JPH11302734A - Production of constant velocity coupling excellent in cold workability and strength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a constant velocity coupling composed of steel excellent in a rolling fatigue life and twisting strength without damaging its cold workability such as cold forgeability and machinability. SOLUTION: A steel having a compsn. contg., by weight, 0.52 to 0.60% C, 0.03 to 0.15% Si, 0.10 to 0.40% Mn, 0.05 to 0.30% Cr, 0.10 to 0.30% Mo, 0.003 to 0.020% S, 0.0005 to 0.005% B, 0.02 to 0.05% Ti, <=0.01% N, 0.005 to 0.05% Al and Mn+Cr+Mo: 0.35 to 0.80%, and the balance Fe with inevitable impurities, that after the heating temp. is regulated to the Ac3 to 1,000 deg.C, is subjected to rolling or forging at >=30% reduction of area, moreover, heated to the Ac1 to 770 deg.C and, subsequently, subjected to spheroidizing of executing slow cooling in the temp. range of 730 to 700 deg.C at a rate of <=15 deg.C/h to regulate its hardness after the spheroidizing to 68 to 78 HRB is used, and the hardness of the surface after induction hardening is regulated to >=60 HRC.

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 constant velocity joint, which is an automotive part containing boron, which is excellent in cold workability, induction hardening, rolling fatigue life and torsional strength.

[0002]

2. Description of the Related Art Conventionally, the outer ring of a constant velocity joint of an automobile has been made of steel equivalent to S48C (JIS standard) or S53C (JIS standard) or steel with improved cold forgeability described in Japanese Patent Publication No. 1-38847. Hardened and used.
However, in order to reduce production costs and improve fuel efficiency, it is necessary to reduce the weight of parts. For this purpose, the rolling fatigue life of these steels must be increased without impairing the cold workability. It is necessary to develop constant velocity joints with excellent characteristics and torsional strength characteristics.

[0003]

The problem to be solved by the present invention is that S4
Impairs cold workability such as cold forgeability and machinability with respect to 8C (JIS standard), S53C (JIS standard) equivalent steel and steel with improved cold forgeability described in Japanese Patent Publication No. 1-38847. An object of the present invention is to provide a constant velocity joint for a vehicle or the like made of steel having excellent rolling fatigue life characteristics and torsional strength characteristics without performing the method.

[0004]

In order to improve the rolling fatigue life and torsional strength characteristics of the present invention, the present inventors are effective in increasing the amount of C and adding Mo. It was found that the addition amount was appropriate in consideration of the cold workability. In order to further improve the cold workability, this problem was solved by optimizing rolling conditions and spheroidizing annealing conditions.

[0005] That is, the means of the present invention for solving the above-mentioned problems are as follows: C: 0.52 to 0.60% by weight;
Si: 0.03 to 0.15%, Mn: 0.10 to 0.4
0%, Cr: 0.05-0.30%, Mo: 0.10
0.30%, S: 0.003 to 0.020%, B: 0.
0005-0.005%, Ti: 0.02-0.05
%, N: 0.01% or less, Al: 0.005 to 0.05
%, Mn + Cr + Mo: 0.35 to 0.80%, the balance consisting of Fe and unavoidable impurities, and a heating temperature of Ac _{3 to} 1000 ° C., followed by rolling or forging at a surface reduction rate of 30% or more. After heating to Ac _{1 to} 770 ° C., 73
Perform spheroidizing annealing by gradually cooling the temperature range of 0 ° C. to 700 ° C. at a rate of 15 ° C./h or less, and set the hardness after the spheroidizing annealing to 68 to
Using 78HRB steel, the surface hardness after induction hardening is set to 60HRC or more. The proper amounts of C and Mo are added, and the production method is found to be suitable for cold workability and rolling. An object of the present invention is to provide a method for manufacturing a constant velocity joint having excellent dynamic fatigue life characteristics and torsional strength characteristics.

The reasons for limiting the present invention are described below. C: C is an element necessary for securing strength after quenching and tempering as a component for a mechanical structure and improving rolling fatigue life characteristics and torsional strength characteristics.
The surface hardness at the time of induction hardening does not satisfy 60 HRC or more and the strength is insufficient. If it exceeds 0.60%, the cold workability is reduced and cracks occur at the time of induction hardening.
Therefore, the content is set to 0.52 to 0.60%.

