KR20090008554A - Steel for bearing having high resistance to the outer particles and the heat treatment method thereof - Google Patents

Abstract

A bearing steel with improved resistance to foreign materials is provided to improve fatigue life relative to the foreign materials by reducing the size of dents due to the foreign materials, decreasing height of protrusions, and easily removing already formed protrusions, and a heat treatment method of the bearing steel with improved resistance to foreign materials is provided. A heat treatment method of a bearing steel with improved resistance to foreign materials comprises: a first carburizing process of carburizing a bearing steel workpiece to a temperature of 920 to 960 deg.C in a carburizing atmosphere of 1.0 to 1.3% of carbon potential for 4 to 6 hours; a carbonitriding process of injecting 3 to 10% by volume of ammonia gas into carburizing gas of the carburizing atmosphere to carburize and nitride the carburized workpiece to a temperature of 830 to 870 deg.C for 2 to 4 hours; a quenching process of rapidly cooling the carbonitrided workpiece to quench the carbonitrided workpiece; a first tempering process of holding the quenched workpiece at 120 to 150 deg.C for 1 to 2 hours, and then slowly cooling the workpiece; a subzero treatment process of holding the workpiece at -70 to -100 deg.C for 1.5 to 2.5 hours; and a second tempering process of holding the subzero-treated workpiece at a predetermined temperature for 1.5 to 2.5 hours, and then slowly cooling the workpiece. The bearing steel comprises, by weight percent, iron(Fe), 0.18 to 0.33% of carbon(C), 0.15 to 0.35% of silicon(Si), 0.60 to 0.85% of manganese(Mn), and 0.90 to 1.20% of chromium(Cr).

Description

Steel for bearing having high resistance to the outer particles and the heat treatment method

1 is a schematic cross-sectional view showing a tapered roller bearing.

2 to 4 are cross-sectional views illustrating damage caused by foreign matter.

5 and 6 are graphs showing the hardness distribution according to the depth of the bearing steel heat-treated by the conventional heat treatment method.

7 and 8 are graphs showing the hardness distribution according to the depth of the bearing steel heat-treated by the heat treatment method according to the present invention.

Figure 9 schematically shows a bearing steel fatigue life test apparatus.

10 is a SEM photograph of the foreign material used in the foreign material test of the bearing steel according to the present invention.

* Description of the symbols for the main parts of the drawings *

100: bearing 110: inner ring

113: dent 115: protrusion

120: outer ring 130: roller (motor)

140: cage (retainer)

1000: Fatigue Life Tester 1010: Housing

1020: mounting portion 1030: test piece

1040: top plate 1041: groove

1050: axis of rotation 1060: ball

1070: retainer 1080: pressurization

1090: Support Ball

The present invention relates to a bearing steel with improved foreign material resistance and a heat treatment method thereof, to increase the hardness of the surface, to increase the amount of residual austenite and to adjust the hardness distribution according to the depth from the surface to reduce the size of the dent due to the foreign material It is related to the bearing steel and its heat treatment method to reduce the height of the protrusions, and once the protrusions are easily extinguished to improve the fatigue life of the foreign materials.

1 is a cross-sectional view showing a tapered roller bearing which is a rolling bearing used in an automobile transmission, a rolling roller, a construction machine, etc., as shown in FIG. 1, an inner ring 110 into which a shaft is inserted, and an outer ring 120 inserted into a housing. And a plurality of rolling chain rollers 130 for rotatably supporting the inner ring 110 and the outer ring 120 between the inner ring 110 and the outer ring 120, and a gap between the rollers 130. It is made of a retainer 140 to maintain a constant. In the above, when the ball is used as a rolling element and grooves are formed in the inner ring 110 and the outer ring 120, the ball bearings become a ball bearing. When the retainer 140 is made of plastic, it is also called a cage.

Such bearings are used in automobile transmissions, construction machinery, etc., and a large load acts at the same time the impact acts, so that the surface in which the inner and outer rings of the bearing come into contact with the rolling elements maintains a high hardness (HRc 58-64) and moves to the center. Increasingly, the hardness is lowered to have toughness against impact, and by having the hardness distribution as described above, sufficient life can be maintained.

In addition, bearings used as accessories of mechanical devices may be used in clean environments and may penetrate fine and hard particles.

