JP5779887B2 - Heat treatment method for raceway member - Google Patents

Description

  The present invention includes first and second race members having raceway surfaces arranged opposite to each other, and rolling elements disposed between both raceway members, and both of the rolling bodies are caused by rolling. The present invention relates to a heat treatment method for the raceway member (the raceway of the rolling bearing, the guide rail and slider of the linear guide, the screw shaft and nut of the ball screw, etc.) of the apparatus in which one of the raceway members moves relative to the other.

It is often the case that foreign matter such as metal chips, shavings, burrs, and wear powder mixed in the lubricating oil damages the bearing rings and rolling elements of the rolling bearing, resulting in a significant decrease in the life of the rolling bearing. Are known.
In order to extend the life of rolling bearings when foreign matter is mixed in the lubricating oil (under foreign matter mixed lubrication), the periphery of the indentation (depressed part) generated on the raceway surface due to the inclusion of foreign matter It is necessary to alleviate the concentration of stress on the part. Therefore, conventionally, carburizing treatment and carbonitriding treatment have been performed for the purpose of increasing the amount of retained austenite on the raceway surface.

  In Patent Document 1, as a heat treatment for a bearing component (an inner ring, an outer ring, or a rolling element of a rolling bearing), after carbonitriding at a temperature exceeding the A1 transformation point (for example, 845 ° C.), a temperature less than the A1 transformation point is disclosed. A carbonitriding / primary quenching process that rapidly quenches, a secondary quenching process in which the carbonitriding temperature is maintained at a temperature that is higher than the A1 transformation point and lower than the carbonitriding temperature (for example, 800 ° C.) and then rapidly cooled to a temperature that is lower than the A1 transformation point; It is described that by carrying out the steps in this order, the amount of retained austenite in the surface layer portion is in the range of 11% to 25%.

  However, in this method, the amount of retained austenite in the surface layer portion is reduced by performing the secondary quenching process on the carbonitrided layer. Further, when the holding temperature in the secondary quenching process is increased in order to increase the amount of retained austenite, the amount of retained austenite in the core portion also increases, so that the dimensional stability decreases. On the other hand, if the retained austenite amount of the core portion can be kept low while keeping the retained austenite amount on the raceway surface high, it is possible to achieve both a long life and excellent dimensional stability under lubrication mixed with foreign matter. .

JP 2006-316821 A

  An object of the present invention is to provide a method for heat-treating the raceway member that can keep the amount of retained austenite in the core portion low while keeping the amount of retained austenite on the raceway surface high.

In order to solve the above-described problems, the present invention includes first and second race members having raceway surfaces arranged opposite to each other, and rolling elements disposed between the raceway members. A heat treatment method for the race member of a device in which one of both race members moves relative to the other by rolling of a moving body, wherein the race member is made of high carbon chromium bearing steel (any of SUJ1 to SUJ5). As shown in FIG. 1, carbonitriding / primary quenching is performed in which the entire track member is carbonitrided while being kept at a temperature equal to or higher than the A1 transformation point (723 ° C.) and then rapidly cooled to a temperature lower than the A1 transformation point. And the surface layer portion of the raceway surface becomes a temperature equal to or higher than the carbonitriding temperature, and other portions (the entire core portion and the surface layer portion other than the raceway surface) are less than the carbonitriding temperature (less than the A1 transformation point). The gauge so that A preheating step of heating the member, a secondary hardening step of quenching to a temperature below MS transformation point (e.g., 200 ° C.) after holding the entire track member to a temperature of 880 ° C. or less than A1 transformation point, the tempering process the It carries out in order.

  The preheating step can be performed by heating the raceway surface by surface heating means such as induction heating (high frequency heating), flame heating, infrared heating, laser heating, or electron beam heating. By heating the raceway surface to a temperature equal to or higher than the carbonitriding temperature by the surface heating means, heat from the raceway surface is transmitted to the core portion of the raceway surface and the surface layer portion and the core portion other than the raceway surface, and the raceway The portion other than the surface surface layer portion (the entire core portion and the surface layer portion other than the raceway surface) can be set to a temperature lower than the carbonitriding temperature. Thereby, a temperature gradient is formed in the depth direction of the raceway surface.

The temperature holding in the secondary quenching step can be performed by atmospheric heating (furnace heating) or a method of heating not only the surface but also the center by the surface heating means described above.
According to the method of the present invention, by performing the preheating step between the carbonitriding / primary quenching step and the secondary quenching step, the retained austenite amount of the core portion is reduced while maintaining the retained austenite amount of the raceway surface high. It can be kept low.
It is preferable that the carbonitriding temperature is set at a temperature of A1 transformation point or higher and 850 ° C. or lower, and the maximum heating temperature of the raceway surface is set to 850 ° C. or higher in the preheating step.

  According to the method of the present invention, it is possible to keep the retained austenite amount of the core portion low while keeping the retained austenite amount of the raceway surface of the raceway member high.

It is a figure explaining the heat processing method of this invention.

Embodiments of the present invention will be described below.
First, a material made of SUJ2 (high carbon chromium bearing steel type 2) was turned into a shape of an outer ring (outer diameter 120 mm, groove bottom thickness 2.5 mm, width 17 mm) of a ball bearing. Next, this outer ring is placed in a heat treatment furnace and kept in a carbonitriding gas atmosphere at 850 ° C. (temperature above the A1 transformation point) for 3 hours for carbonitriding, followed by oil cooling (air cooling only for No. 2) The carbonitriding / primary quenching process was performed.
Next, after performing the preheating process by the following method in No. 1-8, the secondary quenching process was performed by the following method without performing the preheating process in No. 9-11. Next, the tempering process hold | maintained at 160-180 degreeC for 2 hours was performed.

