JPS5928566A - Gas soft nitriding method - Google Patents

Abstract

PURPOSE:To make a surface finish skin brilliant and to uniformize the thickness of a formed compound layer, by a method wherein a gas having a dew point lower than the surface temp. of an object to be treated is introduced into the front chamber of a gas soft nitriding furnace and, thereafter, the object to be treated is conveyed into said front chamber. CONSTITUTION:N2 gas is introduced into the front chamber 10 of a batch type gas soft nitriding furnace for 5-15min from an introducing pipe 10 prior to conveying an object to be treated into said front chamber 10. After the flow amount of the introduced N2 gas is appropriately regulated to make the dew point of the atmospheric gas in the front chamber 10 lower than the surface temp. of the object to be treated, the object to be treated is conveyed into the front chamber 10. When the atmospheric gas in the front chamber 10 becomes stable, the object to be treated is sent to a heating chamber 12 and the introduction of the N2 gas into the front chamber 10 is stopped. Succeedingly, the gas soft nitriding treatment of the object to be treated is performed and the treated one is conveyed to the front chamber 10 after treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas soft nitriding method, and in particular, the present invention relates to a gas soft nitriding method. By introducing this, it is possible to obtain an article with a good finished surface and a uniform compound layer thickness and surface hardness.

Conventionally, in the gas soft-nitriding method, ammonia gas and endothermic modified gas, ammonia gas and exothermic modified gas, organic liquid decomposition gas and an atmosphere gas mainly composed of ammonia gas, etc. have been used. Also in the nitriding method, the dew point temperature of the atmospheric gas in the front chamber is about 10 to 35° C., and the atmospheric gas is transported into the front chamber.

The temperature is higher than the surface temperature of the processed object. When a workpiece at room temperature is brought into the front chamber under such conditions, moisture in the atmospheric gas in the front chamber condenses on the surface of the workpiece, forming water droplets, and the ammonia in the atmospheric gas is dissolved in these water droplets. Ammonia water is produced, and a mottled pattern corroded by the ammonia water appears on the surface of the object to be treated. In addition, carbon monoxide GO in the atmospheric gas is CO
→Since carbon C is precipitated by the reaction of C+CO2, this precipitated carbon C adheres to water droplets on the surface of the object to be treated.

In the conventional method, the object to be treated as described above is sent to a heating chamber for gas nitrocarburizing treatment, which not only deteriorates the surface finish of the treated object but also causes problems such as the formation of problems on the surface of the object. This results in variations in the thickness and surface hardness of the compound layer.

Therefore, in order to prevent water droplets from forming on the surface of the object to be treated in the front chamber, the object to be treated is preheated and carried into the front chamber, and then
A method of performing gas nitrocarburizing treatment in a heating chamber has also been adopted, but this method requires a preheating chamber in addition to the gas nitrocarburizing furnace itself, resulting in large equipment and high equipment costs. Not only is it expensive, but it also has the drawback that a preheating step is added to the original gas nitrocarburizing step, which lengthens the overall processing time.

This invention was made to eliminate the above-mentioned drawbacks, and an object of the invention is to provide a gas nitrocarburizing method in which the dew point temperature of the atmospheric gas in the front chamber is lowered than the surface temperature of the workpiece. It is also an object of the present invention to provide a gas nitrocarburizing method capable of making the finished surface of the treated article bright and uniform in the thickness and hardness of the surface compound layer. A further object of the present invention is to provide a gas nitrocarburizing method with low equipment costs and simple processing steps.

That is, in the present invention, as shown in the illustrated embodiment, when a workpiece is sent to the heating chamber 12 through the front chamber 10 of a gas soft-nitriding furnace and subjected to gas soft-nitriding treatment, the surface temperature of the workpiece is lower than the surface temperature of the workpiece. Also, a gas with a low dew point temperature is introduced into the front chamber 10, and the front chamber 1
The present invention relates to a gas nitrocarburizing method characterized in that the workpiece is carried into the front chamber 10 after the dew point temperature of the atmospheric gas in the room 0 becomes lower than the surface temperature of the workpiece.

