JPH0754038A - Method for quenching by carburizing or carbo-nitriding - Google Patents

Abstract

PURPOSE:To effectively prevent the quenching-strain by the thermal stress strain by stably making the uniform steam film appear in the stage of steam film. CONSTITUTION:The material which is treated by carburizing or carbo-nitriding is quenched by using the quenching oil whole kinematic viscosity: x at 100 deg.C is 9-35cSt, at the temperature of the oil where the kinematic visccosity of the quenching oil is 3-8cSt in the pressure range on the oil level where the lower limit is 60Torr and the upper limit is given in the formula a. Formula a: oil bearing pressure (Torr)=-12.5x+650, (9<=x<=35). The stage of the steam film where the cooling speed is reduced by the circumference of the material to be treated being wrapped by the steam film is increased by the oil quenching under the vacuum condition. The uniform steam film can be stably obtained by the quenching in this condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of carburizing or carbonitriding steel parts, and more particularly to a method of oil quenching a carburized or carbonitrided material under reduced pressure.

[0002]

2. Description of the Related Art Steel parts are subjected to surface treatment such as carburizing and carbonitriding quenching in order to improve wear resistance and fatigue strength. For the carburizing and quenching, the treated material is 900
After heating to a carburizing temperature of about 1000 ° C and exposing it to an atmosphere containing CO to diffuse and infiltrate C from the surface of the treated material, quenching is performed directly from the carburizing temperature, or normalizing is performed again It is performed by refining and then quenching. The treated material that has been carburized and quenched is usually 200
It is used after tempering at around ℃.

The carbonitriding and quenching described above is performed by setting the carburizing temperature to about 900.degree.
In addition, by exposing the treatment material to an atmosphere containing NH ₃ , C and N are diffused and permeated from the surface of the treatment material. By the way, in a general quenching process, since the treated material must be rapidly cooled from the austenitizing temperature, the temperature difference between the surface portion and the central portion of the treated material causes heat treatment of the treated material. Stress is generated. Further, the steel material greatly expands due to the martensitic transformation, and the surface of the treated material cools before the center portion to undergo the martensitic transformation, so that transformation stress occurs in the treated material. In the treated material thus quenched, quenching strain occurs due to thermal stress and transformation stress.

Therefore, how to prevent the above-mentioned quenching distortion while maintaining the quenching hardness is a major problem in the quenching technology. However, the special number of metal special edition (Agne Publishing Co., Ltd.,
(May 1985), oil quenching treatment under reduced pressure changes the generation state of vapor bubbles of quenching oil, thereby reducing quenching strain and improving quenching hardness. It is disclosed that it can be done.

In this reduced pressure quenching, the occurrence of vapor bubbles in the quenching oil is changed by lowering the oil surface pressure, and as a result, quenching is divided into three stages, a vapor film stage, a boiling stage, and a convection stage. It changes the cooling process of oil. In other words, if the oil surface pressure decreases, the amount of steam film generated increases due to the increase in the steam pressure of the quenching oil, and the periphery of the treated material is covered with a steam film, and the cooling rate slows down. . Therefore, it is possible to suppress the occurrence of thermal stress due to rapid cooling, and it is possible to suppress quenching strain due to thermal stress. Further, when the oil surface pressure is lowered, the boiling point of the quenching oil is lowered, so that the boiling stage in which the cooling rate is very fast is carried over to the low temperature side, and the hardening can be completed more completely. Therefore, it is possible to suppress the occurrence of quenching strain and improve quench hardening by oil quenching under reduced pressure.

[0006]

However, even the conventional vacuum oil quenching method as described above could not effectively prevent quenching distortion of the treated material. In particular, the carburized and carbonitrided hardened materials represented by gear parts are more susceptible to quenching distortion than the above-mentioned general quenching treatments, so it is difficult to prevent this effectively.

The inventor of the present invention has made extensive studies as to the reason why quenching distortion cannot be effectively prevented by reduced pressure oil quenching, and as a result, in the above vapor film stage, the vapor film encapsulating the treated material has a different film thickness. It was found that the heat treatment strain was partially broken due to this, and the cooling rate of the treated material became non-uniform due to the location, causing thermal stress strain. The present invention is
It is an object of the present invention to provide a reduced pressure oil quenching method capable of causing a uniform vapor film to appear stably in the vapor film stage and effectively preventing quenching strain due to thermal stress strain.

[0008]

According to the first embodiment of the present invention, which is for solving the above-mentioned problems, there is provided a reduced pressure oil quenching method in which a treated material which is carburized or carbonitrided has a kinematic viscosity at 100 ° C .: x of 9 to 35 c.
A quenching oil of St is used, and the kinematic viscosity of the quenching oil is 3 to 8c.
At the oil temperature of St, the lower limit is 60 Torr and the upper limit is the formula a.
It is characterized in that quenching treatment is performed under the oil surface pressure range shown by.

