JP2012214892A - Bearing ring of rolling bearing and method for producing the same, and rolling bearing - Google Patents
Bearing ring of rolling bearing and method for producing the same, and rolling bearing Download PDFInfo
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Abstract
Description
本発明は、転がり軸受の軌道輪であって圧延鋼板を素材として作製されるもの、およびその製造法、並びに前記軌道輪を用いた転がり軸受に関する。ここでいう軌道輪は、ラジアル軸受では内輪、外輪に相当し、スラスト軸受では軌道盤に相当する。 The present invention relates to a bearing ring for a rolling bearing that is manufactured using a rolled steel plate as a raw material, a manufacturing method thereof, and a rolling bearing using the bearing ring. The bearing ring here corresponds to an inner ring and an outer ring in a radial bearing, and corresponds to a bearing disc in a thrust bearing.
転がり軸受は自動車や産業機械をはじめとする各種機械の回転部分において、荷重を支える重要な部品として使用されている。転がり軸受には大きく分けてラジアル軸受とスラスト軸受がある。ラジアル軸受は環状部品である内輪および外輪の間を転動体が転がる構造を有し、スラスト軸受は２枚の軌道盤の間を転動体が転がる構造を有する。これら内輪、外輪および軌道盤はいずれも、表面上に転動体が転がる走路を有しており、この走路は「軌道」と呼ばれる。本明細書では軌道を持つ転がり軸受の部品を「軌道輪」という。軌道輪は通常、鋼製の部品である。 Rolling bearings are used as important parts for supporting loads in rotating parts of various machines including automobiles and industrial machines. Rolling bearings are roughly classified into radial bearings and thrust bearings. The radial bearing has a structure in which a rolling element rolls between an inner ring and an outer ring, which are annular parts, and the thrust bearing has a structure in which the rolling element rolls between two raceways. Each of these inner ring, outer ring, and trackway has a runway on which rolling elements roll, and this runway is called a “track”. In this specification, a rolling bearing part having a raceway is referred to as a “race ring”. The race is usually a steel part.
転がり軸受の軌道輪は転動体から高い負荷荷重を繰り返し付与される条件下で使用される。そのため軌道輪を構成する鋼材には優れた強度、耐摩耗性および転動疲労特性が要求される。このうち、特に転動疲労特性に関しては鋼中に存在するＡｌ2Ｏ3、ＭｎＳ、ＴｉＮ等の非金属介在物が悪影響を及ぼすことが知られている。これらの介在物は疲労破壊の起点となることから、軌道輪の材料としてはできるだけ清浄度の高い（介在物の少ない）鋼材を使用することが重要であるとされる。すなわち、鋼の高清浄度化が転動疲労特性を向上させるための主要な技術となっている。 The bearing ring of the rolling bearing is used under a condition in which a high load is repeatedly applied from the rolling element. Therefore, excellent strength, wear resistance, and rolling fatigue characteristics are required for the steel material constituting the race. Among these, it is known that non-metallic inclusions such as Al 2 O 3 , MnS, and TiN present in steel have an adverse effect particularly on rolling fatigue characteristics. Since these inclusions become the starting point of fatigue failure, it is considered important to use a steel material having a cleanliness as high as possible (having few inclusions) as a material for the race. That is, increasing the cleanliness of steel is a major technique for improving rolling fatigue characteristics.
例えば特許文献１には、Ｍｎ含有量を０.２０％以下に規制した軸受鋼を母材として、これを電子ビームで溶融させて粒径の大きい非金属介在物を浮上分離させ、鋼中の非金属介在物の直径を１５μｍ以下とする超高清浄度軸受用鋼の製造技術が開示されている。また、特許文献２には、非金属介在物の量や大きさのみならず組成を制御することで転動疲労特性の化善を図る技術が開示されている。 For example, in Patent Document 1, a bearing steel whose Mn content is regulated to 0.20% or less is used as a base material, and this is melted by an electron beam to float and separate non-metallic inclusions having a large particle size. Techniques for manufacturing ultra-high cleanliness bearing steel in which the diameter of non-metallic inclusions is 15 μm or less are disclosed. Patent Document 2 discloses a technique for improving the rolling fatigue characteristics by controlling the composition as well as the amount and size of nonmetallic inclusions.
上述のように、軸受部品の転動疲労特性を向上させるためには、これまで材料である鋼材の清浄度を高めることや、非金属介在物の組成を制御することに主眼が置かれていた。しかしながら、高清浄度鋼を溶製するには製鋼工程で脱酸や不純物低減などに高負荷を要し、製造時間も長くなる。また特殊な手法で非金属介在物の量や形態を制御するためには高価な設備が必要となる。すなわち、従来、軸受部品である軌道輪の転動疲労特性を向上させるためには生産性の低下や製造コストの増大を余儀なくされていた。 As described above, in order to improve the rolling fatigue characteristics of bearing parts, the main focus has been on increasing the cleanliness of steel materials and controlling the composition of non-metallic inclusions. . However, in order to melt high cleanliness steel, a high load is required for deoxidation and impurity reduction in the steel making process, and the production time is also long. Moreover, expensive equipment is required to control the amount and form of non-metallic inclusions by a special method. That is, conventionally, in order to improve the rolling fatigue characteristics of the bearing ring which is a bearing component, productivity has been reduced and manufacturing costs have been increased.
また、軌道輪などの軸受部品は、丸棒形状の鋼材（棒鋼）から切り出して作製されることが一般的である。この場合、プレス成形による連続工程を適用することが難しく、鋼板を素材とする部品と比べ生産性に劣る。 Further, bearing parts such as bearing rings are generally manufactured by cutting out from a round bar-shaped steel material (bar steel). In this case, it is difficult to apply a continuous process by press molding, and the productivity is inferior compared to a part made of a steel plate.
一方、近年では自動車の軽量化や低燃費化のニーズが高まり、それに対応するため転がり軸受にも部品の小型・軽量化および更なる高性能化が求められるようになっている。すなわち、自動車等に使用される軸受の使用環境は従来よりも過酷化する傾向にあり、軸受部品に高清浄度鋼を用いても軸受寿命に関する信頼性が十分に確保できないことも懸念されるようになってきた。 On the other hand, in recent years, there has been a growing need for lighter vehicles and lower fuel consumption, and in order to meet these needs, rolling bearings are required to be smaller, lighter and have higher performance. That is, the usage environment of bearings used in automobiles and the like tends to be harsher than before, and there is a concern that reliability related to bearing life cannot be sufficiently secured even if high cleanliness steel is used for bearing parts. It has become.
本発明はこのような現状に鑑み、清浄度がそれほど高くない鋼材を用いた場合でも、転動疲労特性の大幅な低下が生じず実用的な耐久性が得られる低コストの転がり軸受の軌道輪を提供しようというものである。 In view of such a current situation, the present invention is a low-cost rolling bearing bearing ring that can achieve practical durability without causing a significant decrease in rolling fatigue characteristics even when a steel material that is not so clean is used. Is to provide.
発明者らは詳細な研究の結果、圧延鋼板を素材に用いて軌道の表面と圧延方向とのなす角度が適正範囲となるように成形加工した軌道輪において、上記目的が達成できることを見出した。さらに、介在物の分布形態を適性化した場合には、清浄度が一般的レベルである鋼を用いても高清浄度鋼の丸棒を素材とする従来の軌道輪より優れた転動疲労特性が実現できることを見出した。本発明はこれらの知見に基づいて完成したものである。 As a result of detailed studies, the inventors have found that the above object can be achieved in a race ring formed by using a rolled steel plate as a raw material so that the angle formed between the raceway surface and the rolling direction is within an appropriate range. Furthermore, when the distribution form of inclusions is optimized, rolling fatigue characteristics superior to conventional races made of round bars of high cleanliness steel, even when using steel with a general cleanliness level It was found that can be realized. The present invention has been completed based on these findings.
すなわち本発明では、質量％で、Ｃ：０.０２〜１.２０％、Ｓｉ：０.０２〜２.００％、Ｍｎ：０.１０〜１.５０％、Ｐ：０.００１〜０.０３０％、Ｓ：０.０００５〜：０.０３０％、Ｃｒ：０.０２〜２.００％、Ｏ：０.０００１〜０.００３０％を含有し、必要に応じてさらにＮｉ：２.００％以下、Ｍｏ：０.５０％以下、Ｖ：０.５０％以下、Ｎｂ：０.５０％以下、Ｔｉ：０.２５％以下、Ｂ：０.００５０％以下の１種以上を含有し、残部がＦｅおよび不可避的不純物である組成を有する圧延鋼板から加工された材料からなり、その圧延鋼板の板面に由来する表面（「圧延板面由来表面」という）を軌道面に持つ転がり軸受の軌道輪が提供される。Ｏ含有量については、特段に低減することなく、例えば０.００１０〜０.００３０％としてもよい。 That is, in the present invention, C: 0.02-1.20%, Si: 0.02-2.00%, Mn: 0.10-1.50%, P: 0.001-0. 030%, S: 0.0005-: 0.030%, Cr: 0.02 to 2.00%, O: 0.0001 to 0.0003%, and if necessary, Ni: 2.00 % Or less, Mo: 0.50% or less, V: 0.50% or less, Nb: 0.50% or less, Ti: 0.25% or less, B: 0.0050% or less, A rolling bearing comprising a material processed from a rolled steel sheet having a composition in which the balance is Fe and inevitable impurities, and having a surface derived from the plate surface of the rolled steel plate (referred to as a “rolled plate surface-derived surface”) as a raceway surface. A raceway is provided. About O content, it is good also as 0.0001 to 0.0003%, for example, without reducing especially.
