KR101823907B1 - complex heat treated gear having excellent machinability and low deformability for heat treatment and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a gear for an automobile with reduced heat treatment deformation compared to an existing carburized heat treated gear, high durability, and excellent machinability and a gear manufacturing method, wherein the gear for an automobile has a hardened layer along the contour of the gear surface by performing high-frequency contour quenching after nitriding heat treatment. The gear manufacturing method comprises: a step of hot-forging carburized steel or nitriding steel of SCr420H material of JIS standard, which comprises 0.17-0.23% of carbon (C), 0.15-0.35% of silicon (Si), 0.55-0.90% of manganese (Mn), 0.85-1.25% of chromium (Cr), and the remainder consisting of iron (Fe) and inevitable impurities, and performing nitriding heat treatment for the machined gear in NH_3+CO_2+N_2 gas atmosphere condition within 3 hours at 570°C, so the gear surface is composed of an epsilon phase (Fe2-3N) in which a fraction of a nitriding compound layer is 90% or more. After the nitriding heat treatment, the gear is manufactured by heating the high-frequency contour quenching for less than 50 seconds.

Description

TECHNICAL FIELD The present invention relates to a composite heat treatment gear having excellent machinability and reduced heat treatment distortion and a manufacturing method thereof,

The present invention relates to a composite heat treatment gear having excellent processability and reduced heat treatment deformation and a method of manufacturing the same. Specifically, the present invention relates to an automotive gear having a hardened layer along the outline of a gear surface by carrying out high-frequency contour finishing after nitriding heat treatment, which is excellent in workability with reduction of heat treatment deformation compared with existing carburized heat treated gears, And a method for manufacturing the composite heat treatment gear.

BACKGROUND ART Gears used in transportation machines and industrial machinery such as automobiles are required to have abrasion resistance and strength and impact resistance as well as endurance. Therefore, the surface layer of gears is cured by carburizing heat treatment in order to satisfy such requirements.

As shown in Fig. 1, the carburizing heat treatment is carried out by charging a gear machined with a low carbon steel for carburization (around 0.2% of carbon) into a heat treatment furnace and introducing carbon into the surface portion of the gear at the same time as heating, The core part is made into a low carbon alloy steel, and the surface part has a high hardness and the deep part has a relatively low hardness through quenching (?? naming), thereby realizing abrasion resistance, endurance resistance and impact resistance at the same time. However, in the case of gears manufactured using the conventional carburizing heat treatment, there is a problem of generation of noise at the time of driving the gears due to the costly portion according to the heat treatment time for a long time and the deformation and warping after the heat treatment.

In order to solve this problem, a high frequency contour quenching has been developed in which only the surface portion of the gear is locally heat-treated without using the heat treatment of the whole gear by using a medium carbon steel (carbon amount of about 0.45 to 0.55%) .

The advantages of the high frequency contouring compared to the conventional carburizing heat treatment are the reduction of heat treatment deformation by local heat treatment only on the gear surface portion and the improvement of fatigue strength by the generation of high compression residual stress. However, since heavy carbon steel having a high carbon content is used, there is a problem that the machinability is lowered (productivity is lowered and manufacturing cost is increased) due to an increase in processing load and tool wear at the time of turning and gear processing compared to carburizing steel.

Accordingly, the present invention has proposed a gear for automobile having excellent machinability compared to existing high frequency contour gears, and a manufacturing method thereof, while reducing carburizing heat treatment and heat treatment deformation relative to high frequency contouring, which is a heat treatment method of conventional gears.

Korean Patent Publication No. 10-1535971

Korean Patent Laid-Open No. 10-2011-0139535

Korean Patent Publication No. 10-0646440

It is an object of the present invention to provide a steel sheet which is excellent in workability with reduction in heat treatment deformation and high durability and which is excellent in workability and heat resistance by performing high frequency contour finishing after nitriding heat treatment using carburizing steel or nitriding steel for simultaneously securing processability, And to provide a reduced heat treatment gear.

Another object of the present invention is to improve wear resistance and hardness by permeating nitrogen at a temperature of 500 to 580 캜 during a nitriding heat treatment.

It is still another object of the present invention to provide a semiconductor device which has a low thermal deformation due to a low heat treatment temperature and has a high thermal deformation by a high frequency contour heat treatment rather than a general high frequency heat treatment.

