JP6665737B2 - Method for preparing raceway surface of thrust type ball bearing - Google Patents
Method for preparing raceway surface of thrust type ball bearing Download PDFInfo
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Description
本発明は、鉄鋼、製紙、風力発電及び鉱山等で用いられる各種機械及び各種工作機械、並びに自動車及び鉄道車両等、の部品として、高負荷での過酷な条件下で好適に使用可能なスラスト型球軸受の軌道面作製方法に関する。 The present invention provides a thrust type that can be suitably used under severe conditions under high loads as parts of various machines and various machine tools used in steel, papermaking, wind power generation and mining, and automobiles and railway vehicles. The present invention relates to a method for producing a raceway surface of a ball bearing.
鉄鋼、製紙、風力発電及び鉱山等の各分野で用いられる各種機械等、並びに、自動車及び鉄道車両には、各種の玉軸受が利用されている。これらの玉軸受は、高負荷での過酷な条件下で使用されることから、局所的に亀裂が発生するおそれがある。 BACKGROUND ART Various types of ball bearings are used in various machines and the like used in various fields such as steel, papermaking, wind power generation, and mining, as well as in automobiles and railway vehicles. Since these ball bearings are used under severe conditions under a high load, there is a possibility that cracks are locally generated.
通常、軸受の破壊は、表面直下50〜200μmに存在する硬質介在物を起点として疲労亀裂が進展して表面に至り、鋼材表面が剥離するという現象によることが多い。この現象は、軸受の素材となる棒鋼を圧延する際に、母相である鋼の変形量と硬質介在物の変形量が異なるために硬質介在物周りに空隙が生じ、この空隙が転動時に応力集中を呼び、疲労亀裂発生の起点となることが原因である。 Usually, the fracture of the bearing is often caused by a phenomenon in which a fatigue crack propagates from a hard inclusion existing 50 to 200 μm directly below the surface to reach the surface, and the steel material surface peels off. This phenomenon occurs when rolling the steel bar that is the material of the bearing, because the amount of deformation of the steel that is the parent phase and the amount of deformation of the hard inclusion are different, a gap is created around the hard inclusion, and this gap is generated when rolling. This is called stress concentration, and it is the cause of fatigue crack initiation.
亀裂発生の抑制による転動疲労寿命向上のためには、大きく分けて2つの方法、即ち硬質介在物の数を減らす方法と、硬質介在物周りの空隙を減らす方法と、が有効である。特に、後者の硬質介在物周りの空隙を減らす方法としては、硬質介在物の径を小さくし棒鋼圧延時に生成する空隙自体を小さくする方法や、静水圧応力を掛けて硬質介在物周りに生じた空隙を押し潰す方法が知られている。 In order to improve the rolling fatigue life by suppressing the occurrence of cracks, it is effective to roughly classify two methods, that is, a method of reducing the number of hard inclusions and a method of reducing voids around the hard inclusions. In particular, the latter method of reducing the voids around the hard inclusions, such as reducing the diameter of the hard inclusions and reducing the voids themselves generated during bar rolling, or applying a hydrostatic stress to the voids around the hard inclusions A method of crushing a gap is known.
静水圧応力により介在物周りの空隙を減らす方法は、特許文献1及び特許文献2に開示されている。特許文献1は、HIPにより硬質介在物周りの空隙を減少させる技術である。これに対し、特許文献2は、転動部を有する機械部品を冷鍛成形し、冷鍛時に発生する静水圧応力により介在物と母材と間の空隙を減少させる技術である。 Methods for reducing the voids around inclusions by hydrostatic stress are disclosed in Patent Documents 1 and 2. Patent Literature 1 is a technique for reducing voids around hard inclusions by HIP. On the other hand, Patent Literature 2 discloses a technique for cold forging a mechanical component having a rolling portion and reducing a gap between the inclusion and the base material by hydrostatic stress generated at the time of cold forging.
しかしながら、特許文献1に記載の技術では、空隙を押し潰すのに要する時間が鉄原子の自己拡散律速であるため高温で長時間保持する必要がある。また、特許文献2に記載の技術は、冷間での鍛造を採用しているため、母相の変形抵抗が高く弾性限も高いことから、空隙を押し潰すことは困難で、更に冷鍛時に割れが発生するおそれがある。 However, in the technology described in Patent Document 1, the time required to crush the voids is determined by the self-diffusion of iron atoms, so that it is necessary to maintain the temperature at a high temperature for a long time. In addition, the technology described in Patent Document 2 employs cold forging, so that the deformation resistance of the matrix is high and the elastic limit is high, so that it is difficult to crush the voids. Cracks may occur.
本発明は、上記事情に鑑みてなされたものであって、高温で長時間保持する必要がないスラスト型玉軸受の軌道面作製方法であって、高負荷で使用されるような過酷な条件下でも好適に使用可能なスラスト型玉軸受の軌道面作製方法を提示することを目的とする。 The present invention has been made in view of the above circumstances, and is a method for manufacturing a raceway surface of a thrust type ball bearing that does not need to be maintained at a high temperature for a long time, and is used under a severe condition such as used under a high load. However, an object of the present invention is to provide a method of manufacturing a raceway surface of a thrust ball bearing that can be suitably used.
