JP2008025794A - Needle roller bearing rolling member and needle roller bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a needle roller bearing rolling member and a needle roller bearing, which have improved durability by suppressing the occurrence of peeling, surface crack, breakage, and hydrogen brittle separation. <P>SOLUTION: The bearing ring 11 and a needle roller 13, constituting the thrust needle roller bearing 1, are each formed of steel which contains 0.3-0.4% C, 0.2-0.5% Si, 0.3-0.8% Mn, 0.5-1.2% Ni, 1.6-2.2% Cr, 0.1-0.7% Mo, and 0.3-0.8% V, and Fe and inevitable impurities in the rest, where V is Mo or more, the Mo and V sum is twice as much as Si or more, and the Cr, Mo and V sum is 2.3-3.5%. The hardness of a hardening treatment layer formed on the surface layer portion is Hv 700-780. The maximum grain size of carbide distributed in the hardening treatment layer is 10 μm or smaller and the area rate is 7-25%. The internal hardness is Hv 500-600. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a rolling member for a needle roller bearing and a needle roller bearing, and more specifically, a rolling member for a needle roller bearing that constitutes a long-life needle roller bearing even in a harsh environment, and The present invention relates to a needle roller bearing.

  A needle roller bearing provided with a needle roller having a diameter of a roller as a rolling element of 5 mm or less and a length of the roller of 3 to 10 times the diameter of the roller is a raceway surface of the rolling element. The height of the bearing mainly in the direction of receiving a load in the cross section perpendicular to is small, and the load capacity is large for the size. The needle roller bearing also has a feature that high rigidity is easily obtained. Therefore, the needle roller bearing is expected to be applied to various uses. In a needle roller bearing, due to its structure, slip is likely to occur between a needle roller that is a rolling element and a race member for a needle roller bearing such as a race ring. For this reason, rolling roller members for needle roller bearings such as needle rollers and needle roller bearing raceway members are often subjected to rolling fatigue accompanied by slipping, and the usage environment is often severe.

On the other hand, many studies have been made for the purpose of extending the life of needle roller bearings, and various countermeasures have been proposed (for example, see Patent Documents 1 to 5).
JP 2003-301849 A JP 2004-92745 A Japanese Patent Laid-Open No. 2005-226683 JP 2005-291342 A JP 2005-344783 A

  However, in recent years, the rotational speed of members supported by needle roller bearings has increased in industrial machines, transport machines, etc., for the purpose of further improving the performance of industrial machines, transport machines, etc. in which needle roller bearings are used. In addition, abrupt acceleration / deceleration is often given. In addition, the viscosity of the lubricant tends to be suppressed in order to facilitate an increase in rotational speed and acceleration during acceleration / deceleration. For this reason, the rolling surfaces of raceway members such as bearing rings constituting needle roller bearings and rolling members for needle roller bearings such as needle rollers that are rolling elements are heated to high temperatures, and sliding on the rolling surfaces is caused. In some cases, the metal contact between the rolling members due to the oil film breakage may occur. As a result, the vicinity of the rolling surface is tempered to reduce the hardness, and tensile stress acts on the rolling surface, resulting in problems such as peeling, surface cracks, and cracks. In addition, the lubricant is decomposed and hydrogen is generated by using the new metal surface that appears due to the metal contact between the rolling members as a catalyst, and the rolling surface peels off in a short time due to the penetration of the hydrogen into the rolling member. The phenomenon (hydrogen embrittlement delamination) is also a problem.

  Accordingly, an object of the present invention is to improve the durability of needle roller bearings by improving the occurrence of peeling, surface cracks, cracks and the like and the occurrence of hydrogen embrittlement separation even in the severe environment described above. It is to provide a moving member and a needle roller bearing.

