KR20140005009A - Pressure nitriding heat treatment process - Google Patents

Abstract

The present invention provides a vacuum nitration heat treatment process capable of obtaining effects of reducing costs, gas, and energy with short processes and low processing temperature; enabling nitrification treatment of high quality in a clean process; minimizing deformation of products by nitrifying the products in vacuum in order to maintain the good quality; and being used for various proposes by enabling the products to be widely used.

Description

[0001] The present invention relates to a vacuum nitriding heat treatment process,

The present invention relates to a vacuum nitriding heat treatment method, and more particularly, to a vacuum nitriding heat treatment method which can obtain cost, gas and energy saving effects by a low process temperature and a short process, and can perform a pollution-free cleaning process, a high quality nitriding process, It is intended to provide a vacuum nitriding heat treatment method capable of minimizing deformation of a product and maintaining a good quality, generalizing the application product, enabling multi-purpose use, as well as creating a high added value without requiring post-treatment.

Nitriding is a surface treatment technique in which activated nitrogen is diffused into a steel to obtain a hardened nitrided layer on a steel surface.

When such nitriding is carried out in steel, it is widely used for precision parts, automobile parts, and molds because it can be treated at low temperature below the transformation point, improving wear resistance, fatigue resistance, high temperature strength and corrosion resistance. In addition, nitriding improves the adhesion of the coating layer and is excellent in hardening of the undercoat layer, and thus application to the complex treatment is increasing.

On the other hand, nitriding has a wide range of applied steel in comparison with carburizing, and the treatment temperature is also in the range of 850 to 950 ° C for carburizing, but in the range of 460 to 600 ° C for nitriding, and further heat treatment and post treatment are not necessary. (Including annealing effect)

And the depth of hardening is 0.4 ~ 1.5mm deep in carburizing, but it is characterized by thinness of 0.01 ~ 0.03mm in nitriding. Impact resistance (toughness) is also poor in carburizing but nitriding is common.

Particularly, while the deformation is largely carburized, the nitriding is very small due to the low-temperature process, and the corrosion resistance is the high carbon content in the case of carburizing, which is usually caused by stress corrosion cracking. However, the corrosion resistance is improved by improving the corrosion resistance of the low carbon steel, It is also better than carburizing.

The nitriding is divided into gas nitriding, salt bath nitriding, and ion nitriding. In the case of gas nitriding, however, it is advantageous in that it has high hardness, abrasion resistance, fatigue strength, large capacity and shape restriction. However, it is difficult to control the use of ammonia (toxic gas) And it is necessary to use special steel for long time. The salt bathing is advantageous in that it can be applied in any shape, without short time, resistance to sickness, fatigue strength, rigidity, and facility cost. However, There is a problem that the countermeasure, environmental pollution, the problem of excessive porosity layer in the white layer, and the hardness of the material in the case of repeated nitriding are reduced.

Ion nitration is advantageous in that nitriding is good, process control and phase control are easy, and N ₂ gas is used. However, there is a problem in that it is difficult to nitrify a product (nitriding object) There are disadvantages.

In the conventional method, the product is nitrided by using a nitriding heat treatment furnace, but it is difficult to control the amount of flux in the nitriding process.

In addition, atmospheric nitrification and nitrification of the salt bath can not be neglected, and the diffusion rate of nitrogen into the steel is reduced from 100 times to 10,000 times during the formation of the compound layer. In case of atmospheric pressure nitrification, The gas is used in an amount of about 10,000 liters per hour without consideration.

In addition, the hazardous environment (flame, dust, gas, noise, etc.) generated during the atmospheric pressure metal heat treatment occurred, and there were risk factors such as fire and talent when using oil and salt bath.

Korean Patent Publication No. 10-2011-0126229 Korean Patent Publication No. 10-2002-0088935

Therefore, the vacuum nitriding heat treatment method provided by the present invention can replace carburization at a low process temperature and a short process time, thereby reducing the process cost, gas and energy.

In addition, it is intended to provide a vacuum nitriding heat treatment method which minimizes the use of ammonia gas and which is made of a pollution-free cleaning process.

In the vacuum nitridation heat treatment method provided in the present invention, a product to be subjected to nitridation heat treatment is introduced into a heater chamber of a heat treatment furnace, and then a gas inside the heat treatment furnace is discharged to the outside to form a vacuum atmosphere in a medium vacuum state.