軸受の疲労亀裂は、転動球と接触する母相表面から母相内のヘルツ応力が最大となる表面下200μm以下の表面近傍位置までの極めて狭い領域で発生する。この領域において介在物と母相との密着性が高まれば、転動寿命は向上する。逆に言えば、上記領域外で介在物と母相との間に空隙があったとしても、転動寿命に影響はない。 The fatigue crack of the bearing is generated in an extremely narrow region from the surface of the mother phase in contact with the rolling ball to a position near the surface of 200 μm or less below the surface where the Hertz stress in the mother phase is maximized. If the adhesion between the inclusion and the matrix is increased in this region, the rolling life is improved. Conversely, even if there is a gap between the inclusion and the parent phase outside the above region, the rolling life is not affected.
図1は、厚さ5mmのワーク(金属平板)に円環状の凸部(該金属平板との接触部の断面形状は円弧状)を備える金型を押し付けた際に生ずる静水圧応力の分布を示す模式図である。同図から明らかなように、スラスト型軸受の転動溝を熱間鍛造により作製した場合を模擬して、平板に円環状の凸部を有する金型を押し付けると、金型が下死点にある時に、金型によって形成された母材凹みの部分近傍に、強い圧縮の静水圧場が形成される。この圧縮の静水圧場は、通常の熱間静水圧プレスによって得られる静水圧応力200MPaに比べ大きく、また軸受疲労亀裂発生領域(金属平板の表面直下50〜200μmの領域)を十分にカバーしている。 FIG. 1 shows the distribution of hydrostatic stress generated when a mold having an annular convex portion (the cross-sectional shape of a contact portion with the metal flat plate is arc-shaped) is pressed against a work (metal flat plate) having a thickness of 5 mm. FIG. As is apparent from the figure, simulating the case where the rolling grooves of the thrust type bearing were manufactured by hot forging, and pressing a mold having an annular convex portion on a flat plate, the mold was moved to a bottom dead center. At some point, a strongly compressed hydrostatic field is formed near the base material recess formed by the mold. The hydrostatic pressure field of this compression is larger than the hydrostatic stress of 200 MPa obtained by a normal hot isostatic press, and sufficiently covers the bearing fatigue crack initiation region (the region of 50 to 200 μm immediately below the surface of the flat metal plate). I have.
このような事実を前提に、本発明者らは、熱間鍛造時の静水圧応力を利用し、介在物と母相界面との間に存在する空隙を押し潰すことができないか検討した。 On the premise of such a fact, the present inventors have examined whether it is possible to use the hydrostatic stress at the time of hot forging to crush the gap existing between the inclusion and the matrix interface.
熱間鍛造時に母相に形成される圧縮静水圧応力場は、母相表面からの距離、円環状凸部を有する金型の圧下量、及び鍛造温度に依存する。図2は、3/8inch転動球に対応する軌道面を作製するにあたり、840℃に加熱したワークに金型を0.5mm押し込んだ際の静水圧応力と、ワークに形成される凹溝中心表面からの距離と、の関係を示すグラフである。なお、図2におけるワークは、内径φ25mm、外径φ52mm、及び厚さ5mmの穴空き円盤状である。また、同図における金型は、曲率半径が4.76mmであって、円環状凸部芯の半径が19.25mmである凸部を備える。図2から明らかなように、ワーク表面に近い方が圧縮の静水圧応力は大きい。図3は、図2において使用したワーク及び金型について、図2における条件と同じ鍛造温度条件で、圧下量を変えた場合の、ワーク表面から200μm位置での静水圧応力と圧下量との関係を示すグラフである。図4は、図2において使用したワーク及び金型について、図2における条件と同じ圧下量で、鍛造温度条件を変えた場合の、ワーク表面から200μm位置での静水圧応力と鍛造温度との関係を示すグラフである。図3から明らかなように、静水圧応力は圧下量にほぼ比例して増加する。また、図4から明らかなように、鍛造温度が高くなると静水圧応力は減少する。 The compressive hydrostatic stress field formed in the parent phase during hot forging depends on the distance from the surface of the parent phase, the amount of reduction of the die having the annular projection, and the forging temperature. FIG. 2 shows the hydrostatic stress when a mold is pressed into a work heated to 840 ° C. by 0.5 mm and the center of a concave groove formed in the work when producing a raceway surface corresponding to a 3/8 inch rolling ball. It is a graph which shows the relationship with the distance from the surface. The work in FIG. 2 is a hole-shaped disk having an inner diameter of 25 mm, an outer diameter of 52 mm, and a thickness of 5 mm. In addition, the mold in the figure has a convex portion having a radius of curvature of 4.76 mm and a radius of an annular convex portion core of 19.25 mm. As is clear from FIG. 2, the closer to the work surface, the greater the hydrostatic stress of compression. FIG. 3 shows the relationship between the hydrostatic stress and the amount of reduction at a position of 200 μm from the work surface when the amount of reduction was changed under the same forging temperature conditions as those in FIG. 2 for the work and the mold used in FIG. FIG. FIG. 4 shows the relationship between the hydrostatic stress at the position of 200 μm from the work surface and the forging temperature when the forging temperature condition was changed for the work and the die used in FIG. FIG. As is clear from FIG. 3, the hydrostatic stress increases almost in proportion to the amount of reduction. Further, as is clear from FIG. 4, the hydrostatic stress decreases as the forging temperature increases.