  The rolling member for a needle roller bearing according to the present invention has a diameter of a roller as a rolling element of 5 mm or less, and the length of the roller is 3 to 10 times the diameter of the roller. It is a rolling member for needle roller bearings which constitutes a needle roller bearing provided with. The rolling member for needle roller bearings is 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. 0.8% by mass or less of manganese, 0.5% by mass or more and 1.2% by mass or less of nickel, 1.6% by mass or more and 2.2% by mass or less of chromium, and 0.1% by mass or more and 0.0. 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 unavoidable impurities, the vanadium content being greater than or equal to the molybdenum content, The sum of the content of vanadium and the content of vanadium is more than twice the content of silicon, and the sum of the content of chromium, the content of molybdenum and the content of vanadium is 2.3% by mass or more and 3.5% It is comprised from the steel which is the mass% or less. Furthermore, a cured layer is formed on the surface layer portion. And the hardness of a hardening process layer is Hv700 or more and 780 or less, the maximum 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% or less. It is. 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 a needle roller bearing of the present invention, in the steel constituting the rolling member for a needle roller bearing, the content of silicon that may promote hydrogen embrittlement separation is reduced, and vanadium, nickel, Three components of 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 rolling member for needle roller bearings, and toughness.

  Further, in the rolling member for the needle roller bearing of the present invention, steel having a higher carbon content than that of general carburized steel is adopted as a material to perform carburizing or carbonitriding, and carburizing or carbonitriding. Thus, the size and area ratio of carbides in the cured layer formed in the surface layer portion are adjusted to an appropriate range. Thereby, a compressive stress is formed on the surface of the rolling member for the needle roller bearing, 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 peeling, surface cracks, cracks, and the like is suppressed in the rolling member for the needle roller bearing, and the durability of the rolling member for the needle roller bearing is improved. Furthermore, the static cracking strength and fatigue cracking strength of the rolling members for needle roller bearings can be made compatible, the ease of processing (workability) in the manufacturing process is improved, and the time required for carburizing or carbonitriding is improved. It is shortened and productivity is improved.

  As described above, according to the rolling member for a needle roller bearing of the present invention, durability can be improved by suppressing the occurrence of peeling, surface cracks, cracks and the like, and the occurrence of hydrogen embrittlement separation even in harsh environments. An improved rolling member for a needle roller bearing can be provided.

  Here, the surface layer portion of the rolling member for the needle roller bearing 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 the needle roller bearing. . 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 needle roller bearings and a 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 the problem of difficult processing is less likely to occur. 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 internal hardness of the region inside the hardened layer, specifically, the region having a depth of 1.0 mm or more from the surface of the rolling member for a needle roller bearing to Hv 600 or less, it has toughness. And a 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.

In addition, the hardness of the said hardening process layer and an inside can be investigated, for example by cut | disconnecting the rolling member for needle roller bearings, and measuring a hardening process layer and an inside 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 needle roller bearings 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 needle roller bearings of this invention to said range is demonstrated.

Carbon: 0.3 mass% or more and 0.4% mass% or less Carbide or carbonitriding of the surface layer portion of the rolling member for needle roller bearings ensures cracking strength and imparts compressive stress to the surface layer portion. be able to. However, when low carbon steel like the conventional one is adopted as the material of the rolling member for the needle roller bearing, the internal hardness is low, and the strength is lowered 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 a needle roller bearing in which significant hydrogen intrusion from the environment may occur, the amount added is limited because there is a concern of promoting hydrogen embrittlement separation when 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 an essential element for improving the hardenability and rolling fatigue life of rolling members for needle roller bearings. Since the workability is hindered, the upper limit of the addition amount is limited to 0.8% by mass from the balance between improving the hardenability and increasing the 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 indispensable for ensuring the rolling fatigue life of rolling members for needle roller bearings at high temperatures, and is also effective in improving resistance to corrosion at high temperatures. There is. 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 2.2 mass% or less Chromium is also an essential element for ensuring the rolling fatigue life and high temperature hardness of the rolling member for needle roller bearings. 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, regarding the upper limit of the chromium content, it is necessary to consider the balance with other elements that form carbides such as molybdenum and vanadium, and the possibility of reducing the rolling fatigue life and crack strength by forming large carbides. . In particular, in needle roller bearings in which the area of the contact ellipse between the rolling members is small, the adverse effect on the rolling fatigue life of large carbides is large, so 2.2 mass% was made the upper limit.

