The name of the invention: bearing parts
Technical field
[0001]
　The present invention, needle-shaped bearing (needle bearing), to a bearing component, such as a roller bearing.
　The present application, to January 10, 2014, in Japanese Patent Application No. 2014-3338, filed and April 16, 2014 in Japan, and claims the benefit of priority based on the Japanese Patent Application No. 2014-84952 filed in Japan, these which is incorporated by reference of content here.
Background technique
[0002]
　Needle bearings, roller bearings, bearing parts, such as ball bearings, a state in which foreign substances such as lubricating oil to burrs or wear debris is mixed, i.e. continue to be used even under a contaminated environment. Therefore, in a contaminated environment, improvement of the rolling contact fatigue life of the bearing parts is important. In a contaminated environment, in order to improve the rolling fatigue life of the bearing components, to increase the residual austenite it is known to be effective. Therefore, the bearing parts steel material, has been carried out the surface treatment such as carburizing or nitriding treatment.
[0003]
　However, surface treatment such as carburizing or nitriding treatment of steel for bearing parts, the cost is not as high, the influence of variations in the process atmosphere, there is a problem that variation in quality occurs. Therefore, for example, Patent Document 1, omitting the carburizing and nitriding treatment, the hardening and tempering treatment, the steel material for bearings is rich residual austenite is disclosed. Bearing component disclosed in Patent Document 1, in the steel, C, Mn, was added Ni or Mo, to lower the martensitic transformation starting temperature (Ms point), to secure the amount of residual austenite there. However, in order to ensure the amount of residual austenite, increasing the added amount of the Mn steel, hardenability of the steel material for bearing components is increased. As a result, at the time of cooling after hot rolling, supercooled structures such as martensite is produced, workability and ductility of the bearing components, the toughness decreases.
[0004]
　Further, Patent Document 2, by using a spherical cementite, suppresses the coarsening of the crystal grain size, a method of generating residual austenite is disclosed. However, in the method disclosed in Patent Document 2, it is subjected to a high-temperature and for a long time of spheroidizing heat treatment. As a result, C is dissolved in the austenite phase, the number density of the spherical cementite had become insufficient. Further, the average particle size of prior austenite is coarsened, improvement of sufficient rolling contact fatigue life can not be obtained.
[0005]
　For longer treatment time of spheroidizing annealing, the processing number is increased, the production cost Kasami, production efficiency is known to deteriorate. For this problem, for example, Patent Document 3, was invented by some of the present inventors, without performing spheroidizing heat treatment, which can be wire drawing, bearing components for high carbon steel rolled wire rod is disclosed It is.
CITATION
Patent literature
[0006]
Patent Document 1: Japanese Unexamined Patent Publication No. 2004-124215
Patent Document 2: Japanese Unexamined Patent Publication No. 2007-077432
Patent Document 3: International Publication No. WO2013-108828
Summary of the invention
Problems that the Invention is to Solve
[0007]
　However, as in Patent Document 1, increasing the addition amount of Mn in the steel, for the reasons described above, it was found that it is difficult to process the steel for bearing parts are omitted spheroidizing heat treatment. Moreover, by utilizing the material of Patent Document 3, in order to produce bearing parts excellent in rolling fatigue life under a contaminated environment includes a wire drawing, tissue control by the quenching at a controlled quenching temperature It was found to be necessary.
[0008]
　The present invention has been made in view of such circumstances, in order to ensure good drawability, to suppress the content of Mn, without performing spheroidizing thermal treatment, under a contaminated environment and to provide a superior bearing components in rolling contact fatigue life.
Means for Solving the Problems
[0009]
　The present inventors have found that by refining the average grain size of prior austenite below 8.0 .mu.m, in% by volume the amount of residual austenite found that can be controlled to 15% to 25%. Furthermore, 2000 pieces / mm, the number density of 3.0μm or less voids than 0.02μm particles having a circle equivalent diameter 2 by less, even under a contaminated environment, to improve the rolling contact fatigue life of bearing parts found that it is possible.
[0010]
　The present invention may be summarized as follows.
[0011]
(1) bearing part according to an embodiment of the present invention, the chemical components, by mass%, C: 0.95% ~ 1.10 %, Si: 0.10% ~ 0.70%, Mn: 0 .20% ~ 1.20%, Cr: 0.90% ~ 1.60%, Al: 0.010% ~ 0.100%, N: containing 0.003% ~ 0.030%, P: 0.025% or less, S: 0.025% or less, O: limit 0.0010% to, optionally, Mo: 0.25% or less, Bs: 0.0050% or less, Cu: 1.0% following, Ni: 3.0% or less, Ca: containing 0.0015% or less, the balance being Fe and impurities, metal structure, residual austenite, is a spherical cementite and martensite, the amount of the residual austenite , in volume percent, 15% to 25%, and the average particle size of prior austenite is not more than 8.0 .mu.m, in the metal structure, the number of 3.0μm or less voids than 0.02μm particles having a circle equivalent diameter density There 2,000 / mm 2 or less.
(2) In the bearing component according to the above (1), wherein the chemical composition is, in wt%, Mo: 0.01% ~ 0.25 %, B: 0.0001% ~ 0.0050%, Cu: 0 .1% ~ 1.0%, Ni: 1.0% ~ 3.0%, Ca: may contain one or more 0.0001% - 0.0015%.
