JP2005290496A - Rolling parts and rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide rolling parts and rolling bearing composed of steel having excellent hydrogen fatigue resistance characteristics. <P>SOLUTION: The rolling parts and rolling bearing are composed of steel containing 0.5 to 1.2wt% C, 0.1 to 1wt% Si, 0.1 to 1.5wt% Mn, and 0.1 to 2wt% Cr, and is dispersed with ≥0.1wt% fine V carbide. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to rolling parts and rolling bearings, and more specifically to applications that require durability under severe conditions such as high load, lean lubrication, rolling with sliding, lubrication with foreign matter, and lubrication with water. It relates to suitable rolling parts and rolling bearings.

  When rolling parts such as rolling bearings are used under severe conditions such as high load, lean lubrication, rolling slip, foreign matter lubrication, and water lubrication, the lubricant decomposes and generates hydrogen. When the steel penetrates into the steel, early peeling is likely to occur. Since hydrogen significantly reduces the fatigue strength of steel, cracks are easily generated from the rolling surface or inside the surface layer under practical conditions, and propagate to reach early peeling. However, it is considered that most of the early peeling occurs due to overlapping of circumferential tensile stress that repeatedly acts on the rolling surface. In the future, in order to cope with the downsizing and energy saving of automobiles and the like, the usage conditions of rolling parts tend to become more severe, and steel materials with excellent hydrogen fatigue resistance are required.

In order to improve the hydrogen fatigue resistance characteristics of steel materials, a technology for suppressing the penetration of hydrogen into steel by increasing the Cr content and facilitating the formation of a passive film on the steel surface has been disclosed (patent) Reference 1).
JP 2000-282178 A

  However, when the Cr content is increased, the carbide is coarsened, which may become a stress concentration part and cause early peeling. In addition, the passive film has the effect of delaying the diffusion of hydrogen, but also has the effect of promoting the adsorption of the generated hydrogen on the steel surface. If rolling parts are used at intervals, hydrogen is dissipated at the time of stopping. Therefore, delaying the penetration of hydrogen into the steel is effective in preventing early peeling. However, if it is incorporated in the apparatus and used continuously, the amount of hydrogen that penetrates into the steel increases as the passive film adsorbs a lot of hydrogen, so that early delamination occurs. In the future, it is expected that the number of rolling parts that are continuously operated unattended will increase, and the above technique is insufficient for such applications.

  This invention solves the above problems, and it aims at providing the rolling components and rolling bearing which consist of steel materials excellent in hydrogen fatigue resistance.

  The rolling component of the present invention includes C: 0.5-1.2 wt%, Si: 0.1-1 wt%, Mn: 0.1-1.5 wt%, Cr: 0.1-2 wt%, And it is comprised from the steel which 0.1 wt% or more of fine V carbide disperses.

  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. The action of trapping the diffusible hydrogen has the fine V carbide remaining in an insoluble state at the quenching temperature.

  Since the rolling contact portion of the rolling component is usually required to have high hardness, it is used after being tempered at a low temperature. The fine V carbide exists stably as V carbide during quenching heating or carburizing. The fine V carbide remains stable even after quenching and low temperature tempering.

  In addition, although V couple | bonds with carbon and produces | generates V carbide | carbonized_material, it is easy to couple | bond with nitrogen. In steel, N is contained in an amount of about 0.025 wt% or less, so fine V carbide may contain nitrogen. However, since the carbon concentration is very high, it will be called V carbide.

  Mo carbide and Ti carbide have similar effects, though not as much as V carbide. However, if Mo is not contained in a high concentration, it does not exist as Mo carbide during quenching heating or carburizing and dissolves in the base metal, 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 raises material hardness, in the case of the steel materials used without annealing like medium carbon steel, workability will be impaired when V content rate is too high. For this reason, it is necessary to adjust each content rate appropriately in consideration of the required content rate of other alloy elements.

C: 0.5-1.2 wt%
The reason why the lower limit of C is set to 0.5 wt% is that the induction-hardened steel is usually medium carbon steel, but if C is less than 0.5 wt%, the hardness required for the rolling contact portion cannot be obtained after induction hardening. Because. On the other hand, the upper limit of C is set to 1.2 wt% because, in the case of tempered steel, undissolved carbide remaining after quenching and tempering becomes coarse and toughness decreases. The C concentration, that is, the carbon content here is C in the rolling contact portion, and in the case of carburized steel, it indicates the carbon content of the surface layer after carburizing.

