shows the conditions when the same material is quenched in different quenching steps and the characteristics of the shaft manufactured under each condition.

The coolant in Comparative Example 1 is quenching oil, and in Comparative Example 1, when quenching with hot oil is performed in one cooling step without performing the heat equalization step and realizing the synchronized state. This is an example. In Comparative Example 1, in order to increase the cooling rate, the coolant is agitated and a flow velocity (200 mm / s) opposite to the immersion direction is given.

The coolant in Comparative Example 2 is water, and Comparative Example 2 is an example in which the soaking step is not performed and the synchronized state is realized and quenching is performed in one cooling step. The coolant W in the examples is water, which is an example in which the primary cooling step, the soaking step, and the secondary cooling step are performed. The heat transfer coefficient of the coolant is hot oil: 3800 W / (m ² · K) and water: 11000 W / (m ² · K).

In FIG. 6, for each of Comparative Example 1, Comparative Example 2 and Example, the quenching temperature (° C.), the descending speed Ve (mm / s) of the object to be processed S, and the flow velocity Vq (mm / s) of the coolant W ), The temperature (° C.) of the coolant W, and the synchronization time (s) are shown. Here, the quenching temperature is the temperature before the object S to be treated comes into contact with the liquid surface of the coolant W. The primary cooling time is the period during which the primary cooling step is performed, and in this example, it is the period from the start of immersion of the object to be treated S to the period from the start of immersion of the object to be processed S to the time when the object to be processed S is pulled up onto the liquid surface. Further, the thermalization time is a period during which the thermalization step is performed, and in this example, it is a period from when the object S to be treated is pulled up onto the liquid surface until the immersion is started again. The thermalization end temperature is the surface temperature of the object S to be treated at the stage where the thermalization is completed (in this example, the temperatures at the top and bottom of the surface are the same). The descending velocity Ve and the flow velocity Vq are positive in the vertical direction and downward. The room temperature at the temperature of the coolant W is 25 ° C.

The synchronization time is the time from when the object S to be treated comes into contact with the coolant until the descending speed Ve is set to 0. That is, in each of Comparative Example 2 and Example, Ve = Vq in the synchronized state, but it is controlled so that Ve = 0 when the synchronized time elapses. Therefore, in each of Comparative Examples 2 and Examples, the default synchronization time is 10 seconds from the contact of the object S with the coolant to the martensitic transformation of the surface of the object S.

Comparative Example 1 is an example in which the descending speed Ve of the object to be processed S is set to 200 mm / s, the object to be processed S is held in the quenching oil at 120 ° C. for 300 seconds, and then the object to be processed S is taken out from the quenching oil. In Comparative Example 2, the temperature of the water was set to room temperature, the descending speed Ve of the object to be treated S was set to 200 mm / s, the flow velocity Vq of the water was set to 200 mm / s, and the synchronized state was continued for 10 seconds, and then the descending speed Ve was set to 0. This is an example when the synchronized state is terminated with the flow velocity Vq set to 200 mm / s.

In the embodiment, the temperature of the water is set to room temperature, the descending speed Ve of the object to be processed S is set to 200 mm / s, and the object to be processed S is immersed in water to perform a primary cooling step accompanied by a synchronized state for 4 seconds. The rising speed Ve of the object to be processed S is set to 200 mm / s, the object to be processed S is pulled up to equalize the heat for 16 seconds, and then the object to be processed S is immersed in water to accompany a synchronized state of 10 seconds. This is an example in which the next cooling step is performed, and then the synchronized state is terminated with the descending speed Ve being 0 and the flow velocity Vq being 200 mm / s. In the examples, the temperature of the surface of the object to be treated S at the stage when the soaking was completed was 560 ° C. In each embodiment, the object S to be processed is taken out after being held in the coolant W until the temperature difference between the surface and the inside of the object S to be processed disappears in the state where the synchronized state is completed.

In FIG. 6, as the characteristics of the object to be treated S obtained by Comparative Examples 1, 2 and Examples as described above, the strain amount (bending amount) (μm), the elongation amount (μm), and the surface hardness ( Hv), effective curing depth (mm), and internal hardness (Hv) are shown. The amount of strain (bending amount) indicates how much the cylindrical axis of the object S to be processed is bent in the vertical direction, and indicates the distance between the uppermost part and the lowermost part of the cylindrical axis of the object S to be processed in the vertical direction. .. The amount of elongation is the difference between the length of the object to be treated S in the direction perpendicular to the dipping direction and the axial length of the object to be treated S that has not been heat-treated at room temperature after the completion of quenching. The surface hardness is an average value of the Vickers hardness of the surface of the object S to be treated. The effective curing depth is an average value of the depth at which the Vickers hardness becomes a default value (513 Hv in this example). The internal hardness is the Vickers hardness at the center of the object S to be treated.

In the above examples, when Comparative Example 1 and Example are compared, the strain amounts are 7 μm and 4 μm, respectively. Comparing the quenching oil and water, water has a larger heat transfer coefficient. Therefore, when immersion is performed at the same descending speed, water causes a larger strain. However, in the examples, since the cooling accompanied by the synchronized state is performed, the occurrence of strain is suppressed, and the example in which the coolant is water is more distorted than the comparative example 1 in which the quenching oil is used. The amount is getting smaller.

