JP2009167477A - Sintered clutch hub, compact therefor, and method for manufacturing sintered clutch hub - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a sintered clutch hub which is formed from an iron-based sintered alloy, is inexpensive and has high strength and high contact-pressure fatigue strength, without shortening the die life and causing cracks on products, while inhibiting a dimensional change after a sintering step. <P>SOLUTION: A raw powder of a compact has a composition comprising, by mass ratio, 2 to 4% Cr, 0.3 to 0.8% Mo, 0.4 to 0.8% C and the balance Fe. The compact has a density of 6.6 g/cm<SP>3</SP>or more but less than 7.0 g/cm<SP>3</SP>and has density difference of 0.15 g/cm<SP>3</SP>or less among each part. The sintered clutch hub 1 is formed by sintering the compact. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a clutch hub mainly used for a manual transmission of an automobile, in particular, a low-cost, high-strength, high-pressure fatigue strength sintered clutch hub formed of an iron-based sintered alloy, and molding for the clutch hub. The present invention relates to a body (green compact) and a method for manufacturing the clutch hub.

  Examples of conventional techniques for sintered parts having high strength and high fatigue strength are disclosed in Patent Documents 1 and 2 below.

Patent Document 1 shows a nitriding treatment method for obtaining a sintered body having high fatigue strength. As a material of the sintered body, C: 0.2 to 1.5% by weight ratio, Cr , V, Al, Mn, Mo, Ti, and at least one selected from Ni: 0.5 to 5%, and an iron-based alloy having a balance of Fe. A molded body is made from the alloy powder of the composition (this molded body has a density of 7.1 g / cm ³ is shown in the examples), the molded body is sintered, and then the obtained sintered The body is subjected to nitriding treatment by glow discharge using the sintered body as a cathode, and as a condition at that time, a gas partial pressure in a gas atmosphere containing nitrogen is set to 150 Pa or less to form a hard compound layer on the surface.

On the other hand, the method disclosed in Patent Document 2 is to produce a high-strength sintered body formed of an iron-based sintered alloy as it is sintered, and Cr: 0.5 to After forming steel powder having a composition of 1.5%, Mo: 0.1 to 2%, Mn: 0.08% or less, and the balance Fe, sintering is performed at a temperature of 1100 to 1300 ° C. Cool at a rate of 200 ° C./min. Moldings in this manner, density 6.8 g / cm ³ and 7.0 g / cm ³ is illustrated.
JP 2003-313649 A JP-A-6-340942

The sintered body manufactured by the method of Patent Document 1 sinters a molded body having a density of 7.1 g / cm ³ , so that the molding pressure in powder molding increases, and the molding becomes difficult in addition to molding. There is also a problem that the service life of the metal mold is reduced and the molding cost is increased accordingly.

  In addition, since the molding pressure is increased, the sintered body to be manufactured is a clutch hub having a boss part, a rim part, and an outer diameter tooth part, and the shape is complicated, so the density of each part of the molded body is made uniform. The density difference causes cracking during sintering.

  Furthermore, if a large density difference occurs in each part, the difference in the amount of dimensional change after sintering also increases, making it difficult to correct the dimensions by sizing, and the required dimensional accuracy of the clutch hub cannot be obtained.

On the other hand, the sintered body manufactured by the method of Patent Document 2 is manufactured by the method of Patent Document 1 because the density of the exemplified molded body is 6.8 g / cm ³ and 7.0 g / cm ^3. Compared to a sintered body, it is easier to form a powder and make the density of the formed body uniform. However, this sintered body requires control of the amount of Mn added. The amount of Mn is set to 0.08% or less to suppress the amount of oxide generation and prevent the strength from being reduced. To reduce the amount of Mn to 0.1% or less, iron powder is produced. It is necessary to select a high-purity raw material in the process, and the price of iron powder increases, leading to an increase in cost.

  In the method of Patent Document 2, the strength of the sintered body is increased by cooling (quenching) immediately after sintering at a predetermined speed, and the cooling speed is defined in order to perform the quenching.