(3) The bearing component according to the above (1) or (2) is a Vickers hardness of 750 Hv or more, the iron powder particle size having a hardness of 750 Hv ~ 800 Hv is 100 .mu.m ~ 180 .mu.m, lubricating oil 1L 1g contaminating rolling contact fatigue life under a contaminated environment is an environment to a 10 × 5.0 6 may be greater than or equal to.
Effect of the invention
[0012]
　According to this aspect of the present invention, the amount of the average particle size and residual austenite of prior austenite, by controlling the number density of voids of a predetermined size, even under a contaminated environment, excellent rolling fatigue it can be obtained a bearing component having a lifetime. Then, in automobiles and industrial machinery by applying the bearing component of the above aspect, it is possible to achieve a long life of the machine.
Brief description of the drawings
[0013]
Is a diagram illustrating the FIG. 1 bearing part of the metal structure.
2 is a diagram showing the relationship between the average particle diameter and the amount of retained austenite of the prior austenite.
3 is a diagram showing the relationship between the rolling contact fatigue life of an amount and contaminated environments of residual austenite.
Is a diagram showing the relationship between the rolling contact fatigue properties at number density and contaminated environment in [4] yen equivalent diameter 3.0μm or less voids than 0.02μm in.
DESCRIPTION OF THE INVENTION
[0014]
　To improve the rolling fatigue life under a contaminated environment, the decrease in the number density of voids and increased a predetermined magnitude of an amount of residual austenite is effective. The present inventors have found that the amount of the appropriate residual austenite, and, considering the production conditions to control the amount of residual austenite, the following findings were obtained. The amount of residual austenite (vol%) can be determined from the ratio of the diffraction intensity of the diffraction intensity and residual austenite gamma (220) martensite alpha (211) by for example X-ray diffraction. The amount of retained austenite, for example, can be determined using RINT2500 manufactured by Rigaku Corporation.
[0015]
　With the increase in the amount of retained austenite, even under a contaminated environment is improved rolling contact fatigue life. The amount of stably in order to obtain this effect, the necessary retained austenite, by volume%, is 15% or more. On the other hand, the amount of retained austenite, by volume% and more than 25%, for example, reduced and hardness less than 750Hv in Vickers hardness, the strength of the bearing components is reduced. In addition, increased aging of the dimension (aging) is, lead to a reduced function as a bearing parts. Therefore, in order to improve the rolling fatigue life under a contaminated environment, the amount of residual austenite, by volume%, it is necessary to control 15% to 25%.
[0016]
　During quenching, in order to increase the amount of residual austenite, it is necessary to stabilize the austenite phase. In addition, the low temperature of martensitic transformation temperature (Ms point) is valid. Ms point, C austenite phase, Si, influenced by the amount of solid solution elements such as Mn, are greatly affected by the amount of C that is particularly solid solution austenitic phase. However, in order to increase the amount of C being dissolved, increasing the heating temperature of quenching, the average particle size of the prior austenite becomes coarse. In addition, the amount of C that are dissolved in the martensite after quenching process is increased. For this reason, the rolling contact fatigue life and toughness of the bearing parts is reduced.
[0017]
　Accordingly, the present inventors have focused on the stabilization of austenite phase in crystal grains due to miniaturization. As a result of investigations, steel for bearing parts of the pearlite structure (the pearlite steel) wire drawing, machining strain and introduced, by optimizing the heating temperature of quenching, the average grain size of prior austenite it was found that it is possible to miniaturization. Then, the amount of retained austenite in volume%, was controlled at 15% to 25%, the average particle size of the prior austenite of a bearing component, to obtain a finding that is not more than 8.0 .mu.m.
　It should be noted that the average particle size of the prior austenite is obtained by the following method. First, in the longitudinal center of the bearing parts, by polishing and corrosion perpendicular C section in the longitudinal direction, thereby revealing the prior austenite grain boundaries. Next, the central portion of the range of radius 3mm from the center of C cross-section, to shoot the center at 400 times the field of view using an optical microscope. Then, measured in accordance with the provisions have been counting method from the captured image to JIS G 0551. Incidentally, as measured per sample by four field, the average value of the prior austenite grain size of the obtained 4-field, and the average particle size of prior austenite.
[0018]
　In order to refine the average grain size of prior austenite, it is preferable to control the heating temperature of the whole cross sectional reduction ratio and quenching treatment during wire drawing. The area ratio of the pro-eutectoid cementite in pearlite steel which suppresses the 5% or less, subjected to wire drawing of 50% or more total reduction of area by performing quenching to cool by heating the following further 820 ° C. or higher 890 ° C., the average particle size of prior austenite can be suppressed below 8.0 .mu.m, and, in% by volume the amount of residual austenite can be controlled to 15% to 25%.
[0019]
　The total reduction of area at wire drawing is less than 50%, by heating at the time of quenching, the average particle size of prior austenite are coarsened, it may exceed 8.0 .mu.m. Further, the heating temperature is lower than 820 ° C. of quenching, even if the average particle size refinement of the prior austenite, by solid solution the amount of C is reduced, the amount of retained austenite in volume percent, less than 15% when there is. On the other hand, the heating temperature of quenching is more than 890 ° C., cementite is decomposed, solid solution C is promoted. As a result, becomes insufficient suppression of grain growth average particle size of prior austenite is more than 8.0 .mu.m. Further, due to the increase of solid-solute C content, the amount of retained austenite in volume%, in some cases greater than 25%.