Formula a: Oil surface pressure (Torr) =-12.5x
+650, (9 ≦ x ≦ 35) Further, the reduced pressure oil quenching method of the second invention for solving the above-mentioned problems is the martensitic transformation starting point (hereinafter , M _S point)
A treated material that has been subjected to quenching treatment as described below, at least 1
It is characterized in that the quenching treatment in the second stage is performed by using a quenching agent having a temperature of less than 60 ° C.

The conditions of the carburizing or carbonitriding treatment in the first and second inventions are not particularly limited, and can be the usual conditions of carburizing or carbonitriding treatment. The reasons why the kinematic viscosity of the quenching oil, the oil temperature, and the oil surface pressure are limited as described above in the first and second inventions are shown below. First, the reason for limiting the kinematic viscosity of the quenching oil used is to allow a uniform vapor film to appear stably at the vapor film stage, and to consider the performance as a quenching agent. That is, when the kinematic viscosity x at 100 ° C. is higher than 35 cSt, it becomes difficult to form a uniform vapor film within the above oil temperature / oil surface pressure range, and the desired quenching performance as quenching oil is obtained. Cannot be demonstrated. On the other hand, kinematic viscosity at 100 ° C .: x is 9 cSt
When the temperature is lower, the vapor film is more likely to appear, but the vapor generated from the lower surface of the treated material wraps around to the upper surface, and the vapor film stage at the upper portion of the treated material becomes extremely long, resulting in non-uniform vapor film. Become.

The reason for limiting the oil temperature so that the kinematic viscosity of the quenching oil during quenching treatment is within a predetermined range is to allow a uniform vapor film to appear stably at the vapor film stage. This is also because it was considered that the performance of quenching oil can be stably exhibited. That is, in quenching oil, the lower the kinematic viscosity at the time of quenching, the larger the rate of increase in bubble growth energy with respect to the viscous resistance, so that bubbles tend to be generated, and the amount of vapor film generated increases. For this reason, if the oil temperature is too low and the kinematic viscosity of the quenching oil becomes higher than 8 cSt, it becomes difficult to stably form a uniform vapor film at the vapor film stage. On the other hand, when the oil temperature during quenching is too high and the kinematic viscosity of the quenching oil becomes lower than 3 cSt, the above-mentioned steam entrainment to the upper side is 100 ° C.
Kinematic viscosity in: x occurs even when quenching oil having a range of 9 to 35 cSt is used, and the vapor film stage in the upper portion of the treated material becomes long and the vapor film becomes nonuniform. Therefore, the oil temperature during quenching was limited so that the kinematic viscosity of the quenching oil was 3 to 8 cSt.

Further, the reason why the oil surface pressure is limited as described above is to allow a uniform vapor film to appear stably at the vapor film stage, and also to consider consumption of the quenching oil due to evaporation. Generally, the lower the oil surface pressure, the higher the vapor pressure of the quenching oil, so the rate of increase in the vapor pressure of bubbles relative to (oil surface pressure + hydraulic pressure) increases, and bubbles tend to occur, and vapor film formation occurs. The amount tends to increase. For this reason, when the oil surface pressure becomes higher than the range represented by the above formula a, it becomes difficult for a uniform vapor film to appear stably in the vapor film stage. On the other hand, when the oil surface pressure is lower than 60 Torr, the above-mentioned steam wraps around to the upper side, the steam film becomes non-uniform, and the evaporation amount of oil increases, which is not suitable for practical use.

Here, the vapor pressure of bubbles is in balance with (oil surface pressure + hydraulic pressure). That is, the lower the oil surface pressure and the lower the oil pressure, the lower the vapor pressure of bubbles, and the more likely bubbles are to occur. The vapor pressure of bubbles, that is, the generation state of bubbles, is controlled by the hydraulic pressure as the oil surface pressure decreases. Therefore, the lower the oil surface pressure, the larger the difference between the amount of bubbles generated in the shallow portion and the amount of bubbles generated in the deep portion with respect to the amount of bubbles generated. For this reason, in the first and second inventions, for example, when a plurality of treatment materials are vertically aligned in the depth direction and immersed in oil, the treatment material immersed in a shallow portion and the treatment material immersed in a deep portion In order to make the generation conditions of vapor film uniform with the material and to eliminate the variation between each material, the oil surface pressure is 200 Torr.
The above is preferable, and more preferably 300 To
It is to be rr or more.