本発明者らは、図3及び図4の結果を基に、熱間鍛造時の静水圧応力を利用し、介在物と母相界面との間に存在する空隙を押し潰すことができる条件を、さらに詳細に検討した。鍛造による静水圧応力の上昇は一瞬であるため、介在物と母相が密着するためには200MPa以上の圧縮静水圧応力が必要となる。しかしながら、図3における押し込み量が0.28mm以上で、かつ、図4における鍛造温度が940℃以下の場合であっても、ワーク表面から200μm位置での圧縮静水圧応力が200MPa未満となる場合があることを確認した。 Based on the results of FIG. 3 and FIG. 4, the present inventors utilize hydrostatic stress at the time of hot forging to determine the conditions under which the void existing between the inclusion and the matrix interface can be crushed. , Discussed in more detail. Since the increase in hydrostatic stress due to forging is instantaneous, a compressive hydrostatic stress of 200 MPa or more is required in order for the inclusions and the mother phase to adhere to each other. However, even when the indentation amount in FIG. 3 is 0.28 mm or more and the forging temperature in FIG. 4 is 940 ° C. or less, the compressive hydrostatic stress at a position of 200 μm from the work surface may be less than 200 MPa. Confirmed that there is.
図5は、鍛造温度(鍛造時の加熱温度)と押し込み量とをそれぞれ変動させた場合に、ワーク表面から200μm位置での圧縮静水圧応力が200MPa以上となる領域を示す図である。同図中、色付き部分が、当該圧縮静水圧応力が200MPa以上となる領域である。同図によれば、押し込み量が0.28mm以上で、かつ、鍛造温度が940℃以下の場合であっても、ワーク表面から200μm位置での静水圧応力が200MPa未満となる領域がある。このため、当該圧縮静水圧応力が200MPa以上となるように、鍛造温度と押し込み量とを設定するにあたり、図3及び図4の結果を単に加算して条件設定するよりも、図5の結果を用いる方が好ましいことが判る。 FIG. 5 is a diagram showing a region where the compressive hydrostatic stress at a position of 200 μm from the work surface is 200 MPa or more when the forging temperature (heating temperature during forging) and the indentation amount are respectively changed. In the figure, the colored portion is a region where the compressive hydrostatic stress is 200 MPa or more. According to the figure, even when the indentation amount is 0.28 mm or more and the forging temperature is 940 ° C. or less, there is a region where the hydrostatic stress at a position of 200 μm from the work surface is less than 200 MPa. Therefore, when setting the forging temperature and the indentation amount so that the compressive hydrostatic stress becomes 200 MPa or more, the result of FIG. 5 is more than the condition of simply adding the results of FIG. 3 and FIG. It turns out that it is more preferable to use.
本発明は、上記知見に基づいでなされたものであって、その要旨は以下のとおりである。 The present invention has been made based on the above findings, and the gist is as follows.
[1]オーステナイトを主相とする円環状のワークを用いた、スラスト型玉軸受の軌道面作製方法であって、
鍛造時の鍛造温度T1(℃)と円環状の凸型を有する金型の押し込み量D(mm)とが下記式を満足するように、ワークに対して前記金型を押し付けて、転動溝を形成する鍛造工程と、
上記転動溝が形成されたワークの組織をマルテンサイト主体の組織とするマルテンサイト生成工程と、
を含むことを特徴とする、スラスト型球軸受の軌道面作製方法。
T1<−400D2+752D+664 (1)
[1] A method for manufacturing a raceway surface of a thrust type ball bearing using an annular work having austenite as a main phase,
The die is pressed against a work and rolled so that the forging temperature T 1 (° C.) during forging and the amount of press D (mm) of the die having an annular convex shape satisfy the following formula. Forging process to form a groove,
A martensite generation step of making the structure of the work in which the rolling grooves are formed a structure mainly composed of martensite,
A method for manufacturing a raceway surface of a thrust ball bearing, comprising:
T 1 <−400D 2 + 752D + 664 (1)
[2]上記マルテンサイト生成工程が、ダイレクトクエンチである、上記[1]に記載のスラスト型球軸受の軌道面作製方法。 [2] The method for producing a raceway surface of a thrust ball bearing according to the above [1], wherein the martensite generation step is a direct quench.
[3]上記マルテンサイト生成工程が、徐冷と焼き入れ焼き戻しとからなる、上記[1]に記載の軌道面作製方法。 [3] The method for producing a raceway surface according to the above [1], wherein the martensite generation step comprises slow cooling and quenching and tempering.
[4]上記マルテンサイト生成工程が、ダイクエンチである、上記[1]に記載のスラスト型球軸受の軌道面作製方法。 [4] The method for producing a raceway surface of a thrust ball bearing according to the above [1], wherein the martensite generation step is a die quench.
[5]鍛造時の加熱温度T2(℃)とダイクエンチ終了温度T3(℃)と鍛造時の加熱時間t(hr)が下記式を満足するように、ダイクエンチを行う、上記[4]に記載のスラスト型球軸受の軌道面作製方法。
T3<4.17×10−3T2 2−8.18T2−15.7log10(t)−2.98×103/t/T2+4142 (2)
[5] Die quench is performed so that the forging heating temperature T 2 (° C.), die quench end temperature T 3 (° C.), and forging heating time t (hr) satisfy the following formula. The method for producing a raceway surface of the thrust type ball bearing described in the above.