Si: 0.1 to 1 wt%
The reason why the lower limit of Si is 0.1 wt% is that Si is originally added for deoxidation in refining, and it is difficult to reduce it to 0.1 wt% or less, and there is no point in doing so. Because. 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 wt%, the cold workability and hot workability deteriorate, so this is the upper limit.

Mn: 0.1 to 1.5 wt%
The reason why the lower limit of Mn is set to 0.1 wt% is that Mn combines with S inevitably contained in the steel to precipitate MnS, thereby suppressing grain boundary segregation of S and embrittlement caused thereby. is there. Moreover, since Mn is added to steel for deoxidation treatment in refining as well as Si, it is difficult to reduce it to 0.1 wt% or less, and there is no point in doing so. . Mn is an effective element that improves the hardenability of the steel material. However, if the content of Mn is too high, the material hardness is excessively increased and the workability and machinability are lowered. Therefore, the upper limit of Mn is 1.5 wt%.

Cr:
The reason why the lower limit of Cr is set to 0.1 wt% is that such an amount is contained as an impurity, and various mechanical properties are not improved by making it lower than that. On the other hand, if the content is too high, 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 Cr is 2 wt%.

  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 A3 point increases when the C content is within the eutectoid composition range and the Si content is high. For this reason, depending on the content of Mn and Cr, if the quenching heating temperature is too low, the austenite is not completely formed, so that the hardenability is insufficient. The other is that Mn and Cr stabilize austenite even at low temperatures, so if the quenching heating temperature or carburizing temperature is too high at the lower limit or upper limit of C and the content of Mn or Cr is high, V It is that the carbide does not exist stably. In addition, what is necessary is just to use the equilibrium diagram of a multicomponent system alloy for these confirmation. At present, the equilibrium phase of a multi-component alloy can be easily and accurately obtained by calculation.

  By making rolling parts with steel material containing fine V carbide, it is used under severe conditions such as high load, dilute lubrication, rolling slip condition, foreign matter lubrication, water lubrication, and the lubricant decomposes to hydrogen Even if this occurs, it is possible to prevent premature peeling caused by the penetration into steel.

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

  1-3 is a figure which shows the bearing in which the rolling components in embodiment of this invention are used. FIG. 1 shows a deep groove ball bearing, and a rolling element ball 5 housed in a cage 6 is arranged between an inner ring 3 and an outer ring 4 provided with grooves. The rolling component of the present invention is used for at least one of the inner ring 3, the outer ring 4 and the ball 5. The deep groove ball bearing may be an angular ball bearing including the inner ring, the outer ring, and a ball, and having a groove shape different from that of the deep groove ball bearing. Both the deep groove ball bearing and the angular ball bearing are rolling bearings having at least one rolling component of the present invention.

  FIG. 2 is a view showing a cylindrical roller bearing (rolling bearing) according to another embodiment of the present invention. This cylindrical roller bearing is the same as the configuration shown in FIG. 1 except that the rolling element 5 has a cylindrical shape and is different from the rolling bearing shown in FIG.

  FIG. 3 is a view showing a tapered roller bearing (rolling bearing) according to still another embodiment of the present invention. The tapered roller bearing shown in FIG. 3 is a high-inclined tapered roller bearing with a large cone inclination. As long as it is a rolling bearing and includes an inner ring 3, an outer ring 4, and a rolling element 5, and at least one of them is a rolling part of the present invention, the embodiment of the present invention is performed regardless of the magnitude of the inclination angle. Corresponds to the form.

  The rolling component is a rolling component made of a steel material that is used after being quenched or tempered, including carburizing and induction quenching. Rolling parts suitable for applications that require durability under severe conditions such as high loads, dilute lubrication, slipping conditions, foreign matter-mixed lubrication, and water-mixed lubrication, and the rolling parts as inner rings, outer rings, and rolling elements It is the bearing used for at least one of these. For example, it is a deep groove ball bearing, a cylindrical roller bearing, a tapered roller bearing or the like of a rolling bearing.

