JP5283788B1 - Steel with excellent rolling fatigue life - Google Patents
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/06—Deoxidising, e.g. killing
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- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/064—Dephosphorising; Desulfurising
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
Abstract
【課題】 鋼中の酸素含有量、硫黄含有量およびＡｌ含有量を規制すると共に、ＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比およびＭｇＯ−Ａｌ2Ｏ3系酸化物が全酸化物に占める個数比率を規制して転がり疲労寿命に優れた機械用部品に使用される鋼を提供する。
【解決手段】 表面硬さを５８ＨＲＣ以上とする機械部品に用いる鋼で、鋼中の酸素含有量が質量割合で８ｐｐｍ以下、硫黄含有量が０．００８質量％以下、Ａｌ含有量が０．０１１〜０．０３０質量％であり、鋼中に存在するＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比を０．２５〜１．５０の範囲に規制し、かつＭｇＯ−Ａｌ2Ｏ3系酸化物の全酸化物系介在物に占める個数比率を７０％以上とした、転がり疲労寿命に優れた鋼。
【選択図】 なしPROBLEM TO BE SOLVED: To regulate the oxygen content, sulfur content and Al content in steel, and (MgO) / (Al 2 O 3 ) mass% ratio in average composition of MgO—Al 2 O 3 oxide The present invention provides a steel used for machine parts having excellent rolling fatigue life by regulating the number ratio of MgO-Al 2 O 3 -based oxide to the total oxide.
SOLUTION: Steel used for machine parts having a surface hardness of 58 HRC or more, wherein the oxygen content in the steel is 8 ppm or less by mass, the sulfur content is 0.008 mass% or less, and the Al content is 0.011. The mass% ratio of (MgO) / (Al 2 O 3 ) in the average composition of the MgO—Al 2 O 3 -based oxide present in the steel is 0.25 to 1.50. Steel with excellent rolling fatigue life, which is regulated to a range and the number ratio of MgO—Al 2 O 3 oxide to the total oxide inclusions is 70% or more.
[Selection figure] None
Description
本発明は、軸受、ギア、ハブユニット、トロイダル型ＣＶＴ装置、等速ジョイント、クランクピンなどの優れた転がり疲労寿命が要求される、表面硬さを５８ＨＲＣ以上に硬化させて使用される機械部品や装置として適用される鋼に関するものである。 The present invention relates to a mechanical component used for curing a surface hardness of 58 HRC or more, such as a bearing, a gear, a hub unit, a toroidal type CVT device, a constant velocity joint, a crankpin, etc. The present invention relates to steel applied as a device.
近年、各種機械装置の高性能化によって、転がり疲労寿命が求められる機械部品や装置の使用環境は過酷化している。それに伴い、これらの部品や装置の寿命向上ならびに信頼性向上に対する要求が高まっている。このような要求に対し、鋼材面の対策としては、鋼成分の適正化や転がり疲労寿命に有害な不純物元素の低減が行われており、寿命の向上ならびに信頼性の向上が図られている。 In recent years, due to the improvement in performance of various mechanical devices, the use environment of mechanical parts and devices that require a rolling fatigue life has become severe. Along with this, there are increasing demands for improving the life and reliability of these components and devices. In response to such demands, measures for steel surfaces include optimization of steel components and reduction of impurity elements that are harmful to rolling fatigue life, thereby improving life and improving reliability.
鋼組成に含有の不純物元素のうち、例えば、酸素はアルミナなどの破損の起点となりうる酸化物系介在物を構成する元素である。したがって、特に有害性が高い酸素に関しては、ｐｐｍオーダーへの低減が行われている。さらに高い品質が求められる場合には、ＶＡＲ、ＥＳＲなどの特殊溶解によって、さらなる酸素量の低減が行われる場合もある。また、他の不純物元素に関しても、その含有量を０．０１質量％オーダーまで低減することによって、それらの悪影響を防止する対策がとられている。 Among the impurity elements contained in the steel composition, for example, oxygen is an element that constitutes oxide inclusions that can be a starting point of damage such as alumina. Therefore, especially oxygen with high toxicity has been reduced to the ppm order. When higher quality is required, the oxygen amount may be further reduced by special dissolution such as VAR and ESR. In addition, measures are taken to prevent adverse effects of other impurity elements by reducing their content to the order of 0.01% by mass.
一方、酸化物系介在物の有害性低減についても検討されている。これらの検討のなかで、鋼中に存在する介在物組成をＳｉＯ2−Ａｌ2Ｏ3−ＣａＯ系介在物、もしくはＳｉＯ2−Ａｌ2Ｏ3−ＭｎＯ系介在物とし、加工後における酸化物系介在物のアスペクト比が３．０以上であるものが、加工後の酸化物系介在物中に６０％以上含まれることを特徴とする転動疲労特性に優れた鋼が提案されている（例えば、特許文献１参照）。さらに、鋼中の酸化物個数に関して、｛(ＭｇＯ・Ａｌ2Ｏ3個数＋ＭｇＯ個数)／全酸化物系介在物個数｝の値を０．８０以上とすることを特徴とする高炭素系高寿命軸受鋼が提案されている（例えば、特許文献２参照）。さらに、アルミナ系とスピネル系との合計個数が全酸化物個数の６０％未満であることを特徴とする高炭素クロム軸受鋼およびその製造方法が提案されている（例えば、特許文献３参照）。同特許文献３内に限り、アルミナ系とは（ＭｇＯ）も（ＳｉＯ2）も３％未満で、かつ（ＣａＯ）も（ＣａＯ）／（（ＣａＯ）＋（Ａｌ2Ｏ3））の比で０．０８以下であるものであり、スピネル系とは３％〜２０％の範囲の（ＭｇＯ）に残部が（Ａｌ2Ｏ3）である２元系に、１５％以内の（ＣａＯ）および／または１５％以内の(ＳｉＯ2)が混入する場合があるスピネル型結晶構造のものであるとして定義されている。さらに、介在物径を（縦×横）1/2と定義した場合の、鋼中の３０００ｍｍ2中に存在する最大介在物径を有する酸化物系非金属介在物あるいは１５μｍ以上の介在物径を有する全ての酸化物系非金属介在物の組成が質量％でＳｉＯ2：３０％以上であることを特徴とする転がり疲労寿命に優れた機械用部品に使用される鋼が提案されている（例えば、特許文献４参照）。 On the other hand, reduction of the harmfulness of oxide inclusions has also been studied. Among these studies, the composition of inclusions present in the steel SiO 2 -Al 2 O 3 -CaO based inclusions, or a SiO 2 -Al 2 O 3 -MnO-based inclusions, oxide after processing Steels having excellent rolling fatigue characteristics, in which inclusions having an aspect ratio of 3.0 or more are included in the oxide inclusions after processing by 60% or more (for example, , See Patent Document 1). Further, regarding the number of oxides in the steel, the value of {(MgO · Al 2 O 3 number + MgO number) / total oxide-based inclusions} is 0.80 or more, and the high carbon-based long life Bearing steel has been proposed (see, for example, Patent Document 2). Furthermore, a high carbon chromium bearing steel characterized in that the total number of alumina-based and spinel-based materials is less than 60% of the total number of oxides and a method for manufacturing the same have been proposed (for example, see Patent Document 3). Within the same patent document 3, alumina is less than 3% of (MgO) and (SiO 2 ), and (CaO) is a ratio of (CaO) / ((CaO) + (Al 2 O 3 )). The spinel system is a binary system (MgO) in the range of 3% to 20% and the balance being (Al 2 O 3 ), and within 15% of (CaO) and / or Alternatively, it is defined as having a spinel crystal structure in which up to 15% of (SiO 2 ) may be mixed. Furthermore, when the inclusion diameter is defined as (length × width) 1/2 , the oxide-based nonmetallic inclusion having the maximum inclusion diameter in 3000 mm 2 in steel or the inclusion diameter of 15 μm or more Steels used for machine parts having excellent rolling fatigue life, characterized in that the composition of all oxide-based nonmetallic inclusions having a mass% of SiO 2 : 30% or more have been proposed (for example, , See Patent Document 4).
