JP2012036434A - Bearing steel material - Google Patents
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Abstract
Description
本発明は、鋼中の硫化物を形態制御することによって転動疲労寿命を改善した軸受鋼に関する。 The present invention relates to a bearing steel having improved rolling fatigue life by controlling the form of sulfides in the steel.
自動車や産業機械にとって重要な「玉軸受け」や「コロ軸受け」などの部品には、面圧の高い負荷が繰り返し加えられることから、転動疲労寿命の向上が求められている。従来、これらの部品として、JIS G 4805(1999)に記載される「高炭素クロム軸受鋼鋼材」等の素材が使われている。 Parts such as “ball bearings” and “roller bearings”, which are important for automobiles and industrial machinery, are repeatedly subjected to high surface pressure loads, and therefore there is a need for improved rolling fatigue life. Conventionally, materials such as “high carbon chromium bearing steel” described in JIS G 4805 (1999) are used as these parts.
転動疲労試験で破壊した試験片の破面には酸化物系介在物が見つかることから、これまでに、転動疲労寿命と酸化物系介在物の相関が調査されている。このため、従来から酸化物系介在物の大きさおよび数を低減することで転動疲労寿命の向上が図られている。その結果、最近では鋼中の酸化物系介在物の指標として広く使われる鋼中の全酸素濃度は10ppmを下回るようになっている。 Since oxide inclusions are found on the fracture surface of the specimens broken in the rolling fatigue test, the correlation between the rolling fatigue life and the oxide inclusions has been investigated so far. For this reason, conventionally, the rolling fatigue life has been improved by reducing the size and number of oxide inclusions. As a result, the total oxygen concentration in steel, which is widely used as an index of oxide inclusions in steel, has recently become less than 10 ppm.
しかしながら、全酸素濃度が低減した結果、これまでの酸化物系介在物に代わり、硫化物系介在物を起因とする破壊が顕著に現れるようになっている。一方で、更なる転動疲労寿命の向上に対する要望はますます大きくなってきており、従来の酸化物系介在物に加え、硫化物系介在物の数および大きさを低減する手法、これに加えて、介在物の形状を制御する手法が検討されている。硫化物系介在物の形状を制御できる元素としては、TeやCaなどが挙げられる。 However, as a result of the reduction of the total oxygen concentration, breakage due to sulfide inclusions appears remarkably instead of the oxide inclusions so far. On the other hand, there is an increasing demand for further improvement in rolling fatigue life. In addition to conventional oxide inclusions, a method for reducing the number and size of sulfide inclusions, in addition to this, Techniques for controlling the shape of inclusions are being studied. Examples of elements that can control the shape of sulfide inclusions include Te and Ca.
TeはSと同じ16族元素の快削元素として知られており、溶鋼中ではMnTeを形成する。MnTeが析出した場合、圧延や鍛造時は硫化物系介在物の伸展を抑制することができると言われており、Te快削鋼として実用化されている。 Te is known as a free cutting element of the same group 16 element as S, and forms MnTe in molten steel. When MnTe is precipitated, it is said that extension of sulfide inclusions can be suppressed during rolling and forging, and it is put into practical use as Te free-cutting steel.
また、Caは介在物の形態制御をする際に広く用いられている元素の一つであり、CaはSと親和力が強いことから、溶鋼中ではCaSを形成する。Teと同様に、硫化物系介在物の伸展を抑制することができると言われており、Ca快削鋼として実用化されている。 Ca is one of the elements widely used for controlling the form of inclusions, and since Ca has a strong affinity for S, it forms CaS in molten steel. Like Te, it is said that extension of sulfide inclusions can be suppressed, and it is put into practical use as Ca free-cutting steel.
例えば、特許文献1には、「素材となる棒鋼でのMnSのL/W(長さ/厚み比)を適正値以下に調整する」手法として、特定量のC、Si、Mn、P、Al、O、NiおよびCrに加えて「S:0.005〜0.030%」を含有する鋼に、「Ca:5〜30ppm」または「Ca:5〜30ppmおよびTe:5〜30ppmを含有」させることを特徴とする「熱間鍛造用棒鋼の製造方法」に関する技術が開示されている。この特許文献1で提案された技術は、前記特定の化学組成を有する鋼のうち、CからSまでの元素に加えCaのみを選択して含有する鋼については、鋳片から棒鋼までの圧延比を9.5以下に、また、CからSまでの元素に加えてCaとTeの双方を含有する鋼については、鋳片から棒鋼までの圧延比を63以下にすることによりMnSの形状変形を最小限に抑制するものである。 For example, in Patent Document 1, as a method of “adjusting L / W (length / thickness ratio) of MnS in a steel bar as a raw material to an appropriate value or less”, a specific amount of C, Si, Mn, P, Al In addition to O, Ni, and Cr, steel containing “S: 0.005 to 0.030%” contains “Ca: 5 to 30 ppm” or “Ca: 5 to 30 ppm and Te: 5 to 30 ppm” A technique relating to “a method for producing a hot forging bar” is disclosed. The technique proposed in Patent Document 1 is that the steel having the specific chemical composition, in which steel containing only Ca in addition to the elements from C to S is selected, the rolling ratio from slab to bar steel For steel containing both Ca and Te in addition to the elements from C to S, the shape deformation of MnS can be reduced by reducing the rolling ratio from slab to bar steel to 63 or less. Minimize it.
また、特許文献2には「MnSを微細に分散し、かつその形状を球状に維持する」手法として、特定量のC、Si、Mn、P、Al、OおよびNに加えて「S:0.003〜0.5%」を含有する鋼に、「Zr:0.0003〜0.01%およびTe:0.0003〜0.005%のうちの1種または2種を含有」させることを特徴とする「鍛造性と被削性に優れる鋼」に関する技術が開示されている。この文献では、Zrは、ZrO2をMnSの析出サイトとして利用してMnSを均一分散させるか、または複合硫化物を生成させて変形能を低下させるものであり、TeはMnSの変形能を低下させるものであるとしている。 Patent Document 2 discloses a technique for “dispersing MnS finely and maintaining its shape in a spherical shape” in addition to a specific amount of C, Si, Mn, P, Al, O, and N as “S: 0. 0.003 to 0.5% "is made to contain" one or two of Zr: 0.0003 to 0.01% and Te: 0.0003 to 0.005% " A technique relating to the characteristic “steel excellent in forgeability and machinability” is disclosed. In this document, Zr uses ZrO 2 as a MnS precipitation site to uniformly disperse MnS or forms a composite sulfide to reduce deformability, and Te reduces the deformability of MnS. It is supposed to be
しかしながら、特許文献1では、熱間鍛造の際に割れが起こる棒鋼の表面に比較的近い部分、すなわち鋳造時に冷却速度が大きい部位に存在するMnSの形状を調整することを技術思想とし、鋳片内部に晶出するMnSの形態に関しては言及されていない。また、Caを単独で、またはCaとTeの両方を添加することに伴ってMnSの形態が変わる機構についての明確な説明、および鋼中のS量に対するCaおよびTeの添加割合に関する記述がないことから、発明の効果が安定して得られる技術ではない。さらに、特許文献1に記載の発明では、Te添加に伴う硫化物系介在物の変形能を操作するに留まっており、介在物形状に最も大きな影響を及ぼす凝固形態を制御する思想には至っていない。 However, in Patent Document 1, the technical idea is to adjust the shape of MnS present in a portion relatively close to the surface of the steel bar where cracking occurs during hot forging, that is, in a portion where the cooling rate is high during casting. No mention is made of the form of MnS crystallized inside. In addition, there is no clear explanation about the mechanism by which the form of MnS changes with the addition of Ca alone or both of Ca and Te, and there is no description about the ratio of Ca and Te added to the amount of S in steel. Therefore, this is not a technique for stably obtaining the effects of the invention. Furthermore, in the invention described in Patent Document 1, it is limited to manipulating the deformability of sulfide inclusions due to Te addition, and has not yet reached the idea of controlling the solidification form that has the greatest influence on the inclusion shape. .
