JPH09324211A - Heat treatment in carbo-nitriding atmosphere - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the wear resistance of a sliding part in a short time without executing heat treatment to a base material by executing quenching treatment to the sliding part in a ferrous member after executing austenizing treatment with primary-heating in carbo-nitriding atmosphere. SOLUTION: The sliding part in the ferrous member is set in the carbo- nitriding atmosphere to execute the primary heating. This carbo-nitriding atmosphere is formed in the gas containing high carbon and actual nitrogen of propan, ammonia, etc., or by covering with the powder generating the high carbon and the active nitrogen with heating of nickel carbide and cyanogen, etc. After executing the austenitizing treatment with the primary-heating, the quenching treatment is executed or after executing melting treatment, chilling is executed. By this method, martenstic structure or cementite containing diffused solid-solution of the nitrogen is developed on the surface layer of the sliding part. The primary-heating is desirable to execute with high frequency induction heating or laser beam irradiation, and by this method, the whole heating can simultaneously be executed or by continuously heating, the precision of the heating part can be improved.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a heat treatment method in a carbonitriding atmosphere.

[0002]

2. Description of the Related Art Conventionally, iron-based materials have been used for members that are required to have strength and wear resistance, such as structural members of vehicles, and carbonitriding has been used as a heat treatment method for improving wear resistance and seizure resistance. Quenching is generally performed. Before the quenching treatment, the treatment atmosphere is generally set to about 890.
The material is austenitized by heating and holding at ˜940 ° C. for surface modification.

[0003]

However, the ammonia in the carbonitriding atmosphere is decomposed during the austenitizing treatment, and the dissociation degree of the ammonia is high at the above temperature. For example, when the temperature is 900 ° C. or higher, the residual ammonia is 0.009%. As a result, the formation of the nitride layer on the surface of the member is insufficient, the thickness of the nitrogen diffusion solid solution layer is also insufficient, and the wear resistance is insufficient.

Further, since the entire member is heated and quenched, the deformation is large and the number of steps for correcting the deformation is increased. Further, for example, some parts such as a differential case of a vehicle differential device require 3 to 5 hours to complete the carbonitriding and quenching process, and the productivity is not good.

Therefore, the present invention aims to improve the wear resistance while suppressing the heat treatment deformation and to improve the productivity by limiting the heat treatment in the carbonitriding atmosphere to a part of the member. To do.

[0006]

In order to solve the above-mentioned problems, according to the invention described in claim 1, the sliding part of the iron-based member is heated in a gas containing high carbon and active nitrogen or heated. In a state of being covered with a powder that generates high carbon and active nitrogen, the sliding portion is primarily heated to undergo austenitizing treatment, and then quenching treatment is performed, and martens in which nitrogen is dispersed and solid-solved in the surface layer of the sliding portion. It is characterized by generating a site organization.

Therefore, since the sliding portion is heated but the other portions are not heated, the dissociation degree of ammonia in the atmosphere is low, and a large amount of residual ammonia can be supplied to the heated sliding portion. At the same time, the diffusion solid solution concentration of nitrogen and the thickness of the surface layer increase, and a carburized layer is formed to improve wear resistance.

Further, since the heat treatment portion is limited to the sliding portion, the heat treatment time of the member is shortened and the deformation is also reduced.

According to a second aspect of the present invention, the sliding portion of the iron-based member is covered with a gas containing high carbon and active nitrogen or with a powder that generates high carbon and active nitrogen when heated. Then, the sliding part is primarily heated to be melted and then chilled to generate cementite in which nitrogen is diffused and solid-solved in the surface layer of the sliding part.

Therefore, the melting increases the diffusion solid solution concentration and the thickness of nitrogen in the surface layer of the sliding portion, so that the wear resistance is further improved.

Further, since cementite is precipitated in the internal structure by chilling from the molten state, the strength and wear resistance are further improved.

The invention according to claim 3 is the heat treatment method in the carbonitriding atmosphere according to claim 1 or 2, characterized in that the primary heating of the sliding portion is performed by high frequency heating.

Therefore, in addition to the actions and effects according to the first or second aspect, the entire surface of the sliding portion can be heated at the same time, so that the processing can be performed in a short time regardless of the size of the sliding portion, and the productivity is greatly improved.

The invention according to claim 4 is the heat treatment method in the carbonitriding atmosphere according to claim 1 or 2, characterized in that the primary heating of the sliding portion is performed by laser light.

