Technical field
[0001]
　The present invention relates to a shaft part, more particularly, to a shaft part subjected to induction hardening.
BACKGROUND
[0002]
　Shaft parts used in automobiles and industrial machinery (e.g., transmission shaft) to include those induction hardening or carburizing, which is a type of surface hardening treatment.
[0003]
　As a method for producing a shaft part subjected to quenching, for example, it includes the following method. That is, initially, to produce a crude member having a shape close to the final product. Then, a hole in drilling or the like, to produce the intermediate member closer to the final product. Finally, subjected to quenching (induction hardening or carburizing and quenching) to the intermediate member to obtain a shaft part.
[0004]
　Usually, the shaft parts are opened and various holes, including oil hole, the periphery of the hole, has a strength on the weakest site. Therefore, to increase the strength of the shaft part having a hole must focus strengthen hole and its surroundings. Techniques to increase the torsional fatigue strength of the shaft part is disclosed in US Pat.
[0005]
　Patent Document 1, to form a hardened layer in the oil hole opening, high crankshaft of torsional fatigue strength is disclosed by induction hardening.
[0006]
　Patent Document 2, the compressive residual stress in the surface layer of the oil hole is excellent shaft and its fatigue strength improvement methods fatigue resistance, which is a 50% to 90% of the tensile strength of the steel material disclosed It is.
CITATION
Patent Document
[0007]
Patent Document 1: JP 2001-262230 Patent Publication
Patent Document 2: JP 2006-111962 JP
Summary of the Invention
Problems that the Invention is to Solve
[0008]
　By the way, in these days of automobiles and industrial machinery, for good fuel consumption, size and weight have been strongly demanded. Among them, the shaft part, in addition to the further improvement of the torsional fatigue strength, are both superior static torsional strength required. However, the shaft part obtained by the technique disclosed in Patent Document 1, among other oil hole surface, a boundary portion for performing quenching, since fatigue cracking so-called shrink boundary starting from occurs, significant improvement of fatigue strength It is difficult. Furthermore, for reasons that the ingredients and a surface layer of tissue of the steel material is inappropriate, it may be difficult to achieve both static torsional strength and torsional fatigue strength.
[0009]
　In the technique disclosed in Patent Document 2, by striking the oil hole inner surface by ultrasonic vibration terminal, by generating compressive residual stress on the oil hole inner surface, and enhance the baked boundary. However, the impact by the ultrasonic vibration terminal, it is difficult to apply a uniformly processing the entire oil hole, always strength goals have been no possibility of resulting. Furthermore, for reasons that the ingredients and a surface layer of tissue of the steel material is inappropriate, it may be difficult to achieve both static torsional strength and torsional fatigue strength.
[0010]
　As a method to enhance oil hole, in addition to the striking by the ultrasonic vibration terminal disclosed in Patent Document 2, also conceivable surface modification treatment by shot peening. However, none of these processes require different equipment and devices to the usual process, is economically disadvantageous because the cost is increased.
[0011]
　The present invention was made in view of the above circumstances, and an object thereof is to provide a shaft component having excellent static torsional strength and torsional fatigue strength.
Means for Solving the Problems
[0012]
　The present inventors have found that a method for manufacturing the shaft part and the shaft part which can both static torsional strength and torsional fatigue strength was examined intensively. As a result, the present inventors have found that usually without drilling before induction hardening is performed, the pierceable by drilling by cutting after induction hardening, increases the hardness of the vicinity of the hole, crack occurrence to suppress or progression, was found to static torsional strength and torsional fatigue strength of the shaft part can be improved. Further, if the deformation-induced martensitic transformation many residual austenite by during cutting, it was also found that the static torsional strength and torsional fatigue strength of the shaft part is further improved.
[0013]
　Usually, in order to control the transformation behavior of the strain induced martensite during cutting, it is effective to optimize the cutting conditions. Therefore, the present inventors have found that in order to much as possible transformation of the martensite was attempted to optimize the cutting conditions. However, than optimized only cutting conditions, although static torsional strength and torsional fatigue strength of the shaft part is certainly improved, but failed to reach the target value is.
[0014]
　Accordingly, the inventors have focused in chemical composition and heat treatment conditions of the steel material, we tried to further improve the static torsional strength and torsional fatigue strength. As a result, by employing a particular steel component and the heat treatment conditions, it tends to occur is work-induced martensitic transformation during machining, static torsional strength and torsional fatigue strength of the shaft part is found to be remarkably improved.
[0015]
　Conventionally, in order to control the amount of retained austenite, the adoption of the chemical composition and heat treatment conditions of the particular steel, is conventional. However, not only the amount of retained austenite, in order to control the behavior of the deformation-induced martensitic transformation during machining, to optimize the chemical composition and heat treatment conditions of steel, new technical not performed heretofore is a thought.
[0016]
　By the above, the present inventors have found that dramatically improves static torsional strength and torsional fatigue strength of the shaft part, the chemical composition of the steel material, instead of individually optimized heat treatment conditions and cutting conditions, these to obtain a knowledge that it is desirable to organically optimized associating conditions with each other.
[0017]
　Then, the present inventors have found that the chemical composition of the steel material, an organic optimization of heat treatment conditions and cutting conditions, and tissue and after cutting tissue after induction hardening is appropriately controlled, therefore, the static torsional strength and torsional fatigue strength well balanced improved shaft parts is obtained, to obtain a knowledge that. Based on the above findings, the present inventors have completed an excellent shaft parts static torsional strength and torsional fatigue strength. Its gist is as follows.
[0018]
　[1]
　by mass%, C: 0.35 ~ 0.70% , Si: 0.01 ~ 0.40%, Mn: 0.5 ~ 2.6%, S: 0.005 ~ 0.020% , Al: 0.010 ~ 0.050%, N: containing 0.005 to 0.025%,
　as an impurity
　element, P: 0.050% or
　less, O: 0.003% or less
　in addition, optional as the
　element, Pb: 0.5% or
　less, V, 0.1% or less in total content of one or more selected from the group consisting of Nb and
　Ti, Cr: 3.0% or less, Mo: 3.0 % or less, and, Ni: 3.0% 1 or more selected from the group consisting of
　Cu:
　0 - 0.50%, B: 0 contained to 0.020%
and the balance being Fe and impurities it has a chemical composition satisfying the formula (1),
　has at least one hole to the outer peripheral surface,
　a depth position of 2mm from the outer peripheral surface, One residual austenite volume fraction from the surface 2mm of holes (R1) is 4% to 20%
　at a depth position of 2mm in the axial direction of the hole from the R1 and the outer peripheral surface, and of 20μm from the surface of the hole residual austenite volume fraction of the depth position (R2) Tokara formula (a): Δγ = [( R1-R2) / R1] residual austenite reduction rate [Delta] [gamma] obtained by the × 100 is 40% or more,
and characterized in that to, shaft parts.