Further, in the second aspect of the present invention, in the first quenching step, the oil temperature is restricted to 160 ° C. or higher and the M _s point or lower, because the oil temperature is within this range.
As will be described later, this is because the martensitic transformation start time in the treated material is made uniform to make the martensitic transformation progress evenly, thereby reducing transformation strain (martempering effect). Then, the M of the carburized or carbonitrided steel material
_{The s} point exceeds 160 ° C., and if the oil temperature in the first quenching stage is lower than 160 ° C., the martempering effect becomes small, so the oil temperature was set to 160 ° C. or higher.

Further, in the second aspect of the present invention, the quenching agent used in the second quenching treatment is not particularly limited, and oil, alkali cleaning liquid, water or the like is preferably used. In addition,
When the quenching agent is an oil, it is preferable to use an oil having a kinematic viscosity x of 100 ° C. which is similar to that of the quenching oil used in the first quenching treatment, and the temperature of this oil is 120 ° C. or lower (normal temperature). Up to) is preferred. If the temperature of the oil as the quenching agent is higher than 120 ° C., the effect of the second-stage quenching treatment cannot be expected to be large. When the quenching agent is an alkaline cleaning liquid, the temperature of the quenching agent needs to be not higher than the boiling point of the alkaline cleaning liquid, and is preferably about 40 to 80 ° C. The temperature of the alkaline cleaning solution as a quenching agent is 40
If the temperature is lower than ° C, the cleaning effect will be reduced.

In the carburizing or carbonitriding quenching methods of the first and second aspects of the present invention, when quenching an axisymmetric component, the central axis of the axisymmetric component should be perpendicular to the quenching oil surface. It is preferable to perform the quenching treatment in the state of being held at.
The reason for this will be described below. In conventional quenching under atmospheric pressure, there is almost no vapor film stage, and the treated material is cooled in a so-called nucleate boiling state while generating bubbles immediately after quenching. In the case of cooling in such a nucleate boiling state, since the state of nucleate boiling (state of generation of bubbles) is greatly different between the upper portion and the lower portion of the treatment material, a large difference occurs in cooling characteristics. Therefore, in the case of the conventional quenching treatment under atmospheric pressure, the vertical strain of the treated material becomes larger than the overall strain, which is a problem.
On the other hand, in the case of quenching treatment under reduced pressure as in the first and second inventions, since the vapor film stage in which the periphery of the treated material is covered with the vapor film is extended, the variation in the cooling rate in the vertical direction is increased. Is reduced. Therefore, in the case of quenching treatment under reduced pressure, the total strain of the treated material becomes larger than the strain in the vertical direction of the treated material, which becomes a problem. Here, when quenching an axisymmetric part under reduced pressure, if the part is held so that its central axis and the quenching oil surface are parallel to each other, the central axis is distorted so as to bend, and the overall distortion around the central axis is increased. Grows larger. On the other hand, if the central axis of the axially symmetric part is held perpendicular to the quenching oil surface, the vapor film will easily flow uniformly around the central axis as compared with the case of holding it in parallel, Since the vapor film is likely to appear more uniformly and stably, the total strain around the central axis can be reduced. Such an effect is an effect that appears when the cooling rate in the vertical direction is made uniform by quenching under reduced pressure. Therefore, in the first and second inventions, when processing an axially symmetric part, it is preferable to perform the hardening process while holding the part such that the central axis of the part is perpendicular to the quenching oil surface.

[0017]

In the carburizing or carbonitriding quenching methods of the first and second aspects of the present invention, the oil quenching treatment under reduced pressure increases the vapor pressure of the quenching oil, increasing the amount of vapor film generated. The periphery of the treated material is covered with the vapor film, and the cooling rate becomes slow, so that the vapor film stage becomes long. Therefore, generation of thermal stress due to rapid cooling immediately after quenching can be suppressed, and quenching strain due to thermal stress can be suppressed. Further, if the oil surface pressure is lowered, the boiling point of the quenching oil is lowered, so that the boiling stage in which the cooling rate is very fast is carried over to the low temperature side,
It can be cured more completely. Therefore, it is possible to suppress the occurrence of quenching strain and improve quench hardening by oil quenching under reduced pressure.

In the method of the first aspect of the present invention, quenching treatment is performed under the above conditions, that is, quenching oil having a kinematic viscosity x at 100 ° C. in a predetermined range is used, and a predetermined oil temperature and oil surface pressure are used. By performing the quenching treatment, a uniform vapor film can be stably appeared at the vapor film stage. While the treatment material is covered with a uniform vapor film, the cooling rate in each part of the treatment material is equalized, so that the location of the treatment material, for example, above,
The difference between the cooling rate and the cooling temperature in the middle and the bottom becomes small.
Therefore, according to the method of the first aspect of the present invention, it is possible to extremely effectively prevent quenching strain due to thermal stress of the treated material.

