JP2011058080A - Co-BASED ALLOY EXCELLENT IN ABRASION RESISTANCE AND LUBRICITY, METHOD FOR PRODUCING THE SAME, AND SINTERED COMPACT THEREOF - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Co-based alloy excellent in abrasion resistance and lubricity in which fine graphite is dispersed, particularly a Co-based alloy excellent in abrasion resistance and lubricity which is used for sintered valve seats in motor vehicles or the like, and to provide a method for producing the Co-based alloy and a sintered compact thereof. <P>SOLUTION: The Co-based alloy excellent in abrasion resistance and lubricity includes, by mass%, 2.0 to 3.5% C, 1 to 4% B and the balance being Co and inevitable impurities, wherein graphite is produced in the alloy at an area rate of 5 to 20%. In addition to the Co-based alloy, the Co-based alloy excellent in abrasion resistance and lubricity further includes, by mass%, any one or more elements selected from 4% or less Si, 5% or less Al, 10% or less Cr, 5% or less Mn, and 10% or less Fe. There is also provided a method for producing the Co-based alloy and a sintered compact thereof. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a Co-based alloy having excellent wear resistance and lubricity in which fine graphite is dispersed, and in particular, a Co-based alloy having excellent wear resistance and lubricity used in sintered valve seats for automobiles and the like, and its production. And a sintered body thereof.

Conventionally, sintered valve seats used in automobiles are based on, for example, Fe or low alloy powder, hard particle powder and, if necessary, carbon powder are mixed, and the compact pressed by a mold is sintered. Manufactured. As these hard particles, for example, as disclosed in JP 2004-156101 A (Patent Document 1), C: 0.2 to 3%, Mn: 20 to 40%, Mo: 20 to 70%, the balance As disclosed in powders of Co and unavoidable impurities and Japanese Patent Application Laid-Open No. 2007-238987 (Patent Document 2), Si: 2-3%, Mo: 20-40%, Cr: 7-9%, Co alloys such as powders composed of the balance Co and inevitable impurities have been proposed.

Patent Documents 1 and 2 described above both contain 20% or more of Mo, and as a role of Mo, Patent Document 1 improves hardness and wear resistance by Mo carbide generation and improves solid lubricity by Mo oxide. Are listed. Moreover, the role of Mo in patent document 1 is described that molybdenum silicide is produced | generated by combining with Si and Co, and this silicide improves abrasion resistance and lubricity. Thus, lubricity is required for the hard particles, and therefore Mo is added in a large amount of 20% or more.
JP 2004-156101 A JP 2007-238987 A

  In recent years, in valve seats that are subjected to more severe adhesion, there are cases where the lubricating action of Mo oxide or molybdenum silicide as described above is not always sufficient. Therefore, paying attention to graphite having higher lubricity, the inventors of the present invention have made the present invention as a result of intensive studies on the alloy composition and heat treatment conditions that have sufficient hardness and produce graphite.

The gist of the invention is that
(1) By mass%, C: 2.0 to 3.5%, B: 1 to 4%, consisting of the remainder Co and inevitable impurities, 5 to 20% of graphite is produced in area ratio Co-base alloy with excellent wear resistance and lubricity.
(2) In addition to the above (1), any one of Si: 4% or less, Al: 5% or less, Cr: 10% or less, Mn: 5% or less, Fe: 10% or less in mass% Or a Co-based alloy having excellent wear resistance and lubricity, characterized by comprising two or more kinds.

(3) After the Co-based alloy described in the above (1) or (2) is produced by a gas atomizing method or a liquid quenching method, a thermal history at a temperature of 600 to 1300 ° C. is given to give an area ratio of 5 to 20%. A method for producing a Co-based alloy having excellent wear resistance and lubricity, characterized in that graphite is produced.
(4) A sintered body obtained by sintering using the powder made of the Co-based alloy according to (1) or (2).

  As described above, by using an alloy composition having sufficient hardness and producing graphite according to the present invention, it is possible to obtain a hard lubricating Co-based alloy having excellent lubricity, and tougher solidification. The present invention provides a sintered alloy used for an engine valve seat and the like in an environment where adhesion occurs.

Hereinafter, the present invention will be described in detail.
The most important features of the present invention are the composition that produces graphite and the heat treatment conditions. Co-based alloys containing C include hard particles and stellite-equivalent alloys described in Patent Document 1, but all contain a large amount of elements that combine with C, such as Cr, Mo, and W to generate carbides. Graphite which is a phase composed of C alone is not generated. Therefore, the lubricating action by graphite cannot be expected.

  On the other hand, the alloy of the present invention contains almost no element that forms a carbide by combining with C, and may contain some Cr and Fe, but it is considered to limit the upper limit. Furthermore, sintered alloys used for valve seats and the like are often produced by the atomizing method, but when the alloy of the present invention is produced by the atomizing method, C is probably the base due to rapid solidification of the alloy. However, it was found that no graphite was formed.