本発明の課題は、転がり疲労寿命が求められる機械部品における計算寿命に対して極めて早期の破損を抑制することである。そこで、発明者らは、その信頼性の目安としてＬ1寿命（すなわち、同一ロットの試験片を同じ条件で試験した場合に、そのうちの９９％の試験片がはく離することなく回転するｃｙｃｌｅ数）に注目した。 An object of the present invention is to suppress damage that is extremely early with respect to the calculated life in a machine part that requires a rolling fatigue life. Therefore, the inventors used the L 1 life as a measure of reliability (that is, when the same lot of test pieces are tested under the same conditions, 99% of the test pieces rotate without peeling). I paid attention to.
転がり疲労寿命を向上させるための非金属介在物の制御に関して、発明者らは、とりわけ転がり疲労寿命に対して有害度の高い酸化物系非金属介在物の影響を軽減する手段を鋭意検討した。その結果、従来技術において、むしろ避けるべきであるとされてきた硬質介在物であるＡｌやＭｇを含有する酸化物系主体の介在物組成に改質することによって、Ｌ1寿命が向上することを見出した。 Regarding the control of non-metallic inclusions for improving the rolling fatigue life, the inventors have intensively studied means for reducing the influence of oxide-based non-metallic inclusions that are particularly harmful to the rolling fatigue life. As a result, the L 1 life can be improved by modifying the oxide-based inclusion composition containing Al and Mg, which are hard inclusions that should be avoided in the prior art. I found it.
転がり疲労寿命が求められる部品に対して、特に計算寿命に対して極く早期のはく離を抑制可能な、Ｌ1寿命に優れた鋼とするためには、鋼中の酸素含有量を質量割合で８ｐｐｍ以下、硫黄含有量を０．００８質量％以下とし、Ａｌ含有量を０．０１１〜０．０３０質量％とし、非金属介在物に関して、鋼中に存在するＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比を０．２５〜１．５０の範囲に規制し、より好ましくは０．３０〜１．３０の範囲に規制し、かつＭｇＯ−Ａｌ2Ｏ3系酸化物の全酸化物系介在物に占める個数比率を７０％以上、好ましくは８０％以上に規制すれば良いことが分かった。なお、ここで定義するＭｇＯ−Ａｌ2Ｏ3系非金属介在物には、質量％で１５％以下のＣａＯ、および／または質量％で１５％以下のＳｉＯ2を含有したものを含めて良い。酸素含有量を質量割合で８ｐｐｍ以下、硫黄含有量を０．００８質量％以下とするのは、酸化物系介在物の頻度、ならびに比較的軟質で延伸しやすい硫化物系介在物の大きさと頻度を低減するためである。より好ましくは酸素含有量は質量割合で６ｐｐｍ以下、硫黄含有量は０．００３質量％以下とする。さらに、軟質の介在物に改質させないため、かつ硬質であるものの鋼中で凝集したクラスター状となりやすい純アルミナ（Ａｌ2Ｏ3）を抑制するため、Ａｌ含有量は０．０１１〜０．０３０質量％とする必要がある。 Against rolling parts fatigue life is required, in particular the peeling of the very early capable of suppressing relative calculated life, in order to steel excellent in L 1 life, the oxygen content in the steel at a mass ratio MgO—Al 2 O 3 -based oxide existing in steel with respect to nonmetallic inclusions with 8 ppm or less, sulfur content of 0.008 mass% or less, Al content of 0.011 to 0.030 mass% The mass% ratio of (MgO) / (Al 2 O 3 ) in the average composition of is regulated to a range of 0.25 to 1.50, more preferably regulated to a range of 0.30 to 1.30, and MgO It has been found that the number ratio of the -Al 2 O 3 oxide to the total oxide inclusions may be regulated to 70% or more, preferably 80% or more. The MgO—Al 2 O 3 -based non-metallic inclusions defined herein may include those containing 15% or less of CaO by mass% and / or 15% or less of SiO 2 by mass%. The oxygen content is 8 ppm or less by mass and the sulfur content is 0.008 mass% or less because the frequency of oxide inclusions and the size and frequency of sulfide inclusions that are relatively soft and easy to stretch. This is to reduce the above. More preferably, the oxygen content is 6 ppm or less by mass and the sulfur content is 0.003 mass% or less. Furthermore, in order not to modify the soft inclusions and to suppress pure alumina (Al 2 O 3 ) that is hard but tends to be agglomerated in steel, the Al content is 0.011 to 0.030. It is necessary to set it as the mass%.