[0020]
　Figure 2 shows the relationship between the amount of average particle size and residual austenite of the old austenite, FIG. 3 shows the relationship between the rolling contact fatigue life of an amount and contaminated environments of residual austenite.
　As shown in FIG. 2, the average particle size of the prior austenite is not more than 8.0 .mu.m, the amount of retained austenite in volume percent, of 15% or more. On the other hand, if the average particle size of prior austenite is more than 8.0 .mu.m, the amount of retained austenite is vol%, it has dropped to below 15%. Further, as shown in FIG. 3, the amount of retained austenite by volume%, at a more than 15%, the rolling fatigue life under a contaminated environment is good. However, the amount of retained austenite in volume percent, is less than 15%, the rolling fatigue life under a contaminated environment has decreased.
[0021]
　Next, we propose a method that can reduce the number density of voids. In the metal structure of the bearing component according to the present embodiment, the size of voids in the circle equivalent diameter is 3.0μm or less than 0.02 .mu.m. If the size of the void is less than 0.02μm in circle equivalent diameter, in 2000 times the observation using SEM, unobservable. Further, the size of the voids is greater than 3.0 .mu.m, during processing, the starting point of cracks, can not produce a bearing component according to the present embodiment. Therefore, the size of voids in the circle equivalent diameter is not less than 0.02 .mu.m 3.0 .mu.m or less.
　Voids, usually by wire drawing after spheroidizing heat treatment is produced at the boundary between the ferrite spherical cementite and mother ground weave. And, Boyd is also remaining in the bearing parts after quenching and tempering treatment. In addition, voids, to impair the rolling contact fatigue life and impact properties of the bearing components under a contaminated environment. Results of study of the present inventors, contamination in order to improve the rolling fatigue life under environment, the number density of voids of a predetermined size in the metal structure 2000 / mm 2 important to below it was found is. More preferably 1500 / mm 2 or less.
[0022]
　Accordingly, the present inventors focused on the void generation mechanism, intensive studies suppression of occurrence of voids. As a result, steel and subjected to spheroidizing heat treatment, for pearlitic steel area ratio of pro-eutectoid cementite exceeds 5% when subjected to wire drawing, it was found that coarse voids are generated in large quantities. On the other hand, the pearlitic Holdings in wire drawing, by a pearlitic that suppresses the area ratio of the pro-eutectoid cementite to 5% or less, generation of voids during wire drawing is suppressed, and generation in the bearing part the number density of voids, 2000 / Mm 2 has been found that can be suppressed to below.
　Accordingly, the suppressed material the area ratio of the pro-eutectoid cementite to 5% or less pearlitic steel, was subjected to wire drawing to the material, by a quenching treatment, the average particle size of prior austenite in the bearing part 8. 0μm can be suppressed to below.
　It is to be noted that the number density of a predetermined size of the void is determined in the following manner. In the longitudinal direction around the bearing component is cut in a section parallel to the longitudinal direction. The cut L section was mirror-polished, by a scanning electron microscope (SEM), the central portion of the L cross-section was observed at 2000-fold, taking 10 fields week. Then, by measuring the predetermined size of the number of voids in each field, by dividing the number in field area, number density of voids is determined. Note that the central portion of the L cross-section, and 6mm width region of the center line in the longitudinal direction of the L cross-section, the observation field of view, 0.02 mm 2 is.
[0023]
　Figure 4 shows the relationship between the predetermined size of the void number density and the contamination rolling fatigue life under environmental. Figure 4, as shown in, the number density of 3.0μm or less of the void more than 0.02μm with a circle equivalent diameter size is 2,000 / Mm 2 If it is below, the rolling fatigue life under a contaminated environment is good it is. However, the number density of voids 2000 / Mm 2 by weight, the rolling contact fatigue life under a contaminated environment is reduced.
　Here, the contaminated environment, for example, have a hardness of 750 Hv ~ 800 Hv, the iron powder having a particle size of 100 .mu.m ~ 180 .mu.m, is environmentally obtained by 1g mixed for lubricant 1 L, rolling under foreign object environment dynamic fatigue life may be tested using a radial-type fatigue testing machine.
　In addition, the rolling fatigue life under the contaminated environment is, 5.0 × 10 6 preferably more than once. Rolling fatigue life under contaminated environments, 5.0 × 10 . 6 is less than once, it is sometimes impossible to achieve a long life of the machine.
[0024]
　Next, a description will be given metallographic structure of a bearing component according to the present embodiment. Metal structure of a bearing component according to the present embodiment, the residual austenite, spherical cementite and martensite. Figure 1 shows an SEM photograph of the metallic structure of the bearing component according to the present embodiment. SEM photograph of FIG. 1, the martensitic 1, together with the spherical cementite 2 precipitates, which is the organization to which the voids 3 was produced. Retained austenite, it can not be observed with SEM, using X-ray diffraction method (XRD), determined by the ratio of the diffraction intensity of martensite.