Further, when Comparative Example 1 and Comparative Example 2 are compared with Example, the elongation amounts are 41 μm, 259 μm and 45 μm, respectively. If the inside of the object S to be processed becomes hard at a high temperature, the thermal expansion generated in the object S to be processed is not eliminated, so that the shaft of the object S to be processed remains stretched. Comparing the quenching oil and water, water has a larger heat transfer coefficient. Therefore, if cooling is promoted without equalizing the heat on both sides, the surface of the object to be treated S begins to harden. The internal temperature in water is higher in water. Therefore, if cooling is promoted without soaking in both sides, as shown in Comparative Example 1 and Comparative Example 2, the amount of elongation becomes larger when cooled with water than when cooled with quenching oil. ..

However, in the examples, the thermalization is performed, and the surface of the object to be treated S is cooled to 560 ° C. at the stage when the thermalization is completed. Therefore, the inside of the object to be treated S is also cooled to near the surface temperature. As a result, the amount of elongation of Example is smaller than that of Comparative Example 2, and the amount of elongation of Example is the same as that of Comparative Example 1.

Further, comparing the case where the coolant W is oil as in Comparative Example 1 and the case where the coolant W is water as in the example, when quenching with the same material, the coolant W is The effective curing depth can be made deeper when the coolant W is water than when it is oil. Specifically, when the coolant W is water, these coolants W have a higher heat transfer coefficient than oil, so that cooling can be performed more efficiently.

After austenite is formed on the shaft by the carburizing treatment before quenching, martensite is formed when quenching is performed, and the faster the cooling rate of this cooling, the more efficiently martensite can be formed. Therefore, when the coolant W is water, it is possible to efficiently perform martensitic transformation as compared with the case where the coolant W is a quenching oil. As a result, when the coolant W is water, the time required for quenching to obtain the object S having the same surface hardness as that when the coolant W is quenching oil is very long. Becomes shorter.

Further, when water is used as the coolant W, the effective curing depth in the object S to be treated of the same material can be increased as compared with the case where quenching oil is used. FIG. 7 is a diagram showing the hardness in Comparative Examples 1, 2 and Examples, in which the horizontal axis shows the distance from the center and the vertical axis shows the Vickers hardness. The center is the cylindrical axis of the object S to be processed, and the distance from the cylindrical axis to the lowermost part is shown as a negative value, and the distance from the cylindrical axis to the uppermost part is shown as a positive value.

As shown in this figure, the Vickers hardness of Comparative Example 1 is smaller than that of Example from the surface of the object S to be treated to the entire area inside. As a result, it can be said that Comparative Example 1 has a shallower effective curing depth than Examples. In this way, when water is used as the coolant W when quenching the workpiece S of the same material, it is possible to obtain the workpiece S which is harder and has a deeper effective curing depth than the quenching oil is used. it can.

As described above, since water can be cooled more efficiently than oil, the carburizing time required to obtain the object S to be treated having the same effective curing depth can be shortened. If water is used to obtain an effective curing depth equivalent to that of the quenching oil, it is sufficient that the carbon concentration on the surface of the object to be hardened S is low. Therefore, the time required for the carburizing treatment may be shorter than when the coolant W is a quenching oil. In particular, since the carburizing time is proportional to the square of the carburizing depth, the time required for the carburizing treatment is sufficient if the effective curing depth equivalent to that of the object to be treated S obtained when the coolant W is oil is sufficient. Can be very short. As a result, the period for performing the carburizing treatment and the cost of money can be suppressed.

If the period of the carburizing treatment is shortened and a part having a low carbon concentration on the surface of the object S to be treated can be used as the object S to be treated, the cost for preparing the part can be suppressed. That is, when the carburized part is prepared in advance as the object to be treated S and is cooled after being heated to the austenitizing temperature, the carbon concentration must be increased in advance as compared with quenching with quenching oil. Since the object to be processed S before quenching is made of a soft material, processing for obtaining the object to be processed S is easy. Therefore, the processing cost when manufacturing the object S to be processed is suppressed.

The predetermined period, which is the duration of the synchronized state, may be selected so as to reduce the amount of strain remaining in the object S to be processed after the quenching is completed. That is, if the synchronized state is continued at least until the surface of the object to be processed S undergoes martensitic transformation, the possibility of suppressing the strain remaining on the object to be processed S after the completion of quenching can be increased. However, the predetermined period for keeping the synchronized state may be controlled according to the amount of distortion allowed.

FIG. 8 is a diagram showing the temperature change of the object to be treated S and the martensite fraction in the above-mentioned embodiment. The horizontal axis shows the time logarithmically, the left vertical axis shows the temperature, and the right vertical axis shows the martensite fraction. In FIG. 8, in this graph, the transition of the temperature and the martensite fraction of the object S to be treated is shown for each elapsed time after the object S to be treated comes into contact with the coolant W.

In FIG. 8, the surface temperature and the martensite fraction at the lowermost part of the object S to be treated are shown by solid lines. Further, the surface temperature and martensite fraction at the uppermost portion of the object S to be treated are shown by a alternate long and short dash line, and the temperature and martensite fraction inside (center) of the object S to be treated are indicated by a alternate long and short dash line.