　15.0 ≦ 25.9C + 6.35Mn + 2.88Cr + 3.09Mo + 2.73Ni ≦ 27.2 (1)
　wherein each element symbol in the formula (1), the content of each element (mass%) is substituted .
　[2] Shaft component according to the [1], which has a plastic flow layer with a thickness of 0.5 ~ 15 [mu] m on the surface of the hole.
Effect of the invention
[0019]
　The shaft part of the manufacturing method of the present invention, on the premise of adjusting the chemical composition of the crude member as a material for the shaft part, in particular, the organization of the steel after hardening, the tissue of the shaft part after boring, It has made improvements for. As a result, it is possible to obtain an excellent shaft parts static torsional strength and torsional fatigue strength.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020]
[1] Figure 1 (a) is a schematic view of the shaft parts hardened material or final form, FIG. 1 (b) shows a section A-A 'cut perpendicular to the longitudinal direction of the shaft parts it is a diagram.
FIG. 2 is a depth of 2mm from the outer peripheral surface, and is a view showing the measurement position 21 of the retained austenite volume fraction at a depth position of 20μm from the surface of the hole.
[3] FIG. 3 (a) is a schematic view of the shaft components, FIG. 3 (b), at a depth position of 2mm in the axial direction of the bore from the outer periphery of the shaft part and the axial direction of the bore Te is a diagram showing a cross-section C-C 'cut vertically.
[4] FIG. 4 is a outer peripheral depth position of 2mm in the axial direction of the hole from the shaft part, and in a section cut perpendicular to the axial direction of the bore, the surface layer of a scanning electron microscope image of the hole is there.
FIG. 5 is a side view of a test piece used in the torsion test.
FIG. 6 is a top view of a hole drilled in the shaft part.
DESCRIPTION OF THE INVENTION
[0021]
　Hereinafter, with reference to the accompanying drawings, illustrating a shaft component according to an embodiment of the present invention in detail. In the drawings, the same or corresponding members, and description thereof will not be repeated given the same reference numerals.
[0022]

　Shaft component according to the embodiment of the present invention, in mass%, C: 0.35 ~ 0.70% , Si: 0.01 ~ 0.40%, Mn: 0.5 ~ 2.6 %, S: 0.005 ~ 0.020% , Al: 0.010 ~ 0.050%, N: containing 0.005 to 0.025 percent,
　as the impurity element, P: 0.050% or less,
　O: 0.003% or less
　in addition, as an element
　optional, Pb: 0.5% or
　less, V, 0.1% or less in total content of one or more selected from the group consisting of Nb and
　Ti, Cr : 3.0% or less, Mo: 3.0% or less, and, Ni: 3.0% 1 or more selected from the group consisting
　of, Cu: 0 ~
　0.50%, B: 0 ~ 0. contains 020%
and the balance being Fe and impurities, formula (1): 15.0 ≦ 25.9C + 6.35Mn + 2.8 8Cr + 3.09Mo + have 2.73Ni ≦ 27.2 chemical composition satisfying,
　at least one hole to the outer peripheral surface,
　a depth position of 2mm from the outer peripheral surface, and residual austenite volume fraction from the surface 2mm of holes (R1 ) is 4% to 20%
　at a depth position of 2mm from the R1 and the outer peripheral surface in the axial direction of the hole, and since the surface of the hole residual austenite volume fraction of the depth position of 20μm and (R2) formula (A): Δγ = [( R1-R2) / R1] residual austenite reduction rate [Delta] [gamma] obtained by the × 100 is 40% or more.
[0023]
　A shaft component according to the embodiment of the present invention, the shaft parts used in automobiles and industrial machines, for example, transmission shafts include. Preferred, the shape of the shaft part, diameter 150mm or less, it is tubular or rod-like parts or 5mm long hollow or solid.
[0024]
[Shaft components chemical composition (essential component)]
　shaft part has the following chemical composition. The proportion of each element in the following (%) refers to all mass%.
[0025]
　 C: 0.35 ~ 0.7 0 %
　carbon (C) increases the strength of the shaft part (especially the strength of the core). C further generates residual austenite for increasing the static torsional strength and torsional fatigue strength of the shaft part. If the C content is too low, the effect can not be obtained. On the other hand, if the C content is too high, the strength of the steel material processed into the shaft part is too high. Therefore, the steel machinability is lowered. Moreover, the strain generated at the time of induction hardening increases, quenching crack is generated. Therefore, C content is 0.35% or more and 0.70%. The preferable lower limit of C content is 0.40% or more. The preferable upper limit of the C content is less than 0.65%.
[0026]
　 Si: 0.01 ~ 0.4 0 %
　Silicon (Si) has the effect of improving the hardenability, when the carburizing treatment, thus increasing the carburization anomaly layer. In particular, when the Si content exceeds 0.40% soft tissue called incomplete quenched structure to carburization anomaly layer is greatly increased is generated, torsional fatigue strength of the shaft part is reduced. To prevent the formation of carburized abnormal layer is preferably to a content of Si 0.30% or less, and more preferably set to 0.20% or less. However, it is difficult to make the content of Si in the mass production of the steel to less than 0.01%. Therefore, the content of Si and from 0.01 to 0.40%. In consideration of the manufacturing cost in mass production of steel, in the present invention product it is actually manufactured, Si content is believed to often be contained 0.05% or more.
[0027]
　 Mn: 0.5 ~ 2.6%
　manganese (Mn) is to increase the hardenability of steel to be processed in the shaft part, to increase the residual austenite in the steel. Austenite, compared with austenite containing no Mn, during cutting of the hole after induction hardening, strain-induced martensite easy transformation containing Mn. As a result, the static torsional strength and torsional fatigue strength of the shaft part is increased. If the Mn content is too low, the effect can not be obtained. On the other hand, if the Mn content is too high, residual austenite after induction hardening is excessively increased. Therefore, without generating a sufficient work-induced martensite transformation during cutting of the hole, after cutting becomes excessive retained austenite does not occur sufficiently deformation-induced martensite transformation and thus during cutting, after cutting residual austenite is unlikely to decrease. As a result, the static torsional strength and torsional fatigue strength of the shaft part after cutting is reduced. Therefore, Mn content is from 0.5 to 2.6%. The preferable lower limit of the Mn content is 0.8%, more preferably from 1.4%. The preferable upper limit of the Mn content is 2.0%.