In the method of the first aspect of the present invention, the oil temperature is limited so that the kinematic viscosity of the quenching oil is in the range of 3 to 8 cSt. The area moves. Here, for example, kinematic viscosity at 100 ° C .:
When a quenching oil having a high x is used, the allowable range of the oil temperature shifts to the high temperature side, so the oil temperature may become higher than the M _S point of the treated material. In this case, the martensite transformation does not occur during oil immersion, but after the martensite transformation is started from the quenching oil, the martensite transformation is started to completed by cooling. When the oil temperature is lower than the M _s point of the treated material and higher than the M _f point (the temperature at which the martensitic transformation is completed), the treated material starts the martensitic transformation during oil immersion, After being pulled up from the quenching oil, the martensitic transformation is completed by allowing it to cool. Further, when the oil temperature is lower than the _Mf point, the martensitic transformation of the treated material is started and completed during the oil immersion.

In the method of the second aspect of the invention, the martensitic transformation start time in the treated material is made uniform by performing the transformation under the conditions of the first aspect of the invention and by setting the oil temperature at 160 ° C. or higher and at the M _S point or lower. Can be made uniform (hereinafter,
The Martemper effect). Therefore, in the second aspect of the present invention, it is possible to reduce the quenching strain caused by the transformation stress in addition to the quenching strain caused by the thermal stress. In particular, in the case of the carburized and carbonitrided and quenched treated material, the surface portion having the high carbon layer expands greatly due to the martensitic transformation, so that transformation strain is largely generated. Transformation distortion can be effectively suppressed.

Further, in the method of the second aspect of the present invention, the martensitic transformation of the treated material is started in the first quenching step under the above conditions and completed in the second quenching step, or It is almost completed, and after it is pulled out from the quenching oil, it is completed by allowing it to cool. Then, by performing the second quenching treatment, it is possible to suppress the temperature variation of the treated material after the completion of the first quenching treatment, and it is possible to further suppress the transformation strain.

Further, in the first and second inventions, when quenching an axially symmetric component, quenching is performed with the axially symmetric component held such that its central axis and the quenching oil surface are perpendicular to each other. Compared with the case of holding them in parallel, the treatment makes it easier for the vapor film to flow uniformly around the central axis and makes it easier for the vapor film to appear more uniformly and stably, thus reducing the overall strain around the central axis. .

[0023]

EXAMPLES Examples of the present invention will be described below. (Example 1) As quenching oil, kinematic viscosity at 100 ° C:
x is 8 cSt (test oil), 12 cSt (manufactured by Nippon Grease, trade name: Martempa V2500), 18 cSt (manufactured by Japan Grease, trade name: Martempa V2900), 25
cSt (manufactured by Nippon Grease, trade name: Martempa No.
2), 32 cSt (manufactured by Nippon Grease, trade name: Martempa V3200), and 36 cSt (test oil) were prepared.

Then, using each quenching oil, the oil temperature during quenching is 100 ° C, 130 ° C, 160 ° C, 180 ° C, 200
℃, 220 ℃, 240 ℃ is changed in seven stages, the oil surface pressure for each oil temperature 50 Torr, 100 Tor
r, 200 Torr, 300 Torr, 500 Tor
The carburizing and quenching treatment shown below was carried out by changing to 6 stages of r and 760 Torr.

Gear parts (drive pinion, SCM420) were prepared as treatment materials. Twelve treatment materials are placed on one tray vertically and preheated at about 500 ° C. in a preheating chamber. Then, from endothermic atmosphere gas consisting of CO: 20-23% and H ₂ : 31-40% and propane gas The carburizing atmosphere gas was supplied to the carburizing treatment chamber. In the carburizing chamber, the treated material was first heated to about 950 ° C. in the temperature rising zone, and then carburized and diffused in the carburizing zone and the diffusion zone. The treatment time in the carburizing zone is 160 minutes and the treatment time in the diffusion zone is 80 minutes. The carbon potential value during carburization is 1.0%, and the carbon potential value during diffusion is 0.85%.

After the carburized treatment material was fed into a reduced pressure greenhouse under atmospheric pressure, the reduced pressure greenhouse was decompressed to a predetermined pressure and cooled to about 850 ° C. Then, the treatment material was charged into the reduced pressure oil quenching chamber that was depressurized to a predetermined pressure. The treatment material charged in the reduced pressure oil quenching chamber is immersed in an oil tank containing a predetermined oil at a predetermined oil temperature and oil-quenched. Four minutes after the immersion, the treated material was pulled up from the oil tank, the pressure-reduced oil quenching chamber was restored to the atmospheric pressure with N ₂ gas, and then extracted outside the furnace to complete the carburizing and quenching treatment.

