JP4703505B2 - Rolling member for machine tool and rolling bearing for machine tool - Google Patents

Description

  The present invention relates to a rolling member for a machine tool and a rolling bearing for a machine tool. More specifically, in a machine tool that processes a workpiece by rotating a main shaft, the main shaft that is rotationally driven is used as the main shaft. The present invention relates to a rolling tool for a machine tool and a rolling bearing for a machine tool that constitute a rolling bearing for a machine tool that is rotatably supported with respect to adjacent members.

  In a machine tool that performs cutting, grinding, or the like by rotating the main shaft, the main shaft rapidly accelerates and decelerates and repeatedly rotates and stops. Therefore, in a rolling bearing for a machine tool that supports the main shaft, an oil film breakage is likely to occur between the raceway member and the rolling element constituting the rolling bearing for the machine tool. In order to increase the processing speed and accuracy, rolling bearings for machine tools are often used in a state where a high preload is applied in order to increase rigidity. For this reason, the temperature of the rolling bearing for machine tools tends to increase. In addition, when a rolling bearing such as an angular ball bearing is used as a rolling bearing for machine tools, for example, slip occurs between the raceway member and the rolling element. When used under conditions, damage to the surface (rolling surface) of rolling members for machine tools such as race members and rolling elements tends to occur.

  As a result of being used under such severe use conditions as described above, rolling bearings for machine tools have problems that seizure, peeling, wear, cracking or peeling of the starting point of the surface (rolling surface) is likely to occur.

In response to this, many studies have been made for the purpose of improving the life of rolling bearings for machine tools, and various countermeasures have been proposed (see, for example, Patent Documents 1 to 6).
JP 2002-364648 A JP 2002-180202 A JP 2006-46454 A JP-A-2005-69321 JP-A-11-101246 JP 2000-61705 A

  However, in recent years, in a machine tool, for the purpose of improving the efficiency of processing and production using the machine tool, the processing speed is increased and the cutting amount is increased. In some cases, continuous operation is performed for 24 hours by combining with a robot. Along with this, in a rolling bearing for a machine tool that supports a spindle that is rotationally driven in a machine tool, the rotational speed further increases, the applied load tends to increase, and the continuous operation time tends to increase. Therefore, the rolling bearings for machine tools are used under severe conditions such that the temperature further increases during operation and high-speed rotation in a high-temperature environment. For this reason, the countermeasures described in Patent Documents 1 to 6 described above cannot sufficiently suppress seizure, peeling, abrasion, cracks and separation of the surface starting point, and the like.

  Furthermore, as a result of being used under the severe conditions as described above, the lubricant is decomposed and hydrogen is generated by using the new metal surface appearing by metal contact between the rolling members constituting the rolling bearing for machine tools as a catalyst, A phenomenon (hydrogen embrittlement peeling) in which peeling occurs on the rolling surface in a short period due to the penetration of the hydrogen into the rolling member is also a problem.

  Accordingly, an object of the present invention is to prevent rolling, peeling, abrasion, cracking and peeling of the surface starting point, and the occurrence of hydrogen embrittlement peeling, thereby improving the durability of the rolling member for machine tools. And providing rolling bearings for machine tools.

The rolling member for a machine tool according to the present invention rotates a main shaft that is driven to rotate with respect to a member disposed adjacent to the main shaft in a machine tool that processes a workpiece by rotating the main shaft. It is a rolling member for machine tools which comprises the rolling bearing for machine tools supported freely. The rolling member for machine tool includes 0.3% by mass or more and 0.4% by mass or less of carbon, 0.2% by mass or more and less than 0.5% by mass of silicon, and 0.3% by mass or more and 0.0. 8 mass% or less of manganese, 0.5 mass% or more and 1.2 mass% or less of nickel, 1.6 mass% or more and 2.5 mass% or less of chromium, and 0.1 mass% or more and 0.7 mass% or less. % Of molybdenum and 0.3% by mass or more and 0.8% by mass or less of vanadium, the balance being iron and inevitable impurities, the vanadium content being equal to or greater than the molybdenum content, and the molybdenum content The sum of the amount and the vanadium content is more than twice the silicon content, and the sum of the chromium content, the molybdenum content and the vanadium content is 2.3% by mass or more and 3.5% by mass. It is composed of the following hardened steel. Furthermore, a cured layer is formed on the surface layer portion. And the hardness of the said hardening process layer is Hv700 or more and 780 or less, the largest particle size of the carbide | carbonized_material distributed to a hardening process layer is 10 micrometers or less, and the area ratio of the carbide | carbonized_material in a hardening process layer is 7% or more and 25%. It is as follows. Furthermore, the internal hardness which is an area | region inside a hardening process layer is Hv500 or more and 600 or less.

  In the rolling member for machine tools according to the present invention, the steel constituting the rolling member for machine tools has a reduced content of silicon that may promote hydrogen embrittlement separation, and three components of vanadium, nickel, and molybdenum. Is added in a well-balanced manner. Thereby, generation | occurrence | production of hydrogen embrittlement peeling can be suppressed, ensuring the heat resistance of the rolling member for machine tools, and toughness. Moreover, in the rolling member for machine tools of the present invention, steel having a higher carbon content compared to general carburized steel is adopted as a material, and carburizing or carbonitriding is performed on the member made of the steel. At the same time, the size and area ratio of carbides in the hardened layer formed on the surface layer by carburizing or carbonitriding are adjusted to an appropriate range. Thereby, compressive stress is formed on the surface of the rolling member for machine tool, the surface layer portion is sufficiently cured, and the internal hardness is sufficiently ensured. Furthermore, the breakage which uses a large carbide | carbonized_material as a stress concentration source is suppressed. As a result, the occurrence of seizure, peeling, wear, cracking and peeling of the surface starting point in the rolling member for machine tools is suppressed, and the durability of the rolling member for machine tools is improved. Furthermore, it is possible to achieve both static crack strength and fatigue crack strength of rolling members for machine tools, improve the ease of processing (workability) in the manufacturing process, and shorten the time required for carburizing or carbonitriding. Productivity.

  As described above, according to the rolling member for machine tools of the present invention, the occurrence of hydrogen brittle exfoliation is suppressed and the occurrence of seizure, peeling, abrasion, surface-origin cracking and exfoliation, etc. is suppressed. It is possible to provide a rolling member for a machine tool with improved performance.

  Here, the surface layer portion of the rolling member for machine tools refers to a layer having a depth of 0.05 mm to 0.1 mm, particularly a layer having a depth of 0.1 mm, from the surface of the rolling member for machine tools. A hardened layer is formed on the surface layer portion by carburizing / quenching or carbonitriding / quenching and tempering. The hardened layer refers to a layer formed by carburizing or carbonitriding and having improved steel hardness as a result of increasing the carbon concentration or nitrogen concentration of the steel. By setting the hardness of the hardened layer after tempering to Hv 700 or higher (HRC 60 or higher), sufficient surface hardness can be imparted to the rolling member for machine tools, and sufficient rolling fatigue life can be ensured. On the other hand, since the amount of carbon is limited due to the limitation of the maximum particle size of carbide and the area ratio of carbide in the cured layer, it is difficult to obtain the hardness of the cured layer exceeding Hv780, and the curing treatment after tempering The upper limit value of the layer hardness is set to Hv780 or less.

  The tempering temperature is 180 ° C. or higher and 300 ° C. or lower, preferably 220 ° C. or higher and 300 ° C. or lower, more preferably 240 ° C. or higher and 300 ° C. or lower.

  In addition, considering the component composition of steel, since there are many elements (carbide-forming elements) that have a strong tendency to form carbides, the amount of carbides increases and individual carbides tend to be coarse. On the other hand, when the maximum particle size of the carbide distributed in the hardened layer is 10 μm or less, coarse carbide can be prevented from becoming a stress concentration source. Considering the severe use environment, finer carbide is preferable because it does not become a stress concentration source, and if the maximum particle size of carbide is 5 μm or less, it can be further improved.

Moreover, it can prevent that an excessive carbide | carbonized_material will inhibit workability (grindability) and a processing precision by making the area ratio of the carbide | carbonized_material in a hardening process layer into 25% or less. From the viewpoint of workability, it is more preferable to keep the area ratio of the carbide to 20% or less because it is difficult to cause difficult processing. On the other hand, if the carbide area ratio is less than 7%, the rolling fatigue life may be reduced. Therefore, the carbide area ratio is set in the range of 7% to 25%. The carbide is, for example, Fe ₃ C (cementite), carbide obtained by replacing Fe with an alloy component contained in steel such as chromium or molybdenum (shown as M3C), or M23C6 or M7C3.

  Furthermore, by setting the inner hardness of the region inside the hardened layer, specifically, the depth of 1.0 mm or more from the surface of the rolling member for machine tools to Hv 600 or less, toughness is provided. Residual compressive stress can be formed in the surface layer portion. On the other hand, by setting the internal hardness to Hv 500 or more, it is possible to prevent the occurrence of internal cracks even when a large load is applied.

The hardness of the hardened layer and the internal hardness can be investigated by, for example, cutting a rolling member for machine tools and measuring the hardened layer and the internal hardness with a Vickers hardness meter. Moreover, the maximum particle size and area ratio of the carbide in the cured layer can be investigated as follows, for example. That is, after the rolling member for machine tools is cut and the cut surface is polished, it is corroded with picral (picric acid alcohol solution). Then, 20 visual fields (magnification 400 times, visual field area 0.6 mm ² ) are randomly observed in the region corresponding to the cured layer, and the maximum particle size and area ratio of the carbide are investigated using an image processing device or the like.