[0028]
　 P: 0.050% or less
　phosphorus (P) is an impurity. P lowers the grain boundary strength segregated at the grain boundaries. As a result, the static torsional strength and torsional fatigue strength of the shaft part is reduced. Accordingly, P content is 0.050% or less. The preferable upper limit of the P content is 0.030%. P content is better as low as possible. The preferable lower limit of the P content is 0.0002%.
[0029]
　 S: 0.005 ~ 0.020%
　of sulfur (S) is to form MnS by combining with Mn, increasing the machinability of the steel material. If the S content is too low, the effect can not be obtained. On the other hand, if the S content is too high, it forms coarse MnS, hot workability of the steel, cold workability and torsional fatigue strength of the shaft part is reduced. Thus, S content is 0.005 to 0.020%. The preferable lower limit of the S content is 0.008%. The preferable upper limit of the S content is 0.015%.
[0030]
　 Al: 0.010 ~ 0.050%
　of aluminum (Al) is an element for deoxidizing steel. Al further, AlN was formed by combining the N, refining the crystal grains. As a result, the static torsional strength and torsional fatigue strength of the shaft part is increased. If the Al content is too low, not this effect was obtained. On the other hand, if the Al content is too high, hard and coarse Al 2 O 3 to produce the steel product as machinability is reduced, further, it is also reduced torsional fatigue strength of the shaft part. Therefore, Al content is 0.010 to 0.050%. A preferable lower limit of Al content is 0.020%. The preferable upper limit of Al content is 0.040%.
[0031]
　 N: 0.005 ~ 0.025%
　nitrogen (N) is the grain refining by forming a nitride to increase the static torsional strength and torsional fatigue strength of the shaft part. If the N content is too low, the effect can not be obtained. On the other hand, if the N content is too high, coarse nitrides are generated, the toughness of the steel is lowered. Therefore, N content is from 0.005 to 0.025%. The preferable lower limit of the N content is 0.010%. The preferable upper limit of the N content is 0.020%.
[0032]
　 O: 0.003% or less
　oxygen (O) is an impurity. O forms a hard oxide inclusions bonded with Al. Oxide inclusions lowers the machinability of the steel material, torsional fatigue strength of the shaft part is also reduced. Therefore, O content is 0.003% or less. O content is better as low as possible. The preferable lower limit of the O content is 0.0001%.
[0033]
　The remainder of the chemical composition of the steel is iron (Fe) and impurities. The impurities, ore, scrap is used as a raw material of steel, or a component that mixes the environment, etc. of the production process, it means intentionally not were contained Ingredient steel material.
[0034]
[Shaft chemical composition (optional component) Component]
　steel for machining the shaft component further, in place of part of Fe, and may contain Pb.
[0035]
　 Pb: 0.5% or less
　of lead (Pb) are optional elements may not be contained. If contained, reduction in tool wear during cutting and improvement in chip disposability can be realized. However, if the Pb content is too high, the strength and toughness of the steel decreases, also decreases static torsional strength and torsional fatigue strength of the shaft part. Therefore, Pb content is preferably 0.5% or less. Still more preferred upper limit of the Pb content is 0.4%. In order to obtain the above effect, it is preferable to 0.03% or more Pb content.
[0036]
　Steel for machining the shaft component further, in place of part of Fe, V, may contain one or more selected from the group consisting of Nb and Ti.
[0037]
　 V, Nb and Ti: 0.1% or less in total content
　of vanadium (V), niobium (Nb) and titanium (Ti) is an optional element and may not be contained. These elements, when combined with C and N, to form a precipitate. Precipitates of these elements complements the grain refining of the quenched portions by AlN. Precipitates of these elements increases the static torsional strength and torsional fatigue strength of the shaft part. However, the total content of these elements if it exceeds 0.1%, precipitates are coarsened, torsional fatigue strength decreases. Therefore, V, the total content of Nb and Ti is preferably 0.1% or less. Optionally elemental, V, if any one or more kinds are contained Nb and Ti, the effect can be obtained. V, more preferably the upper limit of the total content of Nb and Ti is 0.08%. V, and to obtain the above effects by Nb and Ti is preferably contained 0.01% or more.
[0038]
　Further steel processed into the shaft part, instead of a part of Fe, Cr, may also contain one or more selected from the group consisting of Mo and Ni. Both of these elements increases the hardenability of steel and increases the residual austenite.
[0039]
　 Cr: 3.0% or less
　chromium (Cr) is an optional element, it may not be contained. Cr increases the hardenability of steel, further, increase the residual austenite. However, if the Cr content is too high, residual austenite after induction hardening is excessively high. In this case, does not occur sufficiently deformation-induced martensitic transformation during machining, even residual austenite is less likely to decrease after cutting. As a result, the static torsional strength and torsional fatigue strength of the shaft part is reduced. Therefore, it is preferable Cr content is 3.0% or less. To obtain the above effect by Cr, preferably containing at least 0.1%. The preferable upper limit of the Cr content is 2.0%.
[0040]
　 Mo: 3.0% or less
　Molybdenum (Mo) is an optional element and may not be contained. If contained, Mo increases the hardenability of steel and increases the residual austenite. Mo further enhances the tempering softening resistance, increase the static torsional strength and torsional fatigue strength of the shaft part. However, if Mo content is too high, residual austenite after induction hardening is excessive. In this case, sufficient deformation-induced martensitic transformation does not occur at the time of cutting. As a result, the static torsional strength and torsional fatigue strength of the shaft part is reduced. Therefore, Mo content is preferably not more than 3.0%. Still more preferred upper limit of the Mo content is 2.0%. To obtain the above effect by Mo, preferably containing at least 0.1%.
[0041]
　 Ni: 3.0% or less
　of nickel (Ni) is an optional element and may not be contained. If contained, Ni enhances hardenability of the steel, increases the residual austenite. Ni further enhance the toughness of the steel material. However, if the Ni content is too high, residual austenite after induction hardening is excessive. In this case, sufficient deformation-induced martensitic transformation does not occur at the time of cutting after quenching. As a result, the static torsional strength and torsional fatigue strength of the shaft part is reduced. Therefore, it is preferable Ni content is 3.0% or less. Still more preferred upper limit of the Ni content is 2.0%. To obtain the above effect by Ni, preferably containing at least 0.1%.
