WO2013058131A1 - 軸受鋼とその製造方法 - Google Patents
軸受鋼とその製造方法 Download PDFInfo
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- C22C—ALLOYS
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/01—Continuous casting of metals, i.e. casting in indefinite lengths without moulds, e.g. on molten surfaces
- B22D11/015—Continuous casting of metals, i.e. casting in indefinite lengths without moulds, e.g. on molten surfaces using magnetic field for conformation, i.e. the metal is not in contact with a mould
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- B22D27/02—Use of electric or magnetic effects
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
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- C21C7/0645—Agents used for dephosphorising or desulfurising
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- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/30—Parts of ball or roller bearings
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- F16C2300/00—Application independent of particular apparatuses
- F16C2300/02—General use or purpose, i.e. no use, purpose, special adaptation or modification indicated or a wide variety of uses mentioned
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- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/30—Parts of ball or roller bearings
- F16C33/58—Raceways; Race rings
- F16C33/62—Selection of substances
Definitions
- a method for producing a bearing steel according to an embodiment of the present invention includes an Al deoxidation step of deoxidizing molten steel using Al; and the molten steel after the Al deoxidation step using Rare Earth Metal.
- C 0.9% to 1.5%
- C (carbon) is an element that secures hardness during quenching to improve fatigue life, and is an element that improves strength by dispersing spherical carbides and martensitic transformation of the matrix.
- the C content needs to be 0.9% or more.
- the C content is set to 0.9% to 1.5%. More preferably, the lower limit value of the C content is 1.0% and the upper limit value is 1.2%.
- Mn 0.1% to 1.5%
- Mn manganese
- Mn manganese
- the Mn content must be 0.1% or more.
- the Mn content is set to 0.1% to 1.5%. More preferably, the lower limit value of the Mn content is 0.2% and the upper limit value is 1.15%. Most preferably, the lower limit of Mn content is more than 0.5% and the upper limit is 1.15%.
- Cr 0.5% to 2.0%
- Cr chromium
- the Cr content must be 0.5% or more.
- the Cr content is set to 0.5% to 2.0%. More preferably, the lower limit of Cr content is 0.9% and the upper limit is 1.6%. Most preferably, the lower limit of Cr content is more than 1.0% and the upper limit is less than 1.6%.
- O 0.0001% to 0.0030%
- O oxygen
- the O content needs to be 0.0001% or more.
- the O content is the total oxygen (TO) which is the sum of oxygen dissolved in steel and oxygen contained in the REM-Ca-Al-O-S composite oxysulfide or Al 2 O 3. : Total Oxygen).
- the Ti content has to be 0.001% or less.
- the Ti content is contained more than the conventional knowledge level due to the effect of the REM-Ca-Al-OS composite oxysulfide.
- the fatigue characteristics are good.
- the Ti content is limited to less than 0.005%, it becomes possible to stably produce bearing steel with good fatigue characteristics.
- the limit range of the Ti content is preferably more than 0.0002% and less than 0.005%. From the viewpoint of steelmaking cost, it is more preferable that the limit range of the Ti content is more than 0.001% and less than 0.005%. Under normal operating conditions, Ti is unavoidably contained in an amount of about 0.003%.
- N 0.015% or less
- nitrogen is an impurity, and is an element that forms nitrides and deteriorates fatigue characteristics, and also adversely affects ductility and toughness by strain aging.
- the N content exceeds 0.015%, the above-described adverse effects become remarkable. Therefore, the N content is limited to 0.015% or less.
- the limit range of the P content is preferably 0.0005% to 0.03%. More preferably, the limit range of the P content is 0.0005% to 0.02%.
- S 0.05% or less
- S sulfur
- S is an impurity and is an element that forms sulfides.
- S content exceeds 0.05%, the effect of immobilizing S of REM and Ca contained in the REM-Ca-Al-O-S composite oxysulfide becomes insufficient, and as D in FIG. Coarse MnS as shown is formed and the fatigue life is impaired. Therefore, it is necessary to limit the S content to 0.05% or less.
- the above is the basic components (basic elements) of steel in this embodiment.
- the above basic elements are contained or limited, and the balance consists of iron and inevitable impurities.
- the following selective elements may be contained in the steel as necessary.
- the effect in the present embodiment is not impaired.
- V 0.05% to 0.70%
- V is an element that generates carbide, nitride, and carbonitride.
- V fine V carbides, nitrides and carbonitrides having an equivalent circle diameter of less than 0.2 ⁇ m are produced, improving the temper softening resistance, increasing the yield point, and refining the prior austenite, etc. It has the effect of.
- the precipitates can be sufficiently precipitated to increase the hardness and the tensile strength.
- the V content is preferably 0.05% to 0.70%. If the V content is less than 0.05%, the above effect cannot be obtained. More preferably, the lower limit of the V content is 0.10%. Even if V less than the lower limit is contained in the steel, the effect in the present embodiment is not impaired. Moreover, in order to reduce the alloy cost, it is not necessary to intentionally add this selective element into the steel, so the lower limit may be set to 0%.
- the upper limit value of the V content is preferably 0.70%.
- the upper limit value of the V content is preferably 0.50%, or more preferably 0.30% or less.
- the temperature at which the Mo-containing carbide precipitates is lower than that of the V-containing carbide.
- Mo-containing carbides are effective in improving the above properties. Therefore, the lower limit of the Mo content is preferably 0.05%. More preferably, the lower limit of the Mo content is 0.10%.
