WO2013168573A1 - Steel having excellent rolling fatigue life - Google Patents

Steel having excellent rolling fatigue life Download PDF

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Publication number
WO2013168573A1
WO2013168573A1 PCT/JP2013/062073 JP2013062073W WO2013168573A1 WO 2013168573 A1 WO2013168573 A1 WO 2013168573A1 JP 2013062073 W JP2013062073 W JP 2013062073W WO 2013168573 A1 WO2013168573 A1 WO 2013168573A1
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Prior art keywords
steel
less
inclusion
flaw detection
mhz
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PCT/JP2013/062073
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French (fr)
Japanese (ja)
Inventor
藤松　威史
常陰　典正
陽亮 青山
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山陽特殊製鋼株式会社
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Priority to KR1020147024344A priority Critical patent/KR20150010697A/en
Publication of WO2013168573A1 publication Critical patent/WO2013168573A1/en

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Classifications

    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/40—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rings; for bearing races
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • 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
    • 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids

Definitions

  • the present invention relates to a mechanical part that is required to have an excellent rolling fatigue life, such as a bearing, a gear, a hub unit, a toroidal CVT device, a constant velocity joint, and a crankpin, and whose surface hardness is hardened to 58 HRC or more. And steel applied as a device.
  • 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.
  • the oxygen amount may be further reduced by special dissolution such as VAR and ESR.
  • measures are taken to prevent adverse effects of other impurity elements by reducing their content to the order of 0.01% by mass.
  • the extreme statistical method is applied to inclusions with a maximum inclusion diameter of approximately 100 ⁇ m or less, and the ultrasonic flaw detection method with a flaw detection frequency of 5 to 25 MHz is applied to inclusions with a maximum inclusion diameter of approximately 100 ⁇ m or more.
  • the ultrasonic flaw detection method with a flaw detection frequency of 5 to 25 MHz is applied to inclusions with a maximum inclusion diameter of approximately 100 ⁇ m or more.
  • Patent Document 4 there is a proposal of an evaluation method using both methods together.
  • a steel that defines the number and size of inclusions as steel having excellent rolling fatigue life can be obtained. It has been proposed (see, for example, Patent Document 5).
  • the inventors of the present invention have an L 1 life (test specimens of the same lot under the same conditions) as a measure of reliability. At the time of testing, attention was paid to the number of cycles in which 99% of the specimens rotate without peeling. And, with the aim of improving it, we conducted intensive research using the evaluation results of non-metallic inclusions in steel by the ultrasonic flaw detection method as an objective index. First, regarding the detection of non-metallic inclusions in steel by ultrasonic flaw detection, among non-metallic inclusions, oxides are significantly harder than the parent phase steel in any processing temperature range from cold to hot.
  • a sulfide is a soft material that easily follows a relatively parent phase steel and deforms during hot and cold rolling and forging. It has been found that sulfides are inclusions that are difficult to detect by ultrasonic flaw detection as compared to oxides due to good adhesion to the matrix. It has been found that the presence of some sulfide inclusions that are actually present in steel but cannot be detected by the ultrasonic flaw detection method may contribute to a reduction in rolling fatigue life. Then, as a result of examining the sulfur content in the steel, it was found that the sulfur content in the steel needs to be regulated to at least 0.003% by mass or less.
  • the oxygen content in the steel is set to 6 ppm or less and the sulfur in the steel is used as described above.
  • the inclusion diameter is The number of non-metallic inclusion pairs having a closest distance between non-metallic inclusions of 20 ⁇ m or more and the inclusion diameter of 20 ⁇ m or more being less than 40 ⁇ m is 2.0 or less per 1000 mm 3 of steel material volume. I found out that I should regulate it.
  • Inclusions having an inclusion diameter of about 20 ⁇ m are not large enough to cause separation with an extremely short life. However, even if the inclusion is about 20 ⁇ m, if the closest distance between non-metallic inclusions having such a size is less than 40 ⁇ m, it behaves as if it is a large inclusion, There is a possibility of causing peeling with a short life. Accordingly, the present inventors, if the occurrence frequency in the steel of such non-metallic inclusions pairs per 1000 mm 3 to 2.0 or less, an excellent practical rolling fatigue life (L 1 life) It has been found that it is possible to obtain steel.
  • non-metallic inclusions whose inclusion diameter exceeds 100 ⁇ m may cause separation with an extremely short life even if they are used alone. Therefore, an ultrasonic wave having a probe frequency exceeding 25 MHz and not exceeding 125 MHz.
  • the maximum diameter of non-metallic inclusions detected when a steel material volume of 3000 mm 3 or more is detected by the flaw detection method needs to be 100 ⁇ m or less.
  • the inclusion diameter is 20 ⁇ m or more, and the closest distance between the inclusions having a diameter of 20 ⁇ m or more is 40 ⁇ m, which causes an extremely early accidental peeling for the calculated life in a part requiring rolling fatigue. Since non-metallic inclusion pairs that are less than the number are present in steel with a very low probability, the accuracy of detecting the presence or absence of them may be low.
  • the extreme value statistical method is applied to nonmetallic inclusions whose maximum inclusion diameter is less than 100 ⁇ m, and the flaw detection frequency is used for nonmetallic inclusions whose inclusion diameter is 100 ⁇ m or more.
  • the extreme value statistical method is an evaluation method based on two-dimensional observation, as in the case described above, the non-metallic inclusions having a small test area and a low inclusion frequency in steel with a diameter of 20 ⁇ m or more are observed. There is a possibility that the quality of the steel material cannot be fully judged.
  • the ultrasonic flaw detection method with a flaw detection frequency of 5 to 25 MHz since the detectable inclusion diameter is about 100 ⁇ m or more, the inclusion diameter is 20 ⁇ m or more, and the inclusion diameter is 20 ⁇ m or more.
  • the ultrasonic beam in the flaw detection frequency band described above is not highly accurate in evaluation, and thus has an excellent L 1 life. There is a need for an evaluation method that can stably provide steel.
  • the non-metallic inclusions having a sulfur content of 0.008 mass% or less and an inclusion diameter detected per 300 mm 3 of steel material volume by an ultrasonic flaw detection method is 20 ⁇ m or more.
  • Steel having an excellent rolling fatigue life specified to be 12 or less per 300 mm 3 (in a thrust type rolling fatigue test, the maximum hertz stress P max 5.3 GPa and the L 10 life> 1.
  • a steel capable of obtaining 0 ⁇ 10 7 cycle) and its evaluation method are proposed.
  • the regulation of the sulfur content is not sufficient, and the inclusion diameter is 20 ⁇ m or more, and the inclusion diameter is 20 ⁇ m or more, which is an index of reliability against accidental damage to the bearing in use extremely early than the calculated life. Since the number of non-metallic inclusion pairs in which the closest distance between the inclusions having a diameter is less than 40 ⁇ m has not been evaluated, it may be impossible to stably provide steel having an excellent L 1 life.
  • the present invention has been made in order to solve such a conventional problem, and the problem to be solved by the present invention is to secure a forging ratio of the steel material at a certain value or more, and the oxygen content in the steel.
  • the non-metallic inclusions in steel are detected in a large volume by ultrasonic flaw detection, and the closest distance between non-metallic inclusions with inclusion diameters of a certain size or more is constant. It is used for machine parts with excellent rolling fatigue life by limiting the number of non-metallic inclusion pairs as follows and limiting the maximum size of non-metallic inclusions in steel by ultrasonic flaw detection. Is to provide steel.
  • the steel is used for a machine part having a surface hardness of 58 HRC or higher, and the forging ratio of the steel to the base metal ingot is 22.0.
  • the ultrasonic flaw detection method in which the oxygen content in the steel is 6 ppm or less and the sulfur content is 0.003% by mass or less and the probe frequency exceeds 25 MHz and is 125 MHz or less,
  • the number of inclusions detected in a volume of 1000 mm 3 is 20 ⁇ m or more, and the number of non-metallic inclusion pairs in which the closest distance between nonmetallic inclusions having a diameter of 20 ⁇ m or more is less than 40 ⁇ m is 2.0 or less.
  • the and beyond the probe frequency 25 MHz the maximum diameter of nonmetallic inclusions detected in steel total volume 3000 mm 3 or more by 125MHz following ultrasonic flaw detection method is 100 ⁇ m or less, rolling is Steel excellent in fatigue life is provided.
  • steel used for machine parts having a surface hardness of 58 HRC or more, wherein the forging ratio of the steel to the base material ingot is 22.0 or more, and oxygen in the steel
  • the content is 6 ppm or less in mass proportion
  • the sulfur content is 0.003 mass% or less
  • the number of non-metallic inclusion pairs in which the object diameter is 20 ⁇ m or more and the closest distance between non-metallic inclusions having a diameter of 20 ⁇ m or more is less than 40 ⁇ m is 2.0 or less, and the probe frequency exceeded 25 MHz, the maximum diameter of nonmetallic inclusions detected in steel total volume 3000 mm 3 or more by 125MHz following ultrasonic flaw detection method is not less 100 ⁇ m or less, with inclusion diameter of above 20 ⁇ m or more, or
  • the number of non-metallic inclusions pair closest distance is less than 40 ⁇ m of non-metallic inclusions each other in the diameter of the 20 ⁇ m or more, flaw detection steel by ultrasonic flaw detection in a total volume of 3000 mm 3 or more, and is 300000Mm 3 or less
  • the maximum diameter of the non-metallic inclusions is 100 ⁇ m or less (evaluated, measured, or confirmed (hereinafter the same)).
  • a steel having an excellent rolling fatigue life which is obtained (evaluated, measured or confirmed (hereinafter the same)) is obtained by flaw detection of a steel material having a total volume of 300,000 mm 3 or less.
  • high carbon chromium bearing steel defined in JIS (Japanese Industrial Standards) standard and SAE (Society of Automotive Engines) standard Or ASTM (American Society for Testing and Materials, or ASTM International) 52100 as defined in Standard A295, as well as 100Cr6 as defined in DIN (Deutsches Institut Furan Normung) standard, and mechanical structural carbon as defined in JIS standard
  • SC steel materials
  • ASTM American Society for Testing and Materials
  • ASTM American Society for Testing and Materials, or ASTM International
  • the number of the nonmetallic inclusion pairs in which the inclusion diameter is 20 ⁇ m or more and the closest distance between the nonmetallic inclusions having a diameter of 20 ⁇ m or more is less than 40 ⁇ m, and the nonmetal maximum diameter of the inclusions, the total volume by the ultrasonic flaw detection method in 3000 mm 3 or more, and is obtained by testing the steel is 300000Mm 3 or less.
