Cylindrical roller bearing and multi-stage rolling mill having same

Abstract

To provide a cylindrical roller bearing capable of realizing suppression in both edge peeling and internal origin peeling of an inner ring simultaneously and improving its service life.SOLUTION: A cylindrical roller bearing comprises: a cylindrical roller that has, as a component, a steel material satisfying the Japanese Industrial Standards for high carbon chromium bearing steel materials, and has a predetermined axial length of a crowning and a chamfering, a predetermined radius of curvature of the crowning, and a predetermined hardness at a depth Z at which orthogonal shear stress is maximized; and an inner ring having predetermined compositions, a predetermined carbon concentration up to the depth Z, a predetermined amount of residual austenite at the depth Z, a predetermined average grain size, and a predetermined hardness.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cylindrical roller bearing and a multi-stage rolling mill having the cylindrical roller bearing. [Background technology]

[0002] Among bearings for rolling equipment, multi-stage rolling mills are used in a severe environment. In the backup roll bearings of multi-stage rolling mills, the outer ring rotates while receiving the rolling load on the outer diameter of the bearing, and the inner ring is a fixed ring. Because the inner ring is a fixed ring, spalling due to rolling fatigue in the load area of ​​the inner ring raceway surface becomes a problem.

[0003] One known method for suppressing flaking is to provide a crowning to the rolling surface of the roller. The crowning reduces the edge stress on the rolling surface, suppressing edge flaking on the raceway surface of the inner ring with which the rolling surface of the roller comes into contact. However, if the crowning is made longer, the contact pressure at the center of the rolling surface of the roller increases, increasing the frequency of internally initiated flaking on the raceway surface of the inner ring.

[0004] Patent Document 1 discloses a rolling bearing having an improved life, characterized by the hardness of the inner and outer races and the rolling elements, the amount of retained austenite, and the like. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-172364 A Summary of the Invention [Problem to be solved by the invention]

[0006] Under these circumstances, an object of the present invention is to provide a cylindrical roller bearing which can simultaneously suppress edge flaking and internally initiated flaking of the inner ring, thereby improving the bearing life. The present invention also aims to provide a multi-stage rolling mill that can improve the maintenance cycle and operation rate by reducing the frequency of bearing replacement.

Means for Solving the Problems

[0007] The cylindrical roller bearing of the present invention includes an inner ring fixed to a fixed shaft and having an inner ring raceway on its outer peripheral surface, Inside an outer ring having an outer ring raceway on its circumferential surface, a plurality of cylindrical rollers rotatably disposed between the inner ring raceway and the outer ring raceway, and the cylindrical rollers have a steel material satisfying the standard of Japanese Industrial Standard G 4805:2019 High-carbon chromium bearing steel steel material as a component, the rolling surface of the cylindrical rollers has a first chamfer, a first crowning, a cylindrical surface, a second crowning, and a second chamfer from the first side in the axial direction toward the second side in the axial direction, the first chamfer is connected to a first end face on the first side in the axial direction, the second chamfer is connected to a second end face on the second side in the axial direction, when the axial length of the first chamfer is LCha, the axial length of the first crowning is LCra, the axial length of the cylindrical surface is LCy, the axial length of the second crowning is LCrb, and the axial length of the second chamfer is LChb, (LCha + LCra + LCy + LCrb + LChb) / 4.8 < LCha + LCra < (LCha + LCra + LCy + LCrb + LChb) / 3.2, and (LCha + LCra + LCy + LCrb + LChb) / 4.8 < LChb + LCrb < (LCha + LCra + LCy + LCrb + LChb) / 3.2 are satisfied, in a cross-section including the central axis of the cylindrical roller, when the radius of curvature of the first crowning is RRa and the radius of curvature of the second crowning is RRb, 900 mm < RRa < 9000 mm, and 900mm <RRb<9000mm Fulfilling The hardness at a depth Z from the cylindrical surface of the cylindrical roller where the orthogonal shear stress is maximum is 682 to 805 HV, The inner ring is As an ingredient, Carbon (C): 0.12~0.50mass%, Manganese (Mn): 0.30 to 0.90 mass%, Silicon (Si): 0.15 to 0.35 mass%, Nickel (Ni): 0.40 to 4.50 mass%, Chromium (Cr): 0.40 to 2.00 mass%, Molybdenum (Mo): 0.15 to 0.90 mass%, and The balance is iron (Fe) and unavoidable impurities. a carbon concentration from the surface of the inner ring raceway to the position of the depth Z is 0.60 to 1.30 mass%, the amount of retained austenite at the depth Z from the surface of the inner ring raceway is 25 to 45 vol%; The average grain size at the depth Z from the surface of the inner ring raceway is 8 to 10; The hardness at the depth Z from the surface of the inner ring raceway is 682 to 770 HV.