酸化物系介在物の平均組成および酸化物系介在物の個数比率を上記の範囲に規制した鋼においては、酸化物が高融点を有する組成であるために、鋼の鋳塊を製造する過程において溶鋼中から小径の酸化物が球状に近い形で晶出する。かつ、球状に近い形で晶出していても、その後に溶鋼中で凝集したクラスター状となりやすい純アルミナ（Ａｌ2Ｏ3）を抑制しているため、溶鋼が凝固した後の鋳塊内において酸化物系介在物は小径でかつ球状に近い形で分散することになる。 In steels in which the average composition of oxide inclusions and the number ratio of oxide inclusions are regulated within the above ranges, the oxide has a high melting point, so in the process of manufacturing the steel ingot A small-diameter oxide crystallizes out of the molten steel in a nearly spherical shape. In addition, even though it is crystallized in a nearly spherical shape, it suppresses the pure alumina (Al 2 O 3 ) that tends to agglomerate in the molten steel afterwards, so it is oxidized in the ingot after the molten steel solidifies The physical inclusions are dispersed in a small diameter and nearly spherical shape.
次いで、熱間加工で鋳塊を圧延して棒鋼とし、その後、棒鋼を素材としてさらなる熱間加工や冷間加工により部品の素材となる棒鋼や鋼管あるいは鍛造品にした場合には、酸化物系介在物は熱間あるいは冷間の加工温度域において母相の鋼より著しく硬質な介在物であるので、加工中に母相に追従して変形しにくいために、加工後も比較的球状に近い形状を維持することができる。 Then, the ingot is rolled into a steel bar by hot working, and then the steel bar is used as a raw material for the part steel by further hot working or cold working. Inclusions are harder than the parent phase steel in the hot or cold working temperature range, so they are less likely to deform following the parent phase during processing. The shape can be maintained.
その後、部品素材は、必要に応じて、例えば、ＣＲＦのようなさらなる冷間加工を経た後に、切削加工され、さらに適正な熱処理により転がり疲れを受ける部品に所望される表面硬さ５８ＨＲＣ以上に調整された後に機械部品として使用されるが、転がり疲れを受ける部品の転送面下の最大応力作用方向は、部品の素材となった鋼材中の非金属介在物の最小断面方向、例えば、比較的に軟質で熱間加工により延伸するような酸化物系介在物や硫化物系介在物においては圧延方向と垂直な方向、とは必ずしも一致しない場合がある。 Thereafter, the part material is adjusted to a surface hardness of 58 HRC or higher as required for a part subjected to rolling fatigue by further heat treatment, if necessary, after undergoing further cold working such as CRF. However, the maximum stress acting direction under the transfer surface of the part subjected to rolling fatigue is the minimum cross-sectional direction of non-metallic inclusions in the steel material used as the material of the part, for example, relatively In oxide inclusions and sulfide inclusions that are soft and stretched by hot working, the direction perpendicular to the rolling direction may not always match.
発明者らは、比較的軟質で熱間加工で延伸する酸化物系介在物を含有させた鋼を試験的に溶製して、同鋼の熱間圧延鋼材を素材として、酸化物系介在物の最大断面方向となる圧延方向と一致する面を転送面として、スラスト式の転がり疲労寿命試験を行い、極く短寿命のはく離に対する信頼性指標としたＬ1寿命を評価したところ、圧延方向と垂直な方向を転送面とした場合に比べて、Ｌ1寿命が低下することを見出した。これは、軟質な酸化物組成を有する介在物の融点が低いために、発生頻度は稀であるものの、大型化した介在物が鋼中に残存し、かつその介在物の熱間圧延後における最大断面（すなわち、欠陥の大きさとみなせる）となる方向が最大応力作用方向とほぼ一致したためと推測され、通常の部品寿命の指標として評価されるＬ10寿命（同一ロットの試験片を同じ条件で試験した場合に、そのうちの９０％の試験片がはく離することなく回転するｃｙｃｌｅ数）には現れにくいが、Ｌ1寿命の評価により明確となったものである。 The inventors experimentally melted a steel containing oxide inclusions that are relatively soft and stretched by hot working, and used the hot rolled steel material of the steel as a raw material, and oxide inclusions. A thrust type rolling fatigue life test was conducted using the surface that coincides with the rolling direction, which is the maximum cross-sectional direction, as a transfer surface, and the L 1 life was evaluated as a reliability index for extremely short life peeling. It has been found that the L 1 life is reduced as compared with the case where the vertical direction is the transfer surface. This is because the inclusion having a soft oxide composition has a low melting point, but the occurrence frequency is rare, but the enlarged inclusion remains in the steel, and the maximum after the inclusion is hot-rolled. L 10 life (tested in the same lot under the same conditions) is presumed that the direction of the cross-section (that can be regarded as the size of the defect) is almost the same as the direction of maximum stress action and is evaluated as an index of normal part life In this case, 90% of the specimens are less likely to appear in the number of cycles that rotate without peeling), but are clarified by the evaluation of the L 1 life.
それに対して、発明者らが提案する鋼中の酸化物系介在物が小径で、かつ球状に近い形状で分散した鋼においては、前記の結果とは異なり、圧延方向と一致する面を転送面とするスラスト式の転がり疲労寿命試験におけるＬ1寿命が改善されていることを見出し、本発明に至ったものである。すなわち、部品の素材となる鋼中の酸化物系介在物を小径で、かつ球状に近い形状で分散させることにより、部品に加工した場合の転送面が元の素材の圧延あるいは延伸方向に対して、如何なる方向に配置されたとしても、常に転がり疲労における最大応力作用方向に対する介在物断面積を最小化することができるため、転がり疲れに対する有害性が軽減され、転がり疲労寿命が向上するものである。 On the other hand, in the steel in which the oxide inclusions in the steel proposed by the inventors have a small diameter and are dispersed in a shape close to a spherical shape, unlike the above results, the surface corresponding to the rolling direction is the transfer surface. It found that L 1 life has been improved in the thrust-type rolling fatigue life test to, and have reached the present invention. In other words, the oxide-based inclusions in the steel used as the component material are dispersed in a small and nearly spherical shape, so that the transfer surface when processed into a component is relative to the rolling or stretching direction of the original material. In any direction, the inclusion cross-sectional area with respect to the maximum stress acting direction in rolling fatigue can always be minimized, thereby reducing the harmfulness to rolling fatigue and improving the rolling fatigue life. .
