JPS58174572A - Gas soft nitriding method - Google Patents

Abstract

PURPOSE:To attain to increase a nitriding speed to a large extent, to reduce operation cost and to enhance safety, by adding CO2 to a gaseous soft nitriding atmosphere comprising an N2 gas, an NH3 gas and an org. solvent decomposing gas to subject a material to be treated to gaseous soft nitridation. CONSTITUTION:A CO2 gas is added to a gaseous soft nitriding atmosphere comprising an N2 gas, an NH3 gas and an org. solvent decomposing gas such as a methanol decomposing gas in an amount of 0.1-10vol%. By using this CO2 added gaseous soft nitriding atmosphere, a material to be treated is subjected to gaseous soft nitriding treatment within a temp. range of 450-650 deg.C. When the CO2 gas is added to mentioned above, CO2 is reacted with a H2 gas imparting bad influence to nitriding reaction to lower H2 partial pressure and, therefore, a nitriding speed can be accerelated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas soft nitriding method, and particularly relates to a gas soft nitriding atmosphere consisting of neutral and inexpensively obtained nitrogen gas, ammonia gas, and cracked gas generated from an organic liquid decomposition device. By adding carbon dioxide to the gas soft nitriding process, the nitriding rate can be greatly increased, operating costs can be reduced, and safety can be improved.

Generally, the gas nitriding method using ammonia gas uses a large amount of expensive ammonia gas and takes a long time to process.
, Or, Ti, V, Mn, Si
It can only be applied to nitriding steel containing nitride-forming elements such as
There are restrictions such as limited use. This gas nitriding method is
Although the purpose is only to perform a nitriding reaction by decomposing ammonia, in the gas soft nitriding method that uses ammonia gas and an endothermic metamorphic gas, both nitriding and carburizing reactions occur at the same time, and the presence of carbon causes nitriding to occur. The reaction is accelerated and carbonitride (ε-Fe>3
This processing method is characterized by the formation of N.

However, in the conventional gas nitriding method and gas soft nitriding method, there is a problem that the hydrogen partial pressure in the furnace increases due to the decomposition reaction of ammonia gas, which slows down the nitriding rate.
In order to lower the hydrogen partial pressure, a large amount of ammonia gas must be supplied, which has the drawback of significantly increasing consumption of expensive ammonia gas and increasing operating costs.

In addition, in the conventional gas nitrocarburizing method, because about 50% of the gas in the furnace is endothermic converted gas, a large amount of carbon oxide and methane gas is generated, which tends to cause sooting in the workpiece. The disadvantage is that there is a high risk of gas purification.

Furthermore, in the conventional gas nitrocarburizing method, a large-sized shift furnace is required to generate endothermic shift gas, which not only increases equipment costs but also requires constant management of the operation of the shift furnace. There's a problem.

This invention was made in order to solve the above problems, and the purpose of this invention is to provide a gas soft nitriding method in which the nitriding rate is significantly increased. Another object of the present invention is to provide a gas soft nitriding method that can be operated safely at low operating costs.
It is an object of the present invention to provide a gas soft nitriding method that can obtain an effective carbonitrided layer in a short time regardless of the species.It is also an object of the present invention to provide an economical gas soft nitriding method that uses a small organic liquid decomposition device. Our goal is to provide the following.

That is, in the present invention, 0.1 - of carbon dioxide is added to a gas soft nitriding atmosphere consisting of nitrogen gas, ammonia gas, and organic liquid decomposition gas at a temperature range of 450 to 650°C.
It relates to a gas nitrocarburizing method characterized in that the material to be treated is subjected to gas nitrocarburizing treatment by adding 10% by volume.

In the gas nitrocarburizing method of the present invention, nitrogen gas is used as a carrier gas, ammonia gas is used as a nitrogen supply gas, and organic liquid agent decomposition gas is used as a carbon supply gas.

When using methanol decomposition gas as the organic liquid decomposition gas, for example, methanol (CH30H) is
The mixture is introduced into a decomposition device heated to 1100° C. and thermally decomposed in the layer separation device to generate carbon monoxide and hydrogen through the reaction of the following formula (1).

