KR101959985B1 - Method of heat treatment of metal parts - Google Patents

Abstract

The present invention relates to a gas carburization heat treatment method of a metal part, capable of securing desired hardness and carburization depth in both of a tooth end portion and a tooth root portion of a gear. To this end, according to the present invention, the gas carburization heat treatment method of a metal part comprises a workpiece charging step, first and second heating steps, a gas injection step, a pressurizing step, a carburization and diffusion step, a temperature decreasing step, a carburization quenching step, an oil quenching step, an annealing step, and a workpiece discharging step.

Description

METHOD OF HEAT TREATMENT OF METAL PARTS [0002]

The present invention relates to a method of heat treating a metal part gas carburization. More specifically, in the carburizing and spreading step, the air circulating pen is stopped to increase the pressure inside the carburizing furnace, and the carburizing operation is carried out by using the pressure inside the carburizing furnace and the radiant heat, And to a method of heat-treating a metal part gas carburizing method capable of securing the depth of carburization.

One of the great contributions to the development of human civilization is the discovery of metals and their use as diverse tools.

Therefore, all mankind developed and developed the technique of handling iron, the most important of which is the heat treatment process which deals with the properties of iron.

In the case of steels, which are widely used as mechanical materials, the chemical composition of the steel or the amount of alloying elements contained in the steel does not change during the steelmaking process. Therefore, when manufacturing a machine or a part, One of them is surface hardening which hardens the surface of the material (SURFACE HARDENING).

The most commonly used methods for surface hardening are carburizing, nitriding, high frequency quenching, flame quenching, discharge hardening, or metal infiltration. However, the most commonly used methods are those having a high thermal efficiency and simple process, Gas carburization, which permeates carbon, is often used.

Conventionally, the carburizing heat treatment is carried out to increase the surface hardness and to withstand a large impact and abrasion resistance. However, since the life of automobiles and machinery is prolonged due to the development of technology, the life of the parts used here is not supported, Which is a cause of deterioration in quality and durability.

Particularly, the conventional heat treatment facility causes the convection to occur in one direction by using the pen provided in the carburizing furnace, so that the depth of the surface portion is effective, but the depth of the hardening is remarkable Resulting in poor quality and durability of parts.

In addition, when it is sensitive to the shape change of the material or requires high precision, the material can be processed through general-purpose pressing and can not be subjected to heat treatment. By performing wire cutting or fine flanking requiring high processing cost, And the external competitiveness is weakened.

In the case of materials that are stressed and stressed, they can not be produced because of the deterioration of the domestic technology level, and they are used for importing from abroad. This leads to unnecessary waste of foreign currency and hinders technological development. It is true.

Prior Art Document: KR Patent Registration No. 10-0628998 (issued on September 27, 2006)

SUMMARY OF THE INVENTION The present invention has been conceived to solve the problems as described above. In the case where the temperature of the carbur furnace is lower than 700 캜, the role of the pen due to convection is important. However, when the temperature of the carburizing furnace is higher than 850 캜, It is effective to heat by radiant heat. Therefore, when the temperature is higher than 850 ℃, it does not operate the pen for air circulation but carburizes the gas by using the pressure inside the carbur furnace and radiant heat. It is possible to secure the desired hardness and the depth of the carburized layer, thereby solving the cause of the crack formation at the end portion of the root portion of the gear and the reduction in the life time due to the lowering of the hardening depth.

In order to accomplish the above object, the present invention provides a method of heat-treating a metal part gas carburizing method, comprising: opening a carburizing furnace opening / closing device; driving the transferring device to put the material into a carburizing furnace; closing the carburizing furnace opening / Charging the object to be treated with gas; A first temperature raising step of raising the temperature of the carburizing furnace to a preheating temperature by operating a pen for air circulation to the carburizing furnace; A preheating step of keeping the temperature at the preheating temperature for a predetermined time while keeping the object to be treated at a uniform temperature; A second heating step of raising the temperature of the carburizing furnace from the preheating temperature to the carburizing temperature; A step of stopping the air circulation pen and raising a pressure inside the carbur furnace to a target pressure; A carburizing and spreading step of maintaining the pressure of the carburizing furnace at the target pressure and carburizing and diffusing the object to be treated for a predetermined time by the pressure and radiant heat inside the carburizing furnace; A temperature lowering step of operating the air circulating pen to lower the temperature of the carburizing furnace to the carburizing temperature; A carburizing and quenching step of cooling the object to be treated while maintaining the temperature at a carburization quenching temperature for a predetermined time; An oil finishing step of opening the carburizing furnace opening / closing device and cooling the cooling channel by injecting the object to be treated into the oil bath; A tempering step of heating the object to be processed to a tempering temperature and maintaining the temperature for a certain period of time for tempering; And moving the object to be processed to the outside by driving the transfer device.

