JP2916069B2 - High-strength induction hardened shaft parts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength induction hardened shaft part, and more particularly to FIGS. 1 (a) to 1 (c).
The present invention relates to an induction hardened shaft component having excellent torsional strength as a shaft component constituting a power transmission system of an automobile, such as a shaft having a spline portion, a shaft with a flange, a shaft with an outer cylinder, and the like.

[0002]

2. Description of the Related Art Shaft parts constituting a power transmission system of an automobile are usually manufactured by forming medium carbon steel into predetermined parts and performing induction hardening-tempering. In accordance with the progress of environmental protection and environmental regulations, there is a strong tendency to increase strength (improve torsional strength). On the contrary,
Japanese Patent Publication No. 63-62571 discloses C: 0.30 to 0.3.
8%, Mn: 0.6-1.5%, B: 0.0005-
0.0030%, Ti: 0.01 to 0.04%, Al:
A method of manufacturing a drive shaft in which steel of 0.01 to 0.04% is formed into a drive shaft and the ratio of the induction hardening depth by induction hardening to the steel member radius is 0.4 or more is disclosed. The maximum torsional strength obtained with the invention material is about 160 kgf / m as shown in FIG.
m ² . Japanese Patent Application Laid-Open No. 4-218641 discloses a steel material for a high-strength shaft component of a specific component characterized by low Si and high Mn, in which Si: 0.05% or less and Mn: more than 0.65 to 1.7 or less. It has been shown that the use of a material having a spline portion can provide a torsional strength of 140 to 160 kgf / mm ² with a material having a spline portion. As described above, the maximum torsional strength that can be realized at present is about 160 kgf / mm ² .

[0003]

However, at present, the strength level of the torsional strength of 160 kgf / mm ² cannot be said to be sufficient as the strength level of a power transmission shaft part of an automobile. Further, in order to increase the strength, improvement of workability and suppression of burn-out cracks are important issues in a part manufacturing process. An object of the present invention is to provide a component having a high workability in the part manufacturing process without causing sintering cracks,
An object of the present invention is to provide a shaft component having an excellent torsional strength of gf / mm ² or more.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies and obtained the following knowledge in order to realize a shaft part having excellent torsional strength by induction hardening. (1) The torsional strength of the induction hardened material is improved in the case of ductile fracture in proportion to the average in-section hardness defined below. Extrapolating from the relationship between torsional strength and average hardness in cross section,
In order to obtain excellent torsional strength of 160 kgf / mm ² or more, HVa needs to be 560 or more. Definition of average hardness in cross section: As shown in FIG. 2, a cross section of radius a is divided concentrically into N rings in the radial direction, and the hardness of the n-th ring portion is HV _n , and the radius is HV _n . when r _n, the interval was Δr _n,

[0005]

(Equation 3)

The above has been obtained from the following findings. FIG. 3 is a view schematically showing shear strain and shear stress when plastic deformation progresses from the surface layer to the inside during the torsional deformation process of the shaft component. In the figure, the solid line indicates the shear strain distribution, the thick solid line indicates the shear stress distribution, and the broken line indicates the shear yield stress distribution. When the torque is 1), the shear stress τ at the surface reaches the shear yield stress τy of the steel material, and plastic deformation starts. When the torsional deformation proceeds to the stage where the torque is 2), the plastic deformation proceeds inside with accompanying work hardening (the difference between the broken line and the solid line in the surface layer is the work hardening amount). In addition,
The alternate long and short dash line in the figure is a hypothetical shear stress distribution assuming that no plastic deformation occurs. Further, at the stage 3) immediately before the torque causes torsional fracture, it is considered that the plastic deformation has progressed to almost the center.

[0007] Here, the torque M _t for a given shear stress distribution tau (r) is given by the following equation (1).

[0008]

(Equation 4)

On the other hand, an apparent shear fracture stress τ _max assuming elastic fracture generally used as an index of torsional strength
Is obtained by the following equation (2).

