JPH06158267A - Continuous type gas carburizing hardening furnace - Google Patents

Abstract

PURPOSE:To shorten a temp. dropping time of a carburization treating material and a cycle time and to stabilize the quenching quality. CONSTITUTION:In a continuous type gas carburizing hardening furnace having a carburizing chamber 20 containing a carburizing zone 22 and a diffusing zone 23 and a quenching chamber 50, a temp. dropping chamber 30 and a reduced pressure holding chamber 40 are arranged in order between the carburizing chamber 20 and the quenching chamber 50. The temp. of the treating material executing the carburization in the carburizing chamber 20 is quickly dropped to the almost prescribed temp. in the temp. dropping chamber 30 in the atmospheric pressure and surely dropped to the prescribed temp. in the next reduced pressure holding chamber 40. The time needed to the temp. dropping can be shortened and the temp. of the treating material can surely be dropped to the prescribed temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous gas carburizing and quenching furnace for carburizing and quenching steel parts.

[0002]

2. Description of the Related Art Among steel parts, killed steel and low alloy steel of 0.1 to 0.25% C are heated to 900 to 1000 ° C.,
A carburizing treatment is performed by exposing to an atmosphere containing CO to diffuse and infiltrate C from the surface of the component. The steel material subjected to the carburizing treatment is directly quenched from the carburizing temperature, or is further tempered to further refine the structure and then is tempered at about 200 ° C. before use.

As a method for carburizing and quenching steel parts, C
Gas carburizing and quenching, in which a carburizing atmosphere gas containing an endothermic atmosphere gas of O, H _{2 and the} like is used to treat at near atmospheric pressure, and a mixed gas of N ₂ gas and hydrocarbon gas is used under reduced pressure. There is vacuum carburizing and quenching to process. In the case of gas carburizing and quenching, a continuous furnace can be formed with a simple structure, but on the other hand, the treated material is colored so as to have a so-called carburizing color of grayish brown or grayish black. On the other hand, in vacuum carburizing and quenching, the carburizing color does not occur and bright skin can be obtained, but in order to make it a continuous furnace, it is necessary to provide a vacuum partition door for each zone and make it a multi-chamber type, which is complicated. It has the drawback that it must be of a different furnace configuration.

By the way, the carburizing color is treated during gas carburizing.
Caused by the adhesion of Cr oxide and soot formed on the material surface
However, the treated material with carburizing color is about 850-9
10 at 00 ° C^-1-10^-2Heat under reduced pressure of Torr
And O₂O due to decrease in partial pressure ₂Is dissociated and the surface of the treated
Becomes bright skin and keeps the treatment material in a depressurized state
Therefore, it is known that the soot can be removed.

Therefore, Japanese Patent Publication No. 62-4465 discloses a method in which a vacuum heat treatment is added to the above gas carburizing and quenching method, and a continuous gas carburizing and quenching furnace used in this method. This continuous gas carburizing and quenching furnace has a carburizing chamber having a carburizing and diffusion zone, a decompression greenhouse, and a quenching chamber. The treatment material is first subjected to carburization / diffusion treatment at a temperature of about 950 ° C. under atmospheric pressure in a carburization treatment chamber supplied with a carburizing atmosphere gas. Then, the treated material subjected to the carburizing treatment is cooled to a temperature of about 850 ° C. under a reduced pressure of about 10 ⁻² Torr in a reduced pressure greenhouse, and then sent to a quenching chamber under atmospheric pressure for oil quenching. After the carburizing treatment as described above, the surface of the treated material can be made to have a bright skin by heating under reduced pressure before quenching and by the dissociation action of O ₂ and the removal of soot. Therefore, by the gas carburizing and quenching method capable of forming a continuous furnace with a simple structure, it is possible to obtain a treated material having bright skin without carburizing color.

[0006]

[Problems to be Solved by the Invention]
In the quenching furnace disclosed in Japanese Unexamined Patent Publication No. 2-4465, a carburized material at a temperature of about 920 to 950 ° C. is cooled to about 850 ° C. in a decompression greenhouse, but under a reduced pressure compared to under atmospheric pressure. In such a case, it is difficult to stably lower the temperature, and variations in the temperature after the temperature decrease are likely to occur, for example, when the temperature is not sufficiently lowered to 850 ° C.