- the lower limit may be set to 0%.
- the Mo content exceeds 1.00%, a supercooled structure is likely to occur during hot rolling or cooling after heat treatment before processing.
- the supercooled structure causes cracks during setting and processing. Therefore, it is preferable to set the upper limit of the Mo content to 1.00%. More preferably, the upper limit of the Mo content is 0.50%.
- the upper limit of the Mo content is preferably 0.20%. Furthermore, in order to precisely control the transformation strain caused by temperature variation during cooling and stabilize the shape accuracy, the upper limit value of the Mo content is preferably set to 0.15%.
- the upper limit value of the W content is preferably 0.20%. Furthermore, in order to precisely control the transformation strain caused by temperature variation during cooling and stabilize the shape accuracy, the upper limit value of the W content is preferably set to 0.15%.
- Ni is an element that suppresses the harmful effects of Cu when coexisting with Cu.
- Cu reduces the hot ductility of steel and often causes cracking and flaws in hot rolling and hot forging.
- Ni when Ni is added simultaneously with Cu, Cu and Ni form an alloy phase to suppress a decrease in hot ductility. Therefore, when Cu is present in the steel, it is preferable to add Ni.
- the Ni content is preferably within the above range, and the content expressed by mass% of Cu and Ni satisfies Cu ⁇ Ni.
- Cu 0.10% to 0.50%
- Cu is an element that improves corrosion resistance and suppresses decarburization.
- the Cu content is preferably 0.10% to 0.50%. If the Cu content is less than 0.10%, the above effect cannot be obtained. Therefore, the lower limit value of the Cu content is preferably 0.10%. More preferably, the lower limit of the Cu content is 0.20%.
- the lower limit may be set to 0%.
- the upper limit value of the Cu content is preferably 0.50%. More preferably, the upper limit value of the Cu content is 0.40%. As described above, it is preferable that the Cu content is within the above range, and the content expressed by mass% of Cu and Ni satisfies Cu ⁇ Ni. As a result, a decrease in hot ductility can be suppressed and the quality of the bearing steel can be maintained well.
- the B content is preferably 0.0005% to 0.0050%. If the B content is less than 0.0005%, the above effect cannot be obtained. Therefore, it is preferable that the lower limit of the B content is 0.0005%. More preferably, the lower limit of the B content is 0.0010%. In addition, even if B of less than a lower limit contains in steel, the effect in this embodiment is not impaired. Moreover, in order to reduce the alloy cost, it is not necessary to intentionally add this selective element into the steel, so the lower limit may be set to 0%.
- the TiN of the REM-Ca-Al-OS-TiN composite oxysulfide is compounded by depositing TiN on the surface of the REM-Ca-Al-OS composite oxysulfide. Represents.
- the TiN present independently of the REM-Ca-Al-O-S composite oxysulfide, which becomes a fracture starting point when repeated stress is applied, is used. It is necessary to reduce the number. Specifically, the number of TiN having a major axis of 5 ⁇ m or more that is independent of the REM-Ca—Al—O—S composite oxysulfide is 0.001 or more and less than 1.0 per 1 mm 2 of the observation surface. Need to be.
- the number of TiNs present independently of the REM-Ca-Al-O-S composite oxysulfide is 1.0 or more per 1 mm 2 of the observation surface, the effect of improving the fatigue properties of the bearing steel is not sufficient.
- the number of TiN present independently of the REM-Ca-Al-O-S composite oxysulfide is smaller.
- the number of TiNs present independently of the REM-Ca-Al-O-S composite oxysulfide was set to 0.001 or more and less than 1.0 per 1 mm 2 of the observation surface.
- the number of TiNs present independently of the complex oxysulfide is 0.001 or more and 0.7 or less, more preferably 0.001 or more and 0.5 or less per 1 mm 2 of the observation surface. It is.
- the presence of inclusions is identified by observing with the above microscope, and composition analysis using EPMA or EDX is performed to identify the types of these inclusions. do it.
- the observation position is, for example, a round bar shape
- the radius when viewed on the observation surface (cross section perpendicular to the longitudinal direction) is r in units of mm, from the surface of the bearing steel (hot work steel) What is necessary is just to observe the area
- the Al content of the REM-Ca-Al-O-S composite oxysulfide is made of Al 2 O 3 It is preferably 10% by mass or less in terms of conversion. Most preferably, the Al content of the REM-Ca-Al-O-S composite oxysulfide is 5% by mass or less in terms of Al 2 O 3 . In order to preferentially precipitate TiN on the REM-Ca-Al-O-S composite oxysulfide, the inclusions must contain 1% by mass or more of Al in terms of Al 2 O 3. Is preferred.
- TiN is complex-deposited using the surface of the REM-Ca-Al-O-S complex oxysulfide as a preferential nucleation site. Then, a REM-Ca-Al-OS-TiN composite oxysulfide is formed. As a result, single precipitation of TiN, which is a hard and pointed square shape, is suppressed.
- this REM-Ca-Al-OS-TiN composite oxysulfide is also a harmless inclusion that has a substantially spherical shape and is unlikely to become a starting point of fracture.
- TiN precipitates together using REM-Ca-Al-O-S composite oxysulfide as a preferential nucleation site is that the crystal lattice structure of REM-Ca-Al-OS composite oxide sulfide and the crystal of TiN This is probably because the lattice structure is similar.
