JP4256701B2 - Inclusion finely dispersed steel with excellent fatigue life - Google Patents

Description

【００５９】
【表２】

【００６０】
【表３】

【００６１】
【表４】

【００６２】
（実施例２）
実施例１と同様の方法により、表５に示す軸受鋼を製造した。この鋼材中に含まれる介在物はＲＥＭ含有介在物の割合が多く、微細なものであった。６５ｍｍφに圧延した棒鋼にて極値統計法（基準面積：１００ｍｍ２ 、ｎ＝１６、評価面積：３００００ｍｍ２ ）により３００００ｍｍ２ での最大介在物サイズを評価した結果、表５に示す良好なサイズが得られた。また、当該鋼材を１０ｍｍφの線材に圧延した後、ミニチュアベアリングに加工し、音響特性および振動特性を評価した結果、表５に示す良好な成績が得られた。なお、表５に示すＲＥＭ成分の内訳を表６に示した。
（比較例２）
実施例２と同様の方法で表５に示す軸受鋼を製造した。但し、この場合にはＲＨ処理末期のＲＥＭ添加を行わないケース、ＲＥＭ添加量（添加方法は実施例１と同様）を本発明の適正ＲＥＭ量の上限以上、下限以下にしたケースおよびＲＨ以降でシール性をわざと悪化させ、ＲＥＭ含有介在物個数割合が本発明を外れるケースも行った。またＴｉがはずれるケースも行った。得られた軸受鋼の介在物サイズ、および音響・振動特性の結果を表５に示すが、実施例２に比べ好ましくない結果となった。
【００６３】
【表５】

