JPH09302454A - Pre-treatment of carburizing quenched material and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a carburizing quenched material having high surface pressure fatigue strength and long fatigue service life. SOLUTION: A first process, in which shot peening is applied to an objective material to execute the carburizing quenched treatment and this surface roughness Ry is made to 6-25μ, and a second process, in which the carburizing quenched treatment is applied to the material to form the carburizing abnormal layer on the rugged surface part and the carburizing hardened layer in the inner part from the carburizing abnormal layer of the material, are executed in order. In the case of using the carburizing quenched material manufactured in such a way, at the initial stage, the ruggedness on the surface is worn with the contacting and the sliding movement with the other material, and the carburizing abnormal layer having comparatively low hardness is removed at the initial stage of using and the carburizing hardness layer in the inner part is exposed onto the surface. By this method, at the same time of removing the carburizing abnormal layer, the surface roughness is made to small by the fitness effect with the contacting other material and the contacting surface having smooth and high strength is developed at the initial stage of using.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pretreatment method for a carburized and quenched material used as a member such as a gear, a bearing, a cam, and a railway wheel, and a method for manufacturing the carburized and quenched material.

[0002]

2. Description of the Related Art Conventionally, for example, gears, bearings, cams,
A member made of steel such as a railway wheel is carburized and quenched in order to obtain a predetermined strength. However, when these members are repeatedly subjected to a contact load, a fatigue phenomenon occurs in a contacted portion and damage such as peeling occurs. The strength of a material against this fatigue phenomenon is generally called surface pressure fatigue strength, and various measures as shown in Table 1 have been proposed to improve the surface pressure fatigue strength.

[0003]

[Table 1] That is, surface finishing (reduction of surface roughness), improvement of surface hardness by shot peening, application of compressive residual stress, or reduction or removal of an abnormal carburized layer has been proposed.

However, these methods increase the manufacturing cost of the steel material itself ((3) and (5) above) and the number of steps ((1), (2) and (4) above). (6)) or high cost process is required ((1) and (6) above). Further, in Japanese Patent Laid-Open No. 3-111551 and Japanese Patent Laid-Open No. 3-107418, after carburizing and quenching treatment after forming and processing as a method for improving the surface pressure fatigue strength of a component in which the surface of a gear or the like is carburized and quenching treated. It is described before that shot peening is performed to roughen the surface. The purpose of shot peening with this technique is to eliminate the directionality of cutting traces and grinding traces that occur during the forming process of gears and the like, and to prevent cracks from occurring due to stress concentration due to cutting traces and grinding traces.

However, the shot peening conditions of this technique are relatively strong and therefore the surface is too rough. Therefore, although stress concentration due to cutting traces or grinding traces can be prevented, stress concentration due to surface roughness of shot peening occurs, making it difficult to further improve fatigue strength.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a pretreatment method and a carburizing method for a carburized and hardened material for obtaining a carburized and hardened material having high surface pressure fatigue strength and long fatigue life. It is an object to be solved to provide a method for manufacturing a hardened material.

[0007]

The pretreatment method for carburizing and quenching material of the present invention for solving the above-mentioned problems is characterized in that the surface roughness Ry of the material to be carburized and quenched is 6 to 25 μm. It is what Further, the method for manufacturing a carburized and quenched material of the present invention which solves the above-mentioned problems includes a first step of setting the surface roughness Ry of the material to be carburized and quenched to be 6 to 25 μm, and carburizing the material to be treated. It is characterized in that the second step of performing the quenching treatment and the second step are sequentially carried out.

The surface roughness Ry in the present invention means
From the roughness curve, the reference length is extracted in the direction of the average line, and the distance between the peak line and the valley bottom line of this extracted portion is measured in the direction of the longitudinal magnification of the roughness curve, and this value is measured in micrometers (μm). Refers to (JIS B 060
1).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the first step of the method for pretreating a carburized and hardened material and the method for manufacturing a carburized and hardened material according to the present invention, at least a portion of a material to be treated which comes into contact with a mating material to be used in combination after manufacture. Roughness is processed by treating the surface of
y is set to 6 to 25 μm. The material to be treated that can be applied to the present invention is steel that can be carburized and quenched.