[0042]
　 Cu: 0 ~
　0.50% Cu increases the strength of steel by solid solution in martensite. Therefore, increased fatigue strength of the steel material. However, if the Cu content is too high, during hot forging was segregated at the grain boundaries of the steel induces hot cracking. Therefore, Cu content is 0.50% or less. Incidentally, it is preferable that the Cu content is 0.40% or less, and still more preferably not more than 0.25%. To obtain the above effect by Cu, preferably it contains more than 0.10%.
[0043]
　 B: 0 ~ 0.020%
　B has an effect of increasing the toughness by suppressing the grain boundary segregation of P. However, the addition of 0.020% or more, resulting abnormal grain growth during carburization, torsional fatigue strength decreases. Therefore, B content is 0.020% or less. Incidentally, B content is preferably in 0.015%, and still more preferably 0.010% or less. To obtain the above effect by B, preferably contains at least 0.0005%.
[0044]
　Incidentally, a shaft component according to the present invention, in its chemical composition, may contain trace elements other than the above as an impurity. Even in this case, an object of the present invention can be achieved. As a specific example, a shaft component according to the present invention, each element described below can be included in the specified range, respectively.
　Rare earth element (REM): 0.0005% or less,
　calcium (Ca): 0.0005% or less,
　magnesium (Mg): 0.0005% or less,
　tungsten (W): 0.001% or less,
　antimony (Sb): 0.001% or less,
　bismuth (Bi): 0.001% or less,
　cobalt (Co): 0.001% or less,
　tantalum (Ta): 0.001% or less,
[0045]
[The content of the relationship of each element]
　relationship of the content of each element constituting the steel is processed into the shaft part, it satisfies the formula (1) shown below.
　15.0 ≦ 25.9C + 6.35Mn + 2.88Cr + 3.09Mo + 2.73Ni ≦ 27.2 (1)
　where the element symbol in the formula (1), content in the steel of the corresponding element (mass%) of It is assigned.
[0046]
　 For formula (1)
　in equation (1) is defined as F1 = 25.9C + 6.35Mn + 2.88Cr + 3.09Mo + 2.73Ni. F1 value is a parameter indicating the stability of the austenite. Equation (1) is an empirical formula obtained by regression analysis from measurements of residual γ volume fraction of hardened steel of various chemical components. If F1 value is too low, austenite thermodynamically unstable, after induction hardening, residual austenite is not sufficiently generated, the static torsional strength and torsional fatigue strength of the shaft part is reduced. On the other hand, if F1 value is too high, increasing the stability of the austenite, residual austenite after induction hardening is excessively increased. In this case, the deformation-induced martensitic transformation is less likely to occur at the time of cutting. Therefore, the static torsional strength and torsional fatigue strength of the shaft part is reduced. Thus, F1 is 15.0 to 27.2. A preferred lower limit of F1 is 16.5, the preferred upper limit is 27.0 or less.
[0047]
　[Holes of the shaft outer peripheral surface]
　shaft component according to the embodiment of the present invention, a vertical or at an angle to the longitudinal direction of the shaft part, a through-hole or non-through holes drilled from the shaft outer circumferential surface a. The diameter of the holes is 0.2 mm ~ 10 mm. Shaft parts has one or more of these holes.
[0048]
Depth position of 2mm from the outer peripheral surface and from the surface of the bore 2mm residual austenite volume fraction (R1) of]
　by induction hardening of the shaft part, the surface layer of the shaft parts (including 2mm depth position from the outer circumferential surface) , residual austenite is generated. This residual austenite is at the time of processing drilling after quenching of the shaft part, in the vicinity of the hole, to deformation-induced martensitic transformation. More specifically, during drilling, the frictional force between the cutting tool and the base material, a part of the residual austenite in the vicinity of the surface layer of the hole, transforms into deformation-induced martensite. On the other hand, the occurrence of deformation-induced martensitic transformation due to this effect is limited to the vicinity of the hole. Leaves about 2mm from the surface of the hole, it does not occur deformation-induced martensitic transformation due to the longer boring. Therefore, 2mm depth position from the outer circumferential surface, and residual austenite volume fraction from the surface 2mm of holes (R1) is a portion that is not affected by drilling after quenching processing, the residual austenite volume fraction before cutting it can be considered.
　Processing associated with drilling-induced martensitic transformation of the result, the strength of the shaft part rises, static torsional strength and torsional fatigue strength is increased. In order to obtain such an effect, the maximum residual austenite volume fraction after quenching (R1) must be at least 4%.
[0049]
　On the other hand, the residual austenite is because it is soft, (R1) is rather strength of the shaft part is reduced more than 20%.
[0050]
[A depth position of 2mm in the axial direction of the hole from the outer peripheral surface, and residual austenite volume fraction of the depth position of 20μm from the surface of the bore (R2)]
　depth 2mm from the outer peripheral surface of the shaft part in the axial bore position, and the residual austenite volume fraction of the depth position of 20μm from the surface of the bore (R2) is a residual austenite volume fraction in the vicinity of the surface which is created by drilling, it is considered as retained austenite volume fraction after cut can. If the volume fraction of retained austenite after cutting is too high, hard martensite is not obtained, the static torsional strength and torsional fatigue strength is lowered.
[0051]
: [R1 and R2 Tocharian formula (A) Δγ = [(R1 -R2) / R1] residual austenite reduction rate determined by × 100 [Delta]
　[gamma]] from R1 and R2 Prefecture, residual austenite reduces obtained by the above formula (A) rate ([Delta] [gamma]) is 40% or more.
[0052]
　Residual austenite reduction rate ([Delta] [gamma]) is indicative of the degree of deformation-induced martensitic transformation during machining. If Δγ is large, many work-induced martensitic transformation due time cutting means that has occurred, the static torsional strength and torsional fatigue strength of the shaft part can be improved. Must Δγ 40% or more in order to obtain such an effect. The value of the preferred Δγ is 42% or more.
[0053]
[A plastic flow layer on the surface of the hole thickness: 0.5 ~ 15 [mu] m]
　plastic flow layer, at the time of cutting a hole, formed on the surface of the hole in the deformation by friction between the cutting tool and the base material that is a layer. The thickness of the plastic flow layer on the surface of the bore is measured by the following method. At a depth position of 2mm from the outer circumference of the shaft part in the axial direction of the bore, and comprises a hole surface portion in the cross section perpendicular to the axial direction of the bore, a surface perpendicular (cross section) for axial bore observed collecting specimen such that the surface (reference numeral 31 in Figure 3 (b)). The mirror-polished specimens corroded with 5% nital solution. Position including a surface of the bore of the corroded surface (31), is observed at 5000 magnification of the scanning electron microscope (SEM). An example of the resulting SEM image shown in FIG. Parts In the figure, the plastic flow layer 41, the plastic flow tissue against the base material center 42 is curved (left direction of the page in FIG. 4 right) circumferential surface of the hole of the shaft parts it is.
