JP3428936B2 - Gas curing method for metal surface - Google Patents

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, 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 treatment method for a metal surface, which is excellent in carburizing characteristics and is also economical.

[0002]

2. Description of the Related Art As a gas carburizing method which is one of conventional typical gas hardening treatment methods for metal surfaces, there are a metamorphic furnace type carburizing method, a drop injection type carburizing method, a hydrocarbon gas and an oxidizing gas in a furnace. There is a direct gas carburizing method that is introduced directly into the. The metamorphic furnace carburizing method mixes hydrocarbon gas and air at a constant ratio to obtain 10
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. Next, 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, in addition to this carrier gas,
The hydrocarbon gas is enriched to achieve a predetermined carbon potential. Such a metamorphic furnace type carburizing method has an advantage that the composition of the carrier gas is constant because the metamorphic furnace is used and the atmosphere can be controlled stably.

In the drop 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 the carrier gas in the converter furnace type, and contains CH ₄ , C ₃ H ₈ , and C ₄
Or added hydrocarbons H _10, etc., an organic liquid that generates free carbon by dispensing or separately droplets to premixed to form a carburizing atmosphere remembering enriched <br/> action. In this case as well, the amount of the organic liquid agent to be dropped into the furnace is required to generate a gas amount that is 1.8 to 4 times (per hour) the internal volume of the furnace.

Such a drop injection type carburizing method does not require a shift converter. Atmosphere can be controlled stably because the carrier gas composition is constant. When methanol is used as the organic liquid agent, the CO concentration in the carrier gas is as high as about 33%, so that there are advantages that the carburizing speed is fast and that the difference in carburizing depth due to the shape of the product hardly occurs. The direct gas carburizing method is a method in which a hydrocarbon gas and an oxidizing gas are directly introduced into a carburizing furnace to perform carburizing. One of CH ₄ , C ₃ H ₈ and C ₄ H ₁₀ and air and CH ₄ are used. , C ₃ H ₈ or C ₄ H ₁₀ and CO ₂ or O ₂ .

Neither of these direct gas carburizing methods requires a shift converter, 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 substantially efficient and economical.

[0006]

However, in addition to the above advantages, the above-mentioned conventional gas hardening treatment methods for metal surfaces such as the metamorphic furnace type carburizing method, the drop injection type carburizing method, and the direct gas carburizing method have the following advantages. There is a problem. The metamorphic carburizing method is
(1) Since a shift converter is required in addition to the carburizing furnace, the number of management items 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 modified by hydrocarbons such as ₃ H ₈ and C ₄ H ₁₀ and air is about 20 to 24.5%.
The carburizing speed is slow due to the low value, and the carburizing depth tends to vary depending on the shape of the product.

The drop injection type carburizing method requires 1.8 to 4 times the volume of gas in the furnace per hour, and although it is not the same as the metamorphic furnace type carburizing method, the amount of the organic liquid agent used is also large. The real efficiency of gas is low and uneconomical. Therefore,
It is considered that the drawbacks can be overcome by reducing the supply amount of the organic liquid agent in the drop injection type carburizing method. However, when carburizing is actually carried out by reducing the amount of methanol supplied to an amount corresponding to gas generation of 1 time or less (per hour) of the carburizing furnace internal volume,
The CO concentration in the gas component in the furnace may be 28% or less. If the CO concentration decreases in this way, the carburizing rate and carburizing characteristics deteriorate.

In the direct gas carburizing method, CH ₄ , C ₃ H ₈ ,
The direct gas carburizing method using 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 metamorphic furnace carburizing method. Therefore, CO in the gas generated in the carburizing furnace is
The concentration is as low as about 20 to 24.5%, so the carburizing speed is slow, and the carburizing depth tends to vary 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 using C ₄ H ₁₀ and CO ₂ is as follows. C ₄ H ₁₀ 4CO ₂ → 8CO (61.5%) + 5H
₂ (38.5%) According to theoretical calculation, the CO gas component ratio should be 61.5%, but according to Japanese Patent Publication No. 6-051904, air enters through the door packing during actual operation. The CO concentration is said to be about 40% due to air intrusion at negative pressure caused by furnace operation. Further, it is clear that the CO concentration also 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 is (1) CO
The concentration is not constant. (2) In addition to the CO-based carburizing reaction, there is a direct carburizing reaction with a hydrocarbon gas, so it is difficult to control the carbon potential, and we have to rely on experience.
(3) Suiting is likely to occur. Furthermore, in the case of (4) long-time carburization, the CO concentration exceeds 40% and the theoretical calculated value is 6
As it becomes 1.5%, there is a problem that the depth of grain boundary oxidation of the treated product after carburization increases.

