JP2006118680A - Bearing for alternator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bearing for an alternator comprising steel with a superior hydrogen fatigue resistance characteristic. <P>SOLUTION: At least one member of an inner ring 4, an outer ring 3, and a rolling element 2 of the bearing 10 for an alternator turnably supporting a shaft 1 attached with a rotor comprises steel of a composition containing at least V as an alloy element, wherein contents of C, Si, Mn, Cr, and V in a surface and a surface layer receiving rolling contact are respectively within ranges of C:≥0.5 mass% and ≤1.2 mass%, Si:≥0.1 mass% and ≤1 mass%, Mn:≥0.1 mass% and ≤1.5 mass%, Cr:≥0.1 mass% and ≤2 mass%, and V:≥0.1 mass%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an alternator bearing and suppresses premature delamination that occurs due to the penetration of hydrogen generated on the rolling surface due to the decomposition of lubricating oil or the like due to its unique use conditions.

  A bearing used for an alternator is accelerating and decelerating under lean lubrication, so that a large slip is likely to occur on the rolling surface. Due to the influence, hydrogen is generated due to decomposition of the lubricant or the like, and early peeling may occur due to intrusion into the rolling element. Since hydrogen significantly reduces the fatigue strength of steel, cracks are easily generated and propagated from the rolling surface or inside the surface layer even under practical conditions, leading to early peeling, but many of these early peelings occur when a large slip is applied. This is considered to be caused by circumferential tensile stress acting on the rolling surface. In the future, in order to cope with downsizing and energy saving, there is no doubt that the use conditions of the alternator bearing will become increasingly severe, and therefore, it is expected that steel materials having better hydrogen fatigue resistance will be required.

For example, Japanese Patent Application Laid-Open No. 2000-282178 is a conventional technique for improving the hydrogen fatigue resistance of steel materials. By adding a large amount of Cr (chromium) to the steel material, a passive film is formed on the surface of the steel, and the penetration of hydrogen into the steel is suppressed. However, the carbide is coarsened by adding a large amount of Cr, which may become a stress concentration source and cause early peeling. Moreover, the passive film has the effect of slowing the diffusion of hydrogen, but also has the effect of promoting the adsorption of the generated hydrogen on the steel surface. If starting and stopping are frequently performed, hydrogen is dissipated at the time of stopping. Therefore, delaying the penetration of hydrogen into the steel may be effective for suppressing early peeling. However, if used continuously, the amount of hydrogen that penetrates into the steel increases as the passive film adsorbs much hydrogen, so it is difficult to suppress early peeling. Therefore, the prior art seems insufficient for such applications.
JP 2000-282178 A

  This invention solves the above problems, and it aims at providing the bearing for alternators which consists of steel materials excellent in hydrogen fatigue resistance.

  In order to solve the above problems, as a result of evaluating the influence of hydrogen on fatigue strength, which will be described later, for case hardening steel, carburized steel, and induction hardening steel (medium carbon steel) having various compositions, at least V (vanadium) ), And the contents of C (carbon), Si (silicon), Mn (manganese), Cr, and V are respectively C: 0.5% by mass or more and 1.2% by mass or less, Si: 0.1 Compositions in the range of mass% to 1 mass%, Mn: 0.1 mass% to 1.5 mass%, Cr: 0.1 mass% to 2 mass%, V: 0.1 mass% or more It has been found that the hydrogen fatigue resistance is greatly improved with the steel material.

  For this reason, the alternator bearing of the present invention is a bearing used for an alternator that converts rotational force into electrical energy by rotating a magnetic pole excited by a rotor with respect to a stator, and includes at least an inner ring, an outer ring, and a rolling element. One member contains at least V as an alloy element, and the content of C, Si, Mn, Cr, V in the surface and the surface layer that undergoes rolling contact is C: 0.5% by mass or more and 1.2, respectively. % By mass or less, Si: 0.1% by mass or more and 1% by mass or less, Mn: 0.1% by mass or more and 1.5% by mass or less, Cr: 0.1% by mass or more and 2% by mass or less, V: 0.1% It consists of a steel material having a composition in the range of mass% or more.

