JP2000001765A - Vacuum carburization method and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive vacuum carburization treatment method which solves the trouble by the excess of a surface carbon concn. including corner parts, allows the treatment under broad carburization pressures and obviates the generation of soot and an apparatus therefor. SOLUTION: Gaseous ethylene or a gaseous mixture composed of the gaseous ethylene and gaseous acetylene is used as a carburizing gas. The supply rate of this carburizing gas is periodically or impulsively changed from a high flow rate level to a low flow rate level and further to the high flow rate level. The pressure of a carburization chamber 10 at the time of the high level is regulated to a range of 1 to 10 kPa, the flow rate level ratio of the low flow rate level to the high flow rate level to 0 to 50% and the time ratio to 50 to 3,000%. Further, the regulation of the pressure in the carburization chamber is executed by regulating a valve or movable orifice mechanism 16 disposed between an evacuation device 12 and a discharge port 17 of the carburization chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for vacuum carburizing steel materials.

[0002]

2. Description of the Related Art Conventionally, gas carburizing has been used for carburizing steel materials.
Vacuum carburizing, plasma carburizing and the like are performed. Although gas carburizing is currently widely practiced, there are problems such as the danger of combustible gas, grain boundary oxidation of the surface of treated products, and short cycle due to high-temperature carburizing. Plasma carburizing is expensive and limited to special carburizing. 900-11 for vacuum carburizing
There is a method in which a saturated hydrocarbon (methane gas, propane gas, butane) is used as a carburizing gas at 00 ° C. at a pressure of 10 to 70 kPa.

Further, as a carburizing treatment method using acetylene, Japanese Patent Laid-Open Publication No. 8-325701 discloses a method in which the pressure of a vacuum carburizing chamber is set to 1 kPa or less, acetylene gas is flowed for a fixed time, and then the gas is stopped for a fixed time. It diffuses carbon inside.

[0004]

In the case of such vacuum carburizing, the carbon concentration in the furnace is higher than that of gas carburizing, so that even at the same temperature, the carbon concentration gradient with the inside becomes large, so that the carburizing time is shortened. Has the advantage that it can be However, in vacuum carburization, the surface, particularly the corner surface, has a smaller area where carbon diffuses into the inside than the plane portion, so that the carbon concentration increases and the amount of retained austenite increases, or a network-like carbide is easily generated. There was a problem. If the amount of retained austenite is too large or a network-like carbide is generated, there is a problem that the quality of the carburized product is greatly reduced. Also, when acetylene exceeds 1 kPa and ethylene exceeds 10 kPa, soot is generated, and there is a problem that the control range is narrow.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to solve the problems caused by excessive surface carbon concentration including corners in a vacuum carburizing method, and to perform soaking at a wide range of carburizing pressures and generate soot. It is an object of the present invention to provide a method and apparatus for carburizing without any cost.

[0006]

According to the present invention, in the vacuum carburizing treatment, ethylene gas or a mixed gas of ethylene gas and acetylene gas is used as a carburizing gas, and the supply amount of the carburizing gas is reduced at least once from a high flow rate level to a low flow rate. From flow level to high flow level to low flow level
The above-mentioned problem has been solved by providing a vacuum carburizing method wherein the pressure is repeatedly changed and the pressure of the carburizing chamber at the high flow rate level of the carburizing gas is set in a range of 1 to 10 kPa.

[0007] By performing vacuum carburization using ethylene gas or a mixed gas of ethylene gas and acetylene gas as the carburizing gas, ethylene and acetylene are efficiently decomposed on the steel surface to supply carbon as a carburizing source. 1 ~ 1 pressure of carburizing chamber
In the range of 0 kPa, a pulsed carburization is performed in which a prescribed amount of gas is flowed for a prescribed time during the carburizing period to permeate carbon into the surface, and during the diffusion period, the carburizing gas is stopped or reduced for a prescribed time and carbon is diffused inside. By doing so, it is possible to suppress the generation of a network-like carbide due to the high concentration of carbon particularly at the corners.