In the example shown in FIG. 8, the primary cooling step is the first 4 seconds, and the primary cooling step is in a synchronized state, but at the initial stage of immersion of the object S to be processed, the object to be processed is as shown in FIG. There is a temperature difference between the lowermost surface and the uppermost surface of S. In this state, when the object S to be treated is immersed in the coolant W, the object S is gradually cooled with a temperature difference between the lowermost surface and the uppermost surface of the object S to be processed. However, in this embodiment, since the synchronized state is formed, the temperature difference between the lowermost portion and the uppermost portion is gradually eliminated, and in the example shown in FIG. 8, the object to be treated S The temperature difference is almost eliminated at the stage (the stage immediately above the martensitic transformation start temperature) before the temperature of the surface of the surface reaches the martensitic transformation start temperature (denoted as the Ms point of the carburized layer in FIG. 8). ..

On the other hand, in this stage (4 seconds from the start), the inside of the object to be processed S is hardly cooled. However, in this embodiment, the thermalization is performed for a total of 16 seconds from the start to a period of 4 to 20 seconds. Therefore, the internal heat is transferred to the surface side during the thermalization step, and as a result, the surface temperature of the object S to be processed becomes 560 ° C. and the internal temperature becomes 620 ° C. in 20 seconds from the start. The two are very close to each other. In the present embodiment, the temperature difference between the lowermost portion and the uppermost portion of the surface of the object to be treated S is almost eliminated by the thermalization step.

In this embodiment, the secondary cooling step is started from this stage (20 seconds from the start). When the secondary cooling step is started, the surface of the object to be treated S becomes below the martensitic transformation start temperature within a few seconds from the start. In this embodiment, since the synchronized state is formed, even if the secondary cooling step is started and a temperature difference occurs between the lowermost portion and the uppermost portion of the object to be processed S in multiple stages, it is gradually eliminated. To go. As a result, the surface of the object to be treated S is below the martensitic transformation start temperature in a state where there is no temperature difference between the upper and lower parts of the object S to be processed in the vertical direction. When the surface of the object to be treated S becomes below the martensitic transformation start temperature, martensite is formed on the surface of the object to be treated S. In addition, the martensite fraction on the surface of the object S to be treated increases with time. When martensite is formed on the surface of the object to be treated S in this way, the surface of the object to be treated S becomes hard and has a function of suppressing distortion.

In FIG. 9, the horizontal axis shows the duration of the synchronized state, and the vertical axis shows the amount of strain and the martensite fraction on the surface. Note that FIG. 9 shows how the amount of strain generated in the object S to be processed changes when the duration of the synchronized state is changed under the same conditions as those shown in FIG. 6 for the object S to be processed as in the embodiment. Shown. The amount of strain of the object to be processed S shown in FIG. 9 is the amount of strain in the state where the object to be processed S is completed after quenching, and is shown by a solid line and a vertical axis on the left in the graph shown in FIG. ing. The martensite fraction on the surface of the object S to be treated shown in FIG. 9 is a value at the stage when the synchronized state is completed, and is shown by a broken line and a vertical axis on the right side in the graph shown in FIG.

As shown in FIG. 9, as the predetermined period (synchronization time) for continuing the synchronized state becomes longer, the martensite fraction, which is the ratio of martensite formed on the surface of the object S to be treated, increases. The amount of strain remaining in the object S to be processed after the completion of quenching decreases as the predetermined period for continuing the synchronized state becomes longer. However, when the amount of strain decreases to the limit value (1 μm in the example shown in FIG. 9), the amount of strain does not decrease thereafter. In the example shown in FIG. 9, when the duration of the synchronized state exceeds 10 seconds, the change in the amount of strain slows down, and thereafter, there is no significant change even if the duration of the synchronized state is lengthened. As described above, when the martensite fraction was analyzed at the stage where the change in the strain amount became almost constant, it was found that the martensite fraction was 28%. Therefore, if the state in which the martensite fraction on the surface of the object to be treated is 28% or more is regarded as the state in which the surface of the object to be treated is transformed into martensite, and the synchronized state is stopped in this state, the object to be treated The distortion of the processed object S can be substantially minimized.

On the other hand, when the allowable range of the strain amount in the object S to be processed is larger, the duration of the synchronized state can be shortened. For example, the synchronization required to reduce the strain amount to 1/15 (6.3 μm shown in FIG. 9) with respect to the strain amount in the state in which the duration of the synchronized state is 0 seconds (conventional quenching shown in FIG. 9). The duration of the state is T ₁ shown in FIG. The martensite fraction for this duration is 6.8%. Therefore, if it is desired to reduce the strain generated in the object S to be processed to 1/15 or less when the synchronized state is not performed, the synchronized state may be continued until the martensite fraction becomes 6.8%.

Further, the duration of the synchronized state required to reduce the strain amount to 1/20 (4.7 μm shown in FIG. 9) with respect to the strain amount in the state where the duration of the synchronized state is 0 seconds is T ₂ . .. The martensite fraction for this duration is 14.5%. Therefore, if it is desired to reduce the strain generated in the object S to be processed to 1/20 or less when the synchronized state is not performed, the synchronized state may be continued until the martensite fraction becomes 14.5%.

Further, the duration of the synchronized state required to reduce the strain amount to 1/30 (3.1 μm shown in FIG. 9) with respect to the strain amount in the state where the duration of the synchronized state is 1 second is T ₃ . .. The martensite fraction at this duration is 21.5%. Therefore, if it is desired to reduce the strain generated in the object S to be processed to 1/30 or less when the synchronized state is not performed, the synchronized state may be continued until the martensite fraction becomes 21.5%.