Therefore, it takes a long time to stably lower the temperature of the treated material, and the cycle time becomes long. Further, when the temperature-treated processing material is discharged from the reduced pressure greenhouse, it is necessary to temporarily restore the reduced pressure greenhouse to an atmospheric pressure with an inert gas such as N ₂ gas or a carburizing atmosphere gas. Here, the N ₂ gas has the property of decarburizing the treated material as the temperature rises, and the carburizing atmosphere gas also has a C.I. P. There is a characteristic that the value decreases as the temperature increases. Therefore, if there are variations in the temperature when the pressure is restored using these gases, the carburizing property of the treated material is affected, and the quenching quality after quenching varies.

The present invention has been made in view of the above circumstances, and it is possible to shorten the cycle time by shortening the temperature lowering time of the carburized material, and further to stabilize the quenching quality. An object is to provide a carburizing and quenching furnace.

[0009]

A continuous gas carburizing and quenching furnace according to the first aspect of the present invention which solves the above problems is a continuous gas carburizing and quenching having a carburizing chamber having a carburizing zone and a diffusion zone, and a quenching chamber. In the furnace, a descending greenhouse and a decompression holding chamber are provided in this order between the carburizing chamber and the quenching chamber.

Further, a continuous gas carburizing and quenching furnace of the second invention for solving the above-mentioned problems is characterized in that, in the carburizing and quenching furnace of the first invention, the quenching chamber is a reduced pressure oil quenching chamber. Is.

[0011]

In the continuous gas carburizing and quenching furnace of the first aspect of the present invention, the treatment material is sequentially sent to the carburizing treatment chamber, the descending greenhouse, the depressurization holding chamber and the quenching chamber by the transfer rollers and the like, and the treatment in each chamber is continuously performed. And synchronously. Hereinafter, the processing in each room will be described in order. The treated material is first heated and held at about 950 ° C. in a carburizing treatment chamber under atmospheric pressure in a predetermined carburizing atmosphere to carry out carburizing treatment. The treated material that has been carburized in the carburizing chamber is sent to a greenhouse where the temperature is reduced to about 850 ° C. The processing material whose temperature has been lowered to about 850 ° C. is sent to the reduced pressure holding chamber. The pressure in the decompression holding chamber when the processing material is fed is set to about atmospheric pressure, and the decompression holding chamber is depressurized to a predetermined pressure after the processing material is fed. Then, the treatment material is held under reduced pressure in the reduced pressure holding chamber at a temperature of about 850 ° C. for a predetermined time. After that, the processing material is discharged from the depressurization holding chamber and sent to the quenching chamber in a state where the depressurization holding chamber is restored to the atmospheric pressure by an inert gas such as N ₂ or a carburizing atmosphere gas. In the quenching chamber, oil quenching and gas quenching are performed under predetermined quenching conditions.

As described above, in the carburizing and quenching furnace of the first invention,
The temperature-decreasing treatment of the carburized treatment material is carried out synchronously across two independent chambers, the greenhouse and the vacuum holding chamber, and in the greenhouse, the temperature is lowered at atmospheric pressure. In other words, in the first greenhouse, the temperature of the treatment material is reduced to almost a predetermined temperature extremely quickly under atmospheric pressure. Then, the treatment material that has been cooled to the substantially predetermined temperature is reliably cooled to the predetermined temperature in the decompression holding chamber. For this reason, the temperature of the material to be treated can be lowered more quickly and more stably than the temperature lowering treatment in only one chamber or the temperature lowering treatment under reduced pressure.

Further, after the processing in the depressurization holding chamber is completed, when the depressurization holding chamber is restored to the atmospheric pressure with N ₂ gas or carburizing gas, the temperature of the treated material is surely lowered to a predetermined temperature. It is possible to suppress deterioration or variation in carburizing property of the treated material due to the influence of the atmospheric temperature on the gas. Further, the vacuum holding chamber for a predetermined time at a predetermined temperature of about 850 ° C., by being vacuum held, O ₂ is dissociated by reduction of O ₂ partial pressure, and because the adhesion of soot are removed, treated material surface Can be bright skin.