  V carbide strongly traps diffusible hydrogen that causes a decrease in fatigue strength, and has the effect of suppressing the accumulation of diffusible hydrogen in stress concentration sources such as non-metallic inclusions that are the starting point of delamination. Usually, since the rolling contact portion of the rolling part is required to have high hardness, it is used after being quenched and tempered at a low temperature. Even if V is added in a small amount, it is stably present as V carbide during quenching heating or carburizing, so that V carbide remains even after low temperature tempering after quenching. Mo (molybdenum) carbide and Ti (titanium) carbide have similar effects although not as much as V carbide. However, if Mo is not added in a large amount, it does not exist as Mo carbide during quenching heating or carburizing and dissolves in the matrix, so that Mo carbide does not remain in a state of low temperature tempering after quenching. Ti has a strong affinity with nitrogen and forms Ti nitride, which is one of non-metallic inclusions. Therefore, the stress concentration source that becomes the starting point of peeling increases. In addition, since V has the fault which raises material hardness, in the case of the steel materials used without annealing like medium carbon steel, if too much V is added, workability will be impaired. Therefore, it is necessary to adjust each addition amount appropriately in consideration of the addition amount of other alloy elements required.

  The reason why the lower limit of the amount of C is 0.5% by mass is that the induction hardened steel is usually medium carbon steel, but if the amount of C is less than 0.5% by mass, the hardness required for the rolling contact portion after induction hardening. This is because no longer can be obtained. On the other hand, the upper limit of the amount of C is set to 1.2% by mass in the case of all-quenched steel because undissolved carbide remaining after quenching and tempering becomes coarse and toughness decreases. In addition, C amount said here is C amount in the surface and surface layer which receive rolling contact, and in the case of carburized steel, it points out C amount of the surface layer after carburizing.

  The reason why the lower limit of the amount of Si is set to 0.1% by mass is that Si is originally contained in steel and it is difficult to reduce it to less than that, and there is no point in doing so. Si has the effect of suppressing softening due to tempering, and is indispensable for inexpensive steel materials used in high temperature applications. However, if it exceeds 1% by mass, the cold workability and the hot workability deteriorate, so this was made the upper limit.

  The reason why the lower limit of the amount of Mn is set to 0.1% by mass is that Mn combines with S inevitably contained in the steel to precipitate MnS, so that S grain boundary segregation is suppressed. Further, since Mn is originally contained in steel as well as Si, it is difficult to reduce it to less than that, and there is no meaning to do so. Mn is an effective element that improves the hardenability of the steel material. However, Mn substitutes Fe (iron) atoms in cementite to form a composite carbide and raises the material hardness. Therefore, if added too much, the workability and machinability are lowered. Therefore, the upper limit of the amount of Mn is 1.5% by mass.

  The reason why the lower limit of the amount of Cr is set to 0.1% by mass is that such an amount is included as an impurity, and removing it does not improve various mechanical properties. On the other hand, when added in a large amount, the carbides become coarse, and this may become a stress concentration source and cause early peeling. Further, the passive film (Cr oxide film) has an effect of slowing the diffusion of hydrogen, but also has an effect of promoting the adsorption of the generated hydrogen to the steel surface. Therefore, the upper limit of the Cr amount is set to 2% by mass or less.

The grounds for setting the upper and lower limits of C, Si, Mn, and Cr are as described above, but there are two things to be careful about their combination. First, since Si stabilizes ferrite even at high temperatures, the amount of C is in the range of hypoeutectoid, and when the amount of Si is large, the A ₃ point increases. Depending on the amount of Mn and Cr, quenching heating If the temperature is too low, quenching will be insufficient. The other is that Mn and Cr stabilize austenite even at low temperatures, so if the amount of C is the lower limit or the upper limit and the amount of Mn or Cr is large, if the quenching heating temperature or the carburizing temperature is too high, V carbide Is no longer stable. In addition, what is necessary is just to use the equilibrium diagram of a multicomponent system alloy for these confirmation. At present, the equilibrium diagram of a multi-component alloy can be obtained easily and accurately by calculation.