また、上記の組成を有する圧延鋼板から加工された材料からなり、その圧延鋼板の板面に由来する表面（「圧延板面由来表面」という）を除去加工して形成した軌道面を有し、軌道面上の任意の点Ａにおける軌道面の法線と、除去加工前の圧延板面由来表面上の最も点Ａに近い点における当該圧延板面由来表面の法線とのなす角度が０〜４５°の範囲にある転がり軸受の軌道輪が提供される。圧延板面由来表面からの除去加工深さは当該圧延鋼板の板厚の３／１０以内とすることがより効果的である。 Moreover, it consists of the material processed from the rolled steel plate which has said composition, and has the track surface formed by removing the surface derived from the plate surface of the rolled steel plate (referred to as "rolled plate surface-derived surface"), The angle formed between the normal line of the raceway surface at an arbitrary point A on the raceway surface and the normal line of the surface derived from the rolled plate surface at the point closest to the point A on the surface of the rolled plate surface before removal processing is 0 to Rolling bearing raceways in the range of 45 ° are provided. It is more effective that the removal depth from the surface of the rolled plate surface is within 3/10 of the thickness of the rolled steel plate.
ここで、「軌道面」とは、軌道の表面（すなわち転動体と接触する部分の表面）を意味する。圧延鋼板とは、熱延鋼板または冷延鋼板を意味する。圧延鋼板を円筒状にプレス成形したのち底部を打ち抜いてリング状に加工した材料の場合、当該材料の円筒表面は「圧延板面由来表面」に該当する。ラジアル軸受の内輪・外輪の場合は、必要に応じてこの円筒状リングの表面に切削、研磨等の除去加工を施すことによって、所定形状の軌道面が形成される。 Here, the “track surface” means the surface of the track (that is, the surface of the portion in contact with the rolling element). The rolled steel sheet means a hot rolled steel sheet or a cold rolled steel sheet. In the case of a material obtained by pressing a rolled steel plate into a cylindrical shape and then punching the bottom portion into a ring shape, the cylindrical surface of the material corresponds to the “rolled plate surface-derived surface”. In the case of the inner and outer rings of the radial bearing, a raceway surface having a predetermined shape is formed by performing removal processing such as cutting and polishing on the surface of the cylindrical ring as necessary.
特に優れた転動疲労特性を実現するためには、圧延鋼板として、下記に定義される介在物配列指数Ｋが１.０以下に調整されたものを採用することができる。
〔介在物配列指数Ｋ〕
鋼板の圧延方向および板厚方向に平行な断面（Ｌ断面）において、一辺の長さが板厚方向に３.０ｍｍ以上（板厚が３.０ｍｍ未満の場合は板厚全長）であり面積Ｓ（ｍｍ2）が３０ｍｍ2以上である矩形領域を設定し、その矩形領域内に粒子の全体または一部が存在する介在物粒子のうち板厚方向最大長さが１μｍ以上のものを測定対象粒子とし、板厚方向端部のいずれか一方の鋼板表面を「基準面」と定めるとき、前記矩形領域内において、各測定対象粒子について基準面側の当該粒子表面から基準面側への板厚方向距離が６０μｍ以下の範囲に粒子表面（前記矩形領域内にあるもの限る）が位置する他の測定対象粒子の数Ｘ（個）を測定し、全測定対象粒子についてのＸの総和ＸALL（個）を求め、ＸALLを矩形領域の面積Ｓ（ｍｍ2）で除した値（個／ｍｍ2）を介在物配列指数Ｋとする。
In order to realize particularly excellent rolling fatigue characteristics, it is possible to employ a rolled steel sheet whose inclusion arrangement index K defined below is adjusted to 1.0 or less.
[Inclusion sequence index K]
In a cross section (L cross section) parallel to the rolling direction and the plate thickness direction of the steel plate, the length of one side is 3.0 mm or more in the plate thickness direction (when the plate thickness is less than 3.0 mm), the area S A rectangular region having (mm 2 ) of 30 mm 2 or more is set, and inclusion particles having a maximum length in the thickness direction of 1 μm or more among inclusion particles in which all or part of the particles are present in the rectangular region are measured particles When the steel plate surface at either end in the plate thickness direction is defined as a “reference plane”, the plate thickness direction from the particle surface on the reference plane side to the reference plane side for each measurement target particle in the rectangular region The number X (number) of other measurement target particles whose particle surfaces (limited to those within the rectangular area) are located within a distance of 60 μm or less is measured, and the total X of all measurement target particles X ALL (numbers) ) is obtained, dividing the X ALL in the area of the rectangular area S (mm 2) Value (the number / mm 2) and inclusions sequence index K.
圧延鋼板から軌道輪へ加工するに際し、プレス成形によりリング状に加工する工程を経ることができる。プレス成形には金型を用いて円筒状に絞るプレス加工や、プレス打抜き加工などが含まれる。 When processing from a rolled steel plate to a raceway, a step of processing into a ring shape by press forming can be performed. The press molding includes press working that uses a mold to form a cylinder and press punching.
また本発明では、上記の軌道輪を部品に用いた転がり軸受が提供される。 In the present invention, a rolling bearing using the above-described raceway ring as a component is provided.
本発明の転がり軸受の軌道輪は、圧延鋼板を素材に用いるものであることから、棒鋼を加工して得られる従来一般的な軌道輪よりも大量生産に適している。また、同等の清浄度を有する棒鋼を素材に用いた軌道輪と比べ、転動疲労特性が良好である。さらに、非金属介在物の分布形態をコントロールした圧延鋼板を素材に用いた軌道輪では、特段に高清浄化された鋼を用いなくても、従来の高清浄度鋼の棒鋼を用いたものより優れた転動疲労特性を実現することができる。したがって本発明は、転がり軸受の低コスト化および信頼性向上に寄与するものである。 Since the bearing ring of the rolling bearing of the present invention uses a rolled steel plate as a raw material, it is more suitable for mass production than a conventional ordinary bearing ring obtained by processing a bar steel. In addition, rolling fatigue characteristics are better as compared with a race using a steel bar having the same cleanliness as a material. In addition, the bearing rings using rolled steel sheets with controlled distribution of non-metallic inclusions are superior to those using conventional high-clean steel bars without using specially high-purity steel. Rolling fatigue characteristics can be realized. Therefore, the present invention contributes to cost reduction and reliability improvement of the rolling bearing.
図１に、従来の棒鋼から切り出した円板について、内部に存在する非金属介在物の存在形態を表す光学顕微鏡写真を示す。円板は、軌道輪の素材部品を採取する場合と同様に、肉厚方向が棒鋼の長手方向に一致するように切り出した。（ａ）は円板の表面、（ｂ）は円板の肉厚方向に平行な断面（写真の上下方向が円板肉厚方向）である。これらの写真からわかるように、棒鋼から切り出した円板では、非金属介在物（黒っぽく見える粒子）は肉厚方向に伸ばされて分布している。この場合、肉厚方向に平行な断面をどのように選んでも、基本的に同様の介在物分布形態が観察される。この円板から例えばリングを切り出してスラスト軸受の軌道輪（軌道盤）として使用する場合には、転動体から受ける荷重の方向は介在物の展伸方向に対して平行となる。このような場合、疲労き裂は展伸している介在物の並びに沿って発生することがこれまでの調査によって確かめられている。 FIG. 1 shows an optical micrograph showing the existence form of nonmetallic inclusions present in a disc cut from a conventional steel bar. The disk was cut out so that the thickness direction coincided with the longitudinal direction of the steel bar, as in the case of collecting the material parts of the race. (A) is the surface of a disk, (b) is a cross section parallel to the thickness direction of a disk (the up-down direction of a photograph is a disk thickness direction). As can be seen from these photographs, in the disk cut out from the steel bar, non-metallic inclusions (particles that look dark) are stretched and distributed in the thickness direction. In this case, basically the same inclusion distribution form is observed no matter how the cross section parallel to the thickness direction is selected. When, for example, a ring is cut out from this disc and used as a bearing ring (bearing disc) of a thrust bearing, the direction of the load received from the rolling element is parallel to the extending direction of the inclusions. In such a case, it has been confirmed by previous investigations that fatigue cracks occur along a line of extending inclusions.
