JP2001214255A - Gas-hardening treatment method for metal surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas-hardening treatment method for a metal surface, which is excellent in control of carbon potential in comparison with a conventional gas carburizing method, fast in the carburizing speed and by which dispersion in carburizing can be made small. SOLUTION: The total amount per unit time of the gas generated in a heating chamber 1 of a carburizing furnace is controlled to be 0.05 to 1.5 times of the inner volume of the heating chamber. Then, at least 50% of the amount of CO contained in the whole generated gas is supplied by the decomposition gas of methanol, and the residual portion is supplied by the reaction of either gas or liquid containing C and H and either gas or liquid containing O. Thereby, carburizing is carried out at 730 to 1,100 deg.C while keeping the concentration of gaseous CO in the whole gas at 28 to 40% in the heating chamber 1 of the carburizing furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas hardening treatment method for a metal surface, for example, to a gas carburizing and gas carbonitriding method for steel parts, which has good atmosphere stability and controllability.
The present invention relates to a gas hardening method for a metal surface which is excellent in carburizing characteristics and economical.

[0002]

2. Description of the Related Art A conventional gas carburizing method, which is one of typical gas hardening methods for metal surfaces, includes a carburizing method of a shift furnace type, a carburizing method of a dropping type, and a method of using a hydrocarbon gas and an oxidizing gas in a furnace. And direct gas carburizing method. In the shift carburizing method, hydrocarbon gas and air are mixed at a certain ratio, and
The carrier gas is introduced into a shift furnace heated to 00 to 1100 ° C. and brought into contact with a nickel catalyst in the shift furnace to produce a carrier gas. Then, the carrier gas is supplied into the carburizing furnace at a flow rate of about 6 to 10 times (per hour) the internal volume of the carburizing furnace. In the carburizing furnace, besides this carrier gas,
The hydrocarbon gas is enriched to a predetermined carbon potential. Such a shift furnace type carburizing method has an advantage that since the shift furnace is used, the composition of the carrier gas is constant and the atmosphere can be stably controlled.

[0003] In the dropping type carburizing method, an organic liquid agent such as methanol is directly dropped into a carburizing furnace heated to a carburizing temperature. Then, it is decomposed as CH ₃ OH → CO + 2H ₂ to generate CO gas and hydrogen gas.
This decomposition product gas corresponds to a carrier gas in the shift furnace type, and is added to CH ₄ , C ₃ H ₈ , C ₄ H ₁₀
Or a premixed or separately added organic liquid which generates free carbon to form a carburizing atmosphere with an enrichment effect. Also in this case, the amount of the organic liquid to be dropped into the furnace needs only to generate a gas amount of 1.8 to 4 times (per hour) of the inside volume of the furnace.

[0004] Such a dropping-type carburizing method does not require a shift furnace. The atmosphere can be stably controlled because the carrier gas composition is constant. The use of methanol as an organic liquid agent has advantages such as a high carburization rate because the CO concentration in the carrier gas is as high as about 33%, and a difference in carburization depth due to the shape of the product. The direct gas carburizing method is a method in which a hydrocarbon gas and an oxidizing gas are directly introduced into a carburizing furnace and carburized. A method using any one of CH ₄ , C ₃ H ₈ , C ₄ H ₁₀ and air and a method using CH ₄ , C ₃ H ₈ , C ₄ H _{10 and} a method using CO ₂ or O ₂ .

[0005] Both of these direct gas carburizing methods do not require a shift furnace, and the amount of gas supplied into the furnace is as small as 0.05 to 1.5 times (per hour) the internal volume of the carburizing furnace. Therefore, there is an advantage that the gas used is highly efficient and economical.

[0006]

However, the above-mentioned conventional gas hardening methods for metal surfaces, such as the conversion furnace type carburizing method, the drip pouring type carburizing method, and the direct gas carburizing method, have the following advantages together with the above-mentioned advantages. Problems. The shift furnace type carburizing method is
(1) Since a metamorphic furnace other than the carburizing furnace is required, the number of items to be managed increases and the running cost also increases.
(2) Since the carrier gas needs to flow about 6 to 10 times (per hour) the internal volume of the carburizing furnace, the actual efficiency of the used gas is extremely low and uneconomical. (3) CH ₄ , C
The CO concentration in the carrier gas converted by a hydrocarbon such as ₃ H ₈ , C ₄ H ₁₀ and air is about 20 to 24.5%.
Therefore, the carburizing speed is slow, and the carburizing depth tends to differ depending on the shape of the product.

