JPH06172960A - Vacuum carburization method - Google Patents

Abstract

PURPOSE:To prevent the generation of soot by cracking of gaseous hydrocarbon in a carburization furnace, by specifying the mixing ratio of the gaseous hydrocarbon and air in an atmosphere for carburization at the time of subjecting the surface of a metallic member to a carburization treatment in the vacuum carburization furnace. CONSTITUTION:The metallic material W to be subjected to the carburization treatment is put into a vacuum heating furnace 11 of a vacuum carburization device. After this heating furnace 11 is internally evacuated to a reduced pressure by a vacuum pump 62, the metallic material W is heated up and gaseous propane and air are supplied into the heating furnace 11 by opening a solenoid valve 33 of a gaseous propane cylinder 30B and a solenoid valve 32 of an air cylinder 30A. The gaseous atmosphere mixture in the heating furnace 11 is sampled from a suction pipe 52 and is subjected to the measurement of the oxygen partial pressure in the gaseous atmosphere by an oxygen partial pressure gage 40. The air and the propane are supplied by the solenoid valves 34, 35 from cylinders 31A, 31B for control so that the ratio of the propane and air in the gaseous atmosphere attains 1:3 to 1:5. The C generated by cracking of the propane in the gaseous atmosphere for carburization is oxidized to CO with the O2 in the air and, therefore, the generation of the soot in the heating furnace 11 is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum carburizing method,
In particular, it relates to a vacuum carburizing method for preventing the generation and adhesion of soot in a vacuum carburizing furnace in vacuum carburizing.

[0002]

2. Description of the Related Art Conventionally, as a vacuum carburizing method and a vacuum carburizing furnace for preventing the generation and adhesion of soot in a vacuum carburizing furnace in vacuum carburizing, for example, JP-A-52-47531,
Japanese Patent Publication No. 54-31976, Japanese Patent Publication No. 62-4464
Various conventional examples have been introduced such as Japanese Patent Publication.

The conventional example introduced in the above-mentioned JP-A-52-47531 is carburizing in a diffusion process in which a carburizing gas is introduced into a vacuum carburizing furnace to carburize a carburized material and then carbon is diffused. By diluting a hydrocarbon-based gas, which is a gas, with nitrogen gas, carburizing is performed while obtaining effects such as controlling excessive decomposition of the carburizing gas in a vacuum carburizing furnace.

Further, the vacuum carburizing method introduced in the above Japanese Patent Publication No. 54-31976 discloses that when a carburized material is charged into a vacuum carburizing furnace for vacuum carburization, the carburizing period of the carburized material is A carburizing gas in which a hydrocarbon gas and a nitrogen gas are mixed at a constant ratio is introduced into a vacuum carburizing furnace to permeate and diffuse carbon under a constant reduced pressure. In the conventional example disclosed in Japanese Patent Publication No. 62-4464, a carburizing material is housed in a heating chamber of a vacuum carburizing furnace and a carburizing gas is introduced into the heating chamber when the carburizing process is performed under reduced pressure. While supplying, while supplying nitrogen gas to the space formed by the inner wall of the vacuum carburizing furnace and the outer wall of the heating chamber, the introduction of the carburizing gas and the supply amount of nitrogen gas, the time of the carburizing period Accordingly, the amount of soot generated in the vacuum carburizing furnace is reduced by gradually reducing the amount.

Further, the carburizing method and carburizing furnace (method and apparatus for controlling the carbon level of the mixed gas reacting in the furnace chamber) introduced in Japanese Patent Publication No. 63-25066 have a carburizing furnace equipped with a carburized material. When entering and carburizing, carbon is permeated and diffused into the carburized material while continuously measuring and controlling the carbon level in the mixed gas existing in the carburizing furnace.

In this method, the reaction product of the mixed gas produced after introducing the fuel containing hydrocarbon (carburizing gas) into the carburizing furnace is not in the water-gas equilibrium state and is in the methane-gas equilibrium state. None, and in the case where the mixed gas contains an excess of methane, the ratio of the carbon monoxide (CO) component contained in the mixed gas existing in the carburizing furnace is measured (first measurement amount). Then, the voltage of the oxygen (O ₂ ) ion-conducting solid electrolyte provided with an electrode that does not catalyze the decomposition of methane is measured (second measurement amount), and the temperature in the carburizing furnace is measured (third measurement amount). Then, the controlled variable of the carbon level is obtained from the first measured amount, the second measured amount, and the third measured amount,
To send the three measured quantities to a computer for determining the carbon level and change the flow rate of fuel or air introduced into the carburizing furnace based on these, until the measured carbon level matches its target value. In addition, the carbon level is automatically controlled by supplying only fuel and air into the carburizing furnace.