図２に、本発明の対象となる圧延鋼板から切り出した円板について、内部に存在する非金属介在物の存在形態を表す光学顕微鏡写真を示す。円板は、圧延鋼板をプレス打抜きすることによって採取した。（ａ）は円板の表面、（ｂ）は円板の肉厚方向および圧延方向に平行な断面（写真の上下方向が円板肉厚方向、左右方向が圧延方向）である。これらの写真からわかるように、圧延鋼板から採取した円板では、非金属介在物（黒っぽく見える粒子）は肉厚方向に対し垂直方向（すなわち圧延方向）に伸ばされて分布している。発明者らの研究によれば、このような円板の表面を軌道面として転動実験を行った場合、図１に示したような介在物分布形態の場合と比べ、転動疲労特性が顕著に向上することがわかった。そのメカニズムについては現時点で必ずしも明確でないが、介在物を起点とするき裂が肉厚方向に繋がりにくいことが要因として挙げられる。 In FIG. 2, the optical micrograph showing the presence form of the nonmetallic inclusion which exists inside is shown about the disk cut out from the rolled steel plate used as the object of this invention. The disc was collected by press punching a rolled steel plate. (A) is the surface of a disk, (b) is the thickness direction of a disk, and a cross section parallel to a rolling direction (the up-down direction of a photograph is a disk thickness direction, and the left-right direction is a rolling direction). As can be seen from these photographs, non-metallic inclusions (particles that look dark) are distributed in a direction perpendicular to the thickness direction (that is, in the rolling direction) in the disk collected from the rolled steel sheet. According to the research by the inventors, when a rolling experiment is performed using the surface of such a disk as a raceway surface, the rolling fatigue characteristics are remarkable as compared to the inclusion distribution form as shown in FIG. It turned out to improve. The mechanism is not necessarily clear at the present time, but it is possible that the crack starting from the inclusion is difficult to connect in the thickness direction.
圧延鋼板を素材としてラジアル軸受の軌道輪（内輪、外輪）を作製する場合を想定すると、プレスにより円筒状に成形した後、底部を打ち抜いてリング状とする工程を採用することが合理的であると考えられる。この場合、前述のように、リングの表面は圧延鋼板の表面に由来する面（「圧延板面由来表面」）となるので、非金属介在物の展伸方向はリング表面と常に平行となる。また、そのリングに切削、研磨等の除去加工を施して玉軸受や円錐ころ軸受の軌道輪を作製する場合でも、非金属介在物の展伸方向と軌道面とのなす角度は通常９０°よりも０°に近い角度となる。したがって、圧延鋼板からプレス成形加工したラジアル軸受の軌道輪についても、展伸している介在物の並びに沿って疲労き裂が肉厚方向に進行しやすいという図１に示したサンプル（介在物の展伸方向と軌道面のなす角度が９０°）に典型的に見られる転動疲労き裂の進行は、顕著に軽減される。 Assuming the case of producing radial bearing race rings (inner and outer rings) using rolled steel as a raw material, it is reasonable to adopt a process of forming a ring shape by punching the bottom after forming it into a cylindrical shape by pressing. it is conceivable that. In this case, as described above, the surface of the ring is a surface derived from the surface of the rolled steel plate (“rolled plate surface-derived surface”), so that the extending direction of the nonmetallic inclusions is always parallel to the ring surface. Even when the ring is subjected to removal processing such as cutting and polishing to produce a bearing ring for a ball bearing or a tapered roller bearing, the angle formed between the extending direction of the non-metallic inclusion and the raceway surface is usually more than 90 °. Is also close to 0 °. Therefore, the radial bearing raceway formed by pressing from a rolled steel plate also has the sample shown in FIG. 1 in which fatigue cracks tend to progress in the thickness direction along the stretch of inclusions. The progression of rolling fatigue cracks typically seen in the extension direction and the raceway angle of 90 °) is significantly reduced.
圧延鋼板から加工された材料において、非金属介在物の展伸方向は圧延板面由来表面に平行となる。発明者らの詳細な検討によれば、圧延板面由来表面を軌道面に持つ転がり軸受の軌道輪は、転動疲労特性の改善に極めて有利であることがわかった。圧延板面由来表面に切削、研磨等の除去加工を施すことにより形成した軌道面の場合、軌道面上の任意の点（その点を点Ａとする）における軌道面の法線と、除去加工前の圧延板面由来表面上の最も点Ａに近い点における当該圧延板面由来表面の法線とのなす角度（この角度を以下単に「軌道面の法線と圧延板面由来表面の法線とのなす角度」ということがある）が、軌道面上どの位置にある点Ａにおいても０〜４５°の範囲にあることが転動疲労特性の改善に有効であり、０〜３０°であることがより好ましい。このような軌道輪は、棒鋼から加工された従来のものと比べ、清浄度が同レベルであれば転動疲労特性は顕著に向上する。 In the material processed from the rolled steel sheet, the extending direction of the non-metallic inclusion is parallel to the surface derived from the rolled sheet surface. According to detailed examinations by the inventors, it has been found that a bearing ring of a rolling bearing having a rolling plate surface-derived surface as a raceway surface is extremely advantageous for improving rolling fatigue characteristics. In the case of a raceway surface formed by performing removal processing such as cutting and polishing on the surface derived from the rolled plate surface, the normal of the raceway surface at any point on the raceway surface (this point is point A) and removal processing The angle formed by the normal of the surface from the rolled plate surface at the point closest to the point A on the surface from the previous rolled plate surface (this angle is hereinafter simply referred to as “the normal of the raceway surface and the normal of the surface of the rolled plate surface”). Is at a point A at any position on the raceway surface, it is effective for improving rolling fatigue characteristics, and is 0 to 30 °. It is more preferable. Such a bearing ring has a significantly improved rolling fatigue characteristic when the cleanliness is the same as that of a conventional one processed from a steel bar.
軌道輪の材料中における介在物の分布状態に着目すると、軌道面に近い表層部での介在物の存在密度が小さいことが転動疲労特性の向上に効果的である。発明者らの検討によれば、圧延板面由来表面に切削、研磨等の除去加工を施すことにより軌道面を形成する場合、軌道面に近い表層部の介在物存在密度を低減するためには、軌道面が圧延板面由来表面からできるだけ浅い位置になるように除去加工深さを調整することが望ましい。圧延鋼板は通常、連続鋳造スラブを熱間圧延し、さらに必要に応じて冷間圧延することによって所定板厚に調整される。転動疲労特性に影響を与える硫化物等の粗大な非金属介在物は鋳造スラブ中において肉厚中央付近に多く分布し、表面から浅い部分には少ない。圧延鋼板中の介在物分布も鋳造スラブ中の介在物分布を反映したものとなる。そのため、軌道面ができるだけ圧延鋼板の表層部付近に位置するように除去加工を施すことが転動疲労特性の向上に有効となる。詳細な検討の結果、圧延板面由来表面からの除去加工深さを当該圧延鋼板の板厚の３／１０以内に管理することによって、転動疲労特性を大幅に向上させることができる。２／１０以内に管理することがより効果的である。 Focusing on the distribution of inclusions in the material of the raceway, the small presence density of inclusions in the surface layer near the raceway surface is effective in improving rolling fatigue characteristics. According to the studies by the inventors, when forming the raceway surface by performing removal processing such as cutting and polishing on the surface derived from the rolled plate surface, in order to reduce the inclusion density of the surface layer portion close to the raceway surface It is desirable to adjust the removal processing depth so that the raceway surface is as shallow as possible from the surface derived from the rolled plate surface. The rolled steel sheet is usually adjusted to a predetermined thickness by hot rolling a continuous cast slab and further cold rolling as necessary. Coarse non-metallic inclusions such as sulfides that affect rolling fatigue characteristics are distributed mostly in the vicinity of the center of the thickness in the cast slab, and few in the shallow part from the surface. The inclusion distribution in the rolled steel sheet also reflects the inclusion distribution in the cast slab. For this reason, it is effective to improve the rolling fatigue characteristics so that the raceway surface is located as close to the surface layer portion of the rolled steel sheet as possible. As a result of detailed investigation, the rolling fatigue characteristics can be greatly improved by managing the removal depth from the surface derived from the rolled sheet surface within 3/10 of the sheet thickness of the rolled steel sheet. It is more effective to manage within 2/10.
板厚１０ｍｍの圧延鋼板中に存在する硫化物系介在物の分布を調べた実験例を紹介する。
調査した鋼板は後述の表１に示す鋼Ｎｏ.１の連続鋳造スラブを熱間圧延により板厚１０ｍｍとしたものである。
図２１に、この鋼板の圧延方向に平行な断面（Ｌ断面）における試料採取位置を模式的に示す。圧延板面からの深さが（ａ）（ｂ）（ｃ）の各深さ位置からＬ断面の観察試料を採取し、光学顕微鏡により各深さ位置において板厚方向２.０ｍｍ×圧延方向２０ｍｍの視野を３０視野観察し、個々の硫化物系介在物について圧延方向長さを測定した。
An experimental example in which the distribution of sulfide inclusions present in a rolled steel sheet having a thickness of 10 mm is introduced.
The investigated steel sheet is a steel No. 1 continuous cast slab shown in Table 1 to be described later with a plate thickness of 10 mm by hot rolling.
FIG. 21 schematically shows a sampling position in a cross section (L cross section) parallel to the rolling direction of the steel sheet. An observation sample having an L cross section is taken from each of the depth positions (a), (b), and (c) from the rolled plate surface, and the thickness direction is 2.0 mm × the rolling direction is 20 mm at each depth position using an optical microscope. 30 fields of view were observed, and the length in the rolling direction was measured for each sulfide inclusion.