In the continuous gas carburizing and quenching furnace of the second aspect of the present invention, the quenching chamber is a reduced pressure oil quenching chamber. Therefore, in addition to the action of the carburizing and quenching furnace of the first aspect of the invention, the following action is also provided. Have That is, by performing oil quenching treatment under reduced pressure, it is possible to completely cure the treated material while suppressing distortion and cracking. This can be explained as follows. First, a quenching and cooling process of quenching oil in a general oil quenching process will be described. This process is divided into three stages, a vapor film stage, a boiling stage, and a convection stage. The vapor film stage is an early stage of quenching, in which the heat transfer from the treated material to the oil is hindered by the vapor film of the oil wrapping the surface of the treated material, and the cooling rate is slow. The next boiling stage is a stage after the temperature of the surface of the treated material gradually decreases and the vapor film surrounding the surface of the treated material is broken, and the cooling rate becomes very fast due to the vigorous stirring effect of boiling. . The final convection stage is a stage in which the temperature of the treated material is lowered to the boiling point of the oil, the boiling is stopped, and the subsequent cooling is performed mainly by convection and transfer, and the cooling rate is very slow. The temperature at which the vapor film stage shifts to the boiling stage is called the characteristic temperature, and the temperature at which the boiling stage falls is called the convection start temperature.

The quenching and cooling process as described above changes as follows when the oil surface pressure falls below the atmospheric pressure. When the oil surface pressure decreases, the vapor pressure of the quenching oil increases, and the boiling point of the quenching oil decreases. When the vapor pressure of the quenching oil rises, the oil easily evaporates, so that the amount of vapor film generated increases and the generation time (vapor film stage) becomes longer. Therefore, the characteristic temperature decreases as the oil surface pressure decreases.
On the other hand, when the boiling point of the quenching oil is lowered, the boiling stage is carried over to the low temperature side, so that the convection start temperature is lowered as the oil surface pressure is reduced.

Looking at the relationship between quenching hardness and strain, the degree of quenching hardness and strain are correlated in oil quenching performed under atmospheric pressure. This quenching strain is greatly affected by thermal stress, and quenching strain decreases as quenching is avoided. Oil quenching under reduced pressure lowers the characteristic temperature as described above and prolongs the vapor film stage with a slow cooling rate. Therefore, in the reduced pressure oil quenching, the generation of thermal stress can be suppressed, and the generation of strain due to thermal stress can be suppressed. On the other hand, the quenching hardness becomes harder as the treated material is rapidly cooled. For this reason, when oil quenching is performed under reduced pressure, the boiling stage having a very high cooling rate is carried over to the low temperature side as described above, and thus it is possible to more completely cure the oil. Therefore, by quenching the oil under reduced pressure, it is possible to suppress the occurrence of quenching strain and to enhance quench hardening. As the oil surface pressure is lowered, the quenching strain can be reduced while maintaining the complete quenching hardness.

[0017]

EXAMPLES The continuous gas carburizing and quenching furnace of the present invention will be specifically described below with reference to examples. (Embodiment 1) As shown in the schematic cross-sectional view of FIG. 1, the continuous gas carburizing and quenching furnace of this embodiment includes a preheating chamber 10, a carburizing treatment chamber 20, a descending greenhouse 30, and a decompression holding chamber 40. , Quenching room 50
And are arranged in this order.

The preheating chamber 10 includes a front door 10a and a rear door 1
0b, the endothermic atmosphere gas is supplied from the carburizing chamber 20. The carburizing chamber 20 has a front door 20a.
It has a rear door 20b and is divided into a temperature raising zone 21, a carburizing zone 22, and a diffusion zone 23 in order from the front. And each zone 2 of this carburizing chamber 20
1, 22, 23 have CO: 20-23%, H ₂ : 31
Carburizing atmospheric gas consisting of endothermic atmospheric gases and C _m H _n gas (such as propane gas) are supplied consisting of 40%.