[0008] The cylindrical roller bearing of the present invention comprises: A cylindrical roller having a steel material satisfying the Japanese Industrial Standard for high carbon chromium bearing steel material as a component, and having a predetermined axial length of a crowning and a chamfer, a predetermined radius of curvature of the crowning, and a predetermined hardness at the depth Z; The inner ring has a predetermined component, a predetermined carbon concentration up to the depth Z, and, at the depth Z, a predetermined amount of retained austenite, a predetermined average grain size, and a predetermined hardness. Therefore, the cylindrical roller bearing of the present invention can simultaneously suppress edge flaking and internally initiated flaking of the inner ring, thereby improving the service life. The reason for this is believed to be as follows. The cylindrical rollers of the cylindrical roller bearing are provided with crowning and chamfering having a predetermined shape in the axial direction, so that edge stress of the inner ring raceway is reduced, and as a result, edge spalling of the inner ring is suppressed. Moreover, the inner ring of the cylindrical roller bearing has a predetermined amount of retained austenite, a predetermined average grain size, and a predetermined hardness at the depth Z. Therefore, edge flaking and internally initiated flaking of the inner ring are suppressed. Furthermore, due to the contact surface pressure of the cylindrical surface of the cylindrical roller, the retained austenite of the inner ring undergoes processing-induced transformation to martensite during use of the cylindrical roller bearing. Therefore, the microstructure of the inner ring is strengthened. As a result, internally initiated flaking of the inner ring is suppressed. Therefore, the cylindrical roller bearing can simultaneously suppress edge flaking and internally initiated flaking of the inner ring, thereby improving the life of the bearing.

[0009] In the cylindrical roller bearing, the inner ring preferably contains, as a component, carbon (C): 0.12 to 0.23 mass %. This makes it possible to increase the toughness of the inner ring, thereby suppressing fracture caused by edge flaking and internally initiated flaking of the inner ring, thereby further improving the life of the cylindrical roller bearing.

[0010] In the cylindrical roller bearing, it is preferable that the outer peripheral surface of the outer ring rolls on the outer peripheral surface of a cylindrical member. The cylindrical roller bearing achieves suppression of edge flaking and internally initiated flaking of the inner ring at the same time, improving the service life, and therefore the outer peripheral surface of the outer ring of the cylindrical roller bearing can roll for a long period of time on the outer peripheral surface of a cylindrical member such as a work roll or backup roll of a rolling mill.

[0011] Moreover, a multi-stage rolling mill of the present invention has the above-mentioned cylindrical roller bearing. The multi-stage rolling mill having the cylindrical roller bearing can improve the maintenance cycle and the availability rate by reducing the frequency of bearing replacement. Effect of the Invention

[0012] According to the cylindrical roller bearing of the present invention, it is possible to simultaneously suppress edge flaking and internally initiated flaking of the inner ring, thereby improving the life of the cylindrical roller bearing. Furthermore, according to the multi-stage rolling mill of the present invention, the frequency of bearing replacement is reduced, thereby improving the maintenance cycle and the availability rate of the multi-stage rolling mill. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic side view of a multi-stage rolling mill according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic front view showing a backup roll in the multistage rolling mill of FIG. [Diagram 3] 3 is a schematic cross-sectional view of a divided roll 15 in FIG. 2 in the axial direction. [Figure 4] FIG. 4 is a schematic cross-sectional view of the cylindrical roller of FIG. [Diagram 5] FIG. 2 is a schematic side view of a rolling fatigue life tester used for measuring life ratios in the examples and comparative examples. [Figure 6] FIG. 2 is a front schematic view of a rolling fatigue life tester used for measuring life ratios in the examples and comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a cylindrical roller bearing according to a first embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a schematic side view of a multi-stage rolling mill according to this embodiment. This rolling mill 10 is a 20-stage cluster rolling mill having a 1-2-3-4 roll arrangement. A material RM to be rolled, such as a thin plate material, is passed between a pair of upper and lower work rolls 11 in the left-right direction of Fig. 1 and rolled. The pair of upper and lower work rolls 11 are supported by four first intermediate rolls 12 (two each on the upper and lower sides). The four first intermediate rolls 12 are supported by six second intermediate rolls 13 (three each on the upper and lower sides). The six second intermediate rolls 13 are supported by eight backup rolls 14 (four each on the upper and lower sides).