Further, the elongation amount in the example is 45 μm, which is suppressed to a value that is very small as compared with the elongation amount of 259 μm in the comparative example 2. Specifically, the amount of elongation in Examples and Comparative Examples changes as shown in FIG. In FIG. 10, the change in the amount of elongation in Examples and Comparative Example 2 is shown with time as the horizontal axis and the amount of elongation as the vertical axis, as in FIG. In FIG. 10, the solid line shows the change in the elongation amount of the example, and the broken line shows the change in the elongation amount of the comparative example 2.

In Comparative Example 2, the quenching is performed in one cooling step without performing the thermalization step. Therefore, in Comparative Example 2, the temperature of the surface of the object S to be treated changes in the same manner as in FIG. 8 at the initial stage, but the temperature does not rise even after 4 seconds and continues to fall, and after 4 seconds, after a while. The surface of the object S to be treated becomes below the martensitic transformation start temperature. When martensite is formed on the surface of the object S to be treated, the volume increases due to the change in the crystal system accompanying the transformation from austenite to martensite.

In FIG. 10, about 10 seconds after the start of cooling, an increase in the amount of elongation due to the increase in the volume appears, and the amount of elongation of the object to be treated S increases. For example, the amount of elongation at time T ₄ is about 650 μm. When cooling is continued from this state, the degree of thermal expansion decreases as the temperature decreases, and as a result, the amount of elongation also decreases, but the decrease in the amount of elongation eventually reaches a limit due to the progress of martensitic transformation. As a result, the amount of elongation as the limit value seen in FIG. 10 is 259 μm shown in FIG.

On the other hand, in the embodiment, since the heat is equalized, when the heat inside the object S to be processed is transferred to the outside through the surface in the heat equalization step, the object S as a whole undergoes thermal expansion. The degree becomes smaller, and the overall tendency of the thermalization process is that the amount of elongation becomes smaller. Then, when the soaking step is completed and the secondary cooling is started 20 seconds after the start, the rapid cooling is started again. In the embodiment, the amount of elongation sharply decreases until the time T ₅ with this rapid cooling. As a result, in the example shown in FIG. 10, elongation amount at time T ₅ is reduced to 330 [mu] m.

As shown in FIG. 8, the time T ₅ is the time when the martensitic transformation starts to be formed on the surface of the object S to be treated in the examples. After this time T ₅ , even in the examples, the volume increases due to the change in the crystal system accompanying the transformation from austenite to martensite. However, the maximum value of the stretch amount due to this increase in volume is 478μm about a elongation amount at the time T ₆ shown in FIG. 10. Therefore, in the comparative example, it is a very small value as compared with the maximum value of about 650 μm of the amount of elongation after the start of martensitic transformation.

Therefore, in the examples in which the elongation amount is only about 478 μm even if the elongation amount increases due to martensitic transformation, when the cooling is continued, the elongation amount decreases until the value becomes very small as compared with the comparative example. That is, when the elongation amount is reduced to the limit as shown in FIG. 10 in the examples, the elongation amount can be reduced to 45 μm shown in FIG. As described above, in the present embodiment, by sandwiching the heat equalization step between the primary cooling step and the secondary cooling step, the start of martensitic transformation can be delayed, and the internal heat is generated in that process. It is possible to reduce the amount of elongation of the object to be processed S by letting it escape. Therefore, the amount of elongation becomes very small in the initial cooling of the secondary cooling step, and the martensitic transformation can be performed in a state where the amount of elongation is reduced. As a result, the elongation finally generated in the object S to be processed can be set to a very small value.

Further, according to the embodiment, the hardness of the object to be treated S can be easily increased. 11A and 11B are diagrams showing the temperature change of the object to be treated S in the above-described embodiment and the tissue transformation point for each temperature. Again, the horizontal axis represents time logarithmically, and the left vertical axis represents temperature. In FIG. 11A, in this graph, the temperature change on the surface of the object to be treated S is shown for each elapsed time after the object to be processed S comes into contact with the coolant W. FIG. 11B shows the temperature change inside the object S to be processed.

As shown in FIGS. 11A and 11B, when a temperature higher than the martensitic transformation start temperature is maintained for a long time from the austenite state on both the surface and the inside, the structure of the object S to be treated undergoes structural transformation to ferrite or bainite. .. However, the region that undergoes microstructure transformation to ferrite and the region that undergoes microstructure transformation to bainite are different between the surface and the inside of the object S to be treated, for reasons such as different carbon concentrations. That is, both ferrite and bainite take longer to undergo tissue transformation on the surface than on the inside.

In particular, bainite precipitates early on the inside, but does not precipitate on the surface for a very long period of time. Therefore, in the present embodiment, it is possible to easily perform thermalization so that the surface of the object to be treated S does not transform into bainite, and in the embodiment, the surface of the object to be treated S becomes bainite. Thermalization is performed over a period that does not cause metamorphosis.

Further, the temperature range in which ferrite is deposited on both the surface and the inside of the object S to be treated exceeds approximately 600 ° C. In this embodiment, the surface of the object to be treated S reaches about 200 ° C. to 560 ° C. by soaking for 16 seconds, and the internal temperature is lowered to about 620 ° C. Therefore, even if the thermalization is continued, the surface does not become higher than 620 ° C. The transformation point of ferrite at the time after soaking is higher than 620 ° C. as shown in FIG. 11A. Therefore, in this embodiment, it is possible to perform thermalization so that the surface of the object to be treated S does not transform into ferrite. As described above, in this embodiment, since the surface of the object to be treated S does not undergo structural transformation to either bainite or ferrite, the surface is efficiently transformed into martensite in the secondary cooling step, and the object to be treated S is transformed. Can be hardened.