CH3 (JH-CO+ 2 Hz (11) In this invention, in the gas soft nitriding atmosphere gas consisting of the above nitrogen gas, ammonia gas and organic liquid decomposition gas,
Furthermore, carbon dioxide is added to perform gas nitrocarburizing treatment.

In the furnace of gas nitrocarburizing treatment according to the present invention::.

The gas reaction is as follows.

Ammonia gas (NH3) is decomposed according to the following formula (2) to generate nitrogen (N), and the object to be treated is nitrided.

2 NH3(-Go2[N)+3H2(2+) Carbon monoxide (CO) in the organic liquid decomposition gas generates carbon (0) through the reaction of the following formula (3), and carburization of the material to be treated is performed. .

2CO;:go[0]+002 (3) Carbon dioxide (CO2) reacts with hydrogen (H□) in the furnace,
Carbon oxide (CO) is generated as shown in the following formula (4).

CO2 + H2 = CO + H20 (4) Carbon monoxide (CO) generated by the decomposition reaction of carbon dioxide (002) is further converted to carbon (CO) by the reaction of the above formula (3).
Since C) is generated, the object to be treated is carburized again.

As mentioned above, by adding carbon dioxide, the hydrogen partial pressure decreases by reacting with hydrogen, which has an adverse effect on the nitriding reaction, so that the nitriding rate can be increased. Furthermore, since there is no need to introduce a large amount of ammonia gas to lower the hydrogen partial pressure, it is possible to reduce the amount of ammonia supplied into the furnace. Furthermore, since carbon monoxide generated by the reaction of carbon dioxide with hydrogen causes a carburizing reaction again, it is also possible to reduce the amount of organic solvent decomposition gas that is the source of carbon oxide.

In this way, in the present invention, the gas soft-nitriding atmosphere gas introduced into the furnace can have a smaller proportion of organic liquid decomposition gas than the proportion of nitrogen gas and ammonia gas, and a small amount of organic liquid decomposition gas can be used. Since it is sufficient to supply the organic liquid, it is sufficient to use a small-sized organic liquid decomposition device that can only decompose the required amount of organic liquid; instead of a large-sized one such as a conventional endothermic gas conversion furnace. There is no need to use it.

An example of a gas soft nitriding furnace for carrying out this invention is shown in FIG. In the figure, reference numeral 10 is a furnace body, and a radiant tube heater 12 is provided inside the furnace body 10.
A stirring fan 14 is installed in the upper part of the furnace. This fan 14 is rotated by a motor B provided outside the top of the furnace to agitate the atmospheric gas inside the furnace. Furthermore, a thermocouple 18 for measuring the temperature inside the furnace is provided inside the furnace body 10. code 2
0 is a gas supply pipe, and nitrogen, ammonia, organic liquid decomposition gas, and dispersion carbon are individually supplied into the furnace body 10 from branch pipes 21, 22, 23, and 24 connected to the gas supply side, respectively. I have to. The object to be treated 25 is charged into the furnace body 10 having the above configuration, and gas soft nitriding treatment is performed.

Gas supplied into the furnace body 10 is supplied to each branch pipe 21,
22, 23, and 24 can be introduced separately, so the nitrogen potential and carbon potential of the atmospheric gas can be arbitrarily changed by appropriately selecting the mixing ratio of each gas according to the material characteristics of the object to be treated 25. Therefore, the composition of carbonitride formed on the object to be treated 25 can be easily changed depending on the purpose of use.

□,,- Next, processing results obtained by the method of the present invention will be explained.

Figure 2 shows CO and 8450 and 5pac as specimens.
It shows the relationship between the amount added (volume %) and the thickness of the compound layer.

Organic liquid decomposition gas is methanol decomposition gas (hereinafter referred to as FD
, 0.4. ), the mixture ratio of the gas soft-nitriding atmosphere when 002 is not added is N2:NH3
: D, Ga = 50: 40: 10, and the amount of N2 was reduced by the amount equivalent to the amount of C02 added, and the temperature was 570°C.
The results were obtained by cooling in oil after treatment at a temperature of 2 hours.