In the composite heat treatment gear of the present invention having excellent processability and reduced heat treatment strain,

Carburizing steel or nitriding steel is subjected to nitriding under a nitriding or softening heat treatment condition and then subjected to normalizing and turning to machine the gear,

In a furnace with the gear 540 ~ 580 ℃, 8 ~ 15 hours to infiltrate the K _N = 2.0 above gas in a heated state after heat treatment nitride, characterized in that the contour is obtained by heating the high-frequency quenching to less than 50 seconds.

The softening treatment conditions are such that NH ₃ + CO ₂ + N ₂ gas is introduced at 540 to 580 ° C for 2 to 8 hrs.

The carburized steel or the nitrided steel may contain carburized steel or nitrided steel containing 0.17 to 0.23% of C, 0.15 to 0.35% of Si, 0.55 to 0.90% of Mn and 0.85 to 1.25% of Cr as a balance of Fe and unavoidable impurities SCR420H, SCr415H and SCM415H materials containing about 0.2% of carbon.

It is also characterized in that carburized steel or nitrided steel containing at least one of Mo: 0.15-0.30%, B: 0.0010 to 0.0030%, S: 0.015 to 0.035% and Nb: 0.015 to 0.035% is used.

Further, a composite heat treatment gear having excellent workability and reduced heat treatment deformation and a manufacturing method thereof,

0.2% carbon alloy steel is subjected to nitriding heat treatment and high frequency contour finishing method to have excellent workability and to have durability and value after heat treatment,

The gear manufacturing method

0.17 to 0.23% of C, 0.15 to 0.35% of Si, 0.55 to 0.90% of Mn, 0.85 to 1.25% of Cr. Hot-forging carburized steel or nitrided steel of JIS standard SCr420H containing Fe and unavoidable impurities as the remainder, and then normalizing the steel;

Machining the gear by turning the normalized steel;

Subjecting the processed gear to a nitriding heat treatment so that the surface of the gear is composed of an epsilon phase (Fe2-3N) of 90% or more of a nitriding compound layer in NH ₃ + CO ₂ + N ₂ gas atmosphere condition at 570 ° C within 3 hours;

After the nitriding heat treatment, the high frequency contour finishing is heated to less than 50 seconds to manufacture the gear.

And the thickness of the nitride compound layer is at least 5 탆 - 8 탆.

The present invention can improve wear resistance and hardness by penetrating nitrogen at a temperature of 500 to 580 캜 during a nitriding heat treatment.

In addition, since the present invention has a low heat treatment temperature, the thermal deformation is small, and the subsequent heat treatment is excellent in thermal deformation by the high frequency contour heat treatment, rather than the general high frequency heat treatment.

1 is a view showing a conventional carburizing heat treatment process.
2 is a view showing a conventional high frequency contour quenching.
3 is a view showing a process of manufacturing gears using the composite heat treatment according to the present invention.
4 is a diagram illustrating a high frequency contouring cycle according to the present invention.
Figs. 5 (a) to 5 (c) are views showing a tooth surface state after the gear endurance test.
5B is a diagram showing the state of the gear surface of the comparative member 1, and FIG. 5C is a view showing the state of the gear surface of the comparative member 2 (FIG. 5A) to be.
6 (a) to 6 (d) are diagrams showing the damage and decomposition states of the compound layers of the present invention and Comparative Examples 1 to 6,
Fig. 6 (a) is a view showing the state of the gear surface of the present invention, Fig. 6 (b) is a comparative material 3, Fig. 6 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.

Further, 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 practiced by those skilled in the art.

The carburized steel used in the present invention is a SCr420H material according to JIS standard, containing 0.17 to 0.23% of C, 0.15 to 0.35% of Si, 0.55 to 0.90% of Mn, 0.85 to 1.25% of Cr, Alloy steel containing Fe and unavoidable impurities was used as the remainder.

 Of course, the carburizing steel used in the present invention is not necessarily limited to the SCr420H material, but SCr420H, SCr420H1, SCr420H1-V, SCr420H1S, SCr420HB, SCr420HBS, SCM420H, SCM420H1-V, SCM420HB, SCr415H, SCM415H or the like may be used.

Further, by using carburized steel or nitrided steel containing at least one of Mo: 0.15-0.30%, B: 0.0010 to 0.0030%, S: 0.015 to 0.035% and Nb: 0.015 to 0.035%, excellent workability and heat treatment deformation Thereby producing the reduced heat treatment gear.