This is because while the carburizing gas supply is kept at a low level, the supply of the carbon source is suppressed and the carbon in the surface layer is diffused into the work by thermal diffusion. The active carburization is repeated again by returning the carburizing gas supply to a higher level. By changing the supply amount of the carburizing gas between the high level and the low level and repeating this, the diffusion of the carbon in the surface layer portion easily proceeds, so that the carburizing treatment without the abnormal surface layer can be performed. In addition, since the flow of the carburizing gas in the narrow hole and the like is improved, the carburizing in the narrow space becomes uniform.

In the present carburizing method, the carburizing source is not supplied excessively, so that the consumption of carburizing gas can be suppressed and the generation of soot in the carburizing chamber can be suppressed, so that the pressure in the carburizing chamber is wider than before. The pressure was set to 1 to 10 kPa. In addition,
In the present method, carburization is insufficient at 1 kPa or less, and soot generation is large at 10 kPa or more.

Although the flow rate of the carburizing gas is changed at a high flow rate, a low flow rate, a high flow rate, and a low flow rate, it is effective to repeat this depending on the carburizing condition. Therefore, in claim 2, the change in the flow rate of the carburizing gas is changed periodically.

Further, as in claim 3, the pulse shape of the change in the flow rate of the carburizing gas is easily controlled.

If the change in the flow rate of the supply gas is small, or if the time at the low flow rate is too short, the diffusion of carbon into the interior at the low flow rate is not promoted. Therefore, in claim 4, the flow rate ratio of the low flow level to the high flow level of the carburizing gas is set to 0 to 50%, and the time ratio of the low flow level to the high flow level is set to 50 to 3,000%. Good.

Depending on the shape of the corners and the required surface texture, appropriate periods and pulse conditions (flow rate and time) are required. For this purpose, it is important to control the supply amount of the carburizing gas and the pressure in the carburizing chamber. The control of the pressure in the carburizing chamber has a greater change when controlling the exhaust gas amount on the discharge side than when changing the supply amount of the carburizing gas. Therefore, in claim 5, the pressure in the carburizing chamber is adjusted by adjusting a valve or a movable orifice mechanism provided between the vacuum exhaust device and the exhaust port of the carburizing chamber. By controlling the flow rate on the exhaust side, the carburizing gas flow rate can be reduced as compared with the control on the inlet side.

In carrying out such a vacuum carburizing method,
As in claim 6, a carburizing chamber provided with a heating device, a vacuum exhaust device for evacuating the carburizing chamber, a device for supplying carburizing gas into the carburizing chamber, and a cooling chamber having a quenching oil tank are provided. In the vacuum carburizing apparatus, a control system for changing the supply amount of the carburizing gas at least once from the high flow level to the low flow level and from the high flow level to the low flow level is provided, and in order to adjust the pressure in the carburizing chamber, exhaust of the carburizing chamber is performed. It can be performed by a vacuum carburizing device provided with a valve or a movable orifice mechanism between the port and the vacuum exhaust device.

[0015]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an overall schematic diagram of a vacuum carburizing apparatus showing an embodiment of the present invention. As shown in FIG.
This vacuum carburizing furnace includes a carburizing chamber 10 equipped with a heating device, a cooling chamber 3 connected to the carburizing chamber, and a transfer device 2 for entering and leaving the product.
It is composed of

The carburizing chamber 10 is provided with a heating element (not shown) for heating the workpiece 8 at a high temperature, and a heat insulating box 9 for keeping the temperature warm. In addition, ethylene gas or a mixed gas of ethylene gas and acetylene gas is supplied from a supply port (not shown) into the carburizing chamber 10, and a gas supply panel 11 for controlling the supply amount of the carburizing gas and a heating element are controlled. A temperature control device 13 is provided.
These configurations are almost the same as the conventional vacuum carburizing device,
Further, in the conventional case, the exhaust port 17 of the carburizing chamber is connected to the vacuum exhaust device 12. However, in this apparatus, a valve 16 for adjusting the pressure in the carburizing chamber is connected between the exhaust port 17 of the carburizing chamber and the vacuum exhaust device 12. The valve 16 is connected to the vacuum exhaust device 12 and the exhaust port 1.
7 is mounted in series with a main exhaust valve (not shown), but may be mounted in parallel. Further, an exhaust valve (not shown) is attached between the vacuum exhaust device 12 and the exhaust port 18 of the cooling chamber 3. Also, the evacuation device 12
May be provided in the cooling chamber 3 and the carburizing chamber 10, respectively.