[0010]

(Equation 5)

Assuming that the amount of work hardening is small because the steel material is a medium / high carbon martensitic steel, the shear stress distribution at the time of fracture almost coincides with the shear yield stress distribution as apparent from FIG. The stress distribution can be approximated as τ _f (r) = K ₁ · HV (r) as a function of the hardness distribution.

[0012]

(Equation 6)

Here, the equivalent hardness HV _eq is defined by the following equation (4) as an index of the hardness corresponding to the uniform hardness material.

[0014]

(Equation 7)

For a material of uniform hardness, K ₂ = 3 / a ³ because HV _eq = HV = constant.

[0016]

(Equation 8)

From equations (3) and (5),

[0018]

(Equation 9)

The corresponding hardness HV _eq divides into N ring section in the radial direction concentrically and the hardness of the n-th annular section HV _n, radius r _n, the distance between [Delta] r _n At this time, it can be approximated as follows.

[0020]

(Equation 10)

Again, the average hardness in the cross section HVa
Defined. FIG. 4 shows the results obtained by determining the average hardness HVa and arranging the torsional strength by HVa for materials having various hardness distributions. The torsional strength has a good correlation with HVa, and is excellent at 160 kgf / mm ² or more. It is clear that HVa needs to be 560 or more in order to obtain a high strength.

(2) However, when the average hardness in the cross section is increased by using the conventional material, the fracture mode changes from “ductile fracture” to “brittle fracture at the grain boundary crack origin”, and the strength increases. Saturates or rather decreases. However, when the following methods are used in combination, brittle fracture due to grain boundary fracture is suppressed, and torsional strength increases with an increase in average hardness in a cross section. 1) Ti-B addition 2) Reduction of P, Cu and O contents 3) Refinement of old austenite grains by carbonitride (A
l, N appropriate amount added)

(3) The effect of increasing the torsional strength by suppressing the brittle fracture is further increased by adding the following method in addition to the above. 1) Increase Si 2) Add Cr, Mo, Ni 3) Apply compressive residual stress by hard shot peening

(4) As the average hardness in the cross section of (1) is increased, the conventional material is liable to cause sintering cracks. However, by taking the above measures (2) and (3), Cracking is suppressed.

(5) When excellent workability is required in the manufacturing process of the shaft part, the workability is improved by limiting the amount of Si. The present invention has been made based on the above-described novel findings, and the gist of the present invention is as follows.

According to the first aspect of the present invention, as a weight ratio, C: 0.35 to 0.70% Si: 0.01 to 0.15% Mn: 0.2 to 2.0% S: 0. 005-0.15% Al: 0.0005-0.05% Ti: 0.005-0.05% B: 0.0005-0.005% N: 0.002-0.02% P: 0.020% or less Cu: 0.05% or less O: Restricted to 0.0020% or less, with the balance being iron and unavoidable impurities, and having an average in-section hardness HVa defined below of 560 or more. It is a high-strength induction hardened shaft part characterized by the following. Definition of average hardness in the cross section: The cross section of radius a is divided concentrically into N rings in the radial direction, and the hardness of the n-th ring-shaped portion is HV.
_n, when the radius was r _n, the interval and Δr _n,

[0027]

[Equation 11]

According to the second aspect of the present invention, as a weight ratio, C: 0.35 to 0.70% Si: more than 0.15 to 2.5% Mn: 0.6 to 2.0% S: 0 0.005 to 0.15% Al: 0.0005 to 0.05% Ti: 0.005 to 0.05% B: 0.0005 to 0.005% N: 0.002 to 0.02% P: 0.020% or less Cu: 0.05% or less O: 0.0020% or less, the balance being iron and unavoidable impurities, and the average in-section hardness HVa defined below as 560 or more A high-strength induction hardened shaft part characterized by the following. Definition of average hardness in the cross section: The cross section of radius a is divided concentrically into N rings in the radial direction, and the hardness of the n-th ring-shaped portion is HV.
_n, when the radius was r _n, the interval and Δr _n,