In this invention, when a workpiece such as a steel part is gas soft-nitrided using a gas soft-nitriding furnace having a front chamber, the surface temperature of the workpiece is After the dew point temperature of the mixed gas with the atmospheric gas flowing out from the heating chamber into the front chamber falls below the surface temperature of the workpiece, the workpiece is brought into the front chamber. Bring it into the room. Any type of gas can be used as the gas introduced into the front chamber as long as it has a dew point temperature lower than the surface temperature of the object to be treated, but oxidizing gases are used for the purpose of brightening the object to be treated. Explosive gas, combustible gas, and toxic gas are also not suitable from a safety standpoint. Nitrogen gas is the most preferable gas if selected from gases that are both highly safe and economically inexpensive. , carbon dioxide, argon, etc. can also be used as necessary. It is preferable to use gases whose dew point temperature is sufficiently lower than the surface temperature of the object to be treated. for example,
The dew point temperature of commercially available nitrogen gas in cylinders is about -50°C, and the dew point temperature of liquid nitrogen in cylinders is about -80°C, so they can be used as they are.

In addition, the flow rate or introduction time of the gas introduced into the front chamber is
In the above-mentioned cylinder nitrogen gas field 9, it is sufficient to continue for about 5 to 15 minutes, and at an appropriate point during that time, the object to be treated is carried into the front chamber, and the atmosphere in the front chamber is waited until the atmospheric gas is stabilized. After sending the object to be processed into the heating chamber, the introduction of nitrogen gas is stopped.

In this way, when the workpiece is carried into the front chamber, the dew point temperature of the atmospheric gas in the front chamber is maintained at a level lower than the surface temperature of the workpiece. Even if atmospheric gas comes into contact with the surface of the treated object, no water droplets will be generated.

Next, a description will be given of the steps when the method of the present invention is applied to the Nototsuchi type gas nitrocarburizing furnace shown in FIG. In the same figure, reference numeral 10 indicates a front chamber, 12 a heating chamber, and 14 an oil tank.The front wall of the front chamber 10 has an entrance door 15, and the partition wall between the front chamber 10 and the heating chamber 12 has an intermediate door 16. Each of these can be opened and closed freely. Further, the front chamber 10 is provided with a nitrogen gas introduction pipe 20, and the heating chamber 12 is provided with an atmospheric gas supply pipe (not shown). A stirring fan 21 is installed in the upper part of the heating chamber 12, and this fan 21 is rotated by a motor 22 installed outside the earthen wall of the heating chamber 12.
The atmospheric gas in the heating chamber 12 is stirred. Still oil tank 14
is provided with a stirring blade 26 which is rotated by a motor 25, and stirs the cooling oil stored in the oil tank 14 via the stirring blade 26.

It is connected to the nitrogen gas introduction pipe 20 of the front chamber 10 for about 5 to 15 minutes before the workpiece (not shown) is brought into the front chamber 10 of the above-mentioned Tsuchi type gas nitrocarburizing furnace. Introduce nitrogen gas from the nitrogen gas cylinder.

After the flow rate of the introduced nitrogen gas is adjusted appropriately so that the dew point temperature of the atmospheric gas in the front chamber 1° is lower than the surface temperature of the workpiece, the workpiece is carried into the front chamber 10. Thus,
After the atmospheric gas in the front chamber 10 becomes stable, the object to be processed is sent to the heating chamber 12, and then the introduction of nitrogen gas into the front chamber 10 is stopped. Next, the object to be treated is subjected to gas nitrocarburizing treatment in the heating chamber 12, and the treated article is returned to the heating chamber 12.
from there to the front room 10. Among the items processed in the heating chamber 12, the items to be gas-cooled are gas-cooled in the front chamber 10, while the items to be oil-cooled are cooled in the oil tank 1 immediately after being carried out to the front chamber 10.
Immerse it in the cooling oil of Step 4 to cool it.

When cooling the article, nitrogen gas may be reintroduced into the front chamber 10 to prevent air from being drawn into the front chamber 10 and to increase the cooling rate when cooling with gas. The cooled articles are transported from the front chamber 10 to the outside of the furnace.

FIG. 2 shows the case where the method of the present invention is applied to a continuous gas nitrocarburizing furnace.
18 is a heating chamber, 18 is a rear chamber, and 14 is an oil tank. The front wall of the front chamber 10 has an entrance door 15, a partition wall between the front chamber 10 and the heating chamber 12, and a partition between the heating chamber 12 and the rear chamber 18. On the wall,
An exit door 19 is provided on the rear wall of the intermediate doors 16 and 17 and the rear chamber 18, respectively, so as to be openable and closable. Reference numeral 20 denotes a nitrogen gas introduction pipe for the front chamber 10; 26, a rear chamber 18;
21 is a stirring fan for the heating chamber 12, 22 is a stirring fan motor, 26 is a stirring blade for the oil tank 14, and 25 is a stirring blade motor.