また、特許文献2では、生成したMnSの変形能を抑制することを技術思想とし、MnSが析出する鋳片の段階でMnSを形態制御し球状化するものではない。このため、鋳片段階で既に製品性能に影響を及ぼす棒状に伸びた長尺なMnSが生成していた場合は、発明の効果が得られないという問題点がある。また、特許文献2に記載の発明でも、特許文献1に記載される発明と同様に、Te添加に伴う硫化物系介在物の変形能を操作するに留まっており、凝固形態を制御する思想には至っていない。 Further, in Patent Document 2, the technical idea is to suppress the deformability of the generated MnS, and MnS is not spheroidized by controlling the form of MnS at the stage of the slab where MnS is deposited. For this reason, there is a problem that the effect of the invention cannot be obtained in the case where long MnS extending in a rod shape that affects the product performance has already been generated at the slab stage. Further, in the invention described in Patent Document 2, as in the invention described in Patent Document 1, it is limited to manipulating the deformability of sulfide inclusions due to Te addition, and the idea of controlling the solidification form is considered. Has not reached.
本発明は上記に示すような課題を踏まえて検討した結果なされたものであり、その目的は、安定的に転動疲労寿命を向上させた軸受鋼鋼材を提供することにある。 The present invention has been made as a result of investigations based on the problems as described above, and an object of the present invention is to provide a bearing steel material that stably improves the rolling fatigue life.
上記の課題を解決するために、本発明者らは、軸受鋼組成の溶鋼にTeを単独で、または、TeおよびCaの両方を添加して、その時の鋳片における硫化物系介在物の形状を詳細に調査した。その結果、以下に示す知見を得た。TeおよびCaのいずれも添加しない場合、硫化物系介在物は棒状共晶として凝固生成し、粗大化する蓋然性が高いことに加え、圧延によって伸展して長尺になる(以下、単に「長尺になる」、「長尺化する」ともいう)ため、製品段階での破壊の基点となる。 In order to solve the above problems, the present inventors added Te alone or both Te and Ca to molten steel having a bearing steel composition, and the shape of sulfide inclusions in the slab at that time Were investigated in detail. As a result, the following knowledge was obtained. When neither Te nor Ca is added, the sulfide inclusions are solidified and formed as rod-like eutectics and have a high probability of coarsening, and are elongated by rolling to become long (hereinafter simply referred to as “long "It is also called" Longer "), which is the starting point for destruction at the product stage.
一方、Teを適量添加した場合、硫化物系介在物としてはMnSよりも融点の低いMnS−MnTeが生成することから、硫化物系介在物は偏晶凝固によって生成し、介在物形状は球状に近くなり、粗大化が抑制される。すなわち、適量のTe添加により、硫化物系介在物を偏晶凝固させることができ、硫化物の形状制御が可能である。このため、鋳片を圧延しても、硫化物系介在物が長尺化して破壊の基点となる蓋然性が低減される。 On the other hand, when an appropriate amount of Te is added, MnS-MnTe having a melting point lower than that of MnS is generated as the sulfide-based inclusions. Therefore, the sulfide-based inclusions are generated by monotectic solidification, and the inclusion shape is spherical. It becomes close, and coarsening is suppressed. That is, by adding an appropriate amount of Te, it is possible to solidify the sulfide inclusions and to control the shape of the sulfide. For this reason, even if the slab is rolled, the probability that the sulfide inclusions become longer and become the starting point of fracture is reduced.
この時、鋳片中の硫化物系介在物の形態はTe添加によって変化するものの、硫化物形態が変化するのは溶鋼中S濃度に応じたある閾値以上にTeを添加した場合であって、閾値以下では硫化物形態がほとんど変化しない。また、硫化物系介在物の形態が変化するTe添加量は、Te添加前にCaを添加した場合と、Caを添加しない場合とでは異なる。 At this time, although the form of the sulfide inclusions in the slab changes with the addition of Te, the form of the sulfide changes when Te is added above a certain threshold according to the S concentration in the molten steel, Below the threshold, the sulfide form hardly changes. Further, the amount of Te added in which the form of sulfide inclusions changes is different between the case where Ca is added before the addition of Te and the case where Ca is not added.
また、上記の鋳片段階での硫化物形態調査に加え、圧延後の鋼材の転動疲労寿命と硫化物形態との相関を調査した。その結果、Teを単独で、または、TeおよびCaの両方を適量添加した鋼材は転動疲労寿命が長く、破壊の基点で見つかる硫化物系介在物は、非添加の場合と比較して小型化していること、言い換えると、長尺化していないことが判明した。 Moreover, in addition to the above-mentioned sulfide form investigation at the slab stage, the correlation between the rolling fatigue life of the steel material after rolling and the sulfide form was investigated. As a result, the steel material to which Te is added alone or to which both Te and Ca are added in an appropriate amount has a long rolling fatigue life, and the sulfide inclusions found at the base point of fracture are reduced in size compared to the case of no addition. In other words, it turned out that it was not long.
本発明はこのような知見に基づきなされたもので、その要旨は、下記(1)〜(4)の軸受鋼鋼材にある。 This invention is made | formed based on such knowledge, The summary exists in the bearing steel materials of following (1)-(4).
(1)質量%で、C:0.5〜1.2%、Si:0.1〜0.9%、Mn:0.1〜2.0%、P:≦0.03%、S:0.0003〜0.03%、O:≦0.005%およびN:≦0.02%を含有し、さらに、Te:0.0002〜0.021%を含有し、残部がFeおよび不純物であり、かつ、SおよびTeの質量%での含有量がTe/S>0.4の条件を満たしており、偏晶凝固した硫化物系介在物を有することを特徴とする軸受鋼鋼材。 (1) By mass%, C: 0.5-1.2%, Si: 0.1-0.9%, Mn: 0.1-2.0%, P: ≦ 0.03%, S: 0.0003-0.03%, O: ≦ 0.005% and N: ≦ 0.02%, further Te: 0.0002-0.021%, the balance being Fe and impurities A bearing steel material characterized by having a content of S and Te in mass% satisfying a condition of Te / S> 0.4, and having a sulfide-based inclusion solidified by crystallites.
(2)質量%で、C:0.5〜1.2%、Si:0.1〜0.9%、Mn:0.1〜2.0%、P:≦0.03%、S:0.0003〜0.03%、O:≦0.005%およびN:≦0.02%を含有し、さらに、Te:0.0001〜0.016%およびCa:0.0001〜0.005%を含有し、残部がFeおよび不純物であり、かつ、S、TeおよびCaの質量%での含有量が(Te+Ca)/S>0.4の条件を満たしており、偏晶凝固した硫化物系介在物を有することを特徴とする軸受鋼鋼材。 (2) By mass%, C: 0.5-1.2%, Si: 0.1-0.9%, Mn: 0.1-2.0%, P: ≦ 0.03%, S: 0.0003-0.03%, O: ≦ 0.005% and N: ≦ 0.02%, Te: 0.0001-0.016% and Ca: 0.0001-0.005 %, The balance being Fe and impurities, and the content of S, Te and Ca in mass% satisfying the condition of (Te + Ca) / S> 0.4 Bearing steel material characterized by having system inclusions.
(3)Feの一部に代えて、質量%で、Al:≦0.04%を含有する、前記(1)または(2)に記載の軸受鋼鋼材。 (3) The bearing steel material according to (1) or (2), which contains Al: ≦ 0.04% by mass% instead of a part of Fe.
(4)Feの一部に代えて、質量%で、Cr:0.05〜2.0%、Ti:0.005〜0.1%、V:0.008〜0.3%、Mo:0.008〜1.0%、Nb:0.008〜0.1%、Ni:0.008〜2.0%およびREM(希土類元素):0.002〜0.01%のうちの1種または2種以上を含有する、前記(1)から(3)までのいずれかに記載の軸受鋼鋼材。 (4) Instead of a part of Fe, by mass%, Cr: 0.05-2.0%, Ti: 0.005-0.1%, V: 0.008-0.3%, Mo: One of 0.008 to 1.0%, Nb: 0.008 to 0.1%, Ni: 0.008 to 2.0%, and REM (rare earth element): 0.002 to 0.01% Or the bearing steel materials in any one of said (1) to (3) containing 2 or more types.