[0007] The drip-injection type carburizing method requires 1.8 to 4 times the gas volume per hour of the furnace inner volume, and although the amount of the organic liquid agent used is not as large as that of the shift furnace type carburizing method, it is used. The real efficiency of gas is low and uneconomical. Therefore,
It is considered that the drawback can be overcome by reducing the supply amount of the organic liquid agent in the drop injection type carburizing method. However, when the amount of methanol actually supplied was reduced to less than one time (per hour) the amount of gas generated in the carburizing furnace and carburized,
The CO concentration in the furnace gas component may be 28% or less. If the CO concentration is reduced in this manner, the carburizing speed and the carburizing characteristics deteriorate.

In the direct gas carburizing method, CH ₄ , C ₃ H ₈ ,
The direct gas carburizing method using any one of C ₄ H ₁₀ and air is economical because the amount of gas used is small, but the gas used in this method is the same as the gas used in the shift furnace type carburizing method. Therefore, CO in the gas generated in the carburizing furnace
Since the concentration is as low as about 20 to 24.5%, the carburizing speed is low, and the carburizing depth tends to differ depending on the shape of the product.

On the other hand, the direct gas carburizing method using any one of CH ₄ , C ₃ H ₈ , and C ₄ H ₁₀ and CO ₂ or O ₂ is economical because the amount of gas used is also small.
For example, the reaction when C ₄ H ₁₀ and CO ₂ are used is as follows. C ₄ H ₁₀ ten _{4CO 2 → 8CO (61.5%)} + 5H
₂ (38.5%) According to theoretical calculation, the component ratio of CO gas should be 61.5%. However, according to Japanese Patent Publication No. 6-051904, at the time of actual operation, intrusion of air from the door packing part The CO concentration is said to be about 40% due to air intrusion at the time of negative pressure caused by furnace operation. It is also clear that the CO concentration changes depending on the amount of enrichment of the hydrocarbon gas, the carburizing time, and the surface area of the product.

As described above, the direct gas carburizing method comprises the steps of (1) CO
The concentration does not become constant. (2) Since there is a direct carburization reaction with hydrocarbon gas other than the CO-based carburization reaction, it is difficult to control the carbon potential, and it is necessary to rely on experience.
(3) Suiting is likely to occur. (4) In the case of carburization for a long time, the CO concentration exceeds 40% and the theoretical calculated value 6
As the content becomes 1.5%, there is a problem that the depth of grain boundary oxidation of the treated product after carburizing increases.

Accordingly, the present invention has been made in view of such unresolved problems of the prior art, and it is possible to greatly reduce the amount of raw material gas used and to greatly reduce the amount of emitted CO ₂ as compared with the conventional art. It is an object of the present invention to provide a gas hardening treatment method for a metal surface which is resource-saving, energy-saving and environmentally excellent, which can be reduced. In addition, the present invention has a superior atmosphere stability compared with the conventional gas carburizing method, thereby having excellent controllability of the carbon potential, and has a higher carburizing speed and a higher carburizing rate than the conventional gas carburizing method. It is an object of the present invention to provide a gas hardening method for a metal surface using a gas that can reduce variation.

Furthermore, the present invention provides a safe and stable carburizing treatment by using a carburizing furnace capable of vacuum-purging at least the front chamber, and has an environmentally excellent gas hardening of a metal surface because there is no frame curtain. It is an object to provide a processing method.

[0013]

According to a first aspect of the present invention, there is provided a method for gas-curing a metal surface, comprising the steps of: The product is 0.05 to 1.5 times the product, and 50% or more of the CO amount in the generated total gas is supplied by the decomposition gas of methanol, and the remainder is mixed with a gas or liquid containing C and H. By supplying the gas by reaction with either a gas or a liquid containing O, the CO concentration in the total gas in the carburizing furnace is kept at 28 to 40% and 730 to 1
It is characterized by carburizing at a temperature of 100 ° C.

According to a second aspect of the present invention, there is provided a gas hardening treatment method for a metal surface according to the first aspect of the present invention, wherein the gas in the furnace further comprises a gas or a liquid containing N and H. 650-1 while adding 0.5-15% of internal gas volume
It is characterized by carbonitriding at a temperature of 100 ° C. Furthermore, a gas hardening treatment method for a metal surface according to the present invention according to claim 3 is the gas hardening treatment method for a metal surface according to the first or second invention, wherein the carburizing furnace or the carbonitriding furnace is other than a heating chamber. Characterized by using one provided with one or more vacuum purge chambers.