  Here, the reason which limited the component range of steel which comprises the rolling member for machine tools of this invention to said range is demonstrated.

Carbon: 0.3% by mass or more and 0.4% by mass or less Carbide or carbonitriding of the surface layer portion of the rolling member for machine tools can ensure cracking strength and apply compressive stress to the surface layer portion. it can. However, when low carbon steel as in the past is employed as the material for the rolling member for machine tools, the internal hardness is low, and the strength becomes low when a large load or impact is applied. Therefore, the lower limit of the carbon content is set to 0.3% by mass in order to ensure sufficient internal hardness. On the other hand, if the carbon content of the material is high, the workability deteriorates, and the surface layer compressive stress and toughness after carburization cannot be secured, so 0.4 mass% was made the upper limit.

Silicon: 0.2% by mass or more and less than 0.5% by mass Conventionally, silicon is an element that imparts heat resistance while being inexpensive, and thus has been actively used. However, in a rolling member for machine tools in which significant hydrogen intrusion from the environment may occur, the addition amount is limited because there is a concern that hydrogen embrittlement peeling may be promoted if there is a large amount of silicon. In consideration of supplementing the heat resistance with other elements, and to cover the deterioration of workability, turning / grindability due to addition of other elements, the amount of silicon added was set to less than 0.5 mass%. On the other hand, in order to increase the temper softening resistance, the lower limit value of the silicon amount was set to 0.2% by mass.

Manganese: 0.3% by mass or more and 0.8% by mass or less Manganese is also an essential element for improving the hardenability of rolling members for machine tools and improving the rolling fatigue life. Therefore, the upper limit of the amount added was limited to 0.8% by mass from the balance between improving hardenability and increasing rolling fatigue life by increasing other elements. However, considering that it is an element essential for deoxidation in the steelmaking process, 0.3% by mass, which is a level contained in ordinary high alloy steel, was set as the lower limit.

Nickel: 0.5% by mass or more and 1.2% by mass or less Nickel is essential for securing the rolling fatigue life of rolling elements for machine tools at high temperatures, and is also effective in improving resistance to corrosion at high temperatures. . For this reason, 0.5 mass% was made into the minimum. On the other hand, if the amount of nickel is large, the amount of retained austenite after quenching increases and a predetermined hardness cannot be ensured, and the cost of steel materials increases. For this reason, the upper limit was made 1.2 mass%.

Chromium: 1.6 mass% or more and 2.5 mass% or less Chromium is also an essential element for securing the rolling fatigue life and high temperature hardness of the rolling member for machine tools. Even in ordinary bearing steel, chromium is contained in an amount of about 1.5% by mass, and in order to obtain a sufficient effect in high-temperature applications, it is necessary to add more than this amount. On the other hand, when the chromium content is high, considering the balance with other elements that form carbides such as molybdenum and vanadium, and the formation of large carbides to reduce the rolling fatigue life and crack strength, % Was the upper limit.

Molybdenum: 0.1 mass% or more and 0.7 mass% or less Molybdenum also has rolling fatigue of rolling members for machine tools at high temperatures like chromium from the viewpoint of improving hardenability and imparting temper softening resistance by carbide formation. It is indispensable for ensuring the life. It is also said that molybdenum carbide and carbonitride trap hydrogen, which is effective in suppressing hydrogen embrittlement delamination. On the other hand, molybdenum is an expensive element, and it is necessary to keep the addition as low as possible from the viewpoint of cost. Therefore, the lower limit is set to 0.1% by mass and the upper limit is set to 0.7% by mass in relation to the addition amount of chromium and vanadium. .

Vanadium: 0.3% by mass or more and 0.8% by mass or less Vanadium forms fine carbides and precipitates at the grain boundaries, and refines the crystal grains to improve the strength and toughness of the rolling member for machine tools. Furthermore, since the carbide works as a hydrogen trap site, it has a function of suppressing hydrogen sensitivity. Therefore, there is an effect of increasing the strength of the rolling member for machine tools used under conditions where hydrogen may enter, and extending the life by suppressing the occurrence of hydrogen embrittlement delamination. When carburizing or carbonitriding at a high temperature and performing high-temperature tempering, the effect becomes remarkable, so this is an especially important element. In addition, it is effective for extending and stabilizing the rolling fatigue life of the rolling member for machine tools. Since the addition of 0.3% by mass or more is necessary to exert these effects, the minimum addition amount was determined to be 0.3% by mass. On the other hand, vanadium is an expensive element, and it is necessary to suppress the addition as little as possible from the viewpoint of cost. Therefore, the upper limit is set to 0.8% by mass in relation to the addition amount of chromium and molybdenum.

  It should be noted that impurity elements such as phosphorus, sulfur, aluminum, and titanium are usually suppressed to a low level in bearing steel, and the same is true for steel constituting the rolling member for machine tools of the present invention. General values are limited to the following ranges.

Phosphorus: 0.03% by mass or less In order to prevent a decrease in toughness due to segregation and a decrease in rolling fatigue life, the content was made 0.03% by mass or less.

Sulfur: 0.03% by mass or less Sulfur: 0.03% by mass or less because the effect of manganese is eliminated and non-metallic inclusions are formed.

Aluminum: 0.05% by mass or less Although heat resistance is imparted, it tends to cause non-metallic inclusions, so 0.05% by mass or less.

Titanium: 0.003% by mass or less TiN that is a non-metallic inclusion forms a cause of a decrease in rolling fatigue life of the rolling member for machine tools, and may cause a peeling start point of hydrogen embrittlement peeling. It was 0.003 mass% or less.

  Further, since silicon has a concern of promoting hydrogen brittle exfoliation, it is necessary to reduce the content thereof and to supplement the decrease in heat resistance due to the reduction of the silicon content by adding chromium, molybdenum, and vanadium. Further, in order to precipitate a large amount of vanadium carbide, it is necessary to suppress the amount of carbon bonded to molybdenum. Therefore, the following relationship is necessary for the contents of chromium, vanadium, molybdenum, and silicon.

  The vanadium content is equal to or greater than the molybdenum content. This is because more vanadium carbide effective in suppressing hydrogen sensitivity is formed, and hydrogen embrittlement separation of the rolling member for machine tools is suppressed.

  The sum of the molybdenum content and the vanadium content is at least twice the silicon content. This is for the purpose of suppressing heat resistance and hydrogen embrittlement separation of the rolling member for machine tools.

  The sum of the chromium content, the molybdenum content and the vanadium content has a lower limit of 2.3% by mass or more in order to improve the heat resistance and rolling fatigue life of the rolling member for machine tools. On the other hand, if the amount is too large, large carbides are formed, the rolling fatigue life is decreased, and the crack strength is also decreased. Therefore, the upper limit is made 3.5% by mass or less.

  In the rolling member for machine tools, preferably, the hardness of the hardened layer after high-temperature tempering at 500 ° C. is Hv550 or higher and 650 or lower.

  Adopting the hardness of the hardened layer after tempering at 500 ° C. as an index for temper softening resistance, and ensuring the rolling fatigue life and strength at high temperature by setting the hardness to Hv550 or higher. Can do. Preferably, the high temperature tempering condition is a condition of holding at 500 ° C. for 1 hour. On the other hand, since the carbon content of the material is limited due to the limitations on the maximum particle size of the carbide and the area ratio of the carbide in the cured layer, the hardness of the cured layer after tempering at 500 ° C. exceeding Hv650 is difficult to obtain. . And in order to achieve this, the special heat processing etc. which raise the manufacturing cost are needed. Therefore, the hardness of the cured layer after tempering at 500 ° C. is set to Hv650 or less.

  In the rolling member for machine tools, preferably, the sum of the molybdenum content and the vanadium content is 0.6% by mass or more and 1.5% by mass or less.

  By defining the lower limit of the sum of the molybdenum content and the vanadium content to the above values, the heat resistance and hydrogen embrittlement resistance of the rolling member for machine tools can be further improved. On the other hand, since it is necessary to suppress the addition as little as possible from the viewpoint of cost, the manufacturing cost of the rolling member for machine tools can be suppressed by defining the upper limit value as described above.

  The rolling bearing for machine tools according to the present invention includes the above-described rolling member for machine tools. According to the rolling bearing for a machine tool of the present invention, the occurrence of hydrogen embrittlement delamination is suppressed, and the occurrence of seizure, peeling, wear, surface-origin cracking and delamination, and the like are improved, thereby improving the machine tool. By providing the rolling member for a machine, the rolling bearing for machine tools with improved durability can be provided. And, by adopting the highly durable rolling bearing for machine tools of the present invention as a bearing for supporting the main shaft, it is possible to operate the machine tool continuously for a long time even when the machining speed and the cutting depth are increased. Become.

  As is apparent from the above description, according to the rolling member for machine tool and the rolling bearing for machine tool of the present invention, the occurrence of hydrogen embrittlement delamination is suppressed, and seizure, peeling, abrasion, cracks and delamination of the surface origin are prevented. By suppressing the occurrence of the above, it is possible to provide a rolling member for machine tools and a rolling bearing for machine tools with improved durability.

  Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  FIG. 1 is a schematic cross-sectional view showing a configuration around a spindle of a machine tool provided with an angular ball bearing (front bearing) and a cylindrical roller bearing (rear bearing) as rolling bearings for a machine tool in an embodiment of the present invention. is there. With reference to FIG. 1, the structure of the machine tool provided with the angular ball bearing and cylindrical roller bearing in one embodiment of this invention is demonstrated.

  Referring to FIG. 1, machine tool 90 in the present embodiment includes a main shaft 91 having a cylindrical shape, a housing 92 that surrounds the outer peripheral surface of main shaft 91, and outer peripheral surfaces of outer ring 11 and outer ring 21. For the machine tool disposed between the main shaft 91 and the housing 92 so that each of the inner peripheral surfaces of the inner ring 12 and the inner ring 22 is in contact with the outer peripheral surface 91A of the main shaft 91. An angular ball bearing 1 (front bearing) and a cylindrical roller bearing 2 (rear bearing) are provided as rolling bearings. Thus, the main shaft 91 is supported so as to be rotatable about the axis with respect to the housing 92.

  In addition, a motor rotor 93B is installed on the main shaft 91 so as to surround a part of the outer peripheral surface 91A. A motor stator 93A is installed on the inner wall 92A of the housing 92 at a position facing the motor rotor 93B. The motor stator 93A and the motor rotor 93B constitute a motor 93 (built-in motor). Thus, the main shaft 91 can be rotated relative to the housing 92 by the power of the motor 93.

  That is, the angular ball bearing 1 and the cylindrical roller bearing 2 are members that are disposed adjacent to the main shaft 91 in the machine tool 90 that processes the workpiece by rotating the main shaft 91. This is a rolling bearing for a machine tool that is rotatably supported with respect to a certain housing 92.

  Next, the operation of the machine tool 90 will be described. Referring to FIG. 1, when power is supplied from a power source (not shown) to motor stator 93A of motor 93, a driving force for rotating motor rotor 93B around the axis is generated. Accordingly, the main shaft 91 rotatably supported by the angular ball bearing 1 and the cylindrical roller bearing 2 with respect to the housing 92 rotates relative to the housing 92 together with the motor rotor 93B. Thus, by rotating the main shaft 91, a tool (not shown) attached to the tip 91B of the main shaft 91 can cut and grind the workpiece, thereby processing the workpiece.

  Next, the angular ball bearing 1 will be described. FIG. 2 is a schematic cross-sectional view showing the configuration of an angular ball bearing as a rolling bearing for machine tools in the present embodiment. FIG. 3 is a schematic partial cross-sectional view showing an enlarged main part of FIG.

  2 and 3, an angular ball bearing 1 includes an outer ring 11 as a first race member that is a rolling member for machine tools, and an inner ring 12 as a second race member that is a rolling member for machine tools. And balls 13 as a plurality of rolling elements which are rolling members for machine tools, and a cage 14. The outer ring 11 is formed with an outer ring rolling surface 11A as an annular first rolling surface. The inner ring 12 is formed with an inner ring rolling surface 12A as an annular second rolling surface facing the outer ring rolling surface 11A. In addition, a plurality of balls 13 is formed with a ball rolling surface 13A (the surface of the ball 13) as a rolling element rolling surface. The balls 13 are in contact with each of the outer ring rolling surface 11A and the inner ring rolling surface 12A at the ball rolling surface 13A, and are arranged at a predetermined pitch in the circumferential direction by an annular retainer 14. It is rotatably held on an annular track. Thereby, the outer ring | wheel 11 and the inner ring | wheel 12 can rotate relatively mutually.

  Here, in the angular ball bearing 1, a straight line connecting the contact point between the ball 13 and the outer ring 11 and the contact point between the ball 13 and the inner ring 12 is a radial direction (a direction perpendicular to the rotation axis of the angular ball bearing 1). ). Therefore, when a radial load is applied, a component force is generated in the axial direction (the direction of the rotation axis of the angular ball bearing 1). Referring to FIG. 1, in machine tool 90 of the present embodiment, two angular ball bearings 1 of the same orientation are arranged on the front side (tip 91B side of main shaft 91) and on the rear side (motor rotor 93B side). Is offset the component force by arranging two angular ball bearings 1 opposite to the front side.

  Furthermore, the outer ring 11, the inner ring 12 and the ball 13 are 0.3% by mass or more and 0.4% by mass or less of carbon, 0.2% by mass or more and less than 0.5% by mass of silicon, and 0.3% by mass. 0.8% by mass or more of manganese, 0.5% by mass or more and 1.2% by mass or less of nickel, 1.6% by mass or more and 2.5% by mass or less of chromium, and 0.1% by mass or more of 0% by mass. 0.7% by mass or less of molybdenum and 0.3% by mass or more and 0.8% by mass or less of vanadium, the balance being iron and inevitable impurities, the content of vanadium being equal to or more than the content of molybdenum, The sum of the molybdenum content and the vanadium content is more than twice the silicon content, and the sum of the chromium content, the molybdenum content and the vanadium content is 2.3 mass% or more. It is comprised from the steel which is 5 mass% or less.

  Further, referring to FIG. 3, hardening treatment layers 11 </ b> B, 12 </ b> B, and 13 </ b> B are formed on the outer ring 11, the inner ring 12, and the surface layers of the balls 13, respectively. The hardness of the cured layers 11B, 12B, and 13B is Hv 700 or higher and 780 or lower, and the maximum particle size of carbides distributed in the cured layers 11B, 12B, and 13B is 10 μm or smaller, and the cured layers 11B, 12B The area ratio of carbides in 13B is 7% or more and 25% or less. Furthermore, the hardness of the interiors 11C, 12C, and 13C, which are regions inside the cured layers 11B, 12B, and 13B, is Hv500 or more and 600 or less.

  In the outer ring 11, the inner ring 12 and the ball 13 as the rolling members for machine tools of the present embodiment, the silicon content that may promote hydrogen embrittlement peeling in the steel constituting the outer ring 11, the inner ring 12 and the ball 13 The three components of vanadium, nickel, and molybdenum are added in a well-balanced manner. Thereby, generation | occurrence | production of hydrogen embrittlement peeling can be suppressed, ensuring the heat resistance of the outer ring | wheel 11, the inner ring | wheel 12, and the ball | bowl 13, and toughness. Further, in the outer ring 11, the inner ring 12 and the ball 13 of the present embodiment, steel having a higher carbon content compared to general carburized steel is adopted as a material, and carburizing or carbonitriding is performed, The size and area ratio of carbides in the cured layers 11B, 12B, and 13B formed on the surface layer by carbonitriding are adjusted to an appropriate range. Thereby, compressive stress is formed on the surfaces of the outer ring 11, the inner ring 12 and the balls 13, the surface layer portion is sufficiently cured, and the internal hardness is sufficiently ensured. Furthermore, the damage which uses a large carbide | carbonized_material as a stress concentration source is suppressed. As a result, the occurrence of seizure, peeling, abrasion, cracking and peeling of the surface origin, and the like are suppressed in the outer ring 11, the inner ring 12 and the ball 13, and durability is improved. Further, the static crack strength and fatigue crack strength of the outer ring 11, the inner ring 12 and the ball 13 can be achieved at the same time, the processability (workability) in the manufacturing process is improved, and the time required for carburizing or carbonitriding is improved. It has been shortened to improve productivity.

  As described above, the outer ring 11, the inner ring 12 and the ball 13 as the rolling members for the machine tool according to the present embodiment are suppressed from occurrence of hydrogen embrittlement peeling, seizure, peeling, wear, surface-origin cracks, The durability is improved by suppressing the occurrence of peeling and the like. As a result, the angular ball bearing 1 as the rolling bearing for a machine tool of the present embodiment is suppressed from occurrence of hydrogen embrittlement delamination and occurrence of seizure, peeling, wear, cracks and delamination of the surface origin, and the like. The durability is improved by being suppressed. Therefore, even when a high preload is applied to improve rigidity and intermittent operation is performed at a high speed for a long time, the angular ball bearing 1 has a long life.

  In the outer ring 11, inner ring 12 and ball 13 of the present embodiment, the hardness of the cured layers 11B, 12B and 13B after high temperature tempering at 500 ° C. is preferably Hv550 or higher and 650 or lower. Thereby, sufficient rolling fatigue life and strength at a high temperature can be ensured without performing special heat treatment or the like that causes an increase in manufacturing cost.

  Further, in the outer ring 11, the inner ring 12 and the ball 13 of the present embodiment, the sum of the molybdenum content and the vanadium content is made of steel that is 0.6 mass% or more and 1.5 mass% or less. Preferably it is.

  By defining the lower limit of the sum of the molybdenum content and the vanadium content to the above values, the heat resistance and hydrogen embrittlement resistance of the outer ring 11, the inner ring 12 and the ball 13 can be further improved. On the other hand, since it is necessary to suppress the addition as little as possible from the viewpoint of cost, the manufacturing cost of the outer ring 11, the inner ring 12 and the ball 13 can be suppressed by defining the upper limit value as described above.

  Next, the cylindrical roller bearing 2 will be described. FIG. 4 is a schematic sectional view showing a configuration of a cylindrical roller bearing as a rolling bearing for machine tools in the present embodiment. FIG. 5 is a schematic partial cross-sectional view showing an enlarged main part of FIG.