The cooling chamber 3 connected to the carburizing chamber 10 is constituted by a quenching oil tank 7, a quenching elevator 5 and an in-furnace transfer device 6, which can be opened and closed by a middle door 15 with the carburizing chamber. . Further, the cooling chamber 3 can be opened and closed by a front door 14. The doors 14 and 15 are adapted to seal the respective chambers. Further, an exhaust port 18 of the cooling chamber 3 is connected between the vacuum exhaust device 12 and the valve 16. In front of the front door 14 of the cooling chamber 3, the transfer table 2 for taking in and out the work is arranged. Reference numerals 1, 4, 4'8 indicate works in the respective devices.

Next, the carburizing method of the present invention will be described.
The following processing is sequentially performed using the apparatus of the present invention shown in FIG. (1) First, the valve 16 is almost fully opened by the vacuum exhaust device 12, and the exhaust valve of the carburizing chamber 10 and the exhaust valve of the cooling chamber 3 (not shown) are opened, that is, the carburizing chamber 10
The carburizing chamber 10 and the cooling chamber 3 are
Is evacuated to 0.05 kPa or less. (2) After reaching a predetermined pressure, the temperature is raised to the carburizing temperature while exhausting the carburizing chamber 10. (3) The front door 14 of the cooling chamber 3 is opened, the work 1 is quenched by the transfer table 2, the work 4 is loaded onto the elevator 5, and the front door 14 is closed. (4) The cooling chamber 3 is evacuated by the vacuum exhaust device 12 to 0.05 kPa.
Evacuate to the following. (5) After reaching the predetermined pressure, the middle door 15 is opened, the processed product 4 is transferred from the cooling chamber 3 into the carburizing chamber 10, and the middle door is closed. (6) The carburizing chamber 10 is vacuum-heated and the work 4 is heated to a predetermined temperature (85
(0 to 1100 ° C). (7) Thereafter, the carburizing gas is supplied from the carburizing gas supply port into the carburizing chamber 10 by the gas supply panel 11. Further, by adjusting the valve 16, the pressure in the carburizing chamber when the carburizing gas is at a high flow rate level is adjusted to be a predetermined pressure in the range of 1 to 10 kPa.

In the carburizing period, the carburizing gas is caused to flow at a predetermined flow rate (high flow level), and in the diffusion period, the carburizing gas is stopped or reduced (low flow level), and this is repeated. The flow level ratio of the low flow level to the high flow level is 0
50%. Set this to a preset time (diffusion /
(Time ratio of carburization 50-3,000%), and periodically repeated during high temperature holding. (8) After the completion of the pulse-shaped carburizing (hereinafter referred to as pulse carburizing) and the end of the high-temperature holding time, the temperature of the carburizing chamber is lowered to the quenching temperature and, if necessary, further soaked and heated.

Although the pressure in the carburizing chamber varies depending on the amount of the carburizing gas, the capacity of the vacuum evacuation device is sufficiently larger than the supply amount of the carburizing gas. 1 to 10 kP at high flow levels of carburizing gas
Since the pressure is adjusted in the range of a and the pressure may be lower at the low flow rate level, the valve may be adjusted at the low flow rate level, but may be adjusted at the high flow rate level.
When the flow rate level ratio is 0, for example, when the flow rate level is low, the flow rate level is set to 0.
It becomes 05 kPa or less.