[0015] Fig. 2 is a schematic front view showing the backup roll 14. The backup roll 14 has six divided rolls 15 arranged in the axial direction. Each divided roll 15 is concentrically and rotatably attached to a shaft 16. The shaft 16 is supported by a saddle 18 supported by a housing 17 of the rolling mill 10 as shown in Fig. 1.

[0016] Fig. 3 is a schematic axial cross-sectional view passing through the center of the shaft 16 of the divided roll 15 of Fig. 2. Each divided roll 15 is a cylindrical roller bearing including an inner ring 20 fitted onto the outer peripheral surface of the shaft 16, an outer ring 21 arranged radially outside the inner ring 20, three cylindrical rollers 22 arranged between the inner ring 20 and the outer ring 21, and a cage 23 that holds the three cylindrical rollers 22.

[0017] The inner ring 20 is fixed to the shaft 16 (not shown). Therefore, relative rotation between the inner peripheral surface 20a of the inner ring 20 and the shaft 16 is prevented. The outer peripheral surface 20b of the inner ring 20 has an inner ring raceway along which the cylindrical rollers 22 roll. The inner peripheral surface 21a of the outer ring 21 has an outer ring raceway along which the cylindrical rollers 22 roll. The outer peripheral surface 21b of the outer ring 21 is in contact with the outer peripheral surface of the second intermediate roll 13 as shown in FIG. 1. As the outer peripheral surface of the second intermediate roll 13 rotates, the outer peripheral surface 21b rolls on the outer peripheral surface of the second intermediate roll 13.

[0018] The dimensions of the cylindrical roller bearing according to the embodiment of the present invention are not particularly limited and may be appropriately set according to the device to which the cylindrical roller bearing is applied. The dimensions of the cylindrical roller bearing shown in the divided roll 15 of this embodiment are, for example, a width W of the outer ring 21 of 20 to 250 mm, a width T of the inner ring 20 of 20 to 250 mm, a diameter d of the inner peripheral surface 20a of the inner ring 20 of 30 to 200 mm, and a diameter D1 of the outer peripheral surface 21b of the outer ring 21 of 60 to 500 mm.

[0019] Figure 4 is a schematic cross-sectional view of the cylindrical roller 22 in the schematic cross-sectional view of the split roll 15 of Figure 3. The cylindrical roller 22 has, as a component, a steel material that meets the standard of Japanese Industrial Standard G 4805:2019 High-carbon chromium bearing steel steel material. Examples of the steel material that meets the standard of Japanese Industrial Standard G 4805:2019 High-carbon chromium bearing steel steel material include SUJ2, SUJ3, SUJ4, and SUJ5, etc. The cylindrical roller 22 has a rolling surface 22a, an end face 22b on the left side in the axial direction of Figure 4, and an end face 22c on the right side. The rolling surface 22a has, from the end face 22b toward the end face 22c, a first chamfer Cha, a first crowning Cra, a cylindrical surface Cy, a second crowning Crb, and a second chamfer Chb. The length L of the cylindrical roller 22 from the end face 22b to the end face 22c is the sum of the axial length LCha of the first chamfer Cha, the axial length LCra of the first crowning Cra, the axial length LCy of the cylindrical surface Cy, the axial length LCrb of the second crowning Crb, and the axial length LChb of the second chamfer Chb. The length L may be appropriately set according to the dimensions of the above-mentioned cylindrical roller bearing and is not particularly limited. The length L of the cylindrical roller 22 in this embodiment is, for example, 19 to 59 mm.

[0020] The sum of the length LCha and the length LCra exceeds 1 / 4.8 of the length L and is less than 1 / 3.2 of the length L. Also, the sum of the length LChb and the length LCrb exceeds 1 / 4.8 of the length L and is less than 1 / 3.2 of the length L. That is, the lengths of the chamfered portion and the crowning portion of the cylindrical roller 22 satisfy the following Formula 1 and Formula 2. (LCha + LCra + LCy + LCrb + LChb) / 4.8 < LCha + LCra < (LCha + LCra + LCy + LCrb + LChb) / 3.2 ··· Formula 1 (LCha + LCra + LCy + LCrb + LChb) / 4.8 < LChb + LCrb < (LCha + LCra + LCy + LCrb + LChb) / 3.2 ··· Formula 2 If the sum of the lengths LCha and LCra, and the sum of the lengths LChb and LCrb exceed 1 / 4.8 of the length L, the edge stress in the orbit of the cylindrical roller 22 is reduced. Therefore, edge peeling on the outer peripheral surface 20b of the inner ring 20 and the inner peripheral surface 21a of the outer ring 21 is suppressed. Also, if the sum of the lengths LCha and LCra, and the sum of the lengths LChb and LCrb are less than 1 / 3.2 of the length L, the contact surface pressure on the inner ring orbit on the outer peripheral surface 20b of the inner ring 20 and the outer ring orbit on the inner peripheral surface 21a of the outer ring 21 by the cylindrical surface Cy of the rolling surface 22a is reduced. Therefore, the occurrence frequency of internal origin peeling on the outer peripheral surface 20b of the inner ring 20 and the inner peripheral surface 21a of the outer ring 21 is suppressed. In the cylindrical roller 22 of the present embodiment, the length LCha and the length LChb are substantially the same length. Also, the length LCra and the length LCrb are substantially the same length. Thereby, the deviation of the contact surface pressure from the rolling surface 22a of the cylindrical roller 22 to the inner ring orbit and the outer ring orbit is reduced. Therefore, edge peeling and internal origin peeling on the outer peripheral surface 20b of the inner ring 20 and the inner peripheral surface 21a of the outer ring 21 are more suppressed. Here, substantially the same means, for example, that one length is 55% to 175% of the other length. Note that the lengths LCha and LChb of the cylindrical roller 22 of the present embodiment are each 0.5 to 2.5 mm. The lengths LCra and LCrb of the cylindrical roller 22 of the present embodiment are each 1.0 to 21.5 mm.