本発明が解決しようとする課題に対して、引用文献１〜４に記載の鋼はいずれもＬ1寿命が評価されておらず、部品の計算寿命に対して極く早期のはく離に対する信頼性が保証された鋼ではない。また、引用文献１に記載の鋼では、鋼中の介在物組成をＳｉＯ2−Ａｌ2Ｏ3−ＣａＯ系、もしくはＳｉＯ2−Ａｌ2Ｏ3−ＭｎＯ系である延伸性の酸化物に制御し、かつ延伸した介在物を多く含ませることが狙いであり、このような鋼では前記の通り、部品の転送面の取り方によってはＬ1寿命に劣る場合がある。 In order to solve the problems to be solved by the present invention, the steels described in Cited Documents 1 to 4 have not been evaluated for the L 1 life, and have reliability against the very early peeling with respect to the calculated life of the component. Not guaranteed steel. Further, the steel described in the cited document 1, by controlling the composition of inclusions in steel SiO 2 -Al 2 O 3 -CaO based, or the oxides of stretchability is SiO 2 -Al 2 O 3 -MnO system and an aim that by containing a larger amount of stretched inclusions, as described above in such steel, depending how to take the transfer surface of the component may be poor in L 1 life.
また、引用文献２に記載の鋼では、鋼中の酸化物個数に関して、｛(ＭｇＯ・Ａｌ2Ｏ3個数＋ＭｇＯ個数)／全酸化物系介在物個数｝の値を０．８０以上に規制しているが、酸化物組成をＭｇＯ・Ａｌ2Ｏ3ないしＭｇＯの化学量論組成を有する酸化物主体に改質することが必須条件であり、そのためには精錬過程におけるＭｇ添加、および鋼材中のＭｇ含有が必須となるため、製造コストアップを招き、汎用性に劣っている。また、酸素含有量や硫黄含有量の規制についても十分とは言えず、Ｌ1寿命に優れた鋼を安定して提供できる技術ではない。 Further, in the steel described in the cited document 2, the value of {(MgO · Al 2 O 3 number + MgO number) / total oxide inclusion number} is regulated to 0.80 or more with respect to the number of oxides in the steel. However, it is indispensable to modify the oxide composition to be mainly an oxide having a stoichiometric composition of MgO.Al 2 O 3 or MgO. For this purpose, Mg addition in the refining process, and Since Mg content is essential, the manufacturing cost is increased and the versatility is poor. Moreover, not sufficient even for regulation of the oxygen content, sulfur content, not a technique that can provide stable and excellent steel L 1 life.
また、引用文献３に記載の鋼では、アルミナ系（Ａｌ2Ｏ3主体）とスピネル系（ＭｇＯ−Ａｌ2Ｏ3系）との合計個数が全酸化物個数の６０％未満であるように規制して介在物組成の軟質化制御を行うことによって、Ｌ10寿命を向上させているのに対し、本発明はＭｇＯ−Ａｌ2Ｏ3系酸化物の合計個数が全酸化物個数の７０％以上であるように規制することで極く短寿命でのはく離に対する信頼性の指標としたＬ1寿命を向上させたものであり、技術的思想が全く異なっている。 Further, in the steel described in Cited Document 3, the total number of alumina (Al 2 O 3 main) and spinel (MgO—Al 2 O 3 ) is regulated to be less than 60% of the total number of oxides. by performing the softening control of composition of inclusions and, while thereby improving the L 10 life, the present invention is MgO-Al 2 O 3 system total number of oxide at least 70% of the total oxide quantity The L 1 life as an index of reliability against peeling at an extremely short life is improved by regulating so that the technical idea is completely different.
また、引用文献４に記載の鋼では、介在物径を（縦×横）1/2と定義した場合の、転がり疲労寿命に対して有害な、少なくとも１５μｍ以上の介在物径を有する全ての酸化物系非金属介在物の組成について、質量％でＳｉＯ2：３０％以上であることを特徴としている。これに対し、本発明の鋼における酸化物系介在物におけるＳｉＯ2の含有率は質量％で１５％以下に規制されることから、引用文献４に記載の鋼とは技術的思想が全く異なるものである。 Further, in the steel described in the cited document 4, all oxides having an inclusion diameter of at least 15 μm or more harmful to the rolling fatigue life when the inclusion diameter is defined as (length × width) 1/2. The composition of the physical non-metallic inclusion is characterized by being SiO 2 : 30% or more by mass%. On the other hand, since the content of SiO 2 in the oxide inclusions in the steel of the present invention is regulated to 15% or less by mass%, the technical idea is completely different from the steel described in Reference 4. It is.
本発明は、このような従来の問題を解決するためになされたもので、本発明が解決しようとする課題は、鋼中の酸素含有量、硫黄含有量、およびＡｌ含有量を規制するとともに、ＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比、およびＭｇＯ−Ａｌ2Ｏ3系酸化物が全酸化物に占める個数比率を規制することにより、転がり疲労寿命に優れた機械用部品に使用される鋼を提供することである。 The present invention was made to solve such conventional problems, and the problems to be solved by the present invention are to regulate the oxygen content, sulfur content, and Al content in steel, weight% ratio of the average composition of MgO-Al 2 O 3 based oxide (MgO) / (Al 2 O 3), and the MgO-Al 2 O 3 based oxide regulates the number ratio of total oxide By this, it is providing the steel used for the machine parts excellent in rolling fatigue life.
上記の課題を解決するための本発明の手段は、第１の手段では、表面硬さを５８ＨＲＣ以上とする機械部品に用いる鋼であって、鋼中の酸素含有量が質量割合で８ｐｐｍ以下、硫黄含有量が０．００８質量％以下、Ａｌ含有量が０．０１１〜０．０３０質量％であり、鋼中に存在するＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比を０．２５〜１．５０の範囲に規制し、かつＭｇＯ−Ａｌ2Ｏ3系酸化物の全酸化物系介在物に占める個数比率を７０％以上とすることを特徴とする転がり疲労寿命に優れた鋼である。 Means of the present invention for solving the above problem is steel used for machine parts having a surface hardness of 58 HRC or more in the first means, wherein the oxygen content in the steel is 8 ppm or less by mass ratio, The sulfur content is 0.008% by mass or less, the Al content is 0.011 to 0.030% by mass, and (MgO) / (in the average composition of MgO—Al 2 O 3 -based oxides present in the steel. The mass% ratio of Al 2 O 3 ) is regulated within the range of 0.25 to 1.50, and the number ratio of the MgO—Al 2 O 3 oxide to the total oxide inclusions is 70% or more. It is a steel excellent in rolling fatigue life.
