JP3194093B2 - Manufacturing method of high torsional strength 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 method for manufacturing a mechanical component having a high torsion strength shaft shape, for example, as shown in FIGS.
As shown in (C), the present invention relates to a method of manufacturing a shaft-shaped mechanical part having excellent torsional strength as a part constituting a power transmission system of an automobile, such as a shaft having a serrated portion, a shaft with a flange, and a shaft with an outer cylinder. Things.

[0002]

2. Description of the Related Art Parts constituting a power transmission system of an automobile include:
With the recent increase in the output of automobile engines, there is a strong tendency to increase the strength (improve the torsional strength). These parts are
Usually, it is manufactured by forming a medium carbon steel into a predetermined part and subjecting it to induction hardening and tempering. The torsional strength of the induction hardened material increases as the induction hardening depth increases, as shown in, for example, "Isuzu Technical Report, No. 67, page 9". However, at present, only about 150 kgf / mm ² of torsional strength (surface maximum shear stress: hereinafter referred to as τ _max ) has been realized.

In Japanese Patent Publication No. 63-62571, C is 0.30 to 0.38%, Mn is 0.6 to 1.5%,
B: 0.0005 to 0.0030%, Ti; 0.01 to
A method of manufacturing a drive shaft in which steel comprising 0.04%, Al; 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. It is shown. However,
As can be seen from FIG. 1 of the drive shaft material according to the above publication, τ _max can be realized only about 160 kgf / mm ² .

[0004]

However, the aforementioned τ
_{At present,} a strength level of _max = 150 to 160 kgf / mm ² cannot be said to be sufficient as a strength level of a power transmission system component of an automobile. On the other hand, in the induction hardened material, quenching cracks are likely to occur as the strength is increased, and its suppression is one of the important issues at present.

It is an object of the present invention that τ _max is 180 kgf / mm ²
It is an object of the present invention to provide a method for producing an induction hardened or carburized hardened part having an excellent torsional strength and a shaft shape with low susceptibility to quenching cracking.

[0006]

Means for Solving the Problems and Actions The present inventors have conducted intensive studies in order to realize a component having excellent torsional strength and low susceptibility to burn cracking, and obtained the following knowledge. . (1) Torsional strength is improved in proportion to the cross-section in an average hardness as defined below, tau _{ma x} is cross-sectional in average hardness to obtain a 180 kgf / mm ² or more superior torsional strength HVA 5
It is necessary to be 50 or more.

Definition of average hardness in cross section: As shown in FIG. 2, the cross section is divided into N rings concentrically in the radial direction, the hardness of the n-th ring portion is HVn, and the area is Sn.
When

[0008]

(Equation 3)

(2) The increase in the average hardness in the cross section can be realized by increasing the quenching depth by using a high carbon steel or by carburizing and quenching by using a medium carbon steel. However, if the quenching depth is too deep, there is a risk of causing quenching cracks, so there is an upper limit to the quenching depth. (3) In addition to the above, the torsional strength is further increased by performing shot peening after induction hardening and tempering or after carburizing and tempering.

The present invention has been made on the basis of the above-described novel findings, and the gist of the present invention is to provide a shaft using steel containing 0.4 to 0.8% by weight of C. When manufacturing a shape machine part, after forming into a predetermined part shape, induction hardening-tempering is performed to set the ratio t / r of the effective hardened layer depth t to the part radius r to 0.4 to 0.8, and When the average hardness in section HVa defined in the above is 550 or more, or when manufacturing a shaft-shaped machine part using steel containing C: 0.3 to 0.5%, it is formed into a predetermined part shape. After the working, the ratio t / r of the effective hardened layer depth t to the part radius r is set to 0.2 to 0.6 by carburizing and tempering, and the average hardness HVa in the cross section defined above is 55.
0 or more, or after the heat treatment, the arc height is set to 0.
A method for producing a high torsional strength shaft-shaped machine part, wherein a shot peening process is performed at a strength of 5 mmA or more.

Hereinafter, the present invention will be described in detail. In the invention of claim 1, the steel containing C: 0.4 to 0.8% by weight is used for the following reason. C is an element effective for increasing the hardness of the induction hardened hardened layer,
If it is less than 0.4%, the hardness is insufficient, and if it exceeds 0.8%, the toughness is deteriorated, and quenching cracks are easily generated. I decided.

Next, according to the first aspect of the present invention, when manufacturing a shaft-shaped mechanical part, after forming into a predetermined part shape,
By induction hardening and tempering, the ratio t / r of the effective hardened layer depth t to the part radius r is set to 0.4 to 0.8, and the average hardness HVa in the cross section defined above is set to 550 or more. However, the reason is described below. 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 0.4 at t / r, the effect of improving the torsional strength is small. If it exceeds, the compressive residual stress of the surface layer decreases, and the risk of occurrence of sintering cracks increases. For the above reasons, the ratio t / r of the effective hardened layer depth t to the component radius r is set to 0.4 to 0.8. Here, the component radius r in the present invention is the radius of the shaft portion shown in FIG.
In the present invention, for a portion whose cross section is non-axisymmetric,
The component radius r is determined using a circle-equivalent radius determined from the cross-sectional area. The effective hardened layer depth is the effective hardened layer depth based on the induction hardened hardened layer depth measuring method specified in JISG 0559.

