WO2006008960A1 - 機械構造用部品およびその製造方法と高周波焼入れ用素材 - Google Patents
機械構造用部品およびその製造方法と高周波焼入れ用素材 Download PDFInfo
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- WO2006008960A1 WO2006008960A1 PCT/JP2005/012397 JP2005012397W WO2006008960A1 WO 2006008960 A1 WO2006008960 A1 WO 2006008960A1 JP 2005012397 W JP2005012397 W JP 2005012397W WO 2006008960 A1 WO2006008960 A1 WO 2006008960A1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/06—Surface hardening
- C21D1/09—Surface hardening by direct application of electrical or wave energy; by particle radiation
- C21D1/10—Surface hardening by direct application of electrical or wave energy; by particle radiation by electric induction
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- 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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
-
- 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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
-
- 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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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
Definitions
- the present invention relates to a machine structural component having a hardened layer formed by induction hardening at least partially.
- the mechanical structural component include a drive shaft, an input shaft, an output shaft, a crankshaft, an inner ring and an outer ring of a constant velocity joint, a hub, and a gear for an automobile.
- Patent Document 2 discloses that the ratio between the hardened layer depth CD and the radius R of the induction-hardened shaft component (CD / R) is limited to 0.3 to 0.7, and this CDZR and the surface after induction hardening.
- CDZR average Vickers hardness Hf from induction hardening
- Hf average Vickers hardness He at the center of the shaft after induction hardening
- Patent Document 1 Japanese Patent Laid-Open No. 2000-154819 (Claims, paragraph [0008])
- Patent Document 2 JP-A-8-53714 (Claims)
- An object of the present invention is to provide a mechanical structural component and a method for manufacturing the same that can further improve fatigue strength after induction hardening, and a material for induction hardening.
- Fatigue strength is improved by increasing the intragranular strength, i.e., hardness, of the hardened layer by induction hardening, but if the hardness is increased to a Vickers hardness of Hv750 or higher, the fracture is changed from intragranular fracture to old austenite. Fatigue strength does not improve even if the hardness is increased further, because it shifts to fracture at grain boundaries.
- the material contains Mo, B, and Ti, and the microstructure before induction quenching is refined into a fine bainite or martensite with work strain introduced by cold working. It is effective to use rapid heating, lower the heating temperature, and shorten the residence time at 800 ° C or higher during the site, further tempering and induction hardening.
- tempering is usually performed after induction quenching, but it is possible to increase the intragranular strength by omitting this.
- the present invention is based on the above findings.
- the gist configuration of the present invention is as follows.
- At least partially has a hardened layer by induction hardening, and the hardened layer has a hardness of Hv750 or more and the average grain size of the prior austenite grains is 7 ⁇ m or less over the entire thickness of the hardened layer.
- the Al content is
- V 0.5 mass% or less
- REM 0.1 mass% or less 5.
- V 0.5 mass% or less
- Bainitic structure and martensite in steel structure before induction hardening of the material A method for manufacturing a machine structural component, wherein the total of either one or both of the textures is adjusted to 10% by volume or more, and the ultimate temperature of the induction hardening is 1000 ° C or less.
- V 0.5 mass% or less
- a material for induction hardening for making steel for machine structural use having a hardened layer having an average prior austenite grain size of 7 m or less by induction hardening at least on a part of the surface,
- the balance has a component composition of Fe and unavoidable impurities, and any one of a bainitic structure and a martensitic structure A material for induction hardening characterized by having a steel structure in which the total of one or both is 10% by volume or more.
- Al 0.005-0.25mass% 15. The material for induction hardening as described in 15 above, wherein the material is for induction hardening.
- V 0.5 mass% or less
- FIG. 1 is a graph showing the effect of heating temperature during induction hardening on the prior austenite grain size of the hardened layer for Mo-added steel and Mo-free steel.
- FIG. 2 Transmission electron micrograph of fine precipitates (Mo-based precipitates) effective for ultra-fine ⁇ grains.
- FIG. 3 is a graph showing the relationship between average prior austenite grain size and torsional fatigue strength for Mo-added steel and Mo-free steel.
- FIG. 4 is a graph showing the relationship between average prior austenite grain size and torsional fatigue strength with and without tempering.
- FIG. 5 is a partial sectional view of a constant velocity joint.
- FIG. 6 is a cross-sectional view showing a quenched structure layer in an inner ring of a constant velocity joint.
- the mechanical structural parts of the present invention have various shapes and structures depending on the parts, such as drive shafts for automobiles, input shafts, output shafts, crankshafts, constant velocity joint inner and outer rings, hubs, and gears.