上記の「硫化物系介在物」とは、主要構成元素がMnおよびSで構成される介在物であって、走査電子顕微鏡付属のエネルギー分散型X線分析装置等で測定した場合、MnとSの占める割合が70原子%以上である介在物をさす。この時、硫化物系介在物にはTeが含まれていてもよいし、TeおよびCaの両方が含まれていてもよい。また、硫化物系介在物は酸化物系介在物を内包していてもよい。この硫化物系介在物は、鋳片1/2W、1/4T部(Wは幅、Tは厚さ方向を示す)から切り出したサンプルを鏡面研磨した上で光学顕微鏡や走査電子顕微鏡等の観察器具を用いることで観察できる。 The above-mentioned “sulfide inclusion” is an inclusion composed of Mn and S as main constituent elements. When measured with an energy dispersive X-ray analyzer attached to a scanning electron microscope, Mn and S This refers to an inclusion in which the proportion occupied by is 70 atomic% or more. At this time, Te may be contained in the sulfide type inclusion, and both Te and Ca may be contained. The sulfide inclusions may include oxide inclusions. This sulfide-based inclusion is observed with an optical microscope, a scanning electron microscope or the like after mirror-polishing a sample cut from a slab 1 / 2W, 1 / 4T portion (W is the width, T is the thickness direction). It can be observed by using an instrument.
本発明の軸受鋼鋼材は、破壊の起点となっていた粗大で長尺な硫化物系介在物の生成を抑制できることから、転動疲労寿命を伸ばすことができる。このため、自動車や産業機械にとって重要な「玉軸受け」や「コロ軸受け」などの部品の素材として利用した場合、安全性の向上およびコスト削減が可能である。 Since the bearing steel material of the present invention can suppress the formation of coarse and long sulfide inclusions that have been the starting point of fracture, the rolling fatigue life can be extended. For this reason, when used as a material for parts such as “ball bearings” and “roller bearings” which are important for automobiles and industrial machines, safety can be improved and costs can be reduced.
以下に、本発明(実施形態を含む)を詳細に説明する。
(A)鋼の化学組成
本発明の軸受鋼鋼材に含まれる各成分の作用効果とその含有量の限定理由について説明する。なお、各成分の「%」はすべて「質量%」を意味する。
The present invention (including embodiments) will be described in detail below.
(A) Chemical composition of steel The effect of each component contained in the bearing steel material of the present invention and the reason for limiting the content thereof will be described. In addition, all “%” of each component means “mass%”.
C:0.5〜1.2%
Cは母材強度を確保するとともに、焼入れ時の表面固さや被削性に影響し、転動疲労寿命にも影響を及ぼす元素である。軸受鋼としての用途を考慮すると、Cは0.5%以上含有させることが必要である。一方、C含有量が過度に高くなると母材の硬さが高くなりすぎて加工性が低下することに加え、切削加工時の工具寿命も著しく低下する。このため、C含有量の上限を1.2%とした。望ましいC含有量は0.55〜1.1%の範囲である。
C: 0.5 to 1.2%
C is an element that secures the strength of the base material, affects the surface hardness and machinability during quenching, and also affects the rolling fatigue life. Considering the application as bearing steel, C is required to be contained by 0.5% or more. On the other hand, when the C content is excessively high, the hardness of the base material becomes too high and the workability is lowered, and the tool life at the time of cutting is significantly reduced. For this reason, the upper limit of the C content is set to 1.2%. The desirable C content is in the range of 0.55 to 1.1%.
Si:0.1〜0.9%
Siは固溶強化作用を有し、焼き入れ性を高めて転動疲労寿命を向上させるのに有効な元素である。また、Siは脱酸元素であり、後述するO(酸素)含有量を0.005%以下に制御するためにも0.1%以上含有させることが必要である。しかしながら、Siを0.9%を超えて含有させると固溶強化が過剰になり、切削時の工具寿命低下を引き起こす。このため、Siの含有量の上限を0.9%とした。望ましいSi含有量は0.15〜0.7%である。
Si: 0.1-0.9%
Si has a solid solution strengthening action, and is an effective element for enhancing the hardenability and improving the rolling fatigue life. Si is a deoxidizing element, and it is necessary to contain 0.1% or more in order to control the O (oxygen) content described later to 0.005% or less. However, if Si is contained in excess of 0.9%, the solid solution strengthening becomes excessive, causing a reduction in tool life during cutting. For this reason, the upper limit of the Si content is set to 0.9%. A desirable Si content is 0.15 to 0.7%.
Mn:0.1〜2.0%
Mnは鋼材の焼入れ性を高める元素であるとともに、被削性を向上させるMnSを形成する元素であり、積極的に添加する。含有量が少なすぎると効果に乏しいため、0.1%以上含有させることが必要である。しかしながら、Mn含有量が過度に高くなると焼き入れ後の表面硬さが高くなりすぎて加工性が低下することに加え、切削加工時の工具寿命も著しく低下する。さらには焼き割れの原因にもなりうる。このため、Mnの含有量の上限を2.0%とした。望ましいMn含有量は0.2〜1.2%である。
Mn: 0.1 to 2.0%
Mn is an element that improves the hardenability of the steel material, and is an element that forms MnS that improves the machinability, and is actively added. If the content is too small, the effect is poor, so it is necessary to contain 0.1% or more. However, if the Mn content is excessively high, the surface hardness after quenching becomes excessively high and the workability is lowered, and the tool life at the time of cutting is significantly reduced. Furthermore, it can cause burn cracking. For this reason, the upper limit of the Mn content is set to 2.0%. A desirable Mn content is 0.2 to 1.2%.
P:≦0.03%
Pは結晶粒界に析出して鋼材の靭性や延性の低下をもたらす元素である。Pの含有量が0.03%を超えると、転動疲労寿命の低下が顕著に現れるようになることから、Pの含有量を0.03%以下とした。望ましいP含有量は0.01%以下である。
P: ≦ 0.03%
P is an element that precipitates at the grain boundaries and causes the toughness and ductility of the steel material to decrease. When the content of P exceeds 0.03%, a decrease in rolling fatigue life appears remarkably, so the content of P is set to 0.03% or less. A desirable P content is 0.01% or less.
S:0.0003〜0.03%
Sは鋼材にとって強度を低下させる有害な元素である一方、快削元素であり、MnSとして被削性を向上させる。添加量は少ないほど好ましいが、被削性を確保するためには0.0003%以上の含有量が必要である。一方、S含有量が高いほど粗大な硫化物系介在物が生成する蓋然性も高くなるが、Te、またはTeとCaの添加に伴う硫化物形態制御の効果が確実に得られる範囲を考慮してSの含有量の上限を0.03%とした。
S: 0.0003 to 0.03%
S is a harmful element that reduces the strength of steel, while it is a free-cutting element and improves machinability as MnS. The smaller the addition amount, the better. However, in order to ensure machinability, a content of 0.0003% or more is necessary. On the other hand, the higher the S content, the higher the probability that coarse sulfide inclusions will be generated. However, considering the range in which the effect of sulfide morphology control associated with the addition of Te or Te and Ca can be reliably obtained. The upper limit of the S content was 0.03%.
O:≦0.005%
Oは鋼材の製造過程で不可避的に含有される元素であり、酸化物系介在物である場合と溶存している場合がある。酸化物系介在物の酸素と溶存している酸素を分離することは困難であるため、本発明におけるO含有量は両者を合わせた全O濃度とする。酸化物系介在物は鋼材の強度、被削性、転動疲労寿命に大きく影響する。溶存している場合、硫化物系介在物の形態に影響を及ぼす。全O濃度が高くなると、粗大な酸化物系介在物が生成する蓋然性が増加することに加え、上記Caの添加効果が十分に得られない。このため、Oの含有量の上限を0.005%とした。望ましいO含有量は0.002%以下である。
O: ≦ 0.005%
O is an element inevitably contained in the manufacturing process of the steel material, and may be an oxide inclusion or may be dissolved. Since it is difficult to separate oxygen from oxide inclusions and dissolved oxygen, the O content in the present invention is the total O concentration of both. Oxide inclusions greatly affect the strength, machinability, and rolling fatigue life of steel materials. When dissolved, it affects the morphology of sulfide inclusions. When the total O concentration is increased, the probability that coarse oxide inclusions are generated increases, and in addition, the above Ca addition effect cannot be sufficiently obtained. For this reason, the upper limit of the content of O is set to 0.005%. A desirable O content is 0.002% or less.