[0054]
　During cutting, large deformation in the surface portion of the hole by friction between the cutting tool and the base material that occurs, the plastic flow layer is formed. The plastic flow layer may deform resistant than the base metal. Therefore, if the thickness is present 0.5μm or more plastic flow layer, torsional strength and torsional fatigue strength of the shaft part can be improved. On the other hand, since plastic flow layer is brittle, if the thickness exceeds 15 [mu] m, the starting point of cracks caused cracking by deformation. Therefore, too thick plastic flow layer reduces the torsional fatigue strength of the shaft part reversed. Further, if the thickness of the plastic flow layer is more than 15 [mu] m, the machinability of the shaft part is reduced, the cutting load on the tool during processing is increased, tool life is significantly reduced. For the above reasons, the thickness of the plastic flow layer of the shaft parts is limited to 0.5 ~ 15 [mu] m. In order to further improve the wear resistance and flexural fatigue strength of the shaft part, the thickness of the surface layer of the plastic flow layer of the shaft part is preferably set to more than 1 [mu] m, and even more preferably from 3μm or more. Further, the upper limit thereof is preferably 13 .mu.m.
[0055]
　Thus, the shaft component according to the present invention, the periphery of the hole can be a factor of lowering the static torsional strength and torsional fatigue strength, with excellent partial strength. Specifically, the shaft part is, as shown in FIG. 6, the periphery of the hole, and a region where the ratio of strain-induced martensitic structure is high (referred to as "strain-induced martensite layer"). Compared to the residual austenite, work-induced martensite for increasing the strength of the tissue, the intensity of the hole periphery of the shaft part (20 [mu] m depth position from the hole surface) is, 2 mm depth position from a distance (hole surface of the hole higher than the strength of). Therefore, the shaft part is excellent in static torsional strength and torsional fatigue strength.
[0056]
　Further, the shaft part is, in the surface layer of the bore, may be provided with a plastic flow layer of appropriate thickness. The plastic flow layer is also excellent in strength than the base metal.
[0057]
　Shaft component according to the embodiment of the present invention are prepared in the following manner.
　By mass%, C: 0.35 ~ 0.70% , Si: 0.01 ~ 0.40%, Mn: 0.5 ~ 2.6%, S: 0.005 ~ 0.020%, Al: 0.010 ~ 0.050%, N: contain .005 to .025%,
　as an impurity element, P: 0.050% or
　less, O: 0.003% or less
　in addition, as an element of an optional,
　pb: 0.5% or
　less, V, 0.1% or less in total content of one or more selected from the group consisting of Nb and
　Ti, Cr: 3.0% or less, Mo: 3.0% or less, and, Ni: 3.0% 1 or more selected from the group consisting
　of, Cu:
　0 - 0.50% B: 0 contained to 0.020%
and the balance being Fe and impurities , obtaining a shaft parts crude member by processing a steel material having a chemical composition satisfying the formula (2) in the shape of the shaft part,
　the crude A process for obtaining a hardened material is subjected to induction hardening process on wood, or 10KHz frequency at the time of induction heating, and following 300 KHz, the heating time at the time of induction heating as below 40 seconds 1 seconds, then quenching it is, tissue from the outer peripheral surface of the depth position of 2mm quenching material, and martensite, a step of obtaining a hardened material comprising a tissue containing residual austenite of 4-20% by volume,
　relative to the hardened material Te subjected to drilling by cutting, comprising the steps of obtaining a shaft part, boring tool feed of 0.02 mm / rev greater during processing, the less 0.2 mm / rev, cutting speed 10 m / min or more, and 50 m / min or less,
　a depth position of 2mm from the outer peripheral surface of the shaft part, and the residual austenite volume fraction from the surface 2mm of the hole and (R1), the outer shaft part At a depth position in the axial direction to 2mm hole from the surface, and because the surface of the bore retained austenite volume fraction of the depth position of 20μm and (R2), wherein (A): Δγ = [( R1-R2) / R1 ] residual austenite reduction rate Δγ obtained by × 100 is 40% or more, the shaft parts are manufactured.
　Equation (1): 15.0 ≦ 25.9C + 6.35Mn + 2.88Cr + 3.09Mo + 2.73Ni ≦ 27.2
　wherein each element symbol in the formula (1), substituting the content of each element (mass%) It is.
[0058]

　method of manufacturing a shaft component according to the present embodiment, the steel and the processed into a shape close to a shape of the shaft part to obtain a shaft part crude member (coarse member manufacturing step), to the crude member comprising a step of obtaining a hardened material is subjected to induction hardening treatment (quenching material manufacturing step), a hole is subjected to drilling by cutting against the hardened material, and a step (boring step) to obtain a shaft part Te .
[0059]
Grain member production step]
　In this step, to produce a crude member having a desired shape close to the shape of the shaft part. First, to prepare the steel.
[0060]
(Chemical composition of steel (essential component)
　the steel has the same chemical composition having the same content as the shaft component according to the embodiment of the present invention described above.
[0061]
(Crude preparation of members)
　steel having the above chemical composition is processed into a shape close to the shape of the shaft part to obtain a shaft part crude members. Processing method can be adopted well-known methods. As the processing method, for example, hot working, cold working, cutting, and the like. Crude members, portions other than the hole was the same shape as the shaft component according to the embodiment of the present invention, at this stage, holes are not opened.
[0062]
[Hardened material production process]
　the crude member obtained in this manner to obtain a hardened material is subjected to induction hardening treatment. Thus, in the hardening material, the tissue from the outer circumferential surface of the shaft part of the depth position of 2mm which is the final form, the residual austenite of 4-20% martensitic and volume fraction.
[0063]
(Induction hardening process)
　induction hardening process, first, subjected to (i) a high-frequency heating, then subjected to (ii) quenching. High-frequency heating and hardening are carried out under the following conditions.
[0064]
　(I) high-frequency heating
　frequency at the time of induction heating: 10 ~ 300 KHz
　if the frequency is too low, the heating range is widened. For this reason, the distortion at the time of quenching increases. On the other hand, if the frequency is too high, the heating range is concentrated only in the surface layer. In this case, hardened layer of the surface becomes thin, static torsional strength and torsional fatigue strength is lowered. Accordingly, the frequency at the time of induction heating is 10 ~ 300 KHz.
