WO2023080029A1 - Steel material for sliding components and production method for steel material for sliding components - Google Patents

Steel material for sliding components and production method for steel material for sliding components Download PDF

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WO2023080029A1
WO2023080029A1 PCT/JP2022/039894 JP2022039894W WO2023080029A1 WO 2023080029 A1 WO2023080029 A1 WO 2023080029A1 JP 2022039894 W JP2022039894 W JP 2022039894W WO 2023080029 A1 WO2023080029 A1 WO 2023080029A1
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steel material
sliding parts
iron carbide
less
volume fraction
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PCT/JP2022/039894
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French (fr)
Japanese (ja)
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なつみ 菊地
基成 西原
達彦 安部
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日本製鉄株式会社
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Priority to JP2023557972A priority Critical patent/JPWO2023080029A1/ja
Priority to CN202280073772.0A priority patent/CN118202078A/en
Publication of WO2023080029A1 publication Critical patent/WO2023080029A1/en

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/30—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for crankshafts; for camshafts
    • 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
    • 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

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  • the present invention relates to a steel material for sliding parts and a method for manufacturing the steel material for sliding parts.
  • Steel materials are widely used in industrial products such as automotive parts, railway vehicle parts, building components, and pipes.
  • carbon steel materials for machine structural use and alloy steel materials for machine structural use are often used as materials for sliding parts such as gears and shafts, typified by power transmission system parts, because of their high mechanical strength.
  • One of the issues to be solved for steel materials for sliding parts is to improve wear resistance from the viewpoint of extending the life of parts and improving reliability. It is considered effective to increase the hardness of steel materials to improve wear resistance. However, increasing the hardness impairs the machinability of the steel material, which entails risks when mass-producing parts. Therefore, as a method for improving the slidability of sliding parts, it is effective to selectively control the structure of only the surface layer and harden only the relevant portion.
  • Japanese Patent Application Laid-Open No. 1-230746 discloses a sliding component comprising a fixed member made of cast iron and a sliding member made of a material having higher hardness than cast iron, wherein the surface layer structure of the fixed member is martensite or martensite. It is disclosed that the hardened layer consists of a mixed phase structure of , pearlite, ferrite and graphite, and the structure consists of oxides.
  • tempered martensite and/or tempered bainite contain retained austenite at an area ratio of 1 to 10%, and carbide precipitates at an area ratio of 5% or more. It describes a gear having a steel material structure with a high nitrogen content and a nitrogen concentration of 2.0 to 6.0% at a depth of 20 ⁇ m from the surface.
  • Japanese Patent Application Laid-Open No. 2010-100881 describes a carburized or carbonitrided sliding part, in which a surface layer portion up to a depth of 10 ⁇ m from the surface of the sliding surface has Vickers at a depth of 10 ⁇ m from the surface of the sliding surface.
  • a sliding part having a hardness of 700 or more, an average particle diameter of cementite particles of 0.6 ⁇ m or less, and a number density of cementite particles in a cross section perpendicular to the sliding surface of 1 piece/ ⁇ m 2 or more is described. ing.
  • An object of the present invention is to provide a steel material for sliding parts that has excellent slidability and workability. Another object of the present invention is to provide a method for producing a steel material for sliding parts that is excellent in slidability and workability.
  • a steel material for sliding parts is a steel material for sliding parts comprising a steel material having a C content of 0.30 to 0.60% by mass, and having a structure of tempered martensite and bainite. At least one of them and iron carbide, the total volume fraction of the tempered martensite and the bainite is 80% or more, the iron carbide is 2.0% or more, and the Vickers hardness is 300 or more and 600 or less and the volume fraction X of the iron carbide and the Vickers hardness Hv satisfy the following relational expression (1).
  • X ⁇ 0.065 ⁇ Hv+36.5 (1)
  • the unit of X is % and the unit of Hv is Hv.
  • a steel material for sliding parts according to an embodiment of the present invention has a chemical composition, in mass %, of C: 0.30 to 0.60%, Si: 0.01 to 2.00%, Mn: 0.00%. 10 to 2.00%, Al: 0.060% or less, N: 0.020% or less, P: 0.10% or less, S: 0.20% or less, Cr: 0 to 0.50%, balance: It may be Fe and impurities.
  • a method for producing a steel material for sliding parts is a method for producing the above-mentioned steel material for sliding parts, wherein after holding the material at a temperature of 830° C. or more and 1100° C. or less, from the holding temperature A step of cooling and quenching so that the cooling rate to 300° C. is 300° C./sec or more, and a step of holding the quenched material at a temperature of 200° C. or more and 600° C. or less and tempering it.
  • FIG. 1 is an uneven image of a steel material acquired by an atomic force microscope.
  • FIG. 2 is an adhesion force image of steel obtained by an atomic force microscope.
  • FIG. 3 is a scatter diagram showing the relationship between the Vickers hardness of steel and the volume fraction of iron carbide.
  • FIG. 4 is a graph showing the relationship between the Vickers hardness of steel and the wear scar width obtained by a sliding test using a ball-on-disk type friction wear tester.
  • FIG. 5 is an example of an uneven image obtained by measuring a test piece whose surface has been processed by Ar ion milling with an atomic force microscope.
  • FIG. 6 is an example of iron carbide detected by image analysis software.
  • FIG. 7 is a schematic diagram of a ball-on-disk type friction and wear tester.
  • the inventors investigated the slidability and workability of steel materials in order to develop steel materials with excellent slidability and workability. As a result, the following findings were obtained.
  • Figures 1 and 2 are images obtained by an atomic force microscope (AFM), where Figure 1 is an uneven image and Figure 2 is an adhesive force image.
  • AFM atomic force microscope
  • FIG. 1 the convex portions are shown in white, and the concave portions are shown in black.
  • FIG. 2 portions with high adhesive strength are displayed in white, and portions with low adhesive strength are displayed in black.
  • FIG. 1 The uneven image in Fig. 1 was obtained by AFM measurement of a sample whose surface was processed by Ar ion milling. As a result of this processing, the iron matrix, which is softer than the iron carbide, is scraped away, leaving the iron carbide as a convex, which makes it possible to search for the iron carbide by AFM.
  • white portions, that is, convex portions are iron carbides.
  • FIG. 2 shows the result of measuring the adhesion force in the same range, and it can be seen from FIGS. 1 and 2 that the adhesion force of iron carbide is small.
  • the seizure resistance can be improved by increasing the volume fraction of iron carbide.
  • the volume fraction of iron carbide is increased, the hardness of the steel material may be lowered and the wear resistance may be lowered.
  • FIG. 3 is a scatter diagram showing the relationship between the Vickers hardness of steel materials produced in Examples described later and the volume fraction of iron carbide.
  • FIG. 4 is a graph showing the relationship between the Vickers hardness of steel and the wear scar width obtained by a sliding test using a ball-on-disk type friction wear tester. The smaller the wear scar width, the higher the wear resistance.
  • the volume fraction X of the iron carbide and the Vickers hardness Hv of the steel satisfy the following relational expression (1). are indicated by solid circle symbols. Note that the triangular symbols in FIG. 4 are for steel materials with an as-quenched structure. X ⁇ 0.065 ⁇ Hv+36.5 (1) The unit of X is % and the unit of Hv is Hv.
  • the steel material for sliding parts according to this embodiment is made of a steel material having a C content of 0.30 to 0.60% by mass.
  • the lower limit of the C content of the steel material for sliding parts according to the present embodiment is preferably 0.32% by mass, more preferably 0.35% by mass, still more preferably 0.38% by mass, and Preferably it is 0.40% by mass.
  • the upper limit of the C content of the steel material for sliding parts according to the present embodiment is preferably 0.58% by mass, more preferably 0.55% by mass.
  • the chemical composition of the steel material for sliding parts according to the present embodiment is not particularly limited as long as the C content is 0.30 to 0.60% by mass. may In the following description, "%" of element content means % by mass.
  • C 0.30-0.60% Carbon (C) enhances the hardenability of steel. As described above, if the C content is out of the appropriate range, it becomes difficult to satisfy the relational expression (1) between the volume fraction of iron carbide and the Vickers hardness, or even if the relational expression (1) is satisfied, In some cases, it may not be possible to obtain a steel material with an excellent balance between dynamicity and workability. Therefore, the C content is 0.30-0.60%.
  • the lower limit of the C content is preferably 0.32%, more preferably 0.35%, still more preferably 0.38%, still more preferably 0.40%.
  • the upper limit of the C content is preferably 0.58%, more preferably 0.55%.
  • Si 0.01-2.00% Silicon (Si) deoxidizes steel. On the other hand, if the Si content is too high, the workability of the steel deteriorates. Therefore, the Si content may be 0.01-2.00%.
  • the lower limit of the Si content is preferably 0.02%, more preferably 0.05%, still more preferably 0.10%.
  • the upper limit of the Si content is preferably 1.50%, more preferably 1.20%, still more preferably 0.80%, still more preferably 0.60%, still more preferably 0 .40%.
  • Mn 0.10-2.00%
  • Mn Manganese
  • the lower limit of the Mn content is preferably 0.20%, more preferably 0.40%, still more preferably 0.60%.
  • the upper limit of the Mn content is preferably 1.80%, more preferably 1.60%, still more preferably 1.50%, still more preferably 1.00%, still more preferably 0 .90%.
  • Al 0.060% or less Aluminum (Al) deoxidizes steel. On the other hand, if the Al content is too high, the workability of the steel deteriorates. Therefore, the Al content may be 0.060% or less.
  • the upper limit of the Al content is preferably 0.050%, more preferably 0.040%, still more preferably 0.030%. When obtaining the deoxidizing effect of Al, the Al content may be 0.020% or more.
  • N 0.020% or less Nitrogen (N) reduces the hot workability of steel. Therefore, the N content may be 0.020% or less.
  • the upper limit of the N content is preferably 0.018%, more preferably 0.015%, still more preferably 0.010%, still more preferably 0.005%.
  • the lower limit of the N content may be 0.0010%.
  • P 0.10% or less Phosphorus (P) is an impurity. P segregates at grain boundaries and lowers the hot workability and toughness of steel. Therefore, the P content may be 0.10% or less.
  • the P content is preferably 0.03% or less, more preferably 0.02% or less. It is preferable that the P content is as low as possible.
  • S 0.20% or less Sulfur (S) is sometimes added to improve the workability (machinability) of steel.
  • the S content may be 0.20% or less.
  • the upper limit of the S content is preferably 0.12%, more preferably 0.08%, still more preferably 0.06%.
  • the S content may be 0.020% or more.
  • Chromium (Cr) is an optional element. That is, the steel material for sliding parts according to this embodiment does not have to contain Cr. Cr increases the hardenability of steel. This effect can be obtained if even a small amount of Cr is contained. On the other hand, if the Cr content is too high, the workability of the steel deteriorates. Therefore, the Cr content may be 0-0.50%.
  • the lower limit of the Cr content is preferably 0.01%, more preferably 0.05%.
  • the upper limit of Cr content is preferably 0.20%.