第２の手段では、前述した転がり疲労寿命に優れた鋼としては、ＪＩＳ規格において規定される高炭素クロム軸受鋼鋼材（ＳＵＪ）、ならびにＳＡＥ規格またはＡＳＴＭ規格Ａ２９５において規定される５２１００、ならびにＤＩＮ規格において規定される１００Ｃｒ６、ならびにＪＩＳ規格において規定される機械構造用炭素鋼鋼材（ＳＣ）、ならびに機械構造用合金鋼鋼材のうちのクロム鋼（ＳＣｒ）およびクロムモリブデン鋼（ＳＣＭ）およびニッケルクロムモリブデン鋼（ＳＮＣＭ）から選択したいずれか１種の鋼が挙げられる。 In the second means, the steel having excellent rolling fatigue life as described above includes high carbon chromium bearing steel (SUJ) defined in JIS standard, 52100 defined in SAE standard or ASTM standard A295, and DIN standard. Among the steels for mechanical structure defined in JIS, carbon steel (SC) for mechanical structure (SC), and alloy steel for mechanical structure, chromium steel (SCr), chromium molybdenum steel (SCM) and nickel chromium molybdenum steel Any one kind of steel selected from (SNCM) is mentioned.
本発明の転がり疲労寿命に優れた鋼では、このような従来の問題を解決するためになされたもので、本発明は、鋼中の酸素含有量、硫黄含有量、Ａｌ含有量を規制すると共に、鋼中のＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比、およびＭｇＯ−Ａｌ2Ｏ3系酸化物が全酸化物に占める個数比率を規制することにより、転がり疲労寿命に優れた機械用部品に使用される鋼が得られる。 The steel with excellent rolling fatigue life of the present invention was made to solve such conventional problems, and the present invention regulates the oxygen content, sulfur content, and Al content in the steel. , (MgO) / (Al 2 O 3 ) mass% ratio in average composition of MgO—Al 2 O 3 oxide in steel, and number ratio of MgO—Al 2 O 3 oxide in the total oxide By controlling the above, steel used for machine parts having excellent rolling fatigue life can be obtained.
本発明の実施の形態である転がり疲労寿命に優れた鋼について、表を参照して以下に詳細に説明をする。 The steel excellent in rolling fatigue life according to the embodiment of the present invention will be described in detail below with reference to the table.
本発明の実施の形態である転がり疲労寿命に優れた鋼は、表面硬さを５８ＨＲＣ以上とする機械部品に用いる鋼であって、鋼中の酸素含有量が質量割合で８ｐｐｍ以下、硫黄含有量が０．００８質量％以下、Ａｌ含有量が０．０１１〜０．０３０質量％であり、鋼中に存在するＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比を０．２５〜１．５０の範囲に規制し、かつＭｇＯ−Ａｌ2Ｏ3系酸化物の全酸化物系介在物に占める個数比率を７０％以上とした鋼である。 The steel excellent in rolling fatigue life according to the embodiment of the present invention is steel used for machine parts having a surface hardness of 58 HRC or more, and the oxygen content in the steel is 8 ppm or less by mass and the sulfur content. Is 0.008 mass% or less, Al content is 0.011 to 0.030 mass%, and (MgO) / (Al 2 O in the average composition of MgO—Al 2 O 3 -based oxides present in steel 3 ) is a steel in which the mass% ratio is regulated in the range of 0.25 to 1.50, and the number ratio of the MgO—Al 2 O 3 oxide to the total oxide inclusions is 70% or more. .
前述した転がり疲労寿命に優れた鋼としては、軸受をはじめとする転動疲労寿命が要求される用途に用いられる鋼種であることが望ましい。具体的には、ＪＩＳ規格において規定される高炭素クロム軸受鋼鋼材（ＳＵＪ）、ＳＡＥ規格またはＡＳＴＭ規格Ａ２９５において規定される５２１００、ＤＩＮ規格において規定される１００Ｃｒ６、ＪＩＳ規格において規定される機械構造用炭素鋼鋼材（ＳＣ）、もしくは機械構造用合金鋼鋼材のうちの中のいずれか１種の鋼材が挙げられる。このＪＩＳ規格において規定される機械構造用合金鋼材としては、その中のクロム鋼（ＳＣｒ）、クロムモリブデン鋼（ＳＣＭ）、またはニッケルクロムモリブデン鋼（ＳＮＣＭ）から選択したいずれかいずれか１種の鋼からなる鋼材である。
また、例えばＳＡＥ規格の４３２０、５１２０、４１４０、１０５３、１０５５などのようにＪＩＳ規格に対応した外国規格鋼についても本発明の適用が可能である。
The steel excellent in rolling fatigue life as described above is desirably a steel type used for applications requiring rolling fatigue life, such as bearings. Specifically, high carbon chromium bearing steel (SUJ) specified in JIS standard, 52100 specified in SAE standard or ASTM standard A295, 100Cr6 specified in DIN standard, for machine structure specified in JIS standard Any one of carbon steel materials (SC) and alloy steel materials for machine structures may be used. As an alloy steel material for machine structure defined in this JIS standard, any one steel selected from chromium steel (SCr), chromium molybdenum steel (SCM), or nickel chromium molybdenum steel (SNCM) therein It is made of steel.
Further, the present invention can be applied to foreign standard steels corresponding to JIS standards such as SAE standards 4320, 5120, 4140, 1053, and 1055.
本発明の鋼の母溶鋼の溶製は電気炉法あるいは高炉−転炉法のいずれで行っても良い。続いて、鋼中のＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比、およびＭｇＯ−Ａｌ2Ｏ3系酸化物の個数比率を評価する方法について以下に述べる。ただし、本発明は以下の実施の形態に限定されるものではない。 Melting of the molten steel of the steel of the present invention may be performed by either an electric furnace method or a blast furnace-converter method. Subsequently, the mass% ratio of (MgO) / (Al 2 O 3 ) in the average composition of the MgO—Al 2 O 3 oxide in steel and the number ratio of the MgO—Al 2 O 3 oxide are evaluated. The method is described below. However, the present invention is not limited to the following embodiments.