  4 and 5, the cylindrical roller bearing 2 basically has the same configuration as the above-described angular ball bearing 1 and has the same effect. However, the cylindrical roller bearing 2 is different from the angular ball bearing 1 in the configuration of the raceway and the rolling element.

  That is, the cylindrical roller bearing 2 includes an outer ring 21 as a first race member that is a rolling member for machine tools, an inner ring 22 as a second race member that is a rolling member for machine tools, and a rolling member for machine tools. The cylindrical roller 23 as a plurality of rolling elements and a cage 24 are provided. The outer ring 21 is formed with an outer ring rolling surface 21A as an annular first rolling surface. The inner ring 22 is formed with an inner ring rolling surface 22A as an annular second rolling surface facing the outer ring rolling surface 21A. Further, the plurality of cylindrical rollers 23 are formed with roller rolling surfaces 23 </ b> A (outer peripheral surfaces of the cylindrical rollers 23) as rolling element rolling surfaces. The cylindrical roller 23 comes into contact with each of the outer ring rolling surface 21A and the inner ring rolling surface 22A at the roller rolling surface 23A, and is arranged at a predetermined pitch in the circumferential direction by an annular retainer 24. It is rotatably held on an annular track. Thereby, the outer ring | wheel 21 and the inner ring | wheel 22 can rotate relatively mutually.

  Furthermore, referring to FIGS. 2 to 5, outer ring 21, inner ring 22, and cylindrical roller 23 as rolling members for a machine tool according to the present embodiment correspond to outer ring 11, inner ring 12, and ball 13 described above, respectively. The cured layers 21B, 22B, and 23B and the inner portions 21C, 22C, and 23C also have the same configuration as the cured layers 11B, 12B, and 13B and the inner portions 11C, 12C, and 13C. Therefore, the outer ring 21, the inner ring 22, and the cylindrical roller 23 have improved durability by suppressing the occurrence of hydrogen brittle peeling and suppressing the occurrence of seizure, peeling, wear, cracks and peeling at the surface origin, and the like. is doing. As a result, in the cylindrical roller bearing 2 as the rolling bearing for machine tools of the present embodiment, the occurrence of hydrogen embrittlement peeling is suppressed, and seizure, peeling, wear, surface-origin cracking and peeling are generated. The durability is improved by being suppressed. Therefore, even when a high preload is applied to improve rigidity and intermittent operation is performed at a high speed for a long time, the cylindrical roller bearing 2 has a long life.

  Next, the manufacturing method of the rolling member for machine tools and the rolling bearing for machine tools in this Embodiment is demonstrated. FIG. 6 is a flowchart showing an outline of a method for manufacturing the rolling member for machine tool and the rolling bearing for machine tool in the present embodiment.

  Referring to FIG. 6, first, in step (S100), 0.3% by mass or more and 0.4% by mass or less of carbon, 0.2% by mass or more and less than 0.5% by mass of silicon, 1% by mass to 0.8% by mass of manganese, 0.5% by mass to 1.2% by mass of nickel, 1.6% by mass to 2.5% by mass of chromium, and 0.1% by mass It contains not less than 0.7% by mass of molybdenum and not less than 0.3% by mass and not more than 0.8% by mass of vanadium, and consists of the balance iron and inevitable impurities. The vanadium content is not less than the molybdenum content. Yes, the sum of molybdenum content and vanadium content is more than twice the silicon content, and the sum of chromium content, molybdenum content and vanadium content is 2.3 mass% or more Steel for preparing steel material composed of steel of 3.5% by mass or less Preparation step is performed. Specifically, for example, steel bars or steel wires having the above components are prepared.

  Next, in the step (S200), a forming step is performed in which the steel material is formed, thereby forming a formed part formed into the approximate shape of the rolling member for machine tools. Specifically, for example, by performing processing such as forging and turning on the above steel bars and steel wires, the outer rings 11, 21, inner rings 12, 22, balls 13 and cylinders shown in FIGS. A molded part molded into a schematic shape such as the roller 23 is produced.

  Next, in the step (S300), a heat treatment step for heat-treating the molded part is performed. Specifically, the molded part produced in the molding step (S200) is subjected to a quenching process after carburizing or carbonitriding, and further after the quenching process, a tempering temperature of 180 ° C to 300 ° C, preferably 220 ° C. A tempering treatment is performed at a temperature of not less than 300 ° C and not more than 300 ° C, more preferably not less than 240 ° C and not more than 300 ° C. Details of this heat treatment step will be described later.

  Next, in step (S400), a finishing step is performed. Specifically, the outer ring 11, 21, the inner ring 12, 22, the ball 13, the cylindrical roller 23, and the like are finished by performing a finishing process such as a grinding process on the molded part that has been subjected to the heat treatment process. Thereby, the outer rings 11, 21, the inner rings 12, 22, the balls 13, the cylindrical rollers 23, and the like as the rolling members for the machine tool in the present embodiment are completed.

  Further, in the process (S500), an assembly process is performed. Specifically, for example, the outer ring 11, inner ring 12 and ball 13 produced in steps (S100) to (S400) are combined with a separately prepared cage 14 or the like, or the outer ring 21, inner ring 22 and cylinder are combined. The roller 23, a separately prepared cage 24, and the like are combined to assemble the angular ball bearing 1, the cylindrical roller bearing 2, and the like as a rolling bearing for a machine tool in the present embodiment. Thereby, the angular ball bearing 1 and the cylindrical roller bearing 2 are completed.

  Next, the details of the heat treatment step (S300) will be described. FIG. 7 is a diagram for explaining a heat treatment method in a heat treatment step included in the method for manufacturing a rolling member for machine tools in the present embodiment. In FIG. 7, the horizontal direction indicates time, and the time elapses toward the right. In FIG. 7, the vertical direction indicates the temperature, and the higher the temperature, the higher the temperature.

Referring to FIG. 7, the molded part produced in the molding step (S200) is heated to a temperature of 800 ° C. or higher and 1000 ° C. or lower, which is a temperature of _one point or higher, for example, 950 ° C., for 360 minutes or longer and 600 minutes or shorter. For example, 480 minutes. At this time, the molded part is heated in an atmosphere in which the carbon potential of the atmospheric gas is adjusted to be greater than or equal to the amount of carbon contained in the surface part of the molded part. Thereby, the carburizing process in which the carbon concentration of the surface layer portion of the molded part is adjusted to a desired concentration is performed. Thereafter, in order to control the amount of remaining carbide and retained austenite, the temperature is once lowered from, for example, about 950 ° C. to about 850 ° C., and kept at this temperature for a while (for example, for 30 minutes or more and 60 minutes or less). Control. Thereafter, the molded part is cooled, for example, by being immersed in oil (oil cooling), from a temperature of A ₁ point or higher to a temperature of M _S point or lower. Thereby, carburizing and quenching is completed, and the molded part is hardened by hardening.

Here, the _point A, when heating the steel shows a point corresponding to a temperature at which steel structure starts transformation from ferrite to austenite. Further, the M _S point, when cooling the austenitized and steel shows that the steel structure is equivalent to a temperature to initiate the martensite. Carbon potential is the carbon concentration contained in the surface layer of steel when the carburization and decarburization reaction reaches equilibrium and the concentration of carbon contained in the steel becomes a constant value. It is a value indicating the ability. That is, the higher the carbon potential, the higher the carburizing ability. The carbon potential of the atmosphere gas can be calculated by measuring the temperature of the atmosphere gas and the composition of the atmosphere gas, that is, the concentration of carbon monoxide and oxygen, or the concentration of carbon monoxide and carbon dioxide. .

Further, the hardened and molded part is heated to a temperature of 180 ° C. or more and 300 ° C. or less, for example, 280 ° C., which is a temperature of ₁ point or less, and held for 30 minutes or more and 240 minutes or less, for example, 120 minutes, Thereafter, it is cooled in air at room temperature (air cooling). Thereby, the tempering process is completed. By the above procedure, the heat treatment step (S300) in the manufacturing method of the outer rings 11, 21, inner rings 12, 22, balls 13 and cylindrical rollers 23 as rolling members for machine tools is completed.

  FIG. 8 is a diagram for explaining a modification of the heat treatment method in the heat treatment step included in the method for manufacturing a machine tool rolling member according to the present embodiment. In FIG. 8, the horizontal direction indicates time, and the time elapses toward the right. In FIG. 8, the vertical direction indicates the temperature, and the higher the temperature, the higher the temperature. With reference to FIG. 8, the detail of the modification of the heat processing method is demonstrated.

With reference to FIG. 8, the molded part produced in the molding step (S200) is heated to a temperature of 800 ° C. or higher and 1000 ° C. or lower, which is a temperature of _one point or higher, for example, 950 ° C., and is 360 minutes or longer and 600 minutes or shorter. For example, 480 minutes. At this time, the molded part is heated in an atmosphere in which the carbon potential of the atmospheric gas is adjusted to be greater than or equal to the amount of carbon contained in the surface part of the molded part. Thereby, the carburizing process in which the carbon concentration of the surface layer portion of the molded part is adjusted to a desired concentration is performed. Thereafter, the molded part is cooled, for example, by being immersed in oil (oil cooling), from a temperature of A ₁ point or higher to a temperature of M _S point or lower. Thereby, primary hardening is completed.