[0025]
　Hereinafter, the chemical composition of the basic elements of a bearing component according to the present embodiment will be described numerical limitation range and its limiting reasons. Here,% described is the mass%.
[0026]
　C: 0.95% ~
　1.10% C (carbon) is an element to enhance the strength. The C content is less than 0.95%, it is impossible to improve the strength and rolling fatigue life of the bearing parts. On the other hand, when the C content exceeds 1.10% carbides are coarsened, and the amount of residual austenite becomes excessive, not only the hardness of the bearing components is reduced, aging dimension (aging) It increases. Therefore, the C content is 0.95% to 1.10%. More reliably, in order not to reduce the rolling fatigue life, C content is preferably 0.96% to 1.05%. More preferably from 0.97% to 1.03%.
[0027]
　Si: 0.10% ~
　0.70% Si (Silicon) is an element functioning as a deoxidizer. In the Si content is less than 0.10%, it is not possible to obtain these effects. On the other hand, when the Si content exceeds 0.70%, SiO in steel 2 -based inclusions occur, the rolling contact fatigue life of the bearing parts is reduced. Therefore, the Si content to 0.10% to 0.70%. More reliably, in order not to reduce the rolling fatigue life, Si content is preferably 0.12% to 0.56%. More preferably from 0.15% to 0.50%.
[0028]
　Mn: 0.20% ~
　1.20% Mn (Manganese) is an element functioning as a deoxidizer and desulfurizing agent. Furthermore, an element useful for securing the amount of hardenability and a residual austenite of steel. The Mn content is less than 0.20%, becomes deoxidation is insufficient, the oxide is generated, the rolling fatigue life of the bearing parts is reduced. On the other hand, when the Mn content exceeds 1.20% by supercooled structures such as martensite occurs at the time of cooling after hot rolling, causing a void generated during wire drawing. Further, when the Mn content exceeds 1.20%, and the amount of residual austenite becomes excessive, the hardness of the bearing components is reduced. Therefore, the Mn content to 0.20% to 1.20%. More reliably deoxidation, in order not to reduce the rolling fatigue life, Mn content is preferably 0.21% to 1.00%. More preferably from 0.25% to 0.80%.
[0029]
　Cr: 0.90% ~
　1.60% Cr (chromium) is an element for improving the hardenability of the steel. Furthermore, to promote spheroidizing of carbides and is an extremely effective element for carbide amount also increases. If the Cr content is less than 0.90%, C the amount of solid solution is increased, the residual austenite is excessively formed. On the other hand, when the Cr content exceeds 1.60% penetration of carbide is insufficient during quenching, lowers the hardness of degradation or bearing components in an amount of residual austenite. Therefore, the Cr content to 0.90% to 1.60%. In order to more reliably improve the rolling contact fatigue life of the bearing component, Cr content is preferably 0.91 to 1.55%. More preferably from 1.10% to 1.50%. Most preferably, it is 1.30% - 1.50%.
[0030]
　Al: 0.010% ~
　0.100% Al (aluminum) is an deoxidizing element. If the Al content is less than 0.010% or, deoxidation is insufficient, by the oxide precipitates, rolling contact fatigue life of the bearing component is reduced. On the other hand, Al content is more than 0.100% occurred AlO-based inclusions, wire drawing workability of decline and bearing parts of the rolling contact fatigue life of the bearing parts for rolled steel is reduced. Therefore, the Al content to 0.010% or to 0.100%. In order not to reduce more reliably rolling contact fatigue life, Al content is preferably 0.015% ~ 0.078%. More preferably from 0.018% to 0.050%.
[0031]
　N: 0.003% ~ 0.030%
　N forms Al or B and nitrides, and fine crystal grains of these nitride functions as pinning particles. Thus, N (nitrogen) is an element suppressing the coarsening of crystal grains. If the N content is less than 0.003%, it is impossible to obtain this effect. On the other hand, when the N content exceeds 0.030%, coarse inclusions generate, rolling contact fatigue life is decreased. Therefore, the N content to 0.003% to 0.030%. In order not to reduce more reliably rolling contact fatigue life, N content is preferably 0.005% ~ 0.029%. More preferably from 0.009% to 0.020%.
[0032]
　P: 0.025% or less
　P (phosphorus) is an impurity which is inevitably contained. If the P content exceeds 0.025%, it segregates at austenite grain boundaries, thereby embrittling the prior austenite grain boundaries, lowering the rolling fatigue life of the bearing parts. Therefore, to limit the P content below 0.025%. In order not to reduce more reliably rolling fatigue life, the P content more than 0.020%, may be further restricted to 0.015% or less. Further, since the P content is as small desired, it contains 0% to the limits. However, to the P content to 0% is not technically easy. Therefore, from the viewpoint of steelmaking cost, the lower limit of the P content may be 0.001%. Considering the normal operating conditions, P content is preferably 0.004% or 0.012%.