Molybdenum: 0.1% to 0.7% by weight Molybdenum also improves the hardenability and imparts temper softening resistance due to carbide formation. Indispensable for ensuring dynamic fatigue 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 grain boundaries, and refines the crystal grains to improve the strength and toughness of the rolling member for needle roller bearings. . 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 needle roller bearings used under conditions where hydrogen may enter, and extending the life by suppressing the occurrence of hydrogen brittle separation. 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 in prolonging and stabilizing the rolling fatigue life of the rolling members for needle roller bearings. 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.

  In addition, impurity elements such as phosphorus, sulfur, aluminum, and titanium are usually suppressed to a low level in the bearing steel, and the same is true for the steel constituting the rolling member for the needle roller bearing 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 mass% or less TiN that is a non-metallic inclusion is formed, which may cause a decrease in the rolling fatigue life of the rolling member for needle roller bearings, and may be a starting point for hydrogen embrittlement separation. Therefore, it was made into 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 brittle separation of the rolling members for needle roller bearings 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 peeling of the rolling member for the needle roller bearing.

  The sum of the chromium content, the molybdenum content, and the vanadium content is set to a minimum of 2.3 mass% or more in order to improve the heat resistance and rolling fatigue life of the rolling member for needle roller bearings. . 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 needle roller bearing, the hardness of the hardened layer after high-temperature tempering at 500 ° C. is preferably 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 needle roller bearing, 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 the needle roller bearing 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 the needle roller bearing can be suppressed by defining the upper limit value as described above.

  A needle roller bearing according to the present invention includes the above-described rolling member for a needle roller bearing. According to the needle roller bearing of the present invention, even in a harsh environment, the rolling for a needle roller bearing with improved durability is achieved by suppressing the occurrence of peeling, surface cracks, cracks, etc. and the occurrence of hydrogen brittle separation. By providing the member, a needle roller bearing with improved durability can be provided.

  As is apparent from the above description, according to the rolling member and needle roller bearing of the present invention, peeling, surface cracks, cracks, etc., and occurrence of hydrogen embrittlement peeling, even in harsh environments By suppressing the above, it is possible to provide a rolling member for a needle roller bearing and a needle roller bearing 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.

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view showing a configuration of a thrust needle roller bearing as a needle roller bearing provided with a rolling member for needle roller bearings according to Embodiment 1 which is an embodiment of the present invention. 2 is a schematic partial cross-sectional view of a raceway ring as a rolling member for a needle roller bearing provided in the thrust needle roller bearing of FIG. 3 is a schematic cross-sectional view of a needle roller as a rolling member for a needle roller bearing provided in the thrust needle roller bearing of FIG. With reference to FIGS. 1-3, the structure of the thrust needle roller bearing as a needle roller bearing in Embodiment 1 of this invention, the bearing ring as a roller member for needle roller bearings, and a needle roller (needle roller) Will be described.

  Referring to FIG. 1, a thrust needle roller bearing 1 according to Embodiment 1 has a disk-like shape, and is a needle roller bearing rolling member (track) arranged so that one main surface faces each other. A pair of race rings 11 as members), a plurality of needle rollers 13 as needle roller bearing rolling members (needle rollers), and an annular retainer 14. The plurality of needle rollers 13 are in contact with the raceway rolling surface 11A formed on one main surface of the pair of raceways 11 facing each other, and are arranged at a predetermined pitch in the circumferential direction by the cage 14. It is rotatably held on an annular track. With the above configuration, the pair of race rings 11 of the thrust needle roller bearing 1 can rotate relative to each other.