[0065]
　Heating time at the time of induction heating 1.0 to 40 seconds
　and the heating time, the output 40 KW, a time from the heating of the crude member is started until the water cooling is started. If the heating time at the time of induction heating is too long, the austenite grains become coarse, static torsional strength and torsional fatigue strength of the shaft part is reduced. On the other hand, if the heating time is too short, cementite is not sufficiently dissolved, the stability of the austenite is lowered. Therefore, after induction hardening, and martensite, the tissue is not obtained consisting of 4-20% residual austenite volume fraction. Therefore, the heating time of the coarse member at the time of induction heating is 1.0 to 40 seconds.
　To control both the heating frequency and the heating time, from the outer circumferential surface region deeper than 2mm is A 3 to be heated to a temperature above points.
[0066]
　(Ii) quenching
　after isothermal holding treatment, subjected to quenching in a known manner. Hardening, for example, it can be water quenched. Thus, the area heated above point A3 is changed to a tissue containing the residual austenite and martensite.
[0067]
(Tempering)
　For greater toughness of the shaft part, was subjected to induction hardening treatment may be subjected to tempering.
[0068]
(Hardened material structure of the manufacturing process after completion of the quenching material)
　for quenching material obtained by performing induction hardening treatment in the conditions described above, the outer peripheral surface of the hardened material (same as the final form of the shaft parts periphery surface of) 2 mm of tissue depth position contains a martensite, and residual austenite of 4-20% by volume.
[0069]
　The measurement of the depth position of 2mm from the outer peripheral surface, and the tissue observed and residual austenite volume fraction from the surface 2mm of holes (R1) in the hardened material is carried out in the following manner. That is, in hardened material is cut perpendicularly to the longitudinal direction of the hardened material. Cutting plane (A-A of FIG. 1 (a) ', to FIG. 1 (b)) in, providing a test strip including the position of 2mm toward the center from the outer periphery (specimen 1).
[0070]
　Tissue from the outer peripheral surface of the depth position of 2mm in hardened material is retained austenite and martensite, these other phases are not present. The structure observation with an optical microscope, the residual austenite is included in martensite. That is, in the structure observation with an optical microscope can not distinguish between the martensite and residual austenite. Therefore, a depth position of 2mm from the outer peripheral surface, and residual austenite volume fraction of 2mm from the surface of the bore of the (R1), is measured by the following method. Performing electrolytic polishing with respect to the test piece 1. And 11.6% of ammonium chloride, and 35.1% glycerol, to prepare an electrolyte solution containing a 53.3% water. Using this electrolyte solution, to the surface of the specimen containing the reference position, carrying out electrolytic polishing in voltage 20V.
[0071]
　The surface of electro-polished test piece is irradiated with X-rays from the outer peripheral surface around the depth position of 2 mm, and analyzes by X-ray diffraction method. The X-ray diffraction, using a Rigaku Corporation under the trade name of RINT-2500HL / PC. The light source uses a Cr tube. Tube voltage 40 kV, tube current is 40 mA, a collimator diameter is 0.5 mm. To remove the Kβ line by V filter, using the Kα line. Data analysis was using the AutoMATE software (manufactured by Rigaku Corporation). Removing the Kα2 components by Rachinger method, a profile of the Kα1 components, were calculated (211) plane and the (220) surface residual austenite volume fraction, based on the integrated intensity ratio of the diffraction peaks of the fcc structure of bcc structure.
　Incidentally, the spot size of the X-ray to be irradiated is set to 1mm or less.
[0072]
　A depth position of 2mm from the outer peripheral surface of the hardened material production process after completion of the quenching material, and the volume fraction of retained austenite at 2mm from the surface of the bore (R1) is 4-20%. This residual austenite is at cutting the next hole making step, to deformation-induced martensitic transformation. As described above, in the shaft component according to the present invention, the strain-induced martensite formed around the holes, reduction of static torsional strength and torsional fatigue strength of the shaft part due to the presence of holes is suppressed. When the volume fraction of retained austenite from the outer peripheral surface at a depth position of 2mm is less than 4%, this effect can not be obtained. On the other hand, when the volume fraction of residual austenite is greater than 20%, cutting later also a lot of soft austenite remains. Therefore, the entire shaft parts are not obtained excellent static torsional strength and torsional fatigue strength.
[0073]
[Boring process (cutting)
　a shaft component according to embodiments of the present invention, bored with a vertical or at an angle to the longitudinal direction of the shaft part, a through-hole or non-through holes, 1 It has pieces or more.
　It was subjected to induction hardening treatment, subjected to drilling by cutting. By cutting, while a hole, to generate a strain-induced martensitic transformation in the surface layer portion of the hole. Thus, reduction of static torsional strength and torsional fatigue strength of the shaft part by the formation of the holes is suppressed, the shaft part superior static torsional strength and torsional fatigue strength is created. Cutting is performed under the following conditions. As the cutting tool, for example, on the surface of the cemented carbide, carbides, nitrides, oxides, carbide drill coated is applied, such as diamond (JIS B 0171: 2014 years, coated specified in No. 1003, 1004 it is possible to use a carbide drill). It is effective in terms of suppression of tool wear and machining efficiency improvements using coated carbide drill.
[0074]
　 Tool feed f: 0.02 mm / rev (rotation) Ultra, 0.2 mm / rev or less
　if feed f is too small, the cutting resistance, i.e., the force which the tool is pressed against the workpiece is too small. In this case, sufficient deformation-induced martensitic transformation does not occur. Therefore, the static torsional strength and torsional fatigue strength of the shaft part is not improved. On the other hand, if the feed is too large, the cutting resistance becomes too large. In this case, there is a possibility that the tool may be damaged during cutting. Thus, the feed f is 0.02 mm / rev greater is 0.2 mm / rev or less. A preferred lower limit of the feed f is 0.03 mm / rev. The preferable upper limit of the feed f is 0.15 mm / rev, more preferably from 0.1 mm / rev.
[0075]
　 Cutting speed v: 10 ~ 50 m / min
　if the cutting speed v is too large, the cutting temperature increases, martensite transformation hardly occurs. Therefore, the static torsional strength and torsional fatigue strength of the shaft part is not improved. On the other hand, if the cutting speed is too small, the cutting efficiency is lowered, the production efficiency decreases. Thus, the cutting speed v is 10 ~ 50 m / min. Preferred upper limit is 40 m / min, more preferably 30 m / min.