本実施の形態の転がり疲労寿命に優れた鋼においては、ＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比、およびＭｇＯ−Ａｌ2Ｏ3系酸化物の個数比率を精度良く評価するため、鋼材断面の任意の箇所から選んだ少なくとも４０ｍｍ2以上の被検面積における介在物径が１μｍ以上の酸化物介在物について、エネルギー分散型Ｘ線分析により酸化物組成の成分分析と酸化物数のカウントを行うものとする。その組成分析結果と酸化物カウント数に基づき、鋼中のＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成、およびＭｇＯ−Ａｌ2Ｏ3系酸化物の個数比率を算出すれば良い。なお、硫化物や窒化物と複合した酸化物については硫化物や窒化物を構成する元素については、その元素については除外してＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成を求めるものとした。 In the steel having an excellent rolling fatigue life of the present embodiment, the (MgO) / (Al 2 O 3 ) mass% ratio in the average composition of the MgO—Al 2 O 3 -based oxide, and the MgO—Al 2 O 3 Energy dispersive X-ray analysis of oxide inclusions with an inclusion diameter of 1 μm or more in a test area of at least 40 mm 2 or more selected from any part of the steel cross section in order to accurately evaluate the number ratio of system oxides Thus, the component analysis of the oxide composition and the count of the number of oxides are performed. Based on the oxide count and its composition analysis result, it may be calculated number ratio of the average composition, and MgO-Al 2 O 3 based oxide MgO-Al 2 O 3 system oxides in the steel. Note that the oxide complexed with sulfides and nitrides for elements constituting the sulfides and nitrides, and shall determine the average composition of MgO-Al 2 O 3 based oxide was excluded for the element .
以上、説明したように本実施の形態の転がり疲労寿命に優れた鋼によれば、鋼中の酸素含有量、硫黄含有量、およびＡｌ含有量を規制するとともに、鋼中のＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成、およびＭｇＯ−Ａｌ2Ｏ3系酸化物が全酸化物に占める個数比率を規制することにより、転がり疲労寿命に優れた機械用部品に使用される鋼を提供することが可能となる。 As described above, according to the steel having an excellent rolling fatigue life according to the present embodiment, the oxygen content, sulfur content, and Al content in the steel are regulated, and MgO—Al 2 O in the steel is regulated. the average composition of the 3-component oxide, and by MgO-Al 2 O 3 based oxide regulates the number ratio of total oxide to provide a steel for use in excellent mechanical parts in the rolling fatigue life Is possible.
次に、実施例である供試材１〜２４および比較例である供試材２５〜３０を挙げて、本発明の転がり疲労寿命に優れた鋼をより具体的に説明する。ただし、本発明はこれらの実施例に限定されるものではない。 Next, the steel materials excellent in rolling fatigue life of the present invention will be described more specifically by taking the test materials 1 to 24 as examples and the test materials 25 to 30 as comparative examples. However, the present invention is not limited to these examples.
表１に供試材の成分組成を示す。表１の供試材１〜６および供試材２５〜２８については高炭素クロム軸受鋼であるＪＩＳのＳＵＪ２鋼を、供試材７および供試材２９についてはＪＩＳのＳＣｒ４２０鋼を、供試材８についてはＪＩＳのＳ５３Ｃ鋼を、供試材９、供試材３０についてはＪＩＳのＳＣＭ４２０鋼を、供試材１０はＪＩＳのＳＮＣＭ４２０鋼を、供試材１１および供試材１２はＳＡＥ規格において規定される５２１００を、供試材１３および供試材１４はＡＳＴＭ規格Ａ２９５において規定される５２１００を、供試材１５および供試材１６はＤＩＮ規格において規定される１００Ｃｒ６を、供試材１７はＪＩＳのＳＵＪ３鋼を、供試材１８はＪＩＳのＳＵＪ５鋼を、供試材１９はＳＡＥの４３２０鋼を、供試材２０はＳＡＥの５１２０鋼を、供試材２１はＪＩＳのＳＣＭ４３５鋼を、供試材２２はＳＡＥの４１４０鋼を、供試材２３はＪＩＳのＳ５５Ｃ鋼を、供試材２４はＳＡＥの１０５３鋼を用いた。供試材１〜３０は、アーク溶解炉で溶製し、続いて取鍋精錬し、さらに真空脱ガス装置で脱ガスを行い連続鋳造により鋳塊を製造した。その際、実施例の供試材１〜２４については、事前に溶鋼の精錬過程において適宜試料を採取して介在物組成を確認しながら、スラグ組成を適切に調整して目的とする酸化物組成範囲と個数比率を満足するように検討した上で、母溶鋼の溶製を行った。一方、比較例の供試材２５および供試材２６については、母溶鋼の精錬過程において溶鋼中へのＡｌの添加を抑制し、Ｓｉ脱酸を主に実施することにより軟質介在物への改質を行った。また、比較例の供試材２７〜３０は母溶鋼の精錬過程で溶鋼中にＡｌを積極添加して脱酸を行うことによりＭｇＯ−Ａｌ2Ｏ3系酸化物が少なく、Ａｌ2Ｏ3を主体とする酸化物となるように改質を行った。 Table 1 shows the component composition of the test materials. For Specimens 1 to 6 and Specimens 25 to 28 in Table 1, JIS SUJ2 steel, which is a high-carbon chromium bearing steel, for Specimen 7 and Specimen 29, JIS SCr420 steel was used. JIS S53C steel for specimen 8, JIS SCM420 steel for specimen 9 and specimen 30, specimen JIS SNCM420 steel for specimen 10, specimen 11 and specimen 12 for SAE standards The specimens 13 and 14 are 52100 defined in ASTM standard A295, the specimens 15 and 16 are 100Cr6 defined in the DIN standard, and the specimen 17 Is JIS SUJ3 steel, specimen 18 is JIS SUJ5 steel, specimen 19 is SAE 4320 steel, specimen 20 is SAE 5120 steel, specimen 21 is JIS The SCM435 steel, 4140 steel test specimen 22 is SAE, test materials 23 to S55C steel JIS, test materials 24 using 1053 steel SAE. Specimens 1 to 30 were melted in an arc melting furnace, subsequently smelted in a ladle, and further degassed with a vacuum degasser to produce an ingot by continuous casting. At that time, with respect to the test materials 1 to 24 of the examples, the target oxide composition is prepared by appropriately adjusting the slag composition while appropriately collecting the sample in advance in the refining process of the molten steel and confirming the inclusion composition. After studying to satisfy the range and the number ratio, the mother molten steel was melted. On the other hand, with respect to the test material 25 and the test material 26 of the comparative example, the addition of Al to the molten steel was suppressed during the refining process of the molten mother steel, and Si deoxidation was mainly carried out to improve the soft inclusions. Done quality. Further, test pieces 27 to 30 of the comparative example has less MgO-Al 2 O 3 based oxide by performing intentionally added to deoxidation of Al in the molten steel in the refining process of the mother molten steel, the Al 2 O 3 Modification was performed so that the main oxide was obtained.