  • the steel excellent in rolling fatigue life of the present invention was made to solve such a conventional problem, and regulates the forging ratio of the steel material and regulates the oxygen content and sulfur content in the steel.
  • non-metallic inclusions in steel are detected in a large volume by ultrasonic flaw detection, and the closest distance between non-metallic inclusions having inclusion diameters greater than a certain size is less than a certain distance.
  • the surface hardness is 58 HRC or more means “the surface hardness is a value of 58 or more on the C scale in the Rockwell hardness test”.
  • 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 has a forging ratio of 22.0 to the ingot as a base material.
  • the oxygen content in the steel is 6 ppm or less by mass and the sulfur content is 0.003 mass% or less.
  • the ultrasonic flaw detection method exceeding the probe frequency 25 MHz and 125 MHz or less, the inclusion diameter detected per 1000 mm 3 of the steel material is 20 ⁇ m or more, and the nonmetallic inclusions having a diameter of 20 ⁇ m or more are used.
  • the closest distance is less than 40 ⁇ m
  • the number of non-metallic inclusion pairs is 2.0 or less
  • the total frequency of steel is 3000 mm 3 or more by ultrasonic flaw detection with a probe frequency exceeding 25 MHz and 125 MHz or less.
  • the maximum diameter of non-metallic inclusions detected in (1) is 100 ⁇ m or less.
  • non-metallic inclusions of a certain size or more from steel In parts subjected to rolling fatigue, it is important to improve properties to reduce non-metallic inclusions of a certain size or more from steel. If non-metallic inclusions with a detrimental size exist under the rolling surface of the bearing, separation will occur, so the size of non-metallic inclusions that appear in the hazardous area under the rolling surface of the bearing will be reduced. This is extremely important for improving the life of the bearing. As inclusion diameters that cause separation very early without reaching the calculated life, non-metallic inclusions having an inclusion diameter of 20 ⁇ m are not harmful by themselves.
  • the ultrasonic flaw detection method is applied as an evaluation method for guaranteeing the characteristics.
  • the inclusion diameter of the nonmetallic inclusion detected per 1000 mm 3 of the volume of the steel material is 20 ⁇ m or more by the ultrasonic flaw detection method exceeding the probe frequency 25 MHz and 125 MHz or less, and 20 ⁇ m thereof.
  • the closest distance between the non-metallic inclusions is less than 40 ⁇ m, the number of non-metallic inclusion pairs is 2.0 or less, and the probe frequency exceeds 25 MHz and the ultrasonic flaw detection method is 125 MHz or less.
  • the maximum diameter of non-metallic inclusions detected with a steel material total volume of 3000 mm 3 or more is regulated to 100 ⁇ m or less.
  • the inclusion diameter of nonmetallic inclusions in an ultrasonic flaw detection method applied as a method for guaranteeing the characteristics is 20 ⁇ m or more, and The number of non-metallic inclusion pairs in which the closest distance between non-metallic inclusions of 20 ⁇ m or more is less than 40 ⁇ m, and the point that the maximum diameter of the non-metallic inclusion of the present embodiment is 100 ⁇ m or less are ultrasonic flaw detection in a total volume of 3000 mm 3 or more by law, and those that have been evaluated by testing the 300000Mm 3 below.
  • the steel having excellent rolling fatigue life according to the third aspect of the present invention is desirably a steel type used for applications requiring rolling fatigue life such as bearings.
  • high carbon chromium bearing steel (SUJ) specified in JIS standard, 52100 specified in SAE standard or ASTM standard A295, 100Cr6 specified in DIN standard, and specified in JIS standard Carbon steel for machine structure (SC) and steel selected from chrome steel (SCr), chrome molybdenum steel (SCM) and nickel chrome molybdenum steel (SNCM) among alloy steels for machine structure .
  • the present invention can be applied to foreign standard steels corresponding to JIS standards such as SAE standards 4320, 5120, 4140, 1053, and 1055.
  • the ultrasonic flaw detection method various types of ultrasonic flaw detectors and probes have already been put into practical use, and these can be used in the present invention.
  • a focus type high frequency probe and the like can be cited.
  • the detection capability of the flat probe is said to be 1 ⁇ 2 wavelength, but the focus probe is 1 ⁇ 4 wavelength. Therefore, the focus probe is suitable for accurate evaluation. is there.
  • the probe frequency in this embodiment is preferably greater than 25 MHz and not greater than 125 MHz, and particularly preferably about 30 to 100 MHz.
  • the nonmetallic inclusions whose nonmetallic inclusions have an inclusion diameter of 20 ⁇ m or more and the closest distance between the nonmetallic inclusions of 20 ⁇ m or more is less than 40 ⁇ m.
  • the number of objects pair, and the maximum diameter of the nonmetallic inclusions is 100 ⁇ m or less, as already described above, the ultrasonic flaw detection method in a total volume of 3000 mm 3 or more, and testing the 300000Mm 3 below, non-metallic inclusions Is preferably detected.
  • the number of nonmetallic inclusion pairs whose inclusion diameter is 20 ⁇ m or more and the closest distance between the nonmetallic inclusions of 20 ⁇ m or more is less than 40 ⁇ m, and the maximum nonmetallic inclusion diameter is 100 ⁇ m or less.
  • the evaluation volume in the ultrasonic flaw detection method according to the present embodiment is very difficult to evaluate in practice because the processing time is enormous in the conventional evaluation method mainly based on microscopic observation.
  • the dead zone region from the surface of the specimen to the depth corresponding to the probe frequency is excluded from the evaluation volume, and if necessary, tissue abnormalities due to heat treatment etc. and measurement noise in ultrasonic flaw detection are detected.
  • Evaluation volume in ultrasonic flaw detection based on the underwater focal length range according to the frequency and performance of the probe after excluding the end of the sensitive specimen from the flaw detection range of the ultrasonic beam at the focal position the need to ensure at 3000 mm 3 or more, and 300000Mm 3 below.
  • the forging and forming ratio of the steel material is regulated, and the oxygen content and the sulfur content in the steel are regulated, and the ultrasonic wave Detecting non-metallic inclusions in steel in a large volume by flaw detection method, and the non-metallic inclusion pairs whose non-metallic inclusions having inclusion diameters above a certain size are less than a certain distance
  • the number and limiting the maximum size of non-metallic inclusions in steel by ultrasonic flaw detection it is possible to provide steel used for machine parts having excellent rolling fatigue life.
  • test materials 1 to 25 as examples and the test materials 26 to 36 as comparative examples are listed in Table 1 and Table 2, and the steel excellent in rolling fatigue life of the present invention will be described more specifically. .
  • the present invention is not limited to these examples.
  • Table 1 shows the component composition of each sample material of the example and the comparative example. In addition, even if it shows with the same specification name, the composition of each test material shown below has a different composition as shown in Table 1, respectively.
  • the specimens 1 to 7 and specimens 26 to 33 in Table 1 are steels having a composition classified as JIS SUJ2 steel, which is a high carbon chromium bearing steel, and the specimens 8 and 34 are JIS SCr420 steel. Steel with a composition classified as JIS SNCM420 steel for specimen 9 and steel with a composition classified as JIS S53C steel for specimen 10 11.
  • Specimen 35 and Specimen 36 are steels having a composition classified as JIS SCM420 steel, and Specimen 12 and Specimen 13 are steels having a composition classified as SAE 52100.
  • the specimen 14 and the specimen 15 are steels having a composition classified as ASTM 52100, the specimen 16 and the specimen 17 are steels having a composition classified as DIN 100Cr6, and the specimen 18 is Steel with a composition classified as JIS SUJ3 steel Steel with a composition classified as JIS SUJ5 steel, specimen 20 with steel with composition classified as SAE 4320 steel, and specimen 21 with steel with composition classified as SAE 5120 steel
  • Sample 22 has a composition classified as JIS SCM435 steel, sample 23 has a composition classified as SAE 4140 steel, and sample 24 has a composition classified as JIS S55C steel.
  • test material 25 steel having a composition classified as SAE 1053 steel was used.
  • Specimen 1-5, Specimen 8-9, Specimen 12, Specimen 14, Specimen 16, Specimen 18, Specimen 20-30, and Specimen 36 are arc melted.
  • the ingot is smelted in a furnace, then smelted in a ladle, and further degassed with a vacuum degassing apparatus to produce an ingot by continuous casting.
  • Specimen 6, Specimen 7, Specimen 10, Specimen 11, Specimen 13, Specimen 15, Specimen 17, Specimen 19, and Specimens 31-35 are arcs. It is made by melting in a melting furnace, then refining a ladle, and further degassing with a vacuum degassing apparatus to produce an ingot with an ingot.
  • the ingot obtained above was hot-worked to obtain a steel material with a diameter of 65 mm in which a steel forging ratio of 22.0 or more was ensured.
  • Thrust type rolling fatigue test The steel materials of Specimens 1 to 7, Specimens 12 to 19, and Specimens 26 to 33 were subjected to spheroidizing annealing at 800 ° C., and the outer diameter was 60 mm and the inner diameter was perpendicular to the longitudinal direction of the steel materials. A test piece made of a disk having a thickness of 20 mm and 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 tempered at 170 ° C. for 90 minutes to obtain a desired hardness of 58 HRC or higher. Then, the obtained test piece was surface-polished and a thrust type rolling fatigue test was performed.
  • the steel materials of Specimen 8, Specimen 9, Specimen 11, Specimen 20, Specimen 21, and Specimens 34 to 36 were subjected to normalization at 925 ° C.
  • the steel materials of the test materials 22 and 23 were subjected to normalization at 870 ° C., and then a test piece made of a disk having an outer diameter of 60 mm, an inner diameter of 20 mm, and a thickness of 8.3 mm perpendicular to the longitudinal direction of the steel material. was made.
  • the test piece was carburized at 930 ° C. and then quenched by oil cooling. Next, the quenched specimen was tempered at 180 ° C. for 90 minutes to obtain a desired hardness of 58 HRC or higher.