  The rolling component includes C: 0.5 to 1.2 wt%, Si: 0.1 to 1 wt%, Mn: 0.1 to 1.5 wt%, Cr: 0.1 to 2 wt%, and By comprising steel in which fine V carbide of 0.1 wt% or more is dispersed, hydrogen fatigue resistance is greatly improved. The above steel is quenched from a temperature range of 800 to 1000 ° C., and the fine V carbide can be a precipitate remaining at the quenching heating temperature.

  Furthermore, the steel forming the rolling part can satisfy the following expressions (1) and (2).

H = 5.8 [Si] + 11.5 [Mn] + 56.2 [V] + 15.2 [Mo] .......... (1)
H ≦ 70 ...................................... (2)
By satisfying the above formulas (1) and (2), it is possible to prevent deterioration of machinability. In addition, although Mo is contained in the said (1) Formula, Mo does not need to be contained in steel.

1. Axial Load Fatigue Test Fatigue test pieces having a test part diameter of 4 mm were manufactured from the steel materials of Invention Examples A-1 to A-10 and Comparative Examples A-11 to A-20 shown in Table 1. After quenching from the quenching heating temperature shown in Table 1, tempering was performed at 180 ° C. As shown in Table 1, the hardness after the heat treatment was HV700 or more.

  The value of H in Table 1 is a value obtained by substituting Si, Mn, V, and Mo into the equation (1). The amount of V carbide in Table 1 is a calculated value of the amount of V carbide that can exist stably when in an equilibrium state at the quenching heating temperature. Among the comparative examples, steels that do not contain V do not have V carbides, and are therefore indicated as “−”. Comparative examples A-11 and A-12 are JIS SUJ2 and JIS SUJ3, respectively.

  From the steel materials of Invention Examples B-1 to B-4 and Comparative Examples B-5 to B-10 shown in Table 2, fatigue test pieces having a test part diameter of 4 mm were manufactured. Carburization was carried out at an appropriate carburizing temperature so that the carbon concentration in the test part was uniformly 0.8 wt% to the inside, and the quenching was performed after being lowered to the quenching heating temperature shown in Table 2, followed by tempering at 180 ° C. . As shown in Table 2, the hardness after the heat treatment was HV700 or more. The value of H in the table is a value obtained by substituting Si, Mn, V, and Mo into the equation (1). The amount of V carbide in the table is a calculated value of the amount of V carbide that can exist stably when in equilibrium at the quenching heating temperature. The steel material with less than 0.01 wt% was marked with “<0.01”. Among the comparative examples, steels that do not contain V do not have V carbides, and are therefore indicated as “−”. In addition, Comparative Example B-5 is JIS SCM420.

  A fatigue test piece having a test part diameter of 4 mm was manufactured from each steel material of Invention Example C-1 and Comparative Examples C-2 to C-12 shown in Table 3. Then, high-frequency heating was performed aiming at the quenching heating temperature shown in Table 3 so that the test portion was uniformly cured to the inside, followed by quenching and tempering at 150 ° C. As shown in Table 3, the hardness after the heat treatment was HV700 or more. The value of H in the table is a value obtained by substituting Si, Mn, V, and Mo into the equation (1). The amount of V carbide in the table is a calculated value of the amount of V carbide that can exist stably when in an equilibrium state at a high-frequency heating temperature. The steel material with less than 0.01 wt% was marked with “<0.01”. Among the comparative examples, steels that do not contain V do not have V carbides, and are therefore indicated as “−”. Comparative example C-2 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 / l dilute sulfuric acid aqueous solution containing 1.4 g / l thiourea was used. The diffusion rate of hydrogen differs depending on the steel type of the steel material, and the hydrogen concentration on the surface varies with the same current density if the steel type is different. After obtaining them in advance, the current density and charging time were adjusted so that the amount of diffusible hydrogen was uniformly 3 wtppm up to the inside of the test section. Here, the diffusible hydrogen amount is a fraction of the weight of hydrogen released from the sample when the temperature is raised from room temperature to 350 ° C. at 180 ° C./h with respect to the sample weight.

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 aborted if there was no breakage. In addition, the diffusible hydrogen introduced into the test piece diffuses in the steel even at room temperature and dissipates over time. However, in this test, a high-speed load is used, 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.