Forming a vacuum atmosphere of a medium vacuum in the inside of the heat treatment furnace so as to have a pressure higher than atmospheric pressure by injecting nitrogen gas;

Operating the heater in the heater chamber to open and close the vent while keeping the internal temperature at a constant pressure;

Exhausting and reducing the nitrogen gas in the heat treatment furnace to form a medium vacuum environment;

An oxidation process in which nitrous oxide gas is introduced into the formed vacuum environment to raise the internal pressure to create a low vacuum environment and the heater is operated to warm the interior;

A reducing step of evacuating nitrous gas (N ₂ O), decompressing the internal pressure to create a medium vacuum environment, adding ammonia gas (NH ₃ ) to the formed vacuum environment, boosting the pressure, and heating in a low vacuum environment;

A nitriding step of continuously injecting ammonia gas and nitrous oxide gas into the heater chamber and mixing them in the heater chamber and adjusting a pressure inside the heater chamber to a predetermined pressure to form a nitride layer having a predetermined thickness on the product;

Exhausting and reducing the mixed ammonia gas and nitrous oxide gas in the heater chamber to form a medium vacuum environment;

A step of injecting nitrogen gas in a medium vacuum environment to increase pressure and cooling, and then evacuating nitrogen gas to the atmosphere and withdrawing the product.

The vacuum nitriding heat treatment method provided in the present invention is capable of adjusting the phase control and surface quality by adjusting the amount of flux in a vacuum of 100 to 300 torr under a vacuum atmosphere and performing nitriding in a vacuum atmosphere, , It is possible to shorten the process to 60 ~ 70% level compared with the conventional process, and it is possible to nitrificate the gas to a level about 1/10 of that of the conventional process, and to perform a nitriding heat treatment requiring no post- You can.

Fig. 1 is a view showing an example of a heat treatment furnace for realizing the present invention
Fig. 2 is an operational example of Fig. 1
FIG. 3 is a graph showing the state and temperature range of each step in the vacuum nitridation heat treatment process provided by the present invention

The vacuum nitriding heat treatment method provided in the present invention is characterized in that the product can control the phase and the surface quality by controlling the flux amount in a vacuum of 100 to 300 torr in a vacuum atmosphere.

Further, according to the present invention, it is possible to shorten the process to a level of 60 ~ 70% compared to the conventional nitriding by performing nitriding in a vacuum atmosphere, and the gas consumption can be reduced to 1/10 level compared with the conventional nitriding process. Thereby providing an unnecessary nitriding heat treatment furnace.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In order to explain the vacuum nitriding heat treatment method of the present invention, a description will be given of the steps after the description of the constitution of the heat treatment furnace body 10 for carrying out the above process.

A vacuum heater chamber 20 is provided inside the heat treatment furnace body 10 so as to be openable and closable by the front and rear door openings 30 and 40. The heater chamber 20 is provided with a heater 21) to heat the product (400).

A vent 50 connected to a vacuum pump (not shown) is installed on one side of the heat treatment furnace 10 so that the inside of the heat treatment furnace 10 can be formed in a vacuum atmosphere.

A gas inlet pipe 60 for introducing nitrous oxide (N ₂ O) and ammonia (NH ₃ ) is installed in the working gas introduced into the heater chamber 20, and the gas inlet pipe 60 is made of nitrous oxide (N ₂ O) and ammonia (NH ₃ ) separately.

A nitrogen gas inlet pipe 70 for introducing nitrogen (N ₂ ) gas for nitriding the product is formed in the heat treatment furnace body 10.

The front and rear doors (3) and (40) are opened and closed by the open / close cylinders (31) and (41), respectively.

The rear opening and closing door 40 is provided with a convection turbine 80 for smoothly causing the gas in the heater chamber 20 to be convectively operated and the gas is introduced into the heat treatment furnace body 10 by the convection turbine 80, A fan 81 capable of circulating therein is installed so as to be located inside the heater chamber 20.

A cooling chamber 90 for cooling the convection turbine 80 with cooling water is formed outside the convection turbine 80.

The convection turbine 80 is fixed to the rear opening and closing door 40 so that the opening and closing door 40 is angularly moved by the opening and closing cylinder 41. When the opening and closing door 40 is opened and closed, The cooling water supply pipe 100 for supplying the cooling water to the heat treatment furnace main body 10 is inclined to one side of the upper part of the heat treatment furnace body 10 so that the expansion and contraction is performed to maintain airtightness between the cooling water supply pipe 100 and the heat treatment furnace body 10. [ A free bending tube 200 constructed of a bellows type using a possible material is installed by flange jointing.

The cooling water supply pipe 100 is also formed as a double pipe so that cooling water for cooling the convection turbine 80 can be supplied and discharged.

The vacuum nitridation heat treatment method of the present invention using the vacuum nitridation heat treatment furnace having the above-described structure is subjected to heat treatment through the following procedure, which will be described in detail below.

The product 400 to be subjected to the nitriding heat treatment is operated by opening and closing the cylinder 31 of the front door 30 and then the product 400 is inserted into the heater chamber 20 and then the door 30 is closed .

A vacuum pump (not shown) is operated to discharge the gas inside the heat treatment furnace 10 to the outside through the vent 50, thereby creating a vacuum atmosphere in a medium vacuum state.

When the inside of the heat treatment furnace body 10 is evacuated to a vacuum atmosphere of a medium vacuum, nitrogen gas is introduced through a nitrogen gas inlet pipe 70 so as to have a pressure of atmospheric pressure (765 torr) or more.