  • the obtained test piece was surface-polished and a thrust type rolling fatigue test was performed.
  • the steel materials of the test material 10, the test material 24, and the test material 25 were normalized at 870 ° C., and then the outer diameter was 60 mm, the inner diameter was 20 mm, and the thickness was 8.
  • a test piece consisting of a 3 mm disk was prepared. This test piece was induction-quenched and then tempered at 180 ° C. for 90 minutes to obtain a desired hardness of 58 HRC or higher. Then, the obtained test piece was surface-polished and a thrust type rolling fatigue test was performed.
  • the thrust type rolling fatigue test was performed at a maximum hertz stress P max of 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.
  • the steel materials of Specimen 8, Specimen 9, Specimen 11, Specimen 20, Specimen 21, and Specimens 34 to 36 were normalized at 925 ° C. Was cut out and quenched and tempered. Further, the steel materials of the test material 10 and the test materials 22 to 25 were subjected to normalization at 870 ° C., L-section test pieces were cut out, and subjected to quenching and tempering treatment. Thereafter, surface polishing was performed on all of the test materials 1 to 36 for the purpose of reducing transmission loss of ultrasonic waves. Each test piece was finished to a thickness of 10 mm by surface polishing, and an ultrasonic flaw detection test was performed.
  • an ultrasonic flaw detector equipped with a focus type high-frequency probe (50 MHz) was used.
  • the volume of ultrasonic flaw detection was set to 4000 mm 3 .
  • the nonmetallic inclusions whose non-metallic inclusions per volume of 1000 mm 3 of the steel material are 20 ⁇ m or more and the closest distance between the nonmetallic inclusions of 20 ⁇ m or more is less than 40 ⁇ m.
  • the number of detected object pairs and the presence / absence of non-metallic inclusions having a maximum diameter exceeding 100 ⁇ m were determined.
  • the test materials 26 to 36 of the comparative example are 20 ⁇ m or more detected per 1000 mm 3 of the steel material volume, and the non-metallic inclusion whose non-metallic inclusions of 20 ⁇ m or more are less than 40 ⁇ m.
  • the detection of non-metallic inclusions with the number of pairs exceeding 2.0 and the maximum diameter exceeding 100 ⁇ m can be seen, which is outside the scope of the present invention.
  • the L 1 life of the test materials 26 to 36 of these comparative examples is three times or less when the L 1 life of the test material 33 of the comparative example is 1.
  • the test materials 1 to 25 of the examples in the present invention have an inclusion diameter of 20 ⁇ m or more and 20 ⁇ m of the inclusion diameter detected per 1000 mm 3 of steel material volume by the ultrasonic flaw detection method.
  • the number of non-metallic inclusion pairs in which the closest distance between the non-metallic inclusions is less than 40 ⁇ m is 2.0 or less, and there is no detection of non-metallic inclusions having a maximum diameter exceeding 100 ⁇ m.
  • the invention according to the first aspect of the invention, the invention according to the second aspect, and the invention according to the third aspect are all satisfied, and each is at least four times the L 1 life of the test material 33 of the comparative example. Yes, L 1 life is excellent.

Abstract

Provided is steel for bearings, crank pins and the like, having an excellent rolling fatigue life, and having an excellent rolling fatigue life when used for devices and machinery parts with a surface hardness of at least 58 HRC. This steel is for machinery parts with a surface hardness of at least 58 HRC. The forging ratio of the steel material with respect to an ingot of the base material is at least 22.0. The oxygen content in the steel is 6 ppm or less in terms of mass ratio, and the sulfur content is 0.003 mass% or less. The diameters of inclusions detected per 1,000 mm3 of steel material are 20 μm or more according to ultrasonic flaw detection at a probe frequency of over 25 MHz to 125 MHz, and at said inclusion diameter of 20 μm or more, the distance of closest approach between non-metallic inclusions is less than 40 μm. The number of non-metallic inclusion pairs is 2.0 or less, and the maximum diameter of non-metallic inclusions detected in a total steel material volume of at least 3,000 mm3 is 100 μm or less according to ultrasonic flaw detection at a probe frequency of over 25 MHz to 125 MHz.

Description

転がり疲労寿命に優れた鋼Steel with excellent rolling fatigue life 関連出願の相互参照Cross-reference of related applications
　本出願は、２０１２年５月７日に出願された日本国特許出願２０１２－１０５９５５号と、２０１３年１月１５日に出願された日本国特許出願２０１３－５０１４号とに基づく優先権を主張するものであり、その全体の開示内容が参照により本明細書に組み込まれる。 This application claims priority based on Japanese Patent Application No. 2012-105955 filed on May 7, 2012 and Japanese Patent Application No. 2013-5014 filed on January 15, 2013 The entire disclosure of which is incorporated herein by reference.
　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、および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 part that is required to have an excellent rolling fatigue life, such as a bearing, a gear, a hub unit, a toroidal CVT device, a constant velocity joint, and a crankpin, and whose surface hardness is hardened to 58 HRC or more. And 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 high 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.
　鋼組成に含有されている不純物元素のうち、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.
　鋼中の酸素量が少ない高清浄度鋼については、種々提案されている。これらの提案の中で、鋼中酸素含有量が１０ｐｐｍ未満であり、かつ、電子ビーム溶融法により浮上させ、凝集させた酸化物系介在物の表面露出面積が１グラム当たり２０μｍ2以下であることを特徴とする高清浄度軸受用鋼が提案されている（例えば、特許文献１参照。）。また、精錬のプロセス制約を受けず、製造コストの増加を招くことなく、汎用の長寿命の鋼が提案されている（例えば、特許文献２参照。）。さらに、疲労強度が要求される部品設計のために必要となる、所定体積中に存在が予測される最大介在物の大きさを保証した鋼が提案されている（例えば、特許文献３参照。）。また、最大介在物径が略１００μｍ以下の介在物については極値統計法を適用し、最大介在物径が略１００μｍ以上の介在物については探傷周波数を５～２５ＭＨｚとした超音波探傷法を適用するなど、両手法を併用する評価方法の提案がある（例えば、特許文献４参照。）。また、さらに径が１００μｍ未満の介在物について探傷周波数を２０～１２５ＭＨｚとした超音波探傷法により評価することにより、転がり疲労寿命に優れた鋼としての介在物の個数と大きさを規定した鋼が提案されている（例えば、特許文献５参照）。 Various proposals have been made for high cleanliness steel with a low oxygen content in the steel. Among these proposals, the oxygen content in the steel is less than 10 ppm, and the exposed surface area of the oxide inclusions floated and aggregated by the electron beam melting method is 20 μm 2 or less per gram. Has been proposed (see, for example, Patent Document 1). In addition, a general-purpose long-life steel has been proposed without being subjected to refining process restrictions and without causing an increase in manufacturing cost (see, for example, Patent Document 2). Furthermore, steel that guarantees the size of the maximum inclusion that is expected to exist in a predetermined volume, which is necessary for designing parts that require fatigue strength, has been proposed (see, for example, Patent Document 3). . The extreme statistical method is applied to inclusions with a maximum inclusion diameter of approximately 100 μm or less, and the ultrasonic flaw detection method with a flaw detection frequency of 5 to 25 MHz is applied to inclusions with a maximum inclusion diameter of approximately 100 μm or more. For example, there is a proposal of an evaluation method using both methods together (see, for example, Patent Document 4). In addition, by evaluating the inclusions having a diameter of less than 100 μm by ultrasonic flaw detection with a flaw detection frequency of 20 to 125 MHz, a steel that defines the number and size of inclusions as steel having excellent rolling fatigue life can be obtained. It has been proposed (see, for example, Patent Document 5).
特開平６－１９２７９０号公報JP-A-6-192790 特開２００２－２２０６３８号公報JP 2002-220638 A 特開平１１－１９４１２１号公報JP-A-11-194121 特開２００６－３１７１９２号公報JP 2006-317192 A 特開２００８－１２１０３５号公報JP 2008-121035 A
　本発明者らは、優れた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えるために、その信頼性の目安としてＬ1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。そして、その向上を目指して、超音波探傷法による鋼中非金属介在物の評価結果を客観的な指標として鋭意研究を行った。先ず、超音波探傷法による鋼中の非金属介在物の検出に関し、非金属介在物のうち、酸化物は冷間から熱間のいずれの加工温度域においても、母相の鋼より著しく硬質な介在物であり、圧延や鍛造時に母相に追従して変形しにくいために、加工後に母相と密着していない部分を有する場合がある。そのため、超音波探傷法によって比較的容易に検出することが可能である。ところで、転がり疲労寿命に対する酸化物系介在物の悪影響を軽減するためには、少なくとも鋼中の酸素含有量を６ｐｐｍ以下とする必要があることが分かった。 In order to suppress the extremely early breakage with respect to the calculated life in a machine part that requires an excellent rolling fatigue life, the inventors of the present invention have an L 1 life (test specimens of the same lot under the same conditions) as a measure of reliability. At the time of testing, attention was paid to the number of cycles in which 99% of the specimens rotate without peeling. And, with the aim of improving it, we conducted intensive research using the evaluation results of non-metallic inclusions in steel by the ultrasonic flaw detection method as an objective index. First, regarding the detection of non-metallic inclusions in steel by ultrasonic flaw detection, among non-metallic inclusions, oxides are significantly harder than the parent phase steel in any processing temperature range from cold to hot. Since it is an inclusion and hardly deforms following the parent phase during rolling or forging, it may have a portion that is not in close contact with the parent phase after processing. Therefore, it can be detected relatively easily by the ultrasonic flaw detection method. By the way, in order to reduce the adverse effect of oxide inclusions on the rolling fatigue life, it has been found that at least the oxygen content in the steel needs to be 6 ppm or less.