2 to 4 illustrate, for example, a case in which foreign matter intrudes into the bearing operating environment. When foreign matter invades the bearing operating environment, the inner ring 110 or the outer ring as shown in FIGS. 2 and 3 are illustrated. The dent 113 generate | occur | produces by the foreign material A on the surface of 12, and the protrusion part 115 is formed in the circumference | surroundings of the dent 113. When the rolling element 130 is in contact with the protrusion 115 while rotating, high stress is generated in the protrusion 115, and when the height H of the protrusion 115 is higher than the thickness of the lubricating film, The inner and outer rings 110 and 120 come into metal contact, which causes the bearing life to be significantly shortened.

In order to improve resistance to foreign substances, carburizing tears such as SCr420H and SCr430H have been used to increase the amount of retained austenite on the surface. Residual austenite increases the radius of curvature of the edge protrusion 115 of the dent 113 and lowers the protrusion height H when the dent 113 is generated by foreign matter, and the protrusion 115 once generated can be easily removed. Make sure However, in the prior art and the method of increasing the residual austenite has a problem that the foreign material resistance is not improved, the life is not sufficiently increased.

The present invention has been proposed to solve the problem that the life of the bearing is shortened by the foreign matter as described above, to increase the hardness of the bearing steel surface, increase the amount of retained austenite, and adjust the hardness distribution according to the depth from the surface It is therefore an object of the present invention to provide a bearing steel and a heat treatment method in which the height of the protrusion by the foreign matter is reduced, and once generated, the protrusion is easily extinguished to improve the resistance to the foreign matter.

In the bearing steel heat treatment method improved foreign material resistance according to the present invention for achieving the above object in the method for heat-treating the bearing steel used as the inner ring, outer ring of the bearing including the inner ring, outer ring, rolling element and cage, The bearing steel contains 0.18 to 0.33% by weight of carbon (C), 0.15 to 0.35% by weight of silicon (Si), 0.60 to 0.85% by weight of manganese (Mn), and 0.90 to 1.20% by weight of chromium (Cr). A first carburizing step of carburizing at a temperature of 920 to 960 ° C. for 4 to 6 hours in a carburizing atmosphere having a carbon potential of 1.0 to 1.3%; A carburizing step of carburizing and carburizing at a temperature of 830 to 870 ° C for 2 to 4 hours by injecting 3 to 10% by volume of ammonia gas to the carburizing gas in the carburizing atmosphere; A quenching step of quenching and quenching; A first tempering step of maintaining at 120-150 ° C. for 1 to 2 hours and slowly cooling; A sub zero treatment step of holding at -70 to -100 ° C for 1.5 to 2.5 hours; It is characterized by consisting of a second tempering step of maintaining at a predetermined temperature for 1.5 to 2.5 hours and slow cooling,

In the above, the first carburizing process and the carburizing step further comprises a second carburizing process is maintained in the same temperature range as the first carburizing process and carburized for a predetermined time in a carbon atmosphere of a lower concentration than the first carburizing process Characterized in that,

The carburizing atmosphere carbon potential of the second carburizing step is in the range of 0.9 to 1.2%, and characterized in that carburizing is carried out for 2 to 4 hours.

The heat treatment temperature of the second tempering process is characterized in that it is maintained 30 ℃ higher than the heat treatment temperature of the first tempering process.

And the surface hardness after the first tempering step is in the range of 62 to 64 HRC, the hardness at a depth of 2 mm from the surface to 49 to 53 HRC, and the residual austenite on the surface is in the range of 50 to 53 volume%; The surface hardness after the sub-zero treatment step is in the range of 68 to 69 HRC, the hardness at a depth of 2 mm from the surface is in the range of 50 to 54 HRC, and the residual austenite on the surface is in the range of 26 to 32% by volume.

On the other hand, the bearing steel with improved foreign material resistance according to the present invention is used as the inner ring and outer ring of the bearing including the inner ring, outer ring, rolling element and cage, the surface hardness is in the range of 860 ~ 880Hv, the amount of residual austenite on the surface It is in the range of 26 to 30% by volume, the hardness decreases away from the surface, and the hardness at a depth of 1.5 to 2.0 mm from the surface is in the range of 530 to 650 Hv.

And preferably, the hardness at a depth of 1.5 mm from the surface is preferably in the range of 530 to 560 Hv.

Hereinafter, a preferred embodiment of the bearing steel heat treatment method and bearing steel with improved foreign material resistance according to the present invention will be described with reference to the accompanying drawings. In the description of the present invention, the same names as those in the prior art are used, and the repetitive description is omitted.

7 and 8 are graphs showing the hardness distribution according to the depth from the surface of the bearing steel heat-treated by the bearing steel heat treatment method improved foreign material resistance according to the present invention, Figure 9 is a schematic view of the bearing steel life test apparatus It is shown.