Si: Si is a necessary element for deoxidation,
If it is less than 0.03%, the effect cannot be obtained sufficiently, and
If the content exceeds 5%, the processability is reduced. Therefore, the content is set to 0.03 to 0.15%.

Mn: Mn is an element necessary for securing hardenability. If it is less than 0.10%, its effect cannot be sufficiently obtained, and if it is contained more than 0.40%, the workability is reduced. Let it. Therefore, the content is set to 0.10 to 0.40%.

Cr: Cr is an element that contributes to hardenability, but if less than 0.05%, its effect cannot be obtained.
%, The carbides are concentrated in the carbide during spheroidizing annealing, the carbide remains during induction hardening, and uniform hardening hardness cannot be obtained. Therefore, the content is 0.05
０．３0.30%.

Mo: Mo is an element that improves the hardenability and also improves the rolling fatigue life and torsional strength. If its content is less than 0.10%, its effect is not sufficient.
When the content exceeds 30%, the hardness after the spheroidizing annealing is increased, and the workability is significantly reduced. Therefore, the content is set to 0.10 to 0.30%.

S: S is MnS and TiS, and is an element for improving machinability. However, if it is less than 0.003%, its effect cannot be sufficiently obtained, and if it exceeds 0.020%, cold workability is deteriorated. Lower. Therefore, the content is 0.003 to 0.02
0%.

B: B is an element that improves the grain boundary strength and hardenability. If B is less than 0.0005%, the effect is not sufficient. Reduces hardenability. Therefore, the content is set to 0.1.
0005 to 0.005%.

Ti: Ti is an element that fixes free-N in steel and improves the effect of B on hardenability.
If it is less than 2%, the effect cannot be sufficiently obtained, and if it exceeds 0.05%, the effect is saturated because the N content in the steel is specified to be 0.01% or less. Therefore, the content is 0.02
% To 0.05%.

N: When N exceeds 0.01%, T
iN increases and adversely affects fatigue properties. for that reason,
The content was set to 0.01% or less.

Al: Al is an element required as a deoxidizing material, and if its content is less than 0.005%, its effect is not sufficient.
When the content exceeds 0.05%, the amount of the alumina-based oxide increases, and the fatigue properties and the workability deteriorate. Therefore, the content was made 0.005 to 0.05%.

Mn + Cr + Mo: Both Mn, Cr and Mo are elements that contribute to the induction hardenability and increase the hardness of the steel material. If the sum is 0.35 or less, a homogeneous hardened structure cannot be obtained and the rolling The life is remarkably shortened.
The hardness after spheroidizing annealing does not satisfy 78 HRB or less. Therefore, the sum of Mn + Cr + Mo is set to 0.35 to 0.5.
80.

Rolling and forging conditions: The reason for heating to Ac ₃ or more is to uniformly austenite without leaving any carbides or ferrite. No structure can be obtained, and heat treatment distortion increases after quenching and tempering. Also, when the heating temperature is 1000 ° C. or higher, fine precipitates grow and the precipitates become relatively large, so that austenite crystal grains during rolling or forging become large, and the amount of ferrite after rolling or forging is reduced. In addition to deteriorating the properties, the crystal grains after quenching and tempering become large, and the grain boundary strength decreases. Therefore, the heating temperature at the time of rolling or forging is set to Ac _{3 to} 1000 ° C. As for the area reduction rate, when it is 30% or less, the amount of ferrite produced is reduced and the workability is reduced.

Spheroidizing annealing conditions: (Heating temperature) In order to obtain a good spheroidized structure, it is necessary to heat to a two-phase region of austenite and spheroidized residual carbide. The heating temperature is less than Ac _1, does not occur divided carbides, lamellar pearlite remain after spheroidizing annealing, not good spheronization tissue is obtained, there is no residual carbide when heated to temperatures above 770 ° C., during cooling Lamella perlite precipitates. Therefore, the heating temperature is set to Ac ₁
~ 770 ° C.