- it has a hardened layer that has been hardened in a part or all that particularly requires fatigue strength, and this hardened layer has a hardness of H v750 or more and the average grain size of prior austenite grains is a hardened layer. It is B essential to be 7 ⁇ m or less over the entire thickness.
- the average prior austenite grain size of the hardened layer by induction hardening exceeds 7 m, even if the hardness of the hardened layer is increased to Hv 750 or higher and the intragranular strength is improved as described later, fatigue fracture will not occur. It will occur starting from the boundary. Therefore, the old layer of the hardened layer
- the particle size of the austenite should be 7 ⁇ m or less, preferably 6 ⁇ m or less, more preferably 5 ⁇ m or less, and even more preferably 3 m or less. This is because the grain boundary strength becomes remarkably stronger as the grain size is refined. Conventionally, even if the intragranular strength is increased, the grain boundary strength does not increase, and the grain boundary strength is rate-determined. However, since the grain boundary strength dramatically increases as the grain size is refined, further enhancement of strength can be expected.
- the average prior austenite grain size of the induction-quenched portion was measured as follows.
- the outermost layer of the hardened layer after induction hardening has a martensite structure of 100% in area ratio. And as it goes from the surface of the hardened layer to the inside, the area of 100% martensite structure continues up to a certain thickness, but after that, the area ratio of martensite structure decreases rapidly.
- the surface force of the induction-quenched portion is also defined as the hardened layer in the region until the area ratio of the martensite structure is reduced to 98%, and the average depth from the surface is the hardened layer thickness.
- the average prior austenite grain size is 7 m at any position.
- the average grain size of the prior austenite grains is assumed to be 7 m or less over the entire thickness of the hardened layer.
- the average particle size of the prior austenite grains is obtained by dissolving 50 g of picric acid in 500 g of water and then dissolving sodium dodecylbenzenesulfonate l lg, salt ⁇ ferrous lg, oxalic acid 1.5 g After corroding with the corrosive solution added, add 5 for each position at a magnification of 400 times (area of 1 field of view: 0.25 mm X 0.2 25 mm) to 1000 times (area of 1 field of view: 0.10 mm X 0.09 mm). The field of view was observed and measured with an image analyzer.
- the thickness is preferably 2 mm or more. More preferably, it is 2.5 mm or more, more preferably 3 mm or more.
- the Vickers hardness Hv of the hardened layer When the Vickers hardness Hv of the hardened layer is less than 750, the intragranular strength of the hardened layer is weak, so even if the prior austenite grains are refined, the corresponding improvement in fatigue strength is expected. I can't wait. That is, as described above, even if the austenite grains are refined and the grain boundary strength is increased, if the intragranular strength is not increased, the intragranular fracture becomes the rate-determining step, and an increase in static strength and fatigue strength cannot be expected. Therefore, in the present invention, the Vickers hardness (corresponding to the strength in the grains) Hv of the hardened layer needs to be 750 or more.
- the upper limit value of the Vickers hardness Hv of the hardened layer is not specified, but if it exceeds 900, the amount of added elements increases, so the machinability, cold forgeability, and fire cracking resistance of the base material decrease. Preferred to be below 900 ,.
- the Vickers hardness is the average of 5 points at 98 mm (lOkgf) at a position of 1Z5 from the surface of the hardened layer thickness.
- the C is an element that has the greatest influence on induction hardenability, increases the intragranular strength of the hardened layer, and contributes to improving fatigue strength by making the induction hardened part thicker.
- the amount is less than 0.3 mass%, the hardened layer must be drastically increased in order to ensure the required torsional fatigue strength. As a result, the occurrence of burning cracks becomes significant. It becomes difficult to obtain a bainite structure to be described later.
- the C content is preferably 0.3 to 1.5 mass%.
- Si increases the intragranular strength of the hardened layer and contributes to the improvement of fatigue strength. Furthermore, it is also an element useful for obtaining a bainitic structure, which will be described later. In this sense, it is preferably contained in an amount of 0.05 mass% or more. However, if it exceeds 3 mass%, it becomes difficult to secure solid formability and cold forgeability by solidifying the ferrite, so it is preferable to make it 3ma SS % or less.
- Mn is an indispensable element for improving induction hardenability and ensuring the thickness of the hardened layer. However, if the amount is less than 0.2 mass%, the effect is poor. Therefore, the amount of Mn is preferably 0.2 mass% or more, and more preferably 0.3 mass% or more. Meanwhile, 2.0 If it exceeds mass%, retained austenite increases after quenching, and the hardness of the surface layer tends to decrease. Therefore, Mn is preferably set to 2.0 mass% or less. If the amount of Mn is too large, it tends to be disadvantageous for machinability, so it is more preferable to make it less than 1.2 mass%, and even more preferred to make it less than 1. mass%! /.