  • the rest of the chemical composition of the steel material for sliding parts according to this embodiment may be Fe and impurities.
  • impurities refers to elements mixed in from ores and scraps used as raw materials for steel, or elements mixed in from the environment during the manufacturing process.
  • the steel material for sliding parts according to this embodiment may consist of a carbon steel material for machine structural use or an alloy steel material for machine structural use.
  • the steel material for sliding parts according to this embodiment preferably consists of a carbon steel material for machine structural use specified in JIS G 4051:2016 or an alloy steel material for machine structural use specified in JIS G 4053:2016.
  • S45C and S50C of JIS G 4051:2016 and SMn438 of JIS G 4053:2016 are particularly preferable.
  • these steel materials may contain 0.20% by mass or less of S in order to improve workability (machinability).
  • the structure of the steel material for sliding parts includes at least one of tempered martensite and bainite (including tempered bainite; the same applies hereinafter) and iron carbide, and the volume fraction of tempered martensite and Total with bainite: 80% or more, iron carbide: 2.0% or more.
  • the sum of the volume fraction of tempered martensite and the volume fraction of bainite is 80% or more.
  • the structure of the steel material for sliding parts according to the present embodiment may contain at least one of tempered martensite and bainite.
  • the steel material for sliding parts is tempered to obtain a structure containing a predetermined amount of iron carbide, thereby ensuring workability of the steel material for sliding parts.
  • the structure of the steel material for sliding parts is as quenched (structure mainly composed of martensite as quenched), it becomes difficult to ensure good workability.
  • the steel material for sliding parts according to the present embodiment preferably contains tempered martensite.
  • the sum of the volume fraction of tempered martensite and the volume fraction of bainite is preferably 85% or more, more preferably 90% or more, and still more preferably 95% or more.
  • iron carbide in calculating the volume fraction of the structure, is treated as an independent structure and iron carbide is distinguished from tempered martensite and bainite. That is, the portion where iron carbide precipitates is not included in the volume of tempered martensite or bainite.
  • the structure of the steel material for sliding parts according to this embodiment has a volume fraction of iron carbide of 2.0% or more.
  • the iron carbide of the steel material for sliding parts according to the present embodiment is at least one of ⁇ carbide and cementite.
  • the iron carbide contained in the steel material for sliding parts may be of one type or of a plurality of types. When multiple types of iron carbide are included, the volume fraction of iron carbide is the sum of the volume fractions of those iron carbides.
  • the lower limit of the volume fraction of iron carbide is preferably 3.0%, more preferably 5.0%, still more preferably 7.0%.
  • the upper limit of the volume fraction of iron carbide is preferably 18.0%, more preferably 15.0%, still more preferably 12.0%, still more preferably 10.0%, and Preferably it is 8.0%.
  • the volume fraction of iron carbide can be adjusted by the C content of the steel material and the tempering conditions. Specifically, the higher the C content, the higher the volume fraction of iron carbide. As for tempering conditions, the higher the holding temperature and the longer the holding time, the higher the volume fraction of iron carbide.
  • the structure of the steel material for sliding parts according to this embodiment may contain a small amount of structure other than tempered martensite, bainite, and iron carbide.
  • Structures other than tempered martensite, bainite, and iron carbide are, for example, ferrite, pearlite, retained austenite, MnS, and the like.
  • the total volume fraction of structures other than tempered martensite, bainite, and carbide in the structure of the steel material for sliding parts according to the present embodiment is preferably 5.0% or less, more preferably 3.0% or less. , more preferably 2.0% or less, and still more preferably 1.0% or less.
  • the steel material for sliding parts according to this embodiment has a Vickers hardness of 300 or more and 600 or less. If the Vickers hardness is less than 300, it becomes difficult to obtain excellent wear resistance. On the other hand, when the Vickers hardness is higher than 600, workability is lowered. From the viewpoint of wear resistance, the lower limit of the Vickers hardness is preferably 350, more preferably 400, still more preferably 450, more preferably 500, still more preferably 530. From the viewpoint of workability, the upper limit of the Vickers hardness is preferably 580, more preferably 560, still more preferably 550, still more preferably 530, still more preferably 520.
  • the Vickers hardness of the steel material for sliding parts can be adjusted by the C content of the steel material, the quenching conditions, and the tempering conditions. Specifically, the higher the C content, the higher the Vickers hardness tends to be. As for the quenching conditions, the higher the cooling rate, the higher the Vickers hardness tends to be. As for the tempering conditions, the lower the holding temperature and the shorter the holding time, the higher the Vickers hardness tends to be.
  • the average minor axis length of the iron carbide is preferably 0.027 ⁇ m or less.
  • the average minor axis length of the iron carbide is preferably 0.025 ⁇ m or less.
  • the steel material for sliding parts according to this embodiment preferably has no nitrided layer, carburized layer, or carbonitrided layer on the surface.
  • the steel material for sliding parts according to the present embodiment has a surface Vickers hardness of 300 or more and 600 or less, and the volume fraction X of iron carbide on the surface and the Vickers hardness Hv satisfy the above-described relational expression (1). is preferred.
  • the "surface Vickers hardness” more specifically means the Vickers hardness of a region at a depth of 100 ⁇ m or less from the surface of the steel material for sliding parts.
  • the volume fraction of iron carbide on the surface more specifically means the volume fraction of iron carbide in the structure of the region at a depth of 100 ⁇ m or less from the surface of the steel material for sliding parts.
  • the material is, for example, a hot forged product.
  • the steel having the above-described chemical composition is melted, continuous casting or blooming rolling is performed to make a steel slab, and the steel slab is hot forged and processed into a rough shape for sliding parts.
  • can be Cutting or the like may be applied to the material after hot forging.
  • the material After holding the material at a temperature of 830°C or higher and 1100°C or lower, it is cooled and quenched so that the cooling rate from the holding temperature to 300°C is 300°C/second or more. If the holding temperature is too low, a uniform texture may not be obtained. On the other hand, if the holding temperature is too high, the crystal grains may become coarse. If the cooling rate is too low, the desired structure may not be obtained. Note that the Vickers hardness of the finally obtained steel material for sliding parts tends to increase as the cooling rate in the quenching process increases.
  • the quenched material is tempered while being held at a temperature of 200°C or higher and 600°C or lower.
  • the higher the holding temperature and the longer the holding time of tempering the lower the Vickers hardness of the finally obtained steel material for sliding parts.
  • the higher the holding temperature and the longer the holding time of tempering the higher the volume fraction of iron carbide in the structure of the finally obtained steel material for sliding parts. If the holding temperature for tempering is out of this range, it becomes difficult to keep the volume fraction of iron carbide and the Vickers hardness within the predetermined ranges.
  • the conditions for quenching and tempering are adjusted according to the chemical composition of the steel material, so that the volume fraction X of iron carbide and the Vickers hardness Hv satisfy the relational expression (1). As a result, the steel material for sliding parts according to the present embodiment is obtained.
  • the steel material for sliding parts according to one embodiment of the present invention has been described above.
  • the steel material for sliding parts according to this embodiment has excellent slidability and workability. Therefore, the steel material for sliding parts according to this embodiment is suitable as a material for sliding parts.
  • a sliding part is, for example, a crankshaft.
  • a 10 kg steel having the chemical composition shown in Table 1 was melted in a vacuum induction melting furnace to produce an ingot.
  • This ingot was hot forged at 950-1200°C to a thickness of 30 mm, a width of 100 mm and a length of 290 mm, and then rolled to a thickness of 7 mm and a width of 110 mm.
  • the rolled material was cut into pieces having a width of 15 mm, a length of 60-120 mm, and a thickness of 7 mm, and subjected to the heat treatment shown in Table 2.
  • the structures before the heat treatment were all ferrite/pearlite (F+P).
  • the numerical values in the "cooling rate" column of "quenching" in Table 2 are the cooling rates from the holding temperature of quenching to 300°C.
  • test pieces After the heat treatment, multiple 20 mm square and 2 mm thick test pieces were taken from each material. Observation of the structure, measurement of Vickers hardness, and evaluation of slidability were performed using these test pieces.
  • FIG. 5 shows an example of a surface unevenness image of a processed test piece obtained by AFM.
  • White indicates convex portions, and black indicates concave portions.
  • White portions in FIG. 5 are iron carbides.
  • the volume fraction of iron carbide was calculated using image analysis software after acquiring uneven images in the range of 2 ⁇ m ⁇ 2 ⁇ m by AFM at three locations on the test piece.
  • ImageJ was used as image analysis software.
  • the image was binarized and the particles were detected using the particle analysis function of the image analysis software.
  • An example of iron carbide detected by image analysis software is shown in FIG.
  • the area ratio of iron carbide was calculated at each of the three observed locations, and the average was obtained. The obtained area ratio was regarded as the volume fraction of iron carbide.
  • the volume fraction of ferrite was calculated using a secondary electron image (unevenness image) of SEM.
  • the surface of the sample was nital-etched to corrode only the ferrite to form a recess, and then a secondary electron image was obtained at a magnification of 1000 times.
  • the acquired image is imported into the image analysis software ImageJ, the relevant area is selected using the freehand selection or polygon selection function, the selected area is masked, binarization is performed in the same way as for iron carbide, and the particles of the image analysis software The relevant regions were detected using the analysis function.
  • the area ratio of ferrite was calculated at each of the three observed points, and the average was obtained. The obtained area ratio was regarded as the volume fraction of ferrite.
  • the volume fraction of retained austenite was measured by X-ray diffraction.
  • the volume fraction of MnS was obtained by photographing the surface of the test piece with an optical microscope (magnification: 210 times, size of field of view: 1218 ⁇ m ⁇ 1218 ⁇ m) to determine the area ratio of MnS, and this area ratio was regarded as the volume fraction. .
  • the sum of the volume fraction of tempered martensite and the volume fraction of bainite is the volume fraction of iron carbide, retained austenite, ferrite, and MnS. It was obtained by subtracting the sum of from 100%.
  • the morphology of the iron carbide was determined by image analysis from the uneven image obtained when determining the volume fraction of the iron carbide. Specifically, the images were binarized, and all particles within each observation field were elliptically approximated using the particle analysis function of the image analysis software. An average minor axis length and an average major axis length were obtained at each of the three observed points, and the average thereof was obtained.
  • the Vickers hardness was measured at 5 points with a test force of 1 kgf (9.807 N), and the average was obtained.
  • Table 3 shows the structure and Vickers hardness of each steel material after heat treatment.
  • M represents as-quenched martensite
  • B represents bainite
  • TM represents tempered martensite
  • restored ⁇ represents retained austenite.
  • the surface of the specimen for the sliding test was mirror-finished.
  • the sliding test was performed using a ball-on-disk type friction wear tester.
  • FIG. 7 shows a schematic diagram of the test machine. Alumina balls were used, the load was 10 N, and the sliding speed was 10 mm/sec. After the sliding test, the width of the sliding marks was measured, and if the average value of the sliding mark width was 160 ⁇ m or less, the wear resistance was evaluated as “good”, and if it exceeded 160 ⁇ m, the wear resistance was poor. It was rated as "impossible”.