(4) Other embodiments:
The above embodiment is an example for carrying out the present invention, and various other embodiments can be adopted. For example, the object to be processed is not limited to the shaft, and various articles such as gears and building parts may be the object to be processed. Further, various postures may be adopted as the posture of the object to be processed at the time of quenching. For example, in many shafts, the shaft length is longer than the diameter, so in the posture in which the shaft axis is oriented vertically as described above, the shaft is supported in the position where the height of the object to be processed is the lowest. It is placed on a table 21 and hardened. However, in the case where the height of the object to be processed is the highest, for example, if the shaft has a shaft length longer than the diameter, the shaft is placed on the support 21 with the axial direction parallel to the vertical direction and quenched. Quenching may be done. Further, the medium responsible for heat exchange during the primary cooling step, the soaking process, and the secondary cooling step may be gas.

Quenching may be a heat treatment in which the metal is heated to a predetermined temperature and then rapidly cooled, and various materials may be assumed as the object to be processed. For example, it is not limited to quenching in which the carburized steel is rapidly cooled as in the above-described embodiment, but is a quenching in which a steel containing carbon is prepared in advance and the steel is rapidly cooled after being heated. You may. Further, the object to be treated may be a material that has been carburized and nitrified, or a material that has been carburized.

Further, the object to be processed may be a target for quenching, and the material is not limited. For example, various steel materials, general rolled steel materials, carbon steel materials, alloy steels, carburizing steels, tool steels, spring steels, bearing steels, hot rolled steel sheets, cold rolled steel sheets, and carbon steel cast steel products can be processed objects. .. Further, steel materials defined in material standards such as JIS, SAE, and DIN, for example, JIS S35C, JIS S45C, JIS SCM440, JIS SCM420, JIS SCM415, JIS SCR440, JIS SCR420, MSB20, DIN, AG20, etc. are processed. It can be a thing. Further, a material obtained by subjecting these materials to a carburizing treatment, a carburizing distilling treatment, or a carburizing treatment can also be an object to be treated.

In the primary cooling step, it is sufficient that the object to be treated can be cooled with a coolant and the cooling can be stopped before the surface of the object to be processed reaches a temperature equal to or lower than the martensitic transformation start temperature. That is, in the heat equalization step, in order to promote the cooling of the inside by soaking the inside and the surface of the object to be treated, it is sufficient that the surface can be cooled within a range that does not cause martensitic transformation. .. In this sense, in the primary cooling step, if the surface of the object to be treated is cooled to just above the martensitic transformation start temperature, the heat equalization can be performed very efficiently.

The coolant in the primary cooling may be various coolants. That is, as in the above-described embodiment, it may be water or various aqueous solutions in which various materials are dissolved in water. It may be quenching oil. Further, the mode of primary cooling may be various modes, and the object to be treated may be immersed in the coolant accumulated in the cooling tank, or the object to be treated may be placed in an empty cooling tank. On the other hand, the coolant may be applied by a shower, or the gaseous coolant may be sprayed onto the object to be treated. However, when the primary cooling is carried out with the same coolant and the same device as the secondary cooling, the primary cooling can be realized by a simple device, which is preferable.

In the thermalization step, it is sufficient that the surface and the inside of the object to be treated can be thermalized. That is, it suffices to provide a step in which the heat inside the object to be processed flows toward the surface. The soaking may be carried out in a state where the primary cooling is stopped, that is, in a state where the surface of the object to be treated does not fall below the martensitic transformation start temperature. Therefore, as in the above-described embodiment, the thermalization may be performed in a state where the object to be processed is not cooled, and the surface of the object to be processed may be kept below the martensitic transformation start temperature, for example. , The heat may be equalized in a state where air cooling by gas or the like is performed, and various configurations can be adopted.

In the secondary cooling step, it is sufficient that the object to be treated can be cooled with a coolant containing water as a main component at least until the surface of the object to be treated is transformed into martensite. That is, in the secondary cooling step, it is sufficient that the object to be processed can be quenched by cooling the object to be processed with a coolant containing water as a main component. Whether or not the surface of the object to be treated has undergone martensitic transformation may be defined by a predetermined period as in the above embodiment, by the martensite fraction, or by the martensite fraction of the surface of the object to be treated. It may be defined by temperature.

The moving device only needs to be able to immerse the object to be processed in the coolant containing water accumulated in the cooling tank as a main component by moving the object to be processed. The moving device may be realized by various configurations. For example, it is possible to move the object to be processed below the liquid surface from the state where the object to be processed is arranged above the liquid surface of the coolant containing water as a main component. It may be various devices. The moving direction of the object to be processed may be parallel to the vertical direction or may be different. The moving speed may be variable. However, even in this case, the relative speed between the object to be treated and the coolant containing water as a main component is maintained at a speed slower than the moving speed of the object to be treated. The coolant containing water as a main component may be water or various aqueous solutions in which other substances are dissolved in water. That is, any coolant having a higher heat transfer coefficient and a higher cooling rate than the quenching oil may be used.