- Al is an element effective for deoxidation of steel. In addition, it is an element effective in suppressing the austenite grain growth during induction hardening and reducing the induction hardening portion. On the other hand, when it exceeds 0.25 mass%, the effect is saturated, and rather the cost of ingredients is increased. Therefore, the A1 amount is preferably 0.25 mass% or less. In addition, since the effect of the above A1 is not expressed when the amount is less than 0.001 mass%, it is more preferable to set it to 0.001 mass% or more. The power of 0.005 mass% or more is more preferable.
- Ti combines with N, which is mixed as an inevitable impurity in steel, and has the effect of preventing B from becoming a BN and losing its induction hardenability. Therefore, it is preferable to contain the amount 0.005 mass% or more. On the other hand, if it exceeds 0.1 mass%, a large amount of TiN is formed, which tends to decrease the fatigue strength as a starting point for fatigue fracture, so the Ti content is preferably 0.005 to 0.1 mass%. More preferably, it is 0.01-0.07 mass%. Furthermore, to ensure that solid solution N precipitates as soot and exhibits the hardenability of B effectively, the amount of Ti and N should be controlled so that Ti (mass%) ZN (mass%) ⁇ 3.42. Is preferred.
- Mo promotes the formation of a bainite structure after hot working, thereby miniaturizing austenite at the time of induction hardening and finely hardening the hardened layer. It also has the effect of suppressing the austenite grain growth during high-frequency quenching heating and making the hardened layer fine.
- the heating temperature of induction hardening is 800 to 1000 ° C, preferably 800 to 950 ° C, austenite grain growth can be remarkably suppressed.
- it is an element effective in improving hardenability, so it can be used to adjust hardenability.
- it has the effect of suppressing the formation of carbides and preventing the decrease in grain boundary strength.
- Mo is a very useful element. If the amount is 0.05 mass% or more, the average prior austenite grain size of the hardened layer is 7 ⁇ m or less. Since it becomes easy to do, it is preferable that it is 0.05 mass% or more. On the other hand, if the amount of Mo exceeds 0.6 mass%, the hardness of the steel during hot working for forming into a part shape increases significantly, resulting in a decrease in workability. Therefore, the Mo amount is preferably 0.05 to 0.6 mass%. More preferably, it is 0.1 to 0.6 mass%, and still more preferably 0.3 to 0.4 mass%.
- the possibility of the refinement effect of the prior austenite grains by Mo includes the drag effect due to solid solution atoms (Solut Drug Effect), the pinning effect, etc. Is considered.
- Solut Drug Effect Solid Solution atoms
- pinning effect etc.
- the extent to which both or other effects are effective is not necessarily clear at this time, but at least it is confirmed that a pin-ung effect may be manifested. Details will be described later.
- B contains a bainite structure or a martensite structure, and is useful for refining the prior austenite grain size of the hardened layer. Further, there is an effect of improving the fatigue strength by improving the induction hardenability with a small amount of additive and increasing the thickness of the hardened layer. In addition, it preferentially prays to the grain boundaries, reduces the concentration of P segregating at the grain boundaries, increases the grain boundary strength, and improves fatigue strength. However, if the amount is less than 0.0003 mass%, the effect is poor. On the other hand, if it exceeds 0.006 mass%, the effect is saturated, and rather the cost of ingredients is increased. Therefore, the amount of B is preferably 0.0003 to 0.006 mass%. More preferably, it is 0.0005-0.004 mass%, More preferably, it is 0.0015-0.003 mass%.
- the S content is preferably 0.1 mass% or less. More preferably, it is 0.06 mass% or less.
- the P increases the intragranular strength of the hardened layer and contributes to the improvement of fatigue strength. However, if the amount exceeds 0.10 mass%, the grain boundary strength is reduced by praying to the grain boundaries. Therefore, the P amount is 0.1 It is preferable to use less than mass%.
- the balance other than the above elements may be Fe and inevitable impurities, but it is particularly preferable to adjust the component composition so as to satisfy at least one of the following formulas (1) to (3).
- the Vickers hardness ⁇ of the hardened layer can be increased to 750 or more and the intragranular strength can be increased, and the average prior austenite particle size is set to 7 m or less. The effect of improving fatigue strength due to miniaturization is remarkably exhibited.
- the tempering process normally performed after induction hardening can be omitted.
- Hv750 or more can be satisfied within the above component composition range without satisfying any of the above formulas (1), (2) and (3). Therefore, when tempering is omitted, it is not always necessary to satisfy at least one of (1), (2) and (3) above.
- inclusion of one or more selected elements among the following elements is effective in further improving fatigue strength.