[0021] The first crowning Cra and the second crowning Crb each have a radius of curvature RRa and a radius of curvature RRb. Here, the radius of curvature RRa and the radius of curvature RRb each satisfy the following equations 3 and 4. 900 mm < RRa < 9000 mm ··· Equation 3 900 mm < RRb < 9000 mm ··· Equation 4 If the radius of curvature RRa and the radius of curvature RRb exceed 900 mm, the stress generated in the Cra portion and the Crb portion can be relaxed. If the radius of curvature RRa and the radius of curvature RRb are less than 9000 mm, the stress generated in the Cy portion can be relaxed. In addition, the first crowning Cra and the second crowning Crb in this embodiment have substantially the same radius of curvature. This reduces bias in the contact surface pressure from the rolling surface 22a of the cylindrical roller 22 to the inner ring raceway and the outer ring raceway. This further suppresses edge peeling on the outer peripheral surface 20b of the inner ring 20 and the inner peripheral surface 21a of the outer ring 21. Here, "substantially the same" means, for example, that one radius of curvature is 70% to 140% of the other radius of curvature.

[0022] The first chamfer Cha and the second chamfer Chb have a radius of curvature of 900 mm or less.

[0023] The cylindrical surface Cy has a radius of curvature of 9000 mm or more. Note that a radius of curvature of 9000 mm or more is a concept that includes a straight line (with an infinite radius of curvature) parallel to the axial direction.

[0024] The hardness at a depth Z from the cylindrical surface Cy of the cylindrical roller 22 where the orthogonal shear stress is maximum is 682 to 805 HV. Here, the orthogonal shear stress indicates the shear stress in a plane parallel to the cylindrical surface Cy of the cylindrical roller 22. Here, the depth Z can be obtained by a known method based on the contact load between the cylindrical roller 22 and the inner ring 20 and the shape of the cylindrical roller 22. The depth Z from the cylindrical surface Cy of the cylindrical roller 22 in this embodiment is located at a depth of 0.2 to 2.5% of the diameter D2 of the cylindrical roller 22 from the cylindrical surface Cy. The diameter D2 may be appropriately set in accordance with the dimensions of the cylindrical roller bearing described above, and is not particularly limited. The diameter D2 of the cylindrical roller 22 in this embodiment is, for example, 9.5 to 55 mm. If the hardness at the depth Z from the cylindrical surface Cy of the cylindrical roller 22 is 682 to 805 HV, the strength of the rolling surface 22a of the cylindrical roller 22 can be ensured. Therefore, peeling is suppressed on the rolling surface 22a of the cylindrical roller 22. The Vickers hardness may be measured by a method in accordance with the Japanese Industrial Standard JIS Z 2244:2009. As the length of the crowning increases, the axial length LCy of the cylindrical surface Cy becomes shorter, increasing the contact pressure that the cylindrical surface Cy exerts on the inner ring 20 and increasing the frequency of internally initiated flaking. For this reason, the inner ring is made of the following material and undergoes the following heat treatment.