Bearing steel heat treatment method improved foreign matter resistance according to the invention to have a hardness distribution as shown in Figure 7 is a first carburizing process, a carburizing settling process, a first tempering process, a sub-zero treatment process, The bearing steel is heat-treated through the process, including the second tempering process, the carbon (C) 0.18 ~ 0.33% by weight, the silicon (Si) 0.15 ~ 0.35% by weight, manganese (Mn) 0.60 ~ 0.85% by weight and chromium (Cr) 0.90 to 1.20% by weight.

The first carburizing process is carburized for 4 to 6 hours in a carburizing atmosphere having a carbon potential of 1.0 to 1.3% at a temperature in the range of 920 to 960 ° C, followed by the carburizing gas atmosphere (carbon potential of 1.0 to 1.3%) of the carburizing process. An additional 3 to 10% by volume of ammonia gas is added to the carburized gas and subjected to carburizing and sedimentation for 2 to 4 hours at a temperature in the range of 830 to 870 ° C (carburizing step). It is preferable to further include a second carburizing process, which is another carburizing process between the first carburizing process and the carburizing and carburizing process, in order to adjust the hardness of the inside of the steel. The second carburizing process maintains the same temperature as the first carburizing process, and carburizes for 2 to 4 hours at a carbon potential of 0.9 to 1.2% lower than that of the first carburizing process. At this time, the carburizing and carburizing process adds 3 to 10% by volume of ammonia gas to the carburizing gas atmosphere having a carbon potential of 0.9 to 1.2%, and performs carburizing and sedimentation for 2 to 4 hours at a temperature in the range of 830 to 870 ° C.

After completion of the carburizing and quenching process, the quenching is quenched, and then maintained at a temperature in the range of 120 to 150 ° C. and then cooled slowly (first tempering step). The surface hardness of the bearing steel after the first tempering step is 62 to 64 HRC range. The hardness at a depth of 2 mm is in the range of 49 to 53 HRC, and the residual austenite on the surface is 50 to 53% by volume. Then, it is maintained at -70 to -100 DEG C for 1.5 to 2.5 hours (sub-zero treatment step), so that the hardness at a depth of 2 mm from the surface to the range of 68 to 69 HRC after the sub-zero treatment is in the range of 50 to 54 HRC. The retained austenite is made 26 to 32% by volume. After the subzero treatment, the temperature is again maintained at a predetermined temperature, preferably about 30 ° C. higher than the first tempering process temperature for 1.5 to 2.5 hours (second tempering process). The bearing steel with improved foreign material resistance according to the present invention completed in the second tempering process has a surface hardness of 860 to 880 HV (in terms of 66 to 68 HRC), and the amount of retained austenite on the surface is in the range of 26 to 32% by volume. The hardness decreases with depth from the surface, and the hardness distribution at a depth of 1.5 to 2 mm from the surface is in the range of 650 to 530 HV. Preferably, the hardness at a depth of 1.5 mm from the surface is in the range of 530 to 560 HV.

Example

7 is a graph showing the heat treatment according to the depth of the SCr420H containing 0.2% by weight of carbon according to the heat treatment method according to the present invention, Figure 8 is a SCr430H containing 0.3% by weight of carbon in the present invention It is a graph showing the heat treatment according to the following heat treatment method and measuring the hardness according to the depth.

And Figure 5 is a graph showing the hardness measured according to the depth from the surface after the heat treatment of the bearing steel (carbon content 0.17 ~ 0.23%) according to the conventional method, Figure 6 is a SCr420H steel according to the method described in US Patent 5,336,338 It is a graph showing the hardness measured according to the depth from the surface after the heat treatment.

FIG. 9 schematically illustrates a foreign material environmental life test apparatus of a bearing steel having a hardness distribution illustrated in FIGS. 5 to 8, and FIG. 10 is a SEM photograph of a foreign material A injected in a foreign material environmental life test. The hardness of the foreign material shown in FIG. 10 was in the range of 702 to 843 HV, and the average hardness was 775 HV.

In briefly explaining the foreign material environmental life test apparatus shown in FIG. 9, in FIG. 9, 1010 illustrates a housing for fixing and installing a bearing steel test piece 1030 for a foreign material life test, and 1020 illustrates a test piece 1030 formed in the housing. ) Shows an installation part, 1040 is a top plate formed with grooves (1041, Groove) for rotating the rolling ball 1060 is rotated, 1050 is a rotating shaft that is connected to a drive such as a motor to rotate the top plate 1040 1050 is shown. And, 1080 is a pressing part, 1090 is a support ball installed between the pressing part 1080 and the housing 1010 so that the load acts on the center of the housing 1010, 1070 is a ball 1060 Retainer is shown to maintain the gap between and prevent the departure. As shown in FIG. 9, the test piece 1030 having a circular cross section is fixedly installed in the housing 1010, and the plurality of balls 1060 are pressed by the pressing unit 1080 while rotating the plurality of balls 1060 to the upper plate 1040. Loads are applied to the ball 1060 and the specimen 1030. And lubricating with a lubricant containing the foreign material shown in FIG.