(Slow cooling temperature zone) In order to obtain a good spheroidized structure, it is necessary to suppress the precipitation of lamellar pearlite and grow the residual carbide by gradually cooling the temperature zone where carbide precipitation occurs. However, at a temperature higher than 730 ° C., the precipitation of carbide hardly occurs, and the precipitation ends at 700 ° C. Therefore, the slow cooling section is set to 730 to 700
° C. Further, a section other than the slow cooling temperature section, that is, a temperature section from the above-mentioned heating temperature to 730 ° C., or 7
The cooling rate in the section from 00 ° C. to normal temperature is not specified, and may be any rate. However, it is preferable to make the cooling rate as fast as possible from the viewpoint of industrial productivity.

(Slow Cooling Rate) When the temperature range of 730 to 700 ° C. is cooled at a rate higher than 15 ° C./h, lamellar pearlite precipitates during cooling, and a good spheroidized structure cannot be obtained. Therefore, the slow cooling rate was set to 15 ° C./h or less.

Hardness: If the hardness after spheroidizing annealing exceeds 78 HRB, cracks will occur during cold forging, and the life of the mold will be significantly reduced, impeding productivity. Deterioration of performance. Therefore, the hardness after spheroidizing annealing was set to 68 to 78 HRB.

Hardness after induction quenching: If the hardness after induction quenching is less than 60 HRC, the rolling fatigue life is reduced and the rolling parts are slid to increase the wear of the parts. Therefore, the hardness after induction hardening was set to 60 HRC or more.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below through examples and comparative examples. Table 1 shows the steel compositions in Examples and Comparative Examples. 1 to 9. Invention steel N
o. 1 to 3 are S53C and S specified in JIS, respectively.
55C and S58C steels have reduced Si and Mn,
This is a steel to which o and B are added. On the other hand, the comparative steel No.
4, 5, and 6 represent S48C, S53C, and S58C, respectively.
Is steel. Comparative steel No. 7, 8 are S48C, S53
It is a steel in which Si and Mn are reduced and B is added to steel C. Comparative steel No. No. 9 is for S58C steel, Si,
Mn is reduced and Mo and B are added to the steel.
r + Mo becomes 0.85%, and 0.35 ≦ Mn + Cr +
The steel does not satisfy Mo ≦ 0.80%.

Each of test steels (inventive steels 1 to 3 and comparative steels 4 to 10) having the chemical composition shown in Table 1 was melted in a 100 kg vacuum melting furnace, heated to 950 ° C., and hot-forged to φ55.
After forging to 750 ° C., a steel material subjected to spheroidizing annealing in which the temperature range of 730 ° C. to 700 ° C. is gradually cooled at a cooling rate of 10 ° C./h is used.
m. Then, after forming material processing by cold forging, turning processing and rolling processing were added to form a constant velocity joint outer ring having a shape shown in FIG. In the figure, the constant velocity joint comprises a mouth part 1 and a shaft part 2, and the shaft part 2 comprises a serration part 4 and a screw part 5. The inside of the mouth part 1 of the constant velocity joint outer ring has six ball rolling grooves 3,
Retainers 8 for holding the balls 7 are formed above and below the ball rolling grooves 3. Further, a constant velocity joint inner ring 6 is mounted in the constant velocity joint outer ring. The effective hardened layer depth (distance from the mirror surface to the point of 500 HV) is about 3.0 m on the mouse rolling surface of the outer race of the constant velocity joint.
m, induction hardening and tempering (tempering conditions: 180 ° C. for 1 hour) was performed so that the effective hardened layer depth of the shaft portion 2 was about 5 mm.

[0025]

[Table 1]

[0026]

EXAMPLES The following tests were conducted on the products described in the embodiments, and the results are shown below. The rolling contact surface of the mouse was subjected to a rolling fatigue life test, and the shaft portion 2 was subjected to a torsional strength test. The rolling fatigue life test is evaluated by combining the constant velocity joint inner ring 6 and the ball 7 as shown in FIG. 2, and the torsional strength test is performed by fixing the mouth part 1 and the serration part 4 and twisting. evaluated. Further, the depth of the hardened layer was set to a position at which the hardness became 500 HV as measured by a Vickers hardness tester, and the hardness of the material after the spheroidizing annealing was measured using a Rockwell hardness tester.