　一方で、本発明者らは、非金属介在物のうちで、硫化物は、熱間や冷間での圧延や鍛造時において、比較的母相の鋼に良く追従して変形しやすい軟質の介在物であり、この母相との密着性が良好であることにより、硫化物は酸化物に比べて超音波探傷法では検出しにくい介在物であることを見出した。そして、実際には鋼中に存在しているものの、超音波探傷法により検出できない一部の硫化物系介在物の存在が、転がり疲労寿命低下の一因となる場合があることが分かった。そこで、鋼中の硫黄含有量について検討した結果、鋼中の硫黄含有量は少なくとも０．００３質量％以下に規制する必要があることを見出した。 On the other hand, among the non-metallic inclusions, the inventors of the present invention have a tendency that a sulfide is a soft material that easily follows a relatively parent phase steel and deforms during hot and cold rolling and forging. It has been found that sulfides are inclusions that are difficult to detect by ultrasonic flaw detection as compared to oxides due to good adhesion to the matrix. It has been found that the presence of some sulfide inclusions that are actually present in steel but cannot be detected by the ultrasonic flaw detection method may contribute to a reduction in rolling fatigue life. Then, as a result of examining the sulfur content in the steel, it was found that the sulfur content in the steel needs to be regulated to at least 0.003% by mass or less.
　さらに本発明者らの鋭意研究によれば、転がり疲労寿命（Ｌ1寿命）の優れた鋼とするためには、上記したように鋼中の酸素含有量を６ｐｐｍ以下とし、かつ鋼中の硫黄含有量を０．００３質量％以下に規制するのに加えて、探触子周波数２５ＭＨｚを超え、１２５ＭＨｚ以下での超音波探傷により、３０００ｍｍ3以上の鋼材体積を探傷した場合において、介在物径が２０μｍ以上で、かつその介在物径が２０μｍ以上の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の個数を鋼材体積１０００ｍｍ3当たりに２．０個以下であるように規制すれば良いことが分かった。介在物径が２０μｍ程度の介在物は、それ単独では極めて短寿命でのはく離をもたらす大きさのものではない。しかし、たとえ２０μｍ程度の介在物であっても、そのような大きさを持つ非金属介在物どうしの最近接距離が４０μｍ未満である場合には、あたかも大型の介在物であるように振る舞い、極めて短寿命でのはく離をもたらす可能性がある。したがって、本発明者らは、そのような非金属介在物対の鋼中の存在頻度を１０００ｍｍ3当たりに２．０個以下にすれば、実用的に転がり疲労寿命（Ｌ1寿命）の優れた鋼を得ることが可能となることを見出した。 Furthermore, according to the earnest study by the present inventors, in order to obtain a steel having an excellent rolling fatigue life (L 1 life), the oxygen content in the steel is set to 6 ppm or less and the sulfur in the steel is used as described above. In addition to restricting the content to 0.003% by mass or less, in the case where a steel material volume of 3000 mm 3 or more is detected by ultrasonic flaw detection exceeding the probe frequency of 25 MHz and 125 MHz or less, the inclusion diameter is The number of non-metallic inclusion pairs having a closest distance between non-metallic inclusions of 20 μm or more and the inclusion diameter of 20 μm or more being less than 40 μm is 2.0 or less per 1000 mm 3 of steel material volume. I found out that I should regulate it. Inclusions having an inclusion diameter of about 20 μm are not large enough to cause separation with an extremely short life. However, even if the inclusion is about 20 μm, if the closest distance between non-metallic inclusions having such a size is less than 40 μm, it behaves as if it is a large inclusion, There is a possibility of causing peeling with a short life. Accordingly, the present inventors, if the occurrence frequency in the steel of such non-metallic inclusions pairs per 1000 mm 3 to 2.0 or less, an excellent practical rolling fatigue life (L 1 life) It has been found that it is possible to obtain steel.
　また、介在物径が１００μｍを超えるような非金属介在物は、それ単独であっても極めて短寿命でのはく離をもたらす原因となるので、探触子周波数２５ＭＨｚを超え、１２５ＭＨｚ以下での超音波探傷法によって、３０００ｍｍ3以上の鋼材体積を探傷した場合に検出される非金属介在物の最大径が１００μｍ以下である必要がある。また、超音波探傷法によって検出することが比較的困難な硫化物系介在物に対して、転がり疲労寿命に対して有害な、近接した介在物分散状態を回避するために、鋼材の鍛錬成形比（＝母材鋳塊の断面積／鋼材の断面積）は少なくとも２２．０以上確保する必要がある。 In addition, non-metallic inclusions whose inclusion diameter exceeds 100 μm may cause separation with an extremely short life even if they are used alone. Therefore, an ultrasonic wave having a probe frequency exceeding 25 MHz and not exceeding 125 MHz. The maximum diameter of non-metallic inclusions detected when a steel material volume of 3000 mm 3 or more is detected by the flaw detection method needs to be 100 μm or less. In addition, for sulfide inclusions that are relatively difficult to detect by ultrasonic flaw detection, the steel forging ratio is reduced to avoid the inclusion inclusion dispersion, which is harmful to rolling fatigue life. It is necessary to secure at least 22.0 or more (= the cross-sectional area of the base material ingot / the cross-sectional area of the steel material).
　上記した、引用文献１～３に記載の鋼では、発生頻度は稀であるものの実用上有害な極めて短寿命でのはく離を抑制した、転がり疲労寿命に優れる鋼を安定して提供する際に、転がり疲れが要求される部品における計算寿命に対して、極めて早期のアクシデンタルなはく離を引き起こす原因となる、介在物径が２０μｍ以上で、かつその２０μｍ以上の径の介在物どうしの最近接距離が４０μｍ未満であるような非金属介在物対は、極めて低い確率で鋼中に存在しているため、それらの有無を検出する精度が低くなる場合がある。また、２次元観察を主体とする従来技術によっては、被検面積が小さいために、鋼材の大体積を検査しようとすると多大な時間を要し、鋼材の良否を精度良く判断することができない場合がある。また、引用文献１に記載の鋼では、介在物の融解および凝集が起こるため、正確な介在物径や介在物どうしの間隔を評価することはできない可能性がある。 In the steels described in the above cited documents 1 to 3, when the occurrence frequency is rare, it is possible to stably provide a steel excellent in rolling fatigue life, in which peeling in an extremely short life that is practically harmful is suppressed. The inclusion diameter is 20 μm or more, and the closest distance between the inclusions having a diameter of 20 μm or more is 40 μm, which causes an extremely early accidental peeling for the calculated life in a part requiring rolling fatigue. Since non-metallic inclusion pairs that are less than the number are present in steel with a very low probability, the accuracy of detecting the presence or absence of them may be low. Also, depending on the prior art mainly based on two-dimensional observation, because the test area is small, it takes a lot of time to inspect a large volume of steel, and it is not possible to accurately judge the quality of the steel There is. Moreover, in the steel described in the cited document 1, since the inclusions melt and aggregate, the accurate inclusion diameter and the interval between the inclusions may not be evaluated.
　また、引用文献４に記載の方法では、最大介在物径が１００μｍ未満である非金属介在物については極値統計法を適用し、介在物径が１００μｍ以上である非金属介在物については探傷周波数を５～２５ＭＨｚとした超音波探傷法を適用するなどの併用による評価方法を提案している。しかしながら、極値統計法は２次元観察による評価方法であるため、上述と同様に被検面積が小さく、鋼中の存在頻度が低い介在物径が２０μｍ以上の非金属介在物について見た場合の鋼材の良否を十分に判断できない可能性がある。一方、探傷周波数を５～２５ＭＨｚとした超音波探傷法では、検出可能な介在物径は１００μｍ以上の程度のものであるため、介在物径が２０μｍ以上で、かつその介在物径が２０μｍ以上の非金属介在物どうしの間隔が４０μｍ未満であるような非金属介在物対の個数については、上記の探傷周波数の帯域の超音波ビームでは評価の精度が高くないことから、Ｌ1寿命に優れた鋼を安定して提供できる評価方法が求められている。 In the method described in the cited document 4, the extreme value statistical method is applied to nonmetallic inclusions whose maximum inclusion diameter is less than 100 μm, and the flaw detection frequency is used for nonmetallic inclusions whose inclusion diameter is 100 μm or more. We have proposed an evaluation method using a combination of methods such as applying an ultrasonic flaw detection method with a frequency of 5 to 25 MHz. However, since the extreme value statistical method is an evaluation method based on two-dimensional observation, as in the case described above, the non-metallic inclusions having a small test area and a low inclusion frequency in steel with a diameter of 20 μm or more are observed. There is a possibility that the quality of the steel material cannot be fully judged. On the other hand, in the ultrasonic flaw detection method with a flaw detection frequency of 5 to 25 MHz, since the detectable inclusion diameter is about 100 μm or more, the inclusion diameter is 20 μm or more, and the inclusion diameter is 20 μm or more. With respect to the number of non-metallic inclusion pairs in which the interval between non-metallic inclusions is less than 40 μm, the ultrasonic beam in the flaw detection frequency band described above is not highly accurate in evaluation, and thus has an excellent L 1 life. There is a need for an evaluation method that can stably provide steel.
　また、引用文献５に記載の方法では、硫黄含有量が０．００８質量％以下で、かつ、超音波探傷法により鋼材体積３００ｍｍ3当たりに検出される介在物径が２０μｍ以上である非金属介在物の個数を３００ｍｍ3当たりに１２個以下であるように規定した、転がり疲労寿命に優れた鋼（スラスト型転がり疲労試験にて、最大ヘルツ応力Ｐmax＝５．３ＧＰａでＬ10寿命＞１．０×１０7ｃｙｃｌｅが得られる鋼）およびその評価方法を提案している。ただし、硫黄含有量の規制が十分では無く、また、使用中の軸受が計算寿命より極めて早期にアクシデンタルに破損することに対する信頼性の指標となる介在物径が２０μｍ以上で、かつその２０μｍ以上の径の介在物どうしの最近接距離が４０μｍ未満であるような非金属介在物対の個数を評価していないため、Ｌ1寿命に優れた鋼を安定して提供できない場合がある。 Further, in the method described in the cited document 5, the non-metallic inclusions having a sulfur content of 0.008 mass% or less and an inclusion diameter detected per 300 mm 3 of steel material volume by an ultrasonic flaw detection method is 20 μm or more. Steel having an excellent rolling fatigue life specified to be 12 or less per 300 mm 3 (in a thrust type rolling fatigue test, the maximum hertz stress P max = 5.3 GPa and the L 10 life> 1. A steel capable of obtaining 0 × 10 7 cycle) and its evaluation method are proposed. However, the regulation of the sulfur content is not sufficient, and the inclusion diameter is 20 μm or more, and the inclusion diameter is 20 μm or more, which is an index of reliability against accidental damage to the bearing in use extremely early than the calculated life. Since the number of non-metallic inclusion pairs in which the closest distance between the inclusions having a diameter is less than 40 μm has not been evaluated, it may be impossible to stably provide steel having an excellent L 1 life.