Next, as shown in FIG. 3, the torsional strength increases in proportion to the average hardness in the cross section, and τ _max is 180.
In order to obtain an excellent torsional strength of kgf / mm ² or more, it is necessary to make the average hardness HVa in the cross section 550 or more,
If it is less than that, the torsional strength is insufficient, so the average hardness HVa in the cross section is set to 550 or more. Next, in the invention of claim 2, steel containing C: 0.3 to 0.5% by weight is used for the following reason. C is an effective element for increasing the core hardness of the carburized and quenched material, but if it is less than 0.3%, the hardness is insufficient, and if it exceeds 0.5%, the toughness is deteriorated and The content is set to 0.3% to 0.5%, since quenching cracks easily occur.

Next, according to the second aspect of the present invention, when manufacturing a shaft-shaped mechanical part, after forming into a predetermined part shape,
By carburizing and quenching-tempering, the ratio t / r of the effective hardened layer depth t to the part radius r is set to 0.2 to 0.6, and the average hardness HVa in the cross section defined above is set to 550 or more. However, the reason is described below. The torsional strength of the carburized and quenched material increases as the carburized and quenched depth increases. However, when the effective hardened layer depth is less than 0.2 at t / r, the effect of improving the torsional strength is small. Excess carburization requires an extremely long time, which significantly increases the production cost. For the above reasons, the ratio t / r between the effective hardened layer depth t and the component radius r is set to be 0.
2 to 0.6. Here, the component radius r in the present invention
Is the radius of the shaft portion shown in FIG. In the present invention, a part having a non-axisymmetric cross section is defined as a component radius r using a circle-equivalent radius obtained from the cross-sectional area. The effective hardened layer depth is the effective hardened layer depth based on the carburized hardened layer depth measuring method defined in JIS G 0557. The reason why the average hardness HVa in the cross section is 550 or more is the same as in the first aspect of the invention. The carbon potential at the time of carburization in the second invention is not particularly defined,
The range of 0.6 to 1.0 wt% is desirable.

Next, in the present invention, after the induction quenching and tempering or the carburizing and quenching and tempering, a shot peening treatment can be performed with an arc height of 0.5 mmA or more. As an index of the strength of shot peening, for example, “Automotive technology, Vol. 41, No. 7,
1987, pp. 726-727, "arc height" is usually used. This is a method in which a shot is projected on a thin steel piece called an Almen strip (three types of N, A, and C depending on the thickness), and the strength of shot peening is evaluated based on the height of the bent arc of the Almen strip (arc height). (The arc height can be converted between the Almen strips N, A, and C). In the present invention, the most commonly used Almen strip A
The strength of shot peening was limited by the arc height when using. The purpose of shot peening in the present invention is to increase the compressive residual stress of the surface layer to further improve the torsional strength. However, if the shot peening strength is less than 0.5 mmA, the effect is small, so the arc height is set to 0.5 mmA or more.

The steel to be used in the present invention is limited only to the range of C as described above, but it is desirable to include components other than C in the following ranges. Si: 0.01 to 0.5% Mn: 0.50 to 2.0% S: 0.01 to 0.10% Al: 0.015 to 0.05% N: 0.005 to 0.020% Further, for the purpose of improving the hardenability, one or more of Cr: 1.5% or less, Ni: 3.5% or less, and Mo: 1.0% or less are contained as necessary.

Further, for the purpose of preventing coarsening of austenite grains during high-frequency heating or carburizing heating, Ti: 0.040% or less, Nb: 0.1% or less, and V: 0. One or more of 3% or less are contained.

P is further restricted to 0.030% or less.
Further, in the present invention, induction hardening conditions, carburizing and quenching conditions and tempering conditions are not particularly limited except as defined above,
Any conditions may be used as long as they satisfy the requirements of the present invention. In the present invention, heat treatments such as normalizing, annealing, spheroidizing annealing, and quenching-tempering can be performed as necessary before induction hardening. If induction hardening, normalizing, annealing, and spheroidizing annealing are not performed before carburizing and quenching,
Hot rolling of steel material to finish temperature; 700-8
It is desirable to perform the cooling at a temperature of 50 ° C. and an average cooling rate of 700 to 500 ° C. after finish rolling;

Hereinafter, the effects of the present invention will be more specifically described with reference to examples. (Example) A steel material having the composition shown in Tables 1 and 2 was prepared by 26 mmφ.
And then annealed under the conditions of 800 ° C. heating and furnace cooling, and then machined into a torsion test piece having a parallel portion of 16 mmφ. Thereafter, a part was subjected to induction quenching under the conditions shown in Table 3, then tempered at 170 ° C. × 1 hour, and the other was carburized and quenched under the conditions shown in Table 4, followed by 17
Tempering was performed at 0 ° C. × 1 hour. These samples were subjected to a torsion test. In addition, about some samples, after the induction hardening-tempering or the carburizing-hardening-tempering, the shot peening process was performed on 0.6-1.5 mmA of arc height conditions.