【００６４】
【表６】

【００６５】
【発明の効果】
以上説明したように、本発明は、鋼中にＲＥＭ系酸化物およびＲＥＭオキシサルファイド系介在物を微細分散させた鋼に関するものであり、特に、酸化物系介在物の悪影響を解消し、良好な耐疲労寿命特性を有する鋼、ならびに音響特性に優れた鋼を提供することが可能となる。
【図面の簡単な説明】
【図１】介在物サイズに及ぼすＲＥＭ−Ｔ．Ｏ×２８０／４８の関係を示す図。
【図２】（ａ）はＣｅの酸化物、オキシサルファイド、硫化物の安定領域を示す図、（ｂ）はＬａの酸化物、オキシサルファイド、硫化物の安定領域を示す図。
【図３】介在物サイズに及ぼすＲＥＭ源の影響を示す図。
【図４】介在物サイズに及ぼす〔Ｓ〕の影響を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel in which oxides and oxysulfide inclusions are finely dispersed. In particular, the present invention eliminates the adverse effects of oxide inclusions and has excellent fatigue life characteristics, and acoustic characteristics. It relates to excellent steel.
[0002]
[Prior art]
Recently, the quality required for steel materials has become increasingly strict and diversified, and there is a strong demand for the development of steel with higher cleanliness and harmless inclusions.
[0003]
The molten steel smelted in a converter or vacuum processing vessel contains a large amount of dissolved oxygen, and this excess oxygen is generally deoxidized by Al having a strong affinity for oxygen. Alumina inclusions are produced. In addition, ladles are often constructed of alumina refractories, and even when deoxidized with Si or Mn instead of Al deoxidation, alumina is a refractory due to the reaction between molten steel and refractory. Dissociates and elutes as Al in the molten steel, and when this Al is reoxidized, alumina is generated in the molten steel.
[0004]
These alumina-based inclusions are hard and agglomerate and coalesce into coarse alumina clusters, causing wire breakage such as tire cords, causing deterioration of rolling fatigue characteristics in steel bars such as bearing steel, It is known that thin steel sheets such as DI can cause cracking during can making. In particular, in the case of bearing steel, it is desired to make the inclusion size as small as possible for the purpose of improving the fatigue life.
[0005]
Miniature bearings used as bearings in home appliances such as VTRs and CD players, general equipment such as instruments and medical equipment, or electronic equipment such as OA equipment and hard disk drives are small and used with relatively light loads. However, it is required that vibration and sound generated from the bearing itself during operation of the device be as low as possible. In particular, in the case of miniature bearings for hard disk drives, noise generation is disliked, so that the demand for noise and vibration reduction is particularly severe. The main cause of generation of sound and vibration is considered to be hard non-metallic inclusions such as Ti carbonitride and alumina inclusions exposed on the bearing surface.
[0006]
Thus, in order to meet the highly required steel quality, the alumina inclusions, which are particularly hard non-metallic inclusions, are reduced, the cleanliness is increased, and the alumina inclusions are modified, And miniaturization and detoxification are major issues.
[0007]
Regarding the reduction and removal of alumina inclusions, reoxidation by degassing, slag reforming, etc., focusing on the reduction of deoxidation products by applying secondary scouring equipment such as RH vacuum degassing equipment and powder blowing equipment Combining prevention and reduction of mixed oxide inclusions by slag cut, the inclusions have been reduced to achieve high cleaning.
[0008]
On the other hand, as a technology for reforming alumina inclusions to make them finer and harmless, it is possible to modify alumina to spinel (MgO.Al ₂ O ₃ ) or MgO by adding an Mg alloy to the molten steel. There is known a method for preventing coarsening due to agglomeration of alumina and avoiding the adverse effect of alumina on the quality of steel materials (for example, see Patent Document 1 and Patent Document 2). In addition, in producing Al killed steel containing acid-soluble Al: 0.005% by mass or more, inclusions produced by introducing an alloy of two or more of Ca, Mg and REM and Al into the molten steel There is known a method for producing an Al killed steel without a cluster that adjusts the content of Al ₂ O ₃ in the range of ₃₀ to 85% by mass (see, for example, Patent Document 3).
[0009]
However, it is difficult to achieve the required level of increasing severity with the above-described method of removing alumina inclusions. Moreover, the following problems also exist in the method of adding inclusions such as Mg and REM to refine inclusions. First, the case of Mg is as follows. Since the molten steel temperature to which Mg is added is equal to or higher than the boiling point of metal Mg (1070 ° C.), Mg easily evaporates. For example, even if mixed with Si, Al, Fe-Si, etc., it is just a mixture and the Mg activity remains at 1, so its evaporation behavior is no different from when it is added with metallic Mg alone. . When alloyed like Al-Mg, Si-Mg, etc., the evaporation loss at the time of addition can be reduced to some extent, but after being dissolved in the molten steel, evaporation cannot be suppressed in the same manner as when added with metal Mg. Therefore, the yield is low.
[0010]
When Mg is added in a vacuum, it will evaporate more rapidly than at normal pressure. Therefore, it is necessary to provide a process for adding it at normal pressure after vacuum refining.