- Cr is effective for improving the hardenability and is an element useful for ensuring the hardening depth, so it may be added. However, if contained excessively, it stabilizes the carbide and promotes the formation of residual carbides, lowers the grain boundary strength, and deteriorates the fatigue strength. Therefore, it is desirable to reduce the Cr content as much as possible, but up to 2.5 mass% is acceptable. Preferably it is 1.5 mass% or less. In order to exhibit the effect of improving hardenability, it is preferable to contain 0.03 mass% or more.
- Cu is effective in improving the hardenability, and also dissolves in ferrite, and this solid solution strengthening improves the fatigue strength. Moreover, by suppressing the formation of carbides, Reduces grain boundary strength and improves fatigue strength. However, if the content exceeds l.Omass%, cracking occurs during hot working, so 1.0 mass% or less is added. More preferably, it is 0.5 mass% or less. In addition, it is desirable to add 0.03 mass% or more because the added strength of less than 0.03 mass% is less effective in improving the hardenability and suppressing the decrease in grain boundary strength. Preferably it is 0.1-1.0 mass%.
- Ni 3.5 mass% or less
- Ni is an element that improves hardenability
- Ni is used when adjusting hardenability. It is also an element that suppresses the formation of carbides, suppresses the decrease in grain boundary strength due to carbides, and improves fatigue strength.
- Ni is an extremely expensive element, and adding more than 3.5 mass% increases the steel material cost. If the addition is less than 0.05 mass%, the effect of improving the hardenability and suppressing the decrease in grain boundary strength is desirable. Preferably it is 0.1-1.0mass%.
- Co is an element that suppresses the formation of carbides, suppresses the decrease in grain boundary strength due to carbides, and improves the fatigue strength.
- Co is an extremely expensive element, and if added over l.Omass%, the cost of the steel material increases, so 1.0 mass% or less should be added.
- O. Olmass% it is desirable to add O. Olmass% or more. Preferably, it is 0.02 to 0.5 mass%.
- Nb 0.1 mass% or less
- Nb not only has an effect of improving hardenability, but also combines with C and N in steel and acts as a precipitation strengthening element. It is also an element that improves resistance to temper softening, and these effects improve fatigue strength. However, even if it exceeds 0.1 ma SS %, the effect is saturated, so 0.1 mass% is the upper limit. In addition, it is desirable to add 0.005 mass% or more because the additive strength of less than 0.005 mass% has a small effect of improving the precipitation strengthening action and the temper softening resistance. Preferably it is 0.01-0.05 mass%.
- V 0.5 mass% or less
- V combines with C and N in steel and acts as a precipitation strengthening element. Also temper softening resistance These elements also improve fatigue strength. However, even if the content exceeds 0.5 mass%, the effect is saturated, so the content should be 0.5 mass% or less. In addition, it is desirable to add O. Olmass% or more because the additive strength of less than 0.01 mass% has a small effect of improving fatigue strength. Preferably, it is 0.03 to 0.3 mass%.
- Ta 0.5 mass% or less
- Ta is effective in delaying the microstructure change and may be added because it has an effect of preventing deterioration of fatigue strength, particularly rolling fatigue.
- the content exceeds 0.5 mass% and the content is increased, it does not contribute to further strength improvement.
- it is preferably 0.02 mass S % or more.
- Hf 0.5 mass% or less
- Hf is effective for delaying the microstructure change and may be added because it has an effect of preventing deterioration of fatigue strength, particularly rolling fatigue.
- the content is made 0.5 mass% or less. In order to exhibit the effect of improving fatigue strength, it is preferably 0.02 mass% or more.
- Sb is effective for delaying the microstructure change and may be added because it has an effect of preventing deterioration of fatigue strength, particularly rolling fatigue.
- the content exceeds 0.015 mass% and the content is increased, the toughness deteriorates, so 0.015 mass% or less, preferably 0.01 Omass% or less.
- it is preferable to set it to 0.005 mass% or more.
- W is an element that improves machinability by the brittle action. However, even if added in excess of 1.0 mass%, the effect is saturated and the cost is increased, which is economically disadvantageous. 1. Therefore, it is preferably contained at Omass% or less. To improve machinability, W is 0.0 It is preferable to contain more than 05mass% U.
- Ca forms a sulfide together with MnS, which improves the machinability by acting as a chip breaker and can be added as required.
- the content exceeds 0.005 mass%, the effect is saturated and the component cost is increased, so the content was set to 0.005 mass% or less.
- the machinability improving effect power S is small, so it is preferable to contain 0.0001 mass% or more! /.
- Mg 0.005 mass% or less
- Mg is a de-oxidizing element and becomes a stress concentration source and has the effect of improving machinability, so it can be added as necessary. However, when added excessively, the effect is saturated and the component cost increases, so it was set to 0.005 mass% or less. If it is less than O.OOOlma ss%, the effect of improving the machinability is small even if it is contained, so it is preferable to contain 0.0001 mass% or more.