  In the alternator bearing of the present invention, at least one member of the inner ring, the outer ring and the rolling element having the above characteristics is obtained by the formula (1) based on the content (mass%) of Si, Mn, V, and Mo. 2) It is preferable that the steel material satisfies the formula.

H = 5.8 [Si] +11.5 [Mn] +56.2 [V] +15.2 [Mo] (1)
H ≦ 70 (2)

  By using a steel material containing V carbide for at least one of the inner ring, outer ring and rolling element of the alternator bearing, the lubricant is decomposed on the rolling surface when the bearing is suddenly accelerated and decelerated under lean lubrication. It is possible to prevent premature delamination caused by hydrogen generated by the intrusion into steel.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a partial cross-sectional view showing an alternator bearing according to an embodiment of the present invention. Referring to FIG. 1, in an alternator 10, a shaft 11 is inserted into an alternator bearing 1, and a pulley 5 is attached to the protruding end. The pulley 5 is provided with an engaging groove 6 on which the transmission belt is hung. Further, a rotor is attached to the shaft 11, and the rotor includes a rotor core and a rotor coil. This rotor is opposed to a stator disposed on the outer periphery of the rotor. This stator is composed of a stator core and a stator coil.

  An alternator bearing 1 that rotatably supports a shaft 11 includes a plurality of steel balls 2 that are rolling elements, and an inner ring 4 and an outer ring 3 that are in contact with the plurality of steel balls 2 on a rolling surface. A retainer 7 holds the inner ring 4 and the outer ring 3.

  This alternator 10 generates a three-phase alternating current in the stator coil by exciting the magnetic pole in the rotor core by supplying an excitation current to the rotor coil by the battery, and rotating the excited magnetic pole by the rotation of the engine. The generated alternating current is rectified by a diode and taken out as direct current.

  Reflecting the recent trend toward higher speed and smaller size, the shaft 11 is rotated at a high speed by a transmission belt, and the rolling elements 2 and the races 3 and 4 are brought into high-speed contact with each other at high speed. The alternator bearing 1 is filled with grease, which is decomposed at the high-pressure, high-speed contact portion to generate hydrogen. Hydrogen is a small element and easily penetrates into the steel material if the conditions of the hydrogen partial pressure and the surface layer part are met. For this reason, damage is caused to a predetermined portion in the steel material to which a load is applied, and a peculiar crack appearing as a white layer is formed on the fracture surface.

  In the alternator bearing according to the embodiment of the present invention, at least one member of the rolling element 2, the outer ring 3 and the inner ring 4 contains at least V as an alloy element and is subjected to rolling contact and C on the surface layer. , Si, Mn, Cr, and V, respectively, C: 05 mass% to 1.2 mass%, Si: 0.1 mass% to 1 mass%, Mn: 0.1 mass% to 1. 5% by mass or less, Cr: 0.1% by mass or more and 2% by mass or less, and V: a steel material having a composition in the range of 0.1% by mass or more.

  According to the present embodiment, at least one member of the rolling element 2, the outer ring 3 and the inner ring 4 is made of a steel material having the above requirements, thereby obtaining an alternator bearing having excellent hydrogen fatigue resistance. Can do.

  Further, at least one member of the rolling element 2, the outer ring 3 and the inner ring 4 is made of a steel material having the above-mentioned requirements, and H obtained by the expression (1) from the contents of Si, Mn, V, and Mo is (2 It is preferable that the steel material satisfies the formula.

H = 5.8 [Si] +11.5 [Mn] +56.2 [V] +15.2 [Mo] (1)
H ≦ 70 (2)
In the above-described embodiment, the bearing for rotatably supporting the shaft 11 has been described as the alternator bearing. However, the alternator bearing of the present invention is not limited to this, and any bearing may be used for the alternator.

  Examples of the present invention will be described below.