(Evaluation by Cooling Curve) In the above carburizing and quenching treatment, at the time of quenching treatment in which the treated material is immersed in an oil tank,
The maximum cooling rate V ₀ and the temperature T ₀ when the maximum cooling rate V ₀ was measured were measured for the upper, middle and lower portions of the treated material. The upper temperature T ₀ shown central, difference between the maximum cooling rate V ₀ which lower, and the maximum cooling rate V ₀
Was calculated.

Based on these results, the quenching oil at 100 ° C.
Kinematic viscosity: x, the oil surface pressure, and the oil temperature, the difference in maximum cooling rate V ₀ between the quenching oils was 30 ° C./sec.
Below, and the difference in temperature T ₀ showing the maximum cooling rate V ₀ is 5
The ranges of the oil surface pressure and the oil temperature when the temperature becomes 0 ° C. or less are shown in FIGS. 1 and 2. The range indicated by the diagonal lines in FIGS. 1 and 2 is the range of the oil surface pressure and the oil temperature that satisfy the above conditions, and these ranges must be satisfied at the same time.

As is clear from these results, 10
Kinematic viscosity at 0 ° C .: x is 9 to 35 cSt, the quenching oil has a kinematic viscosity of 3 to 8 cSt at an oil temperature, the lower limit is 60 Torr, and the upper limit is the oil surface in the range represented by the formula a. By quenching with pressure, the upper, middle, and
It can be seen that the difference in the maximum cooling rate V ₀ in the lower portion can be set to 30 ° C./sec or less and the difference in the temperature T ₀ indicating the maximum cooling rate V ₀ can be set to 50 ° C. or less. In addition, we have developed a device that can observe the quenching state of the treated material in quenching oil under reduced pressure, and by quenching under the above conditions, a uniform vapor film can be formed at the vapor film stage during quenching. It was confirmed that it appeared stably.

Then, the maximum cooling rate V ₀ is 30 ° C. /
sec or less, and the temperature T ₀ indicating the maximum cooling rate V ₀
When the difference was less than 50 ° C., it was possible to extremely effectively suppress the variation in accuracy of the gear parts. On the other hand, when the difference in the maximum cooling rate V ₀ exceeds 30 ° C./sec or the difference in the temperature T ₀ indicating the maximum cooling rate V ₀ exceeds 50 ° C., the variation in the accuracy of the gear parts can be suppressed. There wasn't.

Here, a steel round bar test piece (φ20 × length 4
0mm, SCr420) is prepared, and as shown in Table 1,
Using various quenching oils, and varying the oil temperature and the oil surface pressure, the carburizing and quenching treatment was performed in the same manner as in Example 1 above, and the difference in the maximum cooling rate at that time and the temperature showing the maximum cooling rate. The differences are shown in Table 1. In addition, the test No. 1-8
3 to 10 in order of the results of cooling curves showing the relationship between the cooling rate and the temperature, and the relationship between the cooling time and the temperature.
Shown in. In addition, in FIGS. 3 to 10, solid lines, dotted lines, and alternate long and short dash lines indicate cooling curves at the upper portion, middle portion, and lower portion of the treated material, respectively.

[0032]

[Table 1] No. In the test piece of No. 1, since the kinematic viscosity x of the quenching oil used at 100 ° C. was 36 cSt, which was too high, the difference in the maximum cooling rate V ₀ was large. No. The second test piece, since beyond the scope of the oil surface pressure is shown in too high above formula a, the temperature difference T ₀ indicating the difference and the V ₀ which maximum cooling rate V ₀ are both large. No. In the test piece of No. 4, since the oil surface pressure was too low, the difference in the maximum cooling rate V ₀ was large. N
o. The 5 specimens, the oil surface pressure is too high beyond the range indicated by the formula a, and since the oil temperature is too low, the temperature difference T ₀ indicating the difference and the V ₀ which maximum cooling rate V ₀ Both were great. No. In the test piece of No. 6, since the oil temperature was too low, the difference in the maximum cooling rate V ₀ was large. No. 8
The specimens, kinematic viscosity at 100 ° C. for quenching oil used: x because 8cSt and too low, larger temperature difference T ₀ indicating the maximum cooling rate V _0.