The process of the composite heat treatment gear of the present invention is as follows.

The conditions for hot forging, normalizing and gearing (including turning) are the same as before.

Referring to FIG. 3, in order to simultaneously ensure workability, durability and reduction in heat treatment deformation, a low-strain / high-end gear was fabricated by performing high-frequency contour finishing after nitriding heat treatment using carburizing steel or nitriding steel.

In order to ensure high durability, which is one of the features of the present invention, it is necessary to optimize the nitriding heat treatment condition and the high frequency contour finishing condition since the surface compound layer generated after the nitriding heat treatment must remain after the high frequency contour fineness.

The detailed conditions are as follows.

1) Nitriding heat treatment or softening heat treatment

Nitriding heat treatment

Nitriding of gears After heat treatment, the surface of gears should consist of 90% or more ε phase (Fe2-3N) of nitric oxide compound layer, and its thickness should be at least 5㎛. If the requirement is less than the above requirement, the compound layer is oxidized after the high-frequency contour finishing, which is a subsequent process, to cause loss and decomposition of the compound layer.

If the nitriding and softening heat treatment temperature is less than 540 캜, the nitrogen penetration and diffusion rate is slow, and the desired compound layer thickness and curing depth can not be obtained.

Nitriding and softening When the heat treatment temperature is higher than 580 ° C, phase transformation of the steel occurs, so that the desired cargo phase can not be obtained and heat treatment deformation increases.

Further, when the nitriding heat treatment time is less than 8 hours, nitrogen can not sufficiently penetrate and diffuse into the steel material, and the thickness of the desired compound layer and the depth of hardening can not be obtained.

In addition, when the nitriding heat treatment time exceeds 15 hours, penetration and diffusion of nitrogen are saturated, and there is no effect of further increasing the thickness of the compound layer and the depth of curing.

Softening heat treatment

In the case of softening heat treatment, it is possible to obtain the thickness of the compound layer and the hardening depth in a relatively short period of time as compared with the nitriding heat treatment in which the carbon (C) together with the nitrogen (N) penetrate into the steel at the same time. And the effect is saturated for more than 8 hours.

2) Nitriding heat treatment of the present invention

Therefore, the temperature of the nitriding heat treatment of the present invention is set to 550 ° C to 580 ° C and the condition of NH ₃ + CO ₂ + N ₂ gas atmosphere is set within 3 hours, and the ε phase (Fe 2 - 3N), and the thickness thereof is preferably at least about 5 탆 - 8 탆.

The compound layer has a hardness of HV 800-830 and serves to ensure abrasion resistance in contact with the counter gear.

After the nitriding heat treatment as described above, the high frequency contour filling is heated to less than 50 seconds.

At this time, if the time of the high frequency contour filling is prolonged, since the compound layer is decomposed due to the heating for a long time, the heating time for the total high frequency contour filling is preferably less than 50 seconds.

Further, in order to obtain a desired compound phase in the nitriding heat treatment, K _N -T (Lehrer) The K _N value (gas atmosphere) and temperature (T) should be adjusted as shown in the parallel state diagram.

The K _N value is regulated by measuring the hydrogen partial pressure using a hydrogen sensor in the furnace.

The equation is K _N = (In-furnace NH ₃ gas partial pressure) / (in-furnace H ₂ gas partial pressure) ^3/2 .

PNH3 = partial pressure of NH ₃ in the atmosphere that

PH2 = H ₂ partial pressure in the atmosphere (produced by decomposition at NH ₃ )

Comparative Table 1 shows the comparison of the gears during the carburizing heat treatment and the high frequency contour finishing of the composite heat treatment of the present invention and the comparative materials 1 and 2.

Comparison Table 1

As shown in FIG. 4, the present invention was subjected to a contour high-frequency heat treatment at a temperature of 900 DEG C, followed by tempering at 180 DEG C for 2 hours.

At this time, the surface hardness was HV 810 ~ 830 and the depth of hardening was 1.1 mm, and the tooth surface state after the durability test was not damaged as shown in FIG. 5 (a).

5 (a) to 5 (c) show tip wear of the present invention and comparative materials 1 and 2 at the time of gear processing. This is the result of processing 500 gears.