When the pressure of the heat treatment furnace 10 is increased while the internal temperature is increased by operating the heater 21 in the heater chamber 20, the vent 50 is opened to exhaust the exhaust gas until a desired pressure is reached, So as to adjust the internal pressure of the heater chamber 20 to the set pressure.

A nitrogen gas is exhausted through a vent 50 to reduce the pressure to create a medium vacuum environment. Subsequently, nitrous oxide gas is introduced through the gas inlet pipe 60 to increase the pressure inside the heater chamber 20, A vacuum environment is established and the heater 21 is operated to warm the inside.

After the oxidation process is finished, nitrous oxide gas (N ₂ O) is exhausted through the vent 50 for the next reduction process, and the inner pressure is reduced to form a medium vacuum environment composition. Ammonia gas (NH ₃ ) is introduced and pressurized to perform heating in a low vacuum environment.

Ammonia gas and nitrous oxide gas are continuously and simultaneously injected through the gas inlet pipe 60 for the next nitriding process (so-called soaking) so as to be mixed with each other in the heater chamber 20.

When the pressure inside the heater chamber 20 becomes equal to or higher than a predetermined pressure, the vent is exhausted through the vent 50. When the pressure inside the heater chamber 20 becomes a desired pressure, the vent 50 is closed to adjust the pressure to be maintained. If the predetermined period of time is continued under such conditions, a nitrided layer having a predetermined thickness is formed on the product 400.

When the nitriding process is completed, ammonia gas and nitrous oxide gas mixed in the heater chamber 20 are exhausted through the vent 50, and the pressure is reduced to form a medium vacuum environment.

Nitrogen gas is introduced through a nitrogen gas inlet pipe 70 in a vacuum environment to cool down while the pressure is increased. After completion of the cooling, nitrogen gas is exhausted to the atmosphere through the vent 50 and then the door 30 is opened, (400).

Although the heating operation of the heater 21 has been described step by step in the above description of the process, if the pressure inside the heater chamber 20 is equal to or more than a predetermined pressure (200 torr) And the temperature and time are shown in detail in the graph of Fig.

In the heat treatment main body furnace 10 for performing the vacuum nitridation heat treatment process of the present invention, the fan 81 rotationally driven by the convection turbine 80 causes the reaction gas supplied into the heater chamber 20 to flow into the product 400 And when the rear opening / closing door 40 is opened, the reaction gas is discharged from the inside of the heater chamber 20, thereby cooling the inside of the heater chamber 20 .

When the reaction gas in the heater chamber 20 is exhausted to the outside of the heater chamber 20 due to the opening of the front and rear doors 30 and 40 in the heater chamber 20, Heat exchange is performed between the reaction gas and the reaction gas.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. That is, those skilled in the art will appreciate that many modifications and variations can be made in the present invention without departing from the spirit or scope of the appended claims. Accordingly, all such appropriate changes and modifications and equivalents may be resorted to, falling within the scope of the invention.

1: heat treatment furnace body 20: heater chamber
21: heater 22: electrode
30, 40: opening / closing door 31, 41: opening / closing cylinder
50: vent 60: gas inlet pipe
70: nitrogen gas inlet pipe 80: convection turbine
81: Fan 90: Cooling chamber
100: Cooling water supply pipe 200: Free bending pipe
300: heat exchanger 400: product

Claims (1)

A step of introducing a product to be subjected to nitriding heat treatment into a heater chamber of a heat treatment furnace and discharging the gas inside the heat treatment furnace to the outside to thereby form a vacuum atmosphere in a medium vacuum state;
Forming a vacuum atmosphere of a medium vacuum in the inside of the heat treatment furnace so as to have a pressure higher than atmospheric pressure by injecting nitrogen gas;
Operating the heater in the heater chamber to open and close the vent while keeping the internal temperature at a constant pressure;
Exhausting and reducing the nitrogen gas in the heat treatment furnace to form a medium vacuum environment;
An oxidation process in which nitrous oxide gas is introduced into the formed vacuum environment to raise the internal pressure to create a low vacuum environment and the heater is operated to warm the interior;
A reducing step of evacuating nitrous gas (N ₂ O), decompressing the internal pressure to create a medium vacuum environment, adding ammonia gas (NH ₃ ) to the formed vacuum environment, boosting the pressure, and heating in a low vacuum environment;
A nitriding step of continuously injecting ammonia gas and nitrous oxide gas into the heater chamber and mixing them in the heater chamber and adjusting a pressure inside the heater chamber to a predetermined pressure to form a nitride layer having a predetermined thickness on the product;
Exhausting and reducing the mixed ammonia gas and nitrous oxide gas in the heater chamber to form a medium vacuum environment;
A step of injecting nitrogen gas in a medium vacuum environment to increase pressure and cooling, and then exhausting nitrogen gas to the atmosphere and withdrawing the product.

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