- the REM-Ca-Al-O-S complex oxysulfide immobilizes S, thereby suppressing the formation of coarse MnS. Then, when the REM-Ca-Al-O-S composite oxysulfide is combined with TiN, the number of TiNs precipitated alone in the metal structure is reduced. As a result, fatigue characteristics are improved. However, the precipitation amount of MnS and the precipitation amount of TiN existing independently of the REM-Ca-Al-OS composite oxysulfide contained in the metallographic structure of the bearing steel according to the present embodiment are, of course, Less is ideal but does not need to be reduced to zero.
- MnS drawn with a major axis of 10 ⁇ m or more has a bad influence on fatigue life because it becomes a starting point of fracture when repeated stress is applied. Since all the MnS drawn with a major axis of 10 ⁇ m or more have an adverse effect on fatigue life, there is no upper limit for this major axis.
- TiN having a major axis of 5 ⁇ m or more which exists independently of the REM-Ca—Al—O—S composite oxysulfide, has an adverse effect on fatigue life because its angular shape serves as a starting point for fracture. All TiN having a major axis of 5 ⁇ m or more has an adverse effect on fatigue life, so there is no upper limit for the major axis.
- FIG. 3 shows the total number of MnS having a major axis of 10 ⁇ m or more and REM-Ca—Al—O—S composite oxysulfide independently existing TiN having a major axis of 5 ⁇ m or more (MnS and TiN present alone). ) And the fatigue characteristics (L10 fatigue life) of the bearing steel.
- the total number of MnS and TiN is preferably controlled within the above range. More preferably, the total number is 4 or less per 1 mm 2 of the observation surface. Most preferably, the total number is 3 or less per 1 mm 2 of the observation surface.
- the lower limit of the total number of MnS and TiN is more than 0.001.
- the order in which deoxidizers are charged when refining molten steel is important.
- deoxidation is performed by adding Al to the molten steel whose component composition is adjusted.
- REM is added to the molten steel after the Al deoxidation step as a REM deoxidation step, and deoxidation is performed for 5 minutes to 10 minutes.
- a vacuum degassing treatment may be performed by adding Ca to the molten steel after the REM deoxidation step as a vacuum degassing step.
- Misch metal or the like may be used for the addition of REM, and bulk misch metal may be added to the molten steel at the end of refining. Further, if necessary, a flux such as CaO—CaF 2 may be added to the molten steel after the REM deoxidation step and before the vacuum degassing step to appropriately desulfurize and improve the inclusions. .
- the reason for performing the Al deoxidation step first is that deoxidation using an element other than Al results in high cost.
- the reason for performing the REM deoxidation step after the Al deoxidation step is that Al 2 O 3 produced in the Al deoxidation step and Al—Ca—O composite produced by reacting with Ca inevitably contained in the molten steel This is because the oxide is reacted with REM to reduce the amount remaining in the metal structure.
- the reason for performing deoxidation for 5 minutes or more and 10 minutes or less in the REM deoxidation process is that Al—Ca—O composite oxide remains in less than 5 minutes and cannot be prevented.
- the upper limit value of the deoxidation time in the REM deoxidation step is not particularly limited, but the effect is saturated if it exceeds 10 minutes.
- the reason for performing the flux process after the REM deoxidation process and before the vacuum degassing process is that if the flux is added before the REM, that is, if the flux process is performed before the REM deoxidation process,
- the Al content of the REM-Ca-Al-O-S composite oxysulfide exceeds 20% by mass in terms of Al 2 O 3 , and as a result, the melting point of the composite oxysulfide is lowered and is easily crushed. It is. Since this crushed complex oxysulfide has an adverse effect on fatigue properties as in the case of stretched inclusions, the effect of modifying inclusions by the addition of REM becomes insufficient.
- the molten steel after the REM deoxidation process or the vacuum degassing process is cast to obtain a slab.
- the molten steel is swung in the mold in the horizontal direction at a rate of 0.1 m / min to 0.5 m / min to be cast and solidified.
- REM-Ca-Al-OS composite oxysulfide formed by ladle refining such as Al deoxidation and REM deoxidation described above has a specific gravity of about 6, which is close to the specific gravity of steel, which is 7. Therefore, the REM-Ca-Al-O-S composite oxysulfide is difficult to float and separate in the molten steel, and when the molten steel is injected into the mold, the REM-Ca-Al-O-S composite oxysulfide penetrates deeply into the unsolidified layer of the slab by the downward flow. It tends to segregate at the center of the piece.
- the molten steel in the mold is swirled in the horizontal direction as necessary, and the inclusions can be uniformly dispersed. preferable.
- the REM-Ca-Al-OS complex oxysulfide can be uniformly dispersed.
- the rotational speed in the mold is less than 0.1 m / min, the effect of uniformly dispersing the REM-Ca-Al-O-S composite oxysulfide is small.
- the upper limit of the range of the turning speed assumed under normal conditions is 0.5 m / min.
- electromagnetic force may be applied.
- the slab after the casting step is heated to a temperature range of 1270 ° C. to 1300 ° C., and after this heating, holding is performed for 60 seconds or more in a temperature range of 1200 ° C. to 1250 ° C. .
- the slab cooled to room temperature may be reheated and held, or a slab that has not been cooled to room temperature may be reheated and held.
- heating may be performed for a long time of about 72 hours in a furnace having a temperature range of 1200 ° C. to 1250 ° C., and there is no problem in controlling complex oxysulfides. Therefore, the upper limit value of the holding time in the temperature range of 1200 ° C. to 1250 ° C. is not particularly limited, but this upper limit value may be set to 100 hours in consideration of normal operating conditions.
