WO2015147067A1 - Composant en acier pour cémentation à haute température présentant d'excellentes résistance à l'écaillage et résistance à la fatigue oligocyclique - Google Patents

Composant en acier pour cémentation à haute température présentant d'excellentes résistance à l'écaillage et résistance à la fatigue oligocyclique Download PDF

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WO2015147067A1
WO2015147067A1 PCT/JP2015/059152 JP2015059152W WO2015147067A1 WO 2015147067 A1 WO2015147067 A1 WO 2015147067A1 JP 2015059152 W JP2015059152 W JP 2015059152W WO 2015147067 A1 WO2015147067 A1 WO 2015147067A1
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strength
cycle fatigue
steel
fatigue strength
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武浩 酒道
新堂　陽介
藤田　学
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株式会社神戸製鋼所
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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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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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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
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/20—Carburising
    • C23C8/22—Carburising of ferrous surfaces
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations
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    • C21—METALLURGY OF IRON
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment

Definitions

  • the present invention relates to a steel part for high-temperature carburizing excellent in spalling strength and low cycle fatigue strength.
  • steel parts used after high-temperature carburizing treatment especially carburizing steel parts useful as materials for gears, bearings, shafts and power transmission parts such as CVT (Continuously Variable Transmission) pulleys.
  • CVT Continuous Variable Transmission
  • spalling strength The carburized steel parts used for the various applications described above are required to have excellent strength against spalling (this is referred to as “spalling strength”).
  • spalling when there is little or no sliding between parts, a shearing stress is generated by sliding contact load, and a crack is generated in the inside, and it develops, and fatigue failure that leads to delamination It is a phenomenon.
  • the damage form is changing from the conventional surface-origin type damage (pitching) to the spalling due to the increase in the load load accompanying the increase in output and miniaturization of the power transmission component.
  • Patent Document 1 While containing a relatively large amount of S and controlling the atomic ratio of Mn and S within a predetermined range, 5,000 sulfide inclusions per unit area of MnS as a main component are contained per mm. A technique for improving the strength of parts by providing two or more has been proposed.
  • Patent Document 3 the Nb content is reduced to 0.04% or less, and the relationship between the content of Mo, Ni, B, Si, P, and V, the carburization concentration of the steel surface layer, and the surface hardness is a predetermined relationship. It has been proposed to achieve carburized and hardened steel and carburized parts that are excellent in low cycle fatigue properties by defining the formula so as to satisfy the equation.
  • Patent Document 4 proposes a gear component that achieves both tooth root strength and tooth surface strength by appropriately controlling the chemical composition while reducing the Ti content to 0.05% or less. Yes.
  • Patent Document 1 since the S content is large, the spalling strength is decreased. As described in the above-mentioned Patent Document 2, if the content of Ti or N is only specified, the coarsening of crystal grains is inevitable, and the strength of the steel material tends to decrease. Further, Ti remaining without being bonded to C tends to precipitate as coarse TiN in a normal manufacturing method, and the spalling strength tends to decrease.
  • the technique of the above-mentioned Patent Document 3 basically has a low Nb content, so that coarsening of crystal grains cannot be avoided, and there is a problem that the strength of the steel material is reduced.
  • the present invention has been made in view of the above circumstances, and its purpose is to exhibit excellent low cycle fatigue strength without reducing spalling strength, such as gears, bearings, shafts, and CVT pulleys.
  • the object is to provide steel parts for high-temperature carburizing that are useful as materials for power transmission parts and the like.
  • the steel parts for high-temperature carburizing of the present invention that can solve the above-mentioned problems are, by mass%, C: 0.10 to 0.3%, Si: 0.03 to 1.50%, Mn: 0.2 to 1.8%, P: more than 0% and 0.03% or less, S: more than 0% and 0.03% or less, Cr: 0.30 to 2.50%, Al: more than 0% and 0.08% or less, N : More than 0% and 0.0150% or less, Nb: 0.05 to 0.3%, Ti: 0.05 to 0.1% and B: 0.0005 to 0.005%, respectively, the balance being Iron and inevitable impurities, the average C concentration from the surface to a depth of 0.05 mm is 0.50% or more, and the following A, B and C are defined by the following formulas (1) to (3), respectively.
  • A exp ⁇ Dm / 10 + Nm 1/2 / 50 ⁇ ⁇ exp ⁇ Dt / 15 + Nt 1/2 / 50 ⁇ (1)
  • B exp ⁇ Hs / 650 + ECD 1/2 + Hi / 250 ⁇ (2)
  • C exp [Hs / 650 ⁇ ECD ⁇ ⁇ (0.89 ⁇ Hi ⁇ 202.16) / 250 ⁇ 2 ] (3) 3.7 ⁇ A ⁇ 0.47 ⁇ B + 1.14 ⁇ 0 (4) C ⁇ 0.66 (5)
  • Dm is the average equivalent circle diameter ( ⁇ m) of MnS in the non-carburized part
  • Nm is the number density (pieces / mm 2 ) of MnS in the non-carburized part
  • Dt is the average circle of TiN in the non-carburized part.