  • Table 4 shows the Vickers hardness of each steel material, the volume fraction of carbides (iron carbides), and the results of the sliding test. The workability was evaluated as “good” if the Vickers hardness was 600 or less, and as “poor” if it exceeded 600. In the comprehensive evaluation, samples with “good” workability and wear resistance were rated as “acceptable”, and samples with either “poor” workability or wear resistance were rated as “fail”.
  • the steel materials of 4 to 7, 9, 10 and 14 to 17 have a Vickers hardness of 300 to 600, and the volume fraction X of iron carbide and the Vickers hardness Hv satisfy the relational expression (1). These test materials had a wear scar width of 160 ⁇ m or less after the sliding test, indicating excellent wear resistance. Moreover, these test materials had a Vickers hardness Hv of 600 or less and were excellent in workability.
  • the steel material No. 11 has the structure as quenched. No. The steel material No. 11 had good wear resistance, but had a Vickers hardness Hv exceeding 600 and was inferior in workability.
  • FIG. 3 is a scatter diagram showing the relationship between the Vickers hardness of steel and the volume fraction of iron carbide.
  • FIG. 4 is a graph showing the relationship between the Vickers hardness of steel and the wear scar width obtained by a sliding test using a ball-on-disk type friction wear test. 3 and 4, the volume fraction X of the iron carbide and the Vickers hardness Hv of the steel material satisfy the relational expression (1) by the white circle symbol, and the relational expression (1) is satisfied. Those that are not are indicated by a solid circle symbol.
  • the triangular symbols in FIG. 4 are for the steel material (No. 11) with the as-quenched structure. From FIGS. 3 and 4, it can be seen that excellent wear resistance can be obtained if the volume fraction X of iron carbide and the Vickers hardness Hv of the steel material satisfy the relational expression (1).

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Abstract

Provided is a steel material for sliding components that has excellent sliding properties and workability. The steel material for sliding components: comprises a steel material having 0.30%–0.60% by mass C content; has a structure that includes iron carbide and at least either tempered martensite or bainite; has a total, by volume fraction, of at least 80% tempered martensite and bainite and at least 2.0% iron carbide; and has a Vickers hardness Hv of 300–600. The volume fraction X of the iron carbide and the Vickers hardness Hv fulfill the relational expression (1).　X ≥ –0.065 × Hv + 36.5 (1). The unit for X is % and the unit for Hv is Hv.

Description

摺動部品用鋼材及び摺動部品用鋼材の製造方法Steel material for sliding parts and method for manufacturing steel material for sliding parts
　本発明は、摺動部品用鋼材及び摺動部品用鋼材の製造方法に関する。 The present invention relates to a steel material for sliding parts and a method for manufacturing the steel material for sliding parts.
　鉄鋼材料は、自動車用部品、鉄道車両用部品、建築部材、パイプ等の工業製品に広く用いられている。特に、機械構造用炭素鋼鋼材や機械構造用合金鋼鋼材は、機械的強度の高さゆえ、歯車やシャフト等、動力伝達システム部品に代表される摺動部品の材料として使われることが多い。 Steel materials are widely used in industrial products such as automotive parts, railway vehicle parts, building components, and pipes. In particular, carbon steel materials for machine structural use and alloy steel materials for machine structural use are often used as materials for sliding parts such as gears and shafts, typified by power transmission system parts, because of their high mechanical strength.
　摺動部品の最大の課題は、部品同士の摩擦や摩耗であり、これらは機械システム全体の不具合や低効率化の原因と考えられている。今後、機械システムの小型軽量化が進むことで、摺動部品の環境は一層厳しくなることが予想される。例えば自動車のエンジン部品であるクランクシャフトでは、小型軽量化とともに、回転摺動部の耐焼付性改善が恒久的な課題となっている。これらの問題を解決するために、現行よりも摺動性に優る摺動部品用鋼材を開発し、機械システム全体の小型軽量化に備える必要がある。 　The biggest problem with sliding parts is friction and wear between parts, and these are considered to be the causes of malfunctions and low efficiency of the entire mechanical system. In the future, as mechanical systems become smaller and lighter, the environment for sliding parts is expected to become even more severe. For example, in the case of crankshafts, which are engine parts for automobiles, it is a permanent issue to reduce the size and weight and to improve the seizure resistance of rotating sliding parts. In order to solve these problems, it is necessary to develop steel materials for sliding parts that have better slidability than the current ones, and prepare for the reduction in size and weight of the entire mechanical system.
　摺動部品用鋼材の解決すべき課題の一つに、部品寿命の延長及び信頼性向上の観点から、耐摩耗性の改善が挙げられる。耐摩耗性の改善には、鋼材の硬度を引き上げることが有効と考えられる。しかし、硬度を引き上げることは、鋼材の被加工性を損なうことになり、部品量産時にはリスクを伴う。そのため、摺動部品の摺動性を向上させる方法として、表層のみを選択的に組織制御し、当該部のみを硬化させる方法が有効である。 One of the issues to be solved for steel materials for sliding parts is to improve wear resistance from the viewpoint of extending the life of parts and improving reliability. It is considered effective to increase the hardness of steel materials to improve wear resistance. However, increasing the hardness impairs the machinability of the steel material, which entails risks when mass-producing parts. Therefore, as a method for improving the slidability of sliding parts, it is effective to selectively control the structure of only the surface layer and harden only the relevant portion.
　例えば特開平１－２３０７４６号公報には、鋳鉄よりなる固定部材と、鋳鉄より高硬度の材料よりなる摺動部材とを具備する摺動部品において、固定部材の表層組織を、マルテンサイト又はマルテンサイトとパーライトとフェライトと黒鉛との混相組織よりなる硬化層、及び酸化物からなる組織とすることが開示されている。 For example, Japanese Patent Application Laid-Open No. 1-230746 discloses a sliding component comprising a fixed member made of cast iron and a sliding member made of a material having higher hardness than cast iron, wherein the surface layer structure of the fixed member is martensite or martensite. It is disclosed that the hardened layer consists of a mixed phase structure of , pearlite, ferrite and graphite, and the structure consists of oxides.
　硬度の制御以外の方法として、鋼材中の析出物を制御して凝着を抑制することで、耐焼付性を向上させる方法がある。特開２０１３－２２７６７４号公報には、表層部において、焼戻しマルテンサイト及び／又は焼戻しベイナイトに、面積率で１～１０％で残留オーステナイトが存在すると共に、炭化物が面積率で５％以上析出している鋼材組織を有し、且つ表面から２０μｍ深さにおける窒素濃度が２．０～６．０％である歯車が記載されている。 As a method other than controlling hardness, there is a method of improving seizure resistance by controlling the precipitates in the steel material to suppress adhesion. In JP-A-2013-227674, in the surface layer, tempered martensite and/or tempered bainite contain retained austenite at an area ratio of 1 to 10%, and carbide precipitates at an area ratio of 5% or more. It describes a gear having a steel material structure with a high nitrogen content and a nitrogen concentration of 2.0 to 6.0% at a depth of 20 μm from the surface.
　特開２０１０－１００８８１号公報には、浸炭又は浸炭窒化された摺動部品であって、摺動面の表面から深さ１０μｍまでの表層部において、摺動面の表面からの深さ１０μｍにおけるビッカース硬さ：７００以上、セメンタイト粒子の平均粒子径：０．６μｍ以下、摺動面に対して垂直方向の断面におけるセメンタイト粒子の数密度：１個／μｍ２以上、である摺動部品が記載されている。 Japanese Patent Application Laid-Open No. 2010-100881 describes a carburized or carbonitrided sliding part, in which a surface layer portion up to a depth of 10 μm from the surface of the sliding surface has Vickers at a depth of 10 μm from the surface of the sliding surface. A sliding part having a hardness of 700 or more, an average particle diameter of cementite particles of 0.6 μm or less, and a number density of cementite particles in a cross section perpendicular to the sliding surface of 1 piece/μm 2 or more is described. ing.
特開平１－２３０７４６号公報JP-A-1-230746 特開２０１３－２２７６７４号公報JP 2013-227674 A 特開２０１０－１００８８１号公報JP 2010-100881 A
　回転軸やクランクシャフト等の摺動部品では、摺動部品同士の表面の摩擦・摩耗を抑制し、過負荷による機械的損傷や熱亀裂等のダメージが抑制された状態で機能させることが重要である。耐摩耗性を向上させる手段として硬度向上があるが、加工性を損なう要因ともなり得る。また、摺動部品では焼付きを防ぐために凝着しにくさが重要である。 For sliding parts such as rotary shafts and crankshafts, it is important to suppress friction and wear on the surfaces of the sliding parts so that they function in a state where damage such as mechanical damage and thermal cracks due to overload is suppressed. be. Hardness can be improved as a means of improving wear resistance, but it can also be a factor that impairs workability. In addition, resistance to adhesion is important for sliding parts in order to prevent seizure.
　本発明の課題は、摺動性及び加工性に優れた摺動部品用鋼材を提供することである。本発明の他の課題は、摺動性及び加工性に優れた摺動部品用鋼材の製造方法を提供することである。 An object of the present invention is to provide a steel material for sliding parts that has excellent slidability and workability. Another object of the present invention is to provide a method for producing a steel material for sliding parts that is excellent in slidability and workability.
　本発明の一実施形態による摺動部品用鋼材は、Ｃ含有量が０．３０～０．６０質量％である鋼材からなる摺動部品用鋼材であって、組織が、焼戻しマルテンサイト及びベイナイトの少なくとも一方と鉄炭化物とを含み、体積分率が、前記焼戻しマルテンサイトと前記ベイナイトとの合計：８０％以上、前記鉄炭化物：２．０％以上であり、ビッカース硬さが３００以上６００以下であり、前記鉄炭化物の体積分率Ｘと前記ビッカース硬さＨｖとが、下記の関係式（１）を満たす。
　　Ｘ≧－０．０６５×Ｈｖ＋３６．５　　　（１）
　Ｘの単位は％であり、Ｈｖの単位はＨｖである。 A steel material for sliding parts according to one embodiment of the present invention is a steel material for sliding parts comprising a steel material having a C content of 0.30 to 0.60% by mass, and having a structure of tempered martensite and bainite. At least one of them and iron carbide, the total volume fraction of the tempered martensite and the bainite is 80% or more, the iron carbide is 2.0% or more, and the Vickers hardness is 300 or more and 600 or less and the volume fraction X of the iron carbide and the Vickers hardness Hv satisfy the following relational expression (1).
X≧−0.065×Hv+36.5 (1)
The unit of X is % and the unit of Hv is Hv.
　本発明の一実施形態による摺動部品用鋼材は、鋼材の化学組成が、質量％で、Ｃ：０．３０～０．６０％、Ｓｉ：０．０１～２．００％、Ｍｎ：０．１０～２．００％、Ａｌ：０．０６０％以下、Ｎ：０．０２０％以下、Ｐ：０．１０％以下、Ｓ：０．２０％以下、Ｃｒ：０～０．５０％、残部：Ｆｅ及び不純物であってもよい。 A steel material for sliding parts according to an embodiment of the present invention has a chemical composition, in mass %, of C: 0.30 to 0.60%, Si: 0.01 to 2.00%, Mn: 0.00%. 10 to 2.00%, Al: 0.060% or less, N: 0.020% or less, P: 0.10% or less, S: 0.20% or less, Cr: 0 to 0.50%, balance: It may be Fe and impurities.