[0011]
Furthermore, as shown in Table 1, the spinel generated by the modification is not as hard as alumina, but is hard, so when vibration and acoustic characteristics are required like a miniature bearing, it is still not enough. There is also a problem.
[0012]
Next, problems of the prior art in the case of REM will be described. In the case of REM addition as disclosed in Patent Document 3, in order to prevent formation of alumina clusters, a composite inclusion having a low melting point is obtained by adding two or more selected from REM, Mg, and Ca. Although it may be effective for prevention, inclusions cannot be reduced to the size required by bearing steel. This is because if inclusions with a low melting point are used, these inclusions aggregate and coalesce and become coarser.
[0013]
Furthermore, in the case of REM addition, since REM has the effect of improving the fatigue life by spheroidizing inclusions, it can be added as necessary for the form control of inclusions, but addition exceeding 0.010% by mass is inclusion It is also known that the amount of REM added must be 0.010% by mass or less because the fatigue life is decreased on the contrary (for example, Patent Document 4). However, there is no elucidation or suggestion of the mechanism and the state of inclusion composition.
[0014]
REM is an element that combines with oxygen to form a REM oxide and also easily forms a sulfide by combining with sulfur. Therefore, it is believed that the presence of excess REM beyond the amount that binds to oxygen produces sulfides, rather increases the inclusion size and adversely affects fatigue life characteristics. Therefore, in order to control the inclusion size, it is necessary to control the amount of REM added and strictly control the inclusion composition. In other words, it is necessary to prevent the formation of coarse sulfides by balancing the REM addition amount with the oxygen content and eliminating excessive REM. Also, sulfides need to be fine because they affect fatigue life characteristics. As described above, since REM easily forms sulfides, it is necessary to reduce the sulfur content in order to further reduce the inclusion size. These technical ideas are not disclosed in Patent Document 3.
[0015]
Patent Document 4 discloses a technique for improving the acoustic characteristics of miniature bearings used as bearings in home appliances such as VTRs and CD players, general equipment such as instruments and medical equipment, or electronic equipment such as OA equipment and hard disk drives. : 7 ppm or less and O: 7 ppm or less, the bearing steel which aims at reduction of the amount of Ti inclusions and the size thereof is disclosed. Patent Document 5 discloses that bearing steel is used, and after quenching or carbonitriding, high temperature tempering at 350 ° C. or higher is performed, the amount of retained austenite in the carbonitrided layer is completely 0%, and the surface hardness is HRC57. The above-described rolling bearing steel is disclosed. However, oxide inclusions are hard because they are based on Al ₂ O _3, and T.I. Even if the absolute amount is reduced by lowering O (total oxygen), the acoustic characteristics cannot be further improved. Moreover, even if alumina is modified to fine spinel by adding Mg, it is not as strong as alumina as shown in Table 1, but it is hard, so it cannot be adequately dealt with. On the other hand, since the REM inclusions are soft as shown in Table 1, it is beneficial to improve the acoustic characteristics by modifying the hard Al ₂ O ₃ inclusions to soft REM inclusions by adding REM. is there.
[0016]
[Patent Document 1]
Japanese Patent Laid-Open No. 05-311225 [Patent Document 2]
Japanese Patent Laid-Open No. 09-263820 [Patent Document 3]
JP 11-279695 A [Patent Document 4]
JP 2000-45048 A [Patent Document 5]
Japanese Patent Application Laid-Open No. 08-312651
[Problems to be solved by the invention]
The present invention advantageously solves the problems in the conventional method as described above, finely disperses oxides and oxysulfide inclusions, and has a steel with good fatigue life characteristics and a steel with excellent acoustic characteristics. The purpose is to provide.
[0018]
Here, the REM-containing oxysulfide indicates the following. Since REM forms an oxide as described above and also easily forms sulfides, when S is present, a compound in which REM, O, and S are combined is formed. This is called REM oxysulfide, and the stoichiometric composition is represented by RE ₂ O ₂ S when REM is represented by RE.
[0019]
[Means for Solving the Problems]
As a result of repeated experiments and examinations in order to solve the problems of the prior art, the present invention has newly found out the amount of REM added to make inclusions finer, the optimum control mode of inclusion composition, and the steel material condition. The summary is as follows.
[0020]