  Next, the raceway ring 11 and the needle roller 13 as the rolling members for the needle roller bearing constituting the thrust needle roller bearing 1 which is a needle roller bearing will be described. With reference to FIGS. 1 to 3, the raceway ring 11 and the needle roller 13 have a roller diameter of 5 mm or less as a rolling element, and the length of the roller is 3 to 10 times the roller diameter. It is a rolling member for needle roller bearings which constitutes needle roller bearing 1 provided with needle rollers 13 which are. And the race 11 and the needle roller 13 are 0.3 mass% or more and 0.4% mass% or less carbon, 0.2 mass% or more and less than 0.5 mass% silicon, and 0.3 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 2.2% 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, the hardened layers 11B and 13B are formed on the surface layer portions of the race 11 and the needle rollers 13, respectively. The hardness of the cured layers 11B and 13B is Hv 700 or more and 780 or less, the maximum particle size of carbides distributed in the cured layers 11B and 13B is 10 μm or less, and the area of the carbides in the cured layers 11B and 13B. The rate is 7% or more and 25% or less. Furthermore, the hardness of the inner portions 11C and 13C, which are regions inside the cured layers 11B and 13B, is Hv500 or more and 600 or less.

  In the raceway ring 11 and the needle roller 13 as the rolling members for the needle roller bearing of the first embodiment, in the steel constituting the raceway ring 11 and the needle roller 13, there is a possibility that silicon that may promote hydrogen embrittlement delamination. While the content is reduced, 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 bearing ring 11 and the needle roller 13, and toughness. Further, in the raceway ring 11 and the needle roller 13 of the first embodiment, steel having a higher carbon content than that of general carburized steel is adopted as a material, and carburization or carbonitriding is performed, and carburization or carbonization is performed. The size and area ratio of carbides in the cured layers 11B 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 race ring 11 and the needle rollers 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 peeling, surface cracks, cracks, and the like, and the occurrence of hydrogen embrittlement peeling are suppressed in the raceway ring 11 and the needle roller 13, and the durability of the raceway ring 11 and the needle roller 13 is improved. Further, the static crack strength and the fatigue crack strength of the bearing ring 11 and the needle roller 13 are compatible, the ease of processing (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 bearing ring 11 and the needle roller 13 as the rolling members for the needle roller bearing according to the present invention are free from peeling, surface cracks, cracks and the like, and occurrence of hydrogen brittle peeling even in a severe environment. By being suppressed, durability is improved. As a result, the thrust needle roller bearing 1 as the needle roller bearing of the first embodiment suppresses the occurrence of peeling, surface cracks, cracks, and the occurrence of hydrogen embrittlement even in a harsh environment. By providing the bearing ring 11 and the needle roller 13 with improved durability, durability is improved.

  In the raceway ring 11 and the needle roller 13 of the first embodiment, the hardness of the cured layers 11B 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 raceway ring 11 and needle roller 13 of the first 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 value of the sum of the molybdenum content and the vanadium content to the above values, the heat resistance and hydrogen embrittlement resistance of the race 11 and needle roller 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 bearing ring 11 and the needle roller 13 can be suppressed by defining the upper limit value as described above.

  Next, the rolling member for needle roller bearings and the method for manufacturing the needle roller bearing in the first embodiment will be described. FIG. 4 is a flowchart showing an outline of a rolling member for a needle roller bearing and a method for manufacturing the needle roller bearing in the first embodiment.

  Referring to FIG. 4, 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 or more and 0.8% by mass or less of manganese, 0.5% by mass or more and 1.2% by mass or less of nickel, 1.6% by mass or more and 2.2% by mass or less 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 a process (S200), the shaping | molding process which produces the molded component shape | molded by the schematic shape of the rolling member for needle roller bearings is implemented by shape | molding the said steel material. Specifically, for example, forging, turning, and the like are performed on the above steel bars, steel wires, and the like, so that they are formed into schematic shapes such as the race ring 11 and the needle rollers 13 shown in FIGS. A molded part 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 bearing ring 11 and the needle rollers 13 are finished by performing a finishing process such as a grinding process on the molded part subjected to the heat treatment step. Thereby, the race ring 11 and the needle rollers 13 as the rolling members for the needle roller bearing in the first embodiment are completed.