(9) After the temperature of the carburizing chamber 10 has decreased to the quenching temperature, the inner door 15 is opened, and the work 4 is moved to the cooling chamber 3 by the internal transfer device 6 and carried out onto the elevator 5. Then, the middle door 15 is closed, the elevator 5 is lowered, and the work 4 'is immersed in the oil in the oil tank 7 to perform quenching. At this time, nitrogen gas is introduced to below the atmospheric pressure. (10) After holding in the oil for a predetermined time, lift the elevator 5 to drain the oil. (11) The cooling chamber 3 is set to the atmospheric pressure. (12) The front door 14 is opened, the work 4 is carried out to the transfer table 2 outside the furnace, the front door 14 is closed, and (13) the cooling chamber 3 is evacuated to 0.05 kPa by the vacuum exhaust device 12.
By evacuating to a vacuum below, one cycle of vacuum carburizing is completed.

[0022]

(Embodiment 1) Next, an embodiment of vacuum carburization using the present apparatus shown in FIG. 1 will be described. In Example 1, ethylene gas was used as the carburizing gas. Material is SCM415, outer diameter 20
After processing the round bar having a length of 10 mm into a carburizing chamber and heating the temperature of the carburizing chamber to 930 ° C., ethylene gas was supplied at a flow rate of 1 Lit / min for 1 minute, and the pressure of the carburizing chamber was increased to 1.3 kPa. Carburize while adjusting the exhaust valve so that the ethylene gas is stopped and diffused for 4 minutes, and then ethylene gas is supplied at a pressure of 1.3 kPa for 1 minute, and then the ethylene gas is stopped for 4 minutes. This was repeated for 1 hour (total 12 times) by pulse carburization, cooled to a quenching temperature of 850 ° C., kept at this temperature for 30 minutes, transferred to a cooling chamber, and oil-cooled.

A carbon analysis of the treated product subjected to the vacuum carburizing treatment revealed that the carbon concentration on the surface was 0.81%, and the distance from the surface where the carbon concentration was 0.3% was 0.55 mm, which was an appropriate value. Met. No network carbides were found in the corner structure, the retained austenite was normal, and no soot was generated.

(Embodiment 2) Next, Embodiment 2 of the present invention using a mixed gas of 70% ethylene gas and 30% acetylene gas as the carburizing gas will be described. In Example 2, the apparatus shown in FIG. 1 was used, and the material was SCM415 and the outer diameter was 2
The processed product of the round bar having a length of 0 mm and a length of 10 mm is transported to the carburizing chamber,
After heating the temperature of the carburizing chamber to 930 ° C., while adjusting the exhaust valve so that the pressure in the carburizing chamber becomes 2.6 kPa, a mixed gas of 70% of ethylene gas and 30% of acetylene gas is supplied at a flow rate of 1 Lit / min for 1 minute. Then, while adjusting the exhaust valve so that the pressure in the carburizing chamber becomes 0.13 kPa, the mixed gas was supplied at a flow rate of 0.1 Lit / min.
After being subjected to pulse carburization repeated for 1 hour (10 times), cooled to a quenching temperature of 850 ° C., kept at this temperature for 30 minutes, transferred to a cooling chamber and oil-cooled.

The carbon analysis of the treated product showed that the carbon concentration on the surface was 0.84% and the distance from the surface at which the carbon concentration was 0.3% was 0.58 mm, which was an appropriate value. Further, no network-like carbide was observed in the structure of the corner portion, the retained austenite was normal, and no soot was generated.

[0026]

According to the method of the present invention, pulse carburization is performed in which the supply amount of ethylene gas or a mixed gas of ethylene gas and acetylene gas is repeatedly changed at least once from a high flow level to a low flow level and further to a high flow level. Therefore, carburizing treatment without an abnormal surface layer can be performed, and carburizing in a narrow space becomes uniform. In particular, there is no problem due to excessive surface carbon concentration including the corners. Further, since the pressure of the carburizing chamber at the time of the high flow rate of the carburizing gas is set in the range of 0.1 to 10 kPa, a method for carburizing at low cost without generating soot is provided.

In addition, since pulse carburizing can suppress the consumption of carburizing gas without excessively supplying a carburizing source, it is possible to provide a new vacuum carburizing apparatus which can reduce the total running cost, and is very industrially possible. It is informative.