- the reason for heating to a temperature range of 1270 ° C. to 1300 ° C. is that when the temperature is lower than 1270 ° C., the solution treatment temperature is insufficient, and the REM-Ca—Al—O—S complex acid precipitated during cooling after the casting process. This is because TiN independent of sulfides cannot be dissolved and dissolved. If it exceeds 1300 ° C., expensive equipment is required for heating, and heating costs also increase.
- the reason for holding in the temperature range of 1200 ° C. to 1250 ° C. after the heating is that TiN dissolved by the heating is preferentially complex precipitated on the surface of the REM-Ca—Al—O—S complex oxysulfide. Because. In order to deposit TiN using the surface of the REM-Ca-Al-O-S composite oxysulfide as a preferential nucleation site and to sufficiently grow it, it is necessary to hold for 60 seconds or more. Moreover, industrially, it may be heated for a long time of about 72 hours in order to homogenize the material. Even in this case. There is no problem in controlling complex oxysulfides.
- the slab after the heating and holding step is subjected to plastic working such as hot forging or hot rolling to obtain a hot work steel (bearing steel).
- This hot working is preferably performed in a temperature range of A rm (temperature at which hypercombination steel starts to generate cementite from austenite during cooling) and 1200 ° C. or less. Doing hot working at a temperature below the A rm, plastic workability is deteriorated cementite fraction is increased, also performed at 1200 ° C. greater, leading to excessive use and cost increase of energy for heating Because.
- it is preferable from a viewpoint of cost to use for the hot working process without cooling the slab after a heating holding process.
- it is good also as a product (bearing steel or bearing) which gives a shape to a hot-worked steel material in this hot-working process, and has a final shape.
- the hot-worked steel material after the hot working process is hard, it is preferable to perform a softening heat treatment process in which the hot-worked steel material is subjected to heat treatment such as spheroidizing annealing.
- this softening heat treatment step it is preferable to hold the hot-worked steel material in a temperature range of 700 ° C. to 750 ° C. for 30 hours to 50 hours. When the holding time is less than 30 hours, the softening is insufficient, and when the holding time exceeds 50 hours, the effect is saturated.
- the spheroidization of the carbide proceeds, and the hot-worked steel material can be made into the softened steel material.
- the Al deoxidation process, the REM deoxidation process, and the vacuum degassing to add the flux process or Ca as required are performed in the order shown in Tables 1 to 3.
- the process was applied.
- the numerical value indicated by the underline indicates that it is outside the scope of the present invention.
- Metal Al was used in the Al deoxidation process
- Misch metal was used in the REM deoxidation process
- Ca—Si alloy was used in the vacuum degassing process
- the fatigue characteristics were measured as the L10 fatigue characteristics using the Weibull statistics by measuring the bearing steel by an ultrasonic fatigue test under a load condition of 1000 MPa. The fatigue characteristics were determined to be acceptable when the L10 fatigue characteristics were 10 ⁇ 10 6 times or more. Further, as an evaluation of the mechanical properties, after tempering the bearing steel at 180 ° C., Vickers hardness Hv was measured. Regarding mechanical properties, a case where the 180 ° C. tempering hardness was 600 Hv or more was regarded as acceptable.
- Tables 10-12 The measurement results and evaluation results are shown in Tables 10-12.
- the numerical value indicated by the underline indicates that it is outside the scope of the present invention.
- No. 1-No. 61 is an example of the invention.
- 62-No. 98 is a comparative example.
- Tables 10 to 12 in the invention examples, REM-Ca-Al-O-S composite oxysulfide was combined with TiN (in the table, REM-Ca-Al-OS- (TiN) Al 2 O 3 and Al—Ca—O composite oxide were hardly observed.
- the heating temperature and holding time are below the range of the present invention, and as a result, the number of TiN present independently of the REM-Ca-Al-OS composite oxysulfide is large, and the L10 fatigue characteristics are insufficient. It was. Comparative Example No. In Nos. 67, 68, 73 to 75, and 78 to 98, the additive component is outside the range specified in the present application. As a result, the L10 fatigue characteristics are insufficient, or cracks due to burning and processing occur, and the performance as a bearing cannot be satisfied. Comparative Example No. In No. 69, the amount of REM added exceeded the range of the present invention. Comparative Example No.
- Comparative Example No. No. 71 had a REM deoxidation time that was below the range of the present invention. As a result, the generation rate of oxysulfide was low, the number of stretched sulfides increased, and the L10 fatigue characteristics became insufficient. Comparative Example No. No.