[0007]

However, the above-mentioned Japanese Patent Laid-Open No. 52-47531 and Japanese Patent Publication No. 54-31976.
In the conventional example introduced in Japanese Patent Publication No. 62-4464, the consideration is given to removing the soot generated by the thermal decomposition reaction of the hydrocarbon gas used as the carburizing gas by a chemical principle. There wasn't.

Therefore, in the above-mentioned conventional example, the hydrocarbon-based gas as the carburizing gas causes the following thermal decomposition reaction in the process of raising the temperature of the carburizing gas in the vacuum carburizing furnace. C ₃ H ₈ → CH ₄ + 2H ₂ + 2C _S C ₄ H ₁₀ → CH ₄ + 3H ₂ + 3C _S However, _S in C _S represents Solid.

There has been a problem that a large amount of soot is generated by C _S (solid carbon represented by soot) generated as a result of this reaction. Soot generated in the space inside the vacuum carburizing furnace and on the furnace wall is solid graphite that is not absorbed on the surface of the carburized material, unlike activated carbon, and has no activity in the carburizing reaction. .

The soot adhesion has been a cause of damaging the structure of the vacuum carburizing furnace. Further, the soot also adheres to trays and baskets used in the carburizing process, peels off and falls in the quenching oil tank and in the transport route of the work place, and significantly contaminates the surroundings, which significantly deteriorates the work environment and workability. There was a problem. Further, when the carburizing gas directly contacts the carburized material before the temperature is raised in the vacuum carburizing furnace, a graphite film is generated on the contact surface portion, which causes the carburizing reaction and causes carburizing unevenness. There was a problem that became.

The soot generated during the carburizing reaction is
It is known that propane (C ₃ H ₈ ) which is generally used as a hydrocarbon-based gas is generated particularly remarkably, and it is more difficult to suppress the generation of soot during the carburization reaction. I was trying. And also, in particular,
The carburizing method and carburizing furnace (method and apparatus for controlling the carbon level of a mixed gas that reacts in the furnace chamber) introduced in the above Japanese Patent Publication No. 63-25066 are installed in the carburizing furnace for the purpose of controlling the carbon level. The flow rate of the fuel (carburizing gas) or air to be introduced is controlled, but this requires three measured quantities, so a complicated circuit is required as a control device, and control is difficult. However, there was a problem that the equipment cost and labor were required.

An object of the present invention is to solve such a problem, and to provide a vacuum carburizing method capable of reducing the generation and adhesion of soot in a vacuum carburizing furnace by a simple method as much as possible. The purpose is to do.

[0013]

In order to achieve this object, the present invention provides a vacuum carburizing method for carburizing a carburized material by introducing a carburizing gas into a heating atmosphere under reduced pressure. The present invention provides a vacuum carburizing method characterized by introducing a carburizing gas in which a hydrocarbon-based gas and air are mixed at a ratio within a certain range during a carburizing period of a carburized material.

[0014]

The vacuum carburizing method according to the present invention performs carburizing by introducing a carburizing gas in which a hydrocarbon-based gas and air are mixed at a ratio within a certain range during the carburizing period of the carburized material. a method of carburizing generated as soot (deposit) and optionally carbon (C _S), is reacted with oxygen in the air, it can be modified as carbon monoxide (CO) gas.

That is, for example, as the hydrocarbon gas, propane (C ₃ H ₈ ) or butane (C ₄ H ₁₀ ) is used.
When _{using, C 3 H 8 + 3O 2} → CH 4 + 2H 2 + 6CO C 4 H 10 + 9 / 2O 2 → CH 4 + 3H as ₂ + 9CO, instead of the carbon (C _S) is generated (precipitation) Carbon monoxide (CO) gas is generated. Therefore, it is possible to significantly reduce the generation of soot (C _S) as a solid.