図２２に、各深さ位置における硫化物系介在物のサイズ分布を示す。サイズの小さい介在物は表層部付近（ａ）においても多数存在するが、圧延方向長さが５０μｍ以上の介在物は表層部に近いほど存在割合が大幅に減少する。軌道輪において軌道面に近い表層部にサイズの大きい介在物が多数存在していると、転動疲労特性に悪影響を及ぼしやすい。したがって、軌道面を除去加工によって形成する場合は、圧延板面由来表面からの除去加工深さが深くなりすぎないように管理することが有効である。 FIG. 22 shows the size distribution of sulfide inclusions at each depth position. Although many inclusions having a small size are present in the vicinity of the surface layer portion (a), the presence ratio of inclusions having a length in the rolling direction of 50 μm or more is significantly reduced as the surface layer portion is closer. If a large number of inclusions having a large size are present in the surface layer portion near the raceway surface in the race, the rolling fatigue characteristics are likely to be adversely affected. Therefore, when the raceway surface is formed by removal processing, it is effective to manage so that the removal processing depth from the surface derived from the rolled plate surface does not become too deep.
また、特に優れた転動疲労特性を実現するためには、上記の介在物配列指数Ｋが１.０以下に調整された圧延鋼板を素材に使用することが望ましい。
図３を用いて、介在物配列指数Ｋの定め方を説明する。介在物配列指数Ｋを定めるためには、鋼板の圧延方向および板厚方向に平行な断面（Ｌ断面）において、一辺の長さが板厚方向に３.０ｍｍ以上（板厚が３.０ｍｍ未満の場合は板厚全長）であり面積Ｓ（ｍｍ2）が３０ｍｍ2以上である矩形領域を設定する。また、板厚方向端部のいずれか一方の鋼板表面を「基準面」と定める。図３はＬ断面における当該矩形領域内の一部分を模式的に表したものである。図中、介在物粒子の大きさや数は説明の便宜のため誇張して描いてある。ここでは図の下側にある表面を「基準面」と定める。矩形領域内には種々の大きさの非金属介在物粒子が観察されるが、それらの介在物粒子のうち、当該矩形領域内に粒子の全体または一部が存在し、かつ板厚方向最大長さが１μｍ以上のものを測定対象粒子とする。粒子Ｂ１およびＣ３は、このＬ断面内に現れている板厚方向最大長さが１μｍ未満の粒子であるから、これらの介在物は無いものとして扱う。
In order to realize particularly excellent rolling fatigue characteristics, it is desirable to use a rolled steel sheet in which the inclusion arrangement index K is adjusted to 1.0 or less as a material.
The method for determining the inclusion arrangement index K will be described with reference to FIG. In order to determine the inclusion arrangement index K, the length of one side in the cross section (L cross section) parallel to the rolling direction and the plate thickness direction of the steel plate is 3.0 mm or more in the plate thickness direction (the plate thickness is less than 3.0 mm). In the case of ( 2 ), a rectangular region having a total plate thickness) and an area S (mm 2 ) of 30 mm 2 or more is set. In addition, one steel plate surface at the end in the thickness direction is defined as a “reference plane”. FIG. 3 schematically shows a part of the rectangular area in the L cross section. In the drawing, the size and number of inclusion particles are exaggerated for convenience of explanation. Here, the surface on the lower side of the figure is defined as a “reference plane”. Various sizes of non-metallic inclusion particles are observed in the rectangular region, and among these inclusion particles, all or part of the particles are present in the rectangular region and the maximum length in the thickness direction A particle having a length of 1 μm or more is defined as a measurement target particle. Since the particles B1 and C3 are particles having a plate length direction maximum length of less than 1 μm appearing in the L cross section, they are treated as having no inclusions.
今、測定対象粒子Ａ１に着目する。Ａ１の基準面側の粒子表面から基準面側への板厚方向距離が６０μｍ以下の範囲に他の測定対象粒子の表面（前記矩形領域内にあるもの限る）が存在するかどうかを調べると、粒子Ｃ１が該当する。粒子Ｄ１の表面までの距離は６０μｍを超えているため、該当する粒子はＣ１のみである。したがってこの場合、「粒子Ａ１の基準面側の表面から基準面側への板厚方向距離が６０μｍ以下の範囲に粒子表面が位置する他の測定対象粒子の数Ｘ」を求めるとＸ＝１となる。 Now, focus on the measurement target particle A1. When investigating whether or not the surface of other particles to be measured (limited to those in the rectangular region) exists in a range where the plate thickness direction distance from the particle surface on the reference surface side of A1 to the reference surface side is 60 μm or less, This corresponds to the particle C1. Since the distance to the surface of the particle D1 exceeds 60 μm, the corresponding particle is only C1. Therefore, in this case, when “the number X of other particles to be measured in which the particle surface is located in a range in which the thickness direction distance from the surface on the reference surface side to the reference surface side of the particle A1 is 60 μm or less” is obtained, X = 1. Become.
次に、測定対象粒子Ａ２に着目して、Ａ２の基準面側の粒子表面から基準面側への板厚方向距離が６０μｍ以下の範囲に他の測定対象粒子の表面（前記矩形領域内にあるもの限る）が存在するかどうかを調べると、粒子Ｂ２、Ｃ２、Ｃ４、Ｃ５の４個のみが該当する。この場合、「粒子Ａ２の基準面側の表面から基準面側への板厚方向距離が６０μｍ以下の範囲に粒子表面が位置する他の測定対象粒子の数Ｘ」を求めるとＸ＝４となる。 Next, paying attention to the measurement target particle A2, the surface of another measurement target particle (within the rectangular region) has a thickness direction distance from the particle surface on the reference plane side of A2 to the reference plane side of 60 μm or less. When it is examined whether or not there is a limit, only four particles B2, C2, C4, and C5 are applicable. In this case, when “the number X of other measurement target particles whose particle surfaces are located in a range where the distance in the plate thickness direction from the surface on the reference surface side to the reference surface side of the particle A2 is 60 μm or less” is obtained, X = 4. .
同様に、測定対象粒子Ｂ２に着目して、Ｂ２の基準面側の粒子表面から基準面側への板厚方向距離が６０μｍ以下の範囲に他の測定対象粒子の表面（前記矩形領域内にあるもの限る）が存在するかどうかを調べると、粒子Ｃ４、Ｃ５、Ｄ２の３個のみが該当する。この場合、「粒子Ｂ２の基準面側の表面から基準面側への板厚方向距離が６０μｍ以下の範囲に粒子表面が位置する他の測定対象粒子の数Ｘ」を求めるとＸ＝３となる。 Similarly, paying attention to the measurement target particle B2, the surface of another measurement target particle (within the rectangular region) has a thickness direction distance from the particle surface on the reference surface side of B2 to the reference surface side of 60 μm or less. When it is checked whether or not there is a limit, only three particles C4, C5, and D2 are applicable. In this case, when “the number X of other measurement target particles whose particle surface is located in a range where the distance in the plate thickness direction from the surface on the reference surface side to the reference surface side of the particle B2 is 60 μm or less” is obtained, X = 3. .
同様に、測定対象粒子Ｃ１に着目して、Ｃ１の基準面側の粒子表面から基準面側への板厚方向距離が６０μｍ以下の範囲に他の測定対象粒子の表面（前記矩形領域内にあるもの限る）が存在するかどうかを調べると、粒子Ｄ１のみが該当したとする。この場合、「粒子Ｃ１の基準面側の表面から基準面側への板厚方向距離が６０μｍ以下の範囲に粒子表面が位置する他の測定対象粒子の数Ｘ」を求めるとＸ＝１となる。 Similarly, paying attention to the measurement target particle C1, the surface of another measurement target particle (within the rectangular region) has a thickness direction distance from the particle surface on the reference plane side of C1 to the reference plane side of 60 μm or less. It is assumed that only the particle D1 is applicable. In this case, when “the number X of other measurement target particles whose particle surface is located in a range in which the distance in the plate thickness direction from the surface on the reference surface side to the reference surface side of the particle C1 is 60 μm or less” is obtained, X = 1. .
このようにして矩形領域内の全ての測定対象粒子について上記Ｘの値を測定し、それら各Ｘの総和ＸALL（個）を求め、ＸALLを矩形領域の面積Ｓ（ｍｍ2）で除した値（個／ｍｍ2）を介在物配列指数Ｋとする。この介在物配列指数Ｋが１.０以下である圧延鋼板を素材に使用すると、その鋼の清浄度が一般的なレベルであっても、高清浄度鋼からなる棒鋼を素材に使用した場合よりも優れた転動疲労特性を実現することが可能となる。介在物配列指数Ｋを小さくコントロールするためには、清浄度を高めること（脱酸を十分に行うこと）、トータル圧延率を大きくし軟質な介在物を小さくすることなどの手法が有効である。 In this way, the value of X is measured for all particles to be measured in the rectangular area, the total X ALL (number) of each X is obtained, and X ALL is divided by the area S (mm 2 ) of the rectangular area. The value (pieces / mm 2 ) is taken as the inclusion arrangement index K. When a rolled steel sheet having an inclusion arrangement index K of 1.0 or less is used as a material, even if the steel has a general level of cleanliness, it is more than when a steel bar made of high cleanliness steel is used as the material. It is possible to realize excellent rolling fatigue characteristics. In order to control the inclusion arrangement index K to be small, techniques such as increasing the cleanliness (enough deoxidation), increasing the total rolling ratio, and reducing the soft inclusions are effective.