1. Axial load fatigue test A fatigue test piece having a test section diameter of 4 mm was produced from the inventive steels of A-1 to A-10 and the comparative steels of A-11 to A-20 shown in Table 1, and shown in Table 1. After quenching from the quenching heating temperature, tempering was performed at 180 ° C. As Table 1 shows the hardness after heat treatment, all had a hardness of HV700 or higher. The value of H in Table 1 is a value obtained by substituting Si, Mn, V, and Mo into the above equation (1). In the column of V carbide in Table 1, “〇” if the V carbide is stably present at the quenching heating temperature, dissolves in the matrix because the amount of V added is small, or “V” if V is not included. "showed that. The comparative steel A-11 is JIS-SUJ2, and the comparative steel A-12 is JIS-SUJ3.

  A fatigue test piece having a test part diameter of 4 mm was manufactured from the inventive steels B-1 to B-4 shown in Table 2 and the comparative steels B-5 to B-10, and the C concentration in the test part was uniform to the inside. The steel was carburized at the carburizing temperature shown in Table 2 so as to be 0.8% by mass, lowered to an appropriate quenching heating temperature, quenched, and tempered at 180 ° C. As shown in Table 2, the hardness after heat treatment was HV700 or more. The value of H in Table 2 is a value obtained by substituting Si, Mn, V, and Mo into the above equation (1). In the column of V carbide in Table 2, “◯” if the V carbide is stably present at the carburizing temperature, “V” is dissolved in the matrix due to the small amount of V added, or “X” if V is not included. showed that. The comparative steel B-5 is JIS-SCM420.

  A fatigue test piece having a test part diameter of 4 mm is manufactured from the inventive steels of C-1 to C-5 and the comparative steels of C-6 to C-12 shown in Table 3, and the test part is uniformly cured to the inside. As described above, high-frequency heating was performed aiming at the quenching heating temperature shown in Table 3, followed by quenching and tempering at 150 ° C. As shown in Table 3, the hardness after heat treatment was HV700 or more. The value of H in Table 3 is a value obtained by substituting Si, Mn, V, and Mo into the above equation (1). In the column of V carbide in Table 3, if the V carbide is stably present at the carburizing temperature, “◯”, it will dissolve in the matrix due to the small amount of V added, or “X” if V is not included. showed that. The comparative steel C-6 is JIS-S53C.

  Prior to the fatigue test, the test piece was charged with hydrogen by a cathodic electrolysis method. For hydrogen charging, a 0.05 mol / liter dilute sulfuric acid aqueous solution to which 1.4 g / liter thiourea was added was used. The diffusion rate of hydrogen varies depending on the steel type, and the surface hydrogen concentration varies with the same current density if the steel type is different. After obtaining them in advance, the current density and the charging time were adjusted so that the amount of diffusible hydrogen was uniformly 3 mass-ppm up to the inside of the test section. The amount of diffusible hydrogen referred to here is the fraction of the mass of hydrogen released from room temperature to 350 ° C. with respect to the sample mass when the temperature is raised at 180 ° C./h.

After the test piece was charged with hydrogen, a fatigue test was immediately conducted at room temperature in the atmosphere. The stress ratio in the test is R = −1 and the load frequency is 20 kHz. Even if the number of loadings reached 10 ⁸ times, the test was terminated if it was not broken. In addition, the diffusible hydrogen introduced into the test piece diffuses in the steel even at room temperature and dissipates over time. However, the tests conducted this time are high-speed loads, and the number of loads reaches 10 ⁸ in an extremely short time, so there is no room for diffusible hydrogen to dissipate. Therefore, the influence of diffusible hydrogen on fatigue strength can be rationally evaluated.

Table 4 shows the 10 ⁷ times strength obtained from the regression curve of the SN diagram of all hardened steel. The invention steel in which V carbide exists stably at the quenching heating temperature was 10 ⁷ times stronger than the comparative steel. Tables 5 and 6 show the 10 ⁷ times strength obtained from the regression curves of the SN diagrams of carburized and induction hardened steel, respectively. In these cases, as in the case of the case-hardened steel, the inventive steel in which V carbide is stably present at the quenching heating temperature is 10 ⁷ times stronger than the comparative steel.