- Te 0.1 mass% or less
- Se and Te combine with Mn to form MnSe and MnTe, respectively, which improves the machinability by acting as a chip breaker.
- the content exceeds 0.1 mass%, the effect is saturated and the component cost is increased, so that the content is 0.1 mass% or less.
- Bi improves machinability due to melting, lubrication and embrittlement during cutting, and can be added for this purpose. However, if the effect is saturated even if added over 0.5 mass%, the component cost increases, so it was set to 0.5 mass% or less. In the less than O.Olmass%, so be contained small machinability improving effect, it is preferable to contain more than 0.01 mA SS%.
- Pb improves machinability due to melting, lubrication and embrittlement during cutting. It can be added for the purpose. However, if the effect is saturated even if added over 0.5 mass%, the component cost increases, so it was set to 0.5 mass% or less. In the less than O.Olmass%, so be contained small machinability improving effect, it is preferable to contain more than 0.01 mA SS%.
- Zr forms sulfide with MnS, which improves the machinability by acting as a chip breaker.
- the content exceeds 0.01 mass%, the effect is saturated and the cost of the upper component is increased, so the content was set to 0.01 mass% or less. If it is less than 0.003 mass%, the effect of improving machinability is small even if it is contained. Therefore, it is preferable to contain 0.003 ma SS % or more.
- REM forms a sulfide together with MnS, which improves the machinability by acting as a chip breaker. However, even if REM is added in an amount exceeding 0.1 mass%, the effect is saturated and the cost of the component is increased. In order to improve machinability, REM is preferably contained in an amount of 0.0001 mass% or more.
- the force component composition described above in the preferred component composition range is limited to the above range, and the steel structure before induction hardening is set to the structure described below, so that the above-mentioned 7 m or less The average grain size of the prior austenite grains can be obtained.
- the structure of the base material that is, the structure before quenching (corresponding to the structure other than the hardened layer after induction hardening) has a bainite structure and Z or martensite structure, and is either a bainite structure or a martensite structure.
- the total of one or both is preferably 10% by volume or more. This is because the bainite structure or martensite structure is a structure in which carbides are finely dispersed compared to the ferrite-pearlite structure.
- the area of the ferrite Z carbide interface which is the nucleation site of austenite during quenching heating, increases, and the austenite that is produced becomes finer, it contributes to effectively reducing the grain size of the quenched hardened layer. It is. And by making the hardened hardened layer finer, the grain boundary strength increases and the fatigue strength improves.
- the total of one or both of the bainite structure and the martensite structure is more preferably 20% by volume or more.
- the upper limit of the total structural fraction of one or both of the bainite structure and the martensite structure is preferably about 90% by volume. This is because if the total structural fraction exceeds 90% by volume, the machinability of the austenite grains in the hardened layer due to quenching is saturated and the machinability deteriorates rapidly.
- the martensite structure has the same effect as the bainitic structure.
- the bainitic structure is advantageous in terms of manufacturing because it requires a smaller amount of alloying elements, is advantageous in terms of machinability, and can be produced at a lower cooling rate.
- the structure before quenching is preferably a martensite structure in order to refine the prior austenite grain size of the martensite in the hardened layer after induction hardening.
- the machine structural component of the present invention is obtained by subjecting a steel material having the above-described component composition to hot working such as steel bar rolling or hot forging to form a part shape, and at least a part of the part is heated at a temperature of 80 to 1000 ° Manufactured by induction hardening under C conditions. At least a part of this is a part that requires fatigue strength.
- the following method can be used to reduce the average prior austenite grain size of the induction-hardened portion to 7 ⁇ m or less.
- the total processing rate at 800-1000 ° C during hot processing is 80% or more, and then the temperature range of 700-500 ° C is cooled at a rate of 0.2 ° CZs or more.
- the structure before quenching can be made into a uniform fine bainite and Z or martensite structure (structure fraction of 10% by volume or more).
- bainite and martensite have a ferrite-perlite structure.
- the area of the ferrite Z carbide interface which is the nucleation site of austenite, is increased during induction hardening, which is advantageous for making the austenite finer. .
- the total structural fraction of one or both of bainite and martensite must be 10% by volume or more.
- the cooling rate in the temperature range of 700 to 500 ° C is less than 0.2 ° CZs, the total structural fraction of one or both of bainite and martensite cannot be 10% by volume or more. More preferably, the cooling rate is 0.5 ° CZs or more.
- bainite and Z or martensite yarns prior to induction hardening are subjected to processing of 20% or more in the temperature range below 800 ° C (hereinafter referred to as second calorie process).