In addition, a liquid to be used as a carrier gas is charged into the carburizing furnace in the step of charging the object to be processed; Reducing the internal temperature of the carburizing furnace from the second heating step to the carburizing temperature and then using the gas to be used as the carburizing gas; And carburizing and diffusing the gas generated by the decomposition of the two liquids in the carburizing furnace in the carburizing and spreading step into the object to be treated.

In addition, the gas pipe inside the carburizing furnace is composed of several gas pipes of different lengths, and each of the gas pipes is disposed in the upper part of the carburizing furnace, the material loading tray located in the middle part, And further connected to the object to be processed stacked in the depth direction of the carburizing furnace including the tray.

According to the present invention, the inner pressure is increased by keeping the air circulating pen stationary, so that the inner pressure can be maintained, and the depth of the carburizing layer to the end surface and the root portion of the gear can be made 70% or more of the carburized layer depth of the surface portion There is an effect of improving the carburization efficiency of the article to be treated by solving the cause of the shortening of the life due to crack formation and depth reduction in the root portion.

1 is a view showing a conventional carburizing furnace,
2 is a view showing a carburizing furnace according to a preferred embodiment of the present invention,
FIG. 3 is a graph showing the temperature and the process inside the carburizing furnace within the hour,
4 is a graph showing the hardness of the end surface of the material according to the depth after the carburization process according to the preferred embodiment of the present invention,
5 is a graph showing the hardness of the tip of the material according to the depth after the carburization process according to the preferred embodiment of the present invention,
6 is a graph showing the hardness of the root of the material according to the depth after the carburization process according to the preferred embodiment of the present invention,
FIG. 7 is a photograph showing a carburized structure of the end face of the material after the carburization process according to a preferred embodiment of the present invention,
FIG. 8 is a photograph showing a 200-fold magnification of the carburized structure at the tip of the material after the carburization process according to the preferred embodiment of the present invention,
FIG. 9 is a photograph showing a carburized structure of the root of a material after the carburization process according to a preferred embodiment of the present invention, magnified 200 times. FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to designate the same or similar components throughout the drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. In addition, the preferred embodiments of the present invention will be described below, but it is needless to say that the technical idea of the present invention is not limited thereto and can be variously modified by those skilled in the art.

FIG. 1 is a view showing a conventional carbur furnace, FIG. 2 is a view showing a carburizing furnace according to a preferred embodiment of the present invention, FIG. 3 is a graph showing a temperature and a process inside the carburizing furnace per hour, FIG. 5 is a graph showing the hardness of the tip of the material according to the depth, FIG. 6 is a graph showing the hardness of the root of the material according to the depth, and FIG. Fig. 7 is a photograph showing the carburized structure of the end face of the material at 200 times magnification, Fig. 8 is a photograph showing the carburized structure of the tip of the material at 200 times magnification, It is a picture of a shipyard.

The metal part gas carburizing heat treatment method according to the preferred embodiment of the present invention is characterized in that the metal part gas carburization heat treatment method comprises the steps of charging the object to be processed (a), first heating step (b), preheating step (c), second heating step (I), the tempering step (j), and the step of introducing the object to be treated (k), including the step (e), the carburizing and diffusion step (f) .

Hereinafter, a method for heat-treating a metal part gas carburization according to a preferred embodiment of the present invention will be described in detail.

When the power is applied to the heating element 300 in the step (a) of charging the object to be processed and the internal temperature of the carpet of the PIT TYPE is heated up to 650 DEG C, the object to be processed is placed in the object receiving tray 400 And the carburizing and opening apparatus 600 is opened.

After the opening / closing device 600 is opened, the transfer device is driven to put the material to be treated 400 on the loading tray 400 into the carburizing furnace, close the carburizing furnace opening / closing device 600, Is injected.