　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、鋼材の鍛錬成形比を一定値以上に確保し、かつ鋼中の酸素含有量と硫黄含有量を規制するとともに超音波探傷法により鋼中の非金属介在物を大体積で検出し、かつ一定大きさ以上の介在物径を有する非金属介在物どうしの最近接距離が一定距離以下となるような非金属介在物対の個数を制限し、かつ超音波探傷法による鋼中非金属介在物の最大大きさを制限することにより、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 has been made in order to solve such a conventional problem, and the problem to be solved by the present invention is to secure a forging ratio of the steel material at a certain value or more, and the oxygen content in the steel. In addition, the non-metallic inclusions in steel are detected in a large volume by ultrasonic flaw detection, and the closest distance between non-metallic inclusions with inclusion diameters of a certain size or more is constant. It is used for machine parts with excellent rolling fatigue life by limiting the number of non-metallic inclusion pairs as follows and limiting the maximum size of non-metallic inclusions in steel by ultrasonic flaw detection. Is to provide steel.
　上記の課題を解決するための本発明による第一の態様によれば、表面硬さを５８ＨＲＣ以上とする機械部品に用いる鋼であって、母材鋳塊に対する鋼材の鍛錬成形比が２２．０以上であり、鋼中の酸素含有量が質量割合で６ｐｐｍ以下、硫黄含有量が０．００３質量％以下であり、探触子周波数２５ＭＨｚを超え、１２５ＭＨｚ以下である超音波探傷法により、鋼材の体積１０００ｍｍ3当たりに検出される介在物径が２０μｍ以上で、かつその２０μｍ以上の径の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の個数が２．０個以下であり、かつ、探触子周波数２５ＭＨｚを超え、１２５ＭＨｚ以下の超音波探傷法により鋼材総体積３０００ｍｍ3以上で検出される非金属介在物の最大径が１００μｍ以下である、転がり疲労寿命に優れた鋼が提供される。 According to the first aspect of the present invention for solving the above-mentioned problems, the steel is used for a machine part having a surface hardness of 58 HRC or higher, and the forging ratio of the steel to the base metal ingot is 22.0. By the ultrasonic flaw detection method in which the oxygen content in the steel is 6 ppm or less and the sulfur content is 0.003% by mass or less and the probe frequency exceeds 25 MHz and is 125 MHz or less, The number of inclusions detected in a volume of 1000 mm 3 is 20 μm or more, and the number of non-metallic inclusion pairs in which the closest distance between nonmetallic inclusions having a diameter of 20 μm or more is less than 40 μm is 2.0 or less. , and the and beyond the probe frequency 25 MHz, the maximum diameter of nonmetallic inclusions detected in steel total volume 3000 mm 3 or more by 125MHz following ultrasonic flaw detection method is 100μm or less, rolling is Steel excellent in fatigue life is provided.
　本発明による第二の態様によれば、表面硬さを５８ＨＲＣ以上とする機械部品に用いる鋼であって、母材鋳塊に対する鋼材の鍛錬成形比が２２．０以上であり、鋼中の酸素含有量が質量割合で６ｐｐｍ以下、硫黄含有量が０．００３質量％以下であり、探触子周波数２５ＭＨｚを超え、１２５ＭＨｚ以下の超音波探傷法により、鋼材の体積１０００ｍｍ3当たりに検出される介在物径が２０μｍ以上で、かつその２０μｍ以上の径の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の個数が２．０個以下であり、かつ、探触子周波数２５ＭＨｚを超え、１２５ＭＨｚ以下の超音波探傷法により鋼材総体積３０００ｍｍ3以上で検出される非金属介在物の最大径が１００μｍ以下であり、上記の介在物径が２０μｍ以上で、かつその２０μｍ以上の径の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の個数は、超音波探傷法により総体積３０００ｍｍ3以上で、かつ３０００００ｍｍ3以下である鋼材を探傷することにより得られる（評価された、測定された、または確認された（以下同じ））ものであり、かつ、前記の非金属介在物の最大径が１００μｍ以下であることを評価するための超音波探傷においては総体積３０００００ｍｍ3以下の鋼材を探傷することにより得られる（評価された、測定された、または確認された（以下同じ））ものである、転がり疲労寿命に優れた鋼が提供される。 According to the second aspect of the present invention, steel used for machine parts having a surface hardness of 58 HRC or more, wherein the forging ratio of the steel to the base material ingot is 22.0 or more, and oxygen in the steel The content is 6 ppm or less in mass proportion, the sulfur content is 0.003 mass% or less, and is detected per 1000 mm 3 of steel volume by ultrasonic flaw detection method with probe frequency exceeding 25 MHz and 125 MHz or less. The number of non-metallic inclusion pairs in which the object diameter is 20 μm or more and the closest distance between non-metallic inclusions having a diameter of 20 μm or more is less than 40 μm is 2.0 or less, and the probe frequency exceeded 25 MHz, the maximum diameter of nonmetallic inclusions detected in steel total volume 3000 mm 3 or more by 125MHz following ultrasonic flaw detection method is not less 100μm or less, with inclusion diameter of above 20μm or more, or The number of non-metallic inclusions pair closest distance is less than 40μm of non-metallic inclusions each other in the diameter of the 20μm or more, flaw detection steel by ultrasonic flaw detection in a total volume of 3000 mm 3 or more, and is 300000Mm 3 or less For evaluating that the maximum diameter of the non-metallic inclusions is 100 μm or less (evaluated, measured, or confirmed (hereinafter the same)). In sonic flaw detection, a steel having an excellent rolling fatigue life, which is obtained (evaluated, measured or confirmed (hereinafter the same)) is obtained by flaw detection of a steel material having a total volume of 300,000 mm 3 or less. The
　本発明による第三の態様において、上述した転がり疲労寿命に優れた鋼として、ＪＩＳ（Japanese Industrial Standards）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（Society of Automotive Engineers）規格またはＡＳＴＭ（American Society for Testing and Materials、またはASTM Internationalとも言う）規格Ａ２９５において規定される５２１００、ならびにＤＩＮ（Deutsches Institut fur Normung）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 third aspect of the present invention, as the above-described steel having excellent rolling fatigue life, high carbon chromium bearing steel (SUJ) defined in JIS (Japanese Industrial Standards) standard and SAE (Society of Automotive Engines) standard Or ASTM (American Society for Testing and Materials, or ASTM International) 52100 as defined in Standard A295, as well as 100Cr6 as defined in DIN (Deutsches Institut Furan Normung) standard, and mechanical structural carbon as defined in JIS standard Among steel materials (SC) and alloy steel materials for machine structures, any one steel selected from chromium steel (SCr), chromium molybdenum steel (SCM) and nickel chromium molybdenum steel (SNCM) can be mentioned.
　本発明による好ましい態様としては、上記介在物径が２０μｍ以上で、かつその２０μｍ以上の径の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の個数、および上記非金属介在物の最大径は、超音波探傷法により総体積が３０００ｍｍ3以上で、かつ３０００００ｍｍ3以下である鋼材を探傷することにより得られる。 According to a preferred embodiment of the present invention, the number of the nonmetallic inclusion pairs in which the inclusion diameter is 20 μm or more and the closest distance between the nonmetallic inclusions having a diameter of 20 μm or more is less than 40 μm, and the nonmetal maximum diameter of the inclusions, the total volume by the ultrasonic flaw detection method in 3000 mm 3 or more, and is obtained by testing the steel is 300000Mm 3 or less.
　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、鋼材の鍛錬成形比を規制し、かつ鋼中の酸素含有量と硫黄含有量を規制するとともに超音波探傷法により鋼中の非金属介在物を大体積で検出して、一定大きさ以上の介在物径を有する非金属介在物どうしの最近接距離が一定距離以下であるような非金属介在物対の個数を制限し、かつ超音波探傷法による鋼中非金属介在物の最大大きさを制限することにより、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。 The steel excellent in rolling fatigue life of the present invention was made to solve such a conventional problem, and regulates the forging ratio of the steel material and regulates the oxygen content and sulfur content in the steel. In addition, non-metallic inclusions in steel are detected in a large volume by ultrasonic flaw detection, and the closest distance between non-metallic inclusions having inclusion diameters greater than a certain size is less than a certain distance. To provide steel used for machine parts with excellent rolling fatigue life by limiting the number of metal inclusion pairs and limiting the maximum size of nonmetallic inclusions in steel by ultrasonic flaw detection. Is possible.
　本発明の実施の形態に係る転がり疲労寿命に優れた鋼について、以下に表を参照して詳細に説明をする。 Referring to the table below, the steel excellent in rolling fatigue life according to the embodiment of the present invention will be described in detail.
　本明細書では、「表面硬さを５８ＨＲＣ以上とする」とは「表面硬さをロックウェル硬さ試験におけるＣスケールで５８以上の値とする」ことを意味するものとする。ここで、ロックウェル硬さ試験は、ＪＩＳ（Japanese Industrial Standards）規格で定めるＪＩＳ Ｇ ０２０２に準拠したものである。具体的には、測定は、Ｃスケールで、圧子として先端の曲率半径０．２ｍｍで、かつ、円錐角１２０°のダイヤモンドを用い、基準荷重を９８．０７Ｎ（１０ｋｇｆ）とし、試験荷重を１４７１．０Ｎ（１５０ｋｇｆ）として行われる。そして、測定時の圧子のサンプルへの侵入深さｈ（μｍ）の値を用いて、ＨＲ＝１００－ｈ／２の式からロックウェル硬さが計算される。 In this specification, “the surface hardness is 58 HRC or more” means “the surface hardness is a value of 58 or more on the C scale in the Rockwell hardness test”. Here, the Rockwell hardness test is based on JIS G0202 defined by JIS (Japanese Industrial Standards) standard. Specifically, the measurement was performed on a C scale, using a diamond having a radius of curvature of 0.2 mm at the tip as an indenter and a cone angle of 120 °, a reference load of 98.07 N (10 kgf), and a test load of 1471. It is performed as 0N (150 kgf). Then, using the value of the penetration depth h (μm) of the indenter into the sample at the time of measurement, the Rockwell hardness is calculated from the equation of HR = 100−h / 2.