  • Hs Vickers hardness (HV) at a depth of 0.05 mm from the surface measured with a test force of 300 gf
  • ECD indicates the effective hardened layer depth (mm)
  • Hi indicates the Vickers hardness (HV) at the non-carburized portion measured at a test force of 300 gf.
  • the average equivalent circle diameter of MnS and TiN means the average of the diameters (equivalent circle diameters) when the sizes of MnS and TiN are converted into circles of the same area.
  • the “non-carburized portion” means a portion 0.5 to 2.0 mm deeper than the effective hardened layer depth ECD (position opposite to the hardened layer). It means the inner side (center side) from the 1/4 position.
  • the effective hardened layer depth ECD means the carburized hardened layer depth specified in JIS G 0557 (2006).
  • the Vickers hardness Hs at a depth of 0.05 mm from the surface measured with a test force of 300 gf is 650 HV or more, the effective hardened layer depth ECD is 0.4 mm or more, and the test force is 300 gf. It is preferable that the Vickers hardness Hi in the non-carburized part measured by (1) is 300 HV or more.
  • the steel part for high-temperature carburizing of the present invention may further contain at least one of Ni: more than 0% and not more than 2.0% and Mo: more than 0% and not more than 1.00% by mass as necessary. preferable.
  • the chemical composition is appropriately defined, the average C concentration from the surface to a depth of 0.05 mm is 0.50% or more, and the size and number density of MnS and TiN are different at each part of the component.
  • a steel part for high-temperature carburizing excellent in spalling strength and low cycle fatigue strength can be obtained.
  • Such steel parts for high-temperature carburizing are useful as materials for power transmission parts such as gears, bearings, shafts, and CVT pulleys.
  • FIG. 1 is a pattern diagram showing carburizing heat treatment conditions in the examples.
  • FIG. 2 is a pattern diagram showing tempering process conditions.
  • FIG. 3 is a graph showing the relationship between the precipitation ratio of TiN and MnS and the temperature.
  • FIG. 4 is a schematic explanatory view showing the shape of the test piece used in the roller pitching test.
  • FIG. 5 is a schematic explanatory diagram showing the implementation status of the roller pitching test.
  • FIG. 6 is a schematic explanatory view showing the shape of a test piece used in the four-point bending fatigue test.
  • FIG. 7 is a schematic explanatory view showing an implementation status of a four-point bending fatigue test.
  • FIG. 1 is a pattern diagram showing carburizing heat treatment conditions in the examples.
  • FIG. 2 is a pattern diagram showing tempering process conditions.
  • FIG. 3 is a graph showing the relationship between the precipitation ratio of TiN and MnS and the temperature.
  • FIG. 4 is a schematic explanatory view showing
  • FIG. 8 is a graph showing the relationship between the value (3.7 ⁇ A ⁇ 0.47 ⁇ B + 1.14) on the left side of equation (4) and the spalling intensity in the first embodiment.
  • FIG. 9 is a graph showing the relationship between the value of C defined by the equation (3) and the low cycle fatigue strength in Example 1.
  • FIG. 10 is a graph showing the relationship between the value (3.7 ⁇ A ⁇ 0.47 ⁇ B + 1.14) on the left side of equation (4) and the spalling intensity in the second embodiment.
  • FIG. 11 is a graph showing the relationship between the value of C defined by the expression (3) and the low cycle fatigue strength in Example 2.
  • the present inventors have studied from various angles in order to realize a steel part for high-temperature carburizing excellent in both properties of spalling strength and low cycle fatigue strength. In particular, intensive investigations were made on the influence of the size and number density of MnS and TiN on the above-mentioned properties of parts.
  • the chemical composition is appropriately defined, the average C concentration from the surface to a depth of 0.05 mm is 0.50% or more, and the sizes (Dm, Dt) of MnS and TiN in the non-carburized part Based on the number density (Nm, Nt), when A to C are defined by the above equations (1) to (3), respectively, these satisfy the above equations (4) and (5)
  • the inventors have found that the above object can be achieved by controlling the present invention and completed the present invention.
  • the value of A defined by the above equation (1) indicates the sensitivity of the occurrence and propagation of internal cracks by inclusions, and the value of A increases as the size of inclusions increases and the number density increases. The low cycle fatigue strength decreases.
  • the above formula (1) defines such a relationship.
  • the Vickers hardness Hs at a depth of 0.05 mm from the surface hereinafter sometimes referred to as “surface hardness Hs” and the non-carburized portion.
  • the lower the hardness Hi hereinafter sometimes referred to as “core hardness Hi”
  • the value of B defined by the above equation (2) indicates the resistance to the occurrence and propagation of internal cracks due to shear stress.
  • the above formula (2) defines such a relationship.
  • the surface hardness Hs is less than 650 HV, the core hardness Hi is less than 300 HV, or the effective hardened layer depth ECD is less than 0.4 mm, spalling does not occur.
  • the surface of the part may sink and the low cycle fatigue strength may further decrease.
  • the surface hardness Hs is preferably 650 HV or more, the core hardness Hi is 300 HV or more, and the effective hardened layer depth ECD is preferably 0.4 mm or more.