  Further, in the process (S500), an assembly process is performed. Specifically, the bearing ring 11 and the needle roller 13 manufactured in steps (S100) to (S400) and the separately prepared cage 14 are combined to form the needle roller bearing according to the first embodiment. The thrust needle roller bearing 1 is assembled. Thereby, the thrust needle roller bearing 1 is completed.

  Next, the details of the heat treatment step (S300) will be described. FIG. 5 is a diagram for explaining a heat treatment method in a heat treatment step included in the method of manufacturing the rolling member for a needle roller bearing in the first embodiment. In FIG. 5, the horizontal direction indicates time, and the time elapses toward the right. In FIG. 5, the vertical direction indicates the temperature, and the higher the temperature, the higher the temperature.

Referring to FIG. 5, 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, 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. The heat treatment process (S300) in the manufacturing method of the race 11 and the needle roller 13 as a rolling member for needle roller bearings is completed by the above procedure.

  FIG. 6 is a diagram for explaining a modification of the heat treatment method in the heat treatment step included in the method of manufacturing the rolling member for needle roller bearing in the first embodiment. In FIG. 6, the horizontal direction indicates time, and the time elapses toward the right. In FIG. 6, the vertical direction indicates the temperature, and the higher the temperature, the higher the temperature. With reference to FIG. 6, the detail of the modification of the heat processing method is demonstrated.

Referring to FIG. 6, 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. The heat treatment process (S300) in the manufacturing method of the race 11 and the needle roller 13 as a rolling member for needle roller bearings is completed by the above procedure.

  The above heat treatment improves the cracking strength while carburizing the surface layer portion as compared with the heat treatment method described in FIG. 5, that is, the heat treatment method (normal quenching), which is followed by carburizing treatment once as it is. 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 members for needle roller bearings manufactured by the heat treatment described above have a longer rolling fatigue characteristic, improved crack strength, and reduced aging dimensional change 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. 7 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 a needle roller bearing in the first 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. With reference to FIG. 7, the detail of the other modification of the heat processing method is demonstrated.

Referring to FIG. 7, a molded part finished to a predetermined size by cold working or the like in the molding process 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. It is held for 360 minutes or more and 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 is performed, and thereafter, the time is maintained 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.

Further, the molded part that has been subjected to carbonitriding and quenching 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 is held for 30 minutes or more and 240 minutes or less, for example 120 minutes. Then, 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 race 11 and the needle roller 13 as the rolling member for the needle roller bearing 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.

  By the heat treatment step (S300), the cured layers 11B and 13B are formed on the surface layer portions of the race 11 and the needle roller 13 as the rolling members for the needle roller bearing. The hardness of the cured layers 11B and 13B is Hv 700 to 780, the maximum particle size of carbides distributed in the cured layers 11B and 13B is 10 μm or less, and the area ratio of carbides in the cured layers 11B and 13B is 7% to 25. %, And the hardness of the interiors 11C and 13C, which are regions inside the cured layers 11B and 13B, can be Hv500 or more and 600 or less.

  According to the manufacturing method of the rolling member for the needle roller bearing of the first embodiment described above, the hydrogen brittle separation in the steel constituting the bearing ring 11 and the needle roller 13 as the rolling member for the needle roller bearing. The content of silicon, which may promote the reduction of carbon, is reduced, and the three components of vanadium, nickel, and molybdenum are added in a well-balanced manner, and steel with an increased carbon content compared to general carburized steel is used as a material. Has been. Further, while carburizing or carbonitriding is performed, the size and area ratio of carbides in the cured layers 11B and 13B formed on the surface layer portion by carburizing or carbonitriding can be adjusted to an appropriate range, and curing can be performed. The hardness in the treatment layers 11B and 13B and the insides 11C and 13C can be adjusted to an appropriate range.