A greenhouse 30 provided behind the carburizing chamber 20 via a rear door 20b of the carburizing chamber 20 has a rear door 30a, and like the carburizing chamber 20, CO: 2.
An endothermic atmosphere gas (or N ₂ gas) of 0 to 23% and H ₂ : 31 to 40% and a carburizing atmosphere gas of C _m H _n gas (for example, propane gas) are supplied.

The decompression holding chamber 40, which is connected to the rear of the greenhouse 30 via the first compartment 60, has a front door 40a and a rear door 40b, and is supplied with N ₂ gas. ing. The depressurization holding chamber 40 includes the first vacuum exhaust device 4
Connected to 1. The quenching chamber 50, which is connected to the rear side of the decompression holding chamber 40 via the second compartment 70, has a front door 50a and a rear door 50b, and is supplied with N ₂ gas similarly to the decompression holding chamber 40. It has become so. The quenching chamber 50 includes a lower oil tank 51 and an upper oil removing chamber 52, and includes an elevator mechanism (not shown).

The preheating chamber 10, the carburizing treatment chamber 20, the descending greenhouse 30, the first compartment 60, the decompression holding chamber 40, and the second compartment 70.
A conveyance roller 80 is provided in the quenching chamber 50, and heating means (not shown) is provided in each chamber except the reduced pressure quenching chamber 50. Hereinafter, processing of the continuous gas carburizing and quenching furnace having the above configuration will be described. Note that FIG. 2 shows the temperature and pressure in this process.

First, the processing material such as SCM420 is used in the preheating chamber 1.
No. 0 front door 10a, and the treatment material is heated to 600 to 8 by a heating means (not shown) in an endothermic atmosphere gas.
It is heated to about 00 ° C. As a result, impurities attached to the processing material are removed. Next, the rear door 10 of the preheating chamber 10
The treatment material is sent from the preheating chamber 10 to the temperature raising zone 21 of the carburizing treatment chamber 20 through the front side b and the front door 20a of the carburizing treatment chamber 20. The carburizing atmosphere gas containing the endothermic atmosphere gas is supplied to the temperature raising zone 21, the carburizing zone 22 and the diffusion zone 22 of the carburizing chamber 20. Then, the treatment material is heated to a carburizing temperature of about 950 ° C. in the temperature raising zone 21 by a heating means (not shown).

Thereafter, the treated materials are sequentially carburized zone 22,
Carburization and diffusion treatment are performed in the diffusion zone 23. The processing time in the carburizing zone 22 is 70 to 90 minutes, and the processing time in the diffusion zone 23 is 55 to 70 minutes. The carbon potential value during carburization / diffusion is Cp 0.8 to 1.0. The carburized material is sent to the greenhouse 30 via the rear door 20b of the carburizing chamber 20. A carburizing atmosphere gas containing an endothermic atmosphere gas is supplied to the falling greenhouse 30 as in the carburizing treatment chamber 20. The treated material subjected to the carburizing treatment is held in the greenhouse 30 for 10 to 15 minutes and cooled to about 850 ° C.

The treatment material whose temperature has been lowered to about 850 ° C. in the greenhouse 30 is the rear door 30b, the first compartment 60 and the front door 40a.
It is sent to the reduced pressure holding chamber 40 via. The depressurization holding chamber 40 when the processing material is charged is restored to the atmospheric pressure with N ₂ gas. The depressurization holding chamber 40 charged with the processing material is about 1.3 × 10 ^{4 to} 6.7 × 1 in the first vacuum exhaust device 41.
It is evacuated to 0 ⁴ Pa and the treated material is at a temperature of 850 ° C.
It is held under reduced pressure for 5 minutes.