In this reaction, propane (C ₃ H ₈ ) and butane (C ₄ H ₁₀ ) which are widely used as a carburizing gas in the conventional carburizing process are used. The same effect can be obtained not only when the above is used, but also when another hydrocarbon gas is used. The amount of surface carbon that gives the optimum hardness to the carburized material can be determined by a combination of the carburizing temperature and the ratio of air to hydrocarbon gas. Here, as the carburizing temperature, the most optimum temperature (for example, about 930 to 980 ° C.)
In order to give the carburized material an appropriate surface hardness when carburizing the carburized material, the surface carbon content of the carburized material is set to about 0.7% by weight or more. Is said to be desirable. However, when the diffusion step is performed after the carburizing step, the concentration of carbon on the surface of the carburized material that diffuses inside decreases, so in practice,
In the carburizing step, the surface carbon content of the carburized material is set to about 0.8.
It is necessary to set it to the weight% or more. Then, it is desirable to determine the air ratio to the hydrocarbon-based gas so that the optimum surface carburizing amount can be satisfied.

That is, for example, when propane is used as the hydrocarbon gas, the mixing ratio of air to the hydrocarbon gas is in the range of hydrocarbon gas (propane): air = 1: 3 to 1: 5. It is particularly preferable to set the inside. When the air ratio to the hydrocarbon-based gas (propane) exceeds 5, an optimum temperature (for example, about 930 to 980 ° C.) is selected as the carburizing temperature and the carburized material is carburized. It is not possible to obtain a surface carbon amount (for example, about 0.8% by weight or more) that can provide the optimum surface hardness, and it is not possible to perform good carburization.

On the other hand, air is used to react soot (C _S ), which is ineffective in the carburization reaction, with oxygen in the air to form CO, and suppress the generation of the soot. At this time, for example, when propane is used as the hydrocarbon-based gas and the air ratio to the hydrocarbon-based gas is less than 3, the amount of oxygen that reacts with the soot is insufficient with respect to the amount of the soot generated. , The generation of soot cannot be sufficiently suppressed. Therefore, it is desirable to set the air ratio to the hydrocarbon gas (propane) to 3 or more.

Therefore, when propane is used as the hydrocarbon gas, the mixing ratio of the hydrocarbon gas and air is in the range of hydrocarbon gas (propane): air = 1: 3 to 1: 5. Is particularly preferable. The mixing ratio of the hydrocarbon-based gas and air in the carburizing period of the carburized material is measured by measuring the components of the mixed gas (carburizing gas) existing in the vacuum carburizing furnace, and based on this, the vacuum It is preferable to control the flow rate of the hydrocarbon-based gas and the flow rate of the air supplied to the carburizing furnace so that the carburizing period of the carburized material will always be an optimum value.

The mixing ratio of the hydrocarbon gas and air is the above mixing ratio when propane is used as the hydrocarbon gas, but when other hydrocarbon gas such as butane is used. The mixing ratio may be set so as to always have an optimum value depending on the components of the hydrocarbon gas used.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment according to the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a vacuum carburizing furnace used in a vacuum carburizing method according to an embodiment of the present invention, and FIG.
FIG. 3 is a cross-sectional view taken along the line AA of the vacuum carburizing furnace shown in FIG. 1, and FIG. 3 is a diagram showing a raw material gas supply system of the vacuum carburizing furnace shown in FIG. 1 and an analysis system for monitoring the furnace atmosphere.

The vacuum carburizing furnace 1 shown in FIGS. 1 to 3 comprises a vacuum heating furnace 11 having a heating chamber 2 and a vestibule 4 having a quenching tank 3 containing quenching oil, an intermediate door 5
It has a structure in which it is connected through. The vacuum heating furnace 1
1, a hydrocarbon gas (this embodiment) is provided by a filling cylinder 30 for filling the heating chamber 2 with an atmospheric gas (carburizing gas) and an adjusting cylinder 31 for adjusting the components of the atmospheric gas in the heating chamber 2. Then, an atmospheric gas supply pipe 9 for supplying propane) and air is installed.

The vacuum heating furnace 11 has a heating chamber 2
The oxygen partial pressure gauge 40 for measuring the partial pressure of oxygen contained in the atmosphere gas existing inside is a sample gas suction pipe 52.
Connected through. In this example, a solid electrolyte type oxygen partial pressure meter was used as the oxygen partial pressure meter 40. Then, in the vacuum heating furnace 11, a carbon monoxide partial pressure gauge 41 for measuring the partial pressure of carbon monoxide contained in the atmospheric gas existing in the heating chamber 2, and the carbon monoxide partial pressure gauge 41 contained in the atmospheric gas are contained. A carbon dioxide partial pressure gauge 42 for measuring the partial pressure of the existing carbon dioxide is connected via a sample gas suction pipe 53. The sample gas suction pipe 53 has a flow rate adjusting valve 64 for adjusting the flow rate of the sample gas.
Is installed. The sampling amount of the atmospheric gas is adjusted by opening / closing the flow rate adjusting valve 64. In this example, an infrared analyzer was used as the carbon monoxide partial pressure meter 41 and the carbon dioxide partial pressure meter 42.