  • the surface hardness Hs is more preferably 680 HV or more, and still more preferably 700 HV or more. From the viewpoint of reduction in machinability after carburizing, the surface hardness Hs is preferably 850 HV or less.
  • core part hardness Hi becomes like this.
  • the core hardness Hi is preferably 500 HV or less.
  • the effective hardened layer depth ECD is more preferably 0.7 mm or more, and further preferably 1.0 mm or more. From the viewpoint of an increase in cost associated with a longer carburizing process, the effective hardened layer depth ECD is preferably 1.5 mm or less.
  • the value of C defined by the above equation (3) indicates the resistance to crack initiation and propagation due to a load in a low cycle, and increases as the surface hardness Hs increases, while the effective hardened layer depth is increased. The deeper the ECD and the smaller the core hardness Hi, the smaller it becomes. Further, when the surface hardness Hs is lowered or the core hardness Hi is lowered, plastic deformation may occur before the occurrence of cracks, and the low cycle fatigue strength may further decrease.
  • the above equation (3) defines such a relationship.
  • the preferable range of the surface hardness Hs is the same as described above.
  • the core hardness Hi is preferably 250 HV or higher, more preferably 300 HV or higher, from the viewpoint of not causing “plastic deformation” (described later). From the viewpoint of preventing the occurrence of “brittle fracture” as described later, the core hardness Hi is preferably 450 HV or less.
  • the effective hardened layer depth ECD is preferably 0.25 mm or more, more preferably 0.5 mm or more. From the viewpoint of not causing “brittle fracture”, the effective hardened layer depth ECD is preferably 1.30 mm or less.
  • the surface hardness Hs and the core hardness Hi are values when measured with a test force of 300 gf, that is, 300 ⁇ 9.8 N.
  • the value on the left side of the formula (4) is preferably ⁇ 5.0 or less, more preferably ⁇ 10.0 or less.
  • the lower limit of the value on the left side of the equation (4) is determined based on the A value and the B value, but is preferably ⁇ 20 or more, more preferably ⁇ 15 or more.
  • the value of C is preferably 0.80 or more, and more preferably 1.00 or more.
  • the upper limit of the value of C is preferably 2.00 or less, more preferably 1.50 or less.
  • the carburized layer is composed of martensite, retained austenite and partly troostite or bainite structure, and the non-carburized layer is composed of martensite and partly bainite or It consists of a ferrite structure.
  • the steel component for high-temperature carburizing of the present invention has an appropriate chemical composition in order to exhibit required mechanical properties when applied to materials for power transmission components such as gears, bearings, shafts, and CVT pulleys. It is necessary to adjust to.
  • the basic chemical composition is as follows.
  • C (C: 0.10 to 0.3%) C is an element necessary for ensuring the core hardness Hi of the final product. However, if contained excessively, the workability is lowered and the low cycle fatigue strength is lowered. Therefore, it is necessary to be 0.3% or less. If the amount of C is less than 0.10%, the core hardness Hi becomes too low, and sufficient spalling strength cannot be obtained. From this point of view, the C content is 0.10 to 0.3%.
  • the minimum with preferable C amount is 0.13% or more, More preferably, it is 0.15% or more.
  • the upper limit with the preferable amount of C is 0.27% or less, More preferably, it is 0.25% or less.
  • Si 0.03-1.50%
  • Si is an element effective for suppressing the hardness reduction during the tempering treatment and improving the hardenability of the steel material to ensure the core hardness Hi of the final product.
  • the upper limit was made 1.50% or less.
  • the amount of Si is less than 0.03%, it is insufficient for improving the core hardness Hi. From this point of view, the Si content is set to 0.03 to 1.50%.
  • the minimum with the preferable amount of Si is 0.05% or more, More preferably, it is 0.07% or more.
  • the upper limit with the preferable amount of Si is 1.0% or less, More preferably, it is 0.60% or less.
  • Mn is an element effective for securing the core hardness of the final product by combining with S to suppress the formation of FeS and to suppress the deterioration of forgeability during rolling and to enhance the hardenability of the steel material.
  • Mn content is set to 1.8% or less.
  • the amount of Mn is less than 0.2%, the formation of FeS and the core hardness are insufficient.
  • the minimum with the preferable amount of Mn is 0.30% or more, More preferably, it is 0.35% or more.
  • the upper limit with the preferable amount of Mn is 1.70% or less, More preferably, it is 1.60% or less.
  • P more than 0% and 0.03% or less
  • P is segregated at the grain boundaries to lower the low cycle fatigue strength, so the smaller the content, the better. From this point of view, the P content is 0.03% or less.
  • the amount of P is preferably 0.020% or less, and more preferably 0.015% or less.
  • P is an element inevitably contained in steel, and the production cost increases as the purity is increased. Therefore, the amount of P is preferably 0.001% or more, more preferably 0.005%. That's it.
  • the upper limit of the amount of S is set to 0.03% or less.
  • the amount of S is preferably 0.025% or less, and more preferably 0.020% or less.