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Abstract
Description
本願は、2011年10月20日に、日本に出願された特願2011-230832号に基づき優先権を主張し、その内容をここに援用する。
(1)本発明の一実施態様に係る軸受鋼は、化学成分が、質量%で、C:0.9%~1.5%、Si:0.1%~0.8%、Mn:0.1%~1.5%、Cr:0.5%~2.0%、Al:0.01%~0.05%、Ca:0.00001%~0.0050%、Rare Earth Metal:0.0001%~0.050%、O:0.0001%~0.0030%、を含有し、Ti:0.005%未満、N:0.015%以下、P:0.03%以下、S:0.05%以下、に制限し、残部が鉄および不可避的不純物からなり、金属組織が、介在物として、Rare Earth Metal、Ca、O、S及びAlを含む複合酸硫化物と、TiNと、MnSと、Al2O3と、Al及びCaを含む複合酸化物と、を含有し、前記介在物の合計個数に対して、前記複合酸硫化物の個数が、50%以上100%未満であり、かつ、長径が5μm以上である前記複合酸硫化物の個数が、観察面1mm2あたり、0.001個以上2個以下であり、前記複合酸硫化物と独立に存在する長径が5μm以上である前記TiNの個数が、観察面1mm2あたり、0.001個以上1.0個未満である。
(2)上記(1)に記載の軸受鋼で、前記化学成分の前記S含有量が、S:0.01%超~0.05%、であるとき、前記Ca含有量を、Ca:0.00050%~0.0050%、としてもよい。
(3)上記(1)又は(2)に記載の軸受鋼で、前記化学成分が、さらに、質量%で、V:0.05%~0.70%、Mo:0.05%~1.00%、W:0.05%~1.00%、Ni:0.10%~3.50%、Cu:0.10%~0.50%、Nb:0.005%~0.050%未満、B:0.0005%~0.0050%、のうち少なくとも1つを含有してもよい。
(4)上記(1)~(3)のいずれか一項に記載の軸受鋼で、前記複合酸硫化物のAl含有量が、Al2O3換算で、20質量%以下であってもよい。
(5)上記(1)~(4)のいずれか一項に記載の軸受鋼で、長径が10μm以上である前記MnSの個数と、前記複合酸硫化物と独立して存在する長径が5μm以上である前記TiNとの個数とが、観察面1mm2あたり、合計で5個以下であってもよい。
(6)上記(1)~(5)のいずれか一項に記載の軸受鋼で、前記Cu及び前記Niの質量%で示した含有量が、Cu≦Niを満足してもよい。
(7)本発明の一実施態様に係る軸受鋼の製造方法は、Alを用いて溶鋼を脱酸するAl脱酸工程と;前記Al脱酸工程後の前記溶鋼を、Rare Earth Metalを用いて5分以上10分以下の脱酸を行うREM脱酸工程と;前記REM脱酸工程後の前記溶鋼を、鋳造して、化学成分が、質量%で、C:0.9%~1.5%、Si:0.1%~0.8%、Mn:0.1%~1.5%、Cr:0.5%~2.0%、Al:0.01%~0.05%、Ca:0.00001%~0.0050%、Rare Earth Metal:0.0001%~0.050%、O:0.0001%~0.0030%、を含有し、Ti:0.005%未満、N:0.015%以下、P:0.03%以下、S:0.05%以下、に制限し、残部が鉄および不可避的不純物からなる鋳片を得る鋳造工程と;前記鋳片を、1270℃~1300℃の温度範囲に加熱して、前記加熱後に、1200℃~1250℃の温度範囲で60秒以上の保持を行う加熱保持工程と;前記加熱保持工程後の前記鋳片を、熱間塑性加工して熱間加工鋼材を得る熱間加工工程と;を有する。
(8)上記(7)に記載の軸受鋼の製造方法で、前記溶鋼の化学成分が、質量%で、S:0.01%超~0.05%、を含有するとき、前記REM脱酸工程後で前記鋳造工程前の前記溶鋼に、Caを添加して真空脱ガス処理を行う真空脱ガス工程をさらに有してもよい。
(9)上記(7)又は(8)に記載の軸受鋼の製造方法で、前記鋳片の前記化学成分が、さらに、質量%で、V:0.05%~0.70%、Mo:0.05%~1.00%、W:0.05%~1.00%、Ni:0.10%~3.50%、Cu:0.10%~0.50%、Nb:0.005%~0.050%未満、B:0.0005%~0.0050%、のうち少なくとも1つを含有してもよい。
(10)上記(7)~(9)のいずれか一項に記載の軸受鋼の製造方法で、前記鋳造工程で、前記溶鋼を鋳型内で水平方向に0.1m/分以上0.5m/分以下で旋回させて鋳造してもよい。
(11)上記(7)~(10)のいずれか一項に記載の軸受鋼の製造方法で、前記熱間加工工程後の前記熱間加工鋼材を、700℃~750℃の温度範囲に加熱して、30時間以上50時間以下保持することで軟質化鋼材を得る軟質化熱処理工程をさらに有してもよい。
(12)上記(7)~(11)のいずれか一項に記載の軸受鋼の製造方法で、前記REM脱酸工程後で前記真空脱ガス工程前の前記溶鋼に、さらに、CaO-CaF2を添加して脱硫を行うフラックス工程を有してもよい。
Al(アルミニウム)は、脱酸元素であり、また、REM-Ca-Al-O-S複合酸硫化物の形成に必要な元素である。これらの効果を得るためには、Al含有量が0.01%以上である必要がある。しかし、Al含有量が0.05%を超えると、Al2O3及びAl-Ca-O複合酸化物が、REM-Ca-Al-O-S複合酸硫化物へ変態しない。これは、Al含有量が0.05%超の場合、REM-Ca-Al-O-S複合酸硫化物よりも、Al2O3及びAl-Ca-O複合酸化物が安定状態になるからだと考えられる。