(1) By mass%, C: 0.005 to 1.2% , Si: 0.01 to 0.4 % , Mn: 0.1 to 0.5% , Al: 0.05% or less (0% Ti: 0.001% or less, T. O: Limiting to 0.005% or less and containing REM in an amount satisfying the relationship of the following formula (1), the balance being Fe and inevitable impurities, and having an equivalent circle diameter of 1 μm or more The ratio of the number of REM-containing inclusions among all the inclusions satisfies the following formula (2), and the concentration of Al ₂ O ₃ contained in the REM-containing inclusions is 30% or less (including 0%). An inclusion finely dispersed steel with excellent fatigue life, characterized by
[0021]
-30 <REM (ppm) -T. O (ppm) × 280/48 <50 (1) Formula REM-containing inclusion number / total inclusion number> 0.8 (2) Formula (2) REM contains any of Ce, La, Nd, and Pr The inclusion finely dispersed steel having excellent fatigue life according to (1), characterized in that:
[0022]
(3) The inclusion finely dispersed steel having excellent fatigue life according to (1) or (2) , wherein S as an impurity is limited to 0.003% by mass or less.
[0023]
(4) The inclusion finely dispersed steel excellent in fatigue life according to any one of (1) to (3), further comprising Cr: 0.01 to 1.5% by mass .
[0024]
(5) The inclusion finely dispersed steel having excellent fatigue life according to any one of (1) to (4), wherein the steel is bearing steel.
[0025]
(6) The inclusion finely dispersed steel having excellent fatigue life according to any one of (1) to (4), wherein the steel is used for a miniature bearing used in a hard disk, an AV device, or the like. .
[0026]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
[0027]
First, the component composition of steel specified in the present invention and the reason for limitation will be described. In addition, all component composition is the mass%.
[0028]
First, the reason for limiting the Al content will be described. As described above, the steel according to the present invention converts the oxide composition from Al ₂ O ₃ to REM oxide or REM oxysulfide by adding REM. Al is not essential for all steel grades. It is a component necessary as a deoxidizing element for reducing O and for adjusting the grain size of steel. However, even if the Al content exceeds 0.05%, the effect of adjusting the crystal grain size is saturated, and conversion from Al ₂ O ₃ to REM oxide or REM oxysulfide cannot be achieved. Is not achieved, so the upper limit was made 0.05%. In the case of high Al, it is considered that Al ₂ O ₃ is in a more stable state than REM oxide or REM oxysulfide and cannot be converted to REM oxide or REM oxysulfide.
[0029]
Next, T.W. The O (total oxygen) content will be described. T. in the present invention. The O content substantially coincides with the dissolved oxygen content in the steel and the oxygen content forming the oxide (mainly Al ₂ O ₃ ). Therefore, T.W. The higher the O content, the greater the amount of Al ₂ O _{3 in the} steel to be modified. Therefore, the limit T.I. As a result of examining the O content, T.W. If the O content exceeds 0.0050%, the amount of Al ₂ O ₃ increases too much, and even if REM is added, the total amount of Al ₂ O ₃ in the steel can be converted to REM oxide or REM oxysulfide. It was not possible, and it was found that Al ₂ O ₃ remained in the steel material. Therefore, in the present invention, T.W. The O content needs to be 0.0050% or less.
[0030]
REM is a strong deoxidizing element, and is added to react with Al ₂ O ₃ in the steel and take O of Al ₂ O ₃ to form REM oxide. For that purpose, the amount of Al ₂ O ₃ , ie, T.I. Unless a certain amount or more of REM is added according to the O content, unreacted Al ₂ O ₃ remains, which is not preferable. As a result of further experiments on this point, the REM content and T.I. It has been found that there is a relationship of the following formula (1) with the O content.
[0031]
-30 <REM (ppm) -T. O (ppm) × 280/48 <50 (1) Formula Here, the above formula (1) will be described with reference to FIG. FIG. 1 shows the effect of REM-T. This shows the value of dmax, 3000 (μ) when the influence of O × 280/48 is S = 0.005% and S = 0.002%.
[0032]
The evaluation procedure by the maximum inclusion size extreme value statistical method existing at 30000 mm ² evaluated by the extreme value statistical method is as follows for dmax, 30000 (μ) on the vertical axis.
[0033]
i) Sixteen 10 × 10 mm (100 mm ² ) sharpening samples were prepared.
[0034]
ii) Identify the largest inclusion in each sample and measure its size.
[0035]
iii) Estimate the inclusion size which is considered to exist at 30000 mm ² by the extreme value statistical processing from the 16 maximum inclusion sizes.
[0036]
First, [S] = 0.005% and [S] = 0.002% bearing steel (TO = 8ppm) is melted, REM is added with misch metal, and the refinement behavior of inclusions is investigated. did. The amount of REM to be added was changed, and the influence on the inclusion size at that time was evaluated. Microscope samples were collected from the steel ingot, the maximum inclusion size was evaluated by the extreme value statistical method, and the relationship with the amount of REM added was investigated. The solid line indicates the case where S = 0.005%, and the alternate long and short dash line indicates the case where [S] = 0.002%.
[0037]
T.A. REM-T. It can be seen that the inclusions are stably miniaturized when O × 280/48 is in the range of −30 to 50.