[0025] The inner ring 20 contains, as its components, 0.12-0.50 mass% carbon (C), 0.30-0.90 mass% manganese (Mn), 0.15-0.35 mass% silicon (Si), 0.40-4.50 mass% nickel (Ni), 0.40-2.00 mass% chromium (Cr), 0.15-0.90 mass% molybdenum (Mo), with the balance being iron (Fe) and unavoidable impurities. The inner ring 20 preferably contains, as its components, 0.40-1.00 mass% chromium (Cr) and 0.15-0.35 mass% molybdenum (Mo). Nickel-chromium-molybdenum steel materials that satisfy the above-mentioned content of each component and are specified by the Japanese Industrial Standards, International Standards, and standards of other countries can be used as components of the inner ring 20. Specific examples of nickel-chromium-molybdenum steel materials that can be used for the inner ring 20 include SNCM220, SNCM420, SNCM815, SNCM415, SNCM447, SNCM815, SAE8620, SAE4320, SAE8720, and SAE4322S. The inner ring 20 having the above components suppresses edge flaking and internally initiated flaking on the outer circumferential surface 20b of the inner ring 20. Therefore, the life of the cylindrical roller bearing represented by the divided roll 15 is improved.

[0026] The inner ring 20 preferably contains 0.12 to 0.23 mass % of carbon as a component, which can suppress fracture caused by edge spalling and internally initiated spalling on the outer peripheral surface 20b of the inner ring 20.

[0027] The carbon concentration from the surface of the inner ring raceway on the outer circumferential surface 20b of the inner ring 20 to the position of the depth Z is 0.60 to 1.30 mass %. In this embodiment, the depth Z from the surface of the inner ring raceway of the outer circumferential surface 20b of the inner ring 20 is located at a depth of 0.2 to 2.5% of the diameter D2 of the cylindrical roller 22 from the surface of the inner ring raceway of the outer circumferential surface 20b. The carbon concentration may be measured using a method conforming to Japanese Industrial Standard G 1253:2013. Here, if the carbon concentration up to the position of the depth Z is 0.60 mass% or more, the strength of the outer peripheral surface 20b of the inner ring 20 and a predetermined amount of retained austenite can be ensured. If the carbon concentration up to the position of the depth Z is 1.30 mass% or less, the generation of excess retained austenite at the depth Z described below is suppressed, and the required hardness is ensured. Therefore, during use of the split rolls 15, the retained austenite undergoes processing-induced transformation to martensite, and the microstructure of the inner ring is strengthened. As a result, internally initiated spalling on the outer peripheral surface 20b of the inner ring 20 is suppressed.

[0028] The inner ring 20 having a carbon concentration of 0.60 to 1.30 mass% from the surface of the inner ring raceway of the outer peripheral surface 20b of the inner ring 20 to the position of the depth Z can be obtained by a series of heat treatments, which include a carburizing treatment to cause carbon to penetrate from the surface, a quenching treatment, and a tempering treatment to harden the surface layer. The heat treatments are not particularly limited as long as the carbon concentration from the surface of the inner ring raceway of the outer peripheral surface 20b of the inner ring 20 to the position of the depth Z can be 0.60 to 1.30 mass%. For example, the carburizing, quenching, and tempering treatments can be a treatment method conforming to the Japanese Industrial Standards B 6914:2002. The series of heat treatments can also include a subzero treatment in which the material is cooled to a low temperature of 0°C or less immediately after quenching. A more specific example of the carburizing treatment is gas carburizing, which is performed in an atmosphere having a carbon potential (CP) value of 1.1 mass% at a temperature of 960°C for 26 hours. An example of the quenching treatment is a treatment method at 780 to 870°C for 70 minutes. An example of the tempering treatment is a treatment method at 180°C for 2 hours. An example of the sub-zero treatment is a treatment method in an atmosphere of -20°C for 1 hour.

[0029] The amount of retained austenite at the depth Z from the surface of the inner ring raceway on the outer peripheral surface 20b of the inner ring 20 is 25 to 45 vol%. If the amount of retained austenite at the depth Z is 25 vol% or more, the retained austenite for strengthening the microstructure of the inner ring 20 can be ensured. If the amount of retained austenite at the depth Z is 45 vol% or less, the hardness of the outer peripheral surface 20b of the inner ring 20 can be ensured. Therefore, edge flaking and internally initiated flaking on the outer peripheral surface 20b of the inner ring 20 is suppressed. The amount of retained austenite at the depth Z is determined by polishing from the surface in the radial direction to the depth Z using an electrolytic polishing method, and calculating the ratio of α phase (martensite) to γ ​​phase (austenite) on the surface exposed by electrolytic polishing using an X-ray diffraction method.

[0030] The average crystal grain size at the depth Z from the surface of the inner ring raceway on the outer circumferential surface 20b of the inner ring 20 is 8 to 10, and preferably 9 to 10. The average grain size may be measured by a method conforming to Japanese Industrial Standard G 0551:2013. Here, if the average grain size at the depth Z is No. 8 or more, the strength of the inner ring raceway on the outer peripheral surface 20b of the inner ring 20 can be ensured. If the average grain size at the depth Z is No. 10 or less, the amount of retained austenite at the depth Z can be ensured. Therefore, edge flaking and internally initiated flaking on the outer peripheral surface 20b of the inner ring 20 is suppressed.