　本発明の一実施形態による摺動部品用鋼材の製造方法は、上記の摺動部品用鋼材を製造する方法であって、素材を８３０℃以上１１００℃以下の温度に保持した後、保持温度から３００℃までの冷却速度が３００℃／秒以上になるように冷却して焼入れする工程と、前記焼入れされた素材を２００℃以上６００℃以下の温度に保持して焼戻しをする工程とを備える。 A method for producing a steel material for sliding parts according to an embodiment of the present invention is a method for producing the above-mentioned steel material for sliding parts, wherein after holding the material at a temperature of 830° C. or more and 1100° C. or less, from the holding temperature A step of cooling and quenching so that the cooling rate to 300° C. is 300° C./sec or more, and a step of holding the quenched material at a temperature of 200° C. or more and 600° C. or less and tempering it.
　本発明によれば、摺動性及び加工性に優れた摺動部品用鋼材が得られる。 According to the present invention, a steel material for sliding parts with excellent slidability and workability can be obtained.
図１は、原子間力顕微鏡により取得した鋼材の凹凸像である。FIG. 1 is an uneven image of a steel material acquired by an atomic force microscope. 図２は、原子間力顕微鏡により取得した鋼材の凝着力像である。FIG. 2 is an adhesion force image of steel obtained by an atomic force microscope. 図３は、鋼材のビッカース硬さと鉄炭化物の体積分率との関係を示す散布図である。FIG. 3 is a scatter diagram showing the relationship between the Vickers hardness of steel and the volume fraction of iron carbide. 図４は、鋼材のビッカース硬さと、ボール・オン・ディスク型摩擦摩耗試験機による摺動試験よって得られた摩耗痕幅との関係を示すグラフである。FIG. 4 is a graph showing the relationship between the Vickers hardness of steel and the wear scar width obtained by a sliding test using a ball-on-disk type friction wear tester. 図５は、Ａｒイオンミリングで表面を加工した試験片を原子間力顕微鏡で測定して得た凹凸像の一例である。FIG. 5 is an example of an uneven image obtained by measuring a test piece whose surface has been processed by Ar ion milling with an atomic force microscope. 図６は、画像解析ソフトウェアで検出した鉄炭化物の一例である。FIG. 6 is an example of iron carbide detected by image analysis software. 図７は、ボール・オン・ディスク型摩擦摩耗試験機の概略図である。FIG. 7 is a schematic diagram of a ball-on-disk type friction and wear tester.
　本発明者らは、摺動性及び加工性に優れた鋼材を開発するため、鋼材の摺動性及び加工性を調査した。その結果、以下の知見を得た。 The inventors investigated the slidability and workability of steel materials in order to develop steel materials with excellent slidability and workability. As a result, the following findings were obtained.
　図１及び図２は、原子間力顕微鏡（ＡＦＭ）により取得した像であり、図１は凹凸像、図２は凝着力像である。図１では、凸となっている部分を白色に、凹となっている部分を黒色に表示している。図２では、凝着力が大きい部分を白色に、凝着力が小さい部分を黒色に表示している。 　Figures 1 and 2 are images obtained by an atomic force microscope (AFM), where Figure 1 is an uneven image and Figure 2 is an adhesive force image. In FIG. 1, the convex portions are shown in white, and the concave portions are shown in black. In FIG. 2, portions with high adhesive strength are displayed in white, and portions with low adhesive strength are displayed in black.
　図１の凹凸像は、表面をＡｒイオンミリングによって加工した試料をＡＦＭで測定することによって得たものである。この加工により、鉄炭化物に比べて軟質な鉄基地は削れ、鉄炭化物は凸として残るため、ＡＦＭによる鉄炭化物の探索が可能になる。図１において、白色の部分、すなわち凸となっている部分が鉄炭化物である。同じ範囲で凝着力を測定した結果が図２であり、図１及び図２から、鉄炭化物の凝着力は小さいことが分かる。 The uneven image in Fig. 1 was obtained by AFM measurement of a sample whose surface was processed by Ar ion milling. As a result of this processing, the iron matrix, which is softer than the iron carbide, is scraped away, leaving the iron carbide as a convex, which makes it possible to search for the iron carbide by AFM. In FIG. 1, white portions, that is, convex portions are iron carbides. FIG. 2 shows the result of measuring the adhesion force in the same range, and it can be seen from FIGS. 1 and 2 that the adhesion force of iron carbide is small.
　このことから、鉄炭化物の体積分率を高くすることによって、耐焼付性を向上できると考えられる。一方、鉄炭化物の体積分率を高くすると、鋼材の硬度が低下し、耐摩耗性が低下するとも考えられる。 From this, it is considered that the seizure resistance can be improved by increasing the volume fraction of iron carbide. On the other hand, if the volume fraction of iron carbide is increased, the hardness of the steel material may be lowered and the wear resistance may be lowered.
　図３は、後述する実施例において作製した鋼材のビッカース硬さと鉄炭化物の体積分率との関係を示す散布図である。図４は、鋼材のビッカース硬さと、ボール・オン・ディスク型摩擦摩耗試験機による摺動試験によって得られた摩耗痕幅との関係を示すグラフである。摩耗痕幅が小さいほど、耐摩耗性が高いことを意味する。 FIG. 3 is a scatter diagram showing the relationship between the Vickers hardness of steel materials produced in Examples described later and the volume fraction of iron carbide. FIG. 4 is a graph showing the relationship between the Vickers hardness of steel and the wear scar width obtained by a sliding test using a ball-on-disk type friction wear tester. The smaller the wear scar width, the higher the wear resistance.
　図３及び図４において、鉄炭化物の体積分率Ｘと鋼材のビッカース硬さＨｖとが、下記の関係式（１）を充足しているものを白抜きの丸のシンボル、関係式（１）を充足していないものを中実の丸のシンボルで示している。なお、図４における三角のシンボルは、組織を焼入れままの組織とした鋼材のものである。
　　Ｘ≧－０．０６５×Ｈｖ＋３６．５　　　（１）
　Ｘの単位は％であり、Ｈｖの単位はＨｖである。 In FIGS. 3 and 4, the volume fraction X of the iron carbide and the Vickers hardness Hv of the steel satisfy the following relational expression (1). are indicated by solid circle symbols. Note that the triangular symbols in FIG. 4 are for steel materials with an as-quenched structure.
X≧−0.065×Hv+36.5 (1)
The unit of X is % and the unit of Hv is Hv.
　図３及び図４から、鉄炭化物の体積分率Ｘと鋼材のビッカース硬さＨｖとが関係式（１）を満たせば、優れた耐摩耗性を得られることが分かる。 From FIGS. 3 and 4, it can be seen that excellent wear resistance can be obtained if the volume fraction X of the iron carbide and the Vickers hardness Hv of the steel material satisfy the relational expression (1).
　以上の知見に基づいて、本発明は完成された。以下、本発明の一実施形態による摺動部品用鋼材について詳述する。 The present invention was completed based on the above findings. Hereinafter, a steel material for sliding parts according to one embodiment of the present invention will be described in detail.
　［化学組成］
　本実施形態による摺動部品用鋼材は、Ｃ含有量が０．３０～０．６０質量％である鋼材からなる。Ｃ含有量が高いほど、炭化物の体積分率が高くなる傾向がある。また、Ｃ含有量が高いほど、摺動部品用鋼材のビッカース硬さが高くなる傾向がある。Ｃ含有量の範囲が０．３０～０．６０質量％の範囲から外れると、鉄炭化物の体積率とビッカース硬さとの関係式（１）を満たすことが困難になるか、または関係式（１）を満たしても摺動性と加工性とのバランスに優れた鋼材を得ることができない場合がある。本実施形態による摺動部品用鋼材のＣ含有量の下限は、好ましくは０．３２質量％であり、さらに好ましくは０．３５質量％であり、さらに好ましくは０．３８質量％であり、さらに好ましくは０．４０質量％である。本実施形態による摺動部品用鋼材のＣ含有量の上限は、好ましくは０．５８質量％であり、さらに好ましくは０．５５質量％である。 [Chemical composition]
The steel material for sliding parts according to this embodiment is made of a steel material having a C content of 0.30 to 0.60% by mass. The higher the C content, the higher the carbide volume fraction tends to be. Also, the higher the C content, the higher the Vickers hardness of the steel material for sliding parts. If the C content deviates from the range of 0.30 to 0.60% by mass, it becomes difficult to satisfy the relational expression (1) between the volume fraction of iron carbide and the Vickers hardness, or the relational expression (1 ), it may not be possible to obtain a steel material with an excellent balance between slidability and workability. The lower limit of the C content of the steel material for sliding parts according to the present embodiment is preferably 0.32% by mass, more preferably 0.35% by mass, still more preferably 0.38% by mass, and Preferably it is 0.40% by mass. The upper limit of the C content of the steel material for sliding parts according to the present embodiment is preferably 0.58% by mass, more preferably 0.55% by mass.
　本実施形態による摺動部品用鋼材の化学組成は、Ｃ含有量が０．３０～０．６０質量％であればよく、他は特に限定されないが、例えば以下に説明する化学組成を有していてもよい。以下の説明において、元素の含有量の「％」は、質量％を意味する。 The chemical composition of the steel material for sliding parts according to the present embodiment is not particularly limited as long as the C content is 0.30 to 0.60% by mass. may In the following description, "%" of element content means % by mass.
　Ｃ：０．３０～０．６０％
　炭素（Ｃ）は、鋼の焼入れ性を高める。既述のとおり、Ｃ含有量が適正範囲から外れると、鉄炭化物の体積率とビッカース硬さとの関係式（１）を満たすことが困難になるか、または関係式（１）を満たしても摺動性と加工性とのバランスに優れた鋼材を得ることができない場合がある。したがって、Ｃ含有量は０．３０～０．６０％である。Ｃ含有量の下限は、好ましくは０．３２％であり、さらに好ましくは０．３５％であり、さらに好ましくは０．３８％であり、さらに好ましくは０．４０％である。Ｃ含有量の上限は、好ましくは０．５８％であり、さらに好ましくは０．５５％である。 C: 0.30-0.60%
Carbon (C) enhances the hardenability of steel. As described above, if the C content is out of the appropriate range, it becomes difficult to satisfy the relational expression (1) between the volume fraction of iron carbide and the Vickers hardness, or even if the relational expression (1) is satisfied, In some cases, it may not be possible to obtain a steel material with an excellent balance between dynamicity and workability. Therefore, the C content is 0.30-0.60%. The lower limit of the C content is preferably 0.32%, more preferably 0.35%, still more preferably 0.38%, still more preferably 0.40%. The upper limit of the C content is preferably 0.58%, more preferably 0.55%.
