JPH0790484A - High strength induction-hardened shaft parts - Google Patents

Abstract

PURPOSE:To produce high strength induction-hardened shaft parts excellent in workability by specifying the compsn. constituted of C, Si, Mn, S, Al, Ti, B, N, P, Cu, O and iron and the average hardness in the section. CONSTITUTION:This shaft parts have a compsn. contg., by weight, 0.35 to 0.70% C, 0.01 to 0.15% Si, 0.2 to 2.0% Mn, 0.005 to 0.15% S, 0.0005 to 0.05% Al, 0.005 to 0.05% Ti, 0.0005 to 0.005% B and 0.002 to 0.02% N, in which <=0.020% P, <=0.05% Cu and >=0.0020% 0 are limited, furthermore contg., at need, prescribed amounts of Cr, Mo, Ni, Nb, V, Ca and Pb, and the balance iron with inevitable impurities, and in which the average hardness HVa in the section defined by the formula (the section of the radius (a) is divided concentrically into (n) rings in the radial direction, and the hardness of the (n) th ring-shaped parts is difined as HVn, the radius as rn and the interval as DELTArn) is regulated to >=560. Thus, the shaft parts free from quench cracks and having about >=160kgf/mm<2> torsional strength can be obtd.

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 component, and more specifically, it is shown in FIGS.
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, and a shaft with an outer cylinder.

[0002]

2. Description of the Related Art A shaft component constituting a power transmission system of an automobile is usually manufactured by forming a medium carbon steel into a predetermined component and subjecting it to induction hardening-tempering. The trend toward higher strength (improvement in torsional strength) is strong in line with the progress in compliance with environmental regulations and environmental regulations. On the contrary,
Japanese Patent Publication No. 63-62571 discloses C: 0.30 to 0.3.
8%, Mn: 0.6 to 1.5%, B: 0.0005 to 5%
0.0030%, Ti: 0.01 to 0.04%, Al:
There is disclosed a method for manufacturing a drive shaft in which a steel containing 0.01 to 0.04% is formed into a drive shaft and the ratio of the induction hardening depth by induction hardening and the steel member radius is 0.4 or more. The maximum torsional strength obtained with the invention material is about 160 kgf / m as shown in FIG. 1 of the publication.
m ² . Further, in JP-A-4-218641, a steel material for a high strength shaft component of a specific component system characterized by low Si and high Mn in which Si: 0.05% or less and Mn: more than 0.65 and 1.7 or less. It has been shown that the material with a spline portion can obtain a torsional strength of 140 to 160 kgf / mm ² by using. As described above, the maximum torsional strength that can be realized at present is about 160 kgf / mm ² .

[0003]

However, under the present circumstances, the above-mentioned strength level of the torsional strength of 160 kgf / mm ² cannot be said to be sufficient as the strength level of the power transmission system shaft parts of the automobile. Further, in order to achieve high strength, it is important to improve workability and suppress quenching cracks in the component manufacturing process. The object of the present invention is that the workability is excellent in the manufacturing process of parts, it does not cause quenching cracks, and it is 160 k as a part.
It is intended to provide a shaft component having an excellent torsional strength of gf / mm ² or more.

[0004]

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

[0005]

[Equation 3]

The above is obtained from the following findings. FIG. 3 is a diagram schematically showing the shear strain and the shear stress when the plastic deformation progresses from the surface layer to the inside in the torsional deformation process of the shaft part. In the figure, the solid line shows the shear strain distribution, the thick solid line shows the shear stress distribution, and the broken line shows the shear yield stress distribution. When the torque is 1), the shear stress τ reaches the shear yield stress τy of the steel material on the surface, and plastic deformation starts. When the torsional deformation progresses to the stage where the torque is 2), plastic deformation progresses inward with work hardening (the difference between the broken line and the solid line in the surface layer in the figure is the work hardening amount). In addition,
The one-dot chain line in the figure is a virtual shear stress distribution when it is assumed that plastic deformation does not occur. Further, at the stage of 3) immediately before the torque causes torsional fracture, it is considered that plastic deformation has progressed to almost the center.

The torque M _t for an arbitrary shear stress distribution τ (r) is given by the following equation (1).

[0008]

[Equation 4]

On the other hand, apparent shear fracture stress τ _max assuming elastic fracture, which is generally used as an index of torsional strength.
Is calculated 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 shown in FIG. The stress distribution can be approximated as τ _f (r) = K ₁ · HV (r) as a function of hardness distribution.