Shot peening can be employed for the treatment for roughening the surface of the material to be treated. In this case, the average particle size of the shot peening particles is 0.4-
It is preferably 1.2 mm. Average particle size 0.4m
If it is smaller than m, the processing force may be insufficient and sufficient surface roughness Ry may not be obtained. Average particle size 1.2 mm
If it is larger than the above range, the surface roughness Ry becomes too large, and the intervals of the roughness are widened, so that there is a possibility that the surface becomes less likely to wear.

It is desirable that the shot speed of the shot peening particles is 15 to 45 m / s. If the projection speed is less than 15 m / s, the processing force may be insufficient and sufficient surface roughness Ry may not be obtained, and the projection of particles may become unstable. If the projection speed is higher than 45 m / s, the surface roughness Ry may be too large.

As another processing method for roughening the surface of the material to be processed, a method of pressing a mold having unevenness having no directionality on the surface and transferring the uneven shape to the material to be processed can also be adopted. . In the second step of the present invention, the material subjected to the first step is subjected to carburizing and quenching treatment. That is, quenching treatment is performed after carbon is infiltrated into the surface of the material to be treated having the surface roughness Ry in the range of 6 to 25 μm. Examples of the carburizing and quenching treatment include gas carburizing, liquid carburizing, solid carburizing, vacuum carburizing, and plasma carburizing. Adopted. In particular, gas carburization is desirable because an abnormal carburization layer is likely to be generated uniformly.

In the carburizing and quenching treatment, carbon is first diffused and permeated from the surface of the material to be treated, and then quenching is performed to form a carburized hardened layer having a high hardness on the surface layer of the material to be treated. At this time, a low-hardness layer called an abnormal carburization layer is formed on the outermost surface of the carburized hardened layer. The abnormal carburization layer is formed because oxygen, such as H ₂ O, CO ₂ and CO, contained in the atmospheric gas during the process of diffusing and permeating carbon causes Si, Mn, Cr
This is because an element that enhances the hardenability, such as, is oxidized, and as a result, the hardenability of the outermost surface is reduced and the hardness is lower than that of the carburized hardened layer inside.

The thickness of the abnormal carburized layer formed on the surface of the material to be treated in the second step is preferably 10 to 30 μm. When the thickness is less than 10 μm, as shown in FIG.
Since the amount of abrasion is very small, the surface is not smoothed due to abrasion during use, and the contact stress concentrates on the remaining portions of the surface irregularities, so that the strength is not improved. If it is thicker than 30 μm, as shown in FIG. 2, since the abnormal carburized layer is too thick relative to the surface roughness, it becomes difficult to completely remove the abnormal carburized layer due to abrasion during use, and the abnormal carburized layer remains. Does not improve the strength.

In the second step, the hardness of the carburized hard layer formed inside the carburized abnormal layer of the material to be treated is Hv600.
˜Hv900 is desirable. Since it is necessary to stop wear during use only in the outermost carburized abnormal layer, the carburized hardened layer inside the carburized abnormal layer needs to have Hv 600 or more. Further, if the carburized hardened layer is harder than Hv900, it becomes brittle, so that improvement in strength cannot be expected.

As the pretreatment of the first step of the present invention,
Shape processing and the like of the material to be processed are appropriately performed. Also, the second
As post-processing of the process, for the purpose of removing distortion of heat treatment, for example, additional processing of places such as a fitting part that is required to be accurate, and shot peening to give residual stress are considered. It is necessary that the surface roughness Ry of the receiving portion (contacted surface) does not deviate from the above range of 6 to 25 μm, and the thickness of the abnormal carburizing layer is 10 to 30.
It is desirable not to deviate from the range of μm.