REM(Rare Earth Metal)は強力な脱硫、脱酸元素であり、本発明の一態様の効果を十分に発揮させるために、極めて重要な元素である。ここで、REMとは、原子番号が57のランタンから71のルテシウムまでの15元素に、原子番号が21のスカンジウムと原子番号が39のイットリウムとを加えた合計17元素の総称である。
C(炭素)は、焼入れ時の硬さを確保して疲労寿命を向上させる元素であり、また、球状炭化物の分散とマトリックスのマルテンサイト変態とにより強度を向上させる元素である。これらの効果を得るためには、C含有量が0.9%以上である必要がある。しかし、C含有量が1.5%を超えると、耐磨耗性は向上するものの、母材の硬さが高くなりすぎて切削時の工具寿命が低下し、また焼割れの原因となる。したがって、C含有量を0.9%~1.5%とする。より好ましくは、C含有量の下限値を1.0%、上限値を1.2%とする。
Si(ケイ素)は、焼入れ性を高めて、疲労寿命を向上させる元素である。これらの効果を得るためには、Si含有量が0.1%以上でなければならない。しかし、Si含有量が0.8%超では、上記効果が飽和し、加えて、母材の硬さが高くなって切削時の工具寿命の低下し、また焼割れの原因となる。したがって、Si含有量を0.1%~0.8%とする。より好ましくは、Si含有量はの下限値を0.15%、上限値を0.7%とする。
Mn(マンガン)は、焼入れ性を高めて強度を高め、疲労寿命を向上させる元素である。これらの効果を得るためには、Mn含有量が0.1%以上でなければならない。しかし、Mn含有量が1.5%超では、上記の焼入れ性向上効果が飽和する。しかも、母材の硬さが高くなって切削時の工具寿命の低下をきたし、更には、焼割れの原因ともなる。したがって、Mn含有量を0.1%~1.5%とする。より好ましくは、Mn含有量の下限値を0.2%、上限値を1.15%とする。最も好ましくは、Mn含有量の下限値を0.5%超、上限値を1.15%とする。
Cr(クロミウム)は、焼入れ性を高めて疲労寿命を向上させる元素である。これらの効果を得るためには、Cr含有量が0.5%以上でなければならない。しかし、Cr含有量が2.0%超では、上記効果が飽和する。しかも、母材の硬さが高くなって切削時の工具寿命の低下をきたし、更には、焼割れの原因ともなる。したがって、Cr含有量を0.5%~2.0%とする。より好ましくは、Cr含有量の下限値を0.9%、上限値を1.6%とする。最も好ましくは、Cr含有量の下限値を1.0%超、上限値を1.6%未満とする。
Ca(カルシウム)は、脱酸元素、及び脱硫元素である。Caは、酸化物を軟質化する作用も有する。快削鋼にCaを添加すると、切削中にベラーグ(Belag)という酸化物被膜が切削熱によって生成し、工具表面を被覆・保護して切削工具寿命を延ばすことが知られている。
O(酸素)は、脱酸により鋼から除去されるべき元素であるものの、REM-Ca-Al-O-S複合酸硫化物を析出させるために必要な元素である。この効果を得るためには、O含有量が0.0001%以上である必要がある。ただし、O含有量が0.0030%を超えると、酸化物が多数残存し、疲労寿命の低下を招く。したがって、O含有量の上限値は0.0030%以下とする。なお、上記O含有量は、鋼中に固溶する酸素と、REM-Ca-Al-O-S複合酸硫化物やAl2O3に含まれる酸素などとを合計したトータル酸素(T.O:Total Oxygen)を意味する。
Ti(チタニウム)は不純物であり、TiC、TiNおよびTiSなどの微細介在物を生成し、疲労特性を劣化させる元素である。特にTiNは、角型形状に析出するため、繰り返し応力が負荷された際に応力集中して、破壊起点になりやすい。よって、この角型形状に析出するTiNを抑制することが非常に重要である。
N(窒素)は不純物であり、窒化物を形成して疲労特性を劣化させ、また、歪時効によって延性および靭性に悪影響を及ぼす元素である。N含有量が0.015%を超えると上記弊害が顕著となる。したがって、N含有量を0.015%以下に制限する。
P(リン)は不純物であり、結晶粒界に偏析して疲労寿命を損ねる元素である。P含有量が0.03%を超えると、疲労寿命の低下が著しくなる。したがって、P含有量を0.03%以下に制限する。
S(硫黄)は不純物であり、硫化物を形成する元素である。S含有量が0.05%を超えると、REM-Ca-Al-O-S複合酸硫化物に含まれるREMとCaとのSを固定化する効果が不十分となり、図2中のDとして示すような粗大なMnSが形成されて、疲労寿命を損ねる。したがって、S含有量を0.05%以下に制限する必要がある。
Vは、炭化物、窒化物、炭窒化物を生成する元素である。Vの添加により、円相当径が0.2μm未満の微細なVの炭化物、窒化物、炭窒化物を生成して、焼戻し軟化抵抗の向上、降伏点の上昇、及び、旧オーステナイトの微細化などの効果を有する。V含有量を多くし、焼戻し時間を延長することで、上記析出物を十分に析出させて、硬度と引張強度とを上昇させることもできる。
Moは、焼入れ性を高める元素であり、また、焼戻し軟化抵抗を向上させる元素である。Moは、鋼中でMo含有炭化物を生成する元素でもある。これらの効果を得るため、Mo含有量を0.05%~1.00%とすることが好ましい。
Wは、Moと同様に、焼入れ性を高め、焼戻し軟化抵抗を向上させる元素であり、かつ、鋼中で炭化物として析出する元素である。これらの効果を得るため、W含有量を0.05%~1.00%とすることが好ましい。より好ましくは、W含有量の下限値を0.10%とする。なお、下限未満の量のWが鋼中に含有されても、本実施形態における効果を損なわない。また、合金コストの低減のためには、この選択元素を意図的に鋼中に添加する必要がないので、下限値を0%としてもよい。