　Ｓｉ：０．０１～２．００％
　シリコン（Ｓｉ）は、鋼を脱酸する。一方、Ｓｉ含有量が高すぎると、鋼の加工性が低下する。したがって、Ｓｉ含有量は０．０１～２．００％であってもよい。Ｓｉ含有量の下限は、好ましくは０．０２％であり、さらに好ましくは０．０５％であり、さらに好ましくは０．１０％である。Ｓｉ含有量の上限は、好ましくは１．５０％であり、さらに好ましくは１．２０％であり、さらに好ましくは０．８０％であり、さらに好ましくは０．６０％であり、さらに好ましくは０．４０％である。 Si: 0.01-2.00%
Silicon (Si) deoxidizes steel. On the other hand, if the Si content is too high, the workability of the steel deteriorates. Therefore, the Si content may be 0.01-2.00%. The lower limit of the Si content is preferably 0.02%, more preferably 0.05%, still more preferably 0.10%. The upper limit of the Si content is preferably 1.50%, more preferably 1.20%, still more preferably 0.80%, still more preferably 0.60%, still more preferably 0 .40%.
　Ｍｎ：０．１０～２．００％
　マンガン（Ｍｎ）は鋼の焼入れ性を高める。一方、Ｍｎ含有量が高すぎると、鋼の加工性が低下する。したがって、Ｍｎ含有量は０．１０～２．００％であってもよい。Ｍｎ含有量の下限は、好ましくは０．２０％であり、さらに好ましくは０．４０％であり、さらに好ましくは０．６０％である。Ｍｎ含有量の上限は、好ましくは１．８０％であり、さらに好ましくは１．６０％であり、さらに好ましくは１．５０％であり、さらに好ましくは１．００％であり、さらに好ましくは０．９０％である。 Mn: 0.10-2.00%
Manganese (Mn) increases the hardenability of steel. On the other hand, if the Mn content is too high, the workability of the steel deteriorates. Therefore, the Mn content may be 0.10-2.00%. The lower limit of the Mn content is preferably 0.20%, more preferably 0.40%, still more preferably 0.60%. The upper limit of the Mn content is preferably 1.80%, more preferably 1.60%, still more preferably 1.50%, still more preferably 1.00%, still more preferably 0 .90%.
　Ａｌ：０．０６０％以下
　アルミニウム（Ａｌ）は、鋼を脱酸する。一方、Ａｌ含有量が高すぎると、鋼の加工性が低下する。したがって、Ａｌ含有量は、０．０６０％以下であってもよい。Ａｌ含有量の上限は、好ましくは０．０５０％であり、さらに好ましくは０．０４０％であり、さらに好ましくは０．０３０％である。Ａｌによる脱酸の効果を得る場合には、Ａｌ含有量を０．０２０％以上にしてもよい。 Al: 0.060% or less Aluminum (Al) deoxidizes steel. On the other hand, if the Al content is too high, the workability of the steel deteriorates. Therefore, the Al content may be 0.060% or less. The upper limit of the Al content is preferably 0.050%, more preferably 0.040%, still more preferably 0.030%. When obtaining the deoxidizing effect of Al, the Al content may be 0.020% or more.
　Ｎ：０．０２０％以下
　窒素（Ｎ）は、鋼の熱間加工性を低下させる。したがって、Ｎ含有量は０．０２０％以下であってもよい。Ｎ含有量の上限は、好ましくは０．０１８％であり、さらに好ましくは０．０１５％であり、さらに好ましくは０．０１０％であり、さらに好ましくは０．００５％である。一方、Ｎ含有量を過度に制限すると、製造コストが増加する。そのため、Ｎ含有量の下限を０．００１０％としてもよい。 N: 0.020% or less Nitrogen (N) reduces the hot workability of steel. Therefore, the N content may be 0.020% or less. The upper limit of the N content is preferably 0.018%, more preferably 0.015%, still more preferably 0.010%, still more preferably 0.005%. On the other hand, excessively restricting the N content increases the manufacturing cost. Therefore, the lower limit of the N content may be 0.0010%.
　Ｐ：０．１０％以下
　リン（Ｐ）は、不純物である。Ｐは粒界に偏析し、鋼の熱間加工性や靱性を低下させる。したがって、Ｐ含有量は０．１０％以下であってもよい。Ｐ含有量は、好ましくは０．０３％以下であり、さらに好ましくは０．０２％以下である。Ｐ含有量はできるだけ低い方が好ましい。 P: 0.10% or less Phosphorus (P) is an impurity. P segregates at grain boundaries and lowers the hot workability and toughness of steel. Therefore, the P content may be 0.10% or less. The P content is preferably 0.03% or less, more preferably 0.02% or less. It is preferable that the P content is as low as possible.
　Ｓ：０．２０％以下
　硫黄（Ｓ）は、鋼の加工性（被削性）を高めるために添加される場合がある。一方、Ｓ含有量が高すぎると、鋼の耐焼割れ性が低下する。したがって、Ｓ含有量は０．２０％以下であってもよい。Ｓ含有量の上限は、好ましくは０．１２％であり、さらに好ましくは０．０８％であり、さらに好ましくは０．０６％である。Ｓによる加工性向上の効果を得る場合には、Ｓ含有量を０．０２０％以上にしてもよい。 S: 0.20% or less Sulfur (S) is sometimes added to improve the workability (machinability) of steel. On the other hand, if the S content is too high, the quench cracking resistance of the steel is lowered. Therefore, the S content may be 0.20% or less. The upper limit of the S content is preferably 0.12%, more preferably 0.08%, still more preferably 0.06%. When obtaining the effect of improving workability by S, the S content may be 0.020% or more.
　Ｃｒ：０～０．５０％
　クロム（Ｃｒ）は、任意元素である。すなわち、本実施形態による摺動部品用鋼材は、Ｃｒを含有していなくてもよい。Ｃｒは、鋼の焼入れ性を高める。Ｃｒが少しでも含有されていれば、この効果が得られる。一方、Ｃｒ含有量が高すぎると、鋼の加工性が低下する。したがって、Ｃｒ含有量は０～０．５０％であってもよい。Ｃｒ含有量の下限は、好ましくは０．０１％であり、さらに好ましくは０．０５％である。Ｃｒ含有量の上限は、好ましくは０．２０％である。 Cr: 0-0.50%
Chromium (Cr) is an optional element. That is, the steel material for sliding parts according to this embodiment does not have to contain Cr. Cr increases the hardenability of steel. This effect can be obtained if even a small amount of Cr is contained. On the other hand, if the Cr content is too high, the workability of the steel deteriorates. Therefore, the Cr content may be 0-0.50%. The lower limit of the Cr content is preferably 0.01%, more preferably 0.05%. The upper limit of Cr content is preferably 0.20%.
　本実施形態による摺動部品用鋼材の化学組成の残部は、Ｆｅ及び不純物であってもよい。ここでいう不純物は、鋼の原料として利用される鉱石やスクラップから混入する元素、あるいは製造過程の環境等から混入する元素をいう。 The rest of the chemical composition of the steel material for sliding parts according to this embodiment may be Fe and impurities. The term "impurities" as used herein refers to elements mixed in from ores and scraps used as raw materials for steel, or elements mixed in from the environment during the manufacturing process.
　本実施形態による摺動部品用鋼材は、機械構造用炭素鋼鋼材又は機械構造用合金鋼鋼材からなるものであってもよい。本実施形態による摺動部品用鋼材は、好ましくは、ＪＩＳ　Ｇ　４０５１：２０１６に規定された機械構造用炭素鋼鋼材、又はＪＩＳ　Ｇ　４０５３：２０１６に規定された機械構造用合金鋼鋼材からなる。そのなかでも、ＪＩＳ　Ｇ　４０５１：２０１６のＳ４５Ｃ、及びＳ５０Ｃ、並びにＪＩＳ　Ｇ　４０５３：２０１６のＳＭｎ４３８が特に好ましい。また、これらの鋼材に、加工性（被削性）向上のために０．２０質量％以下のＳを含有させたものを用いてもよい。 The steel material for sliding parts according to this embodiment may consist of a carbon steel material for machine structural use or an alloy steel material for machine structural use. The steel material for sliding parts according to this embodiment preferably consists of a carbon steel material for machine structural use specified in JIS G 4051:2016 or an alloy steel material for machine structural use specified in JIS G 4053:2016. Among them, S45C and S50C of JIS G 4051:2016 and SMn438 of JIS G 4053:2016 are particularly preferable. In addition, these steel materials may contain 0.20% by mass or less of S in order to improve workability (machinability).
　［組織］
　本実施形態による摺動部品用鋼材の組織は、焼戻しマルテンサイト及びベイナイト（焼戻しがされたベイナイトを含む。以下同じ。）の少なくとも一方と鉄炭化物とを含み、体積分率が、焼戻しマルテンサイトとベイナイトとの合計：８０％以上、鉄炭化物：２．０％以上である。 [Organization]
The structure of the steel material for sliding parts according to the present embodiment includes at least one of tempered martensite and bainite (including tempered bainite; the same applies hereinafter) and iron carbide, and the volume fraction of tempered martensite and Total with bainite: 80% or more, iron carbide: 2.0% or more.
　本実施形態による摺動部品用鋼材の組織は、焼戻しマルテンサイトの体積分率とベイナイトの体積分率との合計が８０％以上である。本実施形態による摺動部品用鋼材の組織は、焼戻しマルテンサイト及びベイナイトの少なくとも一方を含んでいればよい。 In the structure of the steel material for sliding parts according to this embodiment, the sum of the volume fraction of tempered martensite and the volume fraction of bainite is 80% or more. The structure of the steel material for sliding parts according to the present embodiment may contain at least one of tempered martensite and bainite.
　本実施形態では、摺動部品用鋼材に焼戻しをして所定量の鉄炭化物を含んだ組織とすることによって、摺動部品用鋼材の加工性を確保する。これに対し、摺動部品用鋼材の組織を焼入れままの組織（焼入れままマルテンサイトを主体とする組織）にした場合、良好な加工性を確保することが困難になる。本実施形態による摺動部品用鋼材は、焼戻しマルテンサイトを含んでいることが好ましい。 In this embodiment, the steel material for sliding parts is tempered to obtain a structure containing a predetermined amount of iron carbide, thereby ensuring workability of the steel material for sliding parts. On the other hand, if the structure of the steel material for sliding parts is as quenched (structure mainly composed of martensite as quenched), it becomes difficult to ensure good workability. The steel material for sliding parts according to the present embodiment preferably contains tempered martensite.
　焼戻しマルテンサイトの体積分率とベイナイトの体積分率との合計が８０％未満の場合、優れた耐摩耗性を得ることが困難になる。焼戻しマルテンサイトの体積分率とベイナイトの体積分率との合計は、好ましくは８５％以上であり、さらに好ましくは９０％以上であり、さらに好ましくは９５％以上である。 When the sum of the volume fraction of tempered martensite and the volume fraction of bainite is less than 80%, it becomes difficult to obtain excellent wear resistance. The sum of the volume fraction of tempered martensite and the volume fraction of bainite is preferably 85% or more, more preferably 90% or more, and still more preferably 95% or more.