  • S is an element inevitably contained in the steel, and the production amount increases as the purity is increased, and in addition, the machinability is lowered, so the S amount is preferably 0.001% or more, More preferably, it is 0.005% or more.
  • Cr 0.30-2.50%
  • Cr is an element effective for improving the hardenability of the steel material and ensuring the core hardness Hi of the final product.
  • the Cr content is less than 0.30%, the core hardness Hi of the final product cannot be sufficiently obtained.
  • the minimum with the preferable amount of Cr is 0.50% or more, More preferably, it is 0.80% or more.
  • the upper limit with the preferable amount of Cr is 2.00% or less, More preferably, it is 1.80% or less.
  • Al more than 0% and 0.08% or less
  • bonds with N in steel materials produces
  • excessive addition produces Al 2 O 3 and reduces workability.
  • the Al content is set to 0.08% or less.
  • the amount of Al is preferably 0.060% or less, more preferably 0.050% or less.
  • Al is useful as a deoxidizing action, and is an element inevitably contained in the steel material. As the purity is increased, the manufacturing cost increases, and further the coarsening of crystal grains is promoted.
  • the content is preferably 001% or more, more preferably 0.005% or more.
  • N (N: more than 0% and 0.0150% or less) N combines with Al and Ti in the steel material to form a nitride, and serves as a starting point for spalling to lower the low cycle fatigue strength. Further, when the amount of N is more than 0.3 times the amount of Ti, N that could not be combined with Ti combines with B to form BN, not only lowering the hardenability of the steel material, but also pinning. Since TiC which is a particle
  • Nb 0.05-0.3%)
  • Nb combines with C and N in the steel material to form Nb (CN), which acts as pinning particles, and is an element effective for preventing crystal grain coarsening during carburization.
  • the Nb amount is set to 0.3% or less.
  • the Nb amount is preferably 0.20% or less, and more preferably 0.10% or less.
  • the Nb amount is set to 0.05% or more.
  • the Nb amount is preferably 0.06% or more, and more preferably 0.07% or more.
  • Ti 0.05-0.1%)
  • Ti combines with C in the steel material to form TiC and acts as pinning particles in the same manner as Nb (CN), and is an element effective in preventing crystal grain coarsening during carburization.
  • the Ti amount is 0.1% or less. did.
  • the amount of Ti is preferably 0.09% or less, and more preferably 0.08% or less. On the other hand, if the amount of Ti is less than 0.05%, a sufficient pinning action cannot be obtained, and the crystal grains become coarse, resulting in a decrease in strength.
  • the Ti amount is set to 0.05% or more.
  • the amount of Ti is preferably 0.06% or more, and more preferably 0.07% or more.
  • B is an element effective for improving the impact strength while greatly improving the hardenability of the steel material in a small amount.
  • the amount of B is preferably 0.004% or less, and more preferably 0.003% or less.
  • the B content is less than 0.0005%, the above effect cannot be obtained.
  • the amount of B is preferably 0.0010% or more, more preferably 0.0015% or more.
  • the basic components in the steel parts for high-temperature carburizing of the present invention are as described above, and the balance is substantially iron. However, it is naturally allowed that inevitable impurities brought into the steel depending on the situation of raw materials, materials, manufacturing equipment, etc. are contained in the steel.
  • the steel part for high-temperature carburizing according to the present invention may further include, if necessary, mass%, Ni: more than 0% and not more than 2.0% and Mo: 0. It is also preferable to contain at least one of more than% and 1.00% or less. The reason for setting the range when these are contained is as follows.
  • Ni more than 0% and 2.0% or less
  • Ni has the effect of improving the toughness of the carburized layer.
  • the upper limit is preferably made 2.0% or less.
  • the amount of Ni is more preferably 1.80% or less, and still more preferably 1.60% or less.
  • Ni amount is 0.01% or more, More preferably, it is 0.05% or more.
  • Mo more than 0% and 1.00% or less
  • Mo is an element that improves the hardenability of the steel material, and has the effect of improving the toughness of the carburized layer.
  • the upper limit is preferably made 1.00% or less.
  • the amount of Mo is more preferably 0.80% or less, and still more preferably 0.60% or less.
  • Mo amount is 0.01% or more, More preferably, it is 0.05% or more.
  • Ni and Mo are both effective elements for improving the toughness of steel parts, and each of them may be used alone or in combination of two kinds.
  • the average C concentration from the surface to a depth of 0.05 mm is 0.50% or more. It is. When the average C concentration is lower than 0.50%, the surface hardness Hs is increased, and good spalling strength cannot be secured.
  • the average C concentration is preferably 0.60% or more, more preferably 0.70% or more.
  • the upper limit of the average C concentration is naturally determined by carburizing conditions such as carbon potential.
  • the size and number density of MnS and TiN satisfy the above formulas (4) and (5) in relation to the hardness (Vickers hardness) at each part of the parts. It is characterized by controlling as follows. In order to satisfy such requirements, it is preferable to appropriately control the conditions in the steel material production stage and the carburizing and quenching treatment conditions.
  • These conditions are preferably controlled as follows. However, it is not necessary to satisfy all of these conditions (a) to (c), and the steel part for high-temperature carburizing of the present invention can be obtained by combining one or more conditions if necessary. It is done.