[0029]

(Equation 12)

According to a third aspect of the present invention, the steel further comprises Cr: 0.03 to 1.5% Mo: 0.05 to 1.0% Ni: 0.1 to 3.5% Nb: 0.01 to 0.3%, V: 0.03 to 0.6%, or one or two of the following: Ca: The high-strength induction hardened shaft part according to claim 1 or 2, comprising one or two of 0.0005 to 0.010% Pb: 0.05 to 0.5%. The invention according to claim 6 or 7 of the present invention, wherein the prior-austenite grain size of the induction hardened layer is 9 or more and the residual stress on the surface is -80 kgf / mm ² or less. High strength induction hardened shaft parts.

[0031]

Hereinafter, the present invention will be described in detail. Claim 1
Is an invention relating to a high-strength induction hardened shaft part which has an excellent torsional strength in a final product, is excellent in workability in a manufacturing process of the shaft part, and does not cause quench cracking. First, the reason why the component content range of the first aspect of the present invention is limited as described above will be described.

C is an element effective for increasing the hardness of the induction hardened hardened layer, but if it is less than 0.35%, the hardness is insufficient, and if it exceeds 0.70%, it may cause an austenite grain boundary. Is remarkable, the grain boundary strength is degraded, the brittle fracture strength is lowered, and sintering cracks easily occur. Therefore, the content is set to 0.35 to 0.70%.

Next, Si is added as a deoxidizing element. However, if the content is less than 0.01%, the effect is insufficient. On the other hand, Si increases the hardness of the material by solid solution hardening. Therefore, the addition of more than 0.15% deteriorates the workability in the manufacturing process of the shaft component. For the above reasons, the content is set to 0.
01-0.15%.

Mn is added for the purpose of improving hardenability. However, if less than 0.20%, this effect is insufficient. On the other hand, if the content exceeds 2.0%, this effect is not saturated but rather causes the toughness of the final product to deteriorate, so the content is set to 0.20 to 2.0%.

S forms MnS in the steel and is added for the purpose of refining austenite grains and improving machinability during induction hardening and heating.
If less, the effect is insufficient. On the other hand, if the content exceeds 0.15%, the effect is saturated, and rather, grain boundary segregation is caused to cause grain boundary embrittlement. For the above reasons, the content of S is 0.00
5 to 0.15%.

Al is added for the purpose of 1) refining austenite grains during induction hardening heating by forming AlN by combining with N, and 2) adding as a deoxidizing element. The effect is insufficient. On the other hand, if it exceeds 0.05%, the effect is saturated, and rather the toughness is deteriorated.
-0.05%.

[0037] Ti also combines with N in steel to form TiN. This causes 1) the refinement of austenite grains during induction hardening and heating, and 2) the prevention of BN precipitation by complete fixation of solid solution N, that is, solidification. It is added for the purpose of securing dissolved B. However, if the content is less than 0.005%, the effect is insufficient, while if it exceeds 0.05%, the effect is saturated, and the toughness is rather deteriorated.
005 to 0.05%.

B is segregated at the austenite grain boundaries in a solid solution state, and is added for the purpose of increasing the grain boundary strength by driving out grain boundary impurities such as P and Cu from the grain boundaries. However, if the content is less than 0.0005%, the effect is insufficient. On the other hand, an excessive addition exceeding 0.005% rather causes grain boundary embrittlement, so that the content is limited to 0.005%.
05 to 0.005%.

Further, N is added for the purpose of refining austenite grains at the time of high-frequency heating by precipitation of carbonitride such as AlN. If less than 0.002%, the effect is insufficient. %, The effect is not saturated but rather forms BN and causes a decrease in solid solution B, so the content was made 0.002 to 0.02%.