Therefore, the present invention has been made by paying attention to such unsolved problems of the prior art, and the amount of raw material gas used can be greatly reduced and the amount of CO ₂ discharged can be greatly reduced. It is an object of the present invention to provide a gas curing treatment method for a metal surface, which can save resources, save energy, and is environmentally superior. Further, the present invention is superior in atmospheric stability as compared with the conventional gas carburizing method, and thereby is also excellent in controllability of carbon potential, and also has a higher carburizing rate and carburizing rate than the conventional gas carburizing method. An object of the present invention is to provide a gas hardening treatment method for a metal surface using a gas that can reduce variations.

Further, according to the present invention, by using a carburizing furnace capable of vacuum-purging at least the anterior chamber, safe and stable carburizing treatment is possible, and since there is no frame curtain, gas hardening of the metal surface is also environmentally excellent. It is intended to provide a processing method.

[0013]

In order to achieve the above-mentioned object, in the method for gas hardening treatment of metal surface of the present invention according to claim 1, the total amount of gas generated in the carburizing furnace is the contents of the carburizing furnace per hour. The product is 0.05 to 1.5 times the product, and 50% or more of the amount of CO in the generated total gas is supplied by the decomposition gas of methanol, and the balance is either a gas or liquid containing C and H. By supplying by reaction with either a gas or a liquid containing O, the CO concentration in the total gas in the carburizing furnace is maintained 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 surface hardening treatment method for a metal surface in a carburizing furnace, wherein the furnace gas according to the first aspect further contains a gas or liquid containing N and H. 650 to 1 while adding 0.5 to 15% of the 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 a third aspect of the present invention is the gas hardening method for a metal surface according to the first or second aspect, wherein the carburizing furnace or the carbonitriding furnace is other than a heating chamber. Is provided with one or more vacuum purge chambers.

In the metal surface gas hardening treatment method of the present invention, methanol is decomposed in the carburizing furnace as follows. CH ₃ OH → CO (33.3%) + 2H ₂ (66.7)
%) That is, methanol is 33.3% CO and 66.7%.
H ₂ can be stably generated in the carburizing furnace. However, if the flow rate of methanol is reduced so that the amount of the generated gas in the furnace becomes 1 time (per hour) or less of the volume in the furnace, the CO concentration in the furnace may be less than 28%.
This is because it is diluted with the enriched hydrocarbon gas. 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 in addition to the methanol and reacted in the furnace so that the CO concentration is 28%. The above is maintained.

In the method for gas hardening treatment of metal surface of the present invention, the method of injecting methanol into the furnace heated to the carburizing temperature or carbonitriding temperature is not limited to the drop injection, but gaseous methanol is injected. You may. Examples of the gas or liquid containing C and H in the present invention include CH ₄ , C ₃ H ₈ ,
There are C ₄ H ₁₀ , C ₇ H _{8 and the} like. Further, examples of the gas or liquid containing O include O ₂ , CO ₂ , and H ₂ O. An example of the reaction by them is shown below.

2C ₃ H ₈ + 3O ₂ → 6CO (42.9%) + 8H ₂ (57.1%) C ₃ H ₈ + 3CO ₂ → 6CO (60%) + 4H ₂ (40%) C ₇ H ₈ + 7H ₂ O → 7 CO (38.9%) + 11 H ₂ (61.1%) For example, by adding C ₃ H ₈ and CO ₂ , a furnace produced from a low flow rate of methanol by utilizing such a reaction. The low CO concentration in the inner atmosphere can be changed to a high CO concentration.