When the relative speed between the object to be treated and the coolant containing water as the main component is slower than the moving speed of the object to be treated and the cooling is relaxed, at least the coolant whose main component is water is to be treated. It suffices to maintain the surface of the object to be treated until it undergoes martensitic transformation after contact. That is, when the object to be treated comes into contact with a coolant containing water as a main component, cooling starts from that portion, so that a difference in surface temperature begins to occur. Therefore, cooling is relaxed at this stage. In such a state where cooling is relaxed, a temperature difference is unlikely to occur on the surface of the object to be treated, so that distortion can be suppressed. Therefore, it is possible to suppress the influence of thermal expansion and suppress the strain at the same time.

In addition, the state in which cooling is relaxed and strain can be suppressed may be maintained until the surface of the object to be treated undergoes martensitic transformation. That is, when the surface is transformed into martensite, the surface of the object to be treated is hardened, so that the object to be treated is unlikely to be distorted even if it is rapidly cooled thereafter. Therefore, after the surface of the object to be treated has undergone martensitic transformation, it may be further rapidly cooled. For example, the relative speed between the object to be treated and the coolant containing water as a main component is the moving speed of the object to be treated. It may be more than that.

Of course, after the surface of the object to be treated has undergone martensitic transformation, the movement of the object to be processed by the moving device may be stopped. In this case, it is possible to adopt a configuration that promotes the replacement of the water-based coolant around the object to be treated, such as by continuing the operation of the fluidizing device that flows the water-based coolant. ..

The relative speed between the object to be treated and the coolant containing water as a main component may be slower than the moving speed of the object to be treated. Therefore, in addition to the configuration in which the operation of the flow device is controlled so that the relative speed between the object to be treated and the coolant containing water as a main component becomes 0 as in the above-described embodiment, various configurations are adopted. It is possible. That is, in the process of moving the object to be processed by the moving device, it is sufficient that the coolant containing water as a main component is moving with a velocity vector having components in the same direction as the object to be processed.

The state in which the surface is transformed into martensite may be a state in which the object to be treated is less likely to be distorted by the martensite. Such a state may be defined by various methods, for example, it may be defined by the elapsed time after the start of carburizing, it may be defined by the temperature of the object to be treated, or the martensite fraction on the surface. May be defined by. That is, the state in which the object to be treated becomes hard due to martensitic transformation and is not easily affected by strain may vary depending on the composition of the object to be processed, etc., but the elapsed time, temperature, and martensite fraction are determined in advance for each object to be processed. Once specified, it can be considered that the surface is martensitic transformed by maintaining the state in which the cooling is relaxed until that state is reached.

The immersion may be any treatment as long as the object to be treated is immersed in a coolant. That is, the heat of the object to be treated may be transferred to the coolant by changing from the state where the coolant is not present around the object to be treated to the state where the object to be treated is immersed in the coolant. .. The immersion may be carried out in any of the primary cooling step and the secondary cooling step.

In the secondary cooling step of quenching, the synchronized state may be realized by holding the object S to be processed inside the static water that does not flow. FIG. 2D is a diagram showing a configuration in which a shower 25 is provided in a cooling tank 101 provided with a moving device 20 and a flow device 30 similar to those in FIG. 1A. In the configuration shown in FIG. 2D, the configurations other than the shower 25 and the cooling tank 101 are almost the same as the configuration shown in FIG. 1A, and the moving device 20 may raise or lower the object S to be processed. The flow device 30 may be able to flow the coolant W containing water as a main component. The cooling tank 101 is higher than the cooling tank 10, and the coolant W is accumulated in the cooling tank 101 in advance.

In the present embodiment, the shower 25 is further provided in the device for carrying out the quenching method. In the present embodiment, the shower 25 includes a plurality of nozzles, and pipes (not shown) are connected to the shower 25. The pipe is connected to a tank (not shown) in which the coolant is stored, and by opening and closing the pressure regulating valve connected to the pipe, the coolant can be discharged from each nozzle and the discharge can be stopped. .. In addition, in FIG. 3C, the coolant discharged from the nozzle is shown by the broken line around the object S to be processed. (In FIGS. 3A to 3D, the flow device 30 is omitted. The same applies hereinafter).

In the present embodiment, the coolant discharged from each nozzle is applied to a plurality of surfaces of the object S to be processed. In the example shown in FIG. 3C, it is schematically shown that the coolant is applied to the upper surface and the side surface of the object S to be treated, but of course, the coolant is applied to the upper surface of the object S to be treated and the coolant is applied. The coolant may be in contact with almost the entire surface of the object to be treated S by flowing on the surface of the object to be processed S. Further, a coolant may be applied to the lower surface of the object S to be treated. In this case, it is possible to adopt a configuration in which the support base 21 is provided with a nozzle and the coolant discharged from the nozzle is applied to the object S to be processed.

In the above configuration, in the state where the object S to be processed is arranged inside the cooling tank 101, the accumulation of the coolant W in the cooling tank 101 is started, and at least the object S to be processed is in contact with the coolant W. The coolant W is not flowed by the fluidizing device 30 until the surface of the object S to be treated undergoes martensitic transformation, and the coolant W is fluidized by the fluidizing device 30 after the surface of the object S to be treated undergoes martensitic transformation. ..

Specifically, as shown in FIG. 2D, after the same treatment as that shown in FIG. 4 is performed in a state where the coolant W is accumulated to a depth that does not contact the initial object S to be treated. , Quenching can be performed by executing the process shown in FIG. 12A. The process shown in FIG. 12A is a process in which steps S195 and S197 are added to the process shown in FIG. 5, and steps S200 and S205 are omitted. That is, in the present embodiment, the primary cooling step is performed by executing steps S100 to S130 in the same manner as the process shown in FIG. FIG. 3A is a diagram showing a process in which primary cooling is performed.