The carburized and hardened material produced according to the present invention can be used for parts such as gears, sliding bearings, cams, railway wheels, etc., which may be worn by sliding with a mating material.

[0018]

The functions and effects of the present invention When the carburizing and quenching material pretreatment method of the present invention and the subsequent carburizing and quenching treatment, and the first step and the second step of the carburizing and quenching material manufacturing method of the present invention are carried out, the carburized and quenched material is carried out. A surface layer in which an abnormal carburizing layer is present is formed on the surface portion of the surface with a shape having a certain degree of surface roughness.
When used in this state, the unevenness of the surface is worn out due to contact and sliding with the mating material at the beginning of use. Due to this abrasion, the carburized abnormal layer having a relatively low hardness is removed at the initial stage of use. As a result, at the same time as the removal of the abnormal carburizing layer, the surface roughness becomes small due to the effect of familiarization with the contact partner, and a smooth contact surface is generated in the initial stage of use.

Further, since the hardened carburized layer inside has a higher hardness than the abnormal carburized layer, the progress of wear becomes very slow after the abnormal carburized layer is removed. That is, as shown in FIG. 3, the surface generated at the initial stage of use is a surface having high hardness and high strength in which the carburized abnormal layer having low strength is removed and the carburized hardened layer inside appears on the surface, and It is a smooth surface that is less likely to cause stress concentration due to its familiarity with the mating material. Therefore, the fatigue life is extended by removing the carburized abnormal layer having low strength and removing the irregularities that cause stress concentration.

Therefore, according to the present invention, it is possible to manufacture a carburized and quenched material having high surface pressure fatigue strength and long fatigue life. Note that if the surface roughness Ry is less than 6 μm, wear is unlikely to occur unless the surface roughness is large to a certain extent, and as shown in FIG. It is not completely removed and remains so that the strength is not improved.

When the surface roughness Ry exceeds 25 μm, the surface roughness is too large for the thickness of the abnormal carburized layer.
That is, as shown in FIG. 5, even if the carburized abnormal layer is worn, the surface is not smoothed and surface irregularities remain, and contact stress concentrates on the remaining portions of the irregularities, so the strength is not improved.

[0022]

EXAMPLES The present invention will be described in more detail below with reference to examples. In carrying out the method for manufacturing a carburized and quenched material of this example, a roller member having a diameter of 24 mm was processed and formed using steel composed of the chemical components shown in Table 2, and this was prepared as a material to be treated.

[0023]

[Table 2] Chemical composition (% by weight) Next, as a first step, the outer peripheral surface of the material to be processed is subjected to shot peening to roughen the surface, and the surface roughness Ry
Of 6 to 25 μm. The conditions of shot peening at this time were that the average particle diameter of shot peening particles was 0.6 mm, the projection speed was 30 m / s, and the surface roughness Ry after the treatment was 8 μm.

Next, as a second step, the material to be treated after the first step was carburized and quenched. In this carburizing and quenching treatment, gas carburizing was carried out at 950 ° C. for 5 hours, and then 85
After holding at 0 ° C. for 30 minutes or more, quenching by 130 ° C. oil cooling and tempering at 150 ° C. were performed. As a result, a carburized abnormal layer having a thickness of about 25 μm was formed on the outer peripheral surface of the material to be treated having irregularities, and a carburized hardened layer having a hardness of about Hv800 was formed inside the carburized abnormal layer.

Although the hardness of the carburized hardened layer changes depending on the tempering temperature, the relationship is as shown in FIG. In the case of this embodiment, the hardness of the carburized hardened layer is Hv600 to Hv9.
The tempering temperature is set in the range of 00. Also,
The thickness of the abnormal carburizing layer formed on the outer peripheral surface of the material to be treated is
Depending on the carburizing method, it is as shown in FIG. 7 for gas carburizing and vacuum carburizing. Therefore, the thickness of the abnormal carburizing layer to be formed is 10 to 30 μm by appropriately selecting the carburizing method.
So that

When the roller member produced as described above is used, the irregularities on the surface are worn by contact and sliding with the mating material at the beginning of use, and the carburized abnormal layer having a relatively low hardness is used at the beginning of use. Will be removed. As a result, at the same time as the removal of the abnormal carburizing layer, the surface roughness becomes small due to the effect of familiarization with the contact partner, and a smooth contact surface is generated in the initial stage of use.