以下、合金成分について説明する。鋼組成に関する「％」は特に断らない限り「質量％」を意味する。
Ｃは、焼入れ・焼戻し等の調質熱処理後における、硬さ、強度、耐摩耗性を確保するために必要な元素であり、本発明ではＣ含有量０.０２％以上の鋼種を対象とする。Ｃ含有量が０.０８％以上の鋼種、あるいは０.３０％以上の鋼種を採用するように管理してもよい。ただし、過剰にＣを含有すると粗大な未溶解炭化物が残存しやすくなり、それに起因して転動疲労特性が低下する場合がある。種々検討の結果、Ｃ含有量は１.２０％以下に制限される。
Hereinafter, the alloy components will be described. “%” In relation to steel composition means “mass%” unless otherwise specified.
C is an element necessary for ensuring hardness, strength, and wear resistance after tempering heat treatment such as quenching and tempering. In the present invention, C is a steel type having a C content of 0.02% or more. . You may manage to employ | adopt the steel grade whose C content is 0.08% or more, or 0.30% or more. However, if C is contained excessively, coarse undissolved carbide tends to remain, and rolling fatigue characteristics may be deteriorated due to this. As a result of various studies, the C content is limited to 1.20% or less.
Ｓｉは、鋼の脱酸に有効な元素であり、また焼戻し軟化抵抗を高める作用も有する。本発明ではＳｉ含有量０.０２％以上の鋼を対象とする。ただし、多量のＳｉ含有は鋼材の加工性を低下させる要因となるので、Ｓｉ含有量は２.００％以下に制限される。 Si is an element effective for deoxidation of steel and also has an effect of increasing temper softening resistance. In the present invention, steel having a Si content of 0.02% or more is targeted. However, since a large amount of Si content causes a decrease in the workability of the steel material, the Si content is limited to 2.00% or less.
Ｍｎは、焼入れ性の向上に有効な元素であり、本発明ではＭｎ含有量０.１０％以上の鋼を対象とする。ただし、多量のＭｎ含有は鋼材の加工性を低下させる要因となるので、Ｍｎ含有量は１.５０％以下に制限される。 Mn is an element effective for improving hardenability, and in the present invention, steel having a Mn content of 0.10% or more is targeted. However, since a large amount of Mn content causes a decrease in the workability of the steel material, the Mn content is limited to 1.50% or less.
Ｐは、焼入れ時にオーステナイト粒界に偏析し、疲労特性や靱性を低下させる要因となるので、少ないことが望ましい。ただし、過剰の脱Ｐは製鋼での負荷を増大させ好ましくない。本発明ではＰ含有量０.００１〜０.０３０％の鋼を対象とする。 P is segregated at the austenite grain boundary during quenching, and causes a decrease in fatigue characteristics and toughness. However, excessive P removal is not preferable because it increases the load in steelmaking. In the present invention, steel with a P content of 0.001 to 0.030% is targeted.
Ｓは、転動疲労破壊の起点となる硫化物系介在物を形成するので、少ないことが望ましい。ただし、過度の脱Ｓは製鋼での負荷を増大させ好ましくない。本発明ではＳ含有量０.０００５〜０.０３０％の鋼を対象とする。 Since S forms sulfide-based inclusions that are the starting point of rolling fatigue failure, it is desirable that S be small. However, excessive desulfurization S is not preferable because it increases the load in steelmaking. In the present invention, steel with an S content of 0.0005 to 0.030% is targeted.
Ｃｒは、焼入れ性の向上に有効であり、また焼鈍時における炭化物の粗大化を抑制する作用を有する。本発明ではＣｒ含有量０.０２％以上の鋼を対象とする。ただし、多量のＣｒ含有は鋼材の加工性を低下させる要因となるので、Ｃｒ含有量は２.００％以下に制限される。 Cr is effective in improving hardenability and has an action of suppressing coarsening of carbides during annealing. In the present invention, steel with a Cr content of 0.02% or more is targeted. However, since a large amount of Cr is a factor that deteriorates the workability of the steel material, the Cr content is limited to 2.00% or less.
Ｏは、転動疲労破壊の起点となる酸化物系介在物を形成するので、できるだけ脱酸された鋼を使用することが軌道輪の転動疲労特性を向上させるうえで有利となる。そのため従来から軌道輪用の鋼材には例えばＯ含有量を０.００１０％（１０ｐｐｍ）未満のレベルにまで低減した高清浄度鋼を使用することが多かった。本発明においてもそのような高清浄度鋼を適用しても構わない。しかし、高清浄度鋼の溶製は製鋼工程での負荷を増大させ、生産性の低下や製造コストの上昇を招く要因となる。この点、本発明に従えば、清浄度を特段に高めた鋼を適用しなくても、高清浄度鋼を使用した従来の軌道輪と同等以上の優れた転動疲労特性を実現することが可能となる。 O forms oxide inclusions that serve as starting points for rolling fatigue failure. Therefore, it is advantageous to use a deoxidized steel as much as possible to improve the rolling fatigue characteristics of the race. Therefore, conventionally, for example, high cleanliness steel in which the O content is reduced to a level of less than 0.0010% (10 ppm) has been often used as a steel material for a bearing ring. In the present invention, such high cleanliness steel may be applied. However, smelting of high cleanliness steel increases the load in the steelmaking process, which causes a decrease in productivity and an increase in manufacturing cost. In this regard, according to the present invention, it is possible to realize excellent rolling fatigue characteristics equivalent to or better than conventional races using high cleanliness steel without applying steel with particularly high cleanliness. It becomes possible.
種々検討の結果、鋼中のＯ含有量は０.００３０％（３０ｐｐｍ）まで許容することができる。良好な転動疲労特性をより安定して実現しやすくするためには、Ｏ含有量を０.００２５％以下、あるいは０.００２０％以下に管理してもよい。鋼の脱酸レベルは要求される転動疲労特性と製造コスト（ひいては部品価格）とのバランスで設定すればよい。Ｏ含有量を０.０００１％以下にまで低減する必要はないので、本発明ではＯ含有量０.０００１〜０.００３０％の鋼を適用対象とする。ただし上述のように、本発明に従えば脱酸レベルが比較的緩い鋼を使用しても転動疲労特性の改善効果が得られる。例えばＯ含有量が０.００１０〜０.００３０％である鋼は本発明に従う軌道輪として種々の用途で高いコストパフォーマンスを発揮しうる。 As a result of various investigations, the O content in the steel can be allowed to 0.0003% (30 ppm). In order to make it easier to realize good rolling fatigue characteristics more stably, the O content may be controlled to 0.0025% or less, or 0.000020% or less. What is necessary is just to set the deoxidation level of steel by the balance of the required rolling fatigue characteristic and manufacturing cost (and part price). Since it is not necessary to reduce the O content to 0.0001% or less, in the present invention, steel having an O content of 0.0001 to 0.0030% is applied. However, as described above, according to the present invention, the rolling fatigue characteristics can be improved even if steel having a relatively low deoxidation level is used. For example, steel having an O content of 0.0001 to 0.0030% can exhibit high cost performance in various applications as a race according to the present invention.
Ｎｉは、焼入れ性の向上に有効な元素であり、必要に応じて含有して構わない。その場合、０.０５％以上の含有量とすることがより効果的である。ただしＮｉは高価な元素であり過剰含有は不経済となる。Ｎｉを含有させる場合、その含有量は２.００％以下の範囲とする。 Ni is an element effective for improving hardenability and may be contained as necessary. In that case, it is more effective to set the content to 0.05% or more. However, Ni is an expensive element, and excessive content becomes uneconomical. When Ni is contained, the content is made 2.00% or less.
Ｍｏは、鋼の靱性向上に有効な元素であり、必要に応じて含有して構わない。その場合、０.０５％以上の含有量とすることがより効果的である。ただしＭｏは高価な元素であり過剰含有は不経済となる。Ｍｏを含有させる場合、その含有量は０.５０％以下の範囲とする。 Mo is an element effective for improving the toughness of steel and may be contained as necessary. In that case, it is more effective to set the content to 0.05% or more. However, Mo is an expensive element, and excessive content becomes uneconomical. When Mo is contained, the content is made 0.50% or less.
Ｖ、Ｎｂ、Ｔｉは、結晶粒の微細化による材料特性の向上に有効な元素であり、必要に応じてこれらの１種以上を含有して構わない。その場合、Ｖは０.０５％以上、Ｎｂは０.０５％以上、Ｔｉは０.００５％以上の含有量とすることがより効果的である。ただしＶは高価な元素であり過剰含有は不経済となるので、Ｖ含有量は０.５０％以下の範囲とする。Ｎｂ、Ｔｉの過剰添加は炭窒化物の生成量を増大させ、それらが転動疲労破壊の起点やき裂伝播経路となるため、Ｎｂ、Ｔｉの含有量はいずれも０.５０％以下の範囲とする。 V, Nb, and Ti are elements that are effective in improving material properties by refining crystal grains, and may contain one or more of these as necessary. In that case, it is more effective to set V to 0.05% or more, Nb to 0.05% or more, and Ti to 0.005% or more. However, since V is an expensive element and excessive content becomes uneconomical, the V content is set to a range of 0.50% or less. Excessive addition of Nb and Ti increases the amount of carbonitride produced, which becomes the starting point of rolling fatigue fracture and the crack propagation path. Therefore, the Nb and Ti contents are both in the range of 0.50% or less. To do.