On the other hand, the movement of the quenching oil used at 100 ° C.
Viscosity: x, oil temperature and oil surface pressure are all within the scope of the present invention
No. 3 and No. The maximum cooling speed was 7 test pieces.
Degree V ₀Difference and this V₀Temperature difference T₀Is small
It was good. Also, under the processing conditions of the present invention,
If it is over 200 Torr, it will be
The difference in the maximum cooling rate between the two processing materials arranged below
V ₀And the maximum cooling rate V₀Temperature difference T₀Gargling
The gap has become smaller. This is Martempa as a quenching oil.
-No. 2 (Kinematic viscosity at 100 ° C: x is 25 cSt)
Oil surface pressure and vapor pressure when the oil temperature is 180 ° C
Ratio P₅₀/ P₁₀₀As shown in Fig. 11, the oil surface pressure
Becomes lower, the vapor pressure ratio P becomes higher.₅₀/ P₁₀₀Is smaller
Therefore, the generation status of bubbles tends to change depending on the depth from the oil surface.
This is because Note that P₅₀Is 50 cm deep from the oil surface
Equilibrium vapor pressure of bubbles in₁₀₀Is 100 from the oil level
The equilibrium vapor pressure of the foam at a depth of cm is shown. Therefore, this
Vapor pressure ratio P of₅₀/ P₁₀₀The smaller the
The difference in the amount of foam generated increases depending on the depth (the shallower the
A large amount will be generated). As a result, under the above conditions, and
By setting the oil surface pressure to 200 Torr or more, better
More preferably, by setting the oil surface pressure to 300 Torr or more.
The treated material immersed in the shallow part and the deeper part.
Between the treated material and the treated material
I was able to confirm that

The kinematic viscosity at 100 ° C. is 8 cSt.
When using quenching oil that is, or the kinematic viscosity of quenching oil is 3c
When the oil temperature becomes higher as it becomes lower than St, the steam generated from the lower and side surfaces of the treated material at the vapor film stage wraps around the upper end surface regardless of the oil surface pressure, and shifts to nucleate boiling at the upper portion of the treated material. Is delayed and the temperature difference showing the maximum cooling rate is 50 ~
It reached 165 ° C. On the other hand, the kinematic viscosity at 100 ° C is 3
When quenching oil of 6 cSt is used, or when the oil temperature is so low that the kinematic viscosity of quenching oil is higher than 8 cSt, steam is not sufficiently generated and the steam film is uneven, regardless of the oil surface pressure. The cooling of the upper part of the treated material was accelerated, and the difference in maximum cooling rate was 30 to 60 ° C./sec.

When the oil surface pressure was set higher than the range represented by the above expression a, steam was scarcely generated, the difference in maximum cooling rate was 40 ° C./sec or more, and the effect of reduced pressure quenching was not effective. On the other hand, when the oil surface pressure is lower than 60 Torr, the vapor film stage becomes too long, and the temperature (characteristic temperature) at which the vapor film stage transitions to the boiling stage becomes too low. The difference became larger than 50 ° C. It is considered that this is because the steam generated from the lower portion and the side surface of the treated material went around to the upper end surface, the heat exchange with the oil was delayed only in the upper portion of the treated material, and the transition to nucleate boiling was shifted to the low temperature side.

Further, in the carburizing and quenching method according to the present embodiment, since the treated material subjected to the carburizing diffusion treatment is held under reduced pressure for a predetermined time and cooled to about 850 ° C., the treated material is reduced due to a decrease in O ₂ partial pressure. O on the surface is dissociated and soot is removed, so that the surface of the treated material can have a bright skin,
Contributes to the improvement of quenching quality. (Example 2) As a processing material, a gear component (drive pinion, SCM420) similar to that of Example 1 was prepared.
Using a quenching oil with a kinematic viscosity of 25 cSt at 00 ° C., an oil temperature of 220 ° C., an oil surface pressure of 300 Torr,
The same carburizing and quenching treatment as in Example 1 was performed.

Within 1 minute after completion of the above carburizing and quenching treatment, N
_{2 Under} recompression, the steel was immersed in a quenching oil at 100 ° C. (kinematic viscosity at 100 ° C. was 25 cSt) for 4 minutes to carry out a second quenching treatment. In the treated material subjected to the carburizing and quenching treatment according to the second embodiment, the oil temperature was 220 ° C. in the first quenching treatment and the temperature was close to the M _s point of the treated material, so that the martensite transformation in the treated material proceeded uniformly. In addition, since the second quenching treatment can suppress the temperature variation at the end of the first quenching, the transformation strain can be suppressed extremely effectively.

(Example 3) As a treating material, the above-mentioned Example 1 was used.
Gear parts similar to (Drive pinion, SCM420)
Prepared by using a quenching oil having a kinematic viscosity of 25 cSt at 100 ° C., an oil temperature of 220 ° C., and an oil surface pressure of 300 To.
As rr, the same carburizing and quenching treatment as in Example 1 was performed.