[0012]

[Equation 6]

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

[0014]

[Equation 7]

In the case of a uniform hardness material, since HV _eq = HV = constant, K ₂ = 3 / a ³

[0016]

[Equation 8]

From equations (3) and (5),

[0018]

[Equation 9]

The equivalent hardness HV _eq is obtained by dividing the cross section into N rings concentrically in the radial direction, the hardness of the n-th ring-shaped portion is HV _n , the radius is r _n , and the interval is Δr _n . At times, it can be approximated as follows.

[0020]

[Equation 10]

[0021] Again, the average hardness HVa in the cross section is
Was defined. FIG. 4 shows the results of determining the average hardness HVa of materials having various hardness distributions and arranging the torsional strength by HVa. The torsional strength has a good correlation with HVa, and is excellent at 160 kgf / mm ² or more. It is clear that it is necessary to set HVa to 560 or more in order to obtain 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 origin of intergranular cracking", and the strength increases. Saturate or rather decrease. However, if the following methods are used in combination, brittle fracture due to intergranular fracture is suppressed, and the torsional strength increases as the average hardness in the cross section increases. 1) Addition of Ti-B 2) Reduction of P, Cu and O contents 3) Refinement of former 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 in Si 2) Addition of Cr, Mo, Ni 3) Addition of compressive residual stress by hard shot peening treatment

(4) When the average hardness in the cross section of (1) above is increased, the conventional material is more likely to cause quench cracking, but by taking the measures of (2) and (3) above 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 new findings, and the gist of the present invention is as follows.

According to the first aspect of the present invention, the weight ratio of C: 0.35 to 0.70% Si: 0.01 to 0.15% Mn: 0.2 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 consisting of iron and unavoidable impurities, and the average hardness HVa in the cross section defined below is 560 or more. It is a high-strength induction-hardened shaft part characterized by the fact that it is present. Definition of average hardness in cross section: A cross section of radius a is divided into N rings concentrically in the radial direction, and the hardness of the nth ring-shaped portion is HV.
_{where n is} the radius, r _{n is} the interval, and Δr _n is the interval,

[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 consisting of iron and unavoidable impurities, and the average hardness HVa in the cross section defined below is 560 or more. It is a high-strength induction-hardened shaft part. Definition of average hardness in cross section: A cross section of radius a is divided into N rings concentrically in the radial direction, and the hardness of the nth ring-shaped portion is HV.
_{where n is} the radius, r _{n is} the interval, and Δr _n is the interval,

[0029]

[Equation 12]

According to the third to fifth aspects 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%. 1 type or 2 types or more, or further contains 1 type or 2 types of Nb: 0.01-0.3%, V: 0.03-0.6%, and further, or: The high-strength induction-hardened shaft part according to claim 1 or 2, which contains 0.0005 to 0.010% Pb: 0.05 to 0.5% of one or two kinds. The invention according to claim 6 or 7 of the present invention is characterized in that the induction-hardened layer has a prior austenite grain size of 9 or more, and further, or has a surface residual stress of -80 kgf / mm ² or less. It is a high-strength induction hardened shaft component.

[0031]

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

C is an element effective in increasing the hardness of the induction hardening layer, but if it is less than 0.35%, the hardness is insufficient, and if it exceeds 0.70%, it becomes austenite grain boundary. Since the precipitation of carbides becomes remarkable, the grain boundary strength is deteriorated, brittle fracture strength is reduced, and quench cracking is likely to occur, the content is set to 0.35 to 0.70%.

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

Mn is added for the purpose of improving hardenability. However, if it is less than 0.20%, this effect is insufficient. On the other hand, if it exceeds 2.0%, this effect is saturated and rather the toughness of the final product is deteriorated, so the content was made 0.20 to 2.0%.

Further, 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 it is less than, the effect is insufficient. On the other hand, if it exceeds 0.15%, the effect is saturated and rather grain boundary segregation occurs to cause grain boundary embrittlement. For the above reasons, the S content is 0.00
It was set to 5 to 0.15%.

Al is added 1) for the purpose of refining austenite grains during induction hardening heating by combining with N to form AlN, and 2) added as a deoxidizing element, but if less than 0.0005%, The effect is insufficient, while on the other hand, if it exceeds 0.05%, the effect is saturated and rather the toughness is deteriorated, so the content is 0.0005.
.About.0.05%.