In this case, the flow rates of methanol and C ₃ H ₈ + CO ₂ may be adjusted beforehand by calculation so as to obtain a predetermined CO concentration. 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 of 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 the CO concentration, the furnace, the atmosphere control in the furnace, and the like and the reasons for limitation will be described in order. (Treatment temperature): The treatment temperature in the present invention is preferably 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, if the treatment temperature is lower than 730 ° C., sustaining easily occurs, while if it exceeds 1100 ° C., coarsening of crystal grains occurs. Therefore, the carburizing treatment temperature is in the range of 730 to 1100 ° C. In the case of carbonitriding, the treatment temperature of 650 to 1100 ° C. is appropriate because the A ₁ transformation point is lowered due to the permeation of N into the steel. If the treatment temperature is lower than 650 ° C, sooting tends to occur, while if it exceeds 1100 ° C, coarsening of crystal grains tends to occur. (Total amount of gas generated in the furnace): If the total amount of gas generated in the carburizing or carbonitriding furnace is less than 0.05 times the furnace internal volume / hour, the atmospheric gas components will be stable due to the large or small surface area of the product. Further, there is a problem that it takes too much time to recover from the dilution of the atmosphere in the furnace by the antechamber N ₂ when opening and closing the door. On the other hand, when the total amount of gas generated in the furnace is larger than 1.5 times the volume in the furnace / hour, it is not preferable from the viewpoint of resource saving and energy saving, and moreover, residual hydrocarbons increase in the furnace, The controllability of carbon potential becomes poor.

Therefore, the total amount of gas generated in the furnace is preferably 0.05 to 1.5 times the internal volume of the furnace / hour. (Raw material gas and CO concentration): In the case of carburizing treatment, a gas or liquid containing methanol and C and H and a gas or liquid containing O are used as the raw material gas. In this case, examples of the gas or liquid containing C and H include CH ₄ , C ₃ H ₈ , C ₄ H ₁₀ ,
There are C ₇ H ₈ etc. Further, 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 raw material gas in the case of carburizing. The supply ratio at that time is as follows in the case of carburization. That is, 50% or more of the CO amount in the total gas generated in the carburizing furnace is supplied by methanol, and the remaining 50% is supplied.
Less than is supplied by the reaction of a gas or liquid containing C and H with a gas or liquid containing O. As a result, the CO concentration in the total gas in the carburizing treatment furnace is set to 28 to 40%.
When the CO concentration is less than 28%, the carburizing rate is slow,
Further, variations in carburizing depth are liable to occur in a single substance or in a lot. On the other hand, when the CO concentration exceeds 40%, the grain boundary oxide layer of the treated product becomes deep.

Therefore, as a carburizing atmosphere in which the carburizing speed is high, the carburizing depth varies little, and the grain boundary oxide layer has a shallow depth,
The appropriate CO concentration in the total gas is 28 to 40%. (Carburizing furnace and carbonitriding furnace): The type of furnace for carrying out the gas carburizing and gas carbonitriding treatment according to the present invention is all of the bit type, batch type and continuous type used in the conventional gas carburizing treatment method. The model of can be applied as it is.

However, in the case of using the conventional frame curtain type batch furnace, if there is a danger of explosion due to the intake of air when loading or unloading items, the volume inside the furnace is 1.5 times or more only when the items are loaded or unloaded. There is no problem if you let gas flow (per hour). However, rather than using a conventional furnace that uses a frame curtain, such as a batch-type furnace, a tray pusher-type continuous furnace, etc., according to claim 3 of the present invention that has one or more vacuum purge chambers in addition to the heating chamber. The use of a furnace has the advantages that it is safe, the atmosphere is stable, and the gas consumption is low. (In-furnace atmosphere control): The method for gas hardening treatment of a metal surface by gas carburizing and forming a gas carburizing chamber according to the present invention is a conventional method because CO gas is stably generated and its concentration is kept substantially constant. similar to the gas carburizing method, O ₂ in the atmosphere
The carbon potential can be controlled by analytically controlling the concentration with an oxygen sensor or analytically controlling the CO ₂ concentration in the atmosphere with an infrared CO ₂ analyzer.

Further, the carbon potential can be more precisely
To control CO and O in the atmosphere ₂Analyzes both components of
And control the carbon potential by controlling the calculation.
CO or CO in the atmosphere₂Both components of
By analyzing and controlling the carbon potential
Good to control.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION 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 carrying out the gas hardening treatment method for a metal surface of the present invention. This furnace includes a front chamber 2 in front of a heating chamber 1 which constitutes a batch type furnace body. The front chamber 2 is divided into upper and lower two stages with a roller table 3 as a boundary, and a quenching oil tank 4 is installed in the lower stage. The upper vacuum purge chamber 5 is provided with an inlet vacuum door 6 which is opened / closed by an elevating cylinder Cy1 at an inlet, and an outlet vacuum door 7 which is opened / closed by an elevating cylinder Cy2 at an outlet. Further, in the vacuum purge chamber 5, the roller table 3 is mounted by the lifting cylinder Cy3.
An elevator 8 that is driven up and down together with a part of the above is installed.