  • the average cooling rate when solidifying molten steel is preferably 0.06 ° C / second or more. MnS and TiN crystallize in the molten steel and become finer as the average cooling rate when the molten steel is solidified is higher. From such a viewpoint, the average cooling rate when solidifying molten steel is more preferably 0.08 ° C./second or more, and further preferably 0.10 ° C./second or more.
  • the upper limit of the average cooling rate when solidifying the molten steel is not particularly limited, but is usually about 0.01 ° C./second.
  • the forging pressure ratio is preferably 25 or more.
  • MnS and TiN become finer as the final size (diameter for shaft parts) is smaller, that is, the forging pressure ratio is larger, and the value of A is smaller.
  • the forging pressure ratio is more preferably 50 or more.
  • the upper limit of the forging pressure ratio is not particularly limited, but is about 500, for example.
  • the forging pressure ratio means “cross-sectional area perpendicular to the casting direction of the slab / cross-sectional area perpendicular to the processing direction of the rolled material or forged material”.
  • the soaking temperature is preferably 1100 to 1300 ° C.
  • the crystallized MnS and TiN are refined, and the value A is reduced. If the soaking temperature is less than 1100 ° C., MnS and TiN are not dissolved, whereas if the soaking temperature exceeds 1300 ° C., the slab surface may be melted during holding. From such a viewpoint, the more preferable lower limit of the soaking temperature is 1150 ° C. or more, and the more preferable upper limit is 1250 ° C. or less.
  • the soaking time is preferably about 0.5 to 3 hours. If the holding time is less than 0.5 hour, the miniaturization of MnS and TiN becomes insufficient. On the other hand, if the holding time exceeds 3 hours, productivity is lowered and cost is increased.
  • the holding time is more preferably 1 hour or more and 2 hours or less.
  • the above-mentioned soaking process is performed before the partial rolling, if the partial rolling is not performed, the soaking process may be performed before rolling or forging.
  • the steel material obtained by rolling or forging may be carburized and quenched in a carburizing furnace after being processed into a predetermined shape.
  • the average C concentration from the surface to 0.05 mm depth is 0.50% or more, and the effective hardened layer depth ECD (EffectiveffCase. Depth) is 0.40 to 1.5 mm.
  • the carbon potential CP, the carburizing temperature, and the carburizing time in the atmosphere may be appropriately controlled. Specifically, the carbon potential CP in the atmosphere is adjusted to 0.50 or more and held at 800 to 1000 ° C. for 0.5 hours or more and less than 5 hours, and then the carbon potential CP is kept at 0.50 or more. And quenching immediately after holding at 800 to 900 ° C. for 0.5 to 2 hours.
  • a mixed gas of modified gas (RX gas) and propane gas may be used.
  • Example 1 A steel ingot having the chemical composition shown in Table 1 below was melted in a converter and a small melting furnace having a capacity of 50 kg or 150 kg. In Table 1, “-” means no addition.
  • the slab was heated and held in a heating furnace at 1250 ° C. for 60 minutes to perform a soaking process, or subjected to block rolling without heating and holding. Further, hot rolling was performed to a predetermined diameter of 32 to 80 mm at a forging pressure ratio shown in Table 2 below.
  • the obtained steel material (hot rolled material or hot forged material) was processed into a predetermined shape, and then carburized and quenched in a gas carburizing furnace.
  • a gas carburizing gas a mixed gas of RX gas and propane gas was used.
  • an average C concentration from the surface to a depth of 0.05 mm (hereinafter sometimes referred to as “surface layer C concentration Cs”): 0.60%
  • effective hardened layer depth ECD 0.75 mm
  • the carbon potential CP in the atmosphere was adjusted to 0.65, held at 950 ° C. for 0.4 to 3.0 hours, and then held at 850 ° C. for 0.5 hours without changing the carbon potential CP.
  • Table 5 shows specific carburizing conditions.
  • FIG. 1 is a pattern diagram showing the carburizing heat treatment conditions at this time.
  • FIG. 2 is a pattern diagram showing tempering processing conditions.
  • the general carburizing temperature is about 920 ° C., and the above 950 ° C. is a holding temperature at which the crystal grains tend to become coarse.
  • the longitudinal section of the carburized part obtained above was investigated, and a sample of 10 mm (radial direction) ⁇ 10 mm (longitudinal direction) was cut out in the longitudinal direction (corresponding to the rolling direction) from 1/4 position of the diameter D of each sample.
  • the cross section was polished.
  • the composition analysis is performed with EPMA (Electron Probe Micro Analyzer) for inclusions with a minor axis of 3 ⁇ m or more existing in an area of 15 ⁇ m 2 scanned from an arbitrary position on the polished surface, and MnS and TiN are determined by using EPMA (Electron Probe Micro Analyzer). Identified.
  • EPMA Electro Probe Micro Analyzer
  • the area and number of MnS and TiN were measured, the number density (number per 1 mm 2 : Nm, Nt) was evaluated by (each detected number / scanning area), and the average equivalent circle diameter (Dm, Dt) was Each was calculated from the average area per piece.