Further, in the vacuum heating furnace 11, a sample for returning the atmospheric gas after the partial pressures are measured by the carbon monoxide partial pressure gauge 41 and the carbon dioxide partial pressure gauge 42 into the heating chamber 2 again. The gas supply pipe 54 is connected via the sample gas suction pump 43. A flow rate adjusting valve 65 for adjusting the flow rate of the sample gas is installed in the sample gas suction pipe 54. The return amount (supply amount) of the atmospheric gas is adjusted by opening / closing the flow rate adjusting valve 65.

Further, the vacuum heating furnace 11 is provided with an exhaust hole 51 for exhausting the gas in the heating chamber 2 to the outside, and an exhaust vacuum pump for adjusting the pressure in the heating chamber 2 is provided therein. 62 is connected via a flow rate adjusting valve 61 for adjusting the flow rate of exhaust gas. The exhaust amount of the exhaust gas is adjusted by opening / closing the flow rate adjusting valve 61.

Further, the vacuum heating furnace 11 is connected with an exhaust pipe 55 for exhausting the gas in the heating chamber 2 to the outside. A flow rate adjusting valve 65 that adjusts the flow rate of the exhaust gas is installed in the exhaust pipe 55, and the exhaust amount of the gas is adjusted by opening and closing the flow rate adjusting valve 65. The heating chamber 2 is provided in the furnace shell via a space portion, and inside thereof, a heater 6 for heating the inside of the heating chamber 2 to an optimum temperature, and a circulation for circulating an atmospheric gas in the heating chamber 2. Vertically movable hearth 8 on which fan 7 and carburized material W are placed
Is provided. A vertically movable hearth elevator 15B that controls the vertical movement of the vertically movable hearth 8 is provided below the vertically movable hearth 8.

The filling cylinder 30 connected to the atmosphere gas supply pipe 9 is an air cylinder 30A containing air and a propane cylinder 3 containing propane.
It is composed of 0B. This filling cylinder 30 is
It is installed to supply the atmosphere gas necessary for carburizing the carburized material W into the heating chamber 2. The air cylinder 30A is connected to the atmospheric gas supply pipe 9 via an electromagnetic valve 32 that adjusts the flow rate of air. The propane cylinder 30B is connected to the atmospheric gas supply pipe 9 via an electromagnetic valve 33 that adjusts the flow rate of propane.

The adjusting cylinder 31 connected to the atmosphere gas supply pipe 9 is an air cylinder 31A containing air and a propane cylinder 3 containing propane.
It is composed of 1B. This adjustment cylinder 31
As will be described later, in the carburizing period of the carburized material W, the heating chamber 2
It is installed to adjust the mixing ratio of propane and air inside. The air cylinder 31A is connected to the atmospheric gas supply pipe 9 via an electromagnetic valve 34 that adjusts the flow rate of air. Also, the propane cylinder 31
B is connected to the atmospheric gas supply pipe 9 through an electromagnetic valve 35 that adjusts the flow rate of propane.

In the oxygen partial pressure gauge 40, based on the partial pressure of oxygen (ratio of oxygen to atmospheric gas) obtained by the oxygen partial pressure gauge 40, the oxygen from the adjusting cylinder 31 to the heating chamber 2 is adjusted.
A flow rate control device 44 is connected to determine the supply amount of propane or air to the inside and automatically control the open / closed states of the electromagnetic valves 34 and 35 based on the supplied amount.

Similarly, the carbon monoxide partial pressure gauge 41 and the carbon dioxide 42 are also connected to the flow rate control device 44, both of which are based on their partial pressures as in the case of the oxygen partial pressure gauge 40. The amount of propane or air supplied can be controlled. And which one to use
It may be selected appropriately. A carburized material transfer device 13 that transfers the carburized material W to a target position when the carburized material W is moved between the vestibile 4 and the heating chamber 2 is installed in the vestibile 4. There is. A cooling fan 14 for cooling the carburized material W after carburization contained in the vestibule 4 is installed in the vestibule 4. Further, in the vestibule 4, there is installed a quenching elevator 15A for taking the carburized material W in and out of the quenching tank 3 when quenching the carburized material W. The vestibule 4 is provided with a charging / extracting door 16 for charging and extracting the carburized material W.