[0033]
　S: 0.025% or less
　S (sulfur) is an impurity which is inevitably contained. When the S content exceeds 0.025%, coarse MnS is formed, reducing the rolling contact fatigue life of the bearing parts. Therefore, to limit the S content to 0.025% or less. In order not to reduce more reliably rolling fatigue life, the S content 0.020% or less, it may be further restricted to 0.015% or less. Since the S content is as small desired, it contains 0% to the limits. However, to the S content to 0% is not technically easy. Therefore, from the viewpoint of steelmaking cost, the lower limit of the S content may be 0.001%. Considering the normal operating conditions, S content is preferably 0.003% ~ 0.011%.
[0034]
　O: 0.0010% or less
　O (oxygen) is an impurity which is inevitably contained. When the O content exceeds 0.0010% oxide inclusions are formed, rolling contact fatigue life of the bearing parts is reduced. Therefore, to limit the O content to below 0.0010%. Since the O content is as small as desired, it includes 0% to the above limits. However, to the O content to 0% is not technically easy. Therefore, from the viewpoint of steelmaking cost, the lower limit of the O content may be 0.0001%. Considering the normal operating conditions, O content is preferably 0.0005% - 0.0010%.
[0035]
　In addition to the basic components and impurity elements as described above, the bearing component according to the present embodiment further optionally Mo, Bs, Cu, may be added at least one or more of Ni and Ca. In this case, Mo for improving the hardenability, B, one or more of Ca for causing the fine Cu and Ni and inclusions can be selected.
　The following is a description of numerical limitation range of these components and their limited reason. Here,% described is the mass%.
[0036]
　Mo: 0.25% or less
　Mo is an element for improving the hardenability. Further, by increasing the grain boundary strength of the steel subjected to quenching, it has the effect of improving the toughness. More reliably, when it is desired to secure the hardenability and toughness, the Mo content is preferably set to 0.01% or more. However, when the Mo content exceeds 0.25%, these effects are saturated. Therefore, Mo content is preferably 0.01% to 0.25%. More preferably, Mo content is 0.01% to 0.23%. More preferably from 0.10% to 0.23%.
[0037]
　B: 0.0050% or less
　B is an element for improving the hardenability in trace amounts. In addition, the effect of suppressing also have a segregation of P and S in the former austenite grain boundaries at the time of quenching. If it is desired to obtain such an effect, it is preferable that the B content of 0.0001% or more. However, B content is more than 0.0050% of these effects are saturated. Therefore, B content is preferably 0.0001% to 0.0050%. More preferably, B content is 0.0003% to 0.0050%. More preferably, from 0.0005% 0.0025%, and most preferably, it is 0.0010% 0.0025%.
[0038]
　Cu: 1.0% or less
　Cu is an element for improving the hardenability. If you want to ensure more reliably hardenability, the Cu content is preferably 0.05% or more. However, when the Cu content exceeds 1.0%, the effect is saturated, further hot workability is deteriorated. Therefore, Cu content is preferably 0.05% to 1.0%. More preferably, Cu content is 0.10% to 0.50%. More preferably 0.19% 0.31%.
[0039]
　Ni: 3.0% or less
　Ni is an element for improving the hardenability. Also it has an effect of improving the toughness of the steel subjected to quenching. If you want to ensure the more reliably hardenability and toughness, the Ni content is preferably 0.05% or more. However, when the Ni content exceeds 3.0%, this effect is saturated. Therefore, Ni content is preferably 0.05% to 3.0%. More preferably, Ni content is 0.10% to 1.5%. More preferably from 0.21% to 1.2%. And most preferably from 0.21% to 1.0%.
[0040]
　Ca: 0.0015% or less
　Ca is formed a CaS solid solution in sulfide is an element to fine sulfides. Due to the miniaturization of the sulfide, if you want to further improve the rolling contact fatigue life, it is preferable that the Ca content of 0.0003% or more. However, Ca content exceeds 0.0015% this effect is saturated. Furthermore, by oxide inclusions it becomes coarse, lowering the rolling fatigue life. Therefore, Ca content is preferably 0.0003% 0.0015%. More preferably, Ca content is 0.0003% 0.0011%. More preferably 0.0005% - 0.0011%.
[0041]
　The bearing component according to the present embodiment contains the above components, chemical composition balance is composed of substantially Fe and inevitable impurities.
[0042]
　Next, a description will be given of the steel to be a bearing part of the material (hot rolled wire rod).
[0043]
　Material to become steel (hot-rolled wire rod) has the same chemical composition and bearing parts. Then, 90% or more pearlite area ratio, it is preferable to have a tissue containing 5% or less of the pro-eutectoid cementite area ratio. The average particle diameter of pearlite blocks (circle equivalent diameter) is at 15μm or less, it is preferable pro-eutectoid cementite thickness is 1.0μm or less. Further, steel as the material (hot rolled wire rod) is, as a tissue, it is preferable not to have a martensite.
[0044]
　Organization of the steel material (hot rolled wire rod), the supercooled structures such as martensite is present, can not be uniformly deformed during wire drawing, it may become a cause of disconnection. Therefore, the main organization of steel, perlite is preferred.
　In addition, the size of the pearlite block is very strong correlation and ductility. In other words, by refining the pearlite, to improve the wire drawing workability. Therefore, the average particle size of the pearlite blocks (circle equivalent diameter) it is preferable that the 15μm or less. The average particle size of pearlite blocks is more than 15 .mu.m, in some cases the effect of improving drawability can not be obtained. On the other hand, making the mean particle diameter of pearlite blocks and 1μm or less, industrial be difficult. Therefore, the average particle size of pearlite blocks is preferably in the 1μm ~ 15μm. More preferably, a 1μm ~ 10μm.