  • FIG. 3 shows the results of calculating the temperature change of the precipitation ratio of MnS and TiN using thermodynamic calculation software “Thermo-calc” (trade name: manufactured by Thermo-calc software). This result supports that it does not dissolve in the temperature range of the carburizing treatment.
  • the measurement conditions of EPMA at this time are as follows (1) to (4).
  • EPMA device JXA 8500F (trade name: manufactured by JEOL Ltd.)
  • EDS analysis energy dispersive X-ray analysis: Thermo Fisher Scientific system six
  • Acceleration voltage 15 kV
  • Scanning current 1.76 nA
  • the spalling strength and low cycle fatigue strength were evaluated by the following methods, and the hardness, the effective hardened layer depth ECD, and the surface layer C concentration Cs were measured. As the hardness, surface hardness Hs and core hardness Hi were measured.
  • the test was conducted using a “RP-201” roller pitching tester (trade name: manufactured by Komatsu Engineering Co., Ltd.). At this time, the life until spalling occurs at a surface pressure of 2.0 to 6.3 GPa is measured, and the test surface pressure when the life reaches 2 million cycles by single regression is defined as the spalling strength (GPa). Calculated.
  • the test piece used in this test was manufactured by processing it into the shape shown in FIG. 4, subjecting it to carburizing and quenching, and polishing the sliding surface.
  • FIG. 5 shows a state in which the test piece 1 (roller) and the load roller 2 roll in contact with each other as a test appearance (implementation status of a roller pitching test).
  • the test conditions are as follows. (1) Rotation speed: 2000rpm (2) Slip rate: 0% (life is judged to be due to spalling only) (3) Load roller: JIS G4805 (2013) high carbon chrome bearing steel SUJ2 (4) Test oil temperature: 120 ° C
  • FIG. 7 shows the external appearance of a four-point bending test (the portion indicated by ⁇ is a support point).
  • 3 is a test piece
  • 4 is a jig
  • 5 is a direction of load. A single swing load was applied from the back while two horizontal portions on the test piece notch side were supported. The frequency at this time was 20 Hz.
  • the roller pitching test piece was cut so as to cross the center of the sliding portion, the cut surface was polished, and the hardness was measured.
  • the surface hardness Hs was an average value obtained by measuring five points from the surface in a depth direction of 0.05 mm.
  • core part hardness Hi was made into the average value which measured the 1/4 position of the diameter D 5 points
  • the effective hardened layer depth ECD was calculated according to JIS G0557.
  • the surface layer C concentration Cs was measured by EPMA analysis. At this time, measurement was performed at a pitch of 0.005 mm from the surface to a position of 0.05 mm in the depth direction, and the average value was defined as the surface layer C concentration Cs.
  • Table 3 shows the average equivalent circle diameter Dm of MnS, the average equivalent circle diameter Dt of TiN, the number density Nm of MnS, and the number density Nt of TiN, together with the steel types used and the production conditions.
  • the spalling strength and low cycle fatigue strength, steel type used, manufacturing conditions, carburizing conditions, carburized parts material (surface C concentration Cs, surface hardness Hs, core hardness Hi, effective hardened layer depth ECD ), Parameters (values of A, B and C), and the value on the left side of equation (4) (3.7 ⁇ A ⁇ 0.47 ⁇ B + 1.14) are shown in Table 4 below.
  • test no. Examples 1 to 3, 5 to 9, 12 to 14, 16 to 19, and 21 are examples that satisfy the requirements defined in the present invention. It can be seen that the spalling strength is 3.70 GPa or more, the low cycle fatigue strength is 2.10 GPa or more, and both the spalling strength and the low cycle fatigue strength are excellent.
  • test no. 4, 10, 11, 15, 20, 22 to 27 are comparative examples in which any of the requirements of the present invention was not satisfied, and it can be seen that at least the spalling strength is reduced.
  • Test No. Nos. 23 to 27 are steel grades Nos. It is a comparative example using the steel materials 6 and 7, regardless of the manufacturing conditions and carburizing conditions, the relationship of the formula (4) is not satisfied, and the spalling strength is deteriorated.
  • FIG. 8 shows the relationship between the value on the left side of equation (4) (3.7 ⁇ A ⁇ 0.47 ⁇ B + 1.14) and the spalling intensity. Moreover, the relationship between the value of C prescribed
  • Example 2 Steel ingots having chemical composition shown in Table 6 below were melted, and the production conditions No. 1 shown in Table 2 above were obtained. In 4 the steel material was obtained. Further, hot rolling was performed to a predetermined diameter of 32 to 80 mm.
  • the steel type No. shown in Table 6 below. 1 to 5 are steel types No. 1 shown in Table 1 above. Same as 1-5.
  • carburizing and quenching treatment was performed in a gas carburizing furnace (carburizing gas: RX gas + propane gas) in the same manner as in Example 1 above.
  • carburizing gas a mixed gas of RX gas and propane gas was used.