On the other hand, P causes grain boundary segregation at austenite grain boundaries, lowers the grain boundary strength, easily causes brittle fracture under torsional stress, and therefore lowers the strength. Especially P
Exceeds 0.02%, the strength is significantly reduced.
0.02% was made the upper limit. In order to further increase the strength, the content of P is desirably 0.009% or less.

Further, Cu also causes grain boundary segregation at austenite grain boundaries like P, which causes a reduction in strength. Especially Cu
Exceeds 0.05%, the strength decreases markedly.
The upper limit was 0.05%.

Further, O causes grain boundary segregation to cause grain boundary embrittlement, and forms hard oxide-based inclusions in the steel.
It tends to cause brittle fracture under torsional stress and causes a decrease in strength. In particular, when O exceeds 0.0020%, the strength decreases remarkably, so the upper limit was made 0.0020%.

Next, the induction hardened shaft part is composed of the above-mentioned components, and the average hardness HVa in the cross section defined above is 56.
The reason for setting the value to 0 or more will be described below. The torsional strength of the induction hardened material increases in proportion to the average hardness in the cross section. 160
In order to obtain an excellent torsional strength of kgf / mm ² or more, it is necessary to set the average hardness HVa in the cross section to 560 or more. For the above reasons, the average hardness HVa in the cross section is set to 560 or more. In addition,
In the present invention, the depth of the hardened layer is not particularly limited.
The ratio t / r of the effective hardened layer depth t to the component radius r based on the induction hardened hardened layer depth measuring method specified in 559 is 0.3.
It is desirable to set it to 0.8. This means that the torsional strength of the induction hardened material is improved as the induction hardened depth is increased. However, when the effective hardened layer depth is less than 0.3 at t / r, the effect of improving the torsional strength is small, and the torsional strength is not improved. If it exceeds 8, the compressive residual stress of the surface layer will decrease, and the risk of occurrence of burn cracking in the shaft component manufacturing process will increase.

A second aspect of the present invention relates to a high-strength induction hardened shaft part which has a higher torsional strength in the final product and does not cause quenching cracks in the manufacturing process. The invention according to claim 2, wherein Si: more than 0.15 to 2.5%, Mn: 0.6.
The reason for using steel containing .about.2.0% is as follows.

Si is added 1) for the purpose of strengthening the grain boundary by suppressing carbide precipitation on the austenite grain boundary, and 2) as a deoxidizing element. However, the effect of strengthening the grain boundary is insufficient with the addition of 0.15% or less, while 2.5% or less.
%, Rather causes excessive grain boundary embrittlement, so the content was made more than 0.15 to 2.5%. In order to further increase the strength, it is desirable to add 0.4% or more of Si.

Mn is added for the purpose of 1) improving hardenability, and 2) forming MnS in steel, 2) refining austenite grains during induction hardening heating, and 3) improving machinability. However, when higher torsional strength is intended, addition of less than 0.60% is insufficient.
On the other hand, Mn causes grain boundary segregation at austenite grain boundaries,
It lowers the grain boundary strength to facilitate brittle fracture under torsional stress, thus reducing the strength. In particular, this tendency becomes remarkable at 2.0% or more. For the above reasons, the content of Mn is set to 0.6 to 2.0%.

Claim 3 is that, by adding Cr, Mo and Ni, 1) increase of induction hardening hardness due to improvement of hardenability, increase of hardened layer depth and 2) occurrence of grain boundary segregation at austenite grain boundary. This is a steel material for shaft parts that has further enhanced strength by preventing brittle fracture by increasing the grain boundary strength or improving the toughness near the grain boundary. However, Cr:
Less than 0.03%, Mo: less than 0.05%, Ni: 0.1
%, The effect is insufficient. On the other hand, Cr: 1.
If the content exceeds 5%, the content of Mo exceeds 1.0%, and the content of Ni exceeds 3.5%, this effect is saturated, and such excessive addition is not preferable from the viewpoint of economy. For the above reasons, these contents are
r: 0.03 to 1.5%, Mo: 0.05 to 1.0%,
Ni: 0.1 to 3.5%.