- second calorie process since the weaving can be further refined and further refinement of the prior austenite grains after induction hardening can be achieved, it is preferable to add a second caking step. Machining in a temperature range of less than 800 ° C may be performed in the hot working process before cooling at the cooling rate (temperature range of 700 to 800 ° C), or cold working may be performed separately after cooling. Or it may be warmed by reheating at a temperature below the A transformation point. Processing at less than 800 ° C is preferably 30% or more.
- Examples of the processing method include cold forging, cold ironing, rolling, and shot.
- the bainite or martensite structure before induction hardening is refined, and as a result, the average grain size of prior austenite grains in the hardened layer obtained after induction hardening becomes finer. As a result, fatigue strength is further improved.
- prior austenite grains having an average grain size of 7 ⁇ m or less can be obtained only with the following induction hardening conditions.
- the heating temperature is less than 800 ° C
- the formation of austenite yarn and weave becomes insufficient, and a cured layer cannot be obtained.
- the heating temperature exceeds 1000 ° C and when the heating rate at 600 to 800 ° C is less than 300 ° CZs, the growth of austenite grains is promoted at the same time.
- the variation in the size of the grains increases, leading to a decrease in fatigue strength. That is, the prior austenite grain size of the finally obtained hardened layer is important to prevent grain growth in the austenite region during quenching heating.
- the pre-structure By setting the pre-structure to be fine bainite or a structure having martensite as described above, there are many nucleation sites for reverse transformation to austenite, so cooling must be carried out before many formed austenite grains grow. If started, the average prior austenite grain size of the quenched structure can be refined. Austenite grains grow at higher temperatures and the longer the holding time in the austenite region, the more the austenite grains grow. In order to obtain, the ultimate temperature during heating is below 1000 ° C, 600
- the rate of temperature rise up to 800 ° C should be 300 ° CZs or higher.
- the temperature reached during heating is 800 to 950 ° C.
- the temperature rising rate at 600 to 800 ° C is preferably 700 ° CZs or more. More preferably, it is 1000 ° CZs or more.
- the residence time of 800 ° C or higher is prolonged during high-frequency heating, austenite grains grow and the final prior austenite grain size tends to increase to over 7 m, so 800 ° C or higher
- the residence time is preferably 5 seconds or less.
- a more preferable heating time is 3 seconds or less.
- Fig. 1 shows the results of examining the relationship between the heating temperature during induction hardening and the prior austenite grain size of the hardened layer for Mo-added steel and Mo-free steel.
- steel materials with the composition shown in the following a steel, b steel, c steel, d steel and e steel are melted in a 150 kg vacuum melting furnace, hot forged to 150 mm square, and then a dummy billet is manufactured. After 80% hot working at 850 ° C, the temperature range from 700 ° C to 500 ° C was cooled at 0.7 ° CZs to produce rolled steel bars. Further, some steel bars were subjected to 20% cold processing after the cooling as the second processing step.
- Step a C: 0.8 mass%, Si: 0.1 mass%, Mn: 0.78 mass%, P: 0.011 mass%, S: 0.019 mass%, Al: 0.024 mass%, Ti: 0.017 mass%, B: 0.0013 mass%, N: 0.0043 mass%, 0: 0.0015 mass%, balance Fe and inevitable impurities.
- Step b C: 0.53 mass%, Si: 0.1 mass%, Mn: 0.74 mass%, P: 0.011 mass%, S: 0.019 mass%, Al: 0.024 mass%, N: 0.0039 mass%, Mo: 0.37 mass%, Ti: 0.018mass%, B: 0.0013mass%, balance Fe and inevitable impurities.
- a torsional fatigue test piece was sampled, subjected to induction hardening at a frequency of 10 to 200 kHz and a heating temperature of 87 to 1050 ° C, and further using a heating furnace at 170 ° C for 30 minutes. Tempering was performed to obtain a test material. The induction hardening conditions were adjusted so that the temperature rise rate was 300 ° CZs or more and the residence time at 800 ° C or more was 1 second or less.
- the stress at which fracture occurred 10 5 times with a stepped torsion test piece of 18 mm in diameter was obtained.
- the average prior austenite particle size of the hardened layer by induction hardening was measured by the above-mentioned method.
- the Vickers hardness at a position of 1/5 of the total surface force of the hardened layer was measured.
- the Vickers hardness was 98 N (lOkgf), and 5 points were hit, and the average value was used.
- the strength of the Mo-added steel can reduce the prior austenite grain size of the hardened layer by lowering the heating temperature during induction hardening.
- the ultimate temperature during heating is 1000 ° C. or lower, preferably 950 ° C. or lower, the particle size of the hardened layer is remarkably reduced.