N:≦0.02%
Nは窒化物を構成し、結晶粒を微細化して母材強度を向上させる元素である。0.02%を超えてNを含有させると粗大な窒化物が生成し、転動疲労寿命の低下を招く。このため、Nの含有量の上限を0.02%とした。
N: ≦ 0.02%
N is an element that constitutes a nitride and refines the crystal grains to improve the strength of the base material. When N is contained in excess of 0.02%, coarse nitrides are generated, and the rolling fatigue life is reduced. For this reason, the upper limit of the content of N is set to 0.02%.
Te:0.0002〜0.021%(単独添加の場合)
Te:0.0001〜0.016%(Caと複合添加の場合)
TeはMnと結合して低融点のMnTeを形成することで、硫化物系介在物の晶出形態を変化させる重要な元素である。すなわち、Teは凝固過程でMnSよりも融点の低いMnS−MnTeを形成することで硫化物の晶出形態を共晶から偏晶へ変化させ、前述のように介在物形状を球状に近いものとすることが可能である。また、硫化物系介在物の伸展を抑制する効果もある。
Te: 0.0002 to 0.021% (in the case of single addition)
Te: 0.0001 to 0.016% (when combined with Ca)
Te is an important element that changes the crystallization form of sulfide inclusions by forming MnTe having a low melting point by combining with Mn. That is, Te forms MnS-MnTe having a melting point lower than that of MnS during the solidification process, thereby changing the crystallization form of sulfide from eutectic to orthorhombic, and the inclusion shape is nearly spherical as described above. Is possible. It also has an effect of suppressing the extension of sulfide inclusions.
このような、Te添加に伴う硫化物系介在物の形態制御効果を得るには、Te単独添加の場合は0.0002%以上の含有量が必要である。一方、TeをCaと複合添加した場合は、CaがCaSを形成することから、後述するように、MnS−MnTeを形成するのに必要なTe量は少なくて済む。このため、Caと複合添加する場合のTeの含有量の下限を0.0001%とした。 In order to obtain the shape control effect of sulfide inclusions accompanying the addition of Te, a content of 0.0002% or more is necessary in the case of adding Te alone. On the other hand, when Te is added in combination with Ca, since Ca forms CaS, the amount of Te necessary to form MnS-MnTe is small as will be described later. For this reason, the lower limit of the Te content when combined with Ca is set to 0.0001%.
また、Te含有量が高くなりすぎると鋳造時の熱間脆化や圧延時の割れなどの問題がでてくるため、Te単独添加の場合は、Teの含有量の上限を0.021%とした。一方、Caと複合添加する場合は、Ca添加量分だけTe添加量を低減できるため、Caと複合添加する場合のTeの含有量の上限は0.016%とした。 Further, if the Te content becomes too high, problems such as hot embrittlement during casting and cracking during rolling occur. Therefore, in the case of adding Te alone, the upper limit of the Te content is 0.021%. did. On the other hand, when compounding with Ca, the amount of Te addition can be reduced by the amount of Ca addition, so the upper limit of the Te content when compounding with Ca is 0.016%.
Ca:0.0001〜0.005%
Caは硫化物系介在物中に固溶し、CaSを形成することで、硫化物晶出時の過冷却を緩和し、硫化物系介在物の粗大化を抑制できる。また、Teと同時に添加した場合はCaTeを形成することで、鋳造時の熱間脆化を引き起こすFeTeの生成を抑制できる。しかしながら、Ca単独添加では硫化物の晶出形態は大きく変化しないことから、Teと複合添加することが必要である。Ca含有量は微量であっても効果が得られるため、下限を0.0001%とした。しかしながら、0.005%を超えてCaを含有させても効果が飽和し、Ca添加に伴って精錬時間が延びるため、溶製費用が増加する。このため、Caの含有量の上限を0.005%とした。
Ca: 0.0001 to 0.005%
Ca dissolves in sulfide inclusions to form CaS, thereby relaxing supercooling during sulfide crystallization and suppressing the coarsening of sulfide inclusions. Moreover, when it adds simultaneously with Te, the production | generation of FeTe which causes the hot embrittlement at the time of casting can be suppressed by forming CaTe. However, when Ca alone is added, the crystallization form of sulfide does not change greatly, so it is necessary to add it together with Te. Since the effect is obtained even if the Ca content is very small, the lower limit was made 0.0001%. However, even if Ca is contained in excess of 0.005%, the effect is saturated, and the refining time is extended with the addition of Ca, so the melting cost increases. For this reason, the upper limit of the Ca content is set to 0.005%.
本発明の軸受鋼鋼材には、必要に応じて、Al、または/および、Cr、Ti、V、Mo、Nb、NiおよびREM(希土類元素)のうちのいずれか1種以上を積極的に添加含有させてもよい。 The bearing steel material of the present invention is positively added with Al or / and any one or more of Cr, Ti, V, Mo, Nb, Ni and REM (rare earth elements) as necessary. You may make it contain.
Al:≦0.04%
Alは強力な脱酸元素であり、鋼中でAl2O3を形成する。上述したCa添加効果を得るには十分に脱酸しておくことが好ましいが、粗大なAl2O3は転動疲労寿命を低下させるために、過剰なAl添加は避けるべきである。このため、添加する場合のAlの含有量は、0.04%以下とするのがよい。
Al: ≦ 0.04%
Al is a strong deoxidizing element and forms Al 2 O 3 in steel. It is preferable to sufficiently deoxidize to obtain the Ca addition effect described above, but excessive Al addition should be avoided because coarse Al 2 O 3 reduces the rolling fatigue life. For this reason, the content of Al when added is preferably 0.04% or less.
Cr:0.05〜2.0%
Crは焼き入れ性を高めて転動疲労寿命を向上させるのに有効な元素であり、その効果は0.05%以上含有させると顕著になる。しかしながら、Crを2.0%を超えて含有させると、焼き入れ後の表面硬さが高くなりすぎて加工性が低下することに加えて、切削加工時の工具寿命も著しく低下する。このため、添加する場合のCr含有量は、0.05〜2.0%とするのがよい。この場合の望ましいCr含有量は0.9〜1.6%である。
Cr: 0.05-2.0%
Cr is an element effective for improving the hardenability and improving the rolling fatigue life, and the effect becomes remarkable when the content is 0.05% or more. However, when Cr is contained in excess of 2.0%, the surface hardness after quenching becomes too high and the workability is lowered, and the tool life at the time of cutting is significantly reduced. For this reason, when Cr is added, the Cr content is preferably 0.05 to 2.0%. The desirable Cr content in this case is 0.9 to 1.6%.
Ti:0.005〜0.1%
Tiは脱酸元素であるとともに、鋼材中で炭化物、窒化物を形成して母材強度を向上させる元素であり、0.005%以上添加することでその効果が得られる。しかしながら、Tiの含有量が0.1%を超えると硬質のTiNの粗大化によって転動疲労寿命が低下する。したがって、添加する場合のTi含有量は、0.005〜0.1%とするのがよい。
Ti: 0.005 to 0.1%
Ti is a deoxidizing element and is an element that improves the strength of the base metal by forming carbides and nitrides in the steel, and its effect can be obtained by adding 0.005% or more. However, if the Ti content exceeds 0.1%, the rolling fatigue life decreases due to the coarsening of hard TiN. Therefore, when Ti is added, the Ti content is preferably 0.005 to 0.1%.
V:0.008〜0.3%
Vは鋼材中で炭化物、窒化物を形成し、フェライト強化によって母材強度を向上させる元素であり、0.008%以上含有させることでその効果が得られる。しかしながら、Vを0.3%を超えて含有させると被削性が低下する。したがって、添加する場合のV含有量は0.008〜0.3%とするのがよい。
V: 0.008 to 0.3%
V is an element that forms carbides and nitrides in the steel and improves the strength of the base material by strengthening ferrite, and the effect can be obtained by adding 0.008% or more. However, if V is contained in excess of 0.3%, the machinability is lowered. Therefore, when V is added, the V content is preferably 0.008 to 0.3%.