[0031] The hardness at the depth Z from the surface of the inner ring raceway of the outer peripheral surface 20b of the inner ring 20 is 682 to 770 HV. If the hardness at the depth Z is 682 HV or more, the strength of the inner ring raceway of the outer peripheral surface 20b of the inner ring 20 can be ensured. If the hardness at the depth Z is 770 HV or less, the amount of retained austenite at the depth Z can be ensured. Therefore, edge flaking and internally initiated flaking on the outer peripheral surface 20b of the inner ring 20 is suppressed.

[0032] The cylindrical roller bearing shown in the split roll 15 of this embodiment simultaneously achieves suppression of edge flaking and internally initiated flaking on the outer circumferential surface 20b of the inner ring 20. This improves the life of the split roll 15. As a result, the rolling mill 10 equipped with the backup roll 14 having the split roll 15 can improve the maintenance cycle and operation rate by reducing the frequency of bearing replacement.

[0033] (Other embodiments) In the first embodiment, a cylindrical roller bearing having three rows of cylindrical rollers 22 arranged between the inner ring 20 and the outer ring 21 is shown, but the number of rows of cylindrical rollers is not limited to this. The cylindrical roller bearing according to the embodiment of the present invention may have multiple rows of cylindrical rollers. As a cylindrical roller bearing applied to a multistage rolling mill, a cylindrical roller bearing having two or three rows of cylindrical rollers is preferable. In the first embodiment, the backup roll 14 is equipped with the cylindrical roller bearing of the present invention shown in the split roll 15. If the number of backup rolls employing the cylindrical roller bearing of the present invention increases, the maintenance cycle and the availability rate of the rolling mill 10 will be further improved. In the first embodiment, the backup roll 14 having six divided rolls 15 in the axial direction is shown, but the number of divided rolls in the backup roll is not limited to this. The backup roll according to the embodiment of the present invention may have a plurality of divided rolls. As a backup roll applied to a multistage rolling mill, a backup roll having 4 to 8 divided rolls is preferable. The multi-stage rolling mill is not limited to the 20-stage cluster rolling mill of the rolling mill 10. The multi-stage rolling mill may also be, for example, a 6-stage cluster rolling mill, a 12-stage cluster rolling mill, or other multi-stage rolling mills. The cylindrical roller bearing according to the embodiment of the present invention is not limited to application to backup rolls, but can also be applied to, for example, the nacelles of wind power generators and the wheels of extra-large dump trucks. EXAMPLES

[0034] The present invention will be described in more detail below with reference to examples, but the embodiments of the present invention are not limited to the following examples. Table 1 shows the components of the materials used in the cylindrical roller test specimens of the examples and comparative examples.

[0035] [Table 1]

[0036] The dimensions of the cylindrical roller test specimens in both the example and comparative example were a diameter D2 of 20 mm and a length of 36 mm.

[0037] The cylindrical rollers made from the above-mentioned materials were subjected to heat treatment under the conditions shown in Table 2 to produce cylindrical roller test specimens for the examples and comparative examples. The carburizing, quenching and tempering treatment was carried out by gas carburizing, quenching and tempering in accordance with Japanese Industrial Standard B 6914: 2002. The quenching and tempering treatments were carried out in accordance with Japanese Industrial Standard B 6913: 1999. The quenching treatment was carried out at the temperature and for the time shown in Table 2, followed by immediate immersion in quenching oil at an oil temperature of 80°C. The sub-zero treatment was carried out by placing the hardened parts in an atmosphere having the temperature shown in Table 2.

[0038] [Table 2]

[0039] The cylindrical roller test specimens prepared in the examples and comparative examples were used to carry out the following evaluations. (1) Vickers hardness: The Vickers hardness was measured by the following procedure. First, the cylindrical roller test piece was cut on a plane perpendicular to the axial direction. Next, the cut surface of the cut cylindrical roller test piece was buffed. After buffing, a test load of 2.94 N was applied using a Vickers hardness tester at a depth of 0.24 mm in the radial direction from the outer peripheral surface of the cylindrical roller test piece, and the Vickers hardness was measured according to a method in accordance with Japanese Industrial Standards Z 2244:2009. The depth of 0.24 mm is the depth at which the orthogonal shear stress becomes maximum in a cylindrical roller bearing assumed to use cylindrical roller test specimens 44 of the examples and comparative examples in a rolling fatigue life test machine 40 described later. This depth was set by adjusting the test conditions of the rolling fatigue life test machine 40 described later, based on the dimensions of the cylindrical roller test specimens of the above-mentioned examples and comparative examples.