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 an elevating cylinder Cy4. In addition, 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 drawing is an exhaust port. The in-furnace drive chain 14 can transfer the work W from the inside of the front chamber 2 to the inside of the heating chamber 1 and vice versa.

Now, using the carburizing furnace with a vacuum purging chamber of FIG. 1 capable of processing the heating chamber 1 having an internal volume of 1.8 m ³ and a gloss of 400 kg, a work W (diameter 15 mm, length 20 mm of SCM415 material, gloss 400 kg) is used. ) Is carburized. 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 nitrogen recompression, the outlet vacuum door 7 and the heat insulation door 11 of the heating chamber 1 are opened, the work W is filled with carburizing gas using the in-furnace drive chain 14, and the workpiece W is transferred into the heating chamber 1 where the temperature is raised. Then, the outlet vacuum door 7 and the heat insulating door 11 of the heating chamber 1 are closed. Carburizing treatment is performed at a predetermined temperature while supplying a gas for carburizing treatment 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 heating and soaking in the pattern shown in the figure, CH ₃ OH: 400 is used as a processing gas.
cc / h, C ₃ H ₈ : 0.31 / min, CO ₂ : 1.6
Flowed at 1 / min. CH ₃ OH: 400 cc / h, C ₃ H ₈ : 0.71 / during the carburizing period, diffusion period and temperature holding period
While flowing a fixed amount of min and analyzing the O ₂ concentration in the heating chamber 1 by an oxygen sensor directly inserted in the heating chamber (not shown), the carbon potential (CP) at that time is 1.1% in the carburizing period and the diffusion period. The introduction of C ₃ H ₈ and air was controlled so that the temperature-holding period was 0.75%.

After the temperature-holding period ends, the work W is taken out of the heating chamber 1 and transferred to the vacuum purge chamber 5, immersed in the quenching tank 4 using the elevator 8 and oil-cooled at 60 ° C. An example carburized workpiece was obtained. On the other hand, as a comparative example, the same work W was treated by the drop carburizing method in the same heat pattern as in FIG. As the introduced gas at that time,
A constant amount of CH ₃ OH: 2000 cc / h was flowed, and while the O ₂ concentration was analyzed by an oxygen sensor, CP was carburized: 1.
The introduction of C ₃ H ₈ and air was controlled so that the concentration was 1% and the diffusion period and the temperature keeping period were 0.75%.

Further, as a comparative example, the same heat pattern as in FIG. 2 was used for the treatment by reducing only the flow rate of the dropping agent in the dropping carburizing method. The gas introduced at that time was CH ₃ OH: 4
While flowing a fixed amount of 00 cc / h and analyzing the O ₂ concentration by an oxygen sensor, C ₃ H ₈ and air are adjusted so that CP becomes a carburizing period: 1.1%, a diffusion period and a temperature keeping period: 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 treatment method of the present invention has a small amount of residual CH ₄ as in the case of the ordinary dropping carburizing method of the comparative example, and the CO concentration is kept constant at about 32% during the carburizing period.
However, the method of reducing the instillation flow rate of the comparative example is the residual C
The amount of H ₄ is similarly small, but the CO concentration is considerably low at about 28% at the end of the treatment. At this time, a test piece for carburizing depth variation (SCM415) installed in advance at nine locations in the furnace was inspected, and the results shown in FIG. 4 were obtained. According to this, the product of the present invention has a 9-point variation result of 0.04 mm, which is as good as or better than that of the conventional drip-injection carburizing method.

FIG. 5 shows the number 9 in the carburizing treatment method of the present invention.
Atmosphere controllability during the 30 ° C carburizing period was exhibited. This is 0.1
A pure iron foil with a thickness of mm is inserted into the furnace for 30 minutes, and the C concentration after that is analyzed. as a result,
In the method of the present invention, it was found that the calculated value and the actual analytical value were almost the same C concentration value, and the controllability was excellent. Next, a second embodiment of the present invention will be described.

This is a case where the same work W is carburized at the same raw material and the same gas flow rate and at the same gas temperature of 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 in the example of the second embodiment is shown by the 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 propane furnace shift conversion system.
The dotted line in Fig. 6 shows the relationship between carburizing time and effective hardened layer depth when carburizing by controlling CP to 1.0% in the same manner by flowing a fixed amount of in and enriching C ₃ H ₈ . It was Further, as a comparative example, a methane furnace transformer scheme, CH _4: 6l / min, air: 121 / min is flowed a certain amount, by enrichment of CH _4, similarly to control 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 seen 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-reactor shift direct carburizing method. Subsequently, a third embodiment of the present invention will be described. This is the same carburizing furnace (FIG. 1) as in the first embodiment, with the same heat pattern (FIG. 2), SCM415 perforated round bar (diameter 20 mm, length 40 mm, diameter 5 mm, depth). A test piece having a 32 mm hole as the center) was carburized as a work.