  As a result, rolling bearings and needle roller bearings with improved durability can be obtained by suppressing the occurrence of peeling, surface cracks, cracks, etc. and the occurrence of hydrogen brittle peeling even in harsh environments. Can be manufactured.

(Embodiment 2)
FIG. 8 is a schematic diagram showing a configuration of a radial needle roller bearing as a needle roller bearing provided with the rolling member for a needle roller bearing according to the second embodiment which is an embodiment of the present invention. FIG. 9 is a schematic partial cross-sectional view of a bearing ring (outer ring) as a rolling member for a needle roller bearing provided in the radial needle roller bearing of FIG. FIG. 10 is a schematic partial cross-sectional view of a race (inner ring) as a rolling member for a needle roller bearing provided in the radial needle roller bearing of FIG. With reference to FIGS. 8-10, the structure of the radial needle roller bearing as a needle roller bearing in Embodiment 2 of this invention, the bearing ring as a rolling member for needle roller bearings, and a needle roller is demonstrated. .

  Referring to FIG. 8, radial needle roller bearing 2 of the second embodiment and thrust needle roller bearing 1 of the first embodiment have basically the same configuration and have the same effects. However, the configuration of the race is different. That is, the radial needle roller bearing 2 includes an annular outer ring 21 as a rolling member for a needle roller bearing (tracking ring) and a rolling member for a needle roller bearing (tracking ring) disposed inside the outer ring 21. An annular inner ring 22, and a plurality of needle rollers 23 as rolling members (rolling elements) for a needle roller bearing which are disposed between the outer ring 21 and the inner ring 22 and are held by an annular cage 24. I have. An outer ring rolling surface 21 </ b> A is formed on the inner circumferential surface of the outer ring 21, and an inner ring rolling surface 22 </ b> A is formed on the outer circumferential surface of the inner ring 22. The outer ring 21 and the inner ring 22 are arranged so that the inner ring rolling surface 22A and the outer ring rolling surface 21A face each other. Further, the plurality of needle rollers 23 are arranged on an annular track by having their outer peripheral surfaces in contact with the inner ring rolling surface 22A and the outer ring rolling surface 21A and being arranged at a predetermined pitch in the circumferential direction by the cage 24. It is held so that it can roll freely. With the above configuration, the outer ring 21 and the inner ring 22 of the radial needle roller bearing 2 can be rotated relative to each other.

  Referring to FIGS. 2, 3, 9, and 10, outer ring 21 and inner ring 22 of the second embodiment correspond to raceway ring 11 of the first embodiment, and basically have the same configuration and effects. is doing. More specifically, the outer ring 21 and the inner ring 22 of the second embodiment are the outer ring rolling surface 21A and the inner ring rolling surface 22A corresponding to the rolling ring rolling surface 11A of the bearing ring 11 of the first embodiment, and a hardened layer. It has a cured layer 21B and a cured layer 22B corresponding to 11B, and an interior 21C and an interior 22C corresponding to the interior 11C. The needle roller 23 of the second embodiment has the same configuration and effect as the needle roller 13 of the first embodiment.

  Therefore, the outer ring 21, the inner ring 22 and the needle roller 23 as the rolling members for the needle roller bearing of the present invention are suppressed in the occurrence of peeling, surface cracks, cracks, etc. and occurrence of hydrogen brittle peeling even in a harsh environment. As a result, durability is improved. As a result, the radial needle roller bearing 2 as the needle roller bearing of the second embodiment suppresses the occurrence of peeling, surface cracks, cracks and the like and the occurrence of hydrogen embrittlement in a harsh environment. By providing the outer ring 21, the inner ring 22 and the needle roller 23 with improved durability, durability is improved.