[0040] (2) Amount of retained austenite: The cylindrical roller specimen was polished from the outer periphery to a depth of 0.24 mm in the radial direction using electrolytic polishing. The surface exposed by electrolytic polishing was subjected to X-ray diffraction analysis to measure the diffracted X-ray intensity of the α phase (martensite) and γ phase (austenite). The amount of retained austenite was calculated from the ratio of the diffracted X-ray intensity of the α phase to that of the γ phase.

[0041] (3) Average grain size: The average grain size was measured using the following procedure. First, the cylindrical roller test specimen was cut on a plane perpendicular to the axial direction. Next, the cut surface of the cut cylindrical roller test specimen was buffed. The buffed surface was etched with an AGS etching solution (a mixed aqueous solution of picric acid, sodium dodecylbenzenesulfonate, sodium chloride, and sodium sulfate) to reveal the prior austenite grain boundaries. After the prior austenite grain boundaries were revealed, the structure at a depth of 0.24 mm in the radial direction from the outer peripheral surface of the cylindrical roller test specimen was observed with an optical microscope. After observation with an optical microscope, the average grain size was calculated using a method in accordance with Japanese Industrial Standards G 0551:2013.

[0042] (4) Lifespan ratio: FIG. 5 is a schematic side view of the rolling fatigue life tester 40 used in the evaluation of the life ratio. FIG. 6 is a schematic front view of the rolling fatigue life tester 40. The rolling fatigue life tester 40 is equipped with one drive roll 41, two balls 42, and three guide rolls 43. The cylindrical roller test piece 44 is supported by the drive roll 41 and the two balls 42. The two balls 42 are supported by the three guide rolls 43. The drive roll 41 is connected to a drive unit for rotating the drive roll 41 (not shown). The drive roll 41 has a rectangular groove formed in the center of the axial direction of the outer circumferential surface. The cylindrical roller test piece 44 rotates while being guided by the rectangular grooves at both end faces. The three guide rolls 43 have annular grooves formed in the center of the axial direction of the outer circumferential surface. The two balls 42 rotate while being guided by the annular grooves of the two guide rolls 43, respectively. Furthermore, drive roll 41 is connected to a load setting unit (not shown) for setting the load from drive roll 41 to cylindrical roller test specimen 44. Cylindrical roller test specimen 44 is supported by two balls 42, and rotates while receiving a load from drive roll 41. Furthermore, rolling fatigue life tester 40 is equipped with a sensor that detects vibration of test specimen 44, and a control unit (not shown) that receives a vibration detection signal from the sensor, stops the drive unit, and records the life time from the start of the test to the reception of the vibration detection signal.

[0043] The life time was measured using cylindrical roller test pieces 44 of the embodiment and the comparative example. The life ratio was calculated by dividing the life time of cylindrical roller test pieces 44 of the embodiment and the comparative example by the life time of cylindrical roller test piece 44 of the comparative example 10, and rounding off the decimal point of the value. At this time, the test conditions were as follows: Maximum contact pressure in Hertz: 5.8GPa Maximum orthogonal shear stress (depth): 1.4GPa (0.24mm) Stress repetition rate: 285Hz Lubricating oil (oil temperature): ISO-VG100 (60±5℃) was adopted.

[0044] Table 3 shows the Vickers hardness, the amount of retained austenite, and the average grain size of the cylindrical roller test specimens 44, as well as the life ratio of the cylindrical roller test specimens 44 in the examples and comparative examples. [Table 3]

[0045] From Table 3, it can be seen that cylindrical roller test specimens 44 of Examples 1 to 8, which have a Vickers hardness of 682 to 770 HV, a retained austenite content of 26 to 45 vol%, and an average crystal grain size of 9 or 10, have a life ratio that is more than six times longer than that of cylindrical roller test specimen 44 of Comparative Example 10. In Comparative Examples 1 to 9, 11, and 12, in which the Vickers hardness is less than 682 HV or exceeds 770 HV, the life ratio is 5 times or less than that of Comparative Example 10. In Comparative Examples 1 to 3, 5 to 8, and 10 to 12, in which the amount of retained austenite is less than 25 vol% or exceeds 45 vol%, the life ratio is 5 times or less than that of Comparative Example 10. Furthermore, in Comparative Examples 9 to 12, in which the average grain size is less than #8 or exceeds #10, the life ratio is 3 times or less than that of Comparative Example 10. From this, it can be seen that a cylindrical roller bearing in which an inner ring made of the material and heat treatment of cylindrical roller test piece 44 of Examples 1 to 8 has an amount of retained austenite of 25 to 45 vol% at the depth from the outer peripheral surface of the inner ring raceway where the orthogonal shear stress is maximum, an average crystal grain size of No. 8 to No. 10, and a Vickers hardness of 682 to 770 HV, has an improved life ratio.