Ti is also combined with N in steel to form TiN. Due to this, 1) refinement of austenite grains during induction hardening heating, and 2) prevention of BN precipitation by completely fixing solid solution N, that is, solidification. It is added for the purpose of ensuring the melt 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 rather the toughness is deteriorated.
It was set to 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 expelling grain boundary impurities such as P and Cu from the grain boundaries. However, if less than 0.0005%, the effect is insufficient, while excessive addition exceeding 0.005% causes rather grain boundary embrittlement, so the content is 0.005%.
It was set to 05 to 0.005%.

Further, N is added for the purpose of refining austenite grains during high frequency heating due to precipitation of carbonitrides such as AlN, but if it is less than 0.002%, its effect is insufficient, while 0.02 If the content exceeds%, the effect is saturated and rather BN is formed to reduce the amount of solid solution B, so the content was made 0.002 to 0.02%.

On the other hand, P causes grain boundary segregation at the austenite grain boundaries, lowers the grain boundary strength, and easily causes brittle fracture under torsional stress, which lowers the strength. Especially P
When 0.02% exceeds 0.02%, the strength decrease becomes remarkable, so
The upper limit was 0.02%. In addition, when aiming at further strengthening, it is desirable that the content of P is 0.009% or less.

Cu, like P, also causes grain boundary segregation at the austenite grain boundaries, which causes a decrease in strength. Especially Cu
Is more than 0.05%, the strength will be significantly reduced.
The upper limit was 0.05%.

Further, O causes grain boundary segregation to cause grain boundary embrittlement, and forms hard oxide inclusions in steel.
It easily causes brittle fracture under torsional stress and causes strength reduction. In particular, when O exceeds 0.0020%, the strength is markedly reduced, so 0.0020% was made the upper limit.

Next, the induction-hardened shaft component is made of the above-mentioned components, and the average hardness HVa in the cross-section defined above is 56.
The reason why it is set to 0 or more will be described below. The torsional strength of the induction hardened material improves 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, and if it is less than that, the torsional strength is insufficient. 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 and the component radius r based on the induction hardening hardened layer depth measuring method defined by 559 is 0.3.
It is desirable to set it to 0.8. This is because the torsional strength of the induction hardened material is improved as the induction hardening depth is increased, but when the effective hardened layer depth is less than 0.3 t / r, the effect of improving the torsional strength is small, and If it exceeds 8, the compressive residual stress of the surface layer will decrease, and the risk of occurrence of quench cracks in the shaft part manufacturing process will increase.

Next, claim 2 is an invention relating to a high-strength induction-hardened shaft component in which the final product has a higher torsional strength and does not cause quench cracks in the manufacturing process. In the invention of claim 2, Si: more than 0.15 to 2.5%, Mn: 0.6
The reason why steel containing ~ 2.0% is used is as follows.

Si is added 1) for the purpose of strengthening the grain boundary by suppressing the precipitation of carbide in the austenite grain boundary, and 2) as a deoxidizing element. However, the effect of grain boundary strengthening is insufficient with addition of 0.15% or less.
%, Excessive addition causes rather grain boundary embrittlement, so the content was set to 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, 2) fineness of austenite grains during induction hardening heating by forming MnS in steel, and 3) improvement of machinability. However, when aiming for higher torsional strength, addition of less than 0.60% is insufficient.
On the other hand, Mn causes segregation at the austenite grain boundaries,
It lowers the grain boundary strength and facilitates brittle fracture under torsional stress, thus lowering the strength. This tendency is particularly remarkable at 2.0% or more. For the above reasons, the Mn content is set to 0.6 to 2.0%.

According to claim 3, the addition of Cr, Mo, and Ni causes 1) increase in induction hardening hardness due to improvement of hardenability, increase in hardened layer depth, and 2) segregation of grain boundary in austenite grain boundaries. It is a steel material for shaft parts that is further strengthened by preventing brittle fracture by increasing grain boundary strength or improving toughness in the vicinity of grain boundaries. However, Cr:
Less than 0.03%, Mo: less than 0.05%, Ni: 0.1
If it is less than%, this effect is insufficient. On the other hand, Cr: 1.
If it exceeds 5%, Mo exceeds 1.0%, and Ni exceeds 3.5%, this effect is saturated, and such excessive addition is not preferable from the economical viewpoint. For the above reasons, the content of these is C
r: 0.03 to 1.5%, Mo: 0.05 to 1.0%,
Ni: 0.1 to 3.5%.