The fatigue life of the test piece 1030 was measured in the above state, and the test piece having the hardness distribution shown in FIG. 6 compared to the test piece having the hardness distribution as shown in FIG. 5 (US Patent No. 5,336,338). Fatigue life increased by 4.5 times, fatigue life of the test piece having a hardness distribution shown in Figures 7 and 8 heat-treated by the heat treatment method according to the present invention increased by 11 times.

Although the embodiments of the present invention have been described above with reference to the drawings, the protection scope of the present invention is not limited thereto, and the scope of protection of the present invention is recognized from the embodiments of the present invention to a range easily implemented by those skilled in the art. Should.

As described above, the life test was performed on the bearing steel heat-treated by the bearing steel heat treatment method of the present invention and the bearing steel heat-treated under the same conditions as before, and the test result was 11 compared to the bearing steel heat-treated according to the conventional method. The life of the ship is improved, and the life is improved by about 2.5 times compared to the bearing steel having the hardness distribution as shown in FIG. 6.

Claims (7)

In the method for heat-treating the bearing steel used as the inner ring, outer ring of the bearing including the inner ring, outer ring, rolling element and cage, the bearing steel is iron (Fe) 0.18 ~ 0.33% by weight, silicon (Si) 0.15 to 0.35% by weight, manganese (Mn) 0.60 to 0.85% by weight, chromium (Cr) 0.90 to 1.20% by weight, carbon potential 1.0 to 1.3% carburizing atmosphere at a temperature of 920 ~ 960 ℃ A first carburizing process which carburizes for 4 to 6 hours at; A carburizing step of carburizing and carburizing at a temperature of 830 to 870 ° C for 2 to 4 hours by injecting 3 to 10% by volume of ammonia gas to the carburizing gas in the carburizing atmosphere; A quenching step of quenching and quenching; A first tempering step of maintaining at 120-150 ° C. for 1 to 2 hours and slowly cooling; A subzero treatment step of maintaining at -70 to -100 캜 for 1.5 to 2.5 hours; The bearing steel heat treatment method with improved foreign material resistance, characterized by comprising a second tempering step of maintaining at a predetermined temperature for 1.5 to 2.5 hours and slow cooling.  The second carburizing process according to claim 1, wherein the second carburizing process is maintained between the first carburizing process and the carburizing carburizing process in the same temperature range as the first carburizing process and carburized for a predetermined time in a carbon atmosphere having a lower concentration than the first carburizing process. Bearing steel heat treatment method with improved foreign material resistance, comprising a.  3. The bearing steel heat treatment method of claim 2, wherein the carburizing atmosphere carbon potential of the second carburizing process is in the range of 0.9 to 1.2% and carburizing for 2 to 4 hours. The heat treatment method of claim 1, wherein the heat treatment temperature of the second tempering process is maintained at 30 ° C. higher than the heat treatment temperature of the first tempering process. 5. The method according to claim 4, wherein the surface hardness after the first tempering step is in the range of 62 to 64 HRC, the hardness at a depth of 2 mm from the surface to 49 to 53 HRC, and the residual austenite on the surface is in the range of 50 to 53 volume%; The foreign material resistance characterized in that the surface hardness after the subzero treatment step is in the range of 68 to 69 HRC, the hardness at a depth of 2 mm from the surface is in the range of 50 to 54 HRC, and the residual austenite on the surface is in the range of 26 to 32 vol%. Improved bearing steel heat treatment method. In the bearing steel used for the inner ring and outer ring of a bearing including an inner ring, an outer ring, a rolling element, and a cage, the surface hardness is in the range of 860 to 880 Hv, and the amount of retained austenite on the surface is in the range of 26 to 30% by volume. The bearing steel with improved foreign material resistance, characterized in that the hardness decreases away from the surface, and the hardness at a depth of 1.5 to 2.0 mm from the surface is in the range of 650 to 530 Hv. 7. The bearing steel with improved foreign material resistance according to claim 6, wherein the hardness at a depth of 1.5 mm from the surface is in the range of 530 to 560 Hv.

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