Further, re-heating is performed in which the molded part subjected to the primary quenching is reheated to a temperature of 730 ° C. or higher and 900 ° C. or lower, which is a temperature of _one point or higher, for example, 850 ° C., and thereafter 30 minutes to 120 minutes. Hold for the following time, for example 50 minutes. At this time, for example, heating is performed in an atmosphere containing RX gas so that the carbon concentration adjusted in the carburizing process becomes a desired concentration. Furthermore, when the molded part is cooled with oil, for example, it is rapidly cooled from a temperature of A ₁ point or more to a temperature of M _S point or less and is hardened by hardening. Thereby, the secondary quenching is completed.

Further, the molded part for which the second quenching has been completed is heated to a temperature of 180 ° C. or higher and 300 ° C. or lower, which is a temperature of ₁ point or lower, for example, 280 ° C., and held for 30 minutes or longer and 240 minutes or shorter, for example, 120 minutes. And then cooled in air at room temperature (air cooling). Thereby, the tempering process is completed. By the above procedure, the heat treatment step (S300) in the manufacturing method of the outer rings 11, 21, inner rings 12, 22, balls 13 and cylindrical rollers 23 as rolling members for machine tools is completed.

  The above heat treatment improves the cracking strength while carburizing the surface layer portion as compared with the heat treatment method described in FIG. 7, that is, the heat treatment method (normal quenching) in which the carburization treatment is performed once as it is, and the aged size is improved. The rate of change can be reduced. Further, it is possible to obtain a microstructure in which the grain size of the austenite crystal grains is less than or equal to half that in the case of performing normal quenching. Therefore, the rolling member for machine tools manufactured by the above heat treatment has a longer rolling fatigue characteristic, a higher cracking strength, and a reduced aging rate. The austenite crystal grains are austenite crystal grains that have undergone phase transformation during quenching heating, and are those that remain at room temperature after being transformed into martensite by cooling (former austenite crystal grains).

  FIG. 9 is a diagram for explaining another modification of the heat treatment method in the heat treatment step included in the method for manufacturing the rolling member for machine tool in the present embodiment. In FIG. 9, the horizontal direction indicates time, and the time elapses toward the right. In FIG. 9, the vertical direction indicates the temperature, and the higher the temperature, the higher the temperature. With reference to FIG. 9, the detail of the other modification of the heat processing method is demonstrated.

Referring to FIG. 9, a molded part finished to a predetermined size by cold working or the like is heated to a temperature of 800 ° C. or higher and 1000 ° C. or lower, which is a temperature of _one point or higher, for example, 920 ° C. for 360 minutes or longer. It is held for 600 minutes or less, for example, 480 minutes. At this time, the molded part is heated in an atmosphere in which the carbon potential of the atmosphere gas is maintained at or above the amount of carbon contained in the surface layer portion of the molded part and ammonia gas is added to the RX gas that is the atmosphere gas. Thereby, the carbonitriding process in which the carbon concentration and the nitrogen concentration in the surface layer portion of the molded part are adjusted to desired concentrations is performed. Thereafter, the molded part is first cooled to a temperature of A ₁ point or lower, and then heated again to a temperature of 730 ° C. or higher and 860 ° C. or lower, which is a temperature of A ₁ point or higher, without cooling to room temperature (room temperature). The reheating that is performed is performed, and then held for 30 minutes to 120 minutes, for example, 50 minutes. At this time, for example, heating is performed in an atmosphere containing RX gas so that the carbon concentration and the nitrogen concentration adjusted in the carbonitriding process become desired concentrations. Furthermore, when the molded part is cooled with oil, for example, it is rapidly cooled from a temperature of A ₁ point or more to a temperature of M _S point or less and is hardened by hardening. Thereby, carbonitriding and quenching is completed.

Furthermore, the molded part that has been subjected to carbonitriding and quenching is heated to a temperature of 180 ° C. or higher and 300 ° C. or lower, for example, 280 ° C., which is a temperature of ₁ point or less, and held for 30 minutes to 240 minutes, for example, 120 minutes. Then, it is cooled in air at room temperature (air cooling). Thereby, the tempering process is completed. With the above procedure, the heat treatment step (S300) in the method for manufacturing the outer rings 11, 21, inner rings 12, 22, balls 13 and cylindrical rollers 23 as rolling members for machine tools is completed.

This makes it possible to reduce the time and energy required for reheating as compared with the case where re-heating is performed after quenching and cooling to room temperature, which is advantageous in that the manufacturing cost can be reduced. is there. The cooling temperature followed after carbonitriding temperature lower than the _point A, that may be a temperature below the transformation point from austenite iron to ferrite may be, for example, 650 ° C. or higher 700 ° C. or less.

  Due to the heat treatment step (S300), the outer ring 11, 21 as the rolling member for machine tool, the inner ring 12, 22, the ball 13 and the cylindrical roller 23, the hardened layer 11B, 12B, 13B, 21B, 22B , 23B are formed. The hardness of the cured layers 11B, 12B, 13B, 21B, 22B, and 23B is Hv 700 or higher and 780 or lower, and the maximum particle size of carbides distributed in the cured layers 11B, 12B, 13B, 21B, 22B, and 23B is 10 μm or smaller, The area ratio of carbides in the cured layers 11B, 12B, 13B, 21B, 22B, and 23B is 7% or more and 25% or less, and the interior is an area inside the cured layers 11B, 12B, 13B, 21B, 22B, and 23B. The hardness of 11C, 12C, 13C, 21C, 22C, and 23C can be Hv500 or more and 600 or less.

  According to the manufacturing method of the rolling member for machine tools of this Embodiment demonstrated above, in the steel which comprises the outer ring | wheels 11 and 21, the inner rings 12, 22, the ball | bowl 13, and the cylindrical roller 23 as a rolling member for machine tools. Steel with reduced content of silicon that may promote hydrogen embrittlement delamination and with a good balance of the three components of vanadium, nickel, and molybdenum, and a higher carbon content than general carburized steel Is adopted as a material. Carburization or carbonitriding is performed, and the size and area ratio of carbides in the cured layers 11B, 12B, 13B, 21B, 22B, and 23B formed in the surface layer portion by carburizing or carbonitriding are within an appropriate range. It is possible to adjust, and the hardness in the cured layers 11B, 12B, 13B, 21B, 22B, 23B and the inside 11C, 12C, 13C, 21C, 22C, 23C can be adjusted to an appropriate range. As a result, the occurrence of hydrogen embrittlement delamination is suppressed, and the occurrence of seizure, peeling, abrasion, surface-origin cracks and delamination, etc. are suppressed, thereby improving the durability of rolling members for machine tools and machine tools. A rolling bearing can be manufactured.

  In the above embodiment, the angular ball bearing and the cylindrical roller bearing have been described as examples of the rolling bearing for machine tool of the present invention. However, the rolling bearing for machine tool of the present invention is not limited to these. For example, the rolling bearing for a machine tool of the present invention may be a deep groove ball bearing or a tapered roller bearing.

  Embodiment 1 of the present invention will be described below. First, a method for producing a test piece to be tested will be described. First, steel materials having chemical components shown in Table 1 were prepared. In Table 1, for the main chemical components, the contents of carbon (C), silicon (Si), manganese (Mn), nickel (Ni), chromium (Cr), molybdenum (Mo) and vanadium (V) are in mass. The balance of the components listed is% iron and inevitable impurities. And the said steel material was shape | molded in the approximate shape of the test piece, and it was set as the molded component.

  Next, heat treatment was performed based on the heat treatment method shown in FIG. Specifically, the molded part was heated to 950 ° C., and at this time, the carbon potential of the atmospheric gas was adjusted to be 1.0, and carburization was performed. Holding at this temperature for 480 minutes, carburization treatment and diffusion treatment were performed. Thereafter, the temperature was lowered to 850 ° C., and the molded part was immersed in oil and rapidly cooled to perform primary quenching. Further, the molded part was reheated to 850 ° C. and held for 50 minutes, immersed again in oil, rapidly cooled from 850 ° C., and subjected to secondary quenching. Further, the molded part was heated to 280 ° C. and held for 120 minutes, then cooled in air at room temperature, and tempered.

  And the test piece was completed by implementing finish processing to the molded part after heat processing. In addition, as shown in Table 1, Table 2 and Table 3, in addition to steel corresponding to the developed steel according to the present invention (No. 1-6), steel having different chemical composition and material from the developed steel (No. 7-30) ) Was evaluated as a comparative steel. The differences between each comparative steel and the developed steel in chemical composition and material are shown in the remarks column of Tables 1 and 2 and the feature column of Table 3. Further, as general bearing steels, the current bearing steel JIS SUJ2 (No. 31) and the current carburized steel JIS SCM420 (No. 32) were also evaluated. However, no. 31 and no. For No. 32, the tempering temperature was 180 ° C., and test specimens were prepared.

  Next, test conditions will be described. In Example 1, a test for investigating the hardness of the test piece and the precipitation state of carbide was performed. Using the test piece for rolling fatigue life test of Example 2 described later, based on the test method shown in JIS Z2244, the Vickers hardness test of the outer peripheral surface of the test piece is performed, and the hardness of the surface layer portion of the test piece (Surface hardness) was investigated. Moreover, the Vickers hardness test was done about the cross section which cut out the test piece, and the internal hardness (internal hardness) of the test piece was investigated. Furthermore, after heating the test piece to 500 ° C. and holding it for 1 hour, the Vickers hardness (500 ° C. tempering hardness) of the outer peripheral surface of the test piece was investigated, and the test was simulated to be used in a high temperature environment. .