Next, when steps S130 to S140 are executed through step S125, the object S to be treated is pulled above the coolant W, and a thermalization step is performed. FIG. 3B is a diagram showing a process in which the thermalization step is performed.

Next, in step S195 shown in FIG. 12A, the discharge by the shower is started. That is, the discharge of the coolant W is started from the nozzle of the shower 25. As a result, as shown in FIG. 3C, the coolant is discharged from the nozzle of the shower 25. In the present embodiment, the coolant W discharged from the shower 25 is accumulated in the cooling tank 101, the uppermost portion of the object to be treated S is below the liquid level of the coolant W, and the uppermost portion of the object to be treated S is The shower is stopped when the distance between the liquid level and the liquid level Sw reaches a default value (step S197). That is, the discharge of the coolant is stopped from the nozzle of the shower 25. FIG. 3D is a diagram showing a state in which the immersion of the object S to be processed is completed and the shower 25 is stopped.

In the present embodiment, the coolant W is not stirred or the like for a predetermined period immediately after the completion of immersion. Therefore, the coolant W does not flow below the liquid level Sw. Therefore, when the immersion is completed, the relative velocity between the object S to be treated and the coolant W inside the liquid level Sw of the coolant W becomes 0. Therefore, the synchronized state is also realized in this embodiment.

In the synchronized state as described above, the relative velocity between the object S to be processed and the coolant W is 0, and the coolant W in which heat from the object S to be processed is transferred in contact with the object S to be processed is to be applied. It stays in contact with the object S and stays around the object S to be processed. Therefore, although the object S in contact with the coolant W is rapidly cooled by the coolant W, the coolant W in contact with the coolant S gradually warms up when the synchronized state is maintained. Cooling is not promoted.

That is, when the coolant W around the object S to be processed moves to another place by stirring or the like, the coolant W that has become hot around the object S to be processed is replaced with the coolant W that has a low temperature. However, in the synchronized state, the coolant W that has become hot in contact with the object S to be treated is not easily replaced by the low temperature coolant, and cooling is not promoted. When the synchronized state is maintained, the cooling rate of the portion that first reaches the liquid level of the coolant W and starts cooling first gradually slows down. On the other hand, the cooling rate of the portion that later reaches the liquid level of the coolant W and starts cooling is faster than the cooling rate of the portion where cooling is started earlier. Therefore, when the synchronized state is maintained, the temperature difference generated on the surface of the object to be processed S gradually becomes smaller, and the occurrence of strain on the object to be processed S can be suppressed.

After that, steps S210, S215, S225, and S230 are the same as the process shown in FIG. 5 described above. That is, when the predetermined period elapses, the flow velocity Vq is set in step S215, the synchronized state is terminated, and the flow by the flow device 30 is started. As a result, the object S to be processed is rapidly cooled. After that, when the quenching is completed (step S225), the object S to be processed is raised and the quenching is completed. Here, too, the predetermined period is a period from when the object S to be treated comes into contact with the coolant W until the surface of the object S to be treated undergoes martensitic transformation, and is predetermined. The default period may be determined by various methods. For example, the period until the martensite fraction on the surface of the object S to be treated reaches the predetermined ratio (for example, 28%) can be set as the default period. Is.

The above embodiment is quenching based on the same principle as the embodiment shown in FIG. For example, when the discharge amount of the coolant W from the shower 25 is adjusted so that the rising speed of the liquid level in the secondary cooling step is 200 mm / s, the falling speed of the object S to be processed by the moving device 20 is 200 mm. Immersion is performed at a rate equivalent to that of the embodiment at / s, and the mixture is cooled in a synchronized state. Therefore, if the predetermined period after the object to be treated S comes into contact with the liquid surface is the same period as in the examples, quenching that is qualitatively the same as in these examples can be performed.

Therefore, it is possible to suppress the occurrence of strain in the object S to be processed. Further, it is possible to easily realize a heat treatment step of maintaining a synchronized state at least until the surface of the object S to be treated undergoes martensitic transformation. Further, after the surface of the object to be treated S is transformed into martensite, the coolant W containing water as a main component is flowed by the flow device 30, so that quenching is completed at an early stage while suppressing the occurrence of strain. Can be made to. Further, in the present embodiment, by interposing a thermalization step between the primary cooling step and the secondary cooling step, the start of martensitic transformation can be delayed, and martensite is in a state where the amount of elongation is reduced. Site transformation can be performed. As a result, the elongation finally generated in the object S to be processed can be set to a very small value. Further, in the present embodiment, it is possible to easily perform thermalization so that the surface of the object to be treated S does not transform into bainite, and the hardness of the object to be treated S can be easily increased. Further, it is possible to perform thermalization so that the surface of the object to be treated S does not transform into ferrite, the surface can be efficiently transformed into martensite, and the object to be processed S can be hardened.