[0038]
Moreover, when S is 0.002, it can be seen that the inclusions are further refined. (It was also found that these inclusion compositions satisfied the formula (2) described later, and the Al ₂ O ₃ content was 30% or less.)
That is, the REM content and T.I. Relationship of O content, [REM (ppm) -T. O (ppm) × 280/48] is defined to be −30 or more and 50 or less as defined in the formula (1), thereby avoiding remaining unreacted Al ₂ O ₃ and aiming at an oxide. It was found that the REM oxide of the composition can be controlled. However, the REM content defined by the above formula (1) and T.I. In relation to the O content, [REM (ppm) -T. If O (ppm) × 280/48] was added in excess of 50 or more, the formation of sulfides was severe and coarse sulfides were formed, resulting in a poor fatigue life. Further, in the above formula (1), [REM (ppm) -T. If O (ppm) × 280/48] is −30 or less, the ability to produce REM oxide or REM oxysulfide is weak and the object of the present invention cannot be achieved.
[0039]
Next, the reason for defining the number ratio of oxide-based and oxysulfide-based inclusions having a particle diameter of 1 μm or more will be described. In the steel refining process, there are inclusions other than REM oxide-based and REM oxysulfide-based inclusions due to inevitable mixing in part. For example, when there is a large amount of slag with a high degree of oxidation from the decarburization refining furnace, and the reduction of the degree of oxidation in the secondary refining process is insufficient, the molten steel is reoxidized by the slag, and the Al ₂ O ₃ system Inclusions increase. If the seal with the atmosphere is insufficient after the REM source is added, the REM content is already used to reform the Al ₂ O ₃ inclusions, and there is no dissolved REM content. Oxidation increases Al ₂ O ₃ inclusions. Furthermore, when the slag basicity in the secondary refining is high, Ca Input is generated from the slag due to the equilibrium reaction between the slag and the molten steel, and this also generates CaO-rich inclusions that cannot be modified by REM. . When these inclusions are present, it is not possible to enjoy the effect of refinement of inclusions due to the addition of REM. Therefore, it is necessary to thoroughly exclude the above-mentioned reoxidation factors. By doing so, the number of inclusions (including sulfides and nitrides) other than REM-containing inclusions is less than 20% of the total, that is, by satisfying the relationship defined by the following formula (2), The fine dispersion of the material was highly stabilized, and further improvement in fatigue life was observed.
[0040]
The method for specifying the number of inclusions is shown below.
[0041]
For this measurement, an analysis / analysis device in which an X-ray microanalyzer and a computer are combined was used and evaluated in the following manner.
[0042]
i) Designation of measurement area of steel material: 1 visual field area was 0.5 mm × 0.5 mm, and 5 visual fields / sample.
[0043]
ii) Electron beam irradiation: The electron beam diameter was 0.5 μm, and each field of view was irradiated 1000 times in the X direction and 1000 times in the Y direction for elemental analysis.
[0044]
iii) Identification of inclusions: Elemental analysis information by electron beam irradiation was computer processed to identify inclusions.
[0045]
iv) Identification of REM-containing inclusions: Elemental analysis information by electron beam irradiation was computer-processed, and inclusions containing REM components were identified as REM-containing inclusions. The composition was quantitatively evaluated.
[0046]
v) Identification of the number: Further, the equivalent circle diameter of the inclusion particles in the above iii) and iv) is calculated, the size of the inclusion is specified, and the above iii existing in the 0.5 mm × 0.5 mm × 5 field of view. ) And iv) were measured.
[0047]
REM content (inclusions) / total number of inclusions> 0.8 (2) The reason that the concentration of Al ₂ O ₃ in the inclusions is defined as 30% or less is that 30% or more of Al ₂ O ₃ is contained. As a result, it was found that the Al ₂ O ₃ content was harder than REM oxide and REM oxysulfide having a content of 30% or less, and the fatigue characteristics were deteriorated and the acoustic characteristics were affected. Therefore, the upper limit of the Al ₂ O ₃ concentration in inclusions is set to 30%.
[0048]
Next, the use of misch metal as the REM source will be described.
[0049]
REM is a rare earth metal (rare earth element), Sc (atomic number 21) belonging to Group 3 of the periodic table, Y (39), and La, Ce, Pr, Nd, Pm, lanthanoids (57 to 71), It is a generic name for 17 elements of Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and has different formation powers for oxides, oxysulfides, and sulfides. In the conventional literature, each element is not specified and handled as having the same property. However, for example, as shown in FIG. 2, La and Ce have different compounds that exist stably even at the same oxygen or S level.
[0050]