  According to the present invention, a low-cost, high-strength, high-pressure fatigue strength sintered clutch hub formed of an iron-based sintered alloy can be produced without causing a decrease in mold life or cracking of the product. It is an object of the present invention to make it possible to manufacture while suppressing the dimensional change after ligation.

In order to solve the above-described problems, in the present invention, the sintered clutch hub is composed of a raw material powder having a mass ratio of Cr: 2 to 4%, Mo: 0.3 to 0.8%, and C: 0.4. -0.8%, remaining Fe, a density of 6.6 g / cm ³ or more and less than 7.0 g / cm ³ , and a density difference of each part is 0.15 g / cm ³ or less. To do. The present invention provides a molded article for the clutch hub.

The molded body is sintered to produce the sintered clutch hub of the present invention. The preparation, density 6.6 g / cm ³ or more in the raw material powder of the above composition, 7.0 g / cm ³ less than the molded body is formed, and then the temperature of the non-oxidizing atmosphere 1200 to 1300 ° C. The molded body This is done by sintering. The present invention also provides such a manufacturing method.

Since the density of the molded article for a clutch hub of the present invention is 6.6 g / cm ³ or more and less than 7.0 g / cm ³ , molding does not become difficult, and the density difference of each part is also 0.15 g / cm ^3. Since it is set to cm ³ or less, the dimensional accuracy can be improved.

In addition to forming this molded body with raw material powder having a composition of Cr: 2 to 4 mass%, Mo: 0.3 to 0.8 mass%, C: 0.4 to 0.8 mass%, and residual Fe, the density is reduced. with 6.6 g / cm ³ or more, the sintered clutch hub of the final product, high strength even without quenching, it is possible to obtain a high surface pressure fatigue strength. Further, by setting the density to less than 7.0 g / cm ^3, it is possible to prevent an increase in molding pressure and prevent a reduction in the life of the molding die, and to reduce the difference in density of each part of the molded article for the clutch hub. It is also possible to suppress the occurrence of cracks in the sintering process. Furthermore, by making the difference in density of each part 0.15 g / cm ³ or less, it becomes possible to reduce the variation in the amount of dimensional change after sintering and to reliably perform dimensional correction by sizing.

  In addition, sintering of the molded body formed of the raw material powder having the above composition is performed at a temperature of 1200 to 1300 ° C. in a non-oxidizing atmosphere to obtain bainite or a structure in which martensite is distributed in bainite, and even without quenching. High strength and high surface fatigue strength are ensured. Specifically, without quenching, a performance with a surface hardness of 85 HRB or more, a tensile strength of 800 MPa or more, a bending fatigue strength of 200 MPa or more, and a surface pressure fatigue strength of 0.8 GPa or more can be obtained.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 to 3 show an example of a sintered clutch hub. The illustrated sintered clutch hub 1 is for a manual transmission of an automobile, and has a boss portion 2, a rim portion 3, and an outer diameter tooth portion 4. The boss portion 2 is provided with a shaft hole 5, and the outer diameter tooth portion 4 is provided with a key groove 6 at a constant pitch in the circumferential direction.

  This sintered clutch hub 1 is made by molding a raw material powder having a composition of Cr: 2 to 4%, Mo: 0.3 to 0.8%, C: 0.4 to 0.8%, and residual Fe by mass ratio. A compact is produced by compression molding, and after the compact is sintered, the size of the sintered body is corrected by sizing.

  The iron-based alloy of the material is Cr that is the nitride-forming element, Mo that is effective for solid solution strengthening, Mo that is effective for precipitation strengthening, and C that is most effective for strengthening the iron-based material is less than 2 mass%, less than 0.3 mass%, If it is less than 0.4 mass%, the purpose of ensuring high strength and high surface pressure fatigue strength is not achieved, while the contents of Cr, Mo and C are 4 mass%, 0.8 mass% and 0.8 mass%, respectively. If it exceeds, problems such as a decrease in compressibility of the powder and a decrease in strength due to excessive precipitation of the hard material occur. Therefore, these components limit the content to the above range.