[0076]
(Shaft part tissue)
　shaft parts are obtained by drilling shown above. Residual austenite volume fraction of the depth position of 2mm from the resulting shaft part periphery surface, and the surface of the bore 2mm (R1) is 4 ~ 20%,
　2mm in the axial direction of the bore from the R1 and the outer peripheral surface at a depth position of, and residual austenite volume fraction of the depth position of 20μm from the surface of the bore (R2) Tokara formula (a): Δγ = [( R1-R2) / R1] retained austenite decreases, which is determined by × 100 rate Δγ is 40% or more.
[0077]
　Measurements at a depth position of 2mm in the axial direction of the hole from the outer peripheral surface, and residual austenite volume fraction of the depth position of 20μm from the surface of the bore (R2) is carried out in the following manner. That is, perpendicular to the longitudinal direction of the shaft part, and through the center of the hole, cutting the shaft part to 2 divides the hole vertically (B-B 'line in FIG. 2). The surface of the hole, about the position of the depth of 2mm from the outer peripheral surface, masked with a hole of φ1mm opened, subjected to electrolytic polishing. Adjust the amount of polishing by changing the electropolishing time, drilling depth 20 [mu] m. The center (reference numeral 21 in FIG. 2) of the hole, by irradiating the X-ray spot size 0.5 mm, the residual austenite volume fraction of 2mm from the above-mentioned depth position of 2mm from the outer peripheral surface and the hole surface (R1 ) measuring method using the same method as in, for measuring the residual austenite volume fraction.
[0078]
　A depth position of 2mm from the outer peripheral surface, and residual austenite volume fraction from the surface 2mm of holes (R1) is a portion that is not affected by drilling after quenching processing, considered residual austenite volume fraction before cutting be able to. On the other hand, at a depth position of 2mm in the axial direction of the hole from the outer peripheral surface, and residual austenite volume fraction of the depth position of 20μm from the surface of the bore (R2), the residual austenite in the vicinity of the surface formed by boring a volume fraction can be considered as the residual austenite volume fraction after cut.
[0079]
　Therefore, the residual austenite reduction rate Δγ of retained austenite before and after cutting, on the basis of the calculated volume ratio (R1) and (R2), is calculated by the equation (A).
　Reduction rate Δγ = [(R1-R2) / R1] × 100 (A)
[0080]
　At a depth position of 2mm from the outer peripheral surface of the shaft part in the axial direction of the bore, and the residual austenite volume fraction of the depth position of 20μm from the surface of the bore (R2), the volume fraction of retained austenite after cutting is too high if, hard martensite is not obtained, the static torsional strength and torsional fatigue strength is lowered.
[0081]
　Residual austenite reduction rate Δγ of retained austenite before and after cutting is 40% or more. By residual austenite is transformed deformation-induced martensite by cutting, static torsional strength and torsional fatigue strength is increased. If the volume reduction rate Δγ is too low, the effect is not sufficiently obtained.
Example
[0082]
　The following are examples of the present invention, the present invention will be specifically described. Incidentally, examples are one aspect of the present invention, the present invention is not limited by the examples below. In the table shown below, items that do not meet the requirements of the present invention, and, for items that do not satisfy the desired manufacturing conditions of the present invention was applied an asterisk (*).
　Using a vacuum melting furnace to obtain a molten steel A ~ P of 150kg having a chemical composition shown in Table 1.
[0083]
[Table 1]

[0084]
　Using molten steel of each steel type, to obtain an ingot by ingot-making method. After heating for 4 hours at 1250 ° C. Each ingot to obtain a round bar having a diameter of 35mm by performing hot forging. Finishing temperature during hot forging was 1000 ℃.
[0085]
　The normalizing treatment was performed on each round bar. Normalizing treatment temperature is 925 ° C., normalizing treatment time was 2 hours. After normalizing treatment and allowed to cool round bars to room temperature (25 ° C.).
[0086]
　Implemented machining relative round bar after allowing to cool, the static torsion test, test pieces for torsion fatigue test (hereinafter, "torsion test specimen" as referred to) 5 to torsion test piece 51 shown is were prepared crude member underlying. In the state of coarse member, the holes of φ3mm has not been opened. Torsion test piece 51 corresponding to the shaft part, cross-section is circular, and cylindrical test section 52, a hole 53 arranged in the test unit 52 the central, cylindrical large-diameter portion 54 disposed on both sides When, and a pair of gripping portions 55 which chamfered periphery of the large diameter portion. Furthermore, for weight reduction, the center of the test piece has a hollow bore 56. As shown in FIG. 5, the overall length of the torsion test piece 51 is 200 mm, the outer diameter of the test unit 52 is 20 mm, the length of the test section 52 is 30 mm, the diameter of the hole 53 is 3 mm, the hollow bore 56 the diameter of which is 6 mm.
[0087]
　The crude members torsion test piece 51, the output 40 KW, based on the conditions shown in Table 2, it was carried out induction hardening.
[0088]
[Table 2]

[0089]
　Incidentally, by using the steel type A in Table 1, the thickness of the surface hardened layer formed by induction hardening conditions a in Table 2, the distance from the surface (thickness) and the measured value and its Vickers hardness (HV) from, it was about 2.5mm.
[0090]
　The crude members of hardened torsional test piece 51 is subjected to a drilling under the conditions shown in Table 3, to obtain a torsion test piece 51 corresponding to the shaft part.
[0091]
[table 3]

[0092]
　During drilling, the cutting tool, the surface of the cemented carbide was subjected to ceramic coating, using a coated carbide drills with a diameter of 3 mm. Further, by using the tip of the coated cemented carbide drill having the diameter of 6mm tip angle 90 °, chamfered in C0.5mm the entrance of the hole.
[0093]
　Then, those subjected to drilling described above and a torsion test piece 51.
[0094]
　Incidentally, by using the steel type A in Table 1, Table 2 of induction hardening conditions a, Vickers hardness cutting conditions near the hole surface formed by α in Table 3, at the thickness direction of the distance 50μm from the hole surface, 840HV , was 695HV 760HV, at the 200μm 710HV, at the 300μm at the 100μm.
[0095]
[Measurement of volume fraction of residual austenite (R1)]
　was cut vertically from the surface of 2mm hole testing section 52 of the torsion test piece 51 with respect to the longitudinal direction of the test piece 51. In cut surface, the test piece is prepared (specimen 1) including the position of 2mm toward the center from the periphery (Figure 1 (b)). It was subjected to electrolytic polishing to the cutting surface. And 11.6% of ammonium chloride, and 35.1% glycerol, to prepare an electrolyte solution containing a 53.3% water. The electrolytic solution with respect to the surface including the reference position, was subjected to electrolytic etching at a voltage 20V.