　本発明の実施の形態に係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、母材である鋳塊に対する鋼材の鍛錬成形比が２２．０以上であり、鋼中の酸素含有量が質量割合で６ｐｐｍ以下で、硫黄含有量が０．００３質量％以下である。さらに、探触子周波数２５ＭＨｚを超え、１２５ＭＨｚ以下の超音波探傷法により、鋼材の体積１０００ｍｍ3当たりに検出される介在物径が２０μｍ以上で、かつその２０μｍ以上の径の非金属介在物どうしの最近接距離が４０μｍ未満である、非金属介在物対の個数が２．０個以下であり、かつ、探触子周波数２５ＭＨｚを超え、１２５ＭＨｚ以下の超音波探傷法により、鋼材総体積３０００ｍｍ3以上で検出される非金属介在物の最大径が１００μｍ以下である鋼である。 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 has a forging ratio of 22.0 to the ingot as a base material. Thus, the oxygen content in the steel is 6 ppm or less by mass and the sulfur content is 0.003 mass% or less. Furthermore, by the ultrasonic flaw detection method exceeding the probe frequency 25 MHz and 125 MHz or less, the inclusion diameter detected per 1000 mm 3 of the steel material is 20 μm or more, and the nonmetallic inclusions having a diameter of 20 μm or more are used. The closest distance is less than 40 μm, the number of non-metallic inclusion pairs is 2.0 or less, and the total frequency of steel is 3000 mm 3 or more by ultrasonic flaw detection with a probe frequency exceeding 25 MHz and 125 MHz or less. The maximum diameter of non-metallic inclusions detected in (1) is 100 μm or less.
　転がり疲労を受ける部品においては、鋼からある大きさ以上の非金属介在物を少なくすることが特性向上に対して重要である。軸受の転走面下に有害な大きさの非金属介在物が存在すれば、はく離を発生させることから、軸受の転走面下の危険部位に出現する非金属介在物の大きさを小さくすることが軸受の寿命向上に対して極めて重要である。計算寿命に達することなく、極めて早期にはく離を引き起こす介在物径としては、介在物径が２０μｍ級の非金属介在物はそれ単独では有害性は低い。ただし、２０μｍ級の非金属介在物であっても、それと同等以上の大きさを有する別の非金属介在物との３次元的な最近接距離が４０μｍ未満である場合には、早期はく離を引き起こす有害介在物として振舞うと考えられる。また、１００μｍを超えるような非金属介在物はそれ単独でも早期はく離の原因となる。したがって、介在物径が２０μｍ以上で、かつその２０μｍ以上の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の個数と、介在物径が１００μｍを超える非金属介在物の存在頻度を極めて少なく、かつそれが評価保証されている鋼を用いることにより、部品の転送面下の危険部位（すなわち、転がり疲労を強く受ける部分）に介在物が存在する確率を極めて低くすることが可能となり、早期はく離を抑制することができる。 In parts subjected to rolling fatigue, it is important to improve properties to reduce non-metallic inclusions of a certain size or more from steel. If non-metallic inclusions with a detrimental size exist under the rolling surface of the bearing, separation will occur, so the size of non-metallic inclusions that appear in the hazardous area under the rolling surface of the bearing will be reduced. This is extremely important for improving the life of the bearing. As inclusion diameters that cause separation very early without reaching the calculated life, non-metallic inclusions having an inclusion diameter of 20 μm are not harmful by themselves. However, even if it is a non-metallic inclusion of a 20 μm class, if the three-dimensional closest distance to another non-metallic inclusion having a size equal to or larger than that is less than 40 μm, it causes early separation. It is considered to behave as a harmful inclusion. In addition, non-metallic inclusions exceeding 100 μm alone cause early peeling. Therefore, the number of nonmetallic inclusion pairs whose inclusion diameter is 20 μm or more and the closest distance between the nonmetallic inclusions of 20 μm or more is less than 40 μm, and the nonmetallic inclusions whose inclusion diameter exceeds 100 μm. By using steel that has a very low existence frequency and is guaranteed to be evaluated, the probability that inclusions will be present in dangerous parts (that is, parts that are subject to rolling fatigue) under the transfer surface of parts is extremely low. This makes it possible to suppress early peeling.
　そこで、本発明による第一の態様に係る転がり疲労寿命に優れた鋼では、その特性を保証する評価方法として、超音波探傷法が適用される。この超音波探傷法では、探触子周波数２５ＭＨｚを超え、１２５ＭＨｚ以下の超音波探傷法により、鋼材の体積１０００ｍｍ3当たりに検出される非金属介在物の介在物径が２０μｍ以上で、かつその２０μｍ以上の非金属介在物どうしの最近接距離が４０μｍ未満である、非金属介在物対の個数が２．０個以下であり、かつ探触子周波数２５ＭＨｚを超え、１２５ＭＨｚ以下の超音波探傷法により、鋼材総体積３０００ｍｍ3以上で検出される非金属介在物の最大径が１００μｍ以下に規制されている。 Therefore, in the steel excellent in rolling fatigue life according to the first aspect of the present invention, the ultrasonic flaw detection method is applied as an evaluation method for guaranteeing the characteristics. In this ultrasonic flaw detection method, the inclusion diameter of the nonmetallic inclusion detected per 1000 mm 3 of the volume of the steel material is 20 μm or more by the ultrasonic flaw detection method exceeding the probe frequency 25 MHz and 125 MHz or less, and 20 μm thereof. The closest distance between the non-metallic inclusions is less than 40 μm, the number of non-metallic inclusion pairs is 2.0 or less, and the probe frequency exceeds 25 MHz and the ultrasonic flaw detection method is 125 MHz or less. The maximum diameter of non-metallic inclusions detected with a steel material total volume of 3000 mm 3 or more is regulated to 100 μm or less.
　さらに、本発明による第二の態様に係る転がり疲労寿命に優れた鋼では、その特性を保証する方法として適用した超音波探傷法における、非金属介在物の介在物径が２０μｍ以上で、かつその２０μｍ以上の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の個数、ならびに本実施の形態の非金属介在物における、最大径が１００μｍ以下である点は、超音波探傷法により総体積３０００ｍｍ3以上で、かつ３０００００ｍｍ3以下を探傷することにより評価されたものである。 Furthermore, in the steel excellent in rolling fatigue life according to the second aspect of the present invention, the inclusion diameter of nonmetallic inclusions in an ultrasonic flaw detection method applied as a method for guaranteeing the characteristics is 20 μm or more, and The number of non-metallic inclusion pairs in which the closest distance between non-metallic inclusions of 20 μm or more is less than 40 μm, and the point that the maximum diameter of the non-metallic inclusion of the present embodiment is 100 μm or less are ultrasonic flaw detection in a total volume of 3000 mm 3 or more by law, and those that have been evaluated by testing the 300000Mm 3 below.
　又さらに、本発明による第三の態様に係る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がり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）、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）から選択したものである鋼が挙げられる。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本発明の適用が可能である。 Still further, the steel having excellent rolling fatigue life according to the third aspect of the present invention 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, and specified in JIS standard Carbon steel for machine structure (SC), and steel selected from chrome steel (SCr), chrome molybdenum steel (SCM) and nickel chrome molybdenum steel (SNCM) among alloy steels for machine structure . For example, the present invention can be applied to foreign standard steels corresponding to JIS standards such as SAE standards 4320, 5120, 4140, 1053, and 1055.
　なお、超音波探傷法においては、既に様々な種類の超音波探傷装置や探触子が実用化されており、本発明ではこれらのものを利用することができる。好ましい探触子としては、焦点型高周波探触子などが挙げられる。フラット型探触子の検出能は１／２波長といわれているが、焦点型探触子では１／４波長であり、したがって、精度の良い評価に対しては焦点型探触子が好適である。なお、本実施の形態における探触子周波数は２５ＭＨｚを超え、１２５ＭＨｚ以下のものが良く、特に好ましくは３０～１００ＭＨｚ程度である。 In the ultrasonic flaw detection method, various types of ultrasonic flaw detectors and probes have already been put into practical use, and these can be used in the present invention. As a preferred probe, a focus type high frequency probe and the like can be cited. The detection capability of the flat probe is said to be ½ wavelength, but the focus probe is ¼ wavelength. Therefore, the focus probe is suitable for accurate evaluation. is there. Note that the probe frequency in this embodiment is preferably greater than 25 MHz and not greater than 125 MHz, and particularly preferably about 30 to 100 MHz.
　本実施の形態の転がり疲労寿命に優れた鋼においては、非金属介在物の介在物径が２０μｍ以上で、かつその２０μｍ以上の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の個数、ならびに非金属介在物の最大径が１００μｍ以下であることは、既に上記したように、超音波探傷法により総体積３０００ｍｍ3以上で、３０００００ｍｍ3以下を探傷し、非金属介在物を検出することが好ましい。 In the steel having an excellent rolling fatigue life according to the present embodiment, the nonmetallic inclusions whose nonmetallic inclusions have an inclusion diameter of 20 μm or more and the closest distance between the nonmetallic inclusions of 20 μm or more is less than 40 μm. the number of objects pair, and the maximum diameter of the nonmetallic inclusions is 100μm or less, as already described above, the ultrasonic flaw detection method in a total volume of 3000 mm 3 or more, and testing the 300000Mm 3 below, non-metallic inclusions Is preferably detected.