　本実施形態では、組織の体積分率の計算において、鉄炭化物を独立した組織として扱い、鉄炭化物を焼戻しマルテンサイト及びベイナイトから区別する。すなわち、鉄炭化物が析出している部分は、焼戻しマルテンサイト又はベイナイトの体積には含めない。 In this embodiment, in calculating the volume fraction of the structure, iron carbide is treated as an independent structure and iron carbide is distinguished from tempered martensite and bainite. That is, the portion where iron carbide precipitates is not included in the volume of tempered martensite or bainite.
　本実施形態による摺動部品用鋼材の組織は、鉄炭化物の体積分率が２．０％以上である。本実施形態による摺動部品用鋼材の鉄炭化物は、具体的には、ε炭化物及びセメンタイトの少なくとも一つである。摺動部品用鋼材に含まれる鉄炭化物は、一種類であっても複数の種類であってもよい。複数の種類の鉄炭化物が含まれている場合、鉄炭化物の体積分率はそれらの鉄炭化物の体積分率の合計とする。 The structure of the steel material for sliding parts according to this embodiment has a volume fraction of iron carbide of 2.0% or more. Specifically, the iron carbide of the steel material for sliding parts according to the present embodiment is at least one of ε carbide and cementite. The iron carbide contained in the steel material for sliding parts may be of one type or of a plurality of types. When multiple types of iron carbide are included, the volume fraction of iron carbide is the sum of the volume fractions of those iron carbides.
　鉄炭化物の体積分率が２．０％未満であると、優れた耐摩耗性を得ることが困難になる。鉄炭化物の体積分率の下限は、好ましくは３．０％であり、さらに好ましくは５．０％であり、さらに好ましくは７．０％である。鉄炭化物の体積分率の上限は、好ましくは１８．０％であり、さらに好ましくは１５．０％であり、さらに好ましくは１２．０％であり、さらに好ましくは１０．０％であり、さらに好ましくは８．０％である。 When the volume fraction of iron carbide is less than 2.0%, it becomes difficult to obtain excellent wear resistance. The lower limit of the volume fraction of iron carbide is preferably 3.0%, more preferably 5.0%, still more preferably 7.0%. The upper limit of the volume fraction of iron carbide is preferably 18.0%, more preferably 15.0%, still more preferably 12.0%, still more preferably 10.0%, and Preferably it is 8.0%.
　鉄炭化物の体積分率は、鋼材のＣ含有量、及び焼戻しの条件によって調整することができる。具体的には、Ｃ含有量が高いほど、鉄炭化物の体積分率が高くなる傾向がある。また、焼戻しの条件については、保持温度が高く、保持時間が長いほど、鉄炭化物の体積分率が高くなる傾向がある。 The volume fraction of iron carbide can be adjusted by the C content of the steel material and the tempering conditions. Specifically, the higher the C content, the higher the volume fraction of iron carbide. As for tempering conditions, the higher the holding temperature and the longer the holding time, the higher the volume fraction of iron carbide.
　本実施形態による摺動部品用鋼材の組織は、焼戻しマルテンサイト、ベイナイト、及び鉄炭化物以外の組織を少量含んでいても良い。焼戻しマルテンサイト、ベイナイト、及び鉄炭化物以外の組織は例えば、フェライト、パーライト、残留オーステナイト、ＭｎＳ等である。本実施形態による摺動部品用鋼材の組織における、焼戻しマルテンサイト、ベイナイト、及び炭化物以外の組織の体積分率は、好ましくは合計で５．０％以下であり、さらに好ましくは３．０％以下であり、さらに好ましくは２．０％以下であり、さらに好ましくは１．０％以下である。 The structure of the steel material for sliding parts according to this embodiment may contain a small amount of structure other than tempered martensite, bainite, and iron carbide. Structures other than tempered martensite, bainite, and iron carbide are, for example, ferrite, pearlite, retained austenite, MnS, and the like. The total volume fraction of structures other than tempered martensite, bainite, and carbide in the structure of the steel material for sliding parts according to the present embodiment is preferably 5.0% or less, more preferably 3.0% or less. , more preferably 2.0% or less, and still more preferably 1.0% or less.
　［ビッカース硬さ］
　本実施形態による摺動部品用鋼材は、ビッカース硬さが３００以上６００以下である。ビッカース硬さが３００未満であると、優れた耐摩耗性を得ることが困難になる。一方、ビッカース硬さが６００よりも高くなると、加工性が低下する。耐摩耗性の観点からは、ビッカース硬さの下限は、好ましくは３５０であり、さらに好ましくは４００であり、さらに好ましくは４５０であり、さらに好ましくは５００であり、さらに好ましくは５３０である。加工性の観点からは、ビッカース硬さの上限は、好ましくは５８０であり、さらに好ましくは５６０であり、さらに好ましくは５５０であり、さらに好ましくは５３０であり、さらに好ましくは５２０である。 [Vickers hardness]
The steel material for sliding parts according to this embodiment has a Vickers hardness of 300 or more and 600 or less. If the Vickers hardness is less than 300, it becomes difficult to obtain excellent wear resistance. On the other hand, when the Vickers hardness is higher than 600, workability is lowered. From the viewpoint of wear resistance, the lower limit of the Vickers hardness is preferably 350, more preferably 400, still more preferably 450, more preferably 500, still more preferably 530. From the viewpoint of workability, the upper limit of the Vickers hardness is preferably 580, more preferably 560, still more preferably 550, still more preferably 530, still more preferably 520.
　摺動部品用鋼材のビッカース硬さは、鋼材のＣ含有量、焼入れの条件、及び焼戻しの条件によって調整することができる。具体的には、Ｃ含有量が高いほど、ビッカース硬さが高くなる傾向がある。焼入れの条件については、冷却速度が大きいほど、ビッカース硬さが高くなる傾向がある。また、焼戻しの条件については、保持温度が低く、保持時間が短いほど、ビッカース硬さが高くなる傾向がある。 The Vickers hardness of the steel material for sliding parts can be adjusted by the C content of the steel material, the quenching conditions, and the tempering conditions. Specifically, the higher the C content, the higher the Vickers hardness tends to be. As for the quenching conditions, the higher the cooling rate, the higher the Vickers hardness tends to be. As for the tempering conditions, the lower the holding temperature and the shorter the holding time, the higher the Vickers hardness tends to be.
　［関係式（１）］
　本実施形態による摺動部品用鋼材は、鉄炭化物の体積分率Ｘと鋼材のビッカース硬さＨｖとが、下記の関係式（１）を満たす。関係式（１）を満たすことによって、優れた耐摩耗性が得られる。
　　Ｘ≧－０．０６５×Ｈｖ＋３６．５　　　（１）
　Ｘの単位は％であり、Ｈｖの単位はＨｖである。 [Relational expression (1)]
In the steel material for sliding parts according to the present embodiment, the volume fraction X of iron carbide and the Vickers hardness Hv of the steel material satisfy the following relational expression (1). Excellent wear resistance can be obtained by satisfying the relational expression (1).
X≧−0.065×Hv+36.5 (1)
The unit of X is % and the unit of Hv is Hv.
　［その他］
　本実施形態による摺動部品用鋼材は、好ましくは、鉄炭化物の平均短軸長さが０．０２７μｍ以下である。このような形状の鉄炭化物を分散させることで、鋼材全体の硬さを保つことができる。鉄炭化物が大きすぎると、基地の柔らかさの影響が大きくなり、耐摩耗性が低下する場合がある。鉄炭化物の平均短軸長さは、好ましくは０．０２５μｍ以下である。 [others]
In the steel material for sliding parts according to the present embodiment, the average minor axis length of the iron carbide is preferably 0.027 μm or less. By dispersing the iron carbides having such a shape, the hardness of the entire steel material can be maintained. If the iron carbide is too large, the influence of the softness of the matrix increases, and wear resistance may decrease. The average minor axis length of the iron carbide is preferably 0.025 μm or less.
　本実施形態による摺動部品用鋼材は、表面に窒化層、浸炭層及び浸炭窒化層のいずれをも有さないことが好ましい。 The steel material for sliding parts according to this embodiment preferably has no nitrided layer, carburized layer, or carbonitrided layer on the surface.
　本実施形態による摺動部品用鋼材は、表面のビッカース硬さが３００以上６００以下であり、表面における鉄炭化物の体積分率Ｘとビッカース硬さＨｖとが、上述した関係式（１）を満たすことが好ましい。 The steel material for sliding parts according to the present embodiment has a surface Vickers hardness of 300 or more and 600 or less, and the volume fraction X of iron carbide on the surface and the Vickers hardness Hv satisfy the above-described relational expression (1). is preferred.
　上記において、「表面のビッカース硬さ」は、より具体的には、摺動部品用鋼材の表面から深さ１００μｍ以下の領域のビッカース硬さを意味する。「表面における鉄炭化物の体積分率」はより具体的には、摺動部品用鋼材の表面から深さ１００μｍ以下の領域の組織における鉄炭化物の体積分率を意味する。 In the above, the "surface Vickers hardness" more specifically means the Vickers hardness of a region at a depth of 100 μm or less from the surface of the steel material for sliding parts. "The volume fraction of iron carbide on the surface" more specifically means the volume fraction of iron carbide in the structure of the region at a depth of 100 µm or less from the surface of the steel material for sliding parts.
　［摺動部品用鋼材の製造方法］
　以下、本実施形態による摺動部品用鋼材の製造方法を説明する。 [Manufacturing method of steel material for sliding parts]
A method for manufacturing a steel material for sliding parts according to this embodiment will be described below.
　上述した化学組成を有する素材を準備する。素材は例えば、熱間鍛造品である。例えば、上述した化学組成を有する鋼を溶製し、連続鋳造又は分塊圧延を実施して鋼片にした後、鋼片を熱間鍛造して摺動部品の粗形状に加工したものを素材とすることができる。熱間鍛造後の素材に切削加工等を施してもよい。 Prepare a material that has the chemical composition described above. The material is, for example, a hot forged product. For example, the steel having the above-described chemical composition is melted, continuous casting or blooming rolling is performed to make a steel slab, and the steel slab is hot forged and processed into a rough shape for sliding parts. can be Cutting or the like may be applied to the material after hot forging.
　素材を８３０℃以上１１００℃以下の温度に保持した後、保持温度から３００℃までの冷却速度が３００℃／秒以上になるように冷却して焼入れする。保持温度が低すぎると、均一な組織が得られない場合がある。一方、保持温度が高すぎると、結晶粒が粗大化する場合がある。冷却速度が小さすぎると、所定の組織が得られない場合がある。なお、焼入れ工程での冷却速度を大きくするほど、最終的に得られる摺動部品用鋼材のビッカース硬さが高くなる傾向がある。 After holding the material at a temperature of 830°C or higher and 1100°C or lower, it is cooled and quenched so that the cooling rate from the holding temperature to 300°C is 300°C/second or more. If the holding temperature is too low, a uniform texture may not be obtained. On the other hand, if the holding temperature is too high, the crystal grains may become coarse. If the cooling rate is too low, the desired structure may not be obtained. Note that the Vickers hardness of the finally obtained steel material for sliding parts tends to increase as the cooling rate in the quenching process increases.