　The average particle diameter (circle equivalent diameter) of the pearlite blocks can be measured using an electron backscatter diffraction apparatus (EBSD).
[0045]
　Proeutectoid cementite, plastic deformability is small. Therefore, it interrupted by wire drawing, a factor to form the void. However, low area ratio of pro-eutectoid cementite, the smaller the thickness, wire drawability is not inhibited. Therefore, the area ratio of the pro-eutectoid cementite is 5% or less, the thickness preferably 1.0μm or less. More preferably, the area ratio of the pro-eutectoid cementite 3% or less, the thickness is 0.8μm or less.
　Area ratio and the thickness of the pro-eutectoid cementite can be determined by SEM observation.
[0046]
　It is described next manufacturing method of a bearing component according to the present embodiment.
[0047]
　Steel as the bearing part of the material according to the present embodiment (hot rolled wire rod), for example, can be manufactured as follows. The following manufacturing method, the steel material as a bearing part of the material (hot rolled wire rod) may be a pearlite steel which suppresses the pro-eutectoid cementite area ratio less than 5%.
[0048]
　Material to be subjected to hot rolling can be employed normal manufacturing conditions. For example, melting the steel adjusting the component composition in the usual manner, and casting, soaking treatment, if necessary, subjected to slabbing, and steel pieces. Then heated resulting steel slab is subjected to hot rolling. Then, after the wound in the form of a ring, and cooled.
　Through the above steps, the steel material consisting of a bearing part of the material according to the present embodiment (hot rolled wire rod) can be produced.
[0049]
　In the casting process, the casting method is not limited in particular, it may be used a vacuum casting method or continuous casting method or the like.
　Also, if necessary, performed on the slab after casting process, soaking treatment (soaking diffusion processing) is a heat treatment for reducing the segregation that occurs casting and the like. Steel slab obtained through these processes are commonly referred to as a billet.
　In addition, the heating temperature of the soaking treatment is preferably 1100 ℃ ~ 1200 ℃. The holding time is preferably 10 hours to 20 hours.
[0050]
　Next, as a process of heating before hot rolling, heating the steel piece. Heating temperature of the steel pieces, preferably in the 900 ℃ ~ 1300 ℃.
[0051]
　Thereafter, the hot-rolling process, with respect to the steel strip, performing hot rolling. In the hot rolling step, it is preferable that the finish rolling temperature is 850 ° C. or less.
　The finish rolling temperature by a 850 ° C. or less, by precipitating by dispersing a pro-eutectoid cementite, it is possible to reduce the pro-eutectoid cementite thickness. And, increasing the nucleation sites of pearlite during transformation, the pearlite block can be miniaturized. More preferred finish rolling temperature is 800 ℃ or less. The temperature of the steel strip during hot rolling can be measured by a radiation thermometer.
　The bearing part of the material, steel through the hot rolling process, namely finishing steel after rolling is generally referred to as hot rolled wire rod.
[0052]
　After the hot rolling step is completed, ie finish after rolling, the hot-rolled wire rod at 800 ℃ or less, wound into a ring shape. This process is generally referred to as winding process.
　In the winding step, when the coiling temperature is high, austenite grain growth, which may pearlite blocks becomes coarse. Therefore, the coiling temperature is preferably 800 ℃ or less. More preferably the winding temperature is 770 ℃ or less.
　Incidentally, after the hot rolling step is completed, it may have a winding before cooling step for cooling as required.
[0053]
　After the winding process, cooling the hot-rolled wire rod up to 600 ℃. This process is generally referred to as a cooling step.
　Cooling rate to 600 ° C. is preferably set to 0.5 ℃ / s ~ 3.0 ℃ / s.
　After winding the rolled wire rod, and cooled to 600 ℃, transformation to pearlite is completed. Cooling rate after coiling may affect the transformation from austenite to pearlite. Therefore, in order to suppress the precipitation of supercooled structures such as martensite and bainite, the cooling rate after coiling is preferably not more than 3.0 ℃ / s. More preferably, not more than 2.3 ℃ / s. On the other hand, the cooling rate after coiling may also affect the precipitation of pro-eutectoid cementite. Therefore, in order to suppress the excessive precipitation and coarsening of pro-eutectoid cementite, cooling rate after coiling is preferably at 0.5 ° C. / s or higher. More preferably, at 0.8 ° C. / s or higher.
[0054]
　Method for producing a conventional bearing components, before wire drawing has a spheroidizing heat treatment step, the bearing component according to the present embodiment is different from the steel as the material, wire drawing, quenching and tempering process applied, it is possible to obtain.
　Specifically, without being subjected to the spheroidizing heat treatment steel as the material is subjected to wire drawing of 50% or more total reduction of area. After that, quenching, tempering process is performed.
[0055]
　For steel as the material, when the wire drawing of 50% or more total reduction of area, the introduced distortion, at the time of quenching, a solid solution and spheroidized cementite is promoted. Therefore, it is the amount of residual austenite can be secured, refining the average grain size of prior austenite.