[0096]
　To the surface of electro-polished test piece, carried out X-ray diffraction in the manner described above, was determined 2mm position from the outer circumferential surface, and the volume fraction of retained austenite of 2mm from the surface of the hole a (R1).
[0097]
[Measurement of volume fraction of residual austenite (R2)]
　perpendicular to the longitudinal direction of the torsion test piece 51, and passes through the center of the hole was cut shaft parts to 2 divides the hole vertically (in Fig. 2 B -B 'line). The surface of the hole, around the depth position of 2mm from the outer peripheral surface, masked with a hole of φ1mm opened, was subjected to electrolytic polishing. Adjust the amount of polishing by changing the electropolishing time, it opened the depth holes of 20 [mu] m.
[0098]
　Against the hole surface, the X-ray diffraction was carried out in the manner described above, at a depth of 2mm from the outer peripheral surface, and the volume fraction of retained austenite of the depth position of 20μm from the hole surface (reference numeral 21 in FIG. 2) (R2 ) was determined.
[0099]
[Static (Measurement of static torsional strength) Torsion Test]
　using a torsion test piece 51 shown in FIG. 5 performs torsion test servo pulser-type torsion testing machine (EHF-TB2KNM manufactured by Shimadzu Corporation), and torsional stresses the relationship of the corner was obtained. Then, the maximum shear stress angle and torsional stress maintain a proportional relationship tau, and the static torsional strength of the so-called proportional limit. The proportional limit is equivalent to the yield stress referred to in the tensile test. In this test, if the static torsional strength of more than 530MPa is a pass in that it has a superior static torsional strength relative to the prior art.
[0100]
[Torsional fatigue test (measurement of the torsional fatigue strength)
　by using a torsion test piece 51 shown in FIG. 5, the load maximum shear stress τ is varied in 50MPa pitch were torsional fatigue test of both swing at a repetition frequency 4Hz . Then, repeated several 10 5 minimum value of maximum shear stress to break before reaching times (tau f, min and), (tau f, min maximum shear stress of the largest non-break at lower stress) (sigma r, max an intermediate point between) as the fatigue limit. Note that the tester with the test machine twist the servo pulser formula. In this test, if the torsional fatigue strength of more than 325MPa is, it is acceptable because it has an excellent torsional fatigue strength relative to the prior art.
[0101]
[Test Results]
　The results for each test and the like described above are shown in Table 4, Table 5.
[0102]
[Table 4]

[0103]
　Note that the retained austenite volume fraction of the outer peripheral surface at a depth position of 2mm in the axial direction of the bore, and the depth position other than 20μm from the surface of the bore (10 [mu] m and 50 [mu] m) and (R2), according to Table 4 of No. 1 conditions was measured in the same manner, 7.8% at 10μm depth, a value of 13.2% at 50μm depth was obtained. In addition, No. described in Table 4 4 conditions was measured in the same manner, 10 [mu] m 13.5% in the depth, the value of 20.0% at 50μm depth was obtained.
[0104]
[table 5]

[0105]
　As is clear from Table 4, the condition is satisfied for the shaft part manufacturing method according to an embodiment of the present invention (i.e., assuming that adjusting the chemical composition of the crude members, in particular, hardened material after induction hardening and organization, and the organization of the shaft parts after drilling, for it has) example by improving the organization of hardened material (residual γ volume ratio (R1)), and tissue (residual γ volume of the shaft parts for any rate of (R2)) also, it can be seen that excellent results are obtained. Therefore, according to the manufacturing method of these test examples, it was demonstrated that it is possible to obtain an excellent shaft parts static torsional strength and torsional fatigue strength.
[0106]
　In contrast, as apparent from Table 5, it does not satisfy the conditions of the method for manufacturing a shaft component according to an embodiment of the present invention (i.e., adjusting the chemical composition of the crude member, hardening material after induction-hardened structure , tissue shaft part after drilling, no added improvement for at least one) for the comparative example, tissue hardening material (residual γ volume ratio (R1)) and the shaft part of the tissue (residual γ volume fraction (R2) at least for either), it can be seen that not the excellent result is obtained. Therefore, according to the manufacturing method of these test examples, it can not be said that it is possible to obtain an excellent shaft parts static torsional strength and torsional fatigue strength.
DESCRIPTION OF SYMBOLS
[0107]
　11 Structure Observation and R1 measurement position
　21 R2 measurement position
　31 scanning electron microscope observing position
　41 plastic flow layer
　42 preform
　51 Torsion test piece
　52 test unit
　53 holes
　54 large diameter portion
　55 handful portion
　56 hollow space
　61 induced martensitic layer

The scope of the claims
[Requested item 1]
　By mass%, C: 0.35 ~ 0.70% , Si: 0.01 ~ 0.40%, Mn: 0.5 ~ 2.6%, S: 0.005 ~ 0.020%, Al: 0.010 ~ 0.050%, N: contain .005 to .025%,
　as an impurity
　element, P: 0.050% or
　less, O: 0.003% or less
　in addition, as an element of an optional,
　pb: 0.5% or
　less, V, 0.1% or less in total content of one or more selected from the group consisting of Nb and
　Ti, Cr: 3.0% or less, Mo: 3.0% or less, and, Ni: 3.0% 1 or more selected from the group consisting
　of, Cu:
　0 - 0.50% B: 0 contained to 0.020%
and the balance being Fe and impurities has the chemical composition satisfying the formula (1),
　has at least one hole to the outer peripheral surface,
　a depth position of 2mm from the outer peripheral surface, or A is 4-20% residual austenite volume fraction of 2mm from the surface of the bore (R1),
　at a depth position of 2mm in the axial direction of the hole from the R1 and the outer peripheral surface, and a depth of 20μm from the surface of the hole residual austenite volume fraction position is (R2) Tokara formula (a): Δγ = [( R1-R2) / R1] residual austenite reduction rate [Delta] [gamma] obtained by the × 100 is 40% or more,
characterized in that , shaft parts.
　15.0 ≦ 25.9C + 6.35Mn + 2.88Cr + 3.09Mo + 2.73Ni ≦ 27.2 (1)
　wherein each element symbol in the formula (1), the content of each element (mass%) is substituted .
[Requested item 2]
　Shaft component according to claim 1, characterized in that it has a plastic flow layer on a surface of the bore.
[Requested item 3]
　Shaft component according to claim 2, the thickness of the plastic flow layer is 0.5 ~ 15 [mu] m, and wherein the.