After the processing in the depressurization holding chamber 40 is completed, the depressurization holding chamber 40 is restored to the atmospheric pressure with N ₂ gas, and the processing material is passed through the rear door 40b, the second compartment 70 and the front door 50a. And sent to the quenching chamber 50. This quenching chamber 50 is N
₂ Gas is supplied to bring it to about atmospheric pressure. Quenching room 5
The treatment material charged in 0 is immersed in the oil tank 51 by an elevator mechanism (not shown) and oil-quenched. 3-5 after soaking
After a lapse of minutes, the treated material is pulled up to the oil removing chamber 52 by an elevator mechanism (not shown). After the oil is removed, the treated material is extracted from the rear door 50b to the outside of the furnace, and the carburizing and quenching process is completed.

As described above, in the carburizing and quenching furnace of this embodiment, the greenhouse 30 and the depressurization holding chamber 40 are arranged in this order between the carburizing chamber 20 and the quenching chamber 50, and the carburizing treatment is carried out. The temperature lowering process of the material is carried out synchronously over the two chambers of the greenhouse 30 and the depressurization holding chamber 40, and the greenhouse 30 is cooled under atmospheric pressure. Therefore, as compared with the temperature lowering process in only one chamber or the temperature lowering process under reduced pressure, the temperature of the processing material can be quickly and surely lowered to a predetermined temperature. Therefore, the cycle time can be shortened by shortening the time required for the temperature lowering process.

Further, in the present embodiment, after the processing in the depressurization holding chamber 40 is completed, the depressurization holding chamber 40 is restored to the atmospheric pressure with N ₂ gas. At this time, the temperature of the processing material is surely lowered to a predetermined temperature. Has been done. Therefore, in this embodiment, the N ₂ gas does not decarburize the treated material under the influence of the high temperature atmosphere, and it is possible to suppress the deterioration or variation of the carburizing property and contribute to the improvement of the quenching quality.

Further, in the reduced pressure holding chamber 40, 850
When the pressure is kept at a temperature of ℃ for a predetermined time,₂
O due to decrease in partial pressure₂Dissociates and removes soot
As a result, the surface of the treated material can be treated as a bright skin.
This also contributes to the improvement of quenching quality. Note that the above
In the embodiment, after the processing in the depressurization holding chamber 40 is completed,
40 for N ₂Gas was restored to atmospheric pressure, but N₂gas
A carburizing atmosphere gas may be used instead of. So
Then, even in this case, the influence of the ambient temperature
The carburizing atmosphere gas causes the carburizing property of the treated material to vary.
And contributes to the improvement of quenching quality.

Further, although the quenching chamber 50 is an oil quenching chamber in the above embodiment, it may be a gas quenching chamber instead. (Embodiment 2) The continuous gas carburizing and quenching furnace of Embodiment 2 shown in the schematic sectional view of FIG. 3 is the same as the carburizing and quenching furnace of Embodiment 1 except that the quenching chamber 50 and the second compartment 70 are Vacuum exhaust device 5
3 and the quenching chamber 50 is a reduced pressure oil quenching chamber. The other structure is the same as that of the first embodiment.

In this carburizing and quenching furnace, as shown in FIG. 4, the preheating chamber 10, the carburizing chamber 20, the lowering greenhouse 30 and the reduced pressure holding chamber 40 are treated in the same manner as in the first embodiment. During the treatment in the depressurization holding chamber 40, the quenching chamber 50
And the second compartment 70 is 0.6 × 1 in the second vacuum exhaust device 53.
It is evacuated to 0 ^{4 to} 6.7 × 10 ⁴ Pa. After the processing in the decompression holding chamber 40 is completed, the processing material is the rear door 4
0b, the second compartment 70, and the front door 50a are fed into the quenching chamber 50. The processing material charged in the quenching chamber 50 is immersed in the oil tank 51 by an elevator mechanism (not shown) and oil-quenched. After 3 to 5 minutes have passed since the immersion, the treatment material is pulled up to the oil removing chamber 52 by an elevator mechanism (not shown),
Be drained. Then, after the oil quenching chamber 50 is restored to the atmospheric pressure with N ₂ gas, the treated material is extracted from the rear door 50b to the outside of the furnace, and the carburizing and quenching process ends.