In claim 4, 1) the austenite grains during high-frequency heating are further refined to prevent grain boundary destruction, and 2) the strength of the core is increased by increasing the hardness of the core by precipitation strengthening. It is a steel material for shaft parts. Nb and V form carbonitrides in steel, have the effect of making austenite grains fine during high frequency heating, and the effect of increasing the hardness of the core by precipitation strengthening. However, if the Nb content is less than 0.01% and the V content is less than 0.03%, the effect is insufficient. On the other hand, Nb: more than 0.30%,
If V: more than 0.60%, the effect is saturated, and such an excessive addition is not preferable from the viewpoint of economy. For the above reasons, these contents are set to Nb: 0.01 to 0.3%,
V: 0.03 to 0.6%.

A fifth aspect of the present invention is directed to a high-strength induction hardened shaft part which has an excellent torsional strength in the final product, has excellent workability in the manufacturing process of the shaft part, and does not cause quench cracking. In the steel of the present invention, C is used to improve machinability.
One or two of a and Pb can be contained. In addition, Ca not only improves machinability, but also has the effect of forming phosphide by combining with P in steel, reducing the amount of segregation of P at the grain boundary and increasing the grain boundary strength. However, if the Ca content is less than 0.0005% and the Pb content is less than 0.05%, these effects are insufficient, while Ca: 0.01%
When the content is more than Pb: more than 0.50%, these effects are saturated,
Rather, it deteriorates the toughness.
0.0005-0.010%, Pb: 0.05-0.5
%.

A sixth aspect of the present invention relates to a shaft component in which austenite grains during high-frequency heating are further refined to increase the strength by preventing grain boundary destruction. In the present invention, the former austenite grain size of the induction hardened layer of the induction hardened shaft part is 9
The reason why the number is higher than that is that brittle fracture due to grain boundary fracture is suppressed by miniaturization of the former austenite grain boundary of the induction hardened layer, but when the crystal grain size is less than 9, this effect is small.

A seventh aspect of the present invention is a shaft component which imparts a large compressive residual stress to the surface of the induction hardened shaft component, thereby suppressing brittle fracture and further increasing the strength. In the present invention, the residual stress on the surface of the induction hardened shaft part is -80 kg.
was set to f / mm ² or less, the brittle fracture is suppressed by the application of compressive residual stress torsional strength is increased by, the effect is due to the residual stress of the surface is particularly pronounced in -80kgf / mm ² or less .

Here, in the induction hardened shaft component of the present invention, the induction hardening conditions and the tempering conditions for manufacturing are not particularly limited, and any conditions may be used as long as the requirements of the present invention are satisfied. For example, if the requirements of the present invention are satisfied, tempering may not be performed. In the present invention, if the requirements of the present invention are satisfied, heat treatments such as normalizing, annealing, spheroidizing annealing, quenching and tempering can be performed as necessary before induction hardening. Before induction hardening, normalizing, annealing,
When the spheroidizing annealing is not performed, the steel material is manufactured by hot rolling at a finishing temperature of 700 to 850 ° C, and an average cooling rate in a temperature range of 700 to 500 ° C after the finish rolling;
It is desirable to carry out under the condition of 5 to 0.7 ° C./sec.

The application of the compressive residual stress to the induction hardened shaft component of the present invention is effective by hard shot peening at an arc height of 1.0 mmA or more after induction hardening and tempering. Here, the arc height is, for example, “Automotive technology, Vol. 41, No. 7, 19
87, pp. 726 to 727 ”, which is an index of the strength of shot peening. However, in the present invention, the conditions for applying the compressive residual stress are not particularly limited, and any conditions may be used as long as the requirements of the present invention are satisfied. Hereinafter, the effects of the present invention will be more specifically described with reference to examples.