Tables 5 and 6 show induction hardening-tempering materials,
Tables 7 and 8 show the evaluation results of the torsional strength of each of the carburized and quenched and tempered steels, the effective hardened layer depth t / r and the average hardness H.
Va, the presence or absence of quenching cracks during high-frequency heating or carburizing and quenching, and the presence or absence of shot peening (the arc height value if present) are also shown. Table 5, Table 6, Table 7, Table 8
As can be seen from FIG.
_max has a 180 kgf / mm ² or more superior torsional strength,
Further, it can be seen that the susceptibility to fire cracking is small.

On the other hand, as for the induction hardened-tempered material, Comparative Example 1 is a case where the content of C is lower than the range of the present invention, and Comparative Example 3 is a case where the effective hardened layer depth t / r and the average hardness HVa Is less than the range of the present invention, and Comparative Example 7
Are cases where the effective hardened layer depth t / r is less than the range of the present invention, and none of them has achieved a torsional strength of τ _max of 180 kgf / mm ² or more. Comparative Example 12 is a case where the content of C exceeds the range of the present invention.
Nos. 1, 20, and 23 are cases where the effective hardened layer depth t / r exceeds the upper limit of the range of the present invention, and all of them show burning cracks.

Next, carburizing and tempering materials are as follows:
Comparative Example a is a case where the content of C is lower than the range of the present invention, and Comparative Example e is an effective hardened layer depth t / r and an average hardness HV.
a is less than the range of the present invention, and Comparative Examples h and n
Are cases where the effective hardened layer depth t / r is less than the range of the present invention, and none of them has achieved a torsional strength of τ _max of 180 kgf / mm ² or more. Comparative Example i is a case where the content of C exceeds the range of the present invention, and Comparative Examples c and o are cases where the effective hardened layer depth t / r exceeds the upper limit of the range of the present invention. In each case, burning cracks occurred.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

[Table 5]

[0028]

[Table 6]

[0029]

[Table 7]

[0030]

[Table 8]

[0031]

As described above, by using the method of the present invention, it is possible to produce a high torsional strength shaft-shaped machine part having excellent torsional strength with τ _max of 180 kgf / mm ² or more and low susceptibility to quenching. It is possible to manufacture a power transmission system component that can tolerate an increase in the output of an automobile engine in recent years, and the industrial effect is extremely remarkable.

[Brief description of the drawings]

FIG. 1 shows an example of a shaft-shaped part, wherein (A) is a shaft having a serration, (B) is a shaft with a flange,
(C) is a diagram showing a shaft with an outer cylinder. The names of each part are as follows.

[Explanation of symbols]

 Reference Signs List 10 shaft, 11, 12 serration 20, 21 shaft, 22 flange 30, 31, 32 shaft, 33 outer cylinder

FIG. 2 is a view showing a state in which the cross section is divided into N rings concentrically in the radial direction for explaining the definition of the average hardness in the cross section.

FIG. 3 shows the average hardness HVA in the cross section and the static torsional strength τ _max
FIG.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-203226 (JP, A) JP-A-1-259129 (JP, A) JP-B-60-27729 (JP, B2) JP-B-63 62571 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 9/00, 9/28, 9/30 C22C 38/00 B21D 53/00 F16C 3/02

Claims (3)

(57) [Claims] When manufacturing a shaft-shaped machine part using steel containing 0.4 to 0.8% by weight of C: after forming into a predetermined part shape, induction hardening and tempering are performed. A high torsional strength characterized in that the ratio t / r of the effective hardened layer depth t to the component radius r is 0.4 to 0.8, and the average in-section hardness HVa defined below is 550 or more. Manufacturing method of shaft-shaped machine parts. Definition of average hardness in the cross section; The cross section is divided into N rings concentrically in the radial direction, and n
When the hardness of the second ring-shaped portion is HVn and the area is Sn, 2. When manufacturing a shaft-shaped machine part using steel containing 0.3 to 0.5% by weight of C: after forming into a predetermined part shape, carburizing quenching and tempering are performed. A high torsional strength characterized in that the ratio t / r of the effective hardened layer depth t to the component radius r is 0.2 to 0.6, and the average in-section hardness HVa defined below is 550 or more. Manufacturing method of shaft-shaped machine parts. Definition of average hardness in the cross section; The cross section is divided into N rings concentrically in the radial direction, and n
When the hardness of the third ring-shaped portion is HVn and the area is Sn, 3. A method for producing a machine component having a high torsional strength shaft shape, wherein the component produced by the method according to claim 1 or 2 is further subjected to shot peening at an arc height of 0.5 mmA or more. .