In the first heating step (b), the air circulating pen 100 for the carburizing furnace is operated, and the temperature of the carburizing furnace is raised to 850 占 폚, which is the preheating temperature, by convection heat generated by air convection generated by the pen.

In the preheating step (c), the preheating temperature of 850 ° C is maintained and the time of 20 to 30 minutes per inch is maintained according to the thickness of the material to be treated. The C.P. (Carbon Potential) at this time is set to 0.5%. The preheating step (S3) is intended to transfer sufficient heat to the interior of the article to be uniformed in temperature on the surface and inside. In the preheating step S3, the operation of the air circulation pen 100 is maintained.

In the second heating step (d), the temperature of the carburizing furnace is raised from 850 占 폚, which is the preheat temperature, to the carburizing temperature of 900 占 폚 to 950 占 폚, while the operation of the air circulating pen 100 is maintained.

When the temperature inside the carburizing furnace reaches the carburizing temperature of 900 to 950 占 폚, the carbon potential (CP) is set to 1.05%, the carburizing gas valve 200 is opened, and the carburizing gas is introduced into the carburizing chamber 400).

In the pressure increasing step (e), the operation of the operating air circulating pen 100 is stopped and the pressure inside the carburizing furnace is raised to + 3 mbar. A pressure gauge 500 is installed on the upper part of the carburizing furnace to increase and maintain the pressure while checking the pressure inside the carburizing furnace.

If the inside temperature of the carburizing furnace is less than 700 ℃, heating by convection heat due to air convection generated by the pen is effective. However, if the temperature is over 850 ℃, heating by radiant heat is more effective than heating by convection heat. And heating is performed by radiant heat.

In the carburizing and spreading step (f), the pressure in the carburizing furnace is maintained at + 3 mbar and the pressure and radiant heat inside the carburizing furnace are treated for 35 hours to form a sufficient carburizing layer thickness without operating the air circulating pen 100 Water is carburized by setting CP (Carbon Potential) to 1.05%, and water is diffused by setting CP (Carbon Potential) to 0.85% for 30 hours to diffuse the carburized carbon.

In the cooling step (g), the air circulating pen is operated again and the temperature of the carburizing furnace is lowered to the carburization quenching temperature of 800 ° C to 850 ° C.

In the carburizing and finishing step (h), the object to be processed is cooled while maintaining the carburization quenching temperature for 10 minutes per 1 inch depending on the thickness of the material to be processed at a temperature of 800 to 850 ° C. C.P. (Carbon Potential) at this time is controlled to 0.85%.

In the oil finishing step (i), the carburizing furnace opening / closing device 600 is opened to lower the internal temperature of the carburizing furnace, and the object to be treated is charged into the oil bath to cool the cooling channel. The temperature of the cooling oil is 50 to 60 ° C. The quenching time is 5 minutes per inch, depending on the thickness of the material to be treated. The hardness of the material to be treated is measured before completing the oil ingressing step (i) and before entering the tempering step (j), where the standard hardness is HRC 58 to 62.

In the tempering step (j), the workpiece is heated again to the tempering temperature of 250 to 300 DEG C, and the temperature is maintained for the tempering time. The tempering time is maintained at a tempering temperature of 250 ° C to 300 ° C for 1 hour per inch, depending on the size of the material to be treated, followed by cooling.

In the object-to-be-processed step (k), the object to be carburized is moved to the outside by driving the transfer device.

When the air circulation pen 100 is operated, the article to be processed is heated by the convection heat due to air circulation by the pen 100, and when the air circulation pen 100 is not operated, The carburizing operation of the object to be processed proceeds.

In addition, carburization of the object to be treated can be carried out by the enemy stock carburizing method.

That is, in the metal part gas carburizing heat treatment method, when the inside of the carburizing furnace is heated up to 650 ° C in the step (k) for charging the object to be treated, a liquid to be used as a carrier gas including methanol is introduced into the carburizing furnace,

In the second heating step (d), when the temperature inside the carburizing furnace is heated to the carburizing temperature of 900 ° C. to 950 ° C., the liquid to be used as carburizing gas including isopropanol, ethyl acetate, propane and paraffin is passed through the gas pipe Reduce,

In the carburization and diffusion step (f), the liquid to be used as the carrier gas and the liquid to be used as the carburizing gas in the carburizing furnace are in a gaseous state by pyrolysis, and the object to be processed is carburized and diffused by the gas generated by pyrolysis do.