- the inventors of the present invention can refine the average prior austenite grains of the hardened layer by induction hardening and improve the fatigue strength in the steel containing Mo, because the fine Mo-based precipitates are dense. It is distributed and it is estimated that the above-mentioned pinning effect will increase.
- FIG. 2 shows an example of a transmission electron microscope image actually obtained.
- the sample thickness in this field of view is approximately 0.
- austenite grows by grain nucleation such as bainite or martensite grain boundaries, packet boundaries, and carbides.
- the fine precipitate described above suppresses the movement of the grain interface as if the balloon (grain interface) was pushed in with a finger (precipitate) when the austenite grain interface reached the precipitate and went beyond it. .
- This kind of interfacial movement suppression is called pin jung. If the total precipitation amount is constant, the pinning force increases as the precipitate is small. If the precipitate diameter is constant, the pinung force increases as the amount of precipitate increases.
- the inventors performed a model calculation in which the precipitation volume fraction of Mo was varied in order to observe the influence of the precipitation dispersion state on the average particle size of the prior austenite grains during the high-frequency heat treatment. That is, assuming that the amount of solid solution of Mo in the precipitation phase is very small, if the precipitation volume fraction of the Mo-based fine precipitate: f and the average particle size: d are determined, The number of Mo-based fine precipitates (precipitation density) per 1 ⁇ m 3 is estimated. If the prior austenite grain size is governed by fine precipitation pinning, its size is inversely proportional to the precipitation density. Therefore, considering the fact that the grain size and density of the precipitates in Fig.
- the grain size and the density of the precipitates that exhibit the pinung effect were investigated.
- the number of precipitates per 1 m 3 which is directly effective in controlling the prior austenite grain average diameter, varies depending on the volume ratio of the precipitates.For example, when the volume ratio force is about 0.2 to 0.4%. It was found that the preferred range in which a sufficient pin-ung effect can be achieved and the refinement of prior austenite grains can be realized is as follows.
- this precipitate was subjected to base metal force extraction, and the residue was identified by X-ray diffraction. As a result, it was presumed to be mainly hep-type ( ⁇ , ⁇ ) (C, N). In addition, it comes with a transmission electron microscope
- FIG. 3 shows the relationship between the prior austenite grain size of the hardened layer and the torsional fatigue characteristics.
- the prior austenite grain size is 7 m or less. It can be seen that the effect of improving torsional fatigue strength is great. This is thought to be because the intragranular strength of the hardened layer is increased by increasing the amount of C, Si or P. Therefore, when the Vickers hardness of the hardened layer was investigated, Hv700 for steel a, Hv740 for steel b, Hv902 for steel c, Hv775 for steel d, Hv760 for steel e, and the hardness of the hardened layer is Hv750 or higher. It was confirmed that the effect of improving fatigue strength due to the refinement of prior austenite grains becomes very large.
- FIG. 4 shows the relationship between the prior austenite grain size of the hardened layer and the torsional fatigue characteristics by comparing the case with tempering and the case without tempering.
- Figure 4 shows that fatigue strength can also be improved by omitting tempering.
- a method that does not perform the tempering process can also be positively adopted.
- parts may crack if tempering is not performed.
- tempering after induction hardening is a commonly performed process.
- This crack is usually a grain boundary fracture and is caused by insufficient grain boundary strength.
- the grain boundary strength is high due to the refinement of the prior austenite grains, cracks are not likely to occur even if the tempering treatment is omitted. Omitting the tempering process is effective in preventing softening by tempering and reducing the tempering process cost.
- the measurement results described above are comparative examples in which all of Nos. 7 and 25 are low in C, Si, and P.
- the inventive example shows the torsional fatigue strength. It can be seen that is further improved.
- the prior austenite grain size becomes coarse and the torsional fatigue strength decreases.
- the old austenite grain size was coarsened and the fatigue strength was reduced, especially because the base metal structure was ferrite pearlite.
- fatigue strength is further improved compared to No. 1 and No. 7 steels, respectively, when no tempering after induction hardening is performed.
- No. 31 steel has a total machining temperature of 800 to 1000 ° C during hot working. Since the rate is small, the prior austenite grain size becomes large and the fatigue strength is low.
- a constant velocity joint 12 shown in Fig. 5 was interposed to transmit power from the drive shaft 10 to the wheel hub 11.
- This constant velocity joint 12 is a combination of an outer ring 13 and an inner ring 14. That is, the inner ring 14 is slidably fixed to the inner side of the mouse part 13a via a ball 15 fitted in a ball raceway groove formed on the inner surface of the mouse part 13a of the outer ring 13, and the drive shaft 10 is attached to the inner ring 14
- the stem portion 13b of the outer ring 13 is connected to the hub 11 by, for example, a spline to transmit power from the drive shaft 10 to the hub 11 of the wheel.