As is clear from the figure, the thickness of the compound layer in both cases of 8450.8POO increases as the amount of CO2 added increases, reaching a maximum when the amount of added CO2 is 5%, but when more than 5% is added, the thickness of the compound layer increases. It will remain almost flat. Therefore, the most preferable amount of CO2 added is 5%, but within the range of 0.1 to 10%, the required thickness of the compound layer □ can be obtained.

Further, although the most preferable treatment temperature is 570°C, it has been confirmed that almost the same results as above can be obtained even in the range of 450 to 650°C.

Figure 3 shows X48! of a compound layer of 845C and 5POC that has been subjected to conventional gas nitrocarburizing treatment using ammonia gas and endothermic metamorphic gas. Diffraction Image: FIG. 4 shows the X-ray diffraction image of a compound layer of 8450 and 5PCC subjected to gas nitrocarburizing treatment according to the present invention.

The treatment conditions for the conventional gas nitrocarburizing method are as follows: The mixing ratio of the atmospheric gas is N831X gas = 50:50, and the treatment is performed at a humidity of 570° C. for 2 hours, followed by oil cooling.

The processing conditions for the gas nitrocarburizing method of this invention are as follows: The mixing ratio of atmospheric gas is N2:NH3:D,G, :002 =45:40:1
0:5, treated at a temperature of 570°C for 2 hours, and then cooled in oil.

As is clear from comparing and contrasting Figures 3 and 4, both methods produce ε-Fe2- in both S450,5POO.
s N and T' -Fe4 N were measured to the same extent, and no significant difference was observed between the two methods. Therefore, by performing gas soft nitriding treatment by the method of the present invention, it is superior to the conventional gas soft nitriding method. It can be seen that equivalent carbonitrides are formed.

As is clear from the above description, the present invention is configured to perform gas soft-nitriding treatment by adding carbon dioxide to the gas soft-nitriding atmosphere gas consisting of nitrogen gas, ammonia gas, and organic liquid decomposition gas. Not only does carbon dioxide reduce the hydrogen partial pressure and greatly increase the nitriding rate, making it possible to rapidly shorten the processing time, but it is also reduced to ammonia gas t', allowing the use of cheaper nitrogen gas. Coupled with this, operating costs are significantly reduced.

Furthermore, according to the present invention, a small amount of organic liquid decomposition gas can be used in place of the endothermic metamorphosed gas that has conventionally been used in large amounts as a carbon supply gas. Since the proportion of neutral nitrogen gas is high, there is no risk of gas explosion (highly safe operation is possible).

In addition, in this invention, since the organic liquid decomposition gas causes a carburizing reaction in the treated material in the same manner as conventional endothermic gas, the material itself does not contain carbon.
It is also possible to increase the surface hardness, and it can be used for all types of steel.

Furthermore, this invention eliminates the need for a large endothermic gas conversion furnace as in the conventional gas nitrocarburizing method, which eliminates the trouble of managing the operation of the conversion furnace and allows it to be replaced with a small and inexpensive organic liquid decomposition device. This makes it possible to provide an extremely economical gas soft-nitriding apparatus.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the gas nitrocarburizing furnace used in the method of the present invention, Figure 2 is a chart showing the relationship between the amount of carbon dioxide added and the thickness of the compound layer, and Figure 3 is a diagram showing the relationship between the amount of carbon dioxide added and the thickness of the compound layer formed by the conventional method. Xj diffraction image of the compound layer. FIG. 4 is an X@ diffraction image of the compound layer formed by the method of the present invention. In the figure, 10 is the furnace body, 20 is the gas supply pipe, 21°22.2
5.24 is a gas branch pipe, and 25 is an object to be processed. Patent Applicant Oriental Engineering Co., Ltd. Agent Patent Attorney Tetsuya Mori Patent Attorney Yoshiaki Naito Patent Attorney Masaru Shimizu Patent Attorney Kaji Yama Korejo - ~ #) %S C - ~ ~ ~ i! ! 1 - ~ m fence ■ "

Claims (1)

[Claims] At a temperature range of 450 to 650°C, 0.1 to 10% by volume of carbon dioxide is added to a gas soft nitriding atmosphere consisting of nitrogen gas, ammonia gas, and organic liquid decomposition gas to perform gas soft nitriding treatment on the object to be treated. A gas nitrocarburizing method characterized by: