Surface quenching method for medium carbon bearing steel

Abstract

The application discloses a surface quenching method for medium-carbon bearing steel and belongs to the technical field of metal material heat treatment. The medium-carbon bearing steel is rapidly heated to 820-950 DEG C by using a medium-frequency induction heating mode, is kept for 15-70 seconds, is water quenched, is tempered at 150-220 DEG C, and is kept for 0.5-5 hours. The method can make the surface hardened layer depth of the medium-carbon bearing steel be greater than or equal to 10 mm, the hardness of the hardened layer be HRC 52-62, and the surface be free of cracks. The method is suitable for surface quenching heat treatment of bearing parts, can obtain a high-hardness surface layer and a favorable internal stress distribution, and can improve the wear resistance and fatigue resistance of the bearing parts while ensuring that the whole workpiece has good strength and toughness.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for materials, specifically to a surface quenching method for medium carbon bearing steel, which is applied to the surface quenching heat treatment of bearing components. Background Technology

[0002] Surface hardening is an important heat treatment method in bearing manufacturing. Its purpose is to obtain a high-hardness surface layer and favorable internal stress distribution to improve the bearing's wear resistance and fatigue resistance, while ensuring good overall strength and toughness. The surface hardening method first rapidly heats the workpiece using a heat source. When the surface temperature reaches a suitable temperature above the critical point (while the core temperature remains below the critical point), it is rapidly cooled. This process hardens the surface layer while the core retains its original structure, achieving the desired combination of strength and toughness.

[0003] To achieve the goal of heating only the surface layer of the workpiece, a high energy density of the heat source is required. Depending on the heating method, surface hardening can be divided into induction heating (high frequency, medium frequency, and industrial frequency) surface hardening, flame heating surface hardening, and electrical contact heating surface hardening. Each heating method has its own advantages and disadvantages, and will yield different hardening qualities. Therefore, the heating method should be selected rationally according to the actual situation. The advantages of induction heating surface hardening include: fast heating speed, high efficiency, small deformation, short time, less surface oxidation and decarburization, high workpiece surface hardness, significantly improved impact toughness and fatigue performance, material savings, increased part lifespan, compact equipment, ease of use, good working conditions, and ease of mechanization and automation. Shaft parts are typically surface hardened using induction heating. The selection of the current frequency is crucial during induction heating hardening; different current frequencies will produce different penetration depths in the part, resulting in hardened layers of varying depths during subsequent hardening. A key characteristic of high-frequency (medium-frequency) current is the surface effect, where the induced current tends to be more concentrated on the surface of the part as the current frequency increases. Higher frequencies result in greater surface current density and shallower current penetration depth; conversely, lower frequencies result in greater current penetration depth. The appropriate current frequency should be selected based on the actual bearing requirements to achieve the desired hardened layer depth. Heating temperature and time must be considered comprehensively to avoid excessive heating temperature, excessive quenching stress, and subsequent workpiece cracking. Furthermore, the cooling rate (quenching medium) after heating and the tempering process after quenching are also crucial steps in determining the final bearing quality. Therefore, a systematic study of the surface quenching process parameters for medium-carbon bearing steel is necessary to specifically meet the application environment's requirements for the final performance of the bearing steel. Currently, existing surface quenching processes for medium-carbon steel generally result in shallow hardened layer depths, typically less than 5mm, and the hardness of the hardened layer is also relatively low, generally HRC45-55. Summary of the Invention

[0004] To address the problems of thin, low-hardness, and unevenly distributed surface hardened layers in existing bearing components in China, which lead to unstable component performance and short service life, the present invention aims to provide a surface quenching method for medium-carbon bearing steel, which is applicable to the surface quenching heat treatment of bearing components.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for surface quenching of medium carbon bearing steel involves rapidly heating the surface of the medium carbon bearing steel to 820-950℃ using a medium-frequency induction heating method with an induction power supply frequency of 3000-8000Hz, holding it at that temperature for 15-70 seconds, then water quenching it, followed by reheating it to 150-220℃ for tempering and holding it at that temperature for 0.5-5 hours.

[0007] Furthermore, in the surface hardening method, the quenching heating temperature is preferably 820-860℃, or 850-890℃, or 880-920℃, or 910-950℃.

[0008] Furthermore, in the surface hardening method, the quenching and holding time is preferably 15-35 seconds, or 30-50 seconds, or 50-70 seconds.

[0009] Furthermore, in the surface quenching method, the tempering heating temperature is preferably 150-180℃, or 170-200℃, or 190-220℃.

[0010] Furthermore, in the surface quenching method, the tempering holding time is preferably 0.5-2.0 hours, or 2.0-4.0 hours, or 3.0-5.0 hours.

[0011] This invention relates to a surface quenching method for medium carbon bearing steel, applied to the surface quenching heat treatment of bearing components. This invention allows the workpiece surface to acquire a hardened structure, improving the wear resistance of bearing components while the core retains its original structure, thus achieving the desired combination of strength and toughness. According to this method, the surface hardened layer depth of medium carbon bearing steel can be ≥10mm, the hardened layer hardness is HRC52-62, and the surface is crack-free, meeting the usage requirements of bearing components.

[0012] The present invention has the following advantages:

[0013] 1. The carbon bearing steel surface quenching method of this invention is applicable to the surface quenching heat treatment of bearings. The heat source of this method acts on the surface layer of the workpiece, with fast heating speed and high thermal efficiency. Since the workpiece is not heated as a whole, the deformation is small, the heating time of the workpiece is short, the amount of surface oxidation and decarburization is small, the surface hardness of the workpiece is high and the hardened layer is deep, the notch sensitivity is small, and the impact toughness, fatigue performance and wear resistance are all excellent. It is conducive to making full use of material potential, saving material consumption, and improving the service life of the workpiece. In addition, the equipment is compact, easy to use, has a good working environment, and is easy to realize mechanization and automation.

[0014] 2. All heat treatment method parameters used in this invention can be applied in industrial applications.

[0015] 3. Experiments show that the method of the present invention can make the surface hardened layer of medium carbon bearing steel ≥10mm in depth, with a hardness of HRC52-62, and no surface cracks, thus meeting the requirements for use of bearing components.

[0016] 4. According to the present invention, a high-hardness surface layer and favorable internal stress distribution can be obtained to improve the wear resistance and fatigue resistance of bearing components, while ensuring that the whole has good strength and toughness.

[0017] 5. The surface quenching method for medium carbon bearing steel proposed in this invention has a wide range of applications. It can be used not only for the heat treatment of bearing-related components in fields such as aviation, aerospace, automobiles, rail transportation, marine engineering, and engineering machinery, but also for other engineering fields and other structural components, such as wear-resistant plates for ore crushers and other components that require high surface hardness and high core toughness. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments, but this is not intended to limit the present invention in any way. The described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. The medium-frequency induction heating equipment and tempering equipment used in the present invention have no special requirements; a common resistance furnace is sufficient for tempering. The composition of the medium carbon bearing steel used in the embodiments and comparative examples of the present invention is shown in Table 1.

[0019] Table 1. Chemical composition of the test steel (mass fraction, %)

[0020] C Si Mn Cr Mo Fe 0.40 0.30 0.80 1.10 0.20 margin

[0021] The surface of medium carbon bearing steel is rapidly heated to 820-950℃, more preferably 820-860℃, or more preferably 850-890℃, or more preferably 880-920℃, or more preferably 910-950℃, using a medium-frequency induction heating method with an induction power supply frequency of 3000-8000Hz. The temperature is held for 15-70 seconds, more preferably 15-35 seconds, or more preferably 30-50 seconds, or more preferably 50-70 seconds. After that, it is water quenched and then tempered. The heating temperature is 150-220℃, more preferably 150-180℃, or more preferably 170-200℃, or more preferably 190-220℃, and the holding time is 0.5-5 hours, more preferably 0.5-2.0 hours, or more preferably 2.0-4.0 hours, or more preferably 3.0-5.0 hours.

[0022] Example 1:

[0023] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 820℃ using a medium frequency induction heating method with an induction power supply frequency of 5000Hz, held for 65 seconds, then water quenched, and then heated to 180℃ for tempering and held for 1 hour.

[0024] Example 2:

[0025] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 870℃ using a medium frequency induction heating method with an induction power supply frequency of 5000Hz, held for 60 seconds, then water quenched, and then heated to 180℃ for tempering and held for 1 hour.

[0026] Example 3:

[0027] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 950℃ using a medium frequency induction heating method with an induction power supply frequency of 5000Hz, held for 30 seconds, then water quenched, and then heated to 180℃ for tempering and held for 2.5 hours.

[0028] Example 4:

[0029] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 930℃ using a medium frequency induction heating method with an induction power supply frequency of 5000Hz, held for 70 seconds, then water quenched, and then heated to 180℃ for tempering and held for 1 hour.

[0030] Example 5:

[0031] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 870℃ using a medium frequency induction heating method with an induction power supply frequency of 5000Hz, held for 15 seconds, then water quenched, and then heated to 160℃ for tempering and held for 1 hour.

[0032] Example 6:

[0033] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 900℃ using a medium frequency induction heating method with an induction power supply frequency of 5000Hz, held for 60 seconds, then water quenched, and then heated to 220℃ for tempering and held for 1 hour.

[0034] Example 7:

[0035] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 930℃ using a medium frequency induction heating method with an induction power supply frequency of 5000Hz, held for 20 seconds, then water quenched, and then heated to 150℃ for tempering and held for 2 hours.

[0036] Example 8:

[0037] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 880℃ using a medium frequency induction heating method with an induction power supply frequency of 5000Hz, held for 40 seconds, then water quenched, and then heated to 180℃ for tempering and held for 0.5 hours.