  The test results are shown in Table 2. In Table 2, surface layer hardness (unit: Hv), internal hardness (unit: Hv), and 500 ° C. tempering hardness (unit: Hv) are shown. In addition, the maximum particle size of carbide distributed in the surface layer portion (maximum carbide diameter, unit: μm) and the area ratio of carbide in the surface layer portion (carbide amount, unit:%) are also shown.

  Referring to Table 2, all of the developed steels (Nos. 1 to 6) have a surface hardness of Hv 700 or higher and an internal hardness of Hv 500 or higher and Hv 600 or lower. Moreover, also about 500 degreeC tempering hardness, all developed steel (No. 1-6) is Hv570 or more, and has shown that hardness does not fall easily after high temperature tempering. On the other hand, there are some comparative steels whose surface hardness cannot satisfy Hv700 (No. 29). Therefore, the developed steel according to the present invention can secure sufficient surface layer hardness as a rolling member for machine tools, has internal hardness that can provide toughness and prevent internal cracks, and strength at high temperatures. It can be seen that can be maintained.

  In addition, the particle size of the carbide in the cured layer was observed using a photograph taken by magnifying 400 times with an optical microscope after etching a cross-section of the test piece using a picric acid alcohol solution (picral). . And in the photograph for arbitrary 40 visual fields, the largest particle size of the carbide | carbonized_material was calculated | required by measuring the particle size of the largest carbide | carbonized_material in a photograph. The area ratio of carbides in the hardened layer was determined by observing the section of the specimen cut out with a picric alcohol solution (picral) with an optical microscope (400 times) and analyzing the image of 20 fields of view. By extracting a carbide having a particle size of 0.5 μm or more, the area ratio of the carbide was obtained. Regarding carbides, the maximum carbides in some comparative steels were larger than 10 μm in particle size (Nos. 8, 22, 25), and the amount of carbides exceeded 25% (Nos. 7, 8, 25).

  Embodiment 2 of the present invention will be described below. A rolling fatigue life test was conducted using the test piece produced by the production method described above. Table 4 shows the test conditions of the rolling fatigue life test.

  The rolling fatigue life test was conducted using a φ12 point contact tester. FIG. 10 is a schematic front view showing the configuration of the main part of the φ12 point contact tester. FIG. 11 is a schematic side view showing the configuration of the main part of the φ12 point contact tester. A rolling fatigue life tester will be described with reference to FIGS. 10 and 11.

  With reference to FIGS. 10 and 11, the φ12 point contact test machine 30 includes a drive roller 32, a guide roller 33, and a steel ball 34. The rolling fatigue life test piece 31 is driven by the drive roller 32 and rotates in contact with the steel ball 34. The steel ball 34 is guided by the guide roller 33 and rolls while exerting a high surface pressure with the rolling fatigue life test piece 31. Lubricating oil is supplied by forced circulation. As described above, the φ12 point contact tester 30 is operated, and the test can be performed twice by changing the location with one test piece using five test pieces. The number of loads (life) until the peeling occurred was investigated. The obtained lifetime was statistically analyzed, and the lifetime at which the cumulative failure probability was 10% was calculated.

  Next, test results will be described. The test results are shown in Table 3. Table 3 shows the ratio of the rolling fatigue life of each test piece when the current bearing steel (No. 31) is 1. Moreover, as described in the remarks column of Table 3, the results of the comparative steel, the current bearing steel, and the current carburized steel that are significantly inferior to the developed steel are underlined. The developed steel (No. 1 to 6) and the comparative steel (No. 7 to 30) all have a longer life than the current bearing steel (No. 31) and the current carburized steel (No. 32). Some of them have a relatively short life (No. 7, 8, 10, 24, 28, 30) which is not more than twice the rolling fatigue life of current bearing steel (No. 31). On the other hand, all the developed steels have a rolling fatigue life of 2.5 times or more that of the current bearing steel (No. 31). Therefore, it can be seen that the rolling fatigue life of the developed steel according to the present invention is greatly improved from the current steel.

  Embodiment 3 of the present invention will be described below. The smearing test was performed using the test piece produced by the production method described above. Table 5 shows the test conditions of the smearing test.

  The smearing test was performed using a two-cylinder tester. FIG. 12 is a schematic diagram showing the configuration of the main part of the two-cylinder testing machine. A two-cylinder testing machine will be described with reference to FIG.

  Referring to FIG. 12, a disk-shaped first test piece 61 is set in the two-cylinder testing machine 60 so as to be rotatable around the first shaft 63 and is rotatable around the second shaft 64. Thus, the disk-shaped second test piece 62 is set. The first shaft 63 and the second shaft 64 are arranged in parallel, and the first shaft 63 and the second shaft 64 are arranged so that the outer peripheral surfaces of the first test piece 61 and the second test piece 62 are in contact with each other. Set at one end of each. Further, a rotational speed meter 65 and a slip ring 66 are disposed at the other ends of the first shaft 63 and the second shaft 64, respectively.

  And while lubricating oil is dripped at the 1st test piece 61, while rotating the 1st test piece 61 at the rotation speed of 200 rpm, the rotation speed of the 2nd test piece 62 is gradually increased from 200 rpm, and the surface of the test piece When smearing occurred, the test was stopped, and the relative rotational speed at that time was recorded. It shows that the greater the relative rotational speed at which smearing occurs, the greater the resistance to smearing.

  Next, test results will be described. The test results are shown in Table 3. Table 3 shows the relative rotational speed at the time of occurrence of smearing of each test piece as a ratio with the current bearing steel (No. 31) as 1. It can be seen that the developed steel (Nos. 1 to 6) has higher resistance to smearing than the current bearing steel (No. 31) and the current carburized steel (No. 32). This is because the heat resistance of the developed steel (No. 1 to 6) is higher than the heat resistance of the current bearing steel (No. 31) and the current carburized steel (No. 32). Conceivable.

  Embodiment 4 of the present invention will be described below. A wear test was conducted using the test piece produced by the production method described above. This test can estimate the wear phenomenon when the lubrication condition is poor due to high temperature. Table 6 shows the test conditions for the wear test.

  The abrasion test was performed using a Sabang type abrasion tester. FIG. 13 is a schematic front view showing the configuration of the main part of the Sabang type wear tester. FIG. 14 is a schematic side view showing the configuration of the main part of the Sabang type wear tester. With reference to FIG. 13 and FIG. 14, a Sabang type wear tester will be described.

  With reference to FIG. 13 and FIG. 14, the Saban-type wear tester 40 includes a load cell 43 and an air slider 44. The flat plate-shaped wear test piece 41 is held by an air slider 44, and the load due to the weight 42 loaded during the wear test is detected by the load cell 43. Then, the mirror-polished surface of the wear test piece 41 and the outer peripheral surface of the counterpart material 45 are brought into contact with each other, and the counterpart material 45 is rotated. Lubricating oil is not directly supplied to the contact surface between the wear test piece 41 and the counterpart material 45, and a part of the counterpart material 45 is immersed in the lubricating oil 46. As described above, the wear strength was investigated by operating the Saban-type wear tester 40 and measuring the wear volume of the test piece after rotating the counterpart material for 60 minutes.

  Next, test results will be described. The test results are shown in Table 3. Table 3 shows the reciprocal of the ratio of the wear volume of each test piece when the current bearing steel (No. 31) is 1. Both the developed steel (No. 1-6) and the comparative steel (No. 7-30) tend to have better wear resistance than the current bearing steel (No. 31) and the current carburized steel (No. 32). However, in some comparative steels, the maximum grain size of the carbide in the surface layer is large and the amount of carbide is large, so that it has the same wear resistance as the current steel or less than the current steel despite its high hardness (No .8, 22, 25). On the other hand, all the developed steels have a wear resistance of 1.8 times or more that of the current bearing steel (No. 31). Therefore, it can be seen that the wear resistance of the developed steel according to the present invention is greatly improved from the current steel and is applicable even when the lubrication conditions are poor.

  Embodiment 5 of the present invention will be described below. An ultrasonic fatigue test was performed using the test piece produced by the production method described above. In the high-speed fatigue test in the tension-compression mode, the fatigue strength with respect to the surface tensile stress due to surface slip and the like can be seen. Moreover, since it can evaluate in a short time, it can test in the state which made hydrogen penetrate | penetrate in steel by electrolytic charge etc. This is a test that can estimate resistance to hydrogen embrittlement. Table 7 shows the test conditions of the ultrasonic fatigue test in the atmosphere, Table 8 shows the test conditions of the ultrasonic fatigue test under the hydrogen charge conditions simulating after hydrogen intrusion, and Table 9 shows the hydrogen charge conditions.

  FIG. 15 is a schematic diagram showing the configuration of the main part of the ultrasonic fatigue testing machine. The ultrasonic fatigue tester will be described with reference to FIG.

  Referring to FIG. 15, an ultrasonic fatigue testing machine 50 includes a horn portion 52 connected to a portion to which an ultrasonic fatigue test piece 51 is fixed, and PZT (lead zirconate titanate) connected to the horn portion 52. A vibrator 53, an amplifier 54 connected to the PZT vibrator 53, and a control device 55 such as a personal computer connected to the amplifier 54 are provided. Further, the ultrasonic fatigue tester 50 faces the end of the ultrasonic fatigue test piece 51 opposite to the side connected to the horn portion 52 in a state where the ultrasonic fatigue test piece 51 is set. A gap gauge 56 is disposed, and the gap gauge 56 is connected to an oscilloscope 57.