T 3 <4.17 × 10 -3 T 2 2 -8.18T 2 -15.7log 10 (t) -2.98 × 10 3 / t / T 2 +4142 (2)
[6]ワークの温度を840℃以下として、転動溝を形成する、上記[1]から[5]のいずれか1つに記載のスラスト型球軸受の軌道面作製方法。 [6] The method for producing a raceway surface of a thrust ball bearing according to any one of the above [1] to [5], wherein the temperature of the workpiece is 840 ° C. or lower and the rolling groove is formed.
[7]圧下量が0.4mm以上となるように、上記転動溝を形成する、上記[1]から[6]のいずれか1つに記載のスラスト型球軸受の軌道面作製方法。 [7] The method for producing a raceway surface of a thrust ball bearing according to any one of [1] to [6], wherein the rolling grooves are formed so that the rolling reduction is 0.4 mm or more.
本発明に係るスラスト型玉軸受の軌道面作製方法では、金型の圧下量と鍛造温度との関係に改良を加えている。その結果、本発明によれば、高温で長時間保持する必要がなくスラスト型玉軸受の軌道面を作製することができる。また、本発明によれば、軌道面直下において介在物と母材間との間の空隙を押し潰して、介在物と母相とを密着させることができるため、玉軸受を高負荷条件下でも好適に使用することができ、ひいてはその長寿命化を図ることができる。 In the method for producing a raceway surface of a thrust ball bearing according to the present invention, the relationship between the amount of reduction of the die and the forging temperature is improved. As a result, according to the present invention, the raceway surface of the thrust type ball bearing can be manufactured without having to hold at a high temperature for a long time. Further, according to the present invention, the gap between the inclusion and the base material can be crushed immediately below the raceway surface, and the inclusion and the parent phase can be brought into close contact with each other. It can be suitably used, and the life can be extended.
以下に、本発明に係るスラスト型玉軸受の軌道面作製方法の実施の形態(以下、「本実施形態」と称する)を説明する。なお、本実施形態は、本発明を限定するものではない。また、本実施形態の構成要素には、当業者が置換可能かつ容易なもの、或いは実質的に同一のものが含まれる。さらに、本実施形態に含まれる各種形態(例えば、好ましい形態)は、当業者が自明の範囲内で任意に組み合わせることができる。 Hereinafter, an embodiment of a method for producing a raceway surface of a thrust type ball bearing according to the present invention (hereinafter, referred to as “the present embodiment”) will be described. Note that the present embodiment does not limit the present invention. The components of the present embodiment include components that can be easily replaced by those skilled in the art, or components that are substantially the same. Furthermore, various forms (for example, preferable forms) included in the present embodiment can be arbitrarily combined within a range obvious to those skilled in the art.
本実施形態に係るスラスト型球軸受の軌道面作製方法は、オーステナイトを主相とする円環状のワークを用いた、軌道面作製方法である。なお、本実施形態に係る軌道面作製方法は、スラスト型玉軸受を念頭に置いているため、スラスト玉軸受の一般的な構成要素のうち、内輪に相当する軸軌道盤、及び外輪に相当するハウジング軌道盤、に対して、軌道面を作製する方法である。ここで、オーステナイトを主相とするとは、ワークの組織のうちオーステナイトが最も多く含まれることを意味する。 The method for producing a raceway surface of a thrust ball bearing according to the present embodiment is a method for producing a raceway surface using an annular work having austenite as a main phase. In addition, since the raceway surface manufacturing method according to the present embodiment has a thrust type ball bearing in mind, it corresponds to the axial raceway plate corresponding to the inner ring and the outer ring among the general components of the thrust ball bearing. This is a method of producing a raceway surface for a housing washer. Here, the expression "austenite as the main phase" means that austenite is most contained in the structure of the work.
ワークは、一般的な鋼に含まれる成分であればいかなる成分をも含むことができる。即ち、ワークは、例えば、Fe、C、Si、Mn、P、S、Cu、Ni、Cr、Al、O、及び不可避的不純物を含むことができ、これら元素の成分組成範囲は特に限定されない。ここで、不可避的不純物とは、ワークを工業的に製造する際に、原料としての鉱石又はスクラップに含まれ得る成分、或いは、製造環境などに起因して混入され得る成分であって、意図的に加えられていない成分を意味する。これに対し、ワークの組織は、オーステナイトが最も多く、残部がフェライト及び各種炭化物(介在物)からなる。 The workpiece can include any component as long as it is a component included in general steel. That is, the work can include, for example, Fe, C, Si, Mn, P, S, Cu, Ni, Cr, Al, O, and unavoidable impurities, and the component composition range of these elements is not particularly limited. Here, the unavoidable impurities are components that can be contained in ore or scrap as a raw material when a work is industrially produced, or components that can be mixed due to a production environment or the like, and Means components not added to On the other hand, the structure of the workpiece is most austenite, and the remainder is composed of ferrite and various carbides (inclusions).
また、ワークは、スラスト型玉軸受の軸軌道盤或いはハウジング軌道盤に加工されるものであるため、円環状をなす。なお、軸軌道盤についてもハウジング軌道盤についても、以下の説明においては同じ操作で軌道面が形成される。 Further, since the work is processed into a shaft raceway or a housing raceway of a thrust type ball bearing, it has an annular shape. In the following description, the track surface is formed by the same operation for both the shaft washer and the housing washer.