Next, a specific example of the vacuum carburizing method according to this example will be described with reference to the drawings. Figure 4
It is a figure which shows the vacuum carburizing process which concerns on a present Example. A description will be given along the flow of this vacuum carburizing process. In this example, the heating chamber 2 having a volume of 4000 liters was used. (Temperature raising / soaking process) First, the vertically movable hearth 8 in the heating chamber 2
The carburized material W is placed at a predetermined position of. In this embodiment,
As the carburized material W, SCR420H (shape: Φ50 ×
10; disk shape) was used.

Next, the exhaust vacuum pump 62 is operated to
The pressure in the heating chamber 2 is changed from atmospheric pressure (760 Torr) to 5T.
The pressure is reduced until it becomes less than orr. The carburized material W is
The temperature is raised to about 0 to 980 ° C., and is maintained for a predetermined time so that the surface of the carburized material W, the core portion, and each part have uniform temperatures. At this time, the circulation fan 7 is operated to enhance heat conduction to the carburized material W. The exhaust vacuum pump 62
Stops when the inside of the heating chamber 2 reaches a predetermined pressure.

When the carburization is carried out at the atmospheric pressure, after the inside of the heating chamber 2 reaches 760 Torr, the exhaust vacuum pump 6
2 is stopped, the flow rate adjusting valve 65 is opened, and the heating chamber 2
The atmospheric gas inside may be released naturally. (Carburizing Step) Next, the electromagnetic valves 32 and 33 are opened, and air and propane are supplied from the filling cylinder 30 into the heating chamber 2 until the pressure in the heating chamber 2 becomes 730 Torr.

Next, the pressure in the heating chamber 2 is 730To.
When rr is reached, the electromagnetic valves 32 and 33 are closed,
Start carburization. The higher the carburizing temperature is, the shorter the carburizing time can be. However, if the carburizing temperature is too high, the crystal nuclei of the carburized material W become coarse, and the optimum strength cannot be obtained. If the carburizing temperature is too low, the carburizing time will be too long and the productivity will be reduced. Therefore, in this example, the carburizing temperature was set in the range of 930 to 980 ° C.

During the carburizing period of the carburized material W, the atmospheric gas in the heating chamber 2 is sampled from the sample gas suction pipe 52, and the oxygen partial pressure gauge 40 is used to measure the partial pressure of oxygen contained in the atmospheric gas ( Know the mixing ratio of air to propane). Based on the data obtained by this operation, the electromagnetic valves 34 and 35 are adjusted so that the mixing ratio of air to propane is always propane: air = 1: 3 to 1: 5.

That is, when the air ratio exceeds 5, the electromagnetic valve 34 is closed and the electromagnetic valve 35 is opened to increase the supply amount of propane. When the air ratio becomes less than 3, Open the electromagnetic valve 34, close the electromagnetic valve 35,
Adjust the air supply. Further, similarly to the above, during the carburizing period of the carburized material W, the adjusting valves 64 and 65 are opened to sample the atmospheric gas in the heating chamber 2 from the sample gas suction pipe 53, and the carbon monoxide partial pressure gauge 41 and the carbon dioxide are measured. The carbon partial pressure meter 42 measures the amount of carbon monoxide and the amount of carbon dioxide contained in the atmospheric gas. Then, the opening / closing state of the electromagnetic valve 34 is controlled based on the data obtained by this work, and adjustment is performed so that an optimum amount of propane gas is always present in the heating chamber 2. Atmosphere gas for which the investigation with the carbon monoxide partial pressure gauge 41 and the carbon dioxide partial pressure gauge 42 has been completed is
It is returned to the heating chamber 2 again via the sample gas supply pipe 54. Here, the circulation of the atmospheric gas is performed by operating the sample gas suction pump 43.

In this way, by adjusting the mixing ratio of propane and air in the heating chamber 2 to an optimum value for carburizing, the inside of the heating chamber 2 is carburized during the carburizing period of the carburized material W. Then, a reaction such as C ₃ H ₈ + 3O ₂ → CH ₄ + 2H ₂ + 6CO occurs. Therefore, it is possible to prevent soot (C _S ) from being generated and attached in the vacuum heating furnace 11. In this way, the carburized material W is carburized for a predetermined time.