  Then, the ultrasonic fatigue test piece 51 is set in the ultrasonic fatigue tester 50, and the power is input to the PZT vibrator 53 via the amplifier 54 while controlling the output by the control device 55. generate. By transmitting this ultrasonic vibration to the ultrasonic fatigue test piece 51 via the horn part 52, the ultrasonic fatigue test piece 51 is resonated. At this time, in the portion where the diameter of the ultrasonic fatigue test piece 51 is the thinnest, the stress amplitude of the tensile compression in the axial direction becomes the maximum. On the other hand, the state of vibration of the ultrasonic fatigue test piece 51 is managed by the gap gauge 56 connected to the oscilloscope 57.

As described above, the ultrasonic fatigue testing machine 50 was operated, and the number of repeated stresses until the ultrasonic fatigue test specimen 51 was peeled or broken was investigated. Furthermore, predicted to the survey conducted for various stresses, the result is broken in normal under the assumption that follows the distribution, the results statistically analyzed to 10% of the test piece stress repeated several 10 ⁷ times Stress (10 ⁷ times fatigue strength) was calculated. As the ultrasonic fatigue test piece 51, one prepared by the above-described manufacturing method and one in which hydrogen was charged under the conditions shown in Table 9 and hydrogen was intruded into the steel were used.

Next, test results will be described. The test results are shown in Table 3. Table 3 shows the ratio of 10 ⁷ times fatigue strength of each test piece when the current carburized steel (No. 32) is 1. Under conditions where there is no hydrogen charge, both developed steel (No. 1-6) and comparative steel (No. 7-30) have fatigue strength (10 ⁷ times strength) equal to or higher than that of the current carburized steel (No. 32). Indicates.

  Under conditions where there is hydrogen charge, some of the comparative steels have lower fatigue strength and are less than the current steel (No. 21, 26, 27, 29). On the other hand, all the developed steels have 1.6 times or more fatigue strength than the current carburized steel (No. 32). Therefore, the developed steel according to the present invention has significantly improved fatigue strength from that of the current steel, and is particularly excellent in conditions where hydrogen has penetrated into the steel. From this, it can be seen that the developed steel according to the present invention is particularly suitable as steel constituting a rolling member for machine tools used in an environment where hydrogen may be generated from the lubricant.

  Embodiment 6 of the present invention will be described below. A peeling test was performed using the test piece produced by the production method described above. Rolling under conditions where the lubricating oil film can be cut in a rolling test on a rough surface, causing fatigue damage (peeling) due to metal contact on the surface. Table 10 shows the test conditions of the peeling test.

  The peeling test was performed using the above-described two-cylinder testing machine described with reference to FIG.

That is, referring to FIG. 12, the first shaft 63 as the drive shaft rotates while the lubricating oil is dropped on the first test piece 61 as the drive side test piece. Thereby, while the 1st test piece 61 rotates, the 2nd test piece 62 as a driven side test piece rotates following the 1st test piece 61, contacting the 1st test piece 61. As described above, the two-cylinder testing machine 60 was operated, and when the rotation of 4.8 × 10 ⁵ times, which is a predetermined rotation number, was completed, the rotation of the first shaft 63 was stopped. Then, the second test piece 62 is removed from the two-cylinder testing machine 60, the area of peeling generated on the outer peripheral surface of the second test piece 62 is investigated, and the peeling area with respect to the area of the outer peripheral surface of the second test piece 62 is checked. The ratio (peeling area ratio) was calculated.

  Next, test results will be described. The test results are shown in Table 3. Table 3 shows the reciprocal of the ratio of the peeling area ratio of each test piece when the current bearing steel (No. 31) is 1. Some comparative steels exhibit peeling resistance equal to or less than that of current steel (Nos. 7, 8, 22, 23, 25). On the other hand, all the developed steels show superior peeling resistance compared to the current steel and comparative steel. Therefore, it can be seen that the developed steel according to the present invention has high peeling resistance even under conditions where the lubricating oil film is cut and lubrication is not properly performed.

  Embodiment 7 of the present invention will be described below. A static crushing strength test was performed using the test piece produced by the production method described above. FIG. 16 is a schematic view showing a test piece for a static crushing strength test. The static crushing strength test will be described with reference to FIG.

  Referring to FIG. 16, static crushing strength test piece 71 has an annular shape having an outer diameter of 60 mm, an inner diameter of 45 mm, and a width of 15 mm. Then, the load is gradually applied in the direction of the load direction 72, and the load at the time when the static crushing strength test piece 71 is broken is measured. Thereafter, the obtained fracture load is converted into a stress value by the stress calculation formulas (A) to (C) of the curved beam shown below.

That is, the fiber stress on the convex surface of the static crushing strength test piece 71 in FIG. 16 (the surface at a distance of + e ₁ from the center line of the static crushing strength test piece 71) is σ ₁ , and the concave surface (the static crushing strength test piece 71 Assuming that the fiber stress in the surface at a distance of −e ₂ from the center line is σ ₂ , σ ₁ and σ ₂ are obtained by the following formulas (see Mechanical Engineering Handbook, A4 Knitting Material Dynamics A4-40). Here, N is the axial force of the cross section including the axis of the static crushing strength test piece 71, A is the cross-sectional area, e ₁ is the outer radius, and e ₂ is the inner radius (see FIG. 16). Further, κ is a section modulus of the curved beam.
σ ₁ = (N / A) + {M / (Aρ ₀ )} [1 + e ₁ / {κ (ρ ₀ + e ₁ )}] (A)
σ ₂ = (N / A) + {M / (Aρ ₀ )} [1-e ₂ / {κ (ρ ₀ −e ₂ )}] (B)
κ = − (1 / A) ∫ _A {η / (ρ ₀ + η)} dA (C)
Next, test results will be described. The test results are shown in Table 3. Table 3 shows the ratio of the static crush strength (stress value at break; crush value) of each test piece when the current bearing steel (No. 31) is 1. The developed steel exhibits a static crushing strength close to that of the current bearing steel (No. 31) and is higher than the current carburized steel (No. 32). Since the current carburized steel (No. 32) has a low internal hardness as shown in Table 2, the inside undergoes plastic deformation under a large load condition, and thus has low strength.

  The eighth embodiment of the present invention will be described below. A ring rotation crack fatigue test was performed using the test piece prepared by the above-described production method. A test piece having the same dimensions and shape as the test piece of the static crushing strength test described above was used. Table 11 shows the test conditions of the ring rotation crack fatigue test.

  FIG. 17 is a schematic diagram showing the configuration of the main part of the ring rotation crack fatigue tester. With reference to FIG. 17, a ring rotation crack fatigue tester will be described.

  Referring to FIG. 17, ring rotation crack fatigue testing machine 80 includes a driving roller 82 having a cylindrical shape, a load roller 83, and a guide roller 84. The drive roller 82, the load roller 83, and the guide roller 84 are arranged so that the rotation axes are parallel and the outer peripheral surface can contact the ring rotation crack fatigue test piece 81. The ring rotation crack fatigue testing machine 80 further includes an oil supply nozzle 86, and the oil is supplied to the pad 85 by the oil supply nozzle 86, so that lubricating oil can be supplied to the ring rotation crack fatigue test piece 81. .

  Next, the test procedure will be described. First, the ring rotation crack fatigue test piece 81 is disposed so as to come into contact with the drive roller 82, the load roller 83, and the guide roller 84 on the outer peripheral surface. The ring rotation cracking fatigue test piece 81 is driven by the rotation of the driving roller 82 while being subjected to a stress compressed in the radial direction by the driving roller 82 and the load roller 83, and is rotated by being guided by the guide roller 84. To do. As described above, the ring rotation crack fatigue tester 80 is operated, the number of tests is 10 times using 10 test pieces, and the time until cracks occur on the outer peripheral surface of the ring rotation crack fatigue test piece 81 is investigated. And the said time was made into the crack life. The obtained lifetime was statistically analyzed, and the lifetime at which the cumulative failure probability was 10% was calculated.

  Next, test results will be described. The test results are shown in Table 3. Table 3 shows the ratio of the crack life of each test piece when the current bearing steel (No. 31) is 1. Both the developed steel (No. 1 to 6) and the comparative steel (No. 7 to 30) show a longer life trend than the current bearing steel (No. 31). However, some comparative steels have a relatively short life (No. 9, 25). This is considered to be the influence of the residual stress and internal hardness of the surface layer portion. On the other hand, all the developed steels have a crack life of 2.5 times or more that of the current bearing steel (No. 31), which is equal to or higher than that of the current carburized steel (No. 32) despite the high internal hardness. It shows the crack life. Therefore, it can be seen that the crack life of the developed steel according to the present invention is greatly improved from the current bearing steel.

  Embodiment 9 of the present invention will be described below. Using the test piece produced by the production method described above, the aging change rate was measured. A test piece having the same dimensions and shape as the test piece of the static crushing strength test described above was used. And the process which heated the said test piece to 150 degreeC and hold | maintained at the said temperature for 1000 hours was performed. And the dimensional change rate (aging dimensional change rate) of the outer diameter of the test piece before and after the treatment was measured. In addition, this test was implemented in order to investigate the time-dependent dimensional change when the rolling member for machine tools was used for a long period of time in the actual use environment in a machine tool.