このような前提の下、本実施形態のスラスト玉軸受の軌道面作製方法においては、以下に示す(A)鍛造工程と、(B)マルテンサイト生成工程とを含む。 Under such a premise, the method for producing a raceway surface of a thrust ball bearing of the present embodiment includes the following (A) forging step and (B) martensite generation step.
(A)鍛造工程
鍛造工程では、鍛造温度T1(℃)と円環状の凸型を有する金型の押し込み量D(mm)とが下記式を満足するように、ワークに対して前記金型を押し付けて、転動溝を形成する。
T1<−400D2+752D+664 (3)
(A) Forging Step In the forging step, the forging temperature T 1 (° C.) and the indentation amount D (mm) of the die having the annular convex shape satisfy the following formula. To form rolling grooves.
T 1 <−400D 2 + 752D + 664 (3)
金型は、スラスト型玉軸受の軸軌道盤及びハウジング軌道盤のそれぞれに、軌道面を形成するために好適な形状となっていればよい。具体的には、金型の構成要素である凸部が、上記両軌道盤の幅方向中央部において両軌道盤の周方向に連続的に当接できるような形状となっていればその他の形状はとくに限定されない。 The mold only needs to have a shape suitable for forming a raceway surface on each of the shaft raceway and the housing raceway of the thrust type ball bearing. More specifically, any other shape can be used as long as the convex portion, which is a component of the mold, is shaped so that it can be continuously abutted in the circumferential direction of both washers at the center in the width direction of the two washers. It is not particularly limited.
上記式は図5に示す色付き部を示し、この領域においては、ワーク表面から200μm位置での静水圧応力が200MPa以上となり、介在物と母相との密着性が高まり、転動寿命が向上する。 The above equation shows the colored portion shown in FIG. 5. In this region, the hydrostatic stress at a position of 200 μm from the work surface becomes 200 MPa or more, the adhesion between the inclusion and the matrix increases, and the rolling life is improved. .
ワークの加熱温度については、後述するマルテンサイト生成工程を考慮すれば、鋼のA3変態温度以上の温度であることが、マルテンサイト生成工程において鍛造後にワークの温度を上昇させることなくマルテンサイト工程を実施することができる点で好ましい。なお、本実施形態における鍛造は、ホットプレス、温間鍛造、熱間鍛造、及び亜熱間鍛造のいずれをも含む概念であり、幅広い鍛造分野において適用され得る技術である。 The heating temperature of the workpiece is given the martensite step described below, it is A 3 transformation temperature or more of the steel, martensite step without raising the temperature of the workpiece after forging the martensite step Is preferred in that it can be carried out. The forging in the present embodiment is a concept including any of hot pressing, warm forging, hot forging, and sub-hot forging, and is a technique that can be applied in a wide range of forging fields.
これに対し、鍛造温度が940℃を超えると鋼材であるワークの変形抵抗が過度に小さくなり、鍛造時に発生する圧縮静水圧応力も過度に小さくなる。具体的には、鍛造温度を940℃超とすると、圧縮静水圧応力が200MPa未満となる場合があり、硬質介在物周りの空隙が十分に潰れず、硬質介在物が母相に密着しない場合がある。このため、鍛造温度は940℃以下とすることが好ましい。なお、鍛造温度を840℃以下とすると、硬質介在物周りの空隙がさらに潰れて、硬質介在物が母相にさらに高度に密着するため、さらに好ましい。 On the other hand, when the forging temperature exceeds 940 ° C., the deformation resistance of the steel work is excessively small, and the compressive hydrostatic stress generated during forging is excessively small. Specifically, when the forging temperature is higher than 940 ° C., the compressive hydrostatic stress may be less than 200 MPa, the gap around the hard inclusion may not be sufficiently collapsed, and the hard inclusion may not adhere to the matrix. is there. For this reason, the forging temperature is preferably set to 940 ° C. or lower. It is more preferable to set the forging temperature to 840 ° C. or lower, because the voids around the hard inclusions are further crushed and the hard inclusions adhere to the matrix more highly.
また、ワークに対して金型を押し付ける際の圧下量については、大きいほど静水圧応力が高まり、空隙を潰すことで介在物を母相と確実に密着させることができる。具体的には、0.27mm未満の圧下量では圧縮静水圧応力が200MPa未満となる場合があり、空隙が残存して介在物を母相に密着しない場合がある。このため、圧下量は0.27mm以上とすることが好ましい。なお、圧下量を0.4mm以上とすると、介在物が母相にさらに高度に密着するため、さらに好ましい。 Further, as for the amount of reduction in pressing the mold against the work, the larger the amount, the higher the hydrostatic pressure stress, and the more the inclusions can be securely adhered to the parent phase by crushing the gap. Specifically, when the rolling amount is less than 0.27 mm, the compressive hydrostatic stress may be less than 200 MPa, and voids may remain and the inclusions may not adhere to the matrix. For this reason, the amount of reduction is preferably 0.27 mm or more. In addition, it is more preferable that the amount of reduction is 0.4 mm or more, because the inclusions adhere to the matrix more highly.
このように、鍛造工程では、鍛造温度と圧下量との関係を好適な範囲に限定することで、硬質介在物周りの空隙を確実に潰し、さらには当該介在物を母相に密着させることができる。 Thus, in the forging process, by limiting the relationship between the forging temperature and the amount of reduction to a suitable range, the gap around the hard inclusion is reliably crushed, and furthermore, the inclusion can be brought into close contact with the matrix. it can.