In the present invention, various elements are studied, and inclusions can be stably refined by adding them with misch metal containing Ce, La, Nd, and Pr as main components (> 98%) rather than using them alone. (FIG. 3).
[0051]
When the S content is high, REM sulfide is easily formed. Even if REM sulfide is not formed, it becomes richer and coarser than the stoichiometric composition of REM oxysulfide. Therefore, as shown in FIG. 4, it is desirable that the S content is low, and by making it 0.003% or less, better material properties can be obtained without forming coarse sulfides.
When Ti exceeds 0.001% by mass, the amount of hard TiN produced is remarkably increased, resulting in deterioration of fatigue life, acoustic characteristics, and vibration resistance. Therefore, the Ti content is set to 0.001. It is necessary to make the mass% or less.
[0052]
In the present invention, the steel material which is an object of the present invention, in particular bearing steel, or taking into account the steel miniature bearing, as another steel reinforcing component, Si: 0.01~0.4%, Mn: 0.1 -0.5%, Cr: 0.01-1.5 % can also be added. In the present invention, the range of good Masui C concentration is 1.2% or less than 0.005%. This is because when C is over 1.2%, the added REM forms carbides with C and the reforming efficiency of Al2O3 decreases, and when it is less than 0.005%, the Al ₂ O ₃ present in the initial stage is reduced. This is because the amount is large and the reforming efficiency decreases.
[0053]
In addition, the manufacturing method of this invention steel is not specifically limited. That is, the melting of the mother molten steel may be either the blast furnace-converter method or the electric furnace method. Further, addition of components to the mother molten steel is not limited, and component elements necessary for the characteristics of each steel material may be arbitrarily added to the mother molten steel. Further, the addition method is not limited, and an addition method by free fall, a method of blowing with an inert gas, and the like can be freely adopted. Furthermore, the method of manufacturing a steel ingot from mother molten steel and rolling it is not limited.
[0054]
Regarding the addition of the REM source, it is added after vacuum refining such as RH. For example, when refining is performed by RH, it is preferable to add as misch metal (bulk) from the top to the molten steel in the vacuum tank from the hopper installed at the top of the vacuum tank at the end of the RH treatment.
[0055]
Examples of the present invention and comparative examples will be described below, and the effects of the present invention will be described.
[0056]
【Example】
Example 1
The molten iron discharged from the blast furnace is subjected to de-P and de-S treatments, and then the molten iron 270t is charged into the converter and subjected to oxygen blowing to produce a base for bearing steel having a predetermined C, P and S content. Molten steel was obtained. Al, Si, Mn, and Cr were added while the mother molten steel was discharged into the ladle and during LF and RH degassing. In LF, the highly oxidized slag discharged from the converter is reduced, the content of iron oxide and MnO is reduced, and the CaO / SiO ₂ ratio is increased by adding CaO to reduce the components that cause reoxidation. Let Further, the Al ₂ O ₃ concentration was adjusted to obtain a slag composition having a high inclusion absorption capacity. In the RH treatment, dehydrogenation and inclusion removal were performed. Further, a predetermined amount of REM was added from an addition hopper provided in the upper part of the RH vacuum chamber at the end of the RH treatment. As the REM, misch metal having the components shown in Table 2 was used. Its size was 35-45 mm.
[0057]
A cast slab was produced from the molten steel thus obtained by a continuous casting method, and the slab was rolled with a steel bar to produce a steel bar for a bearing having a chemical composition shown in Table 3 (diameter 65 mmφ). Inclusions contained in this steel material were fine with a large proportion of REM-containing inclusions. Extremum statistical method (reference area: 100mm ^2, n = 16, evaluation area: 30,000 mm ²⁾ The results of the evaluation of the maximum inclusion size in 30,000 mm ^2, good size shown in Table 3 were obtained. Moreover, as a result of performing the rolling fatigue test of the steel material, good results shown in Table 3 were obtained. The breakdown of the REM components shown in Table 3 is shown in Table 4.
(Comparative Example 1)
Bearing steels shown in Table 3 were produced in the same manner as in Example 1. However, in this case, the case where REM addition at the end of the RH treatment is not performed, the case where the REM addition amount (the addition method is the same as that of Example 1) is set to the upper limit or more and the lower limit or less of the appropriate REM amount of the present invention, and after RH In some cases, the sealability was intentionally deteriorated, and the ratio of the number of inclusions containing REM deviated from the present invention. The inclusion size and rolling fatigue performance of the obtained bearing steel are shown in Table 3, but were unfavorable compared to Example 1.
[0058]
[Table 1]