The formed body is formed into the same shape as the final product. The molding is performed by controlling the molding pressure so that the density of the molded body is 6.6 g / cm ³ or more and less than 7.0 g / cm ³ . Moreover, the boss | hub part 2, the rim | limb part 3, and the outer diameter tooth part 4 are shape | molded separately by a division | segmentation punch, and each part, ie, the boss | hub part 2, the rim | limb part 3, and an outer diameter tooth | gear, is adjusted by adjusting the compression allowance by each division punch. The density difference of the part 4 is controlled to 0.15 g / cm ³ or less.

When the density of the molded body is less than 6.6 g / cm ^3, it is difficult to ensure strength even if a material having the above composition is used. In addition, if the density of the molded body exceeds 7.0 g / cm ³ , a high molding pressure is required, which makes molding difficult, suppresses the reduction in mold life, suppresses the generation of cracks during sintering, and sintering. The purpose of suppressing the subsequent dimensional change is not sufficiently achieved.

  The molded body thus obtained is introduced into a sintering furnace and sintered. The sintering is performed under a temperature condition of 1200 to 1300 ° C. in a non-oxidizing atmosphere, and the sintered structure is bainite or martensite distributed in bainite. High strength is obtained by using the above structure that does not contain ferrite or pearlite. If necessary, the return treatment is performed at a temperature of 150 to 300 ° C.

The non-oxidizing atmosphere for performing sintering is, for example, an N ₂ gas atmosphere, but a vacuum atmosphere can also be used as the non-oxidizing atmosphere. The sintering temperature is set to 1200 to 1300 ° C. in order to sufficiently advance the sintering while suppressing an increase in cost due to unnecessary heating. A sintering time of 10 to 60 minutes is sufficient.

  The sintered clutch hub manufactured under the above conditions can obtain performances with a surface hardness of 85 HRB or more, a tensile strength of 800 MPa or more, a bending fatigue strength of 200 MPa or more, and a surface fatigue strength of 0.8 GPa or more without quenching. The surface fatigue strength here is a value measured with a two-cylinder testing machine.

  If the surface hardness of the clutch hub used under a high load is less than 85 HRB, wear due to sliding with the mating part proceeds and the required durability standard cannot be satisfied. As for the clutch hub, tensile stress repeatedly acts on the tooth surface of the outer diameter tooth portion, the root corner portion, and the key groove portion formed on the outer diameter tooth portion with use. When the clutch hub is used at a high load, it is desired that the tensile strength is 800 MPa or more and the bending fatigue strength is 200 MPa or more in order to withstand the stress, and the surface that slides with the counterpart part is 0.8 GPa. High surface fatigue strength exceeding 1 is desired, and both of these requirements are satisfied.

Example 1
Examples are given below. The raw material powder which mixed the Fe-Cr-Mo alloy powder and the graphite powder in the ratio shown in Examples 1-6 of Table 1 was prepared.
For comparison, a raw material powder obtained by mixing Fe—Cr—Mo alloy powder and graphite powder in the proportions shown in Comparative Examples 1 to 6 in Table 1 and Fe-0.5 mass% Mo-4 mass% Ni-1. A raw material powder prepared by mixing 0.5 mass% graphite powder with 5 mass% Cu-0.5 mass% C partial diffusion alloy powder was also prepared.

And the molded object of the test piece for performance evaluation was produced with the predetermined pressure using each said raw material powder. The density of the compact is also shown in Table 1. In the examples, the density of the molded body was adjusted so that the density of the test pieces after sintering (sintered body density) exceeded 6.7 g / cm ³ .

  Next, each of the fabricated molded bodies (except for Comparative Example 4) was sintered by being held in a nitrogen atmosphere at a temperature of 1250 ° C. for 45 minutes. For Comparative Example 4, the sintering temperature was 1150 ° C., and the atmosphere and sintering time were the same as those of other samples.