(B)マルテンサイト生成工程
次に、マルテンサイト生成工程では、上記のように転動溝が形成されたワークの組織をマルテンサイト主体の組織とする。ここで、マルテンサイト主体の組織とは、ワークの組織のうちマルテンサイトが最も多く含まれる組織を意味する。
(B) Martensite generation step Next, in the martensite generation step, the structure of the work in which the rolling grooves are formed as described above is a structure mainly composed of martensite. Here, the organization mainly composed of martensite means an organization in which martensite is most contained among the organization of the work.
マルテンサイト生成工程としては、(1)ダイレクトクエンチ、(2)徐冷及び焼き入れ焼き戻し、並びに(3)ダイクエンチ等を採用することができる。なお、徐冷後の焼き入れ焼き戻しにより、ワークの強度確保及び焼割れ防止を図ることができる。 As the martensite generation step, (1) direct quench, (2) slow cooling and quenching and tempering, and (3) die quench can be employed. The quenching and tempering after slow cooling can ensure the strength of the work and prevent quenching.
ここで、徐冷とは、鍛造後のワークを例えば空冷することが含まれる。また、ダイレクトクエンチとは、鍛造後のワークが熱いうち(変態が始まる前)に水や油で焼き入れる熱処理方法であれば、いかなる熱処理方法も含む概念である。また、ダイクエンチとは、鍛造後、ワークに金型を押し当てたままワークを抜熱する熱処理方法であれば、いかなる熱処理方法も含む概念である。 Here, the slow cooling includes, for example, air cooling the forged work. Further, the direct quench is a concept including any heat treatment method as long as the work after forging is quenched with water or oil while hot (before the transformation starts). In addition, the die quench is a concept including any heat treatment method as long as it is a heat treatment method that removes heat from a work after pressing a mold against the work after forging.
特にダイクエンチを採用した場合には、以下の利点がある。即ち、鍛造後、金型を下死点で停止させ、ワークに押し付けたまま冷却すると、ワークの金型と接触した面は金型により抜熱急冷され、ワークに形成された軌道面付近は80%以上がマルテンサイトとなる。このようなダイクエンチにより、熱処理歪が軽減され、母相は静水圧応力が掛けられたままの状態で、オーステナイトからマルテンサイトに変態する。従って、変態時に変態塑性が生じ、硬質介在物周りの空隙がより高いレベルで減少し、母相と硬質介在物との間の密着性が極めて向上する。 In particular, when the die quench is adopted, there are the following advantages. That is, after forging, the die is stopped at the bottom dead center, and cooled while being pressed against the work, the surface of the work in contact with the die is extracted and quenched by the die, and the vicinity of the raceway surface formed on the work is 80%. % Or more becomes martensite. Such die quenching reduces heat treatment strain and transforms the parent phase from austenite to martensite while hydrostatic stress is applied. Therefore, transformation plasticity occurs during transformation, the voids around the hard inclusions are reduced at a higher level, and the adhesion between the matrix and the hard inclusions is significantly improved.
ここで、鍛造時の加熱温度T2(℃)とダイクエンチ終了温度T3(℃)と鍛造時の加熱時間t(hr)が下記式を満足するように、ダイクエンチを行うことが好ましい。
T3<4.17×10−3T2 2−8.18T2−15.7log10(t)−2.98×103/t/T2+4142 (4)
Here, it is preferable to perform the die quench so that the heating temperature T 2 (° C.) during forging, the die quench end temperature T 3 (° C.), and the heating time t (hr) during forging satisfy the following formula.
T 3 <4.17 × 10 -3 T 2 2 -8.18T 2 -15.7log 10 (t) -2.98 × 10 3 / t / T 2 +4142 (4)
上記式を満たすようにダイクエンチを行うことで、マルテンサイト変態開始温度以下の温度にまでワークが急冷されることにより、ワークに形成された軌道面付近は85%以上がマルテンサイトとなる。これにより、変態時に変態塑性がさらに生じ、硬質介在物周りの空隙が著しく高いレベルで減少し、母相と硬質介在物との間の密着性がさらに向上する。 By performing the die quench so as to satisfy the above equation, the work is rapidly cooled to a temperature equal to or lower than the martensite transformation start temperature, so that 85% or more of the vicinity of the raceway surface formed on the work becomes martensite. Thereby, transformation plasticity further occurs during transformation, the voids around the hard inclusions are reduced at a remarkably high level, and the adhesion between the matrix and the hard inclusions is further improved.