Ｂは、焼入れ性の向上に有効であり、必要に応じて含有して構わない。その作用は微量のＢ含有によって得られるが、０.０００５％以上の含有量とすることがより効果的である。ただし、過剰に含有させても効果は飽和するので、Ｂを含有させる場合は０.０１０％以下の範囲とすることが望ましく、０.００５％以下に管理しても構わない。 B is effective in improving hardenability and may be contained as necessary. The action is obtained by containing a small amount of B, but it is more effective to set the content to 0.0005% or more. However, since the effect is saturated even if it is contained excessively, when B is contained, the content is preferably set to 0.010% or less, and may be controlled to 0.005% or less.
以上の組成を有する鋼は、一般的な鋼板製造工程を利用して圧延鋼板（熱延鋼板または冷延鋼板）とされる。前述の介在物配列指数Ｋを所定範囲に調整するためには、鋼の清浄度に応じてトータル圧延率を上げることで軟質な介在物を小さくすればよい。圧延鋼板は焼鈍された後、転がり軸受の軌道輪形状に加工される。その加工に際しては、非金属介在物の展伸方向と軌道面とのなす角度が０〜４５°、より好ましくは０〜３０°の範囲となるようにする。具体的には、スラスト軸受の軌道盤とする場合には、圧延鋼板をそのままリング状に打ち抜いた部品をベースとして、切削などにより所定の軌道面を形成すればよい。ラジアル軸受の内輪あるいは外輪とする場合には、圧延鋼板をプレスにて円筒状に絞ったのち底部を打ち抜いてリング状とした部品をベースとして、切削などにより所定の軌道面を形成すればよい。加工後には焼入れ・焼戻し等の調質熱処理を受け、所定の硬さに調整される。 The steel having the above composition is made into a rolled steel plate (hot rolled steel plate or cold rolled steel plate) using a general steel plate manufacturing process. In order to adjust the inclusion inclusion index K described above to a predetermined range, the soft inclusions may be reduced by increasing the total rolling rate in accordance with the cleanliness of the steel. The rolled steel sheet is annealed and then processed into a ring shape of a rolling bearing. In the processing, the angle formed between the extending direction of the non-metallic inclusion and the raceway surface is set to be in the range of 0 to 45 °, more preferably 0 to 30 °. Specifically, when a thrust bearing washer is used, a predetermined raceway surface may be formed by cutting or the like based on a component obtained by punching a rolled steel plate as it is in a ring shape. In the case of an inner ring or an outer ring of a radial bearing, a predetermined raceway surface may be formed by cutting or the like using a ring-shaped part formed by punching a rolled steel plate into a cylindrical shape with a press and then punching the bottom. After processing, it is subjected to tempering heat treatment such as quenching and tempering, and adjusted to a predetermined hardness.
以下の実施例１〜５については、試験片作製の工程および鋼材からの試験片採取位置を表５にまとめて示してある。図２３、図２４に、表５中に示した試験片採取位置の番号に対応する鋼材断面内の試験片採取位置を図示する。 About the following Examples 1-5, the process of test piece preparation and the test piece collection position from steel materials are collectively shown in Table 5. FIG. 23 and FIG. 24 show the test piece sampling positions in the cross section of the steel material corresponding to the numbers of the test piece sampling positions shown in Table 5.
〔実施例１〕
表１に示す鋼の連続鋳造スラブから採取したブロック（２００×２００×９６０ｍｍ）を熱間鍛造することにより幅を２００ｍｍに保って一方向に伸ばし、その後、炭化物の球状化焼鈍を施して供試鋼材（厚さ１００ｍｍ×幅２００ｍｍ）とした。この供試鋼材は熱延鋼板の組織状態を模擬したものである。供試鋼材を組織観察したところ、非金属介在物は図２に示した圧延鋼板と同様に一方向に伸ばされて分布していることが確認された。
[Example 1]
A block (200 x 200 x 960 mm) taken from a continuous cast slab of steel shown in Table 1 was hot forged to keep the width at 200 mm and stretched in one direction, and then subjected to spheroidizing annealing of carbide. A steel material (thickness 100 mm × width 200 mm) was used. This test steel simulates the structure of a hot rolled steel sheet. When the structure of the test steel was observed, it was confirmed that the non-metallic inclusions were stretched in one direction and distributed in the same manner as the rolled steel sheet shown in FIG.
各供試鋼材から、２種類の方向に厚さ９ｍｍの円板を切り出した。１種類は円板の厚さ方向が供試鋼材の厚さ方向と一致するもの（「Ａ片」と呼ぶ）であり、これは介在物の展伸方向が円板の表面と平行になっている。もう１種類は円板の厚さ方向が供試鋼材の長手方向に一致するもの（「Ｂ片」と呼ぶ）であり、これは介在物の展伸方向が円板の表面と垂直になっている。すなわち、介在物の分布状態に関して、Ａ片は圧延鋼板から打ち抜いた円板に相当するもの、Ｂ片は丸棒から切り出した円板に相当するものである。ここでは組成および介在物の分布状態が同一である供試鋼材から切り出した試験片を用いて、試験片の採取方向の相違による影響のみを調べるために、Ｂ片が採取可能な厚さの熱間鍛造材を供試鋼材として用いたものである。各円板の中央部に切削加工で穴を形成してリング状の部材とし、これに焼入れ（８２０℃×３０ｍｉｎ→油冷）・焼戻し（１６０℃×６０ｍｉｎ）の調質熱処理を施して７７０〜８００ＨＶに硬さを調整し、精密加工を施して試験片とした。同一種類の材料につき試験数は１６とした。 From each sample steel, a 9 mm thick disk was cut out in two different directions. One type is one in which the thickness direction of the disc coincides with the thickness direction of the test steel (referred to as “A piece”), and this means that the extension direction of inclusions is parallel to the surface of the disc. Yes. The other type is one in which the thickness direction of the disc coincides with the longitudinal direction of the test steel (referred to as “B piece”). This is because the extension direction of inclusions is perpendicular to the surface of the disc. Yes. That is, regarding the distribution of inclusions, the A piece corresponds to a disc punched from a rolled steel plate, and the B piece corresponds to a disc cut from a round bar. Here, in order to examine only the influence of the difference in the sampling direction of the test piece using the test piece cut out from the test steel material having the same composition and distribution of inclusions, A forged material is used as a test steel material. A hole is formed by cutting in the center of each disk to form a ring-shaped member, which is subjected to a tempering heat treatment of quenching (820 ° C. × 30 min → oil cooling) and tempering (160 ° C. × 60 min) to 770-70 The hardness was adjusted to 800 HV, and precision processing was performed to obtain a test piece. The number of tests was 16 for the same type of material.
得られた試験片を用いて、スラスト式転動疲労試験機にて転動疲労試験を行った。図４に転動疲労試験の方法を模式的に示す。試験条件は以下の通りである。
・試験片形状：φ６３ｍｍ×ｔ９ｍｍ、転動径３８ｍｍ
・鋼球：ＳＵＪ２製φ３／８ｉｎのものを、３個使用
・荷重：３２５ｋｇｆ、最大接触応力：４９０３Ｎ／ｍｍ2
・回転数：１８００ｃｐｍ
・潤滑油：タービン＃６８
・最大繰返し数：１０8回
Using the obtained test piece, a rolling fatigue test was conducted with a thrust type rolling fatigue tester. FIG. 4 schematically shows a rolling fatigue test method. The test conditions are as follows.
・ Specimen shape: φ63mm × t9mm, rolling diameter 38mm
・ Steel balls: Three SUJ2 φ3 / 8 inch balls are used ・ Load: 325 kgf, maximum contact stress: 4903 N / mm 2
・ Rotation speed: 1800 cpm
・ Lubricant: Turbine # 68
・ Maximum number of repetitions: 10 8 times
図５に結果を示す。図中には繰返し数と累積破損率の関係をプロットしてあり、「非破壊サンプル」と表示したプロットは１０8回でも破損しなかった試験片の数を表している。軌道面と非金属介在物の展伸方向とが平行となるＡ片では、それが垂直となるＢ片と比べ、転動疲労特性に関する信頼性が極めて高いことがわかる。このことから、組成および清浄度が同じ材料であれば、圧延鋼板の板面に由来する表面を軌道面とする軌道輪は、棒鋼の断面を軌道面とする軌道輪に対し、極めて優れた転動疲労特性を有する評価することができる。 The results are shown in FIG. In the figure, the relationship between the number of repetitions and the cumulative failure rate is plotted, and the plot labeled “Non-destructive sample” represents the number of specimens that were not damaged even after 10 8 times. It can be seen that the A piece in which the raceway surface and the extending direction of the nonmetallic inclusions are parallel has extremely high reliability in terms of rolling fatigue characteristics as compared to the B piece in which the raceway surface and the non-metallic inclusion are parallel. Therefore, if the material has the same composition and cleanliness, the raceway with the surface derived from the surface of the rolled steel plate as the raceway is superior to the race with the cross section of the steel bar as the raceway. It can be evaluated having dynamic fatigue characteristics.