[0046] These evaluations revealed that cylindrical roller bearings using the materials and heat treatments according to the embodiments of the present invention can simultaneously suppress edge flaking and internally initiated flaking on the inner ring, thereby improving the bearing life. [Explanation of symbols]

[0047] 10: rolling mill, 11: work roll, 12: first intermediate roll, 13: second intermediate roll, 14: backup roll, 15: split roll, 16: shaft, 17: housing, 18: saddle, 20: inner ring, 21: outer ring, 22: cylindrical roller, 20a: inner peripheral surface of inner ring, 20b: outer peripheral surface of inner ring, 21a: inner peripheral surface of outer ring, 21b: outer peripheral surface of outer ring, 22a: rolling surface, 22b: left end face, 22c: right end face, 40: rolling fatigue life test machine, 41: drive roll, 42: ball, 43: guide roll, 44: cylindrical roller test piece, RM: rolled material, W: width of outer ring, T: width of inner ring, d: inner Diameter of peripheral surface, D1: Diameter of outer peripheral surface, Cha: First chamfer, Chb: Second chamfer, Cra: First crowning, Crb: Second crowning, Cy: Cylindrical surface, LCha: Axial length of first chamfer, LChb: Axial length of second chamfer, LCra: Axial length of first crowning, LCrb: Axial length of second crowning, LCy: Axial length of cylindrical surface, L: Axial length of cylindrical roller, RRa: Radius of curvature of first crowning, RRb: Radius of curvature of second crowning, Z: Depth where orthogonal shear stress is maximum, D2: Diameter of cylindrical roller

Claims

1. an inner ring fixed to a fixed shaft and having an inner ring raceway on an outer circumferential surface; an outer ring having an outer ring raceway on an inner circumferential surface; a plurality of cylindrical rollers rollably disposed between the inner ring raceway and the outer ring raceway; Equipped with The cylindrical rollers are The steel material contains components that meet the standards of the Japanese Industrial Standard G 4805:2019 high carbon chromium bearing steel material, the rolling surface of the cylindrical roller has, from a first axial side to a second axial side, a first chamfer, a first crowning, a cylindrical surface, a second crowning, and a second chamfer; the first chamfer is connected to a first end surface on a first axial side; the second chamfer connects to a second end surface on the second axial side; When the axial length of the first chamfer is LCha, the axial length of the first crowning is LCra, the axial length of the cylindrical surface is LCY, the axial length of the second crowning is LCrb, and the axial length of the second chamfer is LChb, (LCha+LCra+LCy+LCrb+LChb) / 4.8<LCa+LCra<(LCha+LCra+LCy+LCrb+LChb) / 3.2, and (LCha+LCra+LCy+LCrb+LChb) / 4.8<LChb+LCrb<(LCha+LCra+LCy+LCrb+LChb) / 3.2 Fulfilling In a cross section including a central axis of the cylindrical roller, when a radius of curvature of the first crowning is RRa and a radius of curvature of the second crowning is RRb, 900 mm < RRa < 9000 mm, and 900mm<RRb<9000mm Fulfilling The hardness at a depth Z from the cylindrical surface of the cylindrical roller where the orthogonal shear stress is maximum is 682 to 805 HV, The inner ring is As an ingredient, Carbon (C): 0.12 to 0.50 mass%, Manganese (Mn): 0.30 to 0.90 mass%, Silicon (Si): 0.15 to 0.35 mass%, Nickel (Ni): 0.40 to 4.50 mass%, Chromium (Cr): 0.40 to 2.00 mass%, Molybdenum (Mo): 0.15 to 0.90 mass%, and The balance contains iron (Fe) and inevitable impurities, The carbon concentration from the surface of the inner ring raceway to the position of the depth Z is 0.60 to 1.30 mass%, the amount of retained austenite at the depth Z from the surface of the inner ring raceway is 25 to 45 vol.%, The average crystal grain size at the depth Z from the surface of the inner ring raceway is 8 to 10; The hardness at the depth Z from the surface of the inner ring raceway is 682 to 770 HV. Cylindrical roller bearing.

2. 2. The cylindrical roller bearing according to claim 1, wherein the inner ring has, as a component, carbon (C): 0.12 to 0.23 mass %.

3. A multi-stage rolling mill comprising the cylindrical roller bearing according to claim 1 or 2.

Images