Within 2 minutes after completion of the above carburizing and quenching treatment, an alkaline cleaning liquid (methacryl CL-5 at 80 ° C. under atmospheric pressure).
700, made by Soda Nicka) for 5 minutes to perform second quenching treatment. The treated material carburized and quenched in Example 3 was also able to extremely effectively suppress the transformation strain, as in Example 2 above. Further, in this embodiment, since the quenching agent used in the second quenching treatment was the alkaline cleaning liquid,
It was possible to wash the quenching oil during the first quenching treatment while performing the second quenching treatment.

(Evaluation of Gear Accuracy of Gear Parts) Example 1
The gear parts (drive pinion, SCM420) according to No. 1 of the test No. Gear parts No. No. 1 to 8, gear part Nos. No. 9, gear part No. subjected to the quenching treatment in Example 3 above. No. 10 and the conventional gear part No. subjected to atmospheric pressure quenching treatment. About 0, the gear precision was evaluated. As shown in FIG. 12, the twist angle (tooth line) error A and the pressure angle (tooth profile) error B were measured for each of 12 test parts on the acceleration surface of the tooth surface, and the average thereof was measured. value:
m and standard deviation: σ was determined. The measurement result of the change amount of the torsion angle error A is shown in FIG.
FIG. 14 shows the measurement results of the amount of change of each. Gear part No. The conventional quenching treatment at atmospheric pressure of 0 is a quenching oil: Martemper No. 2 (same viscosity at 100 ° C: x is 25 cSt), oil temperature: 130 ° C, oil surface pressure: 760To
It was performed under the condition of rr.

As a result, the sample No. whose quenching condition is within the range of the present invention is obtained. It was confirmed that in Nos. 3, 7, 9, and 10, variations in gear precision could be suppressed extremely effectively. (Example 4) As a treatment material, a gear component (module 3.0, helical gear, material SCM42) which is an axisymmetric component.
0) are prepared, and the kinematic viscosity at 100 ° C is 25 cS.
Using quenching oil of t, oil temperature is 220 ° C, oil surface pressure is 3
The same carburizing and quenching treatment as in Example 1 was performed at 00 Torr.

Then, in the quenching process, the gear precision was compared between the case where a large number of gear parts were vertically stacked and the case where they were placed horizontally. Moreover, the kinematic viscosity at 100 ° C. is 25 cSt.
Using quenching oil, set the oil temperature to 130 ° C and the oil surface pressure to 76
The gear accuracy was similarly compared for the case of 0 Torr and quenching under atmospheric pressure. The results are shown in Table 2. Note that the table is described in the range of variation in accuracy (width of 6σ).

[0043]

[Table 2] As is clear from Table 2, in the conventional quenching treatment under atmospheric pressure, the horizontal setting method of holding the axially symmetric component so that its central axis and the quenching oil surface are parallel to each other is better. The variation in gear precision variation is smaller than that in the vertical stacking method in which the central axis of the axially symmetric component is held vertically to the quenching oil surface. This is dominated by the large variation in the cooling rate in the vertical direction when quenching under atmospheric pressure. In the case of vertical stacking, each tooth of each component is deformed in the vertical direction with variations, and a large vertical variation is generated in each tooth.

On the other hand, in the quenching treatment under reduced pressure, the vertically stacking setting method in which the central axis of the axially symmetric component is held perpendicular to the quenching oil surface is the center of the axially symmetric component. The variation in the amount of change in gear precision is smaller than in the horizontal setting method in which the shaft and the quenching oil surface are held in parallel.
This is because, in the case of vacuum quenching, since the cooling rate in the vertical direction is uniform, the variation in strain in the vertical direction becomes small, and the overall strain around the central axis becomes dominant. That is, in the case of reduced pressure quenching, the cooling rate in the vertical direction is uniform, so the variation in the vertical strain is small, and even if stacked vertically, each tooth of each component has a large vertical strain. Does not occur. Further, in the case of vertical stacking in which the central axis and the quenching oil surface are vertical, the vapor film is more uniform around the central axis than in the case of horizontal placement in which the central axis and the quenching oil surface are parallel, and Since it is likely to be stably expressed, variations in the total strain around the central axis are reduced.

In the above-mentioned embodiment, an example in which the carburized material is oil-quenched under reduced pressure has been shown, but the same result can be obtained when carbonitriding instead of carburizing. It was

[0046]

As described above in detail, the first and second inventions of the present invention
The method of the invention has the following effects in addition to the effect of quenching treatment under reduced pressure, which can improve the quench-hardenability of a treated material while reducing thermal stress strain. That is, according to the methods of the first invention and the second invention,
By setting the kinematic viscosity of the quenching oil to be used, the oil temperature during quenching, and the oil surface pressure as predetermined conditions, a uniform vapor film can be stably appeared at the vapor film stage, and thermal stress strain is more effective. Can be prevented.