  The radial needle roller bearing 2 of the present embodiment can be manufactured by the same manufacturing method as the thrust needle roller bearing 1 described in the first embodiment.

  In the first and second embodiments, as an example of the needle roller bearing and the needle roller bearing rolling member according to the present invention, a thrust needle roller bearing, a radial needle roller bearing, and a bearing ring and a needle roller provided therein are provided. Although explained, the needle roller bearing and the needle roller bearing race member of the present invention are not limited to these. For example, the raceway member, which is a rolling member for needle roller bearings, may be a shaft or plate used so that the needle rollers roll on the surface. That is, the raceway member as the rolling member for the needle roller bearing of the present invention may be a member on which a rolling surface for rolling the needle roller is formed.

  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 a heat treatment method similar to that 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 ensure sufficient surface hardness as a rolling member for needle roller bearings, has internal hardness that can provide toughness and prevent internal cracks, and at high temperatures. It can be seen that the strength of 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. 11 is a schematic front view showing the configuration of the main part of the φ12 point contact tester. FIG. 12 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. 11 and 12.

  With reference to FIG. 11 and FIG. 12, the φ12 point contact testing 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 life was statistically analyzed, and the rolling fatigue life 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. 13 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. 13, a disk-shaped first test piece 61 is set in the two-cylinder test machine 60 so as to be rotatable around the first axis 63 and is rotatable around the second axis 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. A rotation speed meter 65 and a slip ring 66 are arranged at the other end of the first shaft 63 and the second shaft 64.

  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. 14 is a schematic front view showing the configuration of the main part of the Sabang type wear tester. FIG. 15 is a schematic side view showing the configuration of the main part of the Sabang type wear tester. With reference to FIG. 14 and FIG. 15, a Sabang type wear tester will be described.

  Referring to FIGS. 14 and 15, 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. 16 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. 16, 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 a steel constituting a rolling member for a needle roller bearing used in an environment where hydrogen is 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 tester described with reference to FIG.

That is, referring to FIG. 13, 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. 17 is a schematic diagram 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. 17, static crushing strength test piece 71 has an annular shape with 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. 17 (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. 17). 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 crushing 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). As shown in Table 2, the current carburized steel (No. 32) has a low internal hardness, and therefore, the inner part is plastically deformed under a large load condition.

  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. 18 is a schematic diagram showing a configuration of a main part of a ring rotation crack fatigue tester. With reference to FIG. 18, a ring rotation crack fatigue tester will be described.

  Referring to FIG. 18, the 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 dimensional change over time when the rolling member for needle roller bearings was used for a long period of time in the actual usage environment of needle roller bearings.

  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 be caused by tempering at 180 ° C. because sufficient hardness cannot be secured as a rolling member for needle roller bearings 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. A needle roller bearing was manufactured using the test piece manufactured by the above-described manufacturing method, and a rolling fatigue life test was performed. Table 12 shows the conditions of the rolling fatigue life test.

  First, a thrust needle roller bearing raceway having an inner diameter of φ60 mm, an outer diameter of φ85 mm, and a thickness of t2 mm was produced by the same method as in Example 1 above. Then, a thrust needle roller bearing was prepared using the raceway ring and a carbonitrided SUJ2 needle roller separately prepared, and subjected to a rolling fatigue test. The number of tests was two each.

  Next, test results will be described. The test results are shown in Table 3. In Table 3, the average value of the time until the occurrence of separation on the raceway in each test piece is shown as “life in needle roller bearing”. In addition, the test result when the rolling element is damaged and seizure occurs is excluded.