It should be noted that the higher the pressure in the heating chamber 2 during carburization is, the higher the pressure is in promoting carburization.
It was adjusted to be in the range of 760 Torr. (Diffusion Step) Next, the electromagnetic valves 34 and 35 are closed to stop the supply of propane and air into the heating chamber 2. Then, the exhaust vacuum pump 62 is operated to reduce the pressure in the heating chamber 2 to 5 Torr or less. By this step, the carbon carburized on the surface of the carburized material W can be diffused toward the core portion. (Quenching Step) Next, the pressure inside the heating chamber 2 and the inside of the vestibule 4 is set to a non-oxidizing and isostatic state. After that, the intermediate door 5 is opened, and the carburized material conveying device 13 moves the carburized material W, which has undergone the carburizing and diffusing steps, from the heating chamber 2 to the vestibule 4. Next, the intermediate door 5 is closed, the quenching elevator 15A is lowered, the carburized material W is immersed in the quenching tank 3, and the carburized material W is quenched with the quenching oil contained in the quenching tank 3. . When the quenching is completed, the quenching elevator 15A is raised, the charging / extracting door 16 is opened, and the carburized material W is taken out.

In this way, the carburized material W was carburized while preventing the generation of soot in the vacuum carburizing furnace 1. Next, the optimum carburizing conditions for the carburized material W (conditions for providing the carburized material W with an optimum surface hardness and for sufficiently preventing the generation of soot) will be determined based on the above-described examples. Therefore, the carburized material W was carburized under the conditions shown in Table 1 in an empty furnace state.

In Table 1, the time which is unavoidable in the process is omitted, and the diffusion time is expressed by the time required for exhausting and quenching the inside of the heating chamber 2.

[0041]

[Table 1]

Next, the surface carburizing amount (% by weight) of the carburized material W carburized under the carburizing conditions shown in Table 1 and the mixing ratio of propane and air (air ratio; air supply amount / propane supply amount)
Was investigated for each carburizing temperature. The result is shown in FIG. The surface carburizing amount (% by weight) of the carburized material W was expressed by an average value of values analyzed by an emission spectroscopic analyzer.

From FIG. 5, it was confirmed that the surface carburizing amount of the carburized material W in the present invention is determined by the combination of the carburizing temperature and the air ratio. Further, in FIG. 5, the carburized product W
The air ratio is 5 or less in order to satisfy the amount of surface carbon (about 0.7% by weight, about 0.8% by weight when the diffusion step is performed) capable of giving the optimum surface hardness to It was confirmed.

On the other hand, in FIG. 5, it was confirmed that the effective air ratio for preventing the generation of soot is 3 or more. From this, it was confirmed that when propane was used as the hydrocarbon-based gas, the mixing ratio of propane and air was preferably in the range of propane: air = 1: 3 to 1: 5. .

The relationship of the mixing ratios is an optimum value when propane is used as the hydrocarbon gas, and for example, when a hydrocarbon gas having another composition such as butane is used. The mixing ratio may be appropriately determined depending on the composition of the hydrocarbon gas used. Next, for some of the conditions shown in Table 1, composition analysis of the atmospheric gas in the heating chamber 2 during the carburizing period of the carburized material W was performed. The result is shown in FIG.

From FIG. 6, it was confirmed that by determining the carburizing temperature and the air ratio, the composition of the atmospheric gas in the heating chamber 2 can be determined and the surface carbon amount of the carburized material W can be determined. Was done. The carburizing process under the conditions shown in Table 1 was carried out in an empty furnace state. However, when the carburized material W is fully loaded, if the raw material supply of the atmospheric gas is too small, the carburizing reaction progresses and the heating chamber 2 The gas inside changes. Also,
If the supply of the atmosphere gas as the raw material is too large, it becomes difficult to prevent the generation of soot in the vacuum heating furnace 11. Therefore,
The supply amounts of propane and air into the heating chamber 2 were set so that the composition of the atmospheric gas did not change in the heating chamber 2 when the material W to be processed was loaded.

Next, under the carburizing conditions shown in Table 2, the carburized material W
Was continuously carburized.