Further, in the method of the second aspect of the present invention, while satisfying the quenching conditions of the first aspect of the invention, the oil temperature during quenching is further increased to 160
A tempering effect of 2 ° C. or more can be obtained, and the second quenching treatment can suppress the temperature variation of the treated material after the completion of the first quenching treatment. It becomes possible to suppress very effectively.

Further, in the method of the first and second aspects of the present invention, when the axially symmetric part is subjected to quenching treatment, the axially symmetric part is held with its central axis and the quenching oil surface being perpendicular to each other. By quenching, compared to the case of holding in parallel,
The overall strain around the central axis can be reduced.

[Brief description of drawings]

FIG. 1 shows the relationship between the kinematic viscosity of quenching oil at 100 ° C. and the oil surface pressure. The difference in the maximum cooling rate between the quenching oils at each part of the treated material is 30 ° C./sec or less, and the maximum cooling is achieved. The range of the oil surface pressure when the temperature difference indicating the speed is 50 ° C. or less is shown.

FIG. 2 shows the relationship between the kinematic viscosity of quenching oil at 100 ° C. and the oil temperature, and for each quenching oil, the difference in maximum cooling rate at each part of the treated material is 30 ° C./sec or less, and the maximum cooling rate is Indicates the range of oil temperature when the temperature difference is 50 ° C. or less.

FIG. 3 Test No. It is a diagram which shows the evaluation result of the cooling curve of No. 1.

FIG. 4 Test No. It is a diagram which shows the evaluation result of the cooling curve of 2.

FIG. 5: Test No. It is a diagram which shows the evaluation result of the cooling curve of FIG.

FIG. 6 Test No. It is a diagram which shows the evaluation result of the cooling curve of FIG.

FIG. 7: Test No. It is a diagram which shows the evaluation result of the cooling curve of FIG.

FIG. 8: Test No. It is a diagram which shows the evaluation result of the cooling curve of No. 6.

FIG. 9: Test No. It is a diagram which shows the evaluation result of the cooling curve of FIG.

FIG. 10: Test No. It is a diagram which shows the evaluation result of the cooling curve of No. 8.

FIG. 11 is a diagram showing a relationship between an oil surface pressure and a vapor pressure ratio P ₅₀ / P ₁₀₀ .

FIG. 12 is a diagram illustrating an A twist angle error and a B pressure angle error in a gear part.

FIG. 13 is a diagram showing a change amount of an A twist angle error in a gear part.

FIG. 14 is a diagram showing a change amount of a B pressure angle error for a gear part.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Haruki Yamada 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor Makoto Sumitomo 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation ( 72) Inventor Kazuo Kanazawa 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Yasuyuki Fujiwara 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Kazuto Fukuhara Osaka 18-21 Chayacho, Kita-ku, Toyosaki Building Nihon Grease Co., Ltd. (72) Inventor Shigeru Asada 18-21 Chaya-cho, Kita-ku, Osaka Toyosaki Building Nihon Grease Co., Ltd

Claims (3)

[Claims] 1. A treated material that has been carburized or carbonitrided is 1
Kinematic viscosity at 00 ° C .: A quenching oil having x of 9 to 35 cSt is used, the oil temperature is such that the kinematic viscosity of the quenching oil is 3 to 8 cSt, the lower limit is 60 Torr, and the upper limit is the oil surface pressure represented by the formula a. A carburizing or carbonitriding quenching method characterized by performing quenching treatment in a range. Formula a: Oil surface pressure (Torr) =-12.5x + 650,
(9 ≦ x ≦ 35) 2. A treated material which has been carburized or carbonitrided is 1
Kinematic viscosity at 00 ° C .: A quenching oil having x of 9 to 35 cSt is used, at an oil temperature at which the kinematic viscosity of the quenching oil is 3 to 8 cSt, and at 160 ° C. or higher and below the martensitic transformation start point. In the temperature range, the lower limit is 60 Torr and the upper limit is the oil surface pressure range represented by the formula a. After the quenching treatment, a second quenching treatment is further performed using a quenching agent having a temperature of at least less than 160 ° C. A carburizing or carbonitriding quenching method characterized by the above. Formula a: Oil surface pressure (Torr) =-12.5x + 650,
(9 ≦ x ≦ 35) 3. The quenching treatment is performed while the treatment material is an axially symmetric component, and the axially symmetric component is held in a state where the central axis of the axially symmetric component is perpendicular to the quenching oil surface. Item 3. A carburizing or carbonitriding quenching method according to Item 1 or 2.