In the perforated test piece of this example, 5 to 30 in the hole with respect to the effective hardened layer depth of the outer peripheral portion.
The ratio of the effective hardened layer depth in mm is shown by the solid line in FIG. On the other hand, as a comparative example, a constant amount of C ₃ H ₈ : 2 l / min and air: 12 l / min was made to flow by a propane furnace shift conversion method, and C ₃ H ₈ was enriched, so that the same heat pattern was obtained. The perforated test piece was carburized. The ratio of the effective hardened layer depth of 5 to 30 mm in the hole to the outermost effective hardened layer depth in that case is shown in FIG.
Is indicated by a dotted line.

Furthermore, as a comparative example, a methane furnace transformer scheme, CH _4: 6l / min, air: 121 / m
The same perforated test piece was carburized in the same heat pattern by flowing a fixed amount of in and enriching CH ₄ . The ratio of the effective hardened layer depth of 5 to 30 mm in the hole to the effective hardened layer depth of the outer peripheral portion in that case is shown by a chain line in FIG. 7.

From the results shown in FIG. 7, it can be seen that the carburizing method of the present invention carburizes comparatively deeply into the hole and is superior in carburizing uniformity as compared with the comparative example. In each of the above-described embodiments, only the case of carburizing treatment is described, but NH ₃ , C ₃ H are used as the source gas in the case of carburizing treatment.
₇ Carbonitriding can be performed in the same manner by adding NO or the like.

[0038]

As described above, according to the present invention,
Compared with conventional gas carburizing and gas carbonitriding methods,
The amount of raw material gas used can be reduced, and
CO ₂The amount can be greatly reduced. Therefore, saving resources and
Energy-friendly and environmentally friendly
A new carburizing and carbonitriding method can be provided.

Further, the method of the present invention is superior in atmospheric stability as compared with the conventional gas carburizing method, and is thereby superior in controllability of carbon potential. Further, the method of the present invention has a higher carburizing rate and less carburizing variation than the conventional gas carburizing method. Further according to the invention,
By using a carburizing furnace equipped with one or more vacuum purging chambers in addition to the heating furnace, safe and stable carburizing or carbonitriding processing is possible, and because there is no frame curtain, carburizing is also environmentally superior. And a carbonitriding method can be provided.

[Brief description of drawings]

FIG. 1 is a schematic view of a batch type carburizing furnace for carrying out the method of the present invention.

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

FIG. 3 is a diagram showing an analysis result of a furnace atmosphere gas at the time of carburizing treatment at 930 ° C.

FIG. 4 is a diagram showing variations in carburizing depth measured at 9 points in a furnace.

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

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 hole depth and the effective hardened layer ratio in the SCM415 perforated round bar.

[Explanation of symbols]

1 ... Heating room 2 ……… front room 4 ... Quenching oil tank 5 ......... vacuum purge chamber 6 ... Inlet vacuum door 7 ... Exit vacuum door 8 ... Heating room 11 ……… Insulation door 12 ………… Stirring fan 13 ... Exhaust port 14 ... Chain for driving in furnace

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-58-213870 (JP, A) JP-A-60-72821 (JP, A) JP-A-6-340959 (JP, A) JP-A-11- 124621 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 8/00-8/80 C21D 1/06 C21D 1/76

Claims (3)

(57) [Claims] 1. The total amount of gas generated in the 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 total generated gas is decomposed into methanol. The CO concentration in the total gas in the carburizing furnace is adjusted to 28 to 40% by supplying the gas by gas and supplying the balance by the reaction of either the gas or liquid containing C and H and the gas or liquid containing O. Hold at 40% 73
A gas hardening treatment method for a metal surface, which comprises carburizing at a temperature of 0 to 1100 ° C. 2. The furnace gas according to claim 1, further comprising N and H
A gas hardening treatment method for a metal surface, which comprises carbonitriding at a temperature of 650 to 1100 ° C. while adding 0.5 to 15% of the gas volume in the carburizing furnace while adding either gas or liquid containing 3. The method for gas hardening treatment of a metal surface according to claim 1, wherein a furnace equipped with one or more vacuum purge chambers other than the heating chamber is used.