  Therefore, it was considered to generate graphite by giving a predetermined thermal history. However, when the alloy of the present invention is produced not by the rapid solidification method but by an ordinary melting method, graphite is already generated at the time of solidification, and thus it is not always necessary to add a thermal history. Thus, the ingot produced by the melting method can be mechanically pulverized and used for sintering. In addition, the predetermined heat history does not need to be performed with the alloy powder of the present invention alone. For example, as in the method for producing a sintered valve seat, the sintering process of a compact that is mixed and pressed with Fe or a low alloy powder It may be. This is because the alloy of the present invention produces graphite in this sintering process.

  The 2nd characteristic in this invention is the point which added B in order to ensure sufficient hardness as a hard particle, without producing | generating a carbide | carbonized_material. As described above, since the hard particles and the stellite equivalent alloy described in Patent Document 1 generate hard carbides, the hard particles have sufficient hardness as hard particles. On the other hand, in the alloy of the present invention, generation of carbides is suppressed in order to generate graphite which is a phase composed of simple C. Therefore, it is necessary to improve the hardness without adding an element that easily generates carbides. Therefore, attention was paid to B which is relatively difficult to produce carbides and which forms a hard phase by combining with Co as a base. This is because B is considered to form a hard Co-based boride which is difficult to combine with C. Furthermore, it discovered that B addition also produced the following unexpected effects.

  It was found that when a powder was prepared by the atomization method without adding B to the alloy of the present invention and subjected to a predetermined heat treatment, graphite was observed, but most of it moved to the surface layer of the powder and concentrated. . In a sintered alloy such as a valve seat, Fe and low alloy powder are in contact with the periphery of the hard particles, and the graphite concentrated on the surface layer contacts and combines with the surrounding Fe to generate carbides. Therefore, a sufficient lubricating action by graphite cannot be obtained. Here, it was found that when a predetermined amount of B was added as in the alloy of the present invention, the concentration of graphite on the surface layer could be suppressed. The cause of this phenomenon is not clear, but the Co-based boride by addition of B is formed in a network shape, and this Co-based boride prevents the graphite generated inside the powder from moving to the powder surface. Inferred.

The reasons why the component composition according to the present invention is limited will be described below.
C: 2.0 to 3.5%
In the alloy of the present invention, C is an essential element for producing graphite having a lubricating action, and if it is added in an amount of less than 2.0%, the formation of graphite is not sufficient. The phase line rises excessively, making dissolution difficult. Preferably it is 2.3 to 3.0% of range.

B: 1-4%
In the alloy of the present invention, B is an essential element for improving the hardness, and when the alloy of the present invention is produced by an atomizing method and a predetermined heat history is added to generate graphite, the concentration of graphite on the powder surface layer is reduced. There is also an inhibitory effect. Addition of less than 1% is not sufficient in improving the hardness and suppressing the concentration of graphite on the surface layer, and if added over 4%, the alloy becomes too hard and brittle, so a sintered body such as a valve seat is manufactured. Problems such as chipping occur during machining. Preferably it is 2 to 3.5% of range.

Si: 4% or less, Al: 5% or less Both Si and Al are elements that hardly form carbides, and have an effect of improving hardness by a compound with Co or solid solution in Co. However, if Si is added in excess of 4% and Al exceeds 5%, the alloy becomes brittle. Preferably, Si is in the range of 3.5% or less, and Al is in the range of 3% or less.

Cr: 10% or less, Mn: 5% or less, Fe: 10% or less C has a high melting point and hardly reacts with Co. Therefore, it may remain undissolved if it is not sufficiently heated at the time of dissolution. Since Cr, Mn, and Fe all react with C, there is an effect of preventing undissolved C from being dissolved. However, if Cr and Fe are added in excess of 10%, some carbides are generated, and the amount of graphite produced is reduced. Further, when Mn exceeds 5%, the alloy becomes brittle. Preferably, Cr is 6% or less, Mn is 3% or less, and Fe is 6% or less.

When the area ratio of graphite graphite having an area ratio of 5 to 20% is less than 5%, the lubricating action is not sufficient, and when the amount of C added is 2 to 3.5%, graphite with an area ratio exceeding 20% is generated. do not do. Preferably it is 7 to 15% of range.

Hard particles produced by a rapid cooling method and used for heat-treated sintered valve seats at 600 to 1300 ° C. often have a particle size of around 100 μm. The atomizing method is a method suitable for producing powders having a particle size before and after the atomizing method. However, when the alloy of the present invention is produced by a quenching method such as an atomizing method or a liquid quenching method, it is considered that C is forcibly dissolved in Co as a base metal, but graphite is not generated. Here, by giving a thermal history of 600 to 1300 ° C. to the atomized powder of the alloy of the present invention, C, which is considered to be forcibly dissolved, is discharged from Co which is a base metal to generate graphite. When the heat history is less than 600 ° C., the formation of graphite is not sufficient, and when the heat history exceeds 1300 ° C., the alloy of the present invention manufactured by the atomizing method is melted. Preferably it is the range of 750-1200 degreeC.