[0054]

EXAMPLE A steel material having the composition shown in Tables 1 to 3 was rolled into a bar of 40 mmφ. From this steel bar, a test piece for drilling for evaluation of machinability, a torsion test piece, and a test piece for evaluating susceptibility to quench cracking were collected. The evaluation of machinability is based on a feed rate of 0.33 mm /
In s, the peripheral speed of the drill (material: SKH51-φ10 mm) is variously changed, the total hole depth at which drilling cannot be performed at each speed is determined, and a peripheral speed-drill life curve is created, and the drill life becomes 1000 mm. The maximum speed was defined as _VL1000, which was used as an evaluation standard for machinability. Tables 1 to 3 also show the evaluation results of _VL1000 . The machinability is as follows:
The steel material of 0.01 to 0.15% is S such as the second invention steel.
i: More than 0.15% to 2.5%, which is relatively superior to the steel material, and it can be seen that the fifth invention steel containing the machinability improving element is particularly excellent in machinability.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

Next, the target shaft component has an application concentrated portion (= notch portion) such as a spline portion.
It breaks at this notch. Therefore, it is necessary to evaluate the strength with a notched material. Accordingly, a notched torsion test piece having a notch with a parallel portion of 16 mmφ, a tip R of 0.25 mm and a depth of 2 mm at the center was used as a test piece for torsional strength evaluation.

[0059]

[Table 4]

Induction hardening was performed under the conditions A to C shown in Table 4, and thereafter tempering was performed at 170 ° C. for 1 hour. These samples were subjected to a torsion test. In addition, about some samples, after induction hardening-tempering, the shot peening process was performed on conditions of 1.0-1.5 mmA of arc heights. Further, in order to evaluate the susceptibility to quenching cracks, a test piece having a notch of 24 mmφ in diameter, 200 mmL in length, a tip R of 0.25 mm and a depth of 3 mm in a longitudinal direction was subjected to induction hardening under the conditions of D shown in Table 4. Do
The presence or absence of burning cracks at the notch bottom was observed.

The steel Nos. 1 to 44 are steels of the present invention,
Steel No. 45 to 63 are comparative steels. Tables 5 to 7 show the results of the evaluation of the torsional strength of each steel material as the ratio of the effective hardened layer depth to the radius t /.
r, the average hardness in section HVa, the prior austenite grain size Nγ of the induction hardened layer, the residual stress on the surface, and the evaluation results of the susceptibility to quenching cracking. The effective hardened layer depth is the effective hardened layer depth based on the induction hardened hardened layer depth measuring method specified in JIS G0559.

[0062]

[Table 5]

[0063]

[Table 6]

[0064]

[Table 7]

As is clear from Tables 5 to 7, all of the steels according to the method of the present invention have excellent torsional strength of 160 kgf / mm ² or more and low susceptibility to fire cracking. Also, in the method of the present invention, Si: 0.
An invention example using a steel material having a ratio of more than 15 to 2.5% and Mn: 0.6 to 2.0% is the first invention steel or the like having a Si: 0.01 to
A relatively higher level of torsional strength is achieved as compared with the invention example using a steel material having 0.15% and Mn: 0.2 to 2.0%. Further, when the former austenite grain size of the induction hardened layer is 9 or more, or when the residual stress on the surface is -80 kgf / mm ² or less, it is understood that a higher level of torsional strength is achieved.

On the other hand, Comparative Examples 3C, 7C, 13C and 18
C, 25C, 31C and 41C are average hardness HVa in the cross section.
Is less than 560, all of which are 160kgf
/ Mm ² or more. Comparative Example 50
Is the case where the content of S is lower than the range of the present invention.
Although having a torsional strength of 60 kgf / mm ² or more, as shown in Table 3, steel No. 50 has poor machinability.