[0059]
[Table 2]

[0060]
[Table 3]

[0061]
[Table 4]

[0062]
(Example 2)
Bearing steels shown in Table 5 were manufactured by the same method as in Example 1. Inclusions contained in this steel material were fine with a large proportion of REM-containing inclusions. As a result of evaluating the maximum inclusion size at 30000 mm 2 by the extreme value statistical method (standard area: 100 mm 2, n = 16, evaluation area: 30000 mm 2) with a steel bar rolled to 65 mmφ, the favorable size shown in Table 5 was obtained. . Moreover, after rolling the said steel material to a 10 mm diameter wire, it processed into the miniature bearing, and as a result of evaluating an acoustic characteristic and a vibration characteristic, the favorable result shown in Table 5 was obtained. The breakdown of the REM components shown in Table 5 is shown in Table 6.
(Comparative Example 2)
Bearing steels shown in Table 5 were produced in the same manner as in Example 2. However, in this case, the case where REM addition at the end of the RH treatment is not performed, the case where the REM addition amount (the addition method is the same as that of Example 1) is set to the upper limit or more and the lower limit or less of the appropriate REM amount of the present invention, and after RH In some cases, the sealability was intentionally deteriorated, and the ratio of the number of inclusions containing REM deviated from the present invention. In some cases, Ti was removed. The results of inclusion size and acoustic / vibration characteristics of the obtained bearing steel are shown in Table 5, which is not preferable as compared with Example 2.
[0063]
[Table 5]

[0064]
[Table 6]

[0065]
【The invention's effect】
As described above, the present invention relates to a steel in which REM oxides and REM oxysulfide inclusions are finely dispersed in steel. In particular, the present invention eliminates the adverse effects of oxide inclusions and is excellent. It is possible to provide steel having fatigue life resistance and steel having excellent acoustic characteristics.
[Brief description of the drawings]
FIG. 1 shows REM-T. The figure which shows the relationship of Ox280 / 48.
2A is a diagram showing stable regions of Ce oxide, oxysulfide, and sulfide, and FIG. 2B is a diagram showing stable regions of La oxide, oxysulfide, and sulfide.
FIG. 3 is a diagram showing the influence of a REM source on inclusion size.
FIG. 4 is a diagram showing the influence of [S] on inclusion size.

Claims (6)

% By mass
C: 0.005 to 1.2%
Si: 0.01 to 0.4%
Mn: 0.1 to 0.5%
Al: 0.05% or less (including 0%)
Including
Ti: 0.001% or less,
T.A. O: 0.005% or less
Limited to
And the amount of REM that satisfies the relationship of the following formula (1) is contained, the balance is Fe and inevitable impurities, and the inclusion containing REM among all the inclusions having an equivalent circle diameter and a particle diameter of 1 μm or more . the number ratio of, along with satisfying the following expression (2), excellent fatigue life concentration of Al ₂ O ₃ contained in the REM-containing inclusions is characterized in that 30% or less (including 0%) Inclusion fine dispersion steel.
-30 <REM (ppm) -T. O (ppm) × 280/48 <50 (1) formula Number of inclusions containing REM / total number of inclusions> 0.8 (2) formula   2. The inclusion finely dispersed steel with excellent fatigue life according to claim 1, wherein REM contains any of Ce, La, Nd, and Pr. The inclusion fine dispersion steel excellent in fatigue life according to claim 1 or 2 , wherein S as an impurity is limited to 0.003% by mass or less. Furthermore, Cr: 0.01-1.5 mass% is included , The inclusion fine dispersion steel excellent in the fatigue life of any one of Claims 1-3 characterized by the above-mentioned.   The inclusion finely dispersed steel having excellent fatigue life according to any one of claims 1 to 4, wherein the steel is a bearing steel.   The inclusion fine dispersion steel having excellent fatigue life according to any one of claims 1 to 4, wherein the steel is used for a miniature bearing used in a hard disk, an AV device, or the like.

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