Mo:0.008〜1.0%
Moは焼き入れ性を高め、母材強度を向上させる元素であり、0.008%以上含有させることでその効果が得られる。しかしながら、Moを1.0%を超えて含有させると、切削加工時の工具寿命が低下する。したがって、添加する場合のMo含有量は0.008〜1.0%とするのがよい。
Mo: 0.008 to 1.0%
Mo is an element that improves the hardenability and improves the strength of the base material, and its effect can be obtained by adding 0.008% or more. However, when Mo is contained in excess of 1.0%, the tool life during cutting is reduced. Therefore, the Mo content when added is preferably 0.008 to 1.0%.
Nb:0.008〜0.1%
Nbは鋼材中で炭化物や炭窒化物を形成し、フェライト強化によって母材強度を向上させる元素であり、0.008%以上含有させることでその効果が得られる。しかしながら、Nbを0.1%を超えて含有させると粗大な窒化物を形成して転動疲労寿命が低下することに加え、切削加工時の工具寿命が低下する。したがって、添加する場合のNb含有量は0.008〜0.1%とするのがよい。
Nb: 0.008 to 0.1%
Nb is an element that forms carbides or carbonitrides in steel and improves the strength of the base metal by strengthening ferrite, and its effect can be obtained by adding 0.008% or more. However, when Nb exceeds 0.1%, coarse nitrides are formed and the rolling fatigue life is reduced, and the tool life during cutting is reduced. Therefore, the Nb content when added is preferably 0.008 to 0.1%.
Ni:0.008〜2.0%
Niは焼き入れ性を高め、母材強度を向上させる元素であり、0.008%以上添加することでその効果が得られる。しかしながら、Niの含有量が2.0%を超えると切削加工時の工具寿命の低下を招き、さらに焼き割れの原因にもなる。したがって、添加する場合のNi含有量は0.008〜2.0%とするのがよい。
Ni: 0.008 to 2.0%
Ni is an element that improves the hardenability and improves the strength of the base material, and its effect can be obtained by adding 0.008% or more. However, if the Ni content exceeds 2.0%, the tool life at the time of cutting will be reduced, and it will cause burn cracking. Therefore, the Ni content when added is preferably 0.008 to 2.0%.
REM(希土類元素):0.002〜0.01%
REMとは、スカンジウム(Sc)、イットリウム(Y)およびランタノイドの17元素を指す。REMはSやOと強い親和力を有し、REM酸化物またはREM硫化物を形成する。REMは鋼材中では化学的にはほぼ等価とみなし、これらの合計含有量をREM含有量とする。REM源としてミッシュメタルを使用する場合は、便宜上La、CeおよびNd含有量の和をREM含有量とみなすことができる。REMは0.002%以上添加することで、REM系介在物が鋼材中に微細分散し、鋼材の被削性が向上する。しかしながら、REMの含有量が0.01%を超えると硬質のREM酸化物の生成量が増大することから、切削加工時の工具寿命の低下を招く。したがって、添加する場合のREM含有量は0.002〜0.01%とするのがよい。
REM (rare earth element): 0.002 to 0.01%
REM refers to 17 elements of scandium (Sc), yttrium (Y) and lanthanoid. REM has strong affinity with S and O, and forms REM oxide or REM sulfide. REM is considered to be chemically equivalent in steel materials, and the total content thereof is taken as the REM content. When misch metal is used as the REM source, the sum of La, Ce and Nd contents can be regarded as the REM content for convenience. By adding 0.002% or more of REM, REM inclusions are finely dispersed in the steel material, and the machinability of the steel material is improved. However, if the REM content exceeds 0.01%, the amount of hard REM oxide generated increases, leading to a reduction in tool life during cutting. Therefore, the REM content when added is preferably 0.002 to 0.01%.
本発明の軸受鋼鋼材は、以上に述べた成分と残部Feおよび不純物で構成されるものとする。なお、Mgは耐火物からの溶出によって溶鋼に混入する不可避な元素であり、一般的には不純物として取り扱われる。溶鋼中のMg濃度が高い場合、硬質なMgOが形成され、鋼材の被削性が低下する。また、MgSが形成されると、硫化物系介在物の晶出基点となり、介在物の球状化が阻害されることから、Mgの含有量は0.002%以下、さらには0.001%以下であることが望ましい。 The bearing steel material of the present invention is composed of the above-described components, the remaining Fe and impurities. Mg is an inevitable element mixed into molten steel by elution from a refractory, and is generally handled as an impurity. When the Mg concentration in the molten steel is high, hard MgO is formed and the machinability of the steel material is lowered. Further, when MgS is formed, it becomes a crystallization starting point of sulfide inclusions, and the spheroidization of inclusions is inhibited. Therefore, the Mg content is 0.002% or less, and further 0.001% or less. It is desirable that
(B)Te/Sおよび(Te+Ca)/S
前記(1)〜(4)に示す本発明の鋼材は、硫化物系介在物の形態制御を行うために、溶鋼中のS含有量に応じて投入するTe量または(Te+Ca)量を調整する必要がある。この技術の根幹は、Teを添加することにより、溶鋼の凝固過程において、MnSよりも融点の低いMnTeを形成させることで、硫化物系介在物をMnSよりも融点の低いMnS−MnTeとし、硫化物系介在物の棒状共晶化を抑制して、偏晶凝固させることにある。
(B) Te / S and (Te + Ca) / S
The steel materials of the present invention shown in the above (1) to (4) adjust the amount of Te or (Te + Ca) to be introduced according to the S content in the molten steel in order to control the form of sulfide inclusions. There is a need. The basis of this technology is that by adding Te, in the solidification process of molten steel, MnTe having a melting point lower than that of MnS is formed, thereby making the sulfide inclusions MnS-MnTe having a melting point lower than that of MnS. The object is to solidify the crystals by suppressing the bar-shaped eutectic formation of the inclusions.
前掲の非特許文献1に報告されているFe−MnS擬2元系状態図によると、通常、MnSはFeを主体とする液相からFeの固相とMnSの固相が形成される共晶反応により生成される。この時に生成されるMnS形態は長尺な棒状共晶であり、圧延するとさらに長尺化するため破壊の基点になりうる。しかしながら、MnSの液相が準安定的に存在しうる条件に整えると、MnSはFeを主体とする液相からFeの固相とMnSの液相が形成される偏晶反応により生成される。偏晶凝固により生成されるMnSの形態は球状であり、圧延しても長尺化する蓋然性が低い。この棒状共晶化の抑制効果、すなわち偏晶凝固による効果を確実に得るには、Te/S>0.4とする必要がある。 According to the Fe-MnS pseudo binary phase diagram reported in the aforementioned Non-Patent Document 1, normally, MnS is a eutectic in which a solid phase of Fe and a solid phase of MnS are formed from a liquid phase mainly composed of Fe. Produced by reaction. The MnS form produced at this time is a long bar-shaped eutectic, and when it is rolled, it becomes longer and can be the starting point of fracture. However, when the liquid phase of MnS is prepared so that the liquid phase can exist metastable, MnS is generated by a monotectic reaction in which a solid phase of Fe and a liquid phase of MnS are formed from a liquid phase mainly composed of Fe. The form of MnS produced by the monotectic solidification is spherical and has a low probability of being elongated even when rolled. Te / S> 0.4 needs to be satisfied in order to reliably obtain the effect of suppressing the bar-like eutecticization, that is, the effect due to the monotectic solidification.
ここで、溶鋼の凝固末期にTeに加えてCaが添加されている場合、溶鋼が十分に脱酸されている条件下において硫化物系介在物はCaS、MnS、MnTeで構成されることになる。すなわち、融点の低いMnS−MnTeを形成するのに必要なTe量はCaSを形成するS分だけ少なくて済むことになる。したがって、TeとCaを複合添加した場合、棒状共晶化の抑制効果を確実に得るには、(Ca+Te)/S>0.4とする必要がある。 Here, when Ca is added in addition to Te at the end of solidification of the molten steel, the sulfide inclusions are composed of CaS, MnS, and MnTe under the condition that the molten steel is sufficiently deoxidized. . That is, the amount of Te necessary to form MnS-MnTe having a low melting point is reduced by the amount of S that forms CaS. Therefore, when Te and Ca are added in combination, it is necessary to satisfy (Ca + Te) / S> 0.4 in order to reliably obtain the rod-like eutectic suppression effect.