According to claim 4, 1) the austenite grains during high frequency heating are further refined to prevent grain boundary destruction, and 2) the hardness is increased by increasing the hardness of the core by precipitation strengthening. It is a steel material for shaft parts. Nb and V form a carbonitride in steel, and have the effect of refining the austenite grains 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 exceeds 0.60%, the effect is saturated, and such excessive addition is not preferable from the economical point of view. For the above reasons, the content of Nb: 0.01 to 0.3%,
V: 0.03 to 0.6%.

A fifth aspect of the present invention is an invention relating to a high-strength induction-hardened shaft component which has excellent torsional strength in the final product, excellent workability in the manufacturing process of the shaft component, and does not cause quench cracking. In the steel of the present invention, C is used for the purpose of improving machinability.
One or two of a and Pb can be contained. Note that Ca not only improves the machinability, but also has the effect of combining with P in the steel to form a phosphide, reducing the grain boundary segregation amount of P, 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%
Above, Pb: above 0.50%, these effects saturate,
Rather, the toughness is deteriorated, so these contents should be Ca:
0.0005 to 0.010%, Pb: 0.05 to 0.5
%.

Next, a sixth aspect of the present invention is a shaft component in which austenite grains during high-frequency heating are further refined to prevent grain boundary breakage and to achieve high strength. In the present invention, the induction-hardened layer of the induction-hardened shaft component has a former austenite grain size of 9
The reason is that the brittle fracture due to grain boundary fracture is suppressed by refining the former austenite grain boundaries of the induction-hardened layer, but this effect is small when the grain size is less than 9.

A seventh aspect of the present invention is a shaft part in which a large compressive residual stress is applied to the surface of an induction-hardened shaft part, thereby suppressing brittle fracture and further strengthening. In the present invention, the residual stress on the surface of the induction hardened shaft component is −80 kg.
The reason for setting f / mm ² or less is that the brittle fracture is suppressed by the application of compressive residual stress to increase the torsional strength, and the effect is particularly remarkable when the residual stress on the surface is −80 kgf / mm ² or less. .

In the induction-hardened shaft component of the present invention, the induction-quenching conditions and the tempering conditions for manufacturing are not particularly limited, and any conditions may be used as long as they satisfy the requirements of the present invention. For example, if the requirements of the present invention are satisfied, tempering may not be performed. Further, in the present invention, if the requirements of the present invention are satisfied, heat treatment such as normalizing, annealing, spheroidizing annealing, and quenching / tempering can be performed as necessary before induction hardening. Before induction hardening, normalization, 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 after finishing rolling, the average cooling rate in the temperature range of 700 to 500 ° C .; 0.0.
It is desirable to carry out under the condition of 5 to 0.7 ° C./second.

Further, in order to apply the compressive residual stress to the induction-hardened shaft part of the present invention, a hard shot peening treatment with an arc height of 1.0 mmA or more after induction hardening-tempering is effective. Here, the arc height is, for example, “Automobile technology, Vol. 41, No. 7, 19
87, pp. 726-727 ", which is an index of the strength of shot peening. However, in the present invention, the condition for applying the compressive residual stress is not particularly limited, and any condition may be used as long as the requirements of the present invention are satisfied. Hereinafter, the effects of the present invention will be described more specifically by way of examples.

[0054]

Example A steel material having the composition shown in Tables 1 to 3 was rolled into a steel bar having a diameter of 40 mm. From this steel bar, a drilling test piece for machinability evaluation, a torsion test piece, and a quench cracking susceptibility evaluation test piece were collected. Machinability is evaluated by a feed rate of 0.33 mm /
At s, the peripheral speed of the drill (material: SKH51-φ10 mm) is variously changed, the total hole depth at which the drill cannot be cut is obtained at each speed, and the peripheral speed-drill life curve is created, and the drill life becomes 1000 mm. The maximum speed was defined as V _L1000 and used as the evaluation standard for machinability. Tables 1 to 3 also show the evaluation results of V _L1000 . The machinability is the same as that of the first invention steel such as Si:
The steel material of 0.01 to 0.15% is S of the second invention steel or the like.
It is understood that i: the steel having a content of more than 0.15 to 2.5% is relatively excellent, and 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 concentration portion (= notch portion) such as a spline portion,
Destroy at this notch. Therefore, strength evaluation requires evaluation with a notched material. Therefore, as a test piece for evaluating the torsional strength, a twisted test piece with a notch having a parallel part of 16 mmφ and a notch having a tip R of 0.25 mm and a depth of 2 mm in the central part was used.