[0048]

[Table 2]

As a result, when the vacuum carburizing furnace 1 is continuously operated under the carburizing conditions shown in Table 2, compared with the conventional case where only propane (containing nitrogen gas if desired) is supplied for carburizing. It was confirmed that soot adhesion to trays and baskets was significantly reduced. In addition, the carburized material W is 5
After processing 0 pieces, the operation of the vacuum carburizing furnace 1 was stopped and the inside of the vacuum heating furnace 11 was checked, but it was confirmed that the adhesion of soot to the heat insulating material, the heating element protection tube, etc. was significantly reduced. .

In this embodiment, as the carburized material W,
Although SCR420H is used, the same effect can be obtained not only by applying SCR420H but also by applying well-known case hardening steel. Further, in the present embodiment, the carburizing temperature of the carburized material W is set to 930 to 9
Although the temperature is set to 80 ° C., the carburizing temperature is not limited to this and may be changed if desired. Then, at this time, the mixing ratio of the hydrocarbon-based gas and the air may be optimally set according to the carburizing temperature.

Further, in this embodiment, the pressure in the heating chamber 2 during the carburizing period of the carburized material W is 700 to 760 Torr.
However, the pressure in the heating chamber 2 is not limited to this, and may be determined as desired. Furthermore, in this embodiment, three types of partial pressure gauges, that is, the oxygen partial pressure gauge 40, the carbon monoxide partial pressure gauge 41, and the carbon dioxide partial pressure gauge 42 are used, but any one partial pressure gauge may be used. Alternatively, one partial pressure gauge may be connected to the flow control device 44, and at least one other partial pressure gauge may be used only for monitoring.

[0052]

As described above, the vacuum carburizing method according to the present invention introduces a carburizing gas in which a hydrocarbon gas and air are mixed at a ratio within a certain range during the carburizing period of the carburized material. to perform the carburizing and carbon (C _S) which has been generated as soot in the conventional carburizing methods, to react with oxygen in the air, to be modified as carbon monoxide (CO) gas, as a solid it is possible to significantly reduce the generation of soot (C _S). As a result, soot adhesion to the vacuum carburizing furnace can be suppressed to a minimum, and the structure of the vacuum carburizing furnace is not damaged. Also, the amount of soot attached to the trays and baskets used in the carburizing process can be greatly reduced,
The work environment and workability in carburizing can be kept good. Further, it is possible to prevent carburization unevenness of the carburized material which has been conventionally caused by the generation of soot. As a result, a carburized material having an improved quality can be obtained by a simple method even in a good working environment.

[Brief description of drawings]

FIG. 1 is a sectional view of a vacuum carburizing furnace used in a vacuum carburizing method according to an embodiment of the present invention.

2 is a cross-sectional view taken along the line AA of the vacuum carburizing furnace shown in FIG.

FIG. 3 is a diagram showing a raw material gas supply system of the vacuum carburizing furnace shown in FIG. 1 and an analysis system for monitoring the atmosphere in the furnace.

FIG. 4 is a diagram showing a vacuum carburizing process according to the present embodiment of the present invention.

FIG. 5 shows a surface carburizing amount (wt%) of a carburized material and a mixing ratio of propane and air (air ratio; air supply amount / propane supply amount) in carburization performed in an example according to the present invention. It is the figure which described the relationship of every carburizing temperature.

FIG. 6 is a diagram showing a composition analysis of atmospheric gas in a heating chamber during a carburizing period of a carburized material W in carburizing performed in an example according to the present invention.

[Explanation of symbols]

 1 Vacuum Carburizing Furnace 2 Heating Chamber 3 Quenching Tank 4 Vestible 9 Atmospheric Gas Supply Pipe 11 Vacuum Heating Furnace 30 Filling Cylinder 30A Air Cylinder 30B Propane Cylinder 31 Adjustment Cylinder 31A Air Cylinder 31B Propane Cylinder 32 Electromagnetic Valve 33 Electromagnetic Valve 34 Electromagnetic Valve 34 35 Electromagnetic Valve 40 Oxygen Partial Pressure Meter 41 Carbon Monoxide Partial Pressure Meter 42 Carbon Dioxide Partial Pressure Meter 43 Sample Gas Suction Pump 44 Flow Control Device 62 Exhaust Vacuum Pump W Carburized Material

Claims (1)

[Claims] 1. A vacuum carburizing method in which a carburizing gas is introduced into a heating atmosphere under reduced pressure to perform carburizing treatment on a carburized material, wherein a hydrocarbon gas and air are supplied during a carburizing period of the carburized material. A vacuum carburizing method comprising introducing a carburizing gas mixed at a ratio within a certain range.