　焼入れされた素材を２００℃以上６００℃以下の温度に保持して焼戻しをする。焼戻しの保持温度が高く、保持時間が長いほど、最終的に得られる摺動部品用鋼材のビッカース硬さが低くなる傾向がある。また、焼戻しの保持温度が高く、保持時間が長いほど、最終的に得られる摺動部品用鋼材の組織における鉄炭化物の体積分率が高くなる傾向がある。焼戻しの保持温度がこの範囲から外れると、鉄炭化物の体積分率及びビッカース硬さを所定の範囲にすることが困難になる。鋼材の化学組成等に応じて焼入れ及び焼戻しの条件を調整し、鉄炭化物の体積分率Ｘとビッカース硬さＨｖとが関係式（１）を満たすようにする。これによって、本実施形態による摺動部品用鋼材が得られる。 The quenched material is tempered while being held at a temperature of 200°C or higher and 600°C or lower. The higher the holding temperature and the longer the holding time of tempering, the lower the Vickers hardness of the finally obtained steel material for sliding parts. Also, the higher the holding temperature and the longer the holding time of tempering, the higher the volume fraction of iron carbide in the structure of the finally obtained steel material for sliding parts. If the holding temperature for tempering is out of this range, it becomes difficult to keep the volume fraction of iron carbide and the Vickers hardness within the predetermined ranges. The conditions for quenching and tempering are adjusted according to the chemical composition of the steel material, so that the volume fraction X of iron carbide and the Vickers hardness Hv satisfy the relational expression (1). As a result, the steel material for sliding parts according to the present embodiment is obtained.
　以上、本発明の一実施形態による摺動部品用鋼材を説明した。本実施形態による摺動部品用鋼材は、優れた摺動性及び加工性を備える。そのため、本実施形態による摺動部品用鋼材は、摺動部品の材料として好適である。摺動部品は例えば、クランクシャフトである。 The steel material for sliding parts according to one embodiment of the present invention has been described above. The steel material for sliding parts according to this embodiment has excellent slidability and workability. Therefore, the steel material for sliding parts according to this embodiment is suitable as a material for sliding parts. A sliding part is, for example, a crankshaft.
　以下、実施例によって本発明をより具体的に説明する。本発明はこれらの実施例に限定されない。 The present invention will be described in more detail below with reference to examples. The invention is not limited to these examples.
　表１に示す化学組成を有する鋼を１０ｋｇ真空誘導溶解炉によって溶製し、インゴットを作製した。 A 10 kg steel having the chemical composition shown in Table 1 was melted in a vacuum induction melting furnace to produce an ingot.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　このインゴットを９５０～１２００℃で熱間鍛造し、厚さ３０ｍｍ、幅１００ｍｍ、長さ２９０ｍｍにした後、厚さ７ｍｍ、幅１１０ｍｍまで圧延した。圧延した材料を幅１５ｍｍ、長さ６０～１２０ｍｍ、厚さ７ｍｍに切断し、表２に記載の熱処理を行った。なお、熱処理前の組織は、いずれもフェライト・パーライト（Ｆ＋Ｐ）であった。表２の「焼入れ」の「冷却速度」の欄の数値は、焼入れの保持温度から３００℃までの冷却速度である。 This ingot was hot forged at 950-1200°C to a thickness of 30 mm, a width of 100 mm and a length of 290 mm, and then rolled to a thickness of 7 mm and a width of 110 mm. The rolled material was cut into pieces having a width of 15 mm, a length of 60-120 mm, and a thickness of 7 mm, and subjected to the heat treatment shown in Table 2. The structures before the heat treatment were all ferrite/pearlite (F+P). The numerical values in the "cooling rate" column of "quenching" in Table 2 are the cooling rates from the holding temperature of quenching to 300°C.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　熱処理後、それぞれの材料から２０ｍｍ角、厚さ２ｍｍの試験片を複数採取した。これらの試験片を用いて組織の観察、ビッカース硬さの測定、及び摺動性の評価を行った。 After the heat treatment, multiple 20 mm square and 2 mm thick test pieces were taken from each material. Observation of the structure, measurement of Vickers hardness, and evaluation of slidability were performed using these test pieces.
　組織観察用の試験片は、Ａｒイオンミリングで表面を加工した。Ａｒイオンビームを試料に対し垂直方向から角度８０°以上で照射することで、鉄炭化物に比べて軟質な鉄基地は削れ、鉄炭化物は凸として残るため、原子間力顕微鏡（ＡＦＭ）による鉄炭化物の探索が可能になる。ＡＦＭで取得した加工済みの試験片の表面凹凸像の一例を図５に示す。白色が凸部、黒色が凹部を示す。図５の白色の部分が鉄炭化物である。 The surface of the specimen for tissue observation was processed by Ar ion milling. By irradiating the sample with an Ar ion beam at an angle of 80° or more from the vertical direction, the iron matrix, which is softer than the iron carbide, is scraped away, leaving the iron carbide as a convex. can be explored. FIG. 5 shows an example of a surface unevenness image of a processed test piece obtained by AFM. White indicates convex portions, and black indicates concave portions. White portions in FIG. 5 are iron carbides.
　鉄炭化物の体積分率は、試験片の３箇所でＡＦＭによって２μｍ×２μｍの範囲で凹凸像を取得し、画像解析ソフトウェアを用いて算出した。画像解析ソフトウェアはＩｍａｇｅＪを使用した。画像解析ソフトウェアによって粒径が検出できるように画像のコントラストや解像度を調整した後に二値化し、画像解析ソフトウェアの粒子解析機能を使って粒子を検出した。画像解析ソフトウェアで検出した鉄炭化物の一例を図６に示す。観察した３箇所のそれぞれで鉄炭化物の面積率を算出し、それらの平均を求めた。得られた面積率を鉄炭化物の体積分率とみなした。 The volume fraction of iron carbide was calculated using image analysis software after acquiring uneven images in the range of 2 μm × 2 μm by AFM at three locations on the test piece. ImageJ was used as image analysis software. After adjusting the contrast and resolution of the image so that the particle size can be detected by the image analysis software, the image was binarized and the particles were detected using the particle analysis function of the image analysis software. An example of iron carbide detected by image analysis software is shown in FIG. The area ratio of iron carbide was calculated at each of the three observed locations, and the average was obtained. The obtained area ratio was regarded as the volume fraction of iron carbide.
　フェライトの体積分率は、ＳＥＭの二次電子像（凹凸像）を使って算出した。試料表面をナイタール腐食し、フェライトのみを腐食させて凹にさせた後、倍率１０００倍で二次電子像を取得した。取得した像を画像解析ソフトウェアＩｍａｇｅＪに取り込み、Ｆｒｅｅｈａｎｄ　ｓｅｌｅｃｔｉｏｎやＰｏｌｙｇｏｎ　ｓｅｌｅｃｔｉｏｎ機能を使って該当領域を選択し、選択箇所をマスキングし、鉄炭化物のときと同様に二値化を行い、画像解析ソフトウェアの粒子解析機能を使って該当領域を検出した。観察した３箇所のそれぞれでフェライトの面積率を算出し、それらの平均を求めた。得られた面積率をフェライトの体積分率とみなした。 The volume fraction of ferrite was calculated using a secondary electron image (unevenness image) of SEM. The surface of the sample was nital-etched to corrode only the ferrite to form a recess, and then a secondary electron image was obtained at a magnification of 1000 times. The acquired image is imported into the image analysis software ImageJ, the relevant area is selected using the freehand selection or polygon selection function, the selected area is masked, binarization is performed in the same way as for iron carbide, and the particles of the image analysis software The relevant regions were detected using the analysis function. The area ratio of ferrite was calculated at each of the three observed points, and the average was obtained. The obtained area ratio was regarded as the volume fraction of ferrite.
　残留オーステナイトの体積分率は、Ｘ線回折によって測定した。ＭｎＳの体積分率は、試験片の表面を光学顕微鏡（倍率：２１０倍、視野の大きさ：１２１８μｍ×１２１８μｍ）で撮影してＭｎＳの面積率を求め、この面積率を体積分率とみなした。焼戻しマルテンサイトの体積分率とベイナイトの体積分率との合計（又はマルテンサイトの体積分率とベイナイトの体積分率との合計）は、鉄炭化物、残留オーステナイト、フェライト、及びＭｎＳの体積分率の和を１００％から引いて求めた。 The volume fraction of retained austenite was measured by X-ray diffraction. The volume fraction of MnS was obtained by photographing the surface of the test piece with an optical microscope (magnification: 210 times, size of field of view: 1218 μm × 1218 μm) to determine the area ratio of MnS, and this area ratio was regarded as the volume fraction. . The sum of the volume fraction of tempered martensite and the volume fraction of bainite (or the sum of the volume fraction of martensite and the volume fraction of bainite) is the volume fraction of iron carbide, retained austenite, ferrite, and MnS. It was obtained by subtracting the sum of from 100%.
　鉄炭化物の形態は、鉄炭化物の体積分率を求める際に取得した凹凸像から画像解析によって求めた。具体的には、画像を二値化し、画像解析ソフトウェアの粒子解析機能を使って各観察視野内のすべての粒子を楕円近似した。観察した３箇所のそれぞれで平均短軸長さ及び平均長軸長さを求め、それらの平均を求めた。 The morphology of the iron carbide was determined by image analysis from the uneven image obtained when determining the volume fraction of the iron carbide. Specifically, the images were binarized, and all particles within each observation field were elliptically approximated using the particle analysis function of the image analysis software. An average minor axis length and an average major axis length were obtained at each of the three observed points, and the average thereof was obtained.
　ビッカース硬さは、試験力１ｋｇｆ（９．８０７Ｎ）で５点測定し、その平均を求めた。 The Vickers hardness was measured at 5 points with a test force of 1 kgf (9.807 N), and the average was obtained.
　各鋼材の熱処理後の組織及びビッカース硬さを表３に示す。表３の組織の体積分率の欄の「Ｍ」は焼入れままマルテンサイト、「Ｂ」はベイナイト、「ＴＭ」は焼戻しマルテンサイト、「残留γ」は残留オーステナイトを表す。 Table 3 shows the structure and Vickers hardness of each steel material after heat treatment. In the volume fraction column of the structure in Table 3, "M" represents as-quenched martensite, "B" represents bainite, "TM" represents tempered martensite, and "retained γ" represents retained austenite.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　摺動試験用の試験片の表面は鏡面仕上げとした。摺動試験は、ボール・オン・ディスク型摩擦摩耗試験機によって行った。図７に試験機の概略図を示す。ボールはアルミナ製のものを使用し、荷重を１０Ｎ、摺動速度を１０ｍｍ／秒とした。摺動試験後、摺動痕の幅を測定し、摺動痕幅の平均値が１６０μｍ以下であれば耐摩耗性が「良」であると評価し、１６０μｍを超えていれば耐摩耗性が「不可」であると評価した。 The surface of the specimen for the sliding test was mirror-finished. The sliding test was performed using a ball-on-disk type friction wear tester. FIG. 7 shows a schematic diagram of the test machine. Alumina balls were used, the load was 10 N, and the sliding speed was 10 mm/sec. After the sliding test, the width of the sliding marks was measured, and if the average value of the sliding mark width was 160 μm or less, the wear resistance was evaluated as “good”, and if it exceeded 160 μm, the wear resistance was poor. It was rated as "impossible".