  • the carbon potential CP in the atmosphere is adjusted so that the surface layer C concentration Cs from the surface to a depth of 0.05 mm is 0.44 to 0.80% and the effective hardened layer depth ECD is 0.29 to 1.33 mm. Is adjusted to a range of 0.45 to 0.75, held at 930 to 960 ° C. for 0.3 to 6.0 hours, and then held at 850 ° C. for 0.5 hours without changing the carbon potential CP. Quenched immediately after.
  • Table 5 also shows specific carburizing conditions. Furthermore, after holding at 170 degreeC for 2 hours, it stood to cool and tempered.
  • Table 7 shows the average circle equivalent diameter Dm of MnS, the average equivalent circle diameter Dt of TiN, the number density Nm of MnS, and the number density Nt of TiN together with the steel types used.
  • “Depression”, “plastic deformation”, “brittle fracture” and “GG” shown in the “Remarks” section of Table 8 below mean that the following phenomenon occurred.
  • test no. 32, 34, 35, 37 to 39, 42 to 45, 48, and 49 satisfy all of the requirements defined in the present invention. It can be seen that the spalling strength is 3.70 GP or more, the low cycle fatigue strength is 2.10 GPa or more, and both the spalling strength and the low cycle fatigue strength are excellent.
  • test no. Reference numerals 31, 33, 36, 40, 41, 46, 47, and 50 to 70 are examples in which any of the requirements of the present invention is not satisfied.
  • Test No. No. 31 has a low surface layer C concentration Cs and a surface hardness Hs lower than the preferred lower limit for the low cycle fatigue strength, causing the above-mentioned “depression” and “plastic deformation”, and the spalling strength and low cycle fatigue strength. Both are falling.
  • Test No. No. 36 the surface layer C concentration Cs decreases, the surface hardness Hs is lower than the preferred lower limit for the low cycle fatigue strength, the value of C defined by the formula (3) is small, and the low cycle fatigue strength decreases. is doing. Test No. In No. 36, the surface hardness Hs is low, but no depression occurs because the core hardness Hi is relatively high.
  • Test No. No. 40 has a lower surface layer C concentration Cs and a lower surface hardness Hs than the preferred lower limit for the low cycle fatigue strength, and does not satisfy the formula (4). Both are falling.
  • the effective hardened layer depth ECD is shallower than the preferred lower limit for the low cycle fatigue strength and does not satisfy the formula (4), and the spalling strength is lowered.
  • Test No. in 46 the value of C defined by the expression (3) is small, and the low cycle fatigue strength is low.
  • Test No. Nos. 50 to 70 are steel grades Nos. This is an example using 8 to 17 steel materials. Of these, test no. No. 50, the surface layer C concentration Cs decreases and the surface hardness Hs is lower than the preferred lower limit for the low cycle fatigue strength, the value of C defined by the equation (3) is small, and the low cycle fatigue strength decreases. ing. Test No. No. 50 has a surface hardness Hs lower than the preferred lower limit for the low cycle fatigue strength, but no depression occurs because the core hardness Hi is much higher than the preferred upper limit for the low cycle fatigue strength.
  • the effective hardened layer depth ECD becomes shallower than the preferred lower limit for the low cycle fatigue strength.
  • No. 52 has a small C value defined by the expression (3), and the core hardness Hi is higher than the preferred upper limit for the low cycle fatigue strength. As a result, all have low cycle fatigue strength.
  • Test No. Nos. 53 to 55 are steel types Nos. Having a low C content.
  • the core hardness Hi is lower than the preferred lower limit for the low cycle fatigue strength.
  • test no. 53 the effective hardened layer depth ECD is shallower than the preferred lower limit for the low cycle fatigue strength, does not satisfy the formula (4), and the spalling strength is lowered.
  • Test No. No. 54 does not satisfy the formula (4), and the spalling strength is lowered.
  • Test No. In No. 55 the effective hardened layer depth ECD is deeper than the preferred upper limit for the low cycle fatigue strength, and the low cycle fatigue strength is reduced. In addition, brittle fracture occurred.
  • Test No. Nos. 56 and 57 are steel types having excessive Si amounts. In this example, the surface layer C concentration Cs is lowered due to poor carburization. Of these, test no. 56, the effective hardened layer depth ECD is shallower than the preferred lower limit for the low cycle fatigue strength, and does not satisfy the formula (4), and the spalling strength and the low cycle fatigue strength are reduced. Sinking and plastic deformation also occurred. Test No. In 57, the value of C defined by the expression (3) is small, and the low cycle fatigue strength is low.
  • Test No. Nos. 58 and 59 are steel types with excessive Mn amounts. This is an example using 11 steel materials.
  • Test No. 58 the effective hardened layer depth ECD becomes shallower than the preferred lower limit for the low cycle fatigue strength.
  • No. 59 has a small C value defined by the expression (3), and the low cycle fatigue strength is low in all cases.
  • Test No. Nos. 60 to 62 are steel types Nos. Having excessive amounts of Ni as preferred components. This is an example using 12 steel materials. Of these, test no. In No. 60, since the core hardness Hi is higher than the preferred upper limit for the low cycle fatigue strength, the low cycle fatigue strength is reduced due to brittle fracture. Test No. In Nos. 61 and 62, the core hardness Hi is higher than the preferable upper limit for the low cycle fatigue strength, and the value of C defined by the equation (3) is small, and the low cycle fatigue strength is reduced.