In the process in the continuous gas soft-nitriding furnace described above, as in the case of the patch-type gas soft-nitriding furnace, before carrying the workpiece into the front chamber 10, nitrogen is introduced into the front chamber 10 from the nitrogen gas introduction pipe 20. After introducing gas to lower the dew point temperature of the atmospheric gas in the front chamber 10 below the surface temperature of the workpiece, the workpiece is carried into the front chamber 101;'f, and the atmospheric gas in the front chamber 10 is After the temperature becomes stable, the object to be processed is sent to the heating chamber 12, and then the introduction of nitrogen gas is stopped. The workpiece sent to the heating chamber 12 is subjected to gas nitrocarburizing treatment, and after the treatment is completed, the workpiece is carried out to the rear chamber 18 where it is cooled with gas or transferred from the rear chamber 18 to the oil tank 14. It is cooled by being immersed in cooling oil. During this cooling, nitrogen gas is introduced into the rear chamber 18 via the nitrogen gas inlet pipe 23 to prevent air from being sucked into the rear chamber 18 and to increase the cooling rate when performing gas cooling. You can also do it like this. The cooled articles are transported out of the furnace from the rear chamber 18.

Table 1 shows the results of tests conducted to compare the surface finish, the thickness of the compound layer formed on the surface, and the surface hardness of articles treated by the method of the present invention and articles treated by the conventional method. It is.

A patch type gas nitrocarburizing furnace was used for the test, and S P C
The test was carried out on objects to be treated made of C and 8450 materials. The gas introduced into the front chamber was commercially available nitrogen gas in a cylinder, and the atmospheric gas in the heating furnace was a mixed gas of 70% ammonia gas and 30% organic liquid decomposition gas, and after treatment at a treatment temperature of 570°C for 2 hours. , oil cooled.

Table 1 As is clear from the results in Table 1, the products treated by the method of the present invention not only have a brighter surface finish, but also have a lower compound layer on the surface than products treated by the conventional method. It can be seen that the thickness of the layer becomes thicker, the surface hardness becomes harder, and a uniform surface layer is obtained with less variation.

As explained above, the present invention introduces a gas whose dew point temperature is lower than the surface temperature of the workpiece into the front chamber of a gas nitrocarburizing furnace to increase the dew point temperature of the atmospheric gas in the front chamber. Since the workpiece is brought into the front chamber after the temperature has been lowered below the surface temperature of the workpiece, gas nitrocarburizing can be carried out in the heating chamber without generating water droplets on the surface of the workpiece carried into the front chamber. It becomes possible to do this. Therefore, according to the present invention, since ammonia does not dissolve into water droplets and precipitated carbon does not adhere to water droplets as in the conventional case, the surface finish can be improved.
Not only can the skin be made to shine, but the thickness of the compound layer formed on the surface is uniform, and the variation in surface hardness is also small. You can get high quality products.

J: Well, with this invention, not only can it be carried out with very little equipment cost without adding large equipment to the conventional gas nitrocarburizing furnace, but the treatment process is also simple.
Processing can be done in a short time.

[Brief explanation of the drawing]

FIG. 1 is a vertical side view of a patch-type gas soft-nitriding furnace used in the method of the present invention, and FIG. 2 is a vertical side view of a continuous-type gas soft-nitriding furnace used in the method of the present invention. In the diagram, 10 is the front chamber, 12 is the heating chamber, and 20 is the nitrogen patent applicant, Oriental Engineering Co., Ltd., agent, patent attorney Nana Mori, and patent attorney Naito.
Yoshiaki, Patent Attorney, Shimizu, Patent Attorney, Sen Kajiyama, Kore

Claims (1)

[Claims] When performing gas soft nitriding treatment on the workpiece sent to the heating chamber via the front chamber of the gas soft-nitriding furnace, a gas with a dew point temperature lower than the surface temperature of the workpiece is introduced into the front chamber, and the temperature inside the front chamber is A gas nitrocarburizing method characterized by carrying the workpiece into a front chamber after the dew point temperature of the atmospheric gas has fallen below the surface temperature of the workpiece.