The SN test curve was obtained by applying the fatigue test result of the sub-hardened steel to the continuous descent type semi-logarithmic curve model of JSMS-SD-6-02, a Japanese material academia standard, and then 10% fatigue strength at 10 ⁷ times was obtained. Table 4 shows the values. In the example of the present invention in which V carbide is present to some extent at the quenching heating temperature, the 10% fatigue strength at 10 ⁷ times was higher than that of the comparative example.

Tables 5 and 6 show the 10% fatigue strength of 10 ⁷ times of carburized quenched steel and induction-hardened steel obtained in the same manner as the above-mentioned hardened steel. In these cases, as in the case of the case-hardened steel, the invention steel in which V carbide is present to some extent at the quenching heating temperature has a higher 10% fatigue strength at 10 ⁷ times than the comparative example.

The practical maximum contact surface pressure of rolling parts is about 4 GPa at the highest, 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 considering the rolling friction. The upper limit is about 700 MPa. In this fatigue test, 3 wtppm of diffusible hydrogen was forcibly introduced and the effect was observed. However, in reality, it is considered rare that high concentration of hydrogen penetrates. That is, if the 10% fatigue strength at 10 ⁷ times is 700 MPa or more, it is considered that the 10% fatigue strength can sufficiently withstand practical use. From this point of view, Tables 1 to 3 show that all of the examples of the present invention contain 0.1 wt% or more of V carbides and have 10% fatigue strength of 700 MPa or more regardless of whether they are full quenching, carburizing quenching or induction quenching. doing.

On the other hand, the 10% fatigue strength at 10 ⁷ times in the comparative example is less than 700 MPa. Accordingly, it can be said that a stable presence of 0.1 wt% or more V carbide at the quenching heating temperature at least V as an alloy element is a necessary condition for maintaining good hydrogen fatigue strength.
2. Workability Test As described above, V is essential for improving hydrogen fatigue resistance. However, if the V content is too high, workability is impaired. Therefore, in order to confirm the workability, the inventive example of Table 1 and the comparative example were subjected to spheroidizing annealing under the same conditions, and then a test piece having a thickness of 10 mm was manufactured. A hole with a diameter of 2 mm was drilled under a certain condition, and the number of holes that could be drilled before the drill broke was examined.

  FIG. 4 shows the relationship between the value of H in Table 1 and the number of holes opened. According to FIG. 4, 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 equation (1), the V content has the largest contribution to the value of H. Therefore, in order to maintain a good balance between the hydrogen fatigue resistance and workability, the value of H is not adjusted by increasing the V content and appropriately adjusting the Si, Mn, and Mo content. Is desirably 70 or less.

  While the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these embodiments of the present invention. . The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  By using the rolling component of the present invention, fine V carbide is stably distributed in the steel and traps hydrogen that has entered the steel, so that early peeling due to repetitive load caused by hydrogen can be suppressed. Furthermore, the machinability can be prevented from being deteriorated by adjusting the composition of V or the like. For this reason, it is expected to be widely used in applications that require durability under severe conditions such as high load, dilute lubrication, rolling with slipping, foreign matter contamination lubrication, and water contamination lubrication.

It is a figure which shows the deep groove ball bearing in embodiment of this invention. It is a figure which shows the cylindrical roller bearing in another embodiment of this invention. It is a figure which shows the tapered roller bearing in another embodiment of this invention. It is a figure which shows the relationship between H in the Example of this invention, and the number of holes drilled.

Explanation of symbols

  3 inner ring, 4 outer ring, 5 rolling elements (ball, cylinder, cone), 6 cage.

Claims (4)

  C: 0.5 to 1.2 wt%, Si: 0.1 to 1 wt%, Mn: 0.1 to 1.5 wt%, Cr: 0.1 to 2 wt%, and 0.1 wt% or more Rolling parts composed of steel in which various V carbides are dispersed.   The rolling part according to claim 1, wherein the rolling part is quenched from a temperature range of 800 to 1000 ° C., and the fine V carbide is a precipitate remaining in a temperature range of 800 to 1000 ° C. 2. The rolling component according to claim 1 or 2, wherein the steel satisfies the following expressions (1) and (2).
H = 5.8 [Si] + 11.5 [Mn] + 56.2 [V] + 15.2 [Mo] .......... (1)
H ≦ 70 ...................................... (2)   A rolling bearing in which the rolling component according to claim 1 is used for at least one of an inner ring, an outer ring, and a rolling element.

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