Comparison of damage of the compound layer according to the nitriding and high frequency contouring conditions of the present invention and comparative materials 3 to 5 is shown in Comparative Table 2 (actual experimental conditions).

Comparison Table 2

[0113] [117] Thus, the temperature of the nitriding heat treatment at 570 ℃, within 3 hours NH ₃ + CO ₂ + N _2, the fraction of the nitride compound layer on a gear surface of the gas atmosphere conditions, the at least 90% ε (Fe2-3N ), And the thickness thereof is at least about 5 탆 - 8 탆.

As the heating time of the high frequency contour finishing is less than 50 seconds, the compound layer is not damaged on the gear surface as shown in Fig. 6 (a).

6 (b), it can be seen that the gear surface is disassembled. As shown in Figs. 6 (c) and 6 (d), the comparative members 4 and 5 are damaged Respectively.

Comparing the damage of the compound layer according to the nitriding and the high frequency contour cutting conditions of the present invention and the comparative materials 3 to 5

The invention nitride: 540 ~ 580 ℃, 8 ~ 15 sigan, K _N = 2.0 above or softening: 540 ~ 580 ℃, appears different from the compounds of the ε-phase in 2-8 hours NH ₃ + CO ₂ + N ₂ conditions substantially A compound layer having a thickness of 5 to 8 탆 is produced (see Fig. 6 (a)).

Therefore, in the present invention, high-frequency contour finishing is performed after nitriding heat treatment using carburized steel or nitrided steel, whereby durability and heat treatment deformation reduction can be secured at the same time.

While the present invention has been described with reference to the preferred embodiments described above and the accompanying drawings, it is to be understood that the invention may be embodied in different forms without departing from the spirit or scope of the invention. Accordingly, the scope of the present invention is defined by the appended claims, and is not to be construed as limited to the specific embodiments described herein.

Claims (9)

Carburizing steel or nitriding steel is subjected to heat treatment under a nitriding or softening heat treatment condition and then subjected to normalizing and turning to machine the gear,
(Fe2-3N) of at least 5 占 퐉 - 8 占 퐉 along the outline of the gear surface with a high frequency contour of 1.5 to 50 seconds after the gear nitriding heat treatment. Reduced complex heat treatment gear. delete The method according to claim 1,
The carburized steel or the nitrided steel may contain carburized steel or nitrided steel containing 0.17 to 0.23% of C, 0.15 to 0.35% of Si, 0.55 to 0.90% of Mn and 0.85 to 1.25% of Cr as a balance of Fe and unavoidable impurities Features Combined heat treatment gear with excellent processability and reduced heat treatment deformation. The method of claim 3,
The carburized steel or the nitrided steel is characterized by further containing materials of SCr420H, SCr420H1, SCr420H1-V, SCr420H1S, SCr420HB, SCr420HBS, SCM420H, SCM420H1-V, SCM420HB, SCr415H and SCM415H containing 0.2% A composite heat treatment gear with reduced heat treatment deformation. The method of claim 3,
The carburized steel or the nitrided steel is characterized by using carburized steel or nitrided steel containing at least one of Mo: 0.15-0.30%, B: 0.0010 to 0.0030%, S: 0.015 to 0.035% and Nb: 0.015 to 0.035% Which is excellent in workability and heat treatment distortion is reduced. delete 0.17 to 0.23% of C, 0.15 to 0.35% of Si, 0.55 to 0.90% of Mn, 0.85 to 1.25% of Cr. Hot-forging carburized steel or nitrided steel containing Fe and unavoidable impurities as the remainder, and then normalizing the steel; And
Machining the gear by turning the normalized steel; And
And nitriding heat treatment of the machining gear,
Characterized in that after the nitriding heat treatment, high-frequency contour finishing is performed for 1.5 to 50 seconds to produce a gear having a cured layer thickness of at least 5 占 퐉 - 8 占 퐉 in? Single phase along the contour of the gear surface, A reduced composite heat treated gear manufacturing method. 8. The method of claim 7,
The nitriding heat treatment is performed in an NH ₃ + CO ₂ + N ₂ gas atmosphere condition at a temperature of 570 ° C. within 3 hours and is composed of an ε phase (Fe 2 -3N) having a nitride compound layer fraction of 90% to 98% Which is characterized by excellent workability and reduced heat treatment strain.
delete

Images