The carburizing furnace includes a to-be-treated water receiving tray 400a disposed at an upper portion inside the carburizing furnace, a to-be-treated water receiving tray 400b located at the middle portion, and a to-be- The support trays may be laminated in multiple layers in the depth direction of the carburizing furnace, so that the to-be-processed articles requiring the carburizing operation can be efficiently loaded using the to-be-treated support trays.

The gas pipe 200 inside the carburizing furnace is made up of several gas pipes of different lengths, and each gas pipe is connected to the target-material receiving tray 400a located at the upper portion of the carburizing furnace, the material receiving tray 400b located at the middle portion, And is connected to a distance close to the material receiving tray including the material receiving tray 400c located at the lower part. When the gas is injected into the carburizing furnace, the distance from the material receiving tray to the material receiving tray The carburizing gas can be injected and the carburizing operation can be performed more effectively on the object to be treated.

Table 1 shows the depths of the effective hardened layer according to the depth of carburization in the surface hardening of metal parts according to the method of heat treating the metal part gas according to the preferred embodiment of the present invention.

Referring to Table 1, when a carburizing operation is performed according to the method for heat-treating a metal part gas according to the preferred embodiment of the present invention, the depth of the effective hardening layer of not less than 70% .

Carburizing depth Effective hardened layer depth This end End Root 1.2 1.4 1.2 1.15 2 2.3 2.08 1.85 2.5 2.8 2.6 2.1 3 3.3 3.2 2.74 3.5 3.8 3.6 3.2 5 5.6 5.2 4.95

Unit: mm

It will be apparent to those skilled in the art that various modifications, substitutions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. will be. Therefore, the embodiments disclosed in the present invention and the accompanying drawings are intended to illustrate and not to limit the technical spirit of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments and the accompanying drawings . The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

100 - Air circulation pen 200 - Gas pipe
300 - Heating element 400a - Upper material receiving tray
400b - Middle part untreated water receiving tray 400c - Lower untreated water receiving tray
500 - Pressure gauge 600 - Switchgear
700 - Temperature sensor

Claims (3)

(a) charging the object to be treated by opening the carburizing furnace opening and closing the carburizing furnace opening / closing device after driving the transferring device into the carburizing furnace;
(b) a first step of raising the temperature of the carbur furnace to the pre-heating temperature by operating the air circulating pen for the carburizing furnace;
(c) a preheating step of maintaining the temperature of the preheating temperature for a predetermined time while maintaining the operation of the air circulating pen so that the object to be processed has a uniform temperature;
(d) a second heating step of raising the temperature of the carburizing furnace from the preheating temperature to the carburizing temperature while maintaining the operation of the air circulating pen;
(e) stopping the air circulation pen and raising the pressure inside the carbur furnace to the target pressure;
(f) a carburizing and spreading step of holding the pressure of the carburizing furnace at a target pressure in a state where the operation of the air circulating pen is stopped and carburizing and diffusing the workpiece for a predetermined time by the pressure inside the carburizing furnace and radiant heat;
(g) moving the pen for air circulation to lower the temperature of the carburizing furnace to the carburizing temperature;
(h) a carburizing and quenching step of cooling the object to be treated while maintaining the temperature at a carburization quenching temperature for a predetermined time;
(i) an oil ingress step of opening the carburizing furnace opening / closing device and cooling the cooling channel by injecting the object into the oil bath;
(j) a tempering step of heating the object to be processed to a tempering temperature, holding the temperature for a predetermined period of time, and cooling to effect tempering;
(k) driving the transfer device to transfer the object to be processed to the outside;
Wherein the metal component gas carburization heat treatment method comprises: The method according to claim 1,
injecting a liquid to be used as a carrier gas into the carburizing furnace in the step (a);
(d) lowering the internal temperature of the carbur furnace to the carburization temperature and then causing the liquid to be used as carburizing gas to pass through the gas pipe into the carburization furnace; And
(f) carries the object to be processed by the gas generated by decomposition of the two liquids by heat inside the carbur furnace
Further comprising the step of heating the metal component gas. 3. The method according to claim 1 or 2,
The gas pipe inside the carburizing furnace is composed of several gas pipes of different lengths, and each gas pipe is connected to the inside of the carburizing furnace in the depth direction of the carburizing furnace
Further comprising the step of heating the metal component gas.

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