上記で得られた鋳塊に、熱間加工を施して直径６５ｍｍの鋼材とした。 The ingot obtained above was hot-worked to obtain a steel material having a diameter of 65 mm.
（スラスト型転がり疲労試験）
供試材１〜６と供試材１１〜１８と供試材２５〜２８の鋼材は８００℃にて球状化焼鈍を施し、鋼材の長手方向に対し平行な方向から外径５２ｍｍで、内径２０ｍｍで、厚さ５．８ｍｍの円盤からなる試験片を作製した。この試験片を８３５℃で２０分保持した後、油冷により焼入れし、次いで１７０℃で９０分の焼戻し処理を行い、所望の５８ＨＲＣ以上の硬さを得て、その後に表面研磨を行ってスラスト型転がり疲労試験を行った。供試材７、供試材９、供試材１０、供試材１９、供試材２０、供試材２９、供試材３０の鋼材は、９２５℃にて焼ならしを施した後、また、供試材２１、２２の鋼材は、８７０℃で焼ならしを施した後、鋼材の長手方向に対し平行な方向から外径５２ｍｍで、内径２０ｍｍで、厚さ８．３ｍｍの円盤からなる試験片を作製した。この試験片を９３０℃で浸炭処理した後、油冷により焼入れし、次いで１８０℃で９０分の焼戻し処理を行い、所望の５８ＨＲＣ以上の硬さを得て、その後に表面研磨を行ってスラスト型転がり疲労試験を行った。供試材８、供試材２３、供試材２４の鋼材は８７０℃で焼ならしを施し、鋼材の長手方向に対し平行な方向から外径５２ｍｍで、内径２０ｍｍで、厚さ８．３ｍｍの円盤からなる試験片を作製した。この試験片を高周波焼入れした後、次いで１８０℃で９０分の焼戻し処理を行い、所望の５８ＨＲＣ以上の硬さを得て、その後に表面研磨を行ってスラスト型転がり疲労試験を行った。スラスト型転がり疲労試験は最大ヘルツ応力Ｐmax：５．３ＧＰａで行った。なお、Ｌ1寿命を求めるうえでは、１．５×１０7ｃｙｃｌｅ程度での打ち切り試験とし、試験評価時間の短縮を図った。
(Thrust type rolling fatigue test)
The steel materials of the test materials 1 to 6, the test materials 11 to 18 and the test materials 25 to 28 were subjected to spheroidizing annealing at 800 ° C., the outer diameter was 52 mm from the direction parallel to the longitudinal direction of the steel materials, and the inner diameter was 20 mm. Thus, a test piece made of a disk having a thickness of 5.8 mm was produced. After holding this test piece at 835 ° C. for 20 minutes, it was quenched by oil cooling and then subjected to tempering treatment at 170 ° C. for 90 minutes to obtain a desired hardness of 58 HRC or more, followed by surface polishing and thrust. A mold rolling fatigue test was conducted. The steel materials of the test material 7, the test material 9, the test material 10, the test material 19, the test material 20, the test material 29, and the test material 30 were subjected to normalization at 925 ° C. Further, the steel materials of the test materials 21 and 22 were annealed at 870 ° C., and then from a disk having an outer diameter of 52 mm, an inner diameter of 20 mm, and a thickness of 8.3 mm from a direction parallel to the longitudinal direction of the steel material. A test piece was prepared. This test piece was carburized at 930 ° C., then quenched by oil cooling, then tempered at 180 ° C. for 90 minutes to obtain a desired hardness of 58 HRC or higher, and then surface polished to obtain a thrust A rolling fatigue test was conducted. The steel materials of Specimen 8, Specimen 23, and Specimen 24 were normalized at 870 ° C., and the outer diameter was 52 mm, the inner diameter was 20 mm, and the thickness was 8.3 mm from the direction parallel to the longitudinal direction of the steel. A test piece made of a disk was prepared. This test piece was induction hardened, and then tempered at 180 ° C. for 90 minutes to obtain a desired hardness of 58 HRC or higher, and then subjected to surface polishing to perform a thrust type rolling fatigue test. The thrust type rolling fatigue test was performed at a maximum Hertz stress Pmax: 5.3 GPa. In obtaining the L 1 life, the test evaluation time was shortened by a censoring test at about 1.5 × 10 7 cycles.
