JP4769287B2 - Bronze powder for powder metallurgy and method for producing the same - Google Patents

Description

  The present invention relates to a bronze powder that is used as a raw material powder for powder metallurgy, has little segregation, has good moldability, and has a stable dimensional change rate during sintering, and a method for producing the same.

Conventionally, as raw material powder for producing bronze-based sintered parts, mixed powder obtained by mixing copper powder and tin powder at a predetermined ratio, or alloy powder produced by an atomizing method or the like has been used.
However, when mixed powder is used, it is difficult to mix uniformly due to differences in specific gravity, particle size, particle shape, etc. of copper powder and tin powder, and even if it can be mixed uniformly, Separation and segregation of components occur at the time of charging and discharging into the hopper and filling into the mold, and the dimensional accuracy, strength and uniformity of the metal structure of the resulting sintered part are lowered. Furthermore, since the Sn liquid phase appears during sintering and the sintering proceeds rapidly, the dimensional change rate becomes unstable and the dimensional accuracy of the product tends to vary.

  In order to suppress the segregation and segregation of the component powder, it is also considered to bond the main component powder and the subcomponent powder using an organic binder. However, in the case of bronze type, almost no diffusion of carbon to the main component copper occurs. Residual carbon in the binder component hinders sintering. In order to prevent this, it is necessary to take a method of assisting adhesion such as suppressing the addition amount of the binder as much as possible and lightly pressing with a press, but there is a problem that the process becomes complicated and the cost is high (Patent Document 1). In addition, segregation and segregation are suppressed when this method is used. However, as in the case of simple mixing, the liquid phase of Sn appears during sintering and the rapid progress of sintering makes the dimensional change rate unstable. Product dimensional accuracy tends to vary.

  On the other hand, when alloy powder is used, there is no problem with segregation and segregation of components, and since sintering is also solid phase sintering, the sinter dimensional change is stable, but the hardness of the powder particles is solid solution hardening. For this reason, it becomes high and the formability becomes worse, and this is extremely disadvantageous particularly when a porous sintered part such as an oil-impregnated bearing is manufactured. In order to reduce the hardness of the particles, the powder may be annealed by heat treatment. In this case, although the substrate hardness is reduced, the fine irregularities on the surface of the powder particles are eliminated and the moldability can hardly be improved.

Also reported as a bronze-based powder with little segregation and good formability, a method for producing partially alloyed powder, in which copper powder and solder powder, or copper powder, solder powder and tin powder are mixed and heat-treated (Patent Document 2). However, solder and tin have a low melting point and very good wettability with copper powder, so when melted at a melting point of 183 to 232 ° C, it spreads quickly on the surface of the copper powder, and then the entire surface of the particle enters the copper powder. Spread. For this reason, there existed a fault which alloying progresses rapidly and a powder tends to become hard for solid solution hardening.
JP-A-8-13502 Japanese Patent Publication No. 4-4361

  In order to solve the above-mentioned problems, an object of the present invention is to provide a bronze powder having good moldability, no separation and segregation of components, and stable sintering dimensional change.

  In order to solve the problem, the copper powder and the bronze alloy powder are mixed, and the mixture is heated to diffusely bond the copper powder and the bronze alloy powder, and then crushed so that the copper powder and the bronze alloy powder are combined. Granulated particles present in the particles are obtained.

  Although the manufacturing method is not limited for the copper powder in this invention, For example, the powder manufactured by the atomizing method, the electrolytic method, etc. can be used. Further, the bronze alloy powder is a Cu—Sn alloy powder produced by an atomizing method, and a tin content of 10 to 50 mass% can be used.

These copper powder and bronze alloy powder are mixed so that the total tin content is 5 to 20% by mass, heat-treated at 400 to 800 ° C. in a non-oxidizing atmosphere, and partially diffusively bonded. Thus, the bronze powder is obtained.
The particle size of the bronze powder of the present invention is not particularly limited, but in