  Using the test piece (having the sintered body density shown in Table 1) produced under the above conditions, the hardness and strength characteristics of the sintered body (Rockwell hardness, tensile strength, bending fatigue strength, surface pressure fatigue strength) ) Was evaluated. Rockwell hardness is measured by a method according to JIS Z 2245, tensile strength is a method according to JIS Z 2241, bending fatigue strength is a method according to JIS Z 2274, and surface pressure fatigue strength is measured by Shimadzu Corporation. Each measurement was made with a 2-cylinder testing machine manufactured by the company. The results are shown in Table 1.

  As can be seen from the data in Table 1, Comparative Examples 2, 3, and 5 in which any component of Cr, Mo, and C is less than the specified value and Comparative Example 4 in which the sintering temperature is less than 1200 ° C. are hardness and strength characteristics. , The performance satisfying all of the numerical values requested by the user (surface hardness of 85 HRB or more, tensile strength of 800 MPa or more, bending fatigue strength of 200 MPa or more, surface pressure fatigue strength of 0.8 GPa or more) is not obtained. Comparative Example 6 satisfies the required performance, but it contains Ni and Cu and is expensive.

-Example 2-
A raw material powder prepared by mixing an Fe—Cr—Mo alloy powder and a graphite powder in the proportions shown in Table 2 is prepared, and the raw material powder is molded with a mold for a sintered clutch hub having the shape shown in FIGS. A molded body was prepared, and the molded body was further sintered in a nitrogen atmosphere at a temperature of 1250 ° C. for 45 minutes. Thereafter, the obtained sintered clutch hub was sized under the same conditions, and then the outer diameter roundness of each clutch hub was measured to evaluate the outer diameter accuracy. Table 2 also shows the results and the density difference (division density difference) between the boss part, rim part, and outer diameter tooth part examined for the green body before sintering. The outer diameter roundness in Table 2 is expressed as a measured value of the difference between the maximum value and the minimum value of the outer diameter tooth portion (reference outer diameter φ90 mm). Moreover, the sintered compact density measured the density of the outer diameter tooth part.

  From the results in Table 2, when the divided density difference of the molded body does not satisfy the specified value of the present application, the outer diameter roundness (outer diameter accuracy) of the product is deteriorated. If this outer diameter roundness exceeds the dimension correction allowance by sizing, sizing itself becomes impossible.

The perspective view which shows an example of the clutch hub of this invention 1 is a plan view of the clutch hub of FIG. Sectional view along line XX in FIG.

Explanation of symbols

1 Sintered clutch hub 2 Boss part 3 Rim part 4 Outer diameter tooth part 5 Shaft hole 6 Keyway

Claims (4)

It is a molded body for a sintered clutch hub, and the composition of the raw material powder is in a mass ratio of Cr: 2 to 4%, Mo: 0.3 to 0.8%, C: 0.4 to 0.8%, the balance A molded article for a sintered clutch hub which is Fe, has a density of 6.6 g / cm ³ or more and less than 7.0 g / cm ³ , and a difference in density of each part is 0.15 g / cm ³ or less.   A sintered clutch hub made by sintering the molded body according to claim 1, wherein the sintered clutch hub has a structure in which bainite or martensite is distributed in bainite.   The sintered clutch hub according to claim 2, having a surface hardness of 85 HRB or more, a tensile strength of 800 MPa or more, a bending fatigue strength of 200 MPa or more, and a surface pressure fatigue strength of 0.8 GPa or more. Raw material powder having a composition of Cr: 2 to 4%, Mo: 0.3 to 0.8%, C: 0.4 to 0.8%, and residual Fe in terms of mass ratio, density 6.6 g / cm ³ or more, 7 A method for producing a sintered clutch hub, comprising forming a molded body of less than 0.0 g / cm ³ and then sintering the molded body in a non-oxidizing atmosphere at a temperature of 1200 to 1300 ° C.

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