In the gas curing method for a metal surface according to the present invention, methanol is decomposed in a carburizing furnace as follows. CH ₃ OH → CO (33.3%) + 2H ₂ (66.7)
%) That is, methanol is 33.3% of CO and 66.7%
H ₂ can be generated stably in a carburizing furnace. However, if the flow rate of methanol is reduced so that the amount of the generated gas in the furnace is not more than one time (per hour) of the furnace volume, the CO concentration in the furnace may be less than 28%.
This is due to dilution with an enriched hydrocarbon gas or the like. In order to compensate for such a decrease in CO concentration, a gas or liquid containing C and H and a gas or liquid containing O are supplied and reacted in the furnace in addition to the methanol to reduce the CO concentration to 28%. The above is maintained.

In the gas hardening method for a metal surface according to the present invention, the method of injecting methanol into a furnace heated to a carburizing temperature or a carbonitriding temperature is not limited to dropping, but injecting gaseous methanol. You may. As the gas or liquid containing C and H in the present invention, for example, CH ₄ , C ₃ H ₈ ,
It is _{C 4 H 10, C 7 H} 8 and the like. Examples of the gas or liquid containing O include O ₂ , CO ₂ , and H ₂ O. An example of the reaction resulting therefrom is shown below.

2C ₃ H ₈ + 3O ₂ → 6CO (42.9%)
_{+ 8H 2 (57.1%) C} 3 H 8 + 3CO 2 → 6CO (60%) + H 2 (40%) C 7 H 8 + 7H 2 O → 7CO (38.9%) + 11H 2 O
(61.1%) For example, by adding C ₃ H ₈ and CO ₂ , such a reaction is used to reduce the low CO concentration in the furnace atmosphere generated from a small flow rate of methanol to the high CO concentration. Can be changed to

In this case, the flow rates of methanol and C ₃ H ₈ + CO ₂ may be adjusted in advance to a predetermined CO concentration by calculation. However, in that case, the flow rate is adjusted so that 50% or more of the CO concentration in the total gas generated in the furnace is supplied by methanol, and the remaining less than 50% is supplied by the reaction between C ₃ H ₈ and CO _2. . Hereinafter, the processing temperature, the total amount of gas generated in the carburizing furnace and the carbonitriding furnace, the raw material gas and CO concentration, the conditions of the furnace and the furnace atmosphere control, and the reasons for limitation will be described in order. (Treatment temperature): The treatment temperature in the present invention is suitably 730 to 1100 ° C in the case of carburizing treatment, and 650 to 1100 ° C in the case of carbonitriding treatment. In the case of carburizing treatment, at a treatment temperature of less than 730 ° C., sooting is likely to occur, while when it exceeds 1100 ° C., crystal grains become coarse, so the carburizing treatment temperature is in the range of 730 to 1100 ° C. In the case of carbonitriding, since the A ₁ transformation point is lowered by infiltration of N into steel, a treatment temperature of 650 to 1100 ° C. is appropriate. If the processing temperature is lower than 650 ° C., sooting tends to occur, while if it exceeds 1100 ° C., crystal grains are likely to be coarsened. (Total gas volume generated in the furnace): When the total gas volume generated in the carburizing or carbonitriding furnace is less than 0.05 times the furnace volume / hour, the atmosphere gas components become stable due to the surface area of the product. difficult, and there is a problem that the time to recover from the dilution of the furnace atmosphere by front chamber N ₂ during door closing too much. On the other hand, when the total gas amount generated in the furnace is larger than 1.5 times the furnace volume / hour, it is not preferable from the viewpoint of resource saving and energy saving, and furthermore, residual hydrocarbons increase in the furnace, The controllability of the carbon potential deteriorates.

Therefore, the total amount of gas generated in the furnace is preferably 0.05 to 1.5 times / hour of the furnace volume. (Raw material gas and CO concentration): As the raw material gas, in the case of carburizing treatment, a gas or liquid containing methanol, C and H, and a gas or liquid containing O are used. In this case, examples of the gas or liquid containing C and H include CH ₄ , C ₃ H ₈ , C ₄ H ₁₀ ,
C ₇ H _{8 and the} like. Examples of the gas or liquid containing O include O ₂ , CO ₂ , and H ₂ O.