上述したTeおよびCaは溶鋼の精錬段階において、金属塊または合金塊として添加することが可能である。また、他の元素と混合した合金ワイヤーとして添加することも可能である。これらの元素は添加歩留まりが低いことから、精錬の後半から末期にかけて添加することが望ましい。さらに、十分に脱酸された溶鋼に対して添加することが望ましい。 Te and Ca described above can be added as a metal lump or alloy lump in the refining stage of molten steel. Moreover, it is also possible to add as an alloy wire mixed with other elements. Since these elements have a low addition yield, it is desirable to add them from the latter half of the refining to the last stage. Furthermore, it is desirable to add to the fully deoxidized molten steel.
一方、硫化物系介在物の棒状共晶化抑制効果は、上記のTe/S>0.4または(Ca+Te)/S>0.4を満たすことで得られ、これを超えてTeまたはCaを過剰に添加しても効果が飽和する。したがって、Te/Sまたは(Ca+Te)/Sは、0.6未満、さらには0.5未満であることが望ましい。 On the other hand, the rod-like eutectic suppression effect of sulfide inclusions is obtained by satisfying the above Te / S> 0.4 or (Ca + Te) / S> 0.4, and beyond this, Te or Ca is contained. The effect is saturated even if added excessively. Therefore, it is desirable that Te / S or (Ca + Te) / S is less than 0.6, more preferably less than 0.5.
(C)硫化物系介在物の形態
本発明の鋼材は、上記の(A)に示した化学組成を満たし、かつ、(B)に示したTe、Ca、Sの関係を満たした上で、一般的な取鍋精錬プロセスを経て、連続鋳造法または造塊法によって製造される。ここでいう取鍋精錬プロセスとは、LF(Ladle Furnace)、VAD(Vacuum Arc Degassing)と称される昇熱装置を持つ取鍋精錬設備、RHと称される真空脱ガス装置を用いる精錬設備を用いて溶鋼温度と成分を調整するプロセスを指す。上記工程によって鋼材中の硫化物は偏晶凝固によって生成されることが必要である。
(C) Form of sulfide inclusions The steel material of the present invention satisfies the chemical composition shown in (A) above and satisfies the relationship of Te, Ca, and S shown in (B). Through a general ladle refining process, it is produced by a continuous casting method or an ingot-making method. The ladle refining process here refers to a ladle refining facility having a heating device called LF (Laddle Furnace) or VAD (Vacuum Arc Degassing), or a refining facility using a vacuum degassing device called RH. Used to refer to the process of adjusting molten steel temperature and composition. It is necessary that the sulfide in the steel material is generated by the monotectic solidification by the above process.
本発明の軸受鋼鋼材は、前記連続鋳造法または造塊法で製造された鋳片または鋼塊を、1000℃を超える温度域で分塊圧延し、得られた鋼片にさらに棒鋼圧延や線材圧延を加えることによって製造することができる。上記工程によって鋼材中の硫化物系介在物は長手方向に伸展される。この時に鋼材の長手方向縦断面に現れる硫化物系介在物は、極力アスペクト比(長さ/厚さ比)が小さい、すなわち偏晶凝固によって生成した介在物であることが必要である。棒状共晶として生成し、長尺化した硫化物系介在物が鋼材内に多数存在する場合、転動疲労試験において、試験片上の軌道面に硫化物が現れる確率が高くなり、転動疲労寿命の大幅な低下をもたらす。一方、棒状共晶の生成を抑制し、硫化物系介在物を偏晶凝固により生成させた場合は、軌道面に硫化物系介在物が現れる確率を大幅に低下させることが可能である。 The bearing steel material of the present invention is obtained by subjecting the slab or steel ingot produced by the continuous casting method or the ingot-making method to ingot rolling in a temperature range exceeding 1000 ° C. It can be manufactured by applying rolling. Through the above process, the sulfide inclusions in the steel material are extended in the longitudinal direction. At this time, the sulfide-based inclusion appearing in the longitudinal cross section of the steel material needs to be an inclusion having an aspect ratio (length / thickness ratio) as small as possible, that is, an inclusion generated by monotectic solidification. When there are many sulfide inclusions that are formed as rod-like eutectic and are elongated in the steel, the rolling fatigue test increases the probability of sulfide appearing on the raceway surface on the specimen, and the rolling fatigue life Cause a significant drop in On the other hand, when the formation of rod-shaped eutectic is suppressed and sulfide inclusions are generated by the monotectic solidification, the probability that sulfide inclusions appear on the raceway surface can be greatly reduced.
なお、上記の連続鋳造法によって製造された鋳片または鋼材中の硫化物系介在物は、光学顕微鏡または走査電子顕微鏡等の観察装置によって観察することが可能である。転動疲労試験において破壊の基点となりうる可能性が高い、100mm2の観察視野内に存在する円相当径で5μm以上の硫化物(この硫化物を、以下、単に「5μm以上の硫化物」ともいう)の全てが観察の対象である。 The sulfide inclusions in the slab or steel produced by the above continuous casting method can be observed with an observation device such as an optical microscope or a scanning electron microscope. A sulfide having a circle equivalent diameter of 5 μm or more present in the observation field of 100 mm 2 , which is likely to be a starting point of fracture in a rolling fatigue test (hereinafter referred to as “sulfide of 5 μm or more”). All) are the objects of observation.
また、上記の硫化物の凝固形態に関して、本発明では顕微鏡観察画像をもとに硫化物形状を数値化することで判別できる。すなわち、偏晶凝固した硫化物は球状に近い形状で孤立して存在している一方、共晶凝固の場合は長く延びた棒状の形状で存在しているので、後述する実施例において示すように、この特徴を数値化し、Te単独で、またはTeとCaの両方を添加した場合と、それらのいずれも添加しない場合とを比較して、球状に近い硫化物の存在割合が大きい場合は、偏晶凝固していると判定し、一方、球状に近い硫化物の存在割合が小さい場合は、すなわち長尺な硫化物の存在割合が大きい場合、硫化物は棒状共晶として生成したものであると判定する。 In addition, the solidification form of the sulfide can be determined by quantifying the sulfide shape based on a microscope observation image in the present invention. That is, while the solidified sulfide is present in an isolated shape in a nearly spherical shape, in the case of eutectic solidification, it exists in the shape of a bar that extends long. When this feature is quantified and compared with the case where Te alone or both of Te and Ca are added and the case where neither of them is added, when the ratio of sulfides close to spherical is large, On the other hand, when the existence ratio of sulfides close to a sphere is small, that is, when the existence ratio of long sulfides is large, the sulfide is produced as a rod-like eutectic. judge.
表1に示す組成の鋼を溶製した。このとき、溶鋼量を約80トンとし、鋼種毎にTe、Ca量を変更して溶製した。 Steels having the compositions shown in Table 1 were melted. At this time, the amount of molten steel was about 80 tons, and the amounts of Te and Ca were changed for each steel type to produce the steel.
精錬段階においては、高炉から出銑された溶銑を溶銑予備処理設備で脱S処理し、転炉型精錬容器にて脱Pおよび脱C処理した後、取り鍋に受鋼した。次に、フラックスインジェクション法によって石灰−蛍石系のフラックスを吹き込み、VADにてArガスを用いて40分程度溶鋼を攪拌した。なお、VADにおいて溶鋼組成を調整した後、溶鋼にTeを添加した。また、Caを添加する場合、ワイヤー添加装置でCaを添加した後、Teを添加した。その後、連続鋳造法により300mm×400mmサイズのモールドで鋳込み、鋳片を得た。 In the refining stage, the hot metal discharged from the blast furnace was de-S treated with a hot metal pretreatment facility, de-P and de-C treated with a converter-type refining vessel, and then received into a ladle. Next, a lime-fluorite-based flux was blown by a flux injection method, and the molten steel was stirred for about 40 minutes using Ar gas by VAD. In addition, after adjusting the molten steel composition in VAD, Te was added to the molten steel. Moreover, when adding Ca, after adding Ca with a wire addition apparatus, Te was added. Then, it cast by the mold of 300 mm x 400 mm size by the continuous casting method, and obtained the slab.