　各鋼材のビッカース硬さ、炭化物（鉄炭化物）の体積分率、及び摺動試験の結果を表４に示す。加工性は、ビッカース硬さが６００以下であれば「良」、６００を超えていれば「不可」と評価した。総合評価は、加工性及び耐摩耗性の両方が「良」であるものを「合格」とし、加工性及び耐摩耗性のいずれかが「不可」であるものを「不可」とした。 Table 4 shows the Vickers hardness of each steel material, the volume fraction of carbides (iron carbides), and the results of the sliding test. The workability was evaluated as "good" if the Vickers hardness was 600 or less, and as "poor" if it exceeded 600. In the comprehensive evaluation, samples with "good" workability and wear resistance were rated as "acceptable", and samples with either "poor" workability or wear resistance were rated as "fail".
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　表４に示すように、Ｎｏ．４～７、９、１０及び１４～１７の鋼材は、ビッカース硬さが３００～６００であり、鉄炭化物の体積分率Ｘとビッカース硬さＨｖとが、関係式（１）を充足した。これらの試験材は、摺動試験後の摩耗痕幅が１６０μｍ以下であり、優れた耐摩耗性を示した。また、これらの試験材は、ビッカース硬さＨｖが６００以下であり、加工性にも優れていた。 As shown in Table 4, No. The steel materials of 4 to 7, 9, 10 and 14 to 17 have a Vickers hardness of 300 to 600, and the volume fraction X of iron carbide and the Vickers hardness Hv satisfy the relational expression (1). These test materials had a wear scar width of 160 μm or less after the sliding test, indicating excellent wear resistance. Moreover, these test materials had a Vickers hardness Hv of 600 or less and were excellent in workability.
　Ｎｏ．１～３、８、１２、及び１３の鋼材は、摺動試験後の摩耗痕幅が１６０μｍを超えていた。これは、鉄炭化物の体積分率Ｘとビッカース硬さＨｖとが、関係式（１）を充足しなかったためと考えられる。 　No. Steel materials Nos. 1 to 3, 8, 12, and 13 had a wear scar width exceeding 160 μm after the sliding test. This is probably because the volume fraction X of the iron carbide and the Vickers hardness Hv did not satisfy the relational expression (1).
　Ｎｏ．１１の鋼材は組織を焼入れままの組織としたものである。Ｎｏ．１１の鋼材は、耐摩耗性は良好であったが、ビッカース硬さＨｖが６００を超えており、加工性が劣っていた。 　No. The steel material No. 11 has the structure as quenched. No. The steel material No. 11 had good wear resistance, but had a Vickers hardness Hv exceeding 600 and was inferior in workability.
　図３は、鋼材のビッカース硬さと鉄炭化物の体積分率との関係を示す散布図である。図４は、鋼材のビッカース硬さと、ボール・オン・ディスク型摩擦摩耗試験による摺動試験よって得られた摩耗痕幅との関係を示すグラフである。図３及び図４において、鉄炭化物の体積分率Ｘと鋼材のビッカース硬さＨｖとが、関係式（１）を充足しているものを白抜きの丸のシンボル、関係式（１）を充足していないものを中実の丸のシンボルで示している。図４における三角のシンボルは、組織を焼入れままの組織とした鋼材（Ｎｏ．１１）のものである。図３及び図４から、鉄炭化物の体積分率Ｘと鋼材のビッカース硬さＨｖとが関係式（１）を満たせば、優れた耐摩耗性を得られることが分かる。 Fig. 3 is a scatter diagram showing the relationship between the Vickers hardness of steel and the volume fraction of iron carbide. FIG. 4 is a graph showing the relationship between the Vickers hardness of steel and the wear scar width obtained by a sliding test using a ball-on-disk type friction wear test. 3 and 4, the volume fraction X of the iron carbide and the Vickers hardness Hv of the steel material satisfy the relational expression (1) by the white circle symbol, and the relational expression (1) is satisfied. Those that are not are indicated by a solid circle symbol. The triangular symbols in FIG. 4 are for the steel material (No. 11) with the as-quenched structure. From FIGS. 3 and 4, it can be seen that excellent wear resistance can be obtained if the volume fraction X of iron carbide and the Vickers hardness Hv of the steel material satisfy the relational expression (1).
　以上、本発明の一実施形態を説明したが、上述した実施形態は本発明を実施するための例示に過ぎない。よって、本発明は上述した実施形態に限定されることなく、その趣旨を逸脱しない範囲内で上述した実施形態を適宜変形して実施することが可能である。 Although one embodiment of the present invention has been described above, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the scope of the invention.

Claims (7)

  1. 　Ｃ含有量が０．３０～０．６０質量％である鋼材からなる摺動部品用鋼材であって、
    　組織が、焼戻しマルテンサイト及びベイナイトの少なくとも一方と鉄炭化物とを含み、体積分率が、前記焼戻しマルテンサイトと前記ベイナイトとの合計：８０％以上、前記鉄炭化物：２．０％以上であり、
    　ビッカース硬さが３００以上６００以下であり、
    　前記鉄炭化物の体積分率Ｘと前記ビッカース硬さＨｖとが、下記の関係式（１）を満たす、摺動部品用鋼材。
    　　Ｘ≧－０．０６５×Ｈｖ＋３６．５　　　（１）
    　Ｘの単位は％であり、Ｈｖの単位はＨｖである。     A steel material for sliding parts made of a steel material having a C content of 0.30 to 0.60% by mass,
    The structure contains at least one of tempered martensite and bainite and iron carbide, and the volume fraction is a total of the tempered martensite and the bainite: 80% or more, the iron carbide: 2.0% or more,
    Vickers hardness is 300 or more and 600 or less,
    A steel material for sliding parts, wherein the volume fraction X of the iron carbide and the Vickers hardness Hv satisfy the following relational expression (1).
    X≧−0.065×Hv+36.5 (1)
    The unit of X is % and the unit of Hv is Hv.
  2. 　請求項１に記載の摺動部品用鋼材であって、
    　前記鋼材の化学組成が、質量％で、
    　Ｃ　：０．３０～０．６０％、
    　Ｓｉ：０．０１～２．００％、
    　Ｍｎ：０．１０～２．００％、
    　Ａｌ：０．０６０％以下、
    　Ｎ　：０．０２０％以下、
    　Ｐ　：０．１０％以下、
    　Ｓ　：０．２０％以下、
    　Ｃｒ：０～０．５０％、
    　残部：Ｆｅ及び不純物である、摺動部品用鋼材。     The steel material for sliding parts according to claim 1,
    The chemical composition of the steel material is, in mass%,
    C: 0.30 to 0.60%,
    Si: 0.01 to 2.00%,
    Mn: 0.10 to 2.00%,
    Al: 0.060% or less,
    N: 0.020% or less,
    P: 0.10% or less,
    S: 0.20% or less,
    Cr: 0 to 0.50%,
    Remainder: Steel material for sliding parts, which is Fe and impurities.
  3. 　請求項１又は２に記載の摺動部品用鋼材であって、
    　前記鉄炭化物の平均短軸長さが０．０２７μｍ以下である、摺動部品用鋼材。     The steel material for sliding parts according to claim 1 or 2,
    A steel material for sliding parts, wherein the iron carbide has an average minor axis length of 0.027 μm or less.
  4. 　請求項１又は２に記載の摺動部品用鋼材であって、
    　表面に窒化層、浸炭層及び浸炭窒化層のいずれをも有さない、摺動部品用鋼材。     The steel material for sliding parts according to claim 1 or 2,
    A steel material for sliding parts having no nitrided layer, carburized layer or carbonitrided layer on its surface.
  5. 　請求項１又は２に記載の摺動部品用鋼材であって、
    　表面のビッカース硬さが３００以上６００以下であり、表面における前記鉄炭化物の体積分率Ｘと前記ビッカース硬さＨｖとが、前記関係式（１）を満たす、摺動部品用鋼材。     The steel material for sliding parts according to claim 1 or 2,
    A steel material for sliding parts, wherein the Vickers hardness of the surface is 300 or more and 600 or less, and the volume fraction X of the iron carbide on the surface and the Vickers hardness Hv satisfy the relational expression (1).
  6. 　請求項１又は２に記載の摺動部品用鋼材であって、
    　前記ビッカース硬さが３００以上５５０以下である、摺動部品用鋼材。     The steel material for sliding parts according to claim 1 or 2,
    A steel material for sliding parts, wherein the Vickers hardness is 300 or more and 550 or less.
  7. 　請求項１又は２に記載の摺動部品用鋼材の製造方法であって、
    　素材を８３０℃以上１１００℃以下の温度に保持した後、保持温度から３００℃までの冷却速度が３００℃／秒以上になるように冷却して焼入れする工程と、
    　前記焼入れされた素材を２００℃以上６００℃以下の温度に保持して焼戻しをする工程とを備える、摺動部品用鋼材の製造方法。     A method for manufacturing a steel material for sliding parts according to claim 1 or 2,
    A step of holding the material at a temperature of 830° C. or more and 1100° C. or less, and then cooling and quenching the material so that the cooling rate from the holding temperature to 300° C. is 300° C./sec or more;
    and tempering the quenched material at a temperature of 200° C. or more and 600° C. or less.
PCT/JP2022/039894 2021-11-08 2022-10-26 Steel material for sliding components and production method for steel material for sliding components WO2023080029A1 (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2006009145A (en) * 2004-05-24 2006-01-12 Komatsu Ltd Rolling member and production method thereof
JP2007308772A (en) * 2006-05-19 2007-11-29 Kobe Steel Ltd Carburized parts and manufacturing method therefor
JP2011084784A (en) * 2009-10-16 2011-04-28 National Institute For Materials Science Steel to be worm-worked
JP2017061747A (en) * 2015-09-25 2017-03-30 新日鐵住金株式会社 Steel, steel materials and slide component, and method for producing steel materials
WO2022065425A1 (en) * 2020-09-28 2022-03-31 日本製鉄株式会社 Crankshaft

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2006009145A (en) * 2004-05-24 2006-01-12 Komatsu Ltd Rolling member and production method thereof
JP2007308772A (en) * 2006-05-19 2007-11-29 Kobe Steel Ltd Carburized parts and manufacturing method therefor
JP2011084784A (en) * 2009-10-16 2011-04-28 National Institute For Materials Science Steel to be worm-worked
JP2017061747A (en) * 2015-09-25 2017-03-30 新日鐵住金株式会社 Steel, steel materials and slide component, and method for producing steel materials
WO2022065425A1 (en) * 2020-09-28 2022-03-31 日本製鉄株式会社 Crankshaft

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