  Next, test results will be described. The test results are shown in Table 3. Referring to Table 3, both the developed steel (No. 3-4) and the comparative steel (No. 28-30) are compared with the current bearing steel (No. 31) and the current carburized steel (No. 32). It can be seen that the aging dimensional change rate is remarkably reduced, and the dimensional stability is greatly improved. This is because the developed steel and the comparative steel have sufficient hardness even if tempering is performed at 280 ° C., so that the current bearing steel and the current carburized steel are used. Is considered to result from the fact that tempering is performed at 180 ° C. because sufficient hardness cannot be secured as a rolling member for machine tools when tempering is performed at 280 ° C. That is, it was confirmed that the developed steel according to the present invention significantly exceeds the current steel in dimensional stability over time.

  The tenth embodiment of the present invention will be described below. Angular contact ball bearings were produced using the test pieces produced by the production method described above, and a rolling fatigue life test was conducted. Table 12 shows the conditions of the rolling fatigue life test.

  First, an angular contact ball bearing ring having an inner diameter of 100 mm, an outer diameter of 150 mm, and a thickness of t24 mm was produced by the same method as in Example 1 above. And the angular contact ball bearing was produced using the said bearing ring and the ball | bowl made from silicon nitride prepared separately, and it used for the rolling fatigue test. The number of tests was two each.

  Next, test results will be described. The test results are shown in Table 3. Table 3 shows the average value of the time until separation occurs on the raceway in each test piece as “lifetime of the angular ball bearing”. Note that test results in the case where seizure does not occur on the raceway and seizure occurs are excluded.

  Referring to Table 3, a bearing provided with a bearing ring that is a rolling member for a machine tool of the present invention composed of the developed steel according to the present invention (rolling bearing for a machine tool of the present invention; Nos. 3 to 4) No peeling occurred on the raceway even after 3000 hours from the start of the test. On the other hand, in the bearings (Nos. 31 to 32) provided with the bearing rings made of SUJ2 and SCM420, which are current steels, peeling occurred on the bearing rings in about 1000 hours. From this, the bearing ring (No. 3-4) which is a rolling member for machine tools of the present invention is about three times as large as the bearing ring (No. 31-32) which is a conventional rolling member. It was confirmed that it had a rolling fatigue life longer than that.

  Moreover, the bearing ring (No. 28-30) comprised from the steel of the comparative example also has a rolling fatigue life of about twice that of the bearing ring (No. 31-32) which is a conventional rolling member. Although it has, the lifetime is shortened compared with the bearing ring (No. 3-4) which is a rolling member for machine tools of this invention.

  From the above, it was confirmed that the rolling member for machine tool and the rolling bearing for machine tool of the present invention were superior in durability compared to the conventional rolling member for machine tool and the rolling bearing for machine tool.

  In the description so far, the test results carried out using the test pieces subjected to carburizing and quenching were explained as examples, but the test was similarly conducted using other test pieces subjected to carbonitriding and quenching. Carried out. As a result, it has been confirmed that the temper softening resistance is higher than that of the test piece subjected to carburizing and quenching, and the result is inferior in material and mechanical characteristics.

  A specific heat treatment method for carbonitriding and quenching is as follows. First, the molded part was heated to 920 ° C., and at this time, the carbon potential of the atmospheric gas was adjusted to be 1.0, and kept at this temperature for 480 minutes. Among them, for 300 minutes, ammonia gas was added to RX gas, which is an atmospheric gas, and an amount of 5% by volume of RX gas was added. Thereby, carbonitriding and diffusion treatment were performed. Thereafter, the temperature was lowered to 850 ° C., and the molded part was immersed in oil and rapidly cooled to perform primary quenching. Further, the molded part was reheated to 850 ° C. and held for 50 minutes, immersed again in oil, rapidly cooled from 850 ° C., and subjected to secondary quenching. Further, the molded part was heated to 280 ° C. and held for 120 minutes, then cooled in air at room temperature, and tempered.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The rolling member for a machine tool and the rolling bearing for a machine tool according to the present invention are members in which a rotating spindle is disposed adjacent to the spindle in a machine tool that processes a workpiece by rotating the spindle. The present invention can be applied particularly advantageously to a rolling member for a machine tool and a rolling bearing for a machine tool that constitute a rolling bearing for a machine tool that is rotatably supported with respect to the machine tool.

It is a schematic sectional drawing which shows the structure around the main axis | shaft of the machine tool provided with the angular ball bearing and cylindrical roller bearing as a rolling bearing for machine tools. It is a schematic sectional drawing which shows the structure of the angular ball bearing as a rolling bearing for machine tools. It is the general | schematic fragmentary sectional view which expanded and showed the principal part of FIG. It is a schematic sectional drawing which shows the structure of the cylindrical roller bearing as a rolling bearing for machine tools. FIG. 5 is a schematic partial cross-sectional view showing an enlarged main part of FIG. 4. It is a flowchart which shows the outline of the manufacturing method of the rolling member for machine tools, and the rolling bearing for machine tools. It is a figure explaining the heat processing method in the heat processing process included in the manufacturing method of the rolling member for machine tools. It is a figure explaining the modification of the heat processing method in the heat processing process included in the manufacturing method of the rolling member for machine tools. It is a figure explaining the other modification of the heat processing method in the heat processing process included in the manufacturing method of the rolling member for machine tools. It is a schematic front view which shows the structure of the principal part of a (phi) 12 point contact test machine. It is a schematic side view which shows the structure of the principal part of a (phi) 12 point contact test machine. It is a schematic diagram which shows the structure of the principal part of a 2 cylinder type testing machine. It is a schematic front view which shows the structure of the principal part of a Saban-type abrasion tester. It is a schematic side view which shows the structure of the principal part of a Saban-type abrasion tester. It is a schematic diagram which shows the structure of the principal part of an ultrasonic fatigue testing machine. It is a schematic diagram which shows the test piece of a static crushing strength test. It is a schematic diagram which shows the structure of the principal part of a ring rotation crack fatigue testing machine.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Angular contact ball bearing, 2 Cylindrical roller bearing, 11, 21 Outer ring, 11A, 21A Outer ring rolling surface, 11B, 12B, 13B, 21B, 22B, 23B Hardened layer, 11C, 12C, 13C, 21C, 22C, 23C Inside , 12, 22 inner ring, 12A, 22A inner ring rolling surface, 13 balls, 13A ball rolling surface, 14, 24 cage, 23 cylindrical roller, 23A roller rolling surface, 30 point contact tester, 31 rolling fatigue life Specimen, 32 Drive roller, 33 Guide roller, 34 Steel ball, 40 Saban type wear tester, 41 Wear test piece, 42 Weight, 43 Load cell, 44 Air slider, 45 Opposite material, 46 Lubricating oil, 50 Ultrasonic fatigue Tester, 51 Ultrasonic fatigue test piece, 52 Horn part, 53 Vibrator, 54 Amplifier, 55 Control device, 56 Clearance gauge, 57 Oscilloscope Loop, 602 cylindrical tester, 61 first test piece, 62 second test piece, 63 first axis, 64 second axis, 65 tachometer, 66 slip ring, 71 static crushing strength test piece, 72 load Direction, 80 Ring Rotation Crack Fatigue Tester, 81 Ring Rotation Crack Fatigue Test Specimen, 82 Drive Roller, 83 Load Roller, 84 Guide Roller, 85 Pad, 86 Oiling Nozzle, 90 Machine Tool, 91 Main Spindle, 91A Outer Surface, 91B Tip , 92 housing, 92A inner wall, 93 motor, 93A motor stator, 93B motor rotor.

Claims (4)

In a machine tool that processes a workpiece by rotating a main shaft, a rolling bearing for a machine tool is configured to rotatably support the main shaft that is rotationally driven with respect to a member that is disposed adjacent to the main shaft. A rolling member for machine tools,
0.3% by mass or more and 0.4% by mass or less of carbon, 0.2% by mass or more and less than 0.5% by mass of silicon, 0.3% by mass or more and 0.8% by mass or less of manganese, 0.5 mass% or more and 1.2 mass% or less nickel, 1.6 mass% or more and 2.5 mass% or less chromium, 0.1 mass% or more and 0.7 mass% or less molybdenum, 0.3 The vanadium is contained in the balance iron and inevitable impurities, the vanadium content is equal to or greater than the molybdenum content, and the sum of the molybdenum content and the vanadium content. Is a quench-treated steel that is more than twice the silicon content, and the sum of the chromium content, the molybdenum content, and the vanadium content is not less than 2.3 mass% and not more than 3.5 mass%. Consisting of
In the surface layer part, a cured layer is formed,
The hardness of the cured layer is Hv 700 or more and 780 or less,
The maximum particle size of the carbide distributed in the cured layer is 10 μm or less,
The area ratio of the carbide in the cured layer is 7% or more and 25% or less,
An internal hardness which is an area inside the hardened layer is Hv500 or more and 600 or less, the rolling member for machine tools,   The rolling member for machine tools according to claim 1, wherein the hardness of the hardened layer after high-temperature tempering at 500 ° C is Hv550 or higher and 650 or lower.   3. The machine tool according to claim 1, wherein the sum of the molybdenum content and the vanadium content is made of steel having a mass ratio of 0.6 mass% to 1.5 mass%. Rolling member for use.   The rolling bearing for machine tools provided with the rolling member for machine tools of any one of Claims 1-3.

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