JPH01219A - Quenching method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Purpose of the invention]

(Field of Industrial Application) The present invention relates to a hardening method used for hardening metal parts, and more specifically to a hardening method that can reduce the amount of deformation and variation thereof caused by hardening treatment. be. (Prior Art) Generally, heat treatment generates thermal stress and transformation stress in steel, causing deformation. Therefore, when designing metal parts to be heat treated, it is necessary to take into consideration the amount of deformation and deformation characteristics, and there is a need to develop heat treatment technology that reduces the amount of deformation and also suppresses the amount of variation. . Particularly in the automobile industry, as high technology and quality continue to advance, there is a demand for quieter cars, and there is a strong demand for reductions in engine noise as well as gear meshing noise. Gear meshing noise can be caused by poor design, poor workmanship, poor installation,
This is caused by a complex interplay of poor lubrication, etc., and the tooth profile, tooth lead, tooth thickness, etc. of the gear specifications shown in the design drawing are only a few pm.
It is said that errors in the number of parts affect meshing noise, and it is necessary to improve machining accuracy and accurately understand and manage the amount of deformation caused by heat treatment. In other words, most gears are used with some kind of surface hardening treatment, and carburizing and quenching is especially effective for gears that are used under high surface pressure, so it is widely used. Almost 100% of train gears
It is no exaggeration to say that it is a carburized and quenched product. Carburizing and quenching is a process of diffusing and penetrating the surface of gears made from case-hardened steel, hardening them and turning them into martensite, giving them high hardness and strength. Due to the volume change due to metamorphosis, when designing,
It is important to design the shape with sufficient consideration of its deformation characteristics. However, for items such as automobile gears, which are produced in large quantities and processed in large quantities in large continuous furnaces, it is difficult to manage and understand the amount of deformation, and a great deal of effort is expended on this task. Therefore, as a heat treatment technique, it is always required to minimize the amount of deformation and its variation. From this point of view, several attempts have been made to reduce the amount of deformation caused by hardening, but none of them have reached a satisfactory level. For example, when processing in a large continuous furnace where the heat source is heavy oil, the temperature distribution inside the furnace varies widely, so carburizing,
°When the temperature is lowered to the quenching temperature after diffusion, the quenching temperature of all gears is made uniform by creating a separate chamber in the furnace or separating it with a door to completely separate it from the carburizing and diffusion zone. There is also a method to prevent fluctuations in quenching temperature by avoiding heavy oil or gas as a heat source and using PID control to reduce temperature fluctuations as a heat source. Furthermore, there is a marquenching process in which the material is once quenched in a salt bath maintained at around 350'C and then slowly cooled. (Problems to be Solved by the Invention) However, even with the method (2), the variation in the amount of tooth profile deformation is as large as several 1071 m, which cannot be said to be small. In addition, method (2) requires a small furnace and is not suitable for producing large spears.On the other hand, when electric heating is applied to a large furnace, there is a large loss in power consumption, which is disadvantageous in terms of cost. Method (2) uses metal salts as a refrigerant, so it requires washing with water and a wastewater treatment device.In addition, if a quenching tank is installed in a continuous furnace, gas will flow into the carburizing atmosphere, resulting in a coal-throwing atmosphere. There were problems such as harming the As mentioned above, in the past, there have been many attempts to prevent deformation by making the quenching temperature uniform, but there have been few studies on the quenching bath or cooling method. All of them employed a stirring method in which the flow of the refrigerant was always from the bottom to the top of the object to be quenched. (Objective of the Invention) The present invention has been made to solve the above-mentioned problems, and its purpose is to reduce the amount of deformation and its dispersion due to hardening treatment, and thereby reduce the amount of deformation caused by hardening treatment. The purpose is to improve dimensional accuracy.