Further, since the change in the flow rate of the carburizing gas is changed periodically, the carburizing becomes more uniform.

Further, since the change in the flow rate of the carburizing gas is controlled in a pulse-like manner, it is easy to control and the conventional vacuum carburizing apparatus can be easily modified into the present apparatus.

Further, by setting the flow rate ratio between the high flow rate level and the low flow rate level to 0 to 50%, and setting the time ratio of the low flow rate level to the high flow rate level to 50 to 3,000%, the carburizing is more reliably performed. Can be done. Since the flow rate is controlled on the exhaust side by adjusting the pressure in the carburizing chamber by adjusting the valve or the movable orifice mechanism, the control is simple, the carburizing gas flow rate can be reduced, and the cost can be further reduced.

A conventional vacuum carburizing apparatus having a carburizing chamber equipped with a heating device, a vacuum exhaust device for exhausting the carburizing chamber, a device for supplying a carburizing gas into the carburizing chamber, and a cooling chamber having a quenching oil tank. In addition, a control system for changing the carburizing gas supply at least once from the high flow level to the low flow level and further to the high flow level, and the control between the exhaust port of the carburizing chamber and the vacuum exhaust device to adjust the pressure in the carburizing chamber. By providing a valve or a movable orifice mechanism in the apparatus, pulse carburizing can be carried out, and there is provided a vacuum carburizing apparatus which has no abnormal surface layer, does not generate soot free from problems due to excessive surface carbon concentration, and has low cost. It became something.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram of a vacuum carburizing apparatus showing an embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 3 Cooling room 7 Oil tank (for quenching) 10 Carburizing chamber 11 Supply device (gas supply panel) 12 Vacuum exhaust device 16 Adjustment valve (valve or movable orifice mechanism) 17 Exhaust port

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsu Harai 1-1-1, Fujikoshi Honcho, Toyama City, Toyama Prefecture Inside Fujikoshi Corporation (72) Inventor Tetsuya Okada 1-1-1, Fujikoshi Honcho, Toyama City, Toyama Prefecture Fujikoshi Co., Ltd. (72) Inventor Naoaki Imai 10

Claims (6)

[Claims] In a vacuum carburizing treatment, ethylene gas or a mixed gas of ethylene gas and acetylene gas is used as a carburizing gas, and a supply amount of the carburizing gas is at least once reduced from a high flow level to a low flow level, and further increased from a high flow level. It is repeatedly changed to a low flow level, and the pressure of the carburizing chamber at the high flow level of the carburizing gas is 1 to 10 kPa
Vacuum carburizing method characterized by being in the range of. 2. The vacuum carburizing method according to claim 1, wherein a change in the flow rate of the carburizing gas is changed periodically. 3. The vacuum carburizing method according to claim 1, wherein the change in the flow rate of the carburizing gas is a pulse. 4. The method according to claim 1, wherein the flow rate ratio of the low flow level to the high flow level of the carburizing gas is 0 to 50% and the time ratio of the low flow level to the high flow level is 50 to 3,000%. The vacuum carburizing method according to claim 1, 2 or 3, wherein 5. The method according to claim 1, wherein the pressure in the carburizing chamber is adjusted by adjusting a valve or a movable orifice mechanism provided between the vacuum exhaust device and an exhaust port of the carburizing chamber. The vacuum carburizing method according to any one of the above. 6. A carburizing chamber having a heating device, a vacuum exhaust device for evacuating the carburizing chamber, a device for supplying a carburizing gas into the carburizing chamber, and a cooling carburization having a quenching oil tank. In the apparatus, a control system for changing the supply amount of the carburizing gas at least once from the high flow level to the low flow level and further from the high flow level to the low flow level is provided, and in order to adjust the pressure in the carburizing chamber, an exhaust port of the carburizing chamber is provided. A vacuum carburizing device comprising a valve or a movable orifice mechanism provided between the vacuum carburizing device and the vacuum exhaust device.