The practical maximum contact surface pressure of rolling parts is about 4 GPa at the maximum, and the circumferential tensile stress that repeatedly acts on the rolling surface when the maximum surface pressure of 4 GPa is applied is calculated even when rolling friction is taken into account. It is about 700 MPa. Moreover, in this fatigue test, the effect of forcibly introducing 3 mass-ppm diffusible hydrogen was observed, but in reality, it is considered rare that a large amount of hydrogen penetrates. That is, it is considered that if the strength at 10 ⁷ times is 700 MPa or more, it can sufficiently withstand practical use. Looking at 10 ⁷ times the strength of the invention steel in Table 1 to Table 3 In this respect, any of the invention steels 10 ⁷ times the strength is at least 700 MPa. On the other hand, the 10 ⁷ times strengths of the comparative steels are all less than 700 MPa. Therefore, it can be said that it is a necessary condition for maintaining good hydrogen fatigue strength that the alloy element contains at least V and the V carbide is stably present at the quenching heating temperature or the carburizing temperature.

2. Workability confirmation test As described above, the addition of V is indispensable for improving the hydrogen fatigue resistance. However, if too much V is added, workability is impaired. Therefore, in order to confirm the workability, the inventive steel of Table 1 and the comparative steel were subjected to spheroidizing annealing under the same conditions, and then a test piece having a thickness of 10 mm was manufactured. Then, a hole with a diameter of 2 mm was drilled under certain conditions, and the number of holes that were drilled before the drill was broken was examined. FIG. 2 shows the relationship between the value of H in Table 1 and the number of vacant holes.

  Referring to FIG. 2, when the value of H is about 70 or less, the life of the drill gradually decreases, and when it exceeds that, the life rapidly decreases. As can be seen from the above equation (1), the amount of V added has the largest contribution to the increase in the value of H. Therefore, in order to keep a good balance between the hydrogen fatigue resistance and workability, the value of H can be increased by adjusting V and adding amounts of Si, Mn, and Mo appropriately. It is desirable to be 70 or less.

  The contents of C, Si, Mn, Cr, and V in the surface and surface layer that receive rolling contact from the above are C: 0.5% by mass to 1.2% by mass, Si: 0.1% by mass to 1%, respectively. It may be a steel material having a composition in the range of mass% or less, Mn: 0.1 mass% or more and 1.5 mass% or less, Cr: 0.1 mass% or more and 2 mass% or less, V: 0.1 mass% or more. For example, the desired hydrogen peeling resistance can be obtained. Moreover, it is preferable that content of V is 2.0 mass% or less.

  The embodiment disclosed this time should be considered as illustrative in all points and not 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 present invention can be applied to a bearing for an alternator that can suppress premature peeling that occurs due to intrusion of hydrogen generated on a rolling surface due to decomposition of lubricating oil or the like due to its unique use conditions.

It is a fragmentary sectional view which shows the bearing for alternators in one embodiment of this invention. It is a figure which shows the relationship between the value of H of Table 1, and the number of vacant holes.

Explanation of symbols

  1 bearing for alternator, 2 rolling element (steel ball), 3 outer ring, 4 inner ring, 5 pulley, 6 engagement groove, 7 cage, 10 alternator, 11 shaft.

Claims (2)

A bearing used in an alternator that converts a rotational force into electric energy by rotating a magnetic pole excited by a rotor with respect to a stator,
At least one member of the inner ring, the outer ring, and the rolling element contains at least V as an alloy element, and the contents of C, Si, Mn, Cr, and V in the surface and the surface layer that undergo rolling contact are C: 0 0.5 mass% to 1.2 mass%, Si: 0.1 mass% to 1 mass%, Mn: 0.1 mass% to 1.5 mass%, Cr: 0.1 mass% to 2 mass %, V: A steel material having a composition in the range of 0.1% by mass or more. An alternator bearing. The at least one member of the inner ring, the outer ring, and the rolling element is a steel material satisfying the formula (2) where H obtained by the formula (1) from the contents of Si, Mn, V, and Mo is characterized in that The alternator bearing according to claim 1.
H = 5.8 [Si] +11.5 [Mn] +56.2 [V] +15.2 [Mo] (1)
H ≦ 70 (2)

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