　超音波探傷において、介在物径が２０μｍ以上で、かつその２０μｍ以上の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の個数、ならびに非金属介在物最大径が１００μｍ以下であることを確認するための探傷総体積を３０００ｍｍ3以上で、かつ３０００００ｍｍ3以下とした理由は、Ｌ1寿命を性能指標とする極めて短寿命でのはく離を抑制可能な転がり疲労寿命に優れる鋼を提供する上で、評価精度の点から満足できる評価結果を得るために必要だからである。なおかつ、本実施の形態の超音波探傷法における評価体積は、従来の顕微鏡観察を主体とする評価方法では、処理時間が膨大となるので、現実的には評価が非常に困難である。さらに汎用的な手段として、超音波探傷法以外の方法では、大体積の鋼材中に存在する介在物どうしの最近接距離を３次元的に評価することは非常に困難である。超音波探傷を行なうに当たっては、試験片の表面から探触子の周波数に応じた深さまでの不感帯領域を評価体積から除外し、必要に応じて熱処理等による組織異常や超音波探傷における測定ノイズの影響を受けやすい試験片の端部を焦点位置での超音波ビームの探傷範囲から除外した上で、探触子の周波数、性能に応じた水中焦点距離範囲に基づいて、超音波探傷における評価体積を３０００ｍｍ3以上で、かつ３０００００ｍｍ3以下を確保する必要がある。また、４０μｍをしきい値とする介在物どうしの間隔を識別できるように適切な探傷ピッチを設定する必要がある。 In ultrasonic flaw detection, the number of nonmetallic inclusion pairs whose inclusion diameter is 20 μm or more and the closest distance between the nonmetallic inclusions of 20 μm or more is less than 40 μm, and the maximum nonmetallic inclusion diameter is 100 μm or less. flaw detection total volume to ensure that it is in 3000 mm 3 or more, and the reason for the 300000Mm 3 or less, the steel is excellent in rolling fatigue life can be suppressed peeling at very short life for the L 1 life and performance index This is because it is necessary to obtain a satisfactory evaluation result in terms of evaluation accuracy. In addition, the evaluation volume in the ultrasonic flaw detection method according to the present embodiment is very difficult to evaluate in practice because the processing time is enormous in the conventional evaluation method mainly based on microscopic observation. Further, as a general-purpose means, it is very difficult to three-dimensionally evaluate the closest distance between inclusions existing in a large-volume steel material by a method other than the ultrasonic flaw detection method. In performing ultrasonic flaw detection, the dead zone region from the surface of the specimen to the depth corresponding to the probe frequency is excluded from the evaluation volume, and if necessary, tissue abnormalities due to heat treatment etc. and measurement noise in ultrasonic flaw detection are detected. Evaluation volume in ultrasonic flaw detection based on the underwater focal length range according to the frequency and performance of the probe after excluding the end of the sensitive specimen from the flaw detection range of the ultrasonic beam at the focal position the need to ensure at 3000 mm 3 or more, and 300000Mm 3 below. In addition, it is necessary to set an appropriate flaw detection pitch so that the interval between inclusions having a threshold value of 40 μm can be identified.
　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、鋼材の鍛錬成形比を規制し、かつ鋼中の酸素含有量と硫黄含有量を規制すると共に、超音波探傷法により鋼中の非金属介在物を大体積で検出し、一定大きさ以上の介在物径を有する非金属介在物どうしの最近接距離が一定距離以下であるような非金属介在物対の個数を制限し、かつ超音波探傷法による鋼中非金属介在物の最大大きさを制限することにより、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 forging and forming ratio of the steel material is regulated, and the oxygen content and the sulfur content in the steel are regulated, and the ultrasonic wave Detecting non-metallic inclusions in steel in a large volume by flaw detection method, and the non-metallic inclusion pairs whose non-metallic inclusions having inclusion diameters above a certain size are less than a certain distance By limiting the number and limiting the maximum size of non-metallic inclusions in steel by ultrasonic flaw detection, it is possible to provide steel used for machine parts having excellent rolling fatigue life.
　次に、実施例として供試材１～２５および比較例として供試材２６～３６を表１および表２に挙げて、本発明の転がり疲労寿命に優れた鋼について、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 test materials 1 to 25 as examples and the test materials 26 to 36 as comparative examples are listed in Table 1 and Table 2, and the steel excellent in rolling fatigue life of the present invention will be described more specifically. . However, the present invention is not limited to these examples.
　表１に実施例と比較例の各供試材の成分組成を示す。なお、以下に示す各供試材の組成は、同じ規格名で示してあっても、表１にそれぞれ示すように、異なる組成を有するものである。表１の供試材１～７および供試材２６～３３には高炭素クロム軸受鋼であるＪＩＳのＳＵＪ２鋼に分類される組成の鋼を、供試材８および３４にはＪＩＳのＳＣｒ４２０鋼に分類される組成の鋼を、供試材９にはＪＩＳのＳＮＣＭ４２０鋼に分類される組成の鋼を、供試材１０にはＪＩＳのＳ５３Ｃ鋼に分類される組成の鋼を、供試材１１、供試材３５および供試材３６にはＪＩＳのＳＣＭ４２０鋼に分類される組成の鋼を、供試材１２および供試材１３にはＳＡＥの５２１００に分類される組成の鋼を、供試材１４および供試材１５にはＡＳＴＭの５２１００に分類される組成の鋼を、供試材１６および供試材１７にはＤＩＮの１００Ｃｒ６に分類される組成の鋼を、供試材１８はＪＩＳのＳＵＪ３鋼に分類される組成の鋼を、供試材１９はＪＩＳのＳＵＪ５鋼に分類される組成の鋼を、供試材２０はＳＡＥの４３２０鋼に分類される組成の鋼を、供試材２１はＳＡＥの５１２０鋼に分類される組成の鋼を、供試材２２はＪＩＳのＳＣＭ４３５鋼に分類される組成の鋼を、供試材２３はＳＡＥの４１４０鋼に分類される組成の鋼を、供試材２４はＪＩＳのＳ５５Ｃ鋼に分類される組成の鋼を、供試材２５はＳＡＥの１０５３鋼に分類される組成の鋼を用いた。供試材１～５、供試材８～９、供試材１２、供試材１４、供試材１６、供試材１８、供試材２０～３０、および供試材３６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ものである。 Table 1 shows the component composition of each sample material of the example and the comparative example. In addition, even if it shows with the same specification name, the composition of each test material shown below has a different composition as shown in Table 1, respectively. The specimens 1 to 7 and specimens 26 to 33 in Table 1 are steels having a composition classified as JIS SUJ2 steel, which is a high carbon chromium bearing steel, and the specimens 8 and 34 are JIS SCr420 steel. Steel with a composition classified as JIS SNCM420 steel for specimen 9 and steel with a composition classified as JIS S53C steel for specimen 10 11. Specimen 35 and Specimen 36 are steels having a composition classified as JIS SCM420 steel, and Specimen 12 and Specimen 13 are steels having a composition classified as SAE 52100. The specimen 14 and the specimen 15 are steels having a composition classified as ASTM 52100, the specimen 16 and the specimen 17 are steels having a composition classified as DIN 100Cr6, and the specimen 18 is Steel with a composition classified as JIS SUJ3 steel Steel with a composition classified as JIS SUJ5 steel, specimen 20 with steel with composition classified as SAE 4320 steel, and specimen 21 with steel with composition classified as SAE 5120 steel Sample 22 has a composition classified as JIS SCM435 steel, sample 23 has a composition classified as SAE 4140 steel, and sample 24 has a composition classified as JIS S55C steel. As the test material 25, steel having a composition classified as SAE 1053 steel was used. Specimen 1-5, Specimen 8-9, Specimen 12, Specimen 14, Specimen 16, Specimen 18, Specimen 20-30, and Specimen 36 are arc melted. The ingot is smelted in a furnace, then smelted in a ladle, and further degassed with a vacuum degassing apparatus to produce an ingot by continuous casting.
　供試材６、供試材７、供試材１０、供試材１１、供試材１３、供試材１５、供試材１７、供試材１９、および供試材３１～３５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インゴットにより鋳塊を製造したものである。 Specimen 6, Specimen 7, Specimen 10, Specimen 11, Specimen 13, Specimen 15, Specimen 17, Specimen 19, and Specimens 31-35 are arcs. It is made by melting in a melting furnace, then refining a ladle, and further degassing with a vacuum degassing apparatus to produce an ingot with an ingot.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　上記で得られた鋳塊に、熱間加工を施して鋼材の鍛錬成形比２２．０以上を確保した直径６５ｍｍの鋼材とした。 The ingot obtained above was hot-worked to obtain a steel material with a diameter of 65 mm in which a steel forging ratio of 22.0 or more was ensured.
（スラスト型転がり疲労試験）
　供試材１～７と供試材１２～１９と供試材２６～３３の鋼材に、８００℃にて球状化焼鈍を施し、鋼材の長手方向に対し垂直に、外径が６０ｍｍ、内径が２０ｍｍ、厚さが５．８ｍｍである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以上の硬さを得た。その後、得られた試験片を表面研磨して、スラスト型転がり疲労試験を行った。供試材８、供試材９、供試材１１、供試材２０、供試材２１、および供試材３４～３６の鋼材は、９２５℃で焼ならしを施した後、また、供試材２２および２３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垂直に外径が６０ｍｍ、内径が２０ｍｍ、厚さが８．３ｍｍである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た。次いで、焼き入れした試験片を、１８０℃で９０分の焼戻し処理を行い、所望の５８ＨＲＣ以上の硬さを得た。その後、得られた試験片を表面研磨して、スラスト型転がり疲労試験を行った。供試材１０、供試材２４、および供試材２５の鋼材は８７０℃で焼ならしを施した後、鋼材長手方向に対し垂直に外径が６０ｍｍ、内径が２０ｍｍ、厚さが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以上の硬さを得た。その後、得られた試験片を表面研磨して、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、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 Specimens 1 to 7, Specimens 12 to 19, and Specimens 26 to 33 were subjected to spheroidizing annealing at 800 ° C., and the outer diameter was 60 mm and the inner diameter was perpendicular to the longitudinal direction of the steel materials. A test piece made of a disk having a thickness of 20 mm and 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 tempered at 170 ° C. for 90 minutes to obtain a desired hardness of 58 HRC or higher. Then, the obtained test piece was surface-polished and a thrust type rolling fatigue test was performed. The steel materials of Specimen 8, Specimen 9, Specimen 11, Specimen 20, Specimen 21, and Specimens 34 to 36 were subjected to normalization at 925 ° C. The steel materials of the test materials 22 and 23 were subjected to normalization at 870 ° C., and then a test piece made of a disk having an outer diameter of 60 mm, an inner diameter of 20 mm, and a thickness of 8.3 mm perpendicular to the longitudinal direction of the steel material. Was made. The test piece was carburized at 930 ° C. and then quenched by oil cooling. Next, the quenched specimen was tempered at 180 ° C. for 90 minutes to obtain a desired hardness of 58 HRC or higher. Then, the obtained test piece was surface-polished and a thrust type rolling fatigue test was performed. The steel materials of the test material 10, the test material 24, and the test material 25 were normalized at 870 ° C., and then the outer diameter was 60 mm, the inner diameter was 20 mm, and the thickness was 8. A test piece consisting of a 3 mm disk was prepared. This test piece was induction-quenched and then tempered at 180 ° C. for 90 minutes to obtain a desired hardness of 58 HRC or higher. Then, the obtained test piece was surface-polished and a thrust type rolling fatigue test was performed. The thrust type rolling fatigue test was performed at a maximum hertz stress P max of 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.