ここで得られた鋳片の1/2W、1/4T部(Wは幅、Tは厚さ方向を示す)から介在物観察用のブロックサンプルを切り出し、樹脂埋め、鏡面研磨した。得られたサンプル中の介在物を光学顕微鏡または走査電子顕微鏡で観察し、硫化物系介在物に関してその形態を調査した。なお、この時の介在物観察では、硫化物系介在物形態が棒状共晶であるか、偏晶であるかを判別することを目的とし、100mm2内に存在する5μm以上の硫化物系介在物の全てについて、その大きさおよび形状を調査した。ここで、画像処理によって下記(1)式に示す凹凸度を算出することで、硫化物系介在物の形状を定量評価した。
凹凸度=(硫化物周囲長)2/(4×π×硫化物面積) ・・・(1)
A block sample for observing inclusions was cut out from the 1/2 W and 1/4 T parts (W is the width and T is the thickness direction) of the slab obtained here, embedded in resin, and mirror-polished. Inclusions in the obtained sample were observed with an optical microscope or a scanning electron microscope, and the morphology of the sulfide inclusions was investigated. In addition, in the observation of inclusions at this time, for the purpose of determining whether the sulfide-type inclusions are rod-like eutectics or monocrystals, sulfide-type inclusions of 5 μm or more existing in 100 mm 2 are used. All of the objects were examined for size and shape. Here, the shape of the sulfide inclusions was quantitatively evaluated by calculating the degree of unevenness shown in the following formula (1) by image processing.
Concavity and convexity = (sulfide circumference) 2 / (4 × π × sulfide area) (1)
すなわち、鋳片段階では、偏晶凝固した硫化物は球状に近い形状であり、共晶反応により生成した硫化物は長く延びた棒状の形状で存在しているので、凹凸度という指標を導入し、凹凸度が3を超える硫化物の割合から、偏晶もしくは共晶の凝固形態を判定した。 In other words, at the slab stage, the solidified sulfides in the form of spheroids have a nearly spherical shape, and the sulfides produced by the eutectic reaction exist in the shape of elongated rods. From the ratio of sulfides with a degree of unevenness exceeding 3, the solidification form of the monotectic or eutectic was determined.
これらの鋳片を1200℃の均熱炉で保持した後、1020から1100℃の温度域で分解圧延し、断面寸法が160mm×160mmの鋼片とした。さらに、この鋼片を1050℃に加熱した後、800〜930℃の温度域で棒鋼圧延して直径70mm(以下、「φ70mm」という)の棒鋼を得た。この時、全圧下比が15以上、1000℃以上の温度域での圧下比が4以上になるように圧下を加えた。 These cast slabs were held in a soaking furnace at 1200 ° C. and then cracked and rolled at a temperature range of 1020 to 1100 ° C. to obtain steel pieces having a cross-sectional dimension of 160 mm × 160 mm. Further, this steel slab was heated to 1050 ° C., and then rolled in a temperature range of 800 to 930 ° C. to obtain a steel bar having a diameter of 70 mm (hereinafter referred to as “φ70 mm”). At this time, the reduction was applied so that the total reduction ratio was 15 or more and the reduction ratio in the temperature range of 1000 ° C. or more was 4 or more.
ここで得られた棒鋼の1/2W、1/4T部から介在物観察用のブロックサンプルを切り出し、樹脂埋め、鏡面研磨した。鋳片段階での調査と同様に、得られたサンプル中の介在物を光学顕微鏡または走査電子顕微鏡で観察し、硫化物系介在物に関してその形態を調査した。なお、この時の介在物観察では、5μm以上の硫化物系介在物のアスペクト比を調査することを目的とし、長手方向に被検面積100mm2の観察を10回行い、その平均から硫化物系介在物のアスペクト比を算出した。アスペクト比が4以下であれば、球状に近い硫化物であると評価し、アスペクト比が4以下の硫化物の割合から、偏晶もしくは共晶の凝固形態を判定した。 A block sample for observing inclusions was cut out from the 1/2 W, 1/4 T part of the steel bar obtained here, embedded in resin, and mirror polished. Similar to the investigation at the slab stage, the inclusions in the obtained sample were observed with an optical microscope or a scanning electron microscope, and the form of the sulfide inclusions was investigated. In addition, in the inclusion observation at this time, for the purpose of investigating the aspect ratio of sulfide inclusions of 5 μm or more, the observation area of 100 mm 2 in the longitudinal direction was observed 10 times, and the average of the sulfide type was observed. The aspect ratio of inclusions was calculated. If the aspect ratio was 4 or less, it was evaluated as a sulfide having a nearly spherical shape, and the solidification form of the monotectic or eutectic was determined from the ratio of the sulfide having an aspect ratio of 4 or less.
上記の方法で得たφ70mmの棒鋼に対して、球状化焼鈍処理(780℃で6時間保持した後、炉冷)を適用し、その後、長手方向が素形材の厚みとなるように直径60mm、厚さ5.5mmの素形材をスライスして採取した。この素形材を830℃で30分加熱した後、油焼入れし、さらに180℃で1時間加熱した後、大気中で放冷することで焼き戻しした。さらに、この素形材の表面をラッピング加工して転動疲労試験片を作成し、転動疲労試験に供した。 A spheroidizing annealing treatment (furnace cooling after holding at 780 ° C. for 6 hours) is applied to the φ70 mm steel bar obtained by the above method, and then the diameter is 60 mm so that the longitudinal direction becomes the thickness of the shaped material. The raw material with a thickness of 5.5 mm was sliced and collected. The shaped material was heated at 830 ° C. for 30 minutes, then quenched with oil, further heated at 180 ° C. for 1 hour, and then tempered by being allowed to cool in the air. Further, a rolling fatigue test piece was prepared by lapping the surface of the shaped material and subjected to a rolling fatigue test.
転動疲労試験条件を表2に示す。 Table 2 shows the rolling fatigue test conditions.
転動疲労試験はスラスト型の転動疲労試験機を用い、繰り返し速度1800cpm(cycle per minute)、最大接触面圧5230MPaの条件とした。転動疲労試験結果は、ワイブル分布確率紙上にプロットし、10%破損確率を示すL10寿命を転動疲労寿命として評価した。この時、同一鋼種内での転動疲労寿命において、Te非添加の条件と比較して15%以上の転動疲労寿命の改善が認められた条件を、改善効果有りと判定した。 The rolling fatigue test was performed using a thrust type rolling fatigue tester under conditions of a repetition rate of 1800 cpm (cycle per minute) and a maximum contact surface pressure of 5230 MPa. Rolling fatigue test results were plotted on paper Weibull distribution probability was evaluated L 10 life showing a 10% failure probability as a rolling contact fatigue life. At this time, in the rolling fatigue life in the same steel type, a condition in which an improvement in the rolling fatigue life of 15% or more was recognized compared with the condition in which Te was not added was determined to have an improvement effect.
表3に、5μm以上の全硫化物数に対する凹凸度が3以上の硫化物数の割合(%)、5μm以上の全硫化物数に対するアスペクト比が4以下の硫化物数の割合(%)、転動疲労寿命、および疲労寿命の改善効果を示す。なお、「疲労寿命の改善効果」の欄の○印は改善効果があったことを、×印は改善効果がなかったことを表す。また、「分類」の欄の「本」は本発明例であることを、「比」は比較例であることを意味する。 Table 3 shows the ratio (%) of the number of sulfides having an unevenness degree of 3 or more to the total number of sulfides of 5 μm or more, and the ratio (%) of the number of sulfides having an aspect ratio of 4 or less to the total number of sulfides of 5 μm or more. The rolling fatigue life and the effect of improving fatigue life are shown. In the “Fatigue life improvement effect” column, a mark “◯” indicates that there was an improvement effect, and a mark “X” indicates that there was no improvement effect. Further, “book” in the “classification” column means an example of the present invention, and “ratio” means a comparative example.
表3に示した各調査項目相互間の関係を、本発明例および比較例と関連づけて視覚的に認識できるように、表3の結果を図1〜図3に表示した。 The results of Table 3 are displayed in FIGS. 1 to 3 so that the relationship between the survey items shown in Table 3 can be visually recognized in association with the present invention example and the comparative example.