Therefore, in addition to the actions and effects according to the first or second aspect, continuous heating can be performed by irradiating the laser beam, so that the heated portion is accurately determined and the deformation is further reduced.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] A heat treatment method according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a differential device including a differential case 1 which is a member for heat treatment according to the present embodiment, and FIG. 2 is an explanatory view.

The differential case 1 includes a case body 1a and a cover 1.
b is connected by a bolt 3, and a pair of side gears 5, 7 and a pinion gear 7, which meshes with these, are provided inside.
7 are arranged. Since the side gears 5 and 5 receive the thrust due to the meshing with the pinion gears 7 and 7 and are pressed against the differential case 1, the conical clutch portions 1c and 5 are formed between the inner circumference of the differential case 1 and the outer circumferences of the side gears 5 and 5.
c are respectively formed. And the side gears 5,
When there is a rotation difference between the five clutch parts 1c, 5c
Slides while receiving thrust corresponding to the driving force.

The differential case 1 is formed by using spheroidal graphite cast iron FCD600 as a compatible material because it is required to improve the wear resistance of the clutch portion 1c in addition to the complicated shape as shown in the drawing in which the differential mechanism is incorporated. Has been done.

Therefore, in the heat treatment of the present embodiment, the clutch portion 1c of the differential case 1 made of this material is locally heat-treated [primary heating by high frequency heating] As shown schematically in FIG. An inert gas in which enriched propane and ammonia are kept at a high concentration is injected into the inside to adjust the atmospheric gas at room temperature. Then, the clutch part 1c
(Shaded portion in FIG. 1) A high frequency current is passed through the coil 13 along the inner circumference to heat the clutch portion 1c to a temperature of 890 to 940 ° C. for 5 to 15 minutes to austenite the clutch portion 1c.

At this time, in the heating portion (clutch portion 1c portion), the diffusion and solid solution of nitrogen begins at about 500 ° C., and a large amount of ammonia is supplied to the clutch portion 1c by the movement of the atmospheric gas having a low dissociation degree. On the surface layer of the portion 1c, a diffusion solid solution layer of nitrogen having a sufficient concentration and a sufficient thickness is formed and a carburized layer is formed.

In addition to the method of injecting the above-mentioned inert gas, powder of nickel carbide, boron carbide, graphite or the like may be applied to the clutch portion 1c as a method of generating high carbon. As a method for generating active nitrogen, heating cyan, applying nickel nitride or boron nitride to the clutch portion 1c, or applying high density energy to nitrogen gas (decomposition of nitrogen gas) Good.

As another atmosphere adjusting method, there is a method in which the sealed container in which the differential case 1 is arranged is evacuated and then an inert gas in which the enriched propane and ammonia are kept at a high concentration is filled.

[Quenching] Next, in the container 11, A
From the austenitizing temperature of the clutch portion 1c by jetting cooling oil from the portion to oil-cool at 120 to 150 ° C. for 1 to 10 seconds or quenching, or the differential case 1 is placed in the container 1
1 is taken out and left to cool in air at room temperature for 1 to 10 minutes to deposit martensite on the clutch portion 1c. After quenching, tempering treatment is performed so that a predetermined tempering hardness is obtained.

In this way, according to the present embodiment, since the portion other than the clutch portion 1c is not heated in the primary heating, a large amount of ammonia can be supplied to the heated clutch portion 1c, so that the sufficient concentration on the surface layer of the clutch portion 1c can be obtained. And a thickness of a nitrogen diffusion solid solution layer is formed, and wear resistance is improved.

Further, since the heat treatment portion is limited to the clutch portion 1c, heat treatment deformation of the differential case 1 is reduced, and since the entire clutch portion 1c is simultaneously heated by the high frequency heating, the heat treatment time is greatly shortened and the differential case 1 Productivity is greatly improved.

[Second Embodiment] A second embodiment of the present invention will be described. The heat treatment target portion of the present embodiment is the clutch portion 1c of the differential case 1 as in the first embodiment. First
Differences from the embodiment will be mainly described, and redundant description will be omitted.

[Primary heating by high frequency heating] Enriched propane and ammonia are kept at a high concentration in an inert gas at room temperature, and the clutch portion 1c is 1100 to 1200 ° C.
It is melted by high-frequency heating at the temperature of 5 to 15 minutes.

[Chilling] Then, from this molten state, 1
Chilling by oil cooling at 20-150 ° C for 1-10 seconds,
Alternatively, it is left to cool in air at room temperature for 1 to 10 minutes to be chilled, and cementite is deposited on the clutch portion 1c based on martensite.

As described above, according to this embodiment, the diffusion and solid solution concentration of nitrogen and the thickness are increased by the melting of the clutch portion 1c, and the wear resistance is further improved.