When the abnormal carburizing layer having a low strength is removed, the carburizing hardened layer having a high hardness is exposed on the surface, and the subsequent progress of wear becomes very slow, resulting in high strength and compatibility with the mating material. This produces a smooth surface where stress concentration is less likely to occur (see FIG. 3). As a result, the carburized abnormal layer having low strength and the irregularities that cause stress concentration are removed, so that the contact pressure fatigue strength can be increased and the fatigue life can be lengthened.

(Test) In the roller member of the above embodiment, the surface roughness Ry applied to the surface of the material to be treated in the first step is 2
Test piece 1 shown in Table 3 with various changes in the range of up to 30 μm
8 to 8 were prepared, and a roller surface fatigue test was conducted to examine the Hertz contact stress and fatigue life (number of repetitions) of each of the test pieces 1 to 8. In addition, the roller member as the mating member of each of the test pieces 1 to 8 has the same surface roughness Ry corresponding to each of the test pieces 1 to 8.
In the same manner as above, a φ96 mm one was used. FIG. 8 shows the result.

[0029]

[Table 3] (Evaluation) As is clear from Table 3 and FIG. 8, the results of the test pieces 1, 4, 5 and 6 are 1.3 times the contact stress and the fatigue life is 7 times the test pieces 1 and 2. You can see that it has doubled. Further, it is estimated that the fatigue life of the test piece 8 is shorter than that of the test pieces 1 and 2 due to stress concentration.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a surface change due to wear when a carburization abnormal layer is thin.

FIG. 2 is an explanatory diagram showing a surface change due to wear when a carburizing abnormal layer is thick.

FIG. 3 is an explanatory diagram showing a surface change due to wear when the surface roughness is within a suitable range.

FIG. 4 is an explanatory diagram showing a surface change due to wear when the surface roughness is small.

FIG. 5 is an explanatory diagram showing a surface change due to wear when the surface roughness is large.

FIG. 6 is a graph showing the relationship between the tempering temperature and the hardness of the carburized hardened layer.

FIG. 7 is a graph showing the relationship between the carburizing and quenching method and the thickness of the abnormal carburizing layer.

FIG. 8 is a graph showing the results of a roller surface fatigue test.

Claims (6)

[Claims] 1. A pretreatment method for a carburized and hardened material, wherein the surface roughness Ry of the material to be carburized and quenched is 6 to 25 μm. 2. The surface roughness Ry of the material to be treated is 6 to 25.
The method for pretreating a carburized and hardened material according to claim 1, wherein shot peening has an average particle diameter of 0.4 to 1.2 mm and a projection speed of 15 to 45 m / s in order to obtain a particle size of μm. 3. A first step in which the surface roughness Ry of the material to be carburized and quenched is 6 to 25 μm, and a second step in which the material to be carburized and quenched is carburized and quenched. A method for manufacturing a carburized and quenched material, which is characterized by the above. 4. The first step performs shot peening, and the shot peening particles have an average particle size of 0.4 to 1.
The method for producing a carburized and quenched material according to claim 3, wherein the carburized and quenched material is 2 mm and the projection speed is 15 to 45 m / s. 5. The method for manufacturing a carburized and hardened material according to claim 3, wherein the abnormal carburized layer formed in the second step has a thickness of 10 to 30 μm. 6. The method for manufacturing a carburized and hardened material according to claim 3, wherein the hardness of the carburized hardened layer formed in the second step is Hv600 to Hv900.