〔実施例２〕
表２に示す鋼１、４の連続鋳造スラブから採取したブロック（２００×２００×９６０ｍｍ）から高さ２００ｍｍ×幅１００ｍｍ×長さ２００ｍｍの小ブロックを切り出し、これに熱間鍛造と熱間圧延を施すことにより幅を概ね一定に保ったまま一方向に伸ばして圧延鋼板（厚さ１５ｍｍ×幅約１００ｍｍ）とし、炭化物の球状化焼鈍を施した。また、表２に示す鋼２、３、５を用いて製造した直径６５ｍｍの棒鋼を用意した。この棒鋼は従来から軸受部品に適用されている高清浄度鋼を用いた材料であり、その長手方向に非金属介在物が展伸している。
[Example 2]
A small block having a height of 200 mm, a width of 100 mm, and a length of 200 mm is cut out from a block (200 × 200 × 960 mm) taken from a continuous cast slab of steels 1 and 4 shown in Table 2, and hot forging and hot rolling are performed on this. As a result, the steel sheet was stretched in one direction while maintaining the width substantially constant to obtain a rolled steel sheet (thickness 15 mm × width about 100 mm), and subjected to spheroidizing annealing of carbide. Moreover, the steel bar of diameter 65mm manufactured using the steel 2, 3, 5 shown in Table 2 was prepared. This steel bar is a material using high cleanliness steel conventionally applied to bearing parts, and non-metallic inclusions extend in the longitudinal direction.
各圧延鋼板および棒鋼から厚さ９ｍｍの円板を切り出した。圧延鋼板から切り出した円板は圧延方向（非金属介在物の展伸方向）が円板の表面と平行になっている。また棒鋼から切り出した円板は棒鋼の長手方向（非金属介在物の展伸方向）が円板の表面と垂直になっている。各円板を切削加工して実施例１と同様の形状のリング状の部材とし、これに焼入れ・焼戻しの調質熱処理を施して、鋼１〜３（ＳＵＪ２）は７７０〜８００ＨＶ、鋼４、５（ＳＣＭ４２０Ｈ）は５２０〜５４０ＨＶにそれぞれ硬さを調整し、精密加工を施して試験片とした。調質熱処理条件は、ＳＵＪ２；焼入れ（８２０℃×３０ｍｉｎ→油冷）・焼戻し（１６０℃×６０ｍｉｎ）、ＳＣＭ４２０Ｈ；焼入れ（９００℃×３０ｍｉｎ→油冷）・焼戻し（１６０℃×６０ｍｉｎ）とした。表２中に示すように、ＳＵＪ２の圧延鋼板由来試験片をＣ片、棒鋼由来試験片をＤ１片、Ｄ２片と呼ぶ。またＳＣＭ４２０Ｈの圧延鋼板由来試験片をＥ片、棒鋼由来試験片をＦ片と呼ぶ。各試験片について実施例１と同様の条件で転動疲労試験を行った。 A 9 mm thick disc was cut out from each rolled steel plate and bar steel. The disc cut out from the rolled steel plate has a rolling direction (the extending direction of the nonmetallic inclusions) parallel to the surface of the disc. Further, in the disk cut out from the steel bar, the longitudinal direction of the steel bar (the extending direction of the nonmetallic inclusions) is perpendicular to the surface of the disk. Each disk is cut into a ring-shaped member having the same shape as in Example 1, and subjected to tempering heat treatment for quenching and tempering. Steels 1 to 3 (SUJ2) are 770 to 800 HV, steel 4; No. 5 (SCM420H) was adjusted to a hardness of 520 to 540 HV and subjected to precision machining to obtain a test piece. Conditioning heat treatment conditions were SUJ2; quenching (820 ° C. × 30 min → oil cooling) / tempering (160 ° C. × 60 min), SCM420H; quenching (900 ° C. × 30 min → oil cooling) / tempering (160 ° C. × 60 min). As shown in Table 2, the SUJ2 rolled steel plate-derived test piece is referred to as C piece, and the steel bar-derived test piece is referred to as D1 piece and D2 piece. Moreover, the test piece derived from the rolled steel plate of SCM420H is called E piece, and the test piece derived from bar steel is called F piece. Each test piece was subjected to a rolling fatigue test under the same conditions as in Example 1.
図６および図７に、それぞれＳＵＪ２相当鋼種（Ｃ片、Ｄ１片、Ｄ２片）およびＳＣＭ４２０Ｈ相当鋼種（Ｅ片、Ｆ片）の結果を示す。いずれの鋼種においても、圧延鋼板から採取した試験片では、棒鋼から採取した試験片と比べ、清浄度が悪い（酸素含有量が高い）にもかかわらず優れた転動疲労特性を実現できることが確認された。すなわち本発明に従えばＯ含有量が０.００１０％（１０ｐｐｍ）以上と脱酸処理の程度が比較的緩い材料であっても、高清浄度鋼（ＳＵＪ２系ではＯ≦５ｐｐｍ以下、ＳＣＭ４２０系ではＯ≦１０ｐｐｍ）を用いた従来の棒鋼由来の材料よりも転動疲労に関する信頼性に勝るものが得られるのである。 6 and 7 show the results of the SUJ2-equivalent steel types (C piece, D1 piece, D2 piece) and the SCM420H equivalent steel types (E piece, F piece), respectively. In all steel types, it was confirmed that the specimens taken from the rolled steel sheet can achieve excellent rolling fatigue characteristics despite the poor cleanliness (high oxygen content) compared to the specimens taken from the bar steel. It was done. That is, according to the present invention, even if the O content is 0.0010% (10 ppm) or more and the material is relatively loose in the degree of deoxidation, high cleanliness steel (O ≦ 5 ppm for SUJ2 system, A material superior in reliability related to rolling fatigue than a conventional steel bar-derived material using (O ≦ 10 ppm) can be obtained.
〔実施例３〕
実施例１で用いた鋼１（ＳＵＪ２）の供試鋼材から、円板表面の法線と、非金属介在物の展伸方向と平行な一平面の法線とのなす角度θが０°、１５°、３０°、４５°、６０°、９０°となるように各種円板を切り出し、実施例１と同様の手法で試験片を作製し、実施例１と同様の転動疲労試験を行った。上記の角度θは「軌道面の法線と圧延板面由来表面の法線とのなす角度」に相当する。θ＝０°の試料は前記Ａ片、θ＝９０°の試料は前記Ｂ片である。図８に転動疲労試験の方法を模式的に示す。
Example 3
From the test steel material of Steel 1 (SUJ2) used in Example 1, the angle θ formed by the normal line on the surface of the disk and the normal line in a plane parallel to the extending direction of the nonmetallic inclusions is 0 °. Various disks were cut out so as to be 15 °, 30 °, 45 °, 60 °, and 90 °, and test pieces were prepared by the same method as in Example 1, and the same rolling fatigue test as in Example 1 was performed. It was. The angle θ corresponds to “an angle formed by the normal of the raceway surface and the normal of the surface derived from the rolled plate surface”. The sample with θ = 0 ° is the A piece, and the sample with θ = 90 ° is the B piece. FIG. 8 schematically shows a rolling fatigue test method.
図９に結果を示す。「軌道面の法線と圧延板面由来表面の法線とのなす角度」に相当する上記θが４５°以下の場合には５０％信頼寿命（累積破損確率５０％寿命）が９０°片（Ｂ片）に対して１.５倍以上となり、高い信頼性が得られる。特にθを０〜３０°とすると５０％信頼寿命は９０°片の２倍以上となり、極めて高い信頼性が確保される。 FIG. 9 shows the result. When the above θ corresponding to the “angle between the normal of the raceway surface and the normal of the surface derived from the rolled plate” is 45 ° or less, the 50% reliable life (cumulative failure probability 50% life) is 90 ° ( B piece) is 1.5 times or more, and high reliability is obtained. In particular, when θ is 0 to 30 °, the 50% reliability life is more than twice that of the 90 ° piece, and extremely high reliability is ensured.
〔実施例４〕
表３に示す鋼の連続鋳造スラブから採取したブロックを用いて、実施例１と同様の手法で「軌道面の法線と圧延板面由来表面の法線とのなす角度」に相当する上記θが０°（Ａ片と同様）および９０°（Ｂ片と同様）の試験片を作製し、実施例１と同様の条件で転動疲労試験を行った。なお、焼入れは８２０℃×３０ｍｉｎ→油冷、焼戻しは１６０℃×６０ｍｉｎの条件で行い、それぞれ表３中に記載した硬さに調整した。
Example 4
Using the block taken from the continuous cast slab of steel shown in Table 3, the above-mentioned θ corresponding to the “angle formed by the normal of the raceway surface and the normal of the surface derived from the rolled plate surface” in the same manner as in Example 1 Specimens of 0 ° (similar to the A piece) and 90 ° (similar to the B piece) were produced, and a rolling fatigue test was performed under the same conditions as in Example 1. In addition, quenching was performed under the conditions of 820 ° C. × 30 min → oil cooling, and tempering was performed at 160 ° C. × 60 min, and each was adjusted to the hardness described in Table 3.