[Structure of the invention]

(Means for Solving the Problems) The present invention takes into account the effects of the quenching temperature and refrigerant temperature, which have traditionally been given particular emphasis, in determining the amount of deformation caused by the quenching process. As a result of basic and careful investigation of the influence of the refrigerant flow state, which had rarely been considered in the past, we found that the influence of the refrigerant flow state is so large that it cannot be ignored, and the flow direction of the refrigerant should be carefully considered. This is based on the completely new knowledge that by doing so, the difference in the local cooling rate of the object to be hardened can be reduced, and the amount of deformation and its dispersion can be minimized. When quenching metal parts, the purpose is to move the refrigerant so that the flow of the refrigerant is from above to below the object to be quenched that has been placed in the refrigerant. (Function) The present invention will be explained in more detail below along with its function. When steel is rapidly heated and cooled, thermal stress and transformation stress are generated, resulting in non-uniform plastic deformation, some of which becomes residual stress and is retained internally, while the rest becomes deformed and is transferred to the outside. appears in Therefore, since quenching involves transformation, it must be considered that some degree of deformation is inevitable. Therefore, various factors that affect the occurrence of heat treatment deformation, namely, the hardenability of the material, the carbon potential of the carburizing atmosphere, the depth of the carburized layer, the quenching temperature, and the coolant temperature. Regarding the refrigerant stirring conditions and the type of refrigerant, we used a large continuous furnace using heavy oil as a heat source and a quenching tank as shown in the tJS1 diagram, with a pitch circle diameter of 26.0 mm and a module of 1.0 mm. Number of teeth: 26. These effects were fundamentally investigated by carburizing and quenching an involute tooth type helical gear with a helix angle of 31.6 degrees. In addition, in FIG. 1, the stirring fan 1 is used to direct the flow of cold tofu to the material to be quenched 3 in the quenching basket jig 2.
(gear), it has a structure that rotates in the direction that flows from the bottom to the ball. 4 is a refrigerant guide cylinder, 5 is a refrigerant guide plate, 6 is a stirring motor, 7 is an elevator cylinder, and 8 is a refrigerant. be. As a result, it was found that among the above-mentioned factors, the one most closely related to heat treatment deformation was the stirring conditions of the refrigerant, and when the relationship between the stirring conditions of the quenching oil and the amount of deformation of the gear tooth tip was further investigated, It was found that those quenched in oil without stirring had the least deformation and the variation was also small. The reason for this is thought to be as follows. In other words, conventional quenching tanks have a structure in which the flow of refrigerant is stirred from the bottom to the top of the object to be quenched, and the oil that comes up from the bottom is stirred after hitting the gears. It will pass upward along the tooth, and at this time, there will be a difference in the cooling rate between the front and back sides of the tooth, and a time lag will occur in the transformation period, resulting in an imbalance in residual stress and a large amount of variation in the amount of deformation. This is considered to be the case. On the other hand, in the case of quenching in oil without stirring, the oil heated by the heat of the object to be quenched causes natural convection and rises upwards, so the cooling rate is almost the same on the entire surface of the tooth. . Therefore, since the transformation occurs simultaneously and the balance of residual stress is good, both the amount of deformation and its dispersion are considered to be small. In addition, within the scope of the above basic investigation, it was confirmed that even with such a quenching method, uneven quenching or incompletely quenched parts did not occur, and the product was finished in a usable condition. However, when such a quenching method is applied to a mass production furnace that is actually used on an industrial scale, the following problems arise. That is, if the oil is quenched without stirring, the high-temperature oil heated by the object to be quenched will remain in the upper part of the quenching tank, which may cause a risk of ignition. In addition, if a large amount of oil is quenched on an industrial scale, uneven quenching may occur, and it was concluded that it would be impossible to eliminate oil agitation. Therefore, as a result of various studies on agitation methods that could provide the material to be quenched with a cooling rate comparable to that of natural convection while stirring the oil, we found that the flow of oil, which had previously been from the bottom to the top, with respect to the material to be quenched. By reversing the direction from top to bottom and making the flow rate twice the natural convection rate, the cooling rate of the material to be quenched is almost the same as that of natural convection, and there is no risk of fire. We came up with a new idea that can also avoid the occurrence of uneven coloring. In carrying out the present invention, the flow rate of the refrigerant depends on the shape and size of the object to be quenched, but in particular in the case of automobile power train parts, the flow rate is 0.001 to i. m/sec, which means that the flow velocity is 0.