In the above-mentioned step S195, since the coolant discharged from the shower 25 is applied to the object S to be processed, the object S to be processed is cooled before being immersed in the accumulated coolant W. This cooling has the effect of suppressing the temperature difference between the upper and lower parts of the object S to be treated before immersion, and this cooling is called auxiliary cooling. In this auxiliary cooling, the coolant discharged from the shower 25 is applied to the entire area from the uppermost portion to the lowermost portion of the object S to be processed, and at the same time, the auxiliary cooling is performed. Therefore, the immersion in the coolant W is started in a state where there is almost no temperature difference between the uppermost portion and the lowermost portion on the surface of the object S to be treated and there is almost no temperature difference between the uppermost portion and the lowermost portion. be able to. Further, the primary cooling step may be performed only by applying the coolant discharged from the shower 25 to the object S to be processed.

When the auxiliary cooling that suppresses the temperature difference on the surface of the object to be processed S is performed, the strain generated in the object to be processed S can be further suppressed as compared with the case where the auxiliary cooling is not performed. FIG. 12B shows a sample obtained by immersing the shaft in a coolant with the apparatus shown in FIG. 2D with the axial direction of the shaft oriented perpendicular to the vertical direction in the same manner as in the embodiment shown in FIG. 6, and holding the sample until quenching is completed. The amount of distortion of is shown. Sample A is an example of a case where the shower 25 is immersed without auxiliary cooling, and sample B is an example of a case where the sample B is immersed after the auxiliary cooling by the shower 25.

In Sample A and Sample B shown in FIG. 12B, the coolant is water and the heat transfer coefficient is 11000 W / (m ² · K). In FIG. 12B, the quenching temperature (° C.), the descending speed Ve (mm / s) of the object to be processed S, the temperature (° C.) of the coolant W, and the shower time (seconds) are shown for Sample A and Sample B. There is. Here, the quenching temperature is the temperature before the object S to be treated comes into contact with the liquid surface of the coolant W. The room temperature at the temperature of the coolant W is 25 ° C. The shower time is the time from when the auxiliary cooling by the shower 25 is started until the lowermost portion of the object S to be treated comes into contact with the liquid level Sw of the coolant W.

In both Sample A and Sample B, the strain generated in the object to be treated S at the stage when the immersion is completed (the stage when the object to be processed S reaches below the liquid level of the coolant W) is regarded as the strain after immersion, and quenching is completed. The strain generated in the object S to be processed at this stage was defined as the amount of strain after quenching. The amount of strain (bending amount) shown in FIG. 12B indicates how much the cylindrical axis of the object S to be processed is bent in the vertical direction, and the distance between the uppermost part and the lowermost part of the cylindrical axis of the object S to be processed in the vertical direction. Is shown. Therefore, the amount of strain shown in FIG. 12B indicates the maximum value of strain generated in the object S to be processed.

Comparing Sample A and Sample B, the amount of strain after immersion is 22 μm for Sample A and 1 μm for Sample B. The amount of strain after quenching is 94 μm for sample A and 0.7 μm for sample B. Therefore, when the auxiliary cooling is performed, there is an effect of suppressing the amount of strain as compared with the case where the auxiliary cooling is not performed. Therefore, if auxiliary cooling is performed by the shower 25 at the initial stage of the secondary cooling step, it is possible to suppress the amount of strain generated in the object S to be processed. Of course, auxiliary cooling by the shower 25 may be performed in the process of the primary cooling step. In this case, the temperature difference generated on the surface of the object to be treated S can be suppressed before the thermalization is performed, and the thermalization can be performed in a state where the object S to be processed is not distorted. is there.

10 ... Cooling tank, 20 ... Moving device, 21 ... Support stand, 22 ... Support part, 25 ... Shower, 30 ... Flow device, 31 ... Shaft, 32 ... Propeller, 101 ... Cooling tank

Claims (6)

It is a quenching method that cools the object to be hardened.
A primary cooling step of cooling the object to be treated with a coolant and stopping the cooling before the surface of the object to be treated reaches a temperature equal to or lower than the martensitic transformation start temperature.
A thermalization step for soaking the surface and the inside of the object to be treated,
At least, a secondary cooling step of cooling the object to be treated with a coolant containing water as a main component until the surface of the object to be treated is transformed into martensite.
Quenching method including. In the secondary cooling step,
The moving device for moving the object to be processed moves the object to be processed inside the coolant containing the water as a main component accumulated in the cooling tank.
At least, the relative between the object to be treated and the coolant containing water as a main component from the time when the object to be treated comes into contact with the coolant containing water as a main component until the surface of the object to be treated undergoes martensitic transformation. The state in which the speed is slower than the moving speed of the object to be processed is maintained.
The quenching method according to claim 1. In the secondary cooling step,
A water-based coolant for the cooling tank in a state where the object to be treated is arranged inside a cooling tank equipped with a flow device for flowing the accumulated water-based coolant. The water-based coolant by the flow device at least from when the object to be treated comes into contact with the water-based coolant until the surface of the object to be treated undergoes martensitic transformation. After the surface of the object to be treated has undergone martensitic transformation, the water-based coolant is flowed by the flow device.
The quenching method according to claim 1. In the primary cooling step,
Cooling of the object to be processed is performed by discharging coolant from a plurality of nozzles.
The quenching method according to any one of claims 1 to 3. In the secondary cooling step,
Cooling of the object to be processed is performed by discharging coolant from a plurality of nozzles.
The quenching method according to any one of claims 1 to 4. In the secondary cooling step,
The surface of the object to be treated is below the martensitic transformation start temperature in a state where there is no temperature difference above and below the object to be processed in the vertical direction.
The quenching method according to any one of claims 1 to 5.