[0059]

[Table 4]

Induction hardening was carried out under the conditions A to C shown in Table 4, and then tempering was carried out at 170 ° C. for 1 hour. A torsion test was performed on these samples. In addition, about some samples, after induction hardening-tempering, the shot peening process was performed on condition of arc height 1.0-1.5 mmA. Further, in order to evaluate the susceptibility to quench cracking, a test piece having a diameter of 24 mmφ, a length of 200 mmL, and a notch having a tip R0.25 mm and a depth 3 mm in the longitudinal direction was used, and induction hardening was performed under the condition D shown in Table 4. Done,
The presence or absence of fire cracks on the notch bottom was observed.

Steel Nos. In Tables 1 to 3 1-44 is the steel of the present invention,
Steel No. 45-63 are comparative steels. Tables 5 to 7 show the results of the torsional strength evaluation of each steel material, in which the ratio of effective hardened layer depth to radius is t /
r, average hardness in cross section HVa, former austenite grain size Nγ of the induction-hardened layer, residual stress on the surface, and evaluation results of quench cracking sensitivity are also shown. The effective hardened layer depth is the effective hardened layer depth based on the induction hardening hardened layer depth measuring method defined in JIS G0559.

[0062]

[Table 5]

[0063]

[Table 6]

[0064]

[Table 7]

As is clear from Tables 5 to 7, it is understood that all the steels according to the method of the present invention have an excellent torsional strength of 160 kgf / mm ² or more and have a low susceptibility to quench cracking. Further, in the method of the present invention, Si: 0.
Inventive examples using steel materials having a content of more than 15 to 2.5% and Mn of 0.6 to 2.0% include Si of the first invention steel and the like: 0.01 to
A relatively higher level of torsional strength is achieved as compared with the invention examples using the steel materials having 0.15% and Mn: 0.2 to 2.0%. Furthermore, when the prior austenite grain size of the induction-hardened layer is No. 9 or more, or when the surface residual stress 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, 41C are the average hardness HVa in the cross section.
Is less than 560, both 160kgf
The torsional strength of / mm ² or more is not achieved. Comparative Example 50
Indicates that the content of S is below the range of the present invention, and 1
Although it has a torsional strength of 60 kgf / mm ² or more, as shown in Table 3, steel No. 50 is inferior in machinability.

Comparative Examples 45, 48, 53, 55 and 57 are cases where the contents of C, Mn, Ti, B and N were below the range of the present invention, and Comparative Examples 46, 47, 49 and 5 were used.
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 exceed the range of the present invention, none of which has achieved a torsional strength of 160 kgf / mm ² or more, and some of the grains In the comparative examples of steel materials for which the field strengthening measures are insufficient, quench cracks have occurred.

[0068]

As described above, by using the method of the present invention, it becomes possible to manufacture an induction-hardened shaft part having an excellent torsional strength of 160 kgf / mm ² or more and free from quenching cracks. The effect is extremely remarkable.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining the definition of average hardness in a cross section, showing a state in which the cross section is divided into n rings concentrically in the 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 in a torsional deformation process of a 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 part

Claims (7)

[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 : 0.0005-0.05% Ti: 0.005-0.05% B: 0.0005-0.005% N: 0.002-0.02% is contained, P: 0.020% or less Cu: 0.05% or less O: limited to 0.0020% or less, the balance consisting of iron and unavoidable impurities, and the average hardness HVa in the cross section defined below is 560 or more. Strength induction hardening shaft parts. Definition of average hardness in cross section: A cross section of radius a is divided into N rings concentrically in the radial direction, and the hardness of the nth ring-shaped portion is HV _n , radius is r _n , and interval is Δr _n 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: 0.0005-0.05% Ti: 0.005-0.05% B: 0.0005-0.005% N: 0.002-0.02% is contained, P: 0.020% Cu: 0.05% or less O: 0.0020% or less, the balance consisting of iron and unavoidable impurities, and an average cross-section hardness HVa defined below is 560 or more. High strength induction hardened shaft parts. Definition of average hardness in cross section: A cross section of radius a is divided into N rings concentrically in the radial direction, and the hardness of the nth ring-shaped portion is HV _n , radius is r _n , and interval is Δr _n 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%. The high-strength induction-hardened shaft component according to claim 1 or 2. 4. The high-strength induction hardened shaft according to claim 1, wherein the steel further contains one or two 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% Pb: 0.05 to 0.5%. parts. 6. The high-strength induction-hardened shaft component according to claim 1, wherein the prior-austenite grain size of the induction-hardened layer is 9 or more. 7. The surface residual stress is −80 kgf / mm ^2.
The high-strength induction-hardened shaft component according to claim 1, which is as follows.