  With reference to Table 3, the bearing (the needle roller bearing of this invention; No. 3-4) provided with the bearing ring which is a rolling member for needle roller bearings of this invention comprised from the developed steel which concerns on this invention ), No separation occurred on the raceway even after 100 hours had elapsed from the start of the test. When the test was continued as it was, peeling occurred in the rolling elements before the race. That is, the bearing rings (Nos. 3 to 4) which are rolling members for needle roller bearings of the present invention are compared to the bearing rings (Nos. 31 to 32) which are conventional rolling members for needle roller bearings. It was confirmed that it had a rolling fatigue life of at least 4 times.

  On the other hand, the bearing rings (Nos. 28 to 30) made of the steel of the comparative example are also more than twice as large as the bearing rings (Nos. 31 to 32), which are conventional rolling members for needle roller bearings. Although it has a rolling fatigue life, the life is shortened compared with the bearing ring (No. 3-4) which is a rolling member for needle roller bearings of the present invention.

  From the above, it was confirmed that the rolling members and needle roller bearings of the present invention have superior durability compared to conventional rolling members and needle roller bearings for needle roller bearings. It was.

  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 and needle roller bearing of the present invention can be particularly advantageously applied to the rolling member and needle roller bearing for use in severe environments.

1 is a schematic cross-sectional view showing a configuration of a thrust needle roller bearing as a needle roller bearing provided with a rolling member for needle roller bearings in Embodiment 1. FIG. It is a general | schematic fragmentary sectional view of the bearing ring as a rolling member for needle roller bearings. It is a schematic sectional drawing of the needle roller as a rolling member for needle roller bearings. 3 is a flowchart showing an outline of a method for manufacturing a rolling member for a needle roller bearing and a needle roller bearing in the first embodiment. It is a figure explaining the heat processing method in the heat processing process included in the manufacturing method of the rolling member for needle roller bearings in Embodiment 1. FIG. 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 needle roller bearings in Embodiment 1. FIG. 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 needle roller bearings in Embodiment 1. FIG. It is the schematic which shows the structure of the radial needle roller bearing as a needle roller bearing provided with the rolling member for needle roller bearings of Embodiment 2. FIG. It is a general | schematic fragmentary sectional view of the bearing ring (outer ring) as a rolling member for needle roller bearings. It is a general | schematic fragmentary sectional view of the bearing ring (inner ring) as a rolling member for needle roller bearings. 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

  1 Thrust needle roller bearing, 2 radial needle roller bearing, 11 bearing ring, 11A raceway rolling surface, 11B, 12B, 13B, 21B, 22B, 23B hardened layer, 11C, 12C, 13C, 21C, 22C, 23C inside, 14, 24 Cage, 21 Outer ring, 21A Outer ring rolling surface, 22 Inner ring, 22A Inner ring rolling surface, 30-point contact test machine, 31 Rolling fatigue life test piece, 32 Drive roller, 33 Guide roller, 34 Steel ball, 40 Sabang 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 gap gauge, 57 oscilloscope, 60 2-cylinder testing machine, 61 1 test piece, 62 2nd test piece, 63 1st axis, 64 2nd axis, 65 tachometer, 66 slip ring, 71 static crush strength test piece, 72 load direction, 80 ring rotary crack fatigue tester, 81 ring Rotating crack fatigue test piece, 82 drive roller, 83 load roller, 84 guide roller, 85 pad, 86 oiling nozzle.

Claims (4)

A needle roller bearing constituting a needle roller bearing having a needle roller having a diameter of 5 mm or less as a rolling element and a length of the roller being 3 to 10 times the diameter of the roller Rolling member for
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 2.2 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 more than twice the silicon content, and the sum of the chromium content, the molybdenum content, and the vanadium content is composed of a steel that is 2.3 mass% or more and 3.5 mass% or less,
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,
A rolling member for a needle roller bearing, wherein the internal hardness which is an area inside the hardened layer is Hv500 or more and 600 or less.   The rolling member for a needle roller bearing 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.   The acicular shape according to claim 1 or 2, 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 roller bearings.   The needle roller bearing provided with the rolling member for needle roller bearings of any one of Claims 1-3.

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