(Regarding Material Hardness and Rolling Contact Fatigue Life Test Results) The effective hardened layer depth after induction hardening and tempering was set to about 3.0.
A rolling fatigue life test was performed using a test piece having a thickness of 0.1 mm.
The test conditions were such that a test was conducted for 100 hours with a constant surface pressure applied, and the surface pressure when peeling occurred in any one of the six ball rolling grooves 3 was evaluated. That is, the higher the surface pressure at the time of peeling, the better the rolling fatigue life. The steel No. of the present invention. Comparative steel Nos. 1 to 3 have the same C content level. 4 to 8, the surface pressure at which delamination occurs is high, and the rolling contact fatigue life is excellent. In addition, the comparative steel No. Compared to 4, 5, 6, 9
The steel No. of the present invention. 1-3 are 0.35 ≦ Mn + Cr + Mo
By setting ≦ 0.80% and optimizing the spheroidizing annealing conditions, the hardness after spheroidizing annealing can be 68 to 78 HRB, cracks can be suppressed during cold forging, and the life of the mold can be reduced. Can be improved.

[0028]

[Table 2]

(Regarding Torsion Strength Test Results) The torsion strength test of the shaft portion 2 was performed using a test piece having an effective hardened layer depth of about 5.0 mm after induction hardening and tempering. The steel No. of the present invention. Comparative steel Nos. 1 to 3 were prepared by adding B and Mo in a composite to increase the grain boundary strength. 4 to 8 have excellent torsional strength. In addition, the comparative steel No. 9 shows the same strength as the steel of the present invention, but is inferior to the steel of the present invention in cold workability.

[0030]

[Table 3]

[0031]

As described above, the effects of the method for manufacturing a constant velocity joint according to the present invention will be described below. 1) In the steel composition, C: 0.52 to 0.60%,
By adding Mo: 0.10 to 0.30% and setting the hardness after induction hardening and tempering to 60 HRC or more, it is possible to manufacture a constant velocity joint having excellent rolling fatigue life and torsional strength. . 2) Further, in the steel composition, the amount of Mn + Cr + Mo is set to 0.35 to 0.80%, and the rolling or forging condition and the spheroidizing annealing condition are optimized to obtain a constant velocity joint having excellent cold workability. Manufacturing is possible. According to the method of the present invention as described above, it is possible to manufacture a constant velocity joint having excellent rolling fatigue characteristics and strength characteristics without impairing cold workability such as cold forgeability and machinability. The weight can be reduced.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a view in which a shape of a constant velocity joint used in a rolling fatigue life test and a torsional strength test is partially broken and partially omitted, (a) is a plan view, and (b) is a front view. .

FIG. 2 is an assembly drawing of a constant velocity joint inner / outer ring and a ball during a rolling fatigue test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mouth part 2 Shaft part 3 Ball rolling groove of mouth part 4 Serration part 5 Screw part 6 Inner ring of constant velocity joint 7 Ball 8 Retainer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masayoshi Saga 19, Matsuyama-cho, Moka-shi, Tochigi Honda Motor Co., Ltd.

Claims (1)

[Claims] (1) C: 0.52 to 0.60% by weight, S
i: 0.03 to 0.15%, Mn: 0.10 to 0.40
%, Cr: 0.05 to 0.30%, Mo: 0.10
0.30%, S: 0.003 to 0.020%, B: 0.
0005-0.005%, Ti: 0.02-0.05
%, N: 0.01% or less, Al: 0.005 to 0.05
%, Mn + Cr + Mo: 0.35 to 0.80%, the balance consisting of Fe and unavoidable impurities, and a heating temperature of Ac _{3 to} 1000 ° C., followed by rolling or forging at a surface reduction rate of 30% or more. After heating to Ac _{1 to} 770 ° C., 73
Perform spheroidizing annealing by gradually cooling the temperature range of 0 ° C. to 700 ° C. at a rate of 15 ° C./h or less, and set the hardness after the spheroidizing annealing to 68 to
A method for producing a constant velocity joint having excellent cold workability, rolling fatigue life, and torsional strength, wherein a steel material having 78 HRB is used and the surface hardness after induction hardening is 60 HRC or more.