Niは、鋼の強度を高める元素である。この効果を得るため、Ni含有量を0.10%~3.50%とすることが好ましい。Ni含有量が0.10%未満では、上記効果が得られない。よって、Ni含有量の下限値を0.10%とすることが好ましい。より好ましくは、Ni含有量の下限値を0.20%とする。なお、下限未満の量のNiが鋼中に含有されても、本実施形態における効果を損なわない。また、合金コストの低減のためには、この選択元素を意図的に鋼中に添加する必要がないので、下限値を0%としてもよい。
Cuは、耐食性を高め、そして、脱炭を抑制する元素である。これらの効果を得るため、Cu含有量を0.10%~0.50%とすることが好ましい。Cu含有量が0.10%未満では、上記効果が得られない。よって、Cu含有量の下限値を0.10%とすることが好ましい。より好ましくは、Cu含有量の下限値を0.20%とする。なお、下限未満の量のCuが鋼中に含有されても、本実施形態における効果を損なわない。また、合金コストの低減のためには、この選択元素を意図的に鋼中に添加する必要がないので、下限値を0%としてもよい。
Nbは、鋼中のC、Nと結びついて、炭化物、窒化物、炭窒化物を生成する元素である。微量の添加でも、添加しない場合と比べて、結晶粒の粗大化を防止する効果を有する。さらに、Nbを、V等の炭化物、窒化物、炭窒化物を生成する元素と複合添加する場合、Nbは、Vよりも窒化物を生成しやすく、その結果、Vが窒化物を生成せずに、オーステナイト粒径の微細化に有効なV含有炭化物が生成し易くなるという効果も有する。このように、微量のNb添加でも、より効果的に、オーステナイト粒径制御や、焼戻し軟化抵抗の付与を行うことができる。
Bは、微量の添加で、鋼の焼入れ性を高める元素である。また、Bは、母材が高炭素鋼である場合、熱間圧延後の冷却過程でBとFeとを含有する炭化物を生成し、フェライトの成長速度を増加させ、鋼材の加工性を向上させる元素である。さらに、Bは、オーステナイト粒界に偏析することで、Pの粒界偏析を抑制して粒界強度を向上させ、そして、疲労強度、衝撃強度を向上させる元素でもある。
比較例No.62~65は、Ca添加量が本発明範囲を下回り、その結果、酸硫化物の生成率が低く、さらに延伸した硫化物個数が多く、L10疲労特性が不十分となった。
比較例No.66は、加熱温度と保持時間が本発明範囲を下回り、その結果、REM-Ca-Al-O-S複合酸硫化物と独立に存在するTiNの個数が多く、L10疲労特性が不十分となった。
比較例No.67、68、73~75、78~98は、添加成分が本願規定の範囲を外れ、その結果、L10疲労特性が不足または焼割れ、加工による割れを生じ、軸受としての性能が満たせない。
比較例No.69は、REM添加量が本発明範囲を上回り、その結果、耐火物への付着が多く、製造不能と判定された。
比較例No.70、72は、取鍋精錬時の処理順序が本発明とは異なるため、その結果、酸硫化物または酸化物の形態が変化し、介在物が大きくなり、L10疲労特性が不十分であった。
比較例No.71は、REM脱酸時間が本発明範囲を下回り、その結果、酸硫化物の生成率が低く、さらに延伸した硫化物個数が多くなり、L10疲労特性が不十分となった。
比較例No.76は、保持温度が本発明範囲を下回り、その結果、REM-Ca-Al-O-S複合酸硫化物と独立に存在するTiNの個数が多く、L10疲労特性が不十分となった。
比較例No.77は、保持温度が本発明範囲を上回り(そのため、その後の冷却時に1200℃~1250℃の温度範囲での保持時間が60秒以下であったため)、その結果、REM-Ca-Al-O-S複合酸硫化物と独立に存在するTiNの個数が多く、L10疲労特性が不十分となった。
B TiN
C 初析セメンタイト
D MnS
Claims (12)
- 化学成分が、質量%で、
C:0.9%~1.5%、
Si:0.1%~0.8%、
Mn:0.1%~1.5%、
Cr:0.5%~2.0%、
Al:0.01%~0.05%、
Ca:0.00001%~0.0050%、
Rare Earth Metal:0.0001%~0.050%、
O:0.0001%~0.0030%、
を含有し、
Ti:0.005%未満、
N:0.015%以下、
P:0.03%以下、
S:0.05%以下、
に制限し、
残部が鉄および不可避的不純物からなり、
金属組織が、
介在物として、Rare Earth Metal、Ca、O、S及びAlを含む複合酸硫化物と、TiNと、MnSと、Al2O3と、Al及びCaを含む複合酸化物と、を含有し、
前記介在物の合計個数に対して、前記複合酸硫化物の個数が、50%以上100%未満であり、かつ、長径が5μm以上である前記複合酸硫化物の個数が、観察面1mm2あたり、0.001個以上2個以下であり、
前記複合酸硫化物と独立に存在する長径が5μm以上である前記TiNの個数が、観察面1mm2あたり、0.001個以上1.0個未満である
ことを特徴とする軸受鋼。 - 前記化学成分の前記S含有量が、
S:0.01%超~0.05%、
であるとき、前記Ca含有量を、
Ca:0.00050%~0.0050%、
とする
ことを特徴とする請求項1に記載の軸受鋼。 - 前記化学成分が、さらに、質量%で、
V:0.05%~0.70%、
Mo:0.05%~1.00%、
W:0.05%~1.00%、