In the case of carbonitriding, NH ₃ , C ₃ H ₇ NO, etc. may be added to the source gas in the case of carburizing. The supply ratio at that time is as follows in the case of carburizing treatment. That is, 50% or more of the total amount of CO in the total gas generated in the carburizing furnace is supplied by methanol, and the remaining 50%
Less than is supplied by a reaction between a gas or liquid containing C and H and a gas or liquid containing O. Thereby, the CO concentration in the total gas in the carburizing furnace is set to 28 to 40%.
When the CO concentration is less than 28%, the carburizing speed is low,
In addition, the carburization depth of a single substance or a lot tends to vary. On the other hand, when the CO concentration exceeds 40%, the grain boundary oxide layer of the processed product becomes deep.

Therefore, the carburizing speed is high, the variation in carburizing depth is small, and the carburizing atmosphere with a shallow grain boundary oxide layer is as follows.
An appropriate CO concentration in the total gas is 28 to 40%. (Carburizing Furnace and Carbonitriding Furnace): The types of furnaces for performing gas carburizing and gas carbonitriding according to the present invention include bit types, batch types, and continuous types used in conventional gas carburizing methods. Is applicable as it is.

However, when a conventional frame curtain type batch furnace is used, if there is a danger of explosion due to the inhalation of air when the goods are taken in and out, the furnace volume is 1.5 times or more only when the goods are taken in and out. There is no problem if gas is flowed (per hour). However, according to claim 3 of the present invention, one or more vacuum purging chambers are provided in addition to the heating chamber, rather than using a conventional furnace using a frame curtain such as a batch type furnace, a tray pusher type continuous furnace, or the like. The use of a furnace is advantageous in that it is safer, has a higher atmosphere stability, and requires less gas consumption. (Atmosphere control in furnace): In the gas hardening method for metal surface by gas carburizing and gas carburizing chamber according to the present invention, CO gas is generated stably and its concentration is kept almost constant. O ₂ in the atmosphere as in the gas carburizing method of
The carbon potential can be controlled by controlling the concentration with an oxygen sensor or controlling the concentration of CO _{2 in} the atmosphere with an infrared CO ₂ analyzer.

Further, the carbon potential can be more precisely determined.
To control CO and O in the atmosphere _TwoAnalyze both components of
Control and control the carbon potential
CO or CO in the atmosphere_TwoOf both components
Analysis and arithmetic control to reduce the carbon potential
It is better to control.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of a gas carburizing furnace showing an example of an apparatus for performing the method for gas-curing a metal surface according to the present invention. This furnace includes a front chamber 2 in front of a heating chamber 1 constituting a batch type furnace main body. The front chamber 2 is divided into upper and lower stages with a roller table 3 as a boundary, and a quenching oil tank 4 is installed in a lower stage. The upper vacuum purge chamber 5 is provided with an inlet vacuum door 6 that is opened and closed by an elevating cylinder Cy1 at the inlet, and an outlet vacuum door 7 that is opened and closed by an elevating cylinder Cy2 at the outlet. In the vacuum purge chamber 5, the roller table 3 is moved by the lifting cylinder Cy3.
The elevator 8 is installed which is driven up and down together with a part of the elevator.

The heating chamber 1 is provided with an inlet / outlet facing the outlet of the front chamber 2 and is opened / closed by a heat insulating door 11 driven by a lifting / lowering cylinder Cy4. A stirring fan 12 is installed in the heating chamber 1 together with a heating source and a thermocouple (not shown). Reference numeral 13 in the figure is an exhaust port. The in-furnace drive chain 14 can transport the work W from the inside of the front chamber 2 to the inside of the heating chamber 1 and can also carry it out.

Now, using a carburizing furnace with a vacuum purge chamber as shown in FIG. 1 capable of processing 400 kg of gross and having an inner volume of 1.8 m ³ in the heating chamber 1, a work W (SCM415 material having a diameter of 15 mm and a length of 20 mm, a gross of 400 kg) ) Will be described. First, only the inlet vacuum door 6 of the vacuum purge chamber 5 is opened, and the outlet vacuum door 7 and the heat insulating door 11 of the heating chamber 1 are closed. In this state, the work W stored in the basket is sent into the vacuum purge chamber 5 and the inlet vacuum door 6 is closed. Next, the air in the vacuum purge chamber 5 is exhausted by a vacuum pump, and the pressure is restored with nitrogen. After the nitrogen pressure is restored, the outlet vacuum door 7 and the heat insulating door 11 of the heating chamber 1 are opened, and the work W is filled with the carburizing gas using the in-furnace drive chain 14 and transported into the heating chamber 1 where the temperature is raised. Then, the exit vacuum door 7 and the heat insulating door 11 of the heating chamber 1 are closed. Carburizing is performed at a predetermined temperature while supplying a gas for carburizing to the heating chamber 1.