  • Test No. Nos. 63 and 64 are steel types with excessive Cr content. This is an example using 13 steel materials. Test No. No. 63, the effective hardened layer depth ECD becomes shallower than the preferred lower limit for the low cycle fatigue strength. In 64, the value of C defined by the expression (3) is small, and the low cycle fatigue strength is low in all cases.
  • Test No. Nos. 65 and 66 are steel type Nos. With a small amount of Cr. This is an example using 14 steel materials. Of these, test no. No. 65 does not satisfy the formula (4), and the low cycle fatigue strength is lowered. Test No. In 66, the effective hardened layer depth ECD is deeper than the preferred upper limit for the low cycle fatigue strength, and the low cycle fatigue strength is reduced. In addition, brittle fracture occurred.
  • Test No. Nos. 67 and 68 are steel grades No. 6 and No. 6 that have an excessive amount of Mo as a preferred component. This is an example using 15 steel materials.
  • Test No. No. 67 the effective hardened layer depth ECD becomes shallower than the preferred lower limit for the low cycle fatigue strength.
  • the value of C defined by the expression (3) is small, and the low cycle fatigue strength is reduced in all cases.
  • Test No. No. 69 is a steel type No. with a small amount of Ti. Although it is an example using 16 steel materials, the coarsening (GG) of a crystal grain generate
  • Test No. No. 70 is a steel type No. with a small amount of Nb. Although it is an example using 17 steel materials, crystal grain coarsening (GG) generate
  • GG crystal grain coarsening
  • FIG. 10 shows the relationship between the value on the left side of equation (4) (3.7 ⁇ A ⁇ 0.47 ⁇ B + 1.14) and the spalling intensity.
  • FIG. 11 shows the relationship between the value of C defined by equation (3) and the low cycle fatigue strength.
  • FIG. Examples Nos. 32, 34, 35, 37 to 39, 42 to 45, 48, 49 Comparative examples of 31, 33, 36, 40, 41, 46, 47, and 50 to 70 are indicated by ⁇ .
  • Test piece 2 Load roller 3 Test piece 4 Jig 5 Load direction

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Abstract

L'invention porte sur un composant en acier pour cémentation à haute température qui présente d'excellentes résistance à l'écaillage et résistance à la fatigue oligocyclique et qui est utile comme matériau pour des composants de transmission d'énergie, etc., produit par réglage approprié de la composition de composants chimiques, réglage de la concentration moyenne de C jusqu'à une profondeur de 0,05 mm à partir de la surface à une valeur supérieure ou égale à 0,50 % et réglage du diamètre moyen de cercle équivalent Dm (μm) et de la densité en nombre Nm (nombre/mm2) de MnS dans une partie non cémentée, du diamètre moyen de cercle équivalent Dt (μm) et de la densité en nombre Nt (nombre/mm2) de TiN dans la partie non cémentée, de la dureté Vickers Hs (HV) en un endroit à 0,05 mm de profondeur à partir de la surface et de la dureté Vickers Hi (HV) au niveau de la partie non cémentée, mesurées avec une force d'essai de 300 gf, et de la profondeur de couche durcie efficace ECD (mm) de manière à satisfaire aux expressions A=exp{Dm/10+Nm1/2/50}×exp{Dt/15+Nt1/2/50}, B=exp{Hs/650+ECD1/2+Hi/250}, C=exp[Hs/650-ECD-{(0,89×Hi-202,16)/250}2], 3,7×A-0,47×B+1,14≦0 et C≧0,66.
PCT/JP2015/059152 2014-03-28 2015-03-25 Composant en acier pour cémentation à haute température présentant d'excellentes résistance à l'écaillage et résistance à la fatigue oligocyclique WO2015147067A1 (fr)

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EP3418411A4 (fr) * 2016-02-19 2019-08-21 Nippon Steel Corporation Acier
US11078961B2 (en) * 2018-04-02 2021-08-03 Nsk Ltd. Intermediary race member of rolling bearing, race, rolling bearing and production method therefor
US20220106671A1 (en) * 2018-12-28 2022-04-07 Nippon Steel Corporation Steel material
US11326244B2 (en) * 2016-07-15 2022-05-10 Aisin Corporation Steel material for CVT sheave, CVT sheave, and method for manufacturing CVT sheave

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JP6828593B2 (ja) * 2017-05-25 2021-02-10 日本製鉄株式会社 浸炭部品
US20220177991A1 (en) * 2019-04-10 2022-06-09 Nippon Steel Corporation Steel shaft component

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EP3418411A4 (fr) * 2016-02-19 2019-08-21 Nippon Steel Corporation Acier
US11326244B2 (en) * 2016-07-15 2022-05-10 Aisin Corporation Steel material for CVT sheave, CVT sheave, and method for manufacturing CVT sheave
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US20220106671A1 (en) * 2018-12-28 2022-04-07 Nippon Steel Corporation Steel material

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