[0038] Example 9:

[0039] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 900℃ using a medium frequency induction heating method with an induction power supply frequency of 5000Hz, held for 40 seconds, then water quenched, and then heated to 180℃ for tempering and held for 5 hours.

[0040] Comparative Example 1:

[0041] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 900℃ using a medium-frequency induction heating method with an induction power supply frequency of 5000Hz, held for 20 seconds, then oil quenched, and then heated to 180℃ for tempering and held for 1 hour.

[0042] Comparative Example 2:

[0043] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 870℃ using a medium frequency induction heating method with an induction power supply frequency of 5000Hz, held for 20 seconds, then water quenched, and then heated to 240℃ for tempering and held for 1 hour.

[0044] Comparative Example 3:

[0045] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 920℃ using a medium frequency induction heating method with an induction power supply frequency of 5000Hz, held for 10 seconds, then water quenched, and then heated to 180℃ for tempering and held for 1 hour.

[0046] Comparative Example 4:

[0047] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 800℃ using a medium frequency induction heating method with an induction power supply frequency of 5000Hz, held for 20 seconds, then water quenched, and then heated to 180℃ for tempering and held for 1 hour.

[0048] Comparative Example 5:

[0049] The surface hardening method is as follows: the surface of medium carbon bearing steel is heated to 970℃ using a medium frequency induction heating method with an induction power supply frequency of 5000Hz, held for 20 seconds, then water quenched, and then heated to 180℃ for tempering and held for 1 hour.

[0050] Table 2. Analysis results of surface hardening layer hardness, depth, and quenching quality of the examples and comparative examples.

[0051]

[0052] The performance design requirements of this invention for medium carbon bearing steel after surface quenching are: hardened layer depth ≥ 10mm, hardened layer hardness HRC52-62, and no surface cracks.

[0053] As can be seen from Examples 1-9, Comparative Examples 1-5, and Table 2:

[0054] The surface quenching method for medium carbon bearing steel designed according to this invention, as described in Examples 1-9, meets the performance design requirements of this invention. In Comparative Example 1, induction heating was followed by oil quenching, which is outside the scope of this invention's technical solution (water quenching). Comparative Example 1, using oil quenching, has a slow cooling rate, insufficient quenching, and low hardness; its surface hardened layer hardness is less than HRC 52, failing to meet the design requirements of this invention (hardened layer hardness HRC 52-62). In Comparative Example 2, the tempering temperature is 240℃, outside the scope of this invention's technical solution (150-220℃). The tempering temperature in Comparative Example 2 is too high, leading to reduced hardness; its surface hardened layer hardness is less than HRC 52. 52. The design requirements of this invention (hardness of the hardened layer HRC52-62) are not met. In Comparative Example 3, the induction heating holding time is 10 seconds, which is outside the scope of the technical solution of this invention (15-70 seconds). The induction heating holding time of Comparative Example 3 is too short, and the surface temperature is not sufficiently conducted to the interior, resulting in a shallow surface hardened layer after quenching. Its surface hardened layer depth is 7.4 mm, which does not meet the design requirements of this invention (hardened layer depth ≥10 mm). In Comparative Example 4, the induction heating temperature is 800℃, which is outside the scope of the technical solution of this invention. Within the scope of the technical solution (820-950℃), the induction heating temperature of Comparative Example 4 is relatively low, resulting in insufficient heat input and a surface hardened layer depth of 8.5mm, which does not meet the design requirements of the present invention (hardened layer depth ≥10mm). In Comparative Example 5, the induction heating temperature is 970℃, which is not within the scope of the technical solution of the present invention (820-950℃). The induction heating temperature of Comparative Example 5 is relatively high. Water quenching at excessively high temperatures leads to excessive stress, causing the workpiece to crack. Its quenching quality does not meet the design requirements of the present invention.

Claims

1. A method for surface quenching of medium carbon bearing steel, characterized in that: During surface quenching heat treatment, medium carbon bearing steel is heated to 820-890℃ using medium frequency induction heating, held for 15-70 seconds, water quenched, and then tempered at 150-180℃ for 2-5 hours. The frequency of the induction power supply for the medium-frequency induction heating is 3000~8000Hz; The method can make the surface hardened layer of medium carbon bearing steel ≥10mm deep, with a hardness of HRC52-62, and the surface free of cracks.

2. The surface quenching method for medium carbon bearing steel according to claim 1, characterized in that, In the surface hardening method, the hardening heating temperature is further set to 820-860℃, or 850-890℃.

3. The surface quenching method for medium carbon bearing steel according to claim 1, characterized in that, The surface hardening method further specifies the hardening and holding time as 15-35 seconds, 30-50 seconds, or 50-70 seconds.

4. The surface quenching method for medium carbon bearing steel according to claim 1, characterized in that, The tempering holding time in the surface quenching method is further set to 2.0-4.0 hours, or 3.0-5.0 hours.

5. The surface quenching method for medium carbon bearing steel according to claim 1, characterized in that: This method is applied to the surface hardening heat treatment of bearing components.

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