Further, since cementite precipitates in the internal structure by chilling from the molten state, the strength and wear resistance are further improved.

[Third Embodiment] A third embodiment of the present invention will be described with reference to FIG. The heat treatment target portion of the present embodiment is the clutch portion 1c of the differential case 1 as in the first embodiment. FIG. 3 is a plan view showing the clutch portion 1c that has been heat-treated. Differences from the first embodiment will be mainly described, and redundant description will be omitted.

[Primary heating by laser heating] Laser light with an output of 500 W to 5 kW is irradiated perpendicularly to the plane of the clutch portion 1c in an inert gas at room temperature in which enriched propane and ammonia are maintained at a high concentration and the light is reflected. The clutch portion 1c is moved at a speed of 0.5 to 2 m / min while being prevented, and is heated to a temperature of 890 to 940 ° C. for 2 to 5 minutes to perform an austenitizing treatment. The portion B in FIG. 3 is the clutch portion 1c.
The heating part of is shown.

[Quenching] Then, without specially setting a quenching step, the material is allowed to stand for a moment to cool from the austenitizing temperature into the air at room temperature. That is, the clutch portion 1c that has deviated from the irradiation point of the laser light is quenched by momentary cooling, and martensite precipitates. After quenching, tempering treatment is performed so that a predetermined surface hardness is obtained.

Thus, according to the present embodiment, a diffusion solid solution layer of nitrogen having a sufficient concentration and thickness is formed on the surface layer of the clutch portion 1c, and wear resistance is improved.

Further, the clutch portion 1 is irradiated with the laser light.
Since the heated portion of c is accurately determined, heat treatment deformation of the clutch portion 1c can be further reduced.

The output of the laser light and the clutch unit 1
Change the setting of the moving speed of c and set the clutch part 1c temperature to 1
If the temperature is set to 100 to 1200 ° C., the clutch portion 1c can be melted and chilled as in the second embodiment.

[0037]

As is apparent from the above description, according to the invention described in claim 1, since a portion other than the sliding portion is not heated, a large amount of ammonia can be supplied to the sliding portion to be heated. The diffusion solid solution concentration and thickness of nitrogen in the surface layer of the part are increased, and a carburized layer is formed to improve wear resistance.

Further, since the heat treatment portion is limited to the sliding portion, the heat treatment time of the member is shortened and the deformation is also reduced.

According to the second aspect of the invention, since the diffusion solid solution concentration and the thickness of nitrogen in the surface layer of the sliding portion are increased by the melting, the wear resistance is further improved.

By chilling from the molten state, cementite is precipitated in the internal structure, and the strength and wear resistance are further improved.

According to the invention described in claim 3, according to claim 1
In addition to the effect of 2 or above, since the entire surface of the sliding portion can be simultaneously heated by the high frequency heating, the processing can be performed in a short time regardless of the size of the sliding portion, and the productivity is significantly improved.

According to the invention of claim 4, claim 1
In addition to the effect of 2 or 3, continuous heating can be performed by laser light irradiation, so that the heated portion is accurately determined and deformation is further reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a differential device including a differential case that undergoes heat treatment according to a first embodiment.

FIG. 2 is an explanatory diagram of the first embodiment.

FIG. 3 is an explanatory diagram of a third embodiment.

[Explanation of symbols]

 1 Differential Case 1c, 5c Clutch Part 11 Container 13 Coil A Gas or Coolant Injecting Port B Laser Light Irradiation Part

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C23C 8/76 C23C 8/76

Claims (4)

[Claims] 1. A sliding part of an iron-based member is covered with a powder that generates high carbon and active nitrogen when heated or in a gas containing high carbon and active nitrogen. A heat treatment method in a carbonitriding atmosphere, characterized in that, after primary heating to perform austenitizing treatment, quenching treatment is performed to generate a martensite structure in which nitrogen is diffused and solid-solved in a surface layer of a sliding portion. 2. The sliding part of the iron-based member is covered with a powder containing high carbon and active nitrogen or powder that generates high carbon and active nitrogen when heated, A method for heat treatment in a carbonitriding atmosphere, which comprises first-heating to melt and then chilling to produce cementite in which nitrogen is diffused and solid-solved in the surface layer of a sliding portion. 3. The heat treatment method in a carbonitriding atmosphere according to claim 1, wherein the primary heating of the sliding portion is performed by high frequency heating. 4. The heat treatment method in a carbonitriding atmosphere according to claim 1, wherein the primary heating of the sliding portion is performed by laser light.