図1は、Te/Sまたは(Te+Ca)/Sと、鋳片における5μm以上の硫化物のうち凹凸度が3以上である硫化物の割合との関係を示す図である。図1に示すように、硫化物系介在物の形態はTe/Sまたは(Te+Ca)/Sが0.4付近で急激に変化しているが、これは硫化物の生成機構が共晶凝固から偏晶凝固に変化したためである。硫化物の生成が偏晶凝固により行われることによって(図1の本発明範囲)、凹凸度が3以上の硫化物数の割合が急激に減少し、硫化物のほとんどが、凹凸度が3より小さい、球状に近い形状を有していることがわかる。 FIG. 1 is a diagram showing the relationship between Te / S or (Te + Ca) / S and the ratio of sulfides having a degree of unevenness of 3 or more among sulfides of 5 μm or more in a slab. As shown in FIG. 1, the form of sulfide inclusions changes abruptly when Te / S or (Te + Ca) / S is around 0.4. This is because the formation mechanism of sulfide is from eutectic solidification. This is due to the change to the monotectic solidification. The generation of sulfide is performed by monotectic solidification (the scope of the present invention in FIG. 1), so that the ratio of the number of sulfides having a degree of unevenness of 3 or more is drastically reduced. It can be seen that it has a small, nearly spherical shape.
図2は、鋳片における5μm以上の硫化物のうち凹凸度が3以上である硫化物の割合と、棒鋼における5μm以上の硫化物系介在物のうちアスペクト比が4以下である硫化物系介在物の割合との関係を示す図である。同図から明らかなように、本発明鋼は鋳片段階で長尺な硫化物が少なく、圧延後においてもアスペクト比が大きい硫化物の割合は低い。一方で、比較例では鋳片段階から長尺な硫化物が多く、圧延後もアスペクト比が大きい硫化物の割合が高い。両者には明確な差異が現れており、これは、硫化物の凝固形態の違いであることが示唆される。 FIG. 2 shows the ratio of sulfides having a degree of unevenness of 3 or more in sulfides of 5 μm or more in a slab, and sulfide-based inclusions having an aspect ratio of 4 or less in sulfide steel inclusions of 5 μm or more in steel bars. It is a figure which shows the relationship with the ratio of a thing. As is clear from the figure, the steel of the present invention has few long sulfides at the slab stage, and the ratio of sulfides having a large aspect ratio is low even after rolling. On the other hand, in the comparative example, there are many long sulfides from the slab stage, and the ratio of sulfides having a large aspect ratio after rolling is high. A clear difference appears between the two, suggesting that this is a difference in the solidification form of sulfide.
図3は、棒鋼における5μm以上の硫化物系介在物のうちアスペクト比が4以下である硫化物系介在物の割合と、各鋼種のTe非添加条件に対して、Te、またはTeとCaを添加した際の疲労寿命の改善率との関係を示す図である。図3に示すように、疲労寿命の改善効果はアスペクト比が4以下である硫化物系介在物の割合と相関があり、疲労寿命の改善率が高いということは、硫化物系介在物が延伸していない形態を有しているのが条件になっていることが分かる。 FIG. 3 shows the ratio of sulfide inclusions having an aspect ratio of 4 or less among sulfide inclusions of 5 μm or more in steel bars, and Te or Te and Ca with respect to the Te non-addition condition of each steel type. It is a figure which shows the relationship with the improvement rate of the fatigue life at the time of adding. As shown in FIG. 3, the fatigue life improvement effect is correlated with the ratio of sulfide inclusions having an aspect ratio of 4 or less, and the high fatigue life improvement rate means that the sulfide inclusions are stretched. It turns out that it has become a condition to have the form which is not.
以上の調査結果から、Te/Sまたは(Te+Ca)/Sを0.4以上とした状態で凝固させることで、硫化物系介在物は凝固形態を偏晶に制御でき、圧延後においてもアスペクト比を低位に留めておくことが可能であることが分かる。 From the above investigation results, by solidifying with Te / S or (Te + Ca) / S being 0.4 or more, the sulfide inclusions can control the solidification form to be monotectic, and the aspect ratio after rolling It can be seen that it can be kept low.
本発明の軸受鋼鋼材は、鋼中の硫化物を形態制御することによって転動疲労寿命を改善した軸受鋼である。自動車や産業機械にとって重要な「玉軸受け」や「コロ軸受け」などの部品の素材として利用した場合、安全性の向上およびコスト削減が可能であり、本発明の社会的貢献度は非常に大きい。 The bearing steel material of the present invention is a bearing steel that has improved rolling fatigue life by controlling the form of sulfides in the steel. When used as a material for parts such as “ball bearings” and “roller bearings” which are important for automobiles and industrial machines, safety can be improved and costs can be reduced, and the social contribution of the present invention is very large.
Claims (4)
SおよびTeの質量%での含有量がTe/S>0.4の条件を満たしており、偏晶凝固した硫化物系介在物を有することを特徴とする軸受鋼鋼材。 In mass%, C: 0.5-1.2%, Si: 0.1-0.9%, Mn: 0.1-2.0%, P: ≦ 0.03%, S: 0.0003 -0.03%, O: ≤0.005% and N: ≤0.02%, further Te: 0.0002-0.021%, the balance being Fe and impurities, and ,
A bearing steel material characterized in that the content of S and Te in mass% satisfies the condition of Te / S> 0.4, and has sulfide-type inclusions solidified by crystallites.
S、TeおよびCaの質量%での含有量が(Te+Ca)/S>0.4の条件を満たしており、偏晶凝固した硫化物系介在物を有することを特徴とする軸受鋼鋼材。 In mass%, C: 0.5-1.2%, Si: 0.1-0.9%, Mn: 0.1-2.0%, P: ≦ 0.03%, S: 0.0003 -0.03%, O: ≤0.005% and N: ≤0.02%, and Te: 0.0001-0.016% and Ca: 0.0001-0.005% And the balance is Fe and impurities, and
A bearing steel material characterized in that the content of S, Te and Ca in mass% satisfies the condition of (Te + Ca) / S> 0.4, and has sulfide-based inclusions solidified by crystallites.
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CN113145807A (en) * | 2021-04-27 | 2021-07-23 | 建龙北满特殊钢有限责任公司 | Rare earth bearing steel ingot for shield machine and production method thereof |
CN114015927A (en) * | 2022-01-07 | 2022-02-08 | 北京科技大学 | Rare earth-containing high-carbon chromium bearing steel and preparation method thereof |
CN115216587A (en) * | 2022-06-02 | 2022-10-21 | 大冶特殊钢有限公司 | Method for improving uniformity of components and structures of large die-cast steel ingot of high-carbon chromium bearing steel and high-carbon chromium bearing steel |
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Cited By (9)
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CN107119239A (en) * | 2017-04-11 | 2017-09-01 | 龙南日升昌新材料研发有限公司 | Bearing steel and preparation method thereof |
WO2019142946A1 (en) | 2018-01-22 | 2019-07-25 | 日本製鉄株式会社 | Bearing steel component, and steel bar for bearing steel component |
KR20200086728A (en) | 2018-01-22 | 2020-07-17 | 닛폰세이테츠 가부시키가이샤 | Bearing steel parts and bar steel for bearing steel parts |
US11459630B2 (en) | 2018-01-22 | 2022-10-04 | Nippon Steel Corporation | Bearing steel component, and steel bar for bearing steel component |
CN110157988A (en) * | 2019-06-27 | 2019-08-23 | 锦州金科高新技术发展有限责任公司 | High-purity, the homogeneous rare earth cold roll steel alloy material of one kind and preparation method |
CN113145807A (en) * | 2021-04-27 | 2021-07-23 | 建龙北满特殊钢有限责任公司 | Rare earth bearing steel ingot for shield machine and production method thereof |
CN114015927A (en) * | 2022-01-07 | 2022-02-08 | 北京科技大学 | Rare earth-containing high-carbon chromium bearing steel and preparation method thereof |
CN115216587A (en) * | 2022-06-02 | 2022-10-21 | 大冶特殊钢有限公司 | Method for improving uniformity of components and structures of large die-cast steel ingot of high-carbon chromium bearing steel and high-carbon chromium bearing steel |
CN115216587B (en) * | 2022-06-02 | 2023-11-24 | 大冶特殊钢有限公司 | Method for improving composition and structure uniformity of large-scale cast steel ingot of high-carbon chromium bearing steel and high-carbon chromium bearing steel |
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