　If the total reduction rate is less than 50% can not be secured retained austenite predetermined amount, also becomes insufficient spheroidized cementite, when the average particle size of prior austenite can not be miniaturized there is. On the other hand, when the whole cross sectional reduction ratio exceeds 97%, there is a possibility that breakage occurs during wire drawing. Therefore, the whole cross sectional reduction ratio is preferably 50% to 97%.
[0056]
　In quenching treatment after wire drawing process, the heating temperature of quenching is to decompose the cementite, in order to form a solid solution of C in austenite, it is preferable that the 820 ℃ or more. When the heating temperature of quenching is less than 820 ℃, there is a case in which the amount of C to be dissolved in the austenite is small, the reduction in hardness and fatigue life. On the other hand, if the heating temperature of quenching is greater than 890 ° C., an average particle diameter of old austenite there is a possibility that coarsened. Therefore, the heating temperature of quenching is preferably in the 820 ℃ ~ 890 ℃.
[0057]
　In tempering, tempering temperature, due to the toughness of securing and hardness adjustment is preferably carried out at 0.99 ° C. or higher. When the tempering temperature is lower than 0.99 ° C., there is a case where the toughness of the bearing component can not be secured. On the other hand, when the tempering temperature exceeds 250 ° C., it decreases the hardness of the bearing products, the rolling fatigue life may be decreased. For this reason, the tempering temperature is preferably set to 150 ℃ ~ 250 ℃.
Example
[0058]
　Hereinafter, examples of the bearing component of the present invention, illustrating the effect of the bearing component according to the present embodiment more specifically. However, conditions in the examples are one condition example employed for confirming the workability and advantageous effects of the present invention, the present invention is not limited to the following examples. Without departing from the gist of the present invention, as long as they achieve the object of the present invention, it is also possible to put into practice after appropriate modifications or variations within the scope adaptable to the gist. Accordingly, the present invention may employ various conditions, which are both included in the technical features of the present invention.
[0059]
　On the table 1 and wire and rod having the ingredients shown in Table 2, by performing a heat treatment or hot forging to obtain a material having a tissue listed in Table 3 and Table 4. Next, with reference to the material, cold, until the diameter becomes Fai12.5Mm, was wire drawing. Next, the material obtained in wire drawing, and cut into 25m lengths, subjected to a quenching treatment and a tempering treatment.
　Then, shaping the resulting material to φ12mm × 22mm, subjected to a finishing process, to produce a bearing parts.
　It should be noted that the hardening process, was held for 30 minutes at a heating temperature of 800 ℃ ~ 900 ℃, it was carried out by oil cooling at 50 ℃.
　Then, for 30 minutes tempering was carried out at the tempering temperature 170 ℃.
[0060]
　Organization evaluation of the bearing parts, were carried out in the following manner.
　First, using SEM and X-ray diffraction method, the average particle diameter of old austenite (.mu.m), the amount of residual austenite (vol%), a predetermined size of the void number density (number / mm 2 was measured).
　The hardness of the bearing components, in the longitudinal center, is cut perpendicular C section in the longitudinal direction, after the central C section is revealing by grinding, in the center C cross section, a center, the center and radius of 6mm It was evaluated by the average value measured 3 points a Vickers hardness tester.
　Incidentally, the Vickers hardness was evaluated as good or 750 Hv.
　Rolling contact fatigue life of the bearing component is measured under the following contaminated environment. Using a radial-type fatigue testing machine, the iron powder having a particle size of 100 .mu.m ~ 180 .mu.m having a hardness of 750 Hv ~ 800 Hv, to measure the rolling fatigue life in contaminated environments obtained by 1g mixed for lubricant 1 L.
　Then, the measured rolling contact fatigue life, the Weibull statistical processing, calculated by the cumulative failure probability of 10%, was evaluated by the value.
[0061]
[Table 1]

[0062]
[Table 2]

[0063]
[table 3]

[0064]
[Table 4]

[0065]
　Table 3 and Table 4, show material of organization, manufacturing methods, organization of bearing parts, the production results and results of evaluation of the hardness and the rolling contact fatigue life. In Table 1 to Table 4, numerical departing from the present invention scope is underlined. Further, in Tables 3 and 4, P is perlite, .theta is cementite, M is martensite, alpha ferrite, gamma means austenite.
[0066]
　A1 ~ A17 are examples of the present invention. The example the present invention, in the table are described as examples. A1 ~ A17, the chemical composition was within the proper range of the present invention. In addition, the average particle size of the prior austenite, the number density of voids in quantity and given the size of the retained austenite also meets the conditions of the present invention, 5.0 × 10 under contaminated environment 6 or more of the excellent times had rolling contact fatigue life. Furthermore, A1 ~. 17, in the material tissues, pro-eutectoid cementite area ratio is 5% or less none. In addition, in the A1 ~ A17, organization of the bearing components, it was both retained austenite, spherical cementite and martensite.
[0067]
　On the other hand, A18 ~ A35, B1, B2 is a comparative example. A18 ~ A35, B1, B2 is, because it does not satisfy either or both of the tissue chemical composition and bearing components defined in the present invention, as compared with the present invention embodiment, the rolling fatigue under a contaminated environment life was poor.