- a constant velocity joint inner ring (outer diameter: 45 mm and inner diameter: 20 mm) is formed by hot forging, and then splined to the mating surface by cutting or rolling cage A groove was formed for.
- the rolling surface of the ball was formed by cutting or cold forging. Cooling after hot forging was carried out under the conditions shown in Table 4.
- the total processing rate in hot forging and cold forging was performed by adjusting the cross-sectional reduction rate of the cross section perpendicular to the axial direction of the rolling surface.
- the rolling contact surface 14a of the ball interposed between the constant velocity joint outer ring is induction hardened at 1050 ° C using an induction hardening device with a frequency of 15 Hz, and then After induction hardening under the conditions shown in Table 4 to obtain a hardened yarn and woven layer 16, tempering was performed in a heating furnace at 180 ° C. for 2 hours. Tempering was omitted for some constant velocity joints.
- the constant velocity joint inner ring obtained by force is fitted with the drive shaft on the mating surface and attached to the mouse part of the constant velocity joint outer ring via a ball (steel ball), while the constant velocity joint outer ring is A constant velocity joint boot was obtained by fitting a hub to the stem (see Fig. 5).
- the specifications of the ball, outer ring, drive shaft and knob are as follows.
- Outer ring induction hardened and tempered steel for machine structural carbon steel
- Hub induction hardened and tempered steel for machine structural carbon steel
- the average austenite grain diameter and hardness of the hardened layer were determined by the same method as described above.
- the invention example has an improved rolling fatigue life.
- Mo, B or Ti is insufficient as in Nos. 26, 27 and 28, the prior austenite grain size becomes coarse and the rolling fatigue life decreases.
- the prior austenite grain size became coarse and the fatigue strength decreased.
- rolling fatigue life is further improved compared to No. 1 steel and No. 7 steel, respectively, when tempering after induction hardening is not performed.
- No. 31 steel has a small total working rate of 800-1000 ° C during hot working, so the prior austenite grain size increases and the rolling fatigue life is low.
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
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US11/587,731 US20080247900A1 (en) | 2004-07-16 | 2005-07-05 | Component for Machine Structure, Method of Producing the Same and Material for Induction Hardening |
JP2006519625A JP4645593B2 (ja) | 2004-07-16 | 2005-07-05 | 機械構造用部品およびその製造方法 |
EP05758220.7A EP1770181B1 (en) | 2004-07-16 | 2005-07-05 | Component for machine structure, method for producing same, and material for high-frequency hardening |
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JP2004010200 | 2004-07-16 | ||
JPPCT/JP2004/010200 | 2004-07-16 |
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WO2006008960A1 true WO2006008960A1 (ja) | 2006-01-26 |
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US (1) | US20080247900A1 (ja) |
EP (1) | EP1770181B1 (ja) |
JP (1) | JP4645593B2 (ja) |
CN (1) | CN100529137C (ja) |
WO (1) | WO2006008960A1 (ja) |
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WO2017002532A1 (ja) * | 2015-06-29 | 2017-01-05 | Ntn株式会社 | 機械部品 |
JP2020158801A (ja) * | 2019-03-25 | 2020-10-01 | 株式会社神戸製鋼所 | 鋼材 |
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Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2012225203A (ja) * | 2011-04-18 | 2012-11-15 | Nippon Parkerizing Co Ltd | 高耐久性エンジンバルブ |
CN104593558A (zh) * | 2015-01-10 | 2015-05-06 | 安徽东星汽车部件有限公司 | 一种高频淬火剂及其制备方法 |
WO2017002532A1 (ja) * | 2015-06-29 | 2017-01-05 | Ntn株式会社 | 機械部品 |
JP2017014550A (ja) * | 2015-06-29 | 2017-01-19 | Ntn株式会社 | 機械部品 |
EP3315625A4 (en) * | 2015-06-29 | 2018-12-26 | NTN Corporation | Machine part |
JP2020158801A (ja) * | 2019-03-25 | 2020-10-01 | 株式会社神戸製鋼所 | 鋼材 |
JP7185574B2 (ja) | 2019-03-25 | 2022-12-07 | 株式会社神戸製鋼所 | 鋼材 |
Also Published As
Publication number | Publication date |
---|---|
EP1770181A4 (en) | 2010-11-24 |
JPWO2006008960A1 (ja) | 2008-05-01 |
EP1770181A1 (en) | 2007-04-04 |
EP1770181B1 (en) | 2013-11-06 |
JP4645593B2 (ja) | 2011-03-09 |
CN1950530A (zh) | 2007-04-18 |
CN100529137C (zh) | 2009-08-19 |
US20080247900A1 (en) | 2008-10-09 |
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