As described above, in the carburizing and quenching furnace of the second embodiment,
By performing the oil quenching treatment under reduced pressure, it is possible to completely cure the treatment material while suppressing distortion and cracking of the treatment material as described above. Therefore, it is possible to significantly improve the quenching quality. Also in the second embodiment, the greenhouse 30
Since the temperature is reduced in the two chambers, the decompression holding chamber 40, the cycle time can be shortened as in the first embodiment. Then, in the carburizing and quenching furnace of Example 2, the quenching chamber 50 and the second compartment 70 are decompressed in advance during the depressurization holding process in the depressurization holding chamber 40, and after the processing in the depressurization holding chamber 40 is completed, It is possible to immediately send the treated material into the quenching chamber 50 and immerse it in the oil tank 51. Therefore, the decompression holding chamber 4
After completion of the treatment at 0, there is no need to restore the reduced pressure holding chamber 40 to the atmospheric pressure, and the time required for this can be saved, and the cycle time is further shortened as compared with the carburizing and quenching furnace of the first embodiment. It is possible to

Further, it is possible to suppress the temperature drop of the processing material after the processing in the reduced pressure holding chamber 40 is completed, which also contributes to the improvement of the quenching quality. Furthermore, the reduced pressure holding chamber 4
Since the quenching chamber 50 can be depressurized slowly during the treatment at 0, the vacuum exhaust device 53 can be downsized. Further, since the rear door 40b of the decompression holding chamber 40 and the front door 50a of the quenching chamber 50 are provided between the decompression holding chamber 40 and the quenching chamber 50, decompression or recompression of each chamber is performed independently. Therefore, it is possible to change the conditions easily because there are few restrictions on equipment operation.

[0033]

As described above in detail, in the continuous gas carburizing and quenching furnace of the first aspect of the present invention, the temperature of the treated material carburized in the two chambers, the greenhouse and the depressurization holding chamber, is rapidly and stably lowered. Therefore, the cycle time can be shortened by shortening the time required for the temperature lowering process.

Further, since the atmospheric temperature of the decompression holding chamber can be stabilized, the quenching quality can be improved without the atmosphere gas being affected by the temperature and the carburizing property of the treated material being lowered. It is possible. Further, the continuous gas carburizing and quenching furnace of the second aspect of the present invention, which is a reduced pressure quenching chamber, exhibits the effects of the reduced pressure oil quenching process in addition to the above effects. That is, according to the carburizing and quenching furnace of the second aspect of the present invention, it is possible to completely quench-harden the treated material while suppressing quenching distortion and cracking, and it is possible to significantly improve the quenching quality. .

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a continuous gas carburizing and quenching furnace according to a first embodiment.

FIG. 2 is a diagram showing temperature and pressure during processing of the continuous gas carburizing and quenching furnace according to the first embodiment.

FIG. 3 is a schematic sectional view showing a continuous gas carburizing and quenching furnace according to a second embodiment.

FIG. 4 is a diagram showing a temperature and a pressure during processing of the continuous gas carburizing and quenching furnace according to the second embodiment.

[Explanation of symbols]

20 ... Carburizing chamber 21 ... Temperature rising zone 22 ...
Carburizing zone 23 ... Diffusion zone 30 ... Greenhouse 40 ...
Decompression holding room 50 ... Quenching room

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasuyuki Fujiwara 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Saburo Ogawa 2-4-7 Kyomachibori, Nishi-ku, Osaka City Chugai Furnace Industrial Co., Ltd. In-house (72) Inventor Yuji Funamoto 2-4-7 Kyomachibori, Nishi-ku, Osaka City Chugai Furnace Industry Co., Ltd.

Claims (2)

[Claims] 1. A continuous gas carburizing and quenching furnace having a carburizing chamber having a carburizing zone and a diffusion zone, and a quenching chamber, wherein a greenhouse and a vacuum holding chamber are provided between the carburizing chamber and the quenching chamber. A continuous gas carburizing and quenching furnace characterized by having and in order. 2. The continuous gas carburizing and quenching furnace according to claim 1, wherein the quenching chamber is a reduced pressure oil quenching chamber.