図１０〜図１９に結果を示す。本発明に従う化学組成を有する鋼を用いたもの（図１０〜図１４）では、「軌道面の法線と圧延板面由来表面の法線とのなす角度」に相当する上記θが０°のもの（０°材）において転動疲労特性の顕著な改善が認められた。これに対し、鋼１１（図１５）はＣ含有量が高すぎたことにより粗大な未溶解セメンタイトがマトリクス中に多く残存しており、それらが破壊の起点となって０°材においても転動疲労特性の改善は小さかった。鋼１２（図１６）はＳ含有量が高すぎたことにより硫化物系介在物が多く生成しており、それらが破壊の起点となって０°材においても転動疲労特性は悪かった。鋼１３（図１７）は酸素含有量が高すぎたことにより酸化物系介在物が多く生成しており、それらが破壊の起点となって０°材においても転動疲労特性の改善は不十分であった。鋼１４（図１８）および鋼１５（図１９）はそれぞれＮｂおよびＴｉの含有量が高すぎたことにより粗大な炭窒化物が多く生成しており、それらが破壊の起点となって０°材においても転動疲労特性の改善は不十分であった。 The results are shown in FIGS. In the case of using the steel having the chemical composition according to the present invention (FIGS. 10 to 14), the θ corresponding to “the angle formed by the normal of the raceway surface and the normal of the surface derived from the rolled plate surface” is 0 °. Remarkable improvement in rolling fatigue characteristics was observed in the case (0 ° material). In contrast, in Steel 11 (FIG. 15), a large amount of coarse undissolved cementite remains in the matrix because the C content is too high. The improvement in fatigue properties was small. Steel 12 (FIG. 16) had a large amount of sulfide inclusions due to its excessively high S content, and these were the starting points for fracture, and the rolling fatigue characteristics were poor even in the 0 ° material. Steel 13 (FIG. 17) has a large amount of oxide inclusions due to its too high oxygen content, which is the starting point of fracture, and the improvement in rolling fatigue properties is insufficient even in the 0 ° material. Met. Steel 14 (FIG. 18) and Steel 15 (FIG. 19) have a large amount of coarse carbonitride due to the excessive content of Nb and Ti, respectively, and these are the origins of fracture, which are 0 ° materials. However, the improvement of rolling fatigue characteristics was insufficient.
〔実施例５〕
表４に示す鋼の連続鋳造スラブから採取したブロックを用いて、実施例２に準じた手法で「軌道面の法線と圧延板面由来表面の法線とのなす角度」に相当する上記θが０°の試験片を作製し、実施例２と同様の条件で転動疲労試験を行った。ここでＣ片は実施例２で使用したＣ片と同様の試験片である。Ｑ片、Ｒ片、Ｓ片は、Ｃ片の作製工程において熱間圧延率を変えることによって前述の介在物配列係数Ｋを高く調整したものである。
Example 5
The above-mentioned θ corresponding to the “angle formed between the normal of the raceway surface and the normal of the surface derived from the rolled plate surface” by the method according to Example 2 using a block taken from the continuous cast slab of steel shown in Table 4 A 0 ° test piece was prepared, and a rolling fatigue test was performed under the same conditions as in Example 2. Here, the C piece is the same test piece as the C piece used in Example 2. The Q piece, the R piece, and the S piece are obtained by adjusting the inclusion arrangement coefficient K to be high by changing the hot rolling rate in the production process of the C piece.
図２０に結果を示す。図中には実施例２の図６に示したＤ１片、Ｄ２片（高清浄度鋼の棒鋼由来材）のプロットが並ぶおおよその位置を破線で示してある。介在物配列係数Ｋを低くコントロールすることによって、特段に高清浄度化を図ることなく高清浄度鋼を用いた従来材よりも優れた転動疲労特性を実現できることがわかる。なお、介在物配列係数Ｋが大きい場合（Ｑ片、Ｒ片、Ｓ片）でも、「軌道面の法線と圧延板面由来表面の法線とのなす角度」に相当する上記θを０〜４５°好ましくは０〜３０°とすることによって転動疲労特性を改善可能であることが別途試験により確認されており、用途に応じて圧延率の低い圧延鋼板を利用することが可能である。 The results are shown in FIG. In the figure, the approximate positions where the plots of the D1 piece and the D2 piece (the steel material derived from high cleanliness steel) shown in FIG. It can be seen that by controlling the inclusion arrangement coefficient K to be low, rolling fatigue characteristics superior to conventional materials using high cleanliness steel can be realized without particularly increasing cleanliness. In addition, even when the inclusion arrangement coefficient K is large (Q piece, R piece, S piece), the above θ corresponding to the “angle formed by the normal of the raceway surface and the normal of the surface derived from the rolled plate surface” is set to 0 to 0. It has been confirmed by a separate test that rolling fatigue characteristics can be improved by setting the angle to 45 °, preferably 0 to 30 °, and a rolled steel sheet having a low rolling rate can be used depending on the application.
〔実施例６〕
表１に示した鋼Ｎｏ.１の連続鋳造スラブを熱間圧延して板厚１０ｍｍの圧延鋼板とした。この熱延鋼板から、図２５に示す［１］〜［５］の各深さ位置が軌道面となる５種類のリング状試験片を作製した。いずれも実施例１と同様の調質熱処理を施した。各試験片につき実施例１と同様の転動疲労試験を行った。試験条件は以下の通りである。ここでは、実施例１の条件よりも高い荷重にて試験を実施した。
・試験片形状：φ６３ｍｍ×ｔ５ｍｍ、転動径３８ｍｍ
・鋼球：ＳＵＪ２製φ３／８ｉｎのものを、３個使用
・荷重：４００ｋｇｆ、最大接触応力：５２５５Ｎ／ｍｍ2
・回転数：１８００ｃｐｍ
・潤滑油：タービン＃６８
・最大繰返し数：１０8回
Example 6
The continuously cast slab of steel No. 1 shown in Table 1 was hot-rolled to obtain a rolled steel plate having a thickness of 10 mm. From this hot-rolled steel sheet, five types of ring-shaped test pieces were produced in which the depth positions [1] to [5] shown in FIG. All were subjected to the same tempering heat treatment as in Example 1. Each test piece was subjected to the same rolling fatigue test as in Example 1. The test conditions are as follows. Here, the test was performed under a higher load than the conditions of Example 1.
・ Specimen shape: φ63mm × t5mm, rolling diameter 38mm
-Steel balls: Three SUJ2 φ3 / 8in balls are used.-Load: 400kgf, maximum contact stress: 5255N / mm 2
・ Rotation speed: 1800 cpm
・ Lubricant: Turbine # 68
・ Maximum number of repetitions: 10 8 times
図２６に結果を示す。圧延板面由来表面からの除去加工深さを当該圧延鋼板の板厚の３／１０以内とした［１］〜［３］のものは、［４］［５］のものと比べ、上記ような厳しい荷重条件での転動疲労特性が顕著に向上した。圧延板面由来表面からの除去加工深さを当該圧延鋼板の板厚の２／１０以内とした［１］［２］のものはさらに優れた転動疲労特性を呈した。 FIG. 26 shows the result. [1] to [3] in which the removal depth from the surface derived from the rolled plate surface is within 3/10 of the thickness of the rolled steel plate is as described above compared to [4] and [5]. The rolling fatigue characteristics under severe load conditions were significantly improved. [1] [2] in which the removal depth from the surface of the rolled sheet surface was within 2/10 of the sheet thickness of the rolled steel sheet exhibited even more excellent rolling fatigue characteristics.
Claims (8)
〔介在物配列指数Ｋ〕
鋼板の圧延方向および板厚方向に平行な断面（Ｌ断面）において、一辺の長さが板厚方向に３.０ｍｍ以上（板厚が３.０ｍｍ未満の場合は板厚全長）であり面積Ｓ（ｍｍ2）が３０ｍｍ2以上である矩形領域を設定し、その矩形領域内に粒子の全体または一部が存在する介在物粒子のうち板厚方向最大長さが１μｍ以上のものを測定対象粒子とし、板厚方向端部のいずれか一方の鋼板表面を「基準面」と定めるとき、前記矩形領域内において、各測定対象粒子について基準面側の当該粒子表面から基準面側への板厚方向距離が６０μｍ以下の範囲に粒子表面（前記矩形領域内にあるもの限る）が位置する他の測定対象粒子の数Ｘ（個）を測定し、全測定対象粒子についてのＸの総和ＸALL（個）を求め、ＸALLを矩形領域の面積Ｓ（ｍｍ2）で除した値（個／ｍｍ2）を介在物配列指数Ｋとする。 The rolling ring bearing ring according to any one of claims 1 to 5, wherein the rolled steel sheet has an inclusion arrangement index K defined below to be adjusted to 1.0 or less.
[Inclusion sequence index K]
In a cross section (L cross section) parallel to the rolling direction and the plate thickness direction of the steel plate, the length of one side is 3.0 mm or more in the plate thickness direction (when the plate thickness is less than 3.0 mm), the area S A rectangular region having (mm 2 ) of 30 mm 2 or more is set, and inclusion particles having a maximum length in the thickness direction of 1 μm or more among inclusion particles in which all or part of the particles are present in the rectangular region are measured particles When the steel plate surface at either end in the plate thickness direction is defined as a “reference plane”, the plate thickness direction from the particle surface on the reference plane side to the reference plane side for each measurement target particle in the rectangular region The number X (number) of other measurement target particles whose particle surfaces (limited to those within the rectangular area) are located within a distance of 60 μm or less is measured, and the total X of all measurement target particles X ALL (numbers) ) is obtained, dividing the X ALL in the area of the rectangular area S (mm 2) Value (the number / mm 2) and inclusions sequence index K.
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| JP2021128054A (en) * | 2020-02-13 | 2021-09-02 | 山陽特殊製鋼株式会社 | Test piece for rolling fatigue test and rolling fatigue testing method |
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| JP7383512B2 (en) | 2020-02-13 | 2023-11-20 | 山陽特殊製鋼株式会社 | Test piece for rolling fatigue test and rolling fatigue test method |
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