なお、ワークとして高炭素クロム軸受鋼鋼材(SUJ2)を用いた場合、鍛造時のワークが930℃で1時間の加熱であればマルテンサイト変態開始温度(Ms点)は150℃程度であり、840℃で1時間の加熱であればMs点は230℃程度となる。これは加熱温度が高いほど球状化セメンタイトが固溶して母相の炭素濃度が増加し、マルテンサイト変態温度が低下することが原因である。このため、耐摩耗性の観点からワークの加熱温度を840℃以下として、球状化セメンタイトの固溶が少ない状態で転動溝を形成することが好ましい。特に、ダイクエンチを採用する場合には、金型温度を100℃以下に保持する必要があり、鍛造、ダイクエンチを繰り返す場合には、金型を水冷する必要がある。 When a high carbon chromium bearing steel material (SUJ2) is used as the work, if the work at the time of forging is heated at 930 ° C. for 1 hour, the martensite transformation start temperature (Ms point) is about 150 ° C., and 840 If the heating is performed at 1 ° C. for 1 hour, the Ms point is about 230 ° C. This is because the higher the heating temperature, the higher the spheroidized cementite solid solution, the higher the carbon concentration of the matrix, and the lower the martensitic transformation temperature. For this reason, from the viewpoint of abrasion resistance, it is preferable to set the heating temperature of the work to 840 ° C. or lower and form the rolling grooves in a state where the solid solution of the spheroidized cementite is small. In particular, when a die quench is adopted, the mold temperature must be kept at 100 ° C. or lower, and when forging and die quench are repeated, the mold needs to be water-cooled.
また、ダイレクトクエンチを採用する場合、徐冷と焼き入れ焼き戻しを採用する場合、及びダイクエンチを採用する場合のいずれについても、ワークの組織がマルテンサイト主体の組織となった後に、鍛造加工部位の表面に対してラッピング加工を施すことで、当該表面の粗度を調整することが好ましい。 Also, in any of the case of employing direct quench, the case of employing slow cooling and quenching and tempering, and the case of adopting die quench, after the structure of the work becomes a structure mainly composed of martensite, the forged part is formed. It is preferable to adjust the roughness of the surface by performing a lapping process on the surface.
以上に示した本実施形態のスラスト型玉軸受の軌道面作製方法では、鍛造という圧縮静水圧応力の上昇が一瞬にして実現される状況下において、玉軸受の軌道面を作製することができる。従って、本実施形態の方法によれば、従来のように鋼材を高温で長時間保持する必要がないため、当該軌道面を迅速に作製することができる。 In the method of manufacturing the raceway surface of the thrust ball bearing according to the present embodiment described above, the raceway surface of the ball bearing can be manufactured in a situation where the increase in the compressive hydrostatic stress, which is called forging, is realized instantaneously. Therefore, according to the method of the present embodiment, it is not necessary to hold the steel material at a high temperature for a long time as in the related art, so that the raceway surface can be quickly manufactured.
また、本実施形態のスラスト型玉軸受の軌道面作製方法では、鍛造温度と圧下量との関係に関する限定に起因して、硬質介在物周りの空隙を確実に潰し、さらには当該介在物を母相に密着させることができる。従って、本実施形態の方法によれば、玉軸受を高負荷条件下でも好適に使用することができ、ひいてはその長寿命化を図ることができる。 Further, in the method of manufacturing the raceway surface of the thrust ball bearing according to the present embodiment, due to the limitation on the relationship between the forging temperature and the rolling reduction, the gap around the hard inclusion is surely crushed, Can be in close contact with the phase. Therefore, according to the method of the present embodiment, the ball bearing can be suitably used even under a high load condition, and the life thereof can be extended.
以下に、実施例によって本発明の効果を実証する。 Hereinafter, the effects of the present invention will be demonstrated by examples.
表1の化学成分(単位は質量%)を有し、残部がFe及び不可避的不純物であるφ60のSUJ2丸棒圧延材を、球状化焼鈍し、外径52mm、内径72.2mm、厚さ5.5mmの試験片(ワーク)を切り出した。 Rolled material of SUJ2 round bar of φ60 having the chemical components shown in Table 1 (unit is% by mass) and the balance being Fe and inevitable impurities was spheroidized to obtain an outer diameter of 52 mm, an inner diameter of 72.2 mm and a thickness of 5 mm. A test piece (work) of 0.5 mm was cut out.
次に、このようにして得られたワークを鍛造した。鍛造は、鍛造試験機(負荷能力6000kN:AIDA製)を用い、凸部(曲率半径Rが4.76mmの円弧断面を有し、かつ環状である)を備える超硬(材質RF06)の上金型と、平板状の下金型とを用いて、ワークに軌道面(転動溝)を成形した。その後、ワークを室温まで冷却した。ワークの鍛造条件及び冷却条件を表2に示す。 Next, the work thus obtained was forged. Forging is carried out using a forging tester (load capacity: 6000 kN: manufactured by AIDA), and a top metal (material RF06) having a convex portion (having a circular arc cross section having a curvature radius R of 4.76 mm and being annular). A raceway surface (rolling groove) was formed on the work using a mold and a flat lower mold. Thereafter, the work was cooled to room temperature. Table 2 shows the forging conditions and cooling conditions of the work.
水準1、2、4〜10は、鍛造時に上金型を下死点で保持し、ワークをダイクエンチ終了温度まで冷却した(ダイクエンチ)後、160℃で1.5時間の焼戻し熱処理を行った。なお、水準6、9については、0.3mmの溝を切削加工により作製し、鍛造時の圧下量を0.3mmとすることにより、最終形状の溝深さを他の水準と同じ0.6mmとなるようにした。同様に水準7、8については、0.15mmの溝を切削加工により作成し、鍛造時の圧下量を0.45mmとすることにより、最終形状の溝深さを他の水準と同じ0.6mmとなるようにした。 For Levels 1, 2, 4 to 10, the upper die was held at the bottom dead center during forging, the work was cooled to the die quench end temperature (die quench), and then tempering heat treatment was performed at 160 ° C. for 1.5 hours. For Levels 6 and 9, a 0.3 mm groove was formed by cutting, and the rolling reduction during forging was set to 0.3 mm, so that the groove depth of the final shape was 0.6 mm, which was the same as other levels. It was made to become. Similarly, for Levels 7 and 8, a groove of 0.15 mm is formed by cutting, and the rolling reduction during forging is set to 0.45 mm, so that the groove depth of the final shape is 0.6 mm, which is the same as other levels. It was made to become.