FIG. 2 shows an example of a heat pattern of the carburizing process in the heating chamber 1. During the temperature rise and soaking in the illustrated pattern, CH ₃ OH: 400
_{cc / h, C 3 H 8} : 0.31 / min, CO 2: 1.6
1 / min was flowed. During the carburizing period, the diffusion period and the cooling period, CH ₃ OH: 400 cc / h, C ₃ H ₈ : 0.71 /
min, and while analyzing the O ₂ concentration in the heating chamber 1 with an oxygen sensor directly inserted into a heating chamber (not shown), the carbon potential (CP) at that time was 1.1% in the carburizing period and the diffusion period. And the introduction of C ₃ H ₈ and air was controlled so that the cooling period was 0.75%.

After the cooling period, the work W is taken out of the heating chamber 1, transferred to the vacuum purge chamber 5, immersed in the quenching tank 4 using the elevator 8, and oil-cooled at 60.degree. Example carburized workpieces were obtained. On the other hand, as a comparative example, the same work W was treated by the drip-injection carburizing method with the same heat pattern as in FIG. As the gas introduced at that time,
CH ₃ OH: A constant amount of 2,000 cc / h is flown, and the O ₂ concentration is analyzed by an oxygen sensor.
The introduction of C ₃ H ₈ and air was controlled so as to be 1% and the diffusion period and the cooling period 0.75%.

Further, as a comparative example, the treatment was carried out with the same heat pattern as in FIG. The gas introduced at that time was CH ₃ OH: 4
At a constant flow rate of 00 cc / h, while analyzing the O ₂ concentration with an oxygen sensor, C ₃ H ₈ and air were adjusted so that the carburizing period was 1.1%, the diffusion period and the temperature-lowering period were 0.75%. Controlled the introduction of.

FIG. 3 shows the result of analyzing the atmospheric gas at that time.
Shown in According to FIG. 3, the carburizing method of the present invention has a small amount of residual CH ₄ and a constant CO concentration of about 32% during the carburizing period, as in the case of the ordinary dropping type carburizing method of the comparative example.
However, the method in which the flow rate of the dropping in the comparative example was reduced was the residual C
Although H ₄ is similarly low, the CO concentration is considerably low at about 28% at the end of the treatment. At this time, test pieces (SCM415) for carburization depth variation, which were previously set at nine locations in the furnace, were inspected, and the results shown in FIG. 4 were obtained. According to this, the product of the present invention had a nine-point variation of 0.04 mm, which was a good result equal to or better than that of the conventional drip-injection type carburizing method.

FIG. 5 shows a graph of 9 in the carburizing method of the present invention.
The atmosphere controllability during the carburizing stage at 30 ° C. was exhibited. This is 0.1
The C concentration was analyzed by inserting a pure iron foil having a thickness of mm into the furnace for 30 minutes. as a result,
In the method of the present invention, the calculated value and the actual analysis value were almost the same C concentration value, and it was found that the controllability was excellent. Next, a second embodiment of the present invention will be described.

This is obtained by carburizing the same workpiece W at the same raw material and the same gas flow rate at 930 ° C. by the same method of the present invention as in the first embodiment. The difference is that the value was controlled to 1.0%. The relationship between the carburizing time and the effective hardened layer depth of the example in the second embodiment is shown by a solid line in FIG.

On the other hand, as a comparative example, C ₃ H ₈ : 2 l / min, air: 12 l / m by a shift method in a propane furnace.
The dotted line in FIG. 6 shows the relationship between the carburizing time and the effective hardened layer depth when carburizing is performed by similarly controlling the CP to 1.0% by flowing a constant amount of in and enriching C ₃ H ₈ . Was. Further, as a comparative example, a constant amount of CH ₄ : 6 l / min and air: 121 / min were flown by the methane furnace shift method, and the CH ₄ was enriched, thereby similarly controlling the CP to 1.0%. The relationship between the carburizing time and the effective hardened layer depth in the case of carburizing is shown by the chain line in FIG.