<Preheating process>
In No. 1-6, by performing induction heating at a high frequency (frequency 30 kHz) for 5 seconds, the surface temperature of the raceway surface (orbital groove) becomes 900 ° C. maximum as measured by a radiation thermometer at the groove bottom position. The surface temperature of the outer peripheral surface was set to a maximum value of 400 ° C. as measured by a radiation thermometer. Portions other than the raceway surface are heated by heat conduction from the raceway surface.

In No. 7, induction heating is performed at a high frequency (frequency 30 kHz) for 4 seconds, so that the surface temperature of the raceway surface (track groove) reaches a maximum value of 850 ° C. as measured by a radiation thermometer at the groove bottom position, and the outer peripheral surface The maximum surface temperature was 250 ° C. as measured with a radiation thermometer. Portions other than the raceway surface are heated by heat conduction from the raceway surface.
In No. 8, induction heating is performed at a high frequency (frequency: 10 kHz) for 4 seconds, so that the surface temperature of the raceway surface (track groove) reaches a maximum value of 850 ° C. as measured by a radiation thermometer at the groove bottom position. The maximum surface temperature was 400 ° C as measured with a radiation thermometer. Portions other than the raceway surface are heated by heat conduction from the raceway surface.

<Secondary quenching process>
In Nos. 1 to 4, 7, and 8, the outer ring was placed in a heating furnace and kept at a temperature of 850 ° C., 820 ° C., or 880 ° C. for 0.5 hour, then cooled with oil and in the middle of cooling (5 seconds After), the outer ring was press-fitted into a straightening mold (not a divided body but a single body) that restrains the outer peripheral surface, and further cooled.
In Nos. 5, 6 and 9, the outer ring was held at 850 ° C. or 880 ° C. by induction heating for 2 seconds, then cooled with water, and during the cooling (after 3 seconds), a straightening die (consisting of a divided body) that restrains the outer peripheral surface The outer ring was press-fitted into an integrated type), and was further cooled.

About the outer ring | wheel after heat processing, the amount of retained austenites ((gamma) _R ) of a raceway surface and a core part was measured by X-ray diffraction. The amount of retained austenite on the raceway surface was measured at a position 0.2 mm deep from the track surface, and the amount of retained austenite on the core portion was measured at a position 1.5 mm deep in the radial direction from the groove bottom. These results are shown in Table 1 below together with the heat treatment conditions.

An outer ring of a rolling bearing that has both a long life and excellent dimensional stability under lubrication mixed with foreign matter when the amount of retained austenite on the raceway surface is 19% by volume or more and the amount of retained austenite in the core is 12% by volume or less. As preferred. The amount of retained austenite on the raceway surface is more preferably 25% by volume or more and 45% by volume or less.
The outer rings of Nos. 1 to 8 corresponding to the embodiments of the present invention have a retained austenite amount of 19 to 32% by volume on the raceway surface and a residual austenite amount of 6 to 11% by volume on the core. Results were obtained. In particular, in No. 1 to 6 where the maximum temperature of the raceway surface is 900 ° C. in the preheating process, the amount of retained austenite in the surface layer portion of the raceway surface is 30% by volume or 32% by volume, and the temperature is 850 ° C. It is a particularly high value as compared with 19% by volume of certain Nos. 7 and 8.

On the other hand, the outer rings of Nos. 9 to 11 do not satisfy either of “the remaining austenite amount of the raceway surface is 19% by volume or more” and “the remaining austenite amount of the core portion is 12% by volume or less”.
From the above, between the carbonitriding / primary quenching process and the secondary quenching process, the surface layer of the raceway surface becomes a temperature higher than the carbonitriding temperature, and other parts (other than the entire core part and the raceway surface) By carrying out a preheating process that heats the outer ring (track member) so that the surface layer portion is lower than the carbonitriding temperature, the amount of retained austenite in the core is reduced while maintaining the amount of retained austenite on the raceway surface high. It can be seen that it can be kept low.
In addition, when the carbonitriding temperature is 850 ° C., the highest heating temperature of the raceway surface in the preheating step is 900 ° C., so that the amount of retained austenite on the raceway surface is higher than when 850 ° C. and good results are obtained. It can be seen that

Claims (2)

First and second track members having track surfaces arranged opposite to each other, and rolling elements disposed between the track members, and one of the track members is rolled by rolling the rolling elements. Is a heat treatment method for the track member of the device that moves relative to the other,
The race member is made of high carbon chromium bearing steel,
A carbonitriding / primary quenching step in which the entire raceway member is maintained at a temperature equal to or higher than the A1 transformation point and subjected to carbonitriding and then rapidly cooled to a temperature lower than the A1 transformation point;
As the surface layer portion of the front Symbol raceway surface becomes the carbonitriding temperature or more, the other portion to a temperature of less than the carbonitriding temperature, and the preheating step of heating the raceway member,
A secondary quenching step in which the entire raceway member is held at a temperature not lower than the A1 transformation point and not higher than 880 ° C. and then rapidly cooled to a temperature not higher than the MS transformation point;
A method for heat-treating a raceway member, wherein tempering steps are performed in this order.   The track member heat treatment method according to claim 1, wherein the carbonitriding temperature is set to a temperature not lower than A1 transformation point and not higher than 850 ° C., and the maximum heating temperature of the raceway surface is not lower than 850 ° C. in the preheating step.

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