Hereinafter, the present invention will be specifically described with reference to examples.
An alloy having the composition shown in Table 1 was produced by a melting method and a gas atomizing method. In the melting method, 5 kg of Co or other metal material is weighed, placed in a vacuum furnace, melted and cast in a vacuum, and the machine from the center between the center and outer periphery of the resulting ingot A test piece was cut out by processing. On the other hand, in the gas atomization method, similarly, 2 kg was weighed and dissolved in a vacuum, and the powder obtained after spraying with nitrogen was classified to 125 μm or less. Similarly, in the liquid quenching method, 20 g is weighed and melted in an atmosphere substituted with nitrogen, and the molten metal is sprayed onto a copper cooling body having a diameter of 300 mm rotating at 2000 revolutions per minute. After grinding, it was classified at 125 μm. Thereafter, heat treatment was performed in vacuum at a temperature shown in Table 1 for 1 hour. The test piece and powder cut out from the ingot were polished with resin, and the area ratio of graphite was measured by image analysis with an optical microscope. Further, the hardness was measured with a micro Vickers hardness tester. The load during measurement was 200 g.

  Further, as the ductility, in the case of the above micro Vickers, the case where no crack was generated from the indentation: ◯, and the case where the crack was generated: x. In addition, using a molded body obtained by treating these powders with HIP (hot isostatic pressing) at 1100 ° C., the mating ring is SCM420, final load 61.8 N, friction speed 3.6 m / s, friction distance 100 m, Ogoshi type A friction test was performed, and Co adhered to the other ring after the test was confirmed by EDX. The Co adhesion state at that time was evaluated as lubricity, and Co was hardly adhered: ◎, Co was partially adhered: ◯, Co was adhered to the entire surface: x was evaluated.

表１に示す、Ｎｏ．１〜１６は本発明例であり、Ｎｏ．１７〜２７は比較例である。

No. 1 shown in Table 1. 1 to 16 are examples of the present invention. 17 to 27 are comparative examples.

  As shown in Table 1, Comparative Example No. Since No. 17 has a low C, the graphite area ratio is as low as 4% and the lubricity of the molded article is poor. Comparative Example No. In No. 18, since B is not contained, graphite is concentrated on the powder surface layer, and a graphite-deficient layer is confirmed inside the surface, and the lubricity of the molded article is poor. Comparative Example No. In No. 19, since the amount of B added was large, the alloy was brittle, and cracks occurred when a load was applied with a micro Vickers hardness meter during hardness measurement. Moreover, since the heat treatment temperature is high, there is a problem that an alloy manufactured by the atomizing method melts.

  Comparative Example No. Since Nos. 20 and 21 had high Si and Al addition amounts, the alloys were brittle, and cracks occurred when a load was applied with a micro Vickers hardness tester during hardness measurement. Comparative Example No. Since No. 22 is high in Cr, the area ratio of graphite is small and the lubricity of the compact is poor. Comparative Example No. Since No. 23 had a high Mn, the alloy was brittle, and cracks occurred when a load was applied with a micro Vickers hardness tester during hardness measurement. Comparative Example No. Since No. 24 is high in Fe, the area ratio of graphite is small and the lubricity of the compact is poor. Comparative Example No. No. 25 has no heat treatment, and Comparative Example No. No. 26 has a low heat treatment temperature, so the graphite area ratio is as low as 1% and 3%, and the lubricity is poor. In Comparative Example 27, since C is high, the liquidus of the alloy rises excessively, and dissolution becomes difficult.

On the other hand, No. which is an example of the present invention. Since Nos. 1 to 16 all satisfy the conditions of the present invention, it became possible to produce graphite with high lubricity. In particular, Example No. of the present invention to which Cr, Mn and Fe were added. 10-16 compared with the additive-free composition, C quickly dissolved in the molten metal, and the dissolution time was shortened.


Patent Applicant Sanyo Special Steel Co., Ltd.
Attorney: Attorney Shiina

Claims (4)

% By mass
C: 2.0 to 3.5%
B: 1-4%
Co-based alloy having excellent wear resistance and lubricity, characterized by comprising 5 to 20% of graphite by area ratio. In addition to claim 1, further in mass%,
Si: 4% or less,
Al: 5% or less,
Cr: 10% or less,
Mn: 5% or less,
Fe: Co-based alloy excellent in wear resistance and lubricity, characterized by comprising any one or more of 10% or less. After producing the Co-based alloy according to claim 1 or 2 by a gas atomization method or a liquid quenching method, a thermal history at a temperature of 600 to 1300 ° C. is given to generate 5 to 20% graphite by area ratio. A method for producing a Co-based alloy having excellent wear resistance and lubricity. A sintered body obtained by sintering using the powder comprising the Co-based alloy according to claim 1 or 2.