From the results shown in FIG. 6, it can be understood that the carburizing method of the present invention has a deeper effective hardened layer at the same carburizing time as compared with the comparative example. That is, it can be said that the carburizing method of the present invention has a higher carburizing rate than the conventional in-furnace direct conversion type carburizing method. Next, a third embodiment of the present invention will be described. This is performed by using the same carburizing furnace (FIG. 1) as in the first embodiment, using the same heat pattern (FIG. 2), and forming an SCM415 perforated round bar (diameter 20 mm, length 40 mm, diameter 5 mm, depth). The test piece is a carburizing process using a test piece (centered on a 32 mm hole) as a workpiece.

In the test piece with a hole in this embodiment, 5 to 30 of the holes correspond to the effective hardened layer depth at the outer peripheral portion.
The ratio of the effective hardened layer depth in mm part is shown by a solid line in FIG. On the other hand, as a comparative example, C ₃ H ₈ : 2 l / min and air: 12 l / min are flowed in a fixed amount by a metamorphic system in a propane furnace, and C ₃ H ₈ is enriched to obtain the same heat pattern. The perforated test piece was carburized. In this case, the ratio of the effective hardened layer depth of the 5 to 30 mm portion in the hole to the effective hardened layer depth of the outer peripheral portion is shown in FIG.
Is indicated by a dotted line.

Further, as a comparative example, CH ₄ : 6 l / min, air: 121 / m
In was flowed in a fixed amount and CH ₄ was enriched to thereby carburize the same perforated test piece with the same heat pattern. In this case, the ratio of the effective hardened layer depth of the 5 to 30 mm portion in the hole to the effective hardened layer depth of the outer peripheral portion is shown by a chain line in FIG.

From the results shown in FIG. 7, it can be seen that the carburizing method of the present invention carburized relatively deeply into the holes and was excellent in carburizing uniformity as compared with the comparative example. In each of the above embodiments, only the case of carburizing treatment has been described. However, NH ₃ , C ₃ H
Carbonitriding can be performed in the same manner by adding ₇ NO and the like.

[0038]

As described above, according to the present invention,
Compared to conventional gas carburizing and gas carbonitriding methods,
Source gas usage, thereby reducing emissions
CO _TwoThe amount can be greatly reduced. Therefore, resource saving, saving
Advantageous from an energy standpoint and environmentally friendly
New carburizing and carbonitriding methods can be provided.

Further, the method of the present invention has better atmosphere stability than the conventional gas carburizing method, and thus has excellent controllability of carbon potential. In addition, the method of the present invention has a higher carburizing speed and less variation in carburizing than the conventional gas carburizing method. Furthermore, according to the present invention,
By using a carburizing furnace equipped with one or more vacuum purge chambers in addition to the heating furnace, safe and stable carburizing or carbonitriding can be performed. And carbonitriding can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a batch carburizing furnace for performing the method of the present invention.

FIG. 2 is a diagram of a heat pattern of a carburizing process.

FIG. 3 is a view showing an analysis result of an atmosphere gas in a furnace at a time of carburizing at 930 ° C.

FIG. 4 is a view showing variations in carburizing depth measured at nine points in a furnace.

FIG. 5 is a diagram showing a relationship between a calculated CP value and a foil analysis C concentration at 930 ° C. carburizing treatment.

FIG. 6 is a graph showing the relationship between carburizing time and effective hardened layer depth at 930 ° C. and 1.0% CP.

FIG. 7 is a diagram showing the relationship between the depth of a hole and the ratio of an effective hardened layer in an SCM415 holed round bar.

[Explanation of symbols]

 1 Heating chamber 2 Front chamber 4 Hardened oil tank 5 Vacuum purge chamber 6 Inlet vacuum door 7 Outlet vacuum door 8 Heating chamber 11 Heat insulation Door 12 Agitating fan 13 Exhaust port 14 Furnace drive chain

Claims (3)

[Claims] 1. The total amount of gas generated in a carburizing furnace is 0.05 to 1.5 times the internal volume of the carburizing furnace per hour, and 50% or more of the CO amount in the generated total gas is decomposed by methanol. The CO concentration in the total gas in the carburizing furnace is 28 to 28 by supplying by gas and supplying the remainder by reacting either gas or liquid containing C and H with gas or liquid containing O. Keep at 40% 73
A gas hardening method for a metal surface, comprising carburizing at a temperature of 0 to 1100C. 2. The furnace gas according to claim 1, further comprising N and H.
A gas or liquid containing 0.5% to 15% of the gas volume in a carburizing furnace and carbonitriding at a temperature of 650 to 1100 ° C. 3. The gas hardening method for a metal surface according to claim 1, wherein a furnace provided with one or more vacuum purge chambers in addition to the heating chamber is used.