（超音波試験）
　非金属介在物の介在物径が２０μｍ以上で、かつその２０μｍ以上の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の個数、ならびに非金属介在物の最大径が１００μｍ以下であることを評価するに当たり、供試材１～７と供試材１２～１９と供試材２６～３３の鋼材は、８００℃で球状化焼鈍を施し、Ｌ断面試験片を切り出し、焼入焼戻し処理を行った。また、供試材８、供試材９、供試材１１、供試材２０、供試材２１、および供試材３４～３６の鋼材は９２５℃で焼ならしを施し、Ｌ断面試験片を切り出し、焼入焼戻し処理を行った。また、供試材１０および供試材２２～２５の鋼材は、８７０℃で焼ならしを施し、Ｌ断面試験片を切り出し、焼入れ焼戻し処理を行った。その後供試材１～３６のいずれに対しても、超音波の伝達損失を軽減する目的で、平面研磨を行った。平面研磨により、いずれの試験片も厚さ１０ｍｍに仕上げて、超音波探傷試験を行った。超音波探傷には、焦点型高周波探触子（５０ＭＨｚ）を備えた超音波探傷装置を用いた。また、超音波探傷の体積は４０００ｍｍ3とした。得られた介在物による反射波のデータから、鋼材の体積１０００ｍｍ3当たりの非金属介在物の２０μｍ以上で、かつその２０μｍ以上の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の検出個数、ならびに最大径が１００μｍを超える非金属介在物の検出有無を求めた。 (Ultrasonic test)
The number of nonmetallic inclusion pairs whose nonmetallic inclusions have a diameter of 20 μm or more and the closest distance between the nonmetallic inclusions of 20 μm or more is less than 40 μm, and the maximum diameter of the nonmetallic inclusions is 100 μm. In evaluating the following, the steel materials of Specimens 1 to 7, Specimens 12 to 19, and Specimens 26 to 33 were subjected to spheroidizing annealing at 800 ° C., and L-section test pieces were cut out and sintered. A tempering treatment was performed. In addition, the steel materials of Specimen 8, Specimen 9, Specimen 11, Specimen 20, Specimen 21, and Specimens 34 to 36 were normalized at 925 ° C. Was cut out and quenched and tempered. Further, the steel materials of the test material 10 and the test materials 22 to 25 were subjected to normalization at 870 ° C., L-section test pieces were cut out, and subjected to quenching and tempering treatment. Thereafter, surface polishing was performed on all of the test materials 1 to 36 for the purpose of reducing transmission loss of ultrasonic waves. Each test piece was finished to a thickness of 10 mm by surface polishing, and an ultrasonic flaw detection test was performed. For ultrasonic flaw detection, an ultrasonic flaw detector equipped with a focus type high-frequency probe (50 MHz) was used. The volume of ultrasonic flaw detection was set to 4000 mm 3 . From the data of the reflected wave by the obtained inclusions, the nonmetallic inclusions whose non-metallic inclusions per volume of 1000 mm 3 of the steel material are 20 μm or more and the closest distance between the nonmetallic inclusions of 20 μm or more is less than 40 μm. The number of detected object pairs and the presence / absence of non-metallic inclusions having a maximum diameter exceeding 100 μm were determined.
　これらの供試材の各試験片について、表面硬さ、５０ＭＨｚの焦点型高周波探触子で評価した超音波探傷による鋼材の体積１０００ｍｍ3当たりの非金属介在物対の検出個数、１００μｍを超える介在物の検出有無、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 specimens, the surface hardness, the number of detected non-metallic inclusion pairs per 1000 mm 3 of steel volume by ultrasonic flaw evaluation evaluated with a 50 MHz focal high-frequency probe, the interposition exceeding 100 μm Table 2 shows the presence / absence of detection of the object and the L 1 life by the thrust type rolling fatigue test.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　表２において、比較例の供試材２６～３６は鋼材体積１０００ｍｍ3当たりに検出される２０μｍ以上で、かつその２０μｍ以上の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の個数が２．０個を超え、かつ最大径が１００μｍを超える非金属介在物の検出が見られるもので、本発明の範囲外のものである。しかもこれらの比較例の供試材２６～３６のＬ1寿命は、比較例の供試材３３のＬ1寿命を１としたときの３倍以下である。これら比較例の供試材２６～３６に対し、本発明における実施例の供試材１～２５は超音波探傷法により鋼材体積１０００ｍｍ3当たりに検出される介在物径が２０μｍ以上、かつその２０μｍ以上の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の個数が２．０個以下であり、かつ最大径が１００μｍを超える非金属介在物の検出が無く、本発明の第一の態様に係る発明、第二の態様に係る発明、および第三の態様に係る発明を満足するものであり、いずれも比較例の供試材３３のＬ1寿命の４倍以上であり、Ｌ1寿命に優れている。 In Table 2, the test materials 26 to 36 of the comparative example are 20 μm or more detected per 1000 mm 3 of the steel material volume, and the non-metallic inclusion whose non-metallic inclusions of 20 μm or more are less than 40 μm. The detection of non-metallic inclusions with the number of pairs exceeding 2.0 and the maximum diameter exceeding 100 μm can be seen, which is outside the scope of the present invention. In addition, the L 1 life of the test materials 26 to 36 of these comparative examples is three times or less when the L 1 life of the test material 33 of the comparative example is 1. Compared to the test materials 26 to 36 of these comparative examples, the test materials 1 to 25 of the examples in the present invention have an inclusion diameter of 20 μm or more and 20 μm of the inclusion diameter detected per 1000 mm 3 of steel material volume by the ultrasonic flaw detection method. The number of non-metallic inclusion pairs in which the closest distance between the non-metallic inclusions is less than 40 μm is 2.0 or less, and there is no detection of non-metallic inclusions having a maximum diameter exceeding 100 μm. The invention according to the first aspect of the invention, the invention according to the second aspect, and the invention according to the third aspect are all satisfied, and each is at least four times the L 1 life of the test material 33 of the comparative example. Yes, L 1 life is excellent.

Claims (3)

  1. 　表面硬さを５８ＨＲＣ以上とする機械部品に用いる鋼であって、母材である鋳塊に対する鋼材の鍛錬成形比が２２．０以上であり、鋼中の酸素含有量が質量割合で６ｐｐｍ以下、硫黄含有量が０．００３質量％以下であり、探触子周波数２５ＭＨｚを超え、１２５ＭＨｚ以下の超音波探傷法により鋼材の体積１０００ｍｍ3当たりに検出される介在物径が２０μｍ以上で、かつその２０μｍ以上の非金属介在物どうしの最近接距離が４０μｍ未満である、非金属介在物対の個数が２．０個以下であり、かつ、探触子周波数２５ＭＨｚを超え、１２５ＭＨｚ以下の超音波探傷法により鋼材総体積３０００ｍｍ3以上で検出される非金属介在物の最大径が１００μｍ以下であることを特徴とする転がり疲労寿命に優れた鋼。 Steel used for machine parts having a surface hardness of 58 HRC or more, wherein the forging ratio of the steel material to the ingot as a base material is 22.0 or more, and the oxygen content in the steel is 6 ppm or less by mass ratio, The sulfur content is 0.003 mass% or less, the probe frequency exceeds 25 MHz, and the inclusion diameter detected per 1000 mm 3 of the volume of the steel material by an ultrasonic flaw detection method of 125 MHz or less is 20 μm or more and 20 μm The ultrasonic flaw detection method in which the closest distance between the nonmetallic inclusions is less than 40 μm, the number of nonmetallic inclusion pairs is 2.0 or less, the probe frequency exceeds 25 MHz, and the frequency is 125 MHz or less. A steel having excellent rolling fatigue life, wherein the maximum diameter of non-metallic inclusions detected at a total volume of 3000 mm 3 or more is 100 μm or less.
  2. 　介在物径が２０μｍ以上で、かつその２０μｍ以上の非金属介在物どうしの最近接距離が４０μｍ未満である非金属介在物対の個数が２．０個以下、ならびに非金属介在物の最大径が１００μｍ以下は、超音波探傷法により総体積３０００ｍｍ3以上かつ３０００００ｍｍ3以下を探傷することにより得られるものであることを特徴とする請求項１に記載の転がり疲労寿命に優れた鋼。 The number of non-metallic inclusion pairs whose inclusion diameter is 20 μm or more and the closest distance between the non-metallic inclusions of 20 μm or more is less than 40 μm is 2.0 or less, and the maximum diameter of non-metallic inclusions is 100μm or less, excellent steel rolling fatigue life of claim 1, characterized in that is obtained by testing the total volume 3000 mm 3 or more and 300000Mm 3 below by ultrasonic flaw detection method.
  3. 　転がり疲労寿命に優れた鋼は、ＪＩＳ規格において規定される高炭素クロム軸受鋼鋼材、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、ならびにＪＩＳ規格において規定される機械構造用合金鋼鋼材のうちのクロム鋼およびクロムモリブデン鋼およびニッケルクロムモリブデン鋼から選択したいずれか１種の鋼であることを特徴とする請求項１又は２に記載の転がり疲労寿命に優れた鋼。 Steels with excellent rolling fatigue life are specified in high carbon chromium bearing steels specified in JIS standards, 52100 specified in SAE standards or ASTM standards A295, and 100Cr6 specified in DIN standards, and in JIS standards. Carbon steel material for machine structure and alloy steel material for machine structure specified in JIS standard, any one steel selected from chrome steel, chrome molybdenum steel and nickel chrome molybdenum steel A steel excellent in rolling fatigue life according to claim 1 or 2.
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