Ni:0.10%~3.50%、
Cu:0.10%~0.50%、
Nb:0.005%~0.050%未満、
B:0.0005%~0.0050%、
のうち少なくとも1つを含有する
ことを特徴とする請求項1又は2に記載の軸受鋼。 - 前記複合酸硫化物のAl含有量が、Al2O3換算で、20質量%以下である
ことを特徴とする請求項1又は2に記載の軸受鋼。 - 長径が10μm以上である前記MnSの個数と、前記複合酸硫化物と独立して存在する長径が5μm以上である前記TiNとの個数とが、観察面1mm2あたり、合計で5個以下である
ことを特徴とする請求項1又は2に記載の軸受鋼。 - 前記Cu及び前記Niの質量%で示した含有量が、Cu≦Niを満足する
ことを特徴とする請求項3に記載の軸受鋼。 - Alを用いて溶鋼を脱酸するAl脱酸工程と;
前記Al脱酸工程後の前記溶鋼を、Rare Earth Metalを用いて5分以上10分以下の脱酸を行うREM脱酸工程と;
前記REM脱酸工程後の前記溶鋼を、鋳造して、化学成分が、質量%で、
C:0.9%~1.5%、
Si:0.1%~0.8%、
Mn:0.1%~1.5%、
Cr:0.5%~2.0%、
Al:0.01%~0.05%、
Ca:0.00001%~0.0050%、
Rare Earth Metal:0.0001%~0.050%、
O:0.0001%~0.0030%、
を含有し、
Ti:0.005%未満、
N:0.015%以下、
P:0.03%以下、
S:0.05%以下、
に制限し、
残部が鉄および不可避的不純物からなる鋳片を得る鋳造工程と;
前記鋳片を、1270℃~1300℃の温度範囲に加熱して、前記加熱後に、1200℃~1250℃の温度範囲で60秒以上の保持を行う加熱保持工程と;
前記加熱保持工程後の前記鋳片を、熱間塑性加工して熱間加工鋼材を得る熱間加工工程と;を有する
ことを特徴とする軸受鋼の製造方法。 - 前記溶鋼の化学成分が、質量%で、
S:0.01%超~0.05%、
を含有するとき、
前記REM脱酸工程後で前記鋳造工程前の前記溶鋼に、Caを添加して真空脱ガス処理を行う真空脱ガス工程をさらに有する
ことを特徴とする請求項7に記載の軸受鋼の製造方法。 - 前記鋳片の前記化学成分が、さらに、質量%で、
V:0.05%~0.70%、
Mo:0.05%~1.00%、
W:0.05%~1.00%、
Ni:0.10%~3.50%、
Cu:0.10%~0.50%、
Nb:0.005%~0.050%未満、
B:0.0005%~0.0050%、
のうち少なくとも1つを含有する
ことを特徴とする請求項7又は8に記載の軸受鋼の製造方法。 - 前記鋳造工程で、前記溶鋼を鋳型内で水平方向に0.1m/分以上0.5m/分以下で旋回させて鋳造する
ことを特徴とする請求項7又は8に記載の軸受鋼の製造方法。 - 前記熱間加工工程後の前記熱間加工鋼材を、700℃~750℃の温度範囲に加熱して、30時間以上50時間以下保持することで軟質化鋼材を得る軟質化熱処理工程をさらに有する
ことを特徴とする請求項7又は8に記載の軸受鋼の製造方法。 - 前記REM脱酸工程後で前記真空脱ガス工程前の前記溶鋼に、さらに、CaO-CaF2を添加して脱硫を行うフラックス工程を有する
ことを特徴とする請求項7又は8に記載の軸受鋼の製造方法。
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JP2004277777A (ja) | 2003-03-13 | 2004-10-07 | Nippon Steel Corp | 疲労寿命に優れた介在物微細分散鋼 |
JP2007254818A (ja) * | 2006-03-23 | 2007-10-04 | Nippon Steel Corp | アルミキルド鋼の連続鋳造鋼片及びその製造方法 |
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JP2017170487A (ja) * | 2016-03-24 | 2017-09-28 | 新日鐵住金株式会社 | 高炭素溶鋼の連続鋳造方法 |
JP2021098880A (ja) * | 2019-12-24 | 2021-07-01 | 日本製鉄株式会社 | Al脱酸鋼の溶製方法 |
JP7311785B2 (ja) | 2019-12-24 | 2023-07-20 | 日本製鉄株式会社 | Al脱酸鋼の溶製方法 |
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US9732407B2 (en) | 2017-08-15 |
KR20140069169A (ko) | 2014-06-09 |
EP2770077A4 (en) | 2015-11-04 |
EP2770077B1 (en) | 2019-07-10 |
IN2014DN03266A (ja) | 2015-07-10 |
US20140261906A1 (en) | 2014-09-18 |
JP5652555B2 (ja) | 2015-01-14 |
CN103890209A (zh) | 2014-06-25 |
JPWO2013058131A1 (ja) | 2015-04-02 |
EP2770077A1 (en) | 2014-08-27 |
KR101616656B1 (ko) | 2016-04-28 |
CN103890209B (zh) | 2015-11-25 |
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