水準3は、鍛造後ワークを空冷により室温まで冷却した後、840℃で30分加熱して60℃の油で焼入れ熱処理をし、さらに160℃で1.5時間の焼戻し熱処理を行った。水準4は、鍛造後ワークを60℃の油に浸漬して冷却した後、160℃で1.5時間の焼戻し熱処理を行った。 In Level 3, after forging, the work was cooled to room temperature by air cooling, heated at 840 ° C. for 30 minutes, quenched with 60 ° C. oil, and further tempered at 160 ° C. for 1.5 hours. In Level 4, after forging, the work was immersed in oil at 60 ° C., cooled, and then tempered at 160 ° C. for 1.5 hours.
いずれのワークも各々10枚ずつ作製し、仕上げ加工として転動溝をラッピング加工し、スラスト型転動疲労試験を行った。 Each of the workpieces was manufactured in a number of 10 pieces, and rolling grooves were wrapped as finishing processing, and a thrust rolling fatigue test was performed.
水準4については、10枚中2枚に反りが生じたていたため、水準4の転動疲労試験は8枚で行った。 As for Level 4, two out of 10 sheets were warped, so the Level 4 rolling fatigue test was performed on 8 sheets.
転動疲労試験の条件は、3/8inch径のSi3N4製転動球を3球用い、荷重8.5kNで行った。転動疲労試験は1.5×108サイクルを耐久とした。その結果を図6に示す。 The conditions of the rolling fatigue test were performed using three rolling balls made of Si 3 N 4 having a / inch diameter and a load of 8.5 kN. The rolling fatigue test endured 1.5 × 10 8 cycles. FIG. 6 shows the result.
図6から明らかなように、鍛造温度と圧下量の関係を本願所定の範囲とした水準1〜7のワークについては、いわゆるワイブル値(例えば、L50寿命及びL10寿命)が優れた値を示している。これは、水準1〜7については、軌道面直下において介在物と母材間とを密着させることができ、玉軸受を高負荷条件下でも好適に使用することができるためである。 As is clear from FIG. 6, so-called Weibull values (for example, L50 life and L10 life) show excellent values for works of levels 1 to 7 in which the relationship between the forging temperature and the amount of reduction is within the predetermined range of the present application. I have. This is because, for Levels 1 to 7, the inclusions and the base material can be brought into close contact with each other immediately below the raceway surface, and the ball bearing can be suitably used even under high load conditions.
これに対し、鍛造温度又は圧下量が本願所定の範囲内にない水準8、9については、上記ワイブル値が優れた値を示していない。これは、水準8、9については、軌道面直下において介在物と母材間とを密着させることが不十分で、玉軸受を高負荷条件下で好適に使用するには至っていないためである。 On the other hand, for the levels 8 and 9 in which the forging temperature or the rolling reduction is not within the predetermined range in the present application, the Weibull value does not show an excellent value. This is because, for Levels 8 and 9, it is insufficient to closely contact the inclusions and the base material immediately below the raceway surface, and the ball bearings have not been suitably used under high load conditions.
一方、水準10ではダイクエンチ終了温度が高く、ワークに形成された軌道面付近のマルテンサイト分率が不十分であったため、疲労寿命が低下している。 On the other hand, at level 10, the die quench end temperature is high, and the martensite fraction near the raceway surface formed on the work is insufficient, so that the fatigue life is reduced.
Claims (7)
鍛造時の鍛造温度T1(℃)と円環状の凸型を有する金型の押し込み量D(mm)とが下記式を満足するように、ワークに対して前記金型を押し付けて、転動溝を形成する鍛造工程と、
前記転動溝が形成されたワークの組織をマルテンサイト主体の組織とするマルテンサイト生成工程と、
を含むことを特徴とする、スラスト型球軸受の軌道面作製方法。
T1<−400D2+752D+664 (1) A method for producing a raceway surface of a thrust type ball bearing using an annular work having austenite as a main phase,
The die is pressed against a work and rolled so that the forging temperature T 1 (° C.) during forging and the amount of press D (mm) of the die having an annular convex shape satisfy the following formula. Forging process to form a groove,
A martensite generation step of making the structure of the work in which the rolling grooves are formed a structure mainly composed of martensite,
A method for manufacturing a raceway surface of a thrust ball bearing, comprising:
T 1 <−400D 2 + 752D + 664 (1)
T3<4.17×10−3T2 2−8.18T2−15.7log10(t)−2.98×103/t/T2+4142 (2) As during forging heating temperature T 2 (° C.) and die quenching end temperature T 3 (° C.) and heating time during forging t (hr) satisfy the following equation, performs die-quenching, thrust-type of claim 4 How to make ball bearing raceway surface.
T 3 <4.17 × 10 -3 T 2 2 -8.18T 2 -15.7log 10 (t) -2.98 × 10 3 / t / T 2 +4142 (2)
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