．． If the flow rate is less than 0.001 m/sec, the flow rate is too slow and it is equivalent to not stirring the mixture properly, and the effect of preventing fire and uneven cooking becomes small. Conversely, if it exceeds 1.0m/sec,
This is because if the flow rate is too high, a difference occurs in the cooling rate, and the amount of deformation tends to increase. It was also confirmed that by intermittently performing the stirring of the present invention, the amount of deformation due to quenching and its variation can be further reduced. This is because forced stirring, in which the refrigerant flows from top to bottom, and natural convection, which flows from bottom to top, are repeated alternately, making the cooling rate uniform over the entire surface of the object to be quenched, resulting in a better balance. This is thought to be due to cooling. Furthermore, as shown in Fig. 1, the structure of the quenching tank is such that the quenching basket jig 2 is completely housed in the refrigerant guide cylinder 4, which increases the cooling rate of the material to be quenched. Desirable for uniformity. In addition, by making the stirring fan 1 variable speed, it is possible to obtain the optimum cooling conditions according to the shape of the object to be quenched. It is desirable that the rotation direction be both forward and reverse so that both directions are possible. EXAMPLES The effects of the present invention will be specifically illustrated below with reference to Examples. Example 1 The stirring motor 6 of the quenching oil tank of a continuous carburizing and quenching furnace as shown in Fig. 1 was modified to reverse the conventional flow of oil 8 and make it flow from top to bottom. Flow velocity 0.02m/s
Adjusted to be ec. Furthermore, there are 6 pieces per side in the basket jig 2. A total of 12 pieces stacked in two layers, pitch circle diameter 26.0 mm, module 1.0. gJi number 26. A double helical gear with an involute tooth profile and a helix angle of 31.6 degrees was inserted and carburized and quenched in this quenching oil. In this case, the amount of deformation of the tooth profile and its dispersion are
Figure 2 shows the results of a comparison with the conventional method in which oil flows from bottom to top. As is clear from this figure, the method of the present invention in which the refrigerant flows from top to bottom not only reduces the amount of deformation of the tooth profile, but also
In particular, the variation in the amount of deformation becomes extremely small, whereas in the case of the conventional method in which the refrigerant flows from the bottom up, the variation in the amount of deformation becomes extremely large. Example 2 Using the same equipment as in Example 1, the same quenching oil as in Example 1 was used as the refrigerant 8 in a quenching tank adjusted to flow from top to bottom at a flow rate of 0.5 m/sec. The same gear set in the basket jig 2 as in Example 1 was carburized and quenched. Then, 1 minute after carburizing, the rotation of the stirring motor 6 was stopped, and after 2 minutes, the stirring motor 6 was rotated again, and after 1 minute, the stirring motor 6 was repeatedly stopped. 15 minutes after coal casting, the basket jig 2 was pulled out. In the same manner as in Example 1, the amount of deformation of the tooth profile and its dispersion were investigated. As a result, it was found that the amount of deformation was within the range of lO±2 pm, and the variation in the amount of deformation was also within the range of ±51 Lmliii, making it possible to further reduce the amount of deformation than in Example 1.゛

【Effect of the invention】

As explained above, the present invention is realized by reversing the flow of refrigerant in the quenching tank from top to bottom, which was conventionally from bottom to top. By simply reversing the rotation of the machine parts, it does not require any major modification, and while maintaining the same mass productivity as before, it is possible to significantly reduce the amount of deformation and variation in the amount of deformation caused by quenching. This greatly contributes to improving dimensional accuracy.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing the structure of a quenching tank, and FIG. 2 is a diagram showing the amount of deformation of a gear tooth profile according to an embodiment of the present invention and a conventional example.

Claims (1)

[Claims] (1) A method for quenching metal parts, which is characterized by moving the refrigerant so that the flow of the refrigerant occurs from above to below the object to be quenched that has been placed in the refrigerant.