（酸化物組成および個数比率の評価）
鋼中に存在するＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比が０．２５〜１．５０であり、かつＭｇＯ−Ａｌ2Ｏ3系酸化物の全酸化物系介在物に占める個数比率が７０％以上であることを評価するにあたり、供試材１〜６と供試材１１〜１８と供試材２５〜２８の鋼材は８００℃にて球状化焼鈍を施した後、供試材７、供試材９、供試材１０、供試材１９、供試材２０、供試材２９、供試材３０の鋼材は、９２５℃にて焼ならしを施した後、また、供試材８、供試材２１〜２４の鋼材は８７０℃で焼ならしを施した後、いずれも鋼材の長手方向に対し平行な方向から長手方向に１０ｍｍ、径方向に１０ｍｍの被検査面積１００ｍｍ2で厚さ７ｍｍの試験片を切り出し、研磨時の非金属介在物の脱落を防止する目的でいずれも焼入焼戻しを行った後、被検査面に鏡面研磨を施し、エネルギー分散型Ｘ線分析により酸化物組成の成分分析と酸化物数のカウントを行った。その組成分析結果と酸化物カウント数に基づき、鋼中のＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比、およびＭｇＯ−Ａｌ2Ｏ3系酸化物の個数比率を算出した。
(Evaluation of oxide composition and number ratio)
The mass% ratio of (MgO) / (Al 2 O 3 ) in the average composition of MgO—Al 2 O 3 -based oxides present in the steel is 0.25 to 1.50, and MgO—Al 2 O 3 In evaluating that the number ratio of the system oxide to the total oxide inclusions is 70% or more, the steel materials of the test materials 1 to 6, the test materials 11 to 18, and the test materials 25 to 28 are 800. After spheroidizing annealing at 0 ° C., the steel materials of the test material 7, the test material 9, the test material 10, the test material 19, the test material 20, the test material 29, and the test material 30 are 925. After normalizing at ℃, and after subjecting the steel materials of the test material 8 and the test materials 21 to 24 to normalization at 870 ° C., both are from a direction parallel to the longitudinal direction of the steel material. dropping longitudinally 10mm, cut out test pieces having a thickness of 7mm in the inspection area 100 mm 2 of 10mm in a radial direction, non-metallic inclusions during polishing After both quenching and tempering for the purpose of preventing, subjected to mirror polishing to be inspected surface were counted oxide number and component analysis of the oxide composition by energy dispersive X-ray analysis. Based on the composition analysis result and the oxide count, the (MgO) / (Al 2 O 3 ) mass% ratio in the average composition of the MgO—Al 2 O 3 -based oxide in the steel, and MgO—Al 2 O 3 The number ratio of the system oxide was calculated.
これらの供試材の各試験片について、表面硬さ、鋼中のＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比、およびＭｇＯ−Ａｌ2Ｏ3系酸化物の個数比率、およびスラスト型転がり疲労試験によるＬ1寿命を表２に示す。 About each test piece of these test materials, surface hardness, mass% ratio of (MgO) / (Al 2 O 3 ) in the average composition of MgO—Al 2 O 3 -based oxide in steel, and MgO—Al Table 2 shows the number ratio of 2 O 3 -based oxides and the L 1 life by the thrust type rolling fatigue test.
表２において、比較例の供試材２５〜３０は、鋼中のＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比、および／または鋼中のＭｇＯ−Ａｌ2Ｏ3系酸化物個数の個数比率が、本発明の請求範囲外のものである。これら比較材の供試材２５〜３０に対し、鋼中のＭｇＯ−Ａｌ2Ｏ3系酸化物の平均組成における（ＭｇＯ）／（Ａｌ2Ｏ3）の質量％比、および鋼中のＭｇＯ−Ａｌ2Ｏ3系酸化物の個数比率のいずれもが、本発明の請求範囲を満足する実施例の供試材１〜２４は比較例に比してＬ1寿命に優れている。 In Table 2, test materials 25 to 30 of the comparative example, the weight percent ratio of the average composition of MgO-Al 2 O 3 based oxide in the steel (MgO) / (Al 2 O 3), and / or steel The number ratio of the number of MgO—Al 2 O 3 based oxides is outside the scope of the present invention. With respect to the test materials 25 to 30 of these comparative materials, the mass% ratio of (MgO) / (Al 2 O 3 ) in the average composition of MgO—Al 2 O 3 -based oxides in steel, and MgO— in steel Any of the number ratios of the Al 2 O 3 -based oxides satisfy the claims of the present invention, and the test materials 1 to 24 of the examples are superior in the L 1 life as compared with the comparative examples.
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| JPH05117804A (en) * | 1991-10-24 | 1993-05-14 | Kobe Steel Ltd | Bearing steel having excellent workability and rolling fatigue property |
| JPH05311225A (en) * | 1991-11-28 | 1993-11-22 | Nippon Steel Corp | Method for preventing aggregation of al2o3 in molten steel |
| JPH083682A (en) * | 1994-06-16 | 1996-01-09 | Nippon Steel Corp | High carbon type long life bearing steel |
| JP2004323938A (en) * | 2003-04-25 | 2004-11-18 | Daido Steel Co Ltd | Bearing steel having excellent rolling life characteristic and its producing method |
| JP2006200027A (en) * | 2005-01-24 | 2006-08-03 | Nippon Steel Corp | High-carbon chromium steel for bearing and production method therefor |
| JP2009127091A (en) * | 2007-11-26 | 2009-06-11 | Sanyo Special Steel Co Ltd | High-frequency induction hardening steel excellent in cold working, rolling member made of the steel and linear-line motion apparatus using the rolling member |
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| JPH0379741A (en) | 1989-08-22 | 1991-04-04 | Daido Steel Co Ltd | Steel excellent in rolling fatigue characteristic |
| CN100334245C (en) * | 2005-06-30 | 2007-08-29 | 宝山钢铁股份有限公司 | Smelting production method of extra pure high carbon chromium bearing steel |
| JP5139667B2 (en) * | 2006-11-09 | 2013-02-06 | 山陽特殊製鋼株式会社 | Steel evaluation method with excellent rolling fatigue life |
| JP2008240019A (en) | 2007-03-26 | 2008-10-09 | Sanyo Special Steel Co Ltd | Steel excellent in rolling contact fatigue life |
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| JPH05117804A (en) * | 1991-10-24 | 1993-05-14 | Kobe Steel Ltd | Bearing steel having excellent workability and rolling fatigue property |
| JPH05311225A (en) * | 1991-11-28 | 1993-11-22 | Nippon Steel Corp | Method for preventing aggregation of al2o3 in molten steel |
| JPH083682A (en) * | 1994-06-16 | 1996-01-09 | Nippon Steel Corp | High carbon type long life bearing steel |
| JP2004323938A (en) * | 2003-04-25 | 2004-11-18 | Daido Steel Co Ltd | Bearing steel having excellent rolling life characteristic and its producing method |
| JP2006200027A (en) * | 2005-01-24 | 2006-08-03 | Nippon Steel Corp | High-carbon chromium steel for bearing and production method therefor |
| JP2009127091A (en) * | 2007-11-26 | 2009-06-11 | Sanyo Special Steel Co Ltd | High-frequency induction hardening steel excellent in cold working, rolling member made of the steel and linear-line motion apparatus using the rolling member |
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