[0068]
　A18 ~ A30, the chemical composition is outside the scope of the present invention embodiment. A18 Because small C content, the lack of the amount of residual austenite, the rolling fatigue characteristics under a contaminated environment was reduced. A22 Because small Mn content, the lack of the amount of residual austenite, the rolling fatigue life under a contaminated environment was reduced. A25 Since the Cr content is excessive, generated carbides, the amount of retained austenite is insufficient. Therefore, the rolling fatigue characteristics under a contaminated environment is reduced. A19 because C content is excessive, due to the formation of coarse carbides, the rolling fatigue life was reduced. A26 because the S content is excessive, due to the formation of sulfides, rolling fatigue life was reduced. A30 Since the N content is excessive, due to the formation of nitrides, the rolling fatigue life was reduced. A20 because of excessive Si content, due to the generation of the inclusions, the rolling contact fatigue life was reduced. A24 because of excessive Al content, due to the generation of the inclusions, the rolling contact fatigue life was reduced. A28 Because O content is excessive, due to the formation of inclusions, the rolling fatigue life was reduced.
[0069]
　A21 is often the Mn content, martensite was produced in the material. Therefore, the decrease in the wire drawing workability, would be coarse and voids number density of the average grain size of prior austenite is increased, the rolling fatigue life was reduced. Moreover, A21, since the Mn content is large, the Ms point is reduced, the amount of residual austenite becomes excessive, as a result, the hardness was reduced. A23 Because small Cr content, the amount of residual austenite becomes excessive, the hardness was reduced. A27 is the grain boundary in excessive P content of embrittlement, the rolling contact fatigue life was reduced. A29 is insufficient content of N, the average particle size of prior austenite had become coarse. Therefore, the amount of retained austenite is insufficient, the rolling fatigue life under a contaminated environment was reduced.
[0070]
　A 31 ~ A35 are components be within the scope of the present invention, since the structure of the bearing parts is out of the scope of the present invention, the rolling fatigue life was reduced. A31 and A32 has a low total reduction of area of ​​the wire drawing, the average particle size of prior austenite had become coarse. Therefore, the amount of retained austenite is insufficient, the rolling fatigue life under a contaminated environment was reduced. A33, because the heating temperature of quenching is low, the amount of retained austenite is insufficient, the rolling fatigue life was reduced. A34, since the heating temperature of quenching is high, cementite had been excessively solid solution. Therefore, by C content was dissolved increases, the amount of residual austenite becomes excessive, the hardness was reduced.
[0071]
　A35 in the production method of the material, for the cooling rate after coiling is fast, martensite has occurred in the material. Therefore, the number density of a predetermined size of the voids is increased, the rolling fatigue life under a contaminated environment was reduced. B1 and B2 are examples subjected to spheroidizing heat treatment, due to the spheroidizing cementite increases the number density of a predetermined size of the void, the rolling fatigue life under a contaminated environment is not degraded It was.
Industrial applicability
[0072]
　According to this aspect of the present invention, in order to ensure good drawability, to suppress the content of Mn, without performing spheroidizing heat treatment, it is possible to obtain a bearing part. As a result, even under a contaminated environment, it is possible to obtain an excellent bearing components in rolling contact fatigue life, it has high industrial applicability.
Description of the code
[0073]
　1 martensite
　2 spherical cementite
　3 void
The scope of the claims
[Claim 1]
　Chemical components, in mass
　　Pasento,
　　C: 0.95
　　Pasento ～ 1.10 Pasento, Si: 0.10 Pasento ～ 0.70 Pasento, Mn: 0.20
　　Pasento ～ 1.20 Pasento, Cr: 0.90 Pasento
　　1.60 Pasento ～,
　　Al: 0.010 Pasento ～ 0.100 Pasento, N: 0.003 Pasento ～ 0.030 Pasento
　contain,
　　P: 0.025 Pasento or
　　less, S: 0.025 Pasento or less,
　　O : 0.0010% or less
　limited to,
　in
　　any, Mo: 0.25% or
　　less, B: 0.0050% or
　　less, Cu: 1.0% or
　　less, Ni: 3.0% or
　　less, Ca: 0.0015 % or less
　containing,
　the balance being Fe and impurities,
　metal structure, residual austenite, are spherical cementite and martensite, the amount of the retained austenite, by volume%, 15% and 25%, and, the average particle size of prior austenite is not more than 8.0 .mu.m,
　in the metal structure, the number density of the equivalent circle diameter 3.0μm or less voids than 0.02μm at the 2,000 / mm 2 or less
and wherein the bearing parts.
[Claim 2]
　The chemical components found in
　　mass%,
　　Mo: 0.01% ~
　　0.25%, Bs: 0.0001% ~ 0.0050%, Cu: 0.1%
　　~ 1.0%, Ni: 1.0
　　~ 3.0%%, Ca: 0.0001% ~ 0.0015%
　containing one or more of
the bearing component according to claim 1, characterized in that.
[Claim 3]
　And the Vickers hardness is 750Hv or more, the rolling of the iron powder particle size is 100μm ~ 180μm with a hardness of 750Hv ~ 800Hv, in the contaminated environment is 1g contaminating environment relative to the lubricating oil 1L fatigue life × 10 5.0 . 6 bearing component according to claim 1 or 2, characterized in that at least.