Comparative Examples 45, 48, 53, 55 and 57 are cases where the contents of C, Mn, Ti, B and N are below the range of the present invention, and Comparative Examples 46, 47, 49 and 5
1, 52, 54, 56, 58, 59, 60, 61, 6
2, 63 are C, Si, Mn, S, Al, Ti, B, N,
This is the case where the contents of P, Cu, O, Ca, and Pb exceeded the range of the present invention. All of them did not achieve a torsional strength of 160 kgf / mm ² or more. In a comparative example of a steel material or the like with insufficient measures for strengthening the field, burn cracking occurs.

[0068]

As described above, by using the method of the present invention, it is possible to manufacture an induction hardened shaft component having excellent torsional strength of 160 kgf / mm ² or more and not causing quenching cracks, The effect is very remarkable.

[Brief description of the drawings]

FIG. 1 (a) is a shaft having a serration portion,
(B) shows a shaft with a flange, and (c) shows a shaft with an outer cylinder.

FIG. 2 is a diagram for explaining the definition of average hardness in a cross-section, and shows a state in which the cross-section is divided into n rings concentrically in a radial direction.

FIG. 3 is a diagram schematically showing a shear strain and a shear force when plastic deformation progresses from the back surface to the inside during the torsional deformation process of the shaft component.

FIG. 4 is a diagram showing the relationship between the average hardness (HVa) of various materials and the torsional strength.

[Explanation of symbols]

 10 Shaft 11, 12 Serration 20, 21 Shaft 22 Flange 30, 31, 32 Shaft 33 Outer cylinder

Continuation of front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C22C 38/00 301 C22C 38/14 C22C 38/60

Claims (7)

(57) [Claims] 1. As a weight ratio, C: 0.35 to 0.70% Si: 0.01 to 0.15% Mn: 0.2 to 2.0% S: 0.005 to 0.15% Al : 0.0005 to 0.05% Ti: 0.005 to 0.05% B: 0.0005 to 0.005% N: 0.002 to 0.02%, P: 0.020% or less Cu: 0.05% or less O: 0.0020% or less, with the balance being iron and unavoidable impurities, and having an average in-section hardness HVa defined below of 560 or more. High-strength induction hardened shaft parts. Defining cross the average hardness; the cross-section of radius a is divided into N rings concentrically in the radial direction and a hardness of n-th ring-shaped portion HV _n, radius r _n, and [Delta] r _n apart When you do, 2. As a weight ratio, C: 0.35 to 0.70% Si: more than 0.15 to 2.5% Mn: 0.6 to 2.0% S: 0.005 to 0.15% Al: 0.0005 to 0.05% Ti: 0.005 to 0.05% B: 0.0005 to 0.005% N: 0.002 to 0.02%, P: 0.020% Cu: 0.05% or less O: 0.0020% or less, with the balance being iron and unavoidable impurities, and having an average in-section hardness HVa defined below of 560 or more. High strength induction hardened shaft parts. Defining cross the average hardness; the cross-section of radius a is divided into N rings concentrically in the radial direction and a hardness of n-th ring-shaped portion HV _n, radius r _n, and [Delta] r _n apart When you do, 3. The steel further contains one or more of Cr: 0.03 to 1.5% Mo: 0.05 to 1.0% Ni: 0.1 to 3.5%. Item 3. The high-strength induction hardened shaft component according to item 1 or 2. 4. The high-strength induction hardened shaft according to claim 1, wherein the steel further contains one or two kinds of Nb: 0.01 to 0.3% V: 0.03 to 0.6%. parts. 5. The high-strength induction hardened shaft according to claim 1, wherein the steel further contains one or two of Ca: 0.0005 to 0.010% and Pb: 0.05 to 0.5%. parts. 6. The high-strength induction hardened shaft part according to claim 1, wherein the prior-austenite crystal grain size of the induction hardened layer is 9 or more. 7. The residual stress on the surface is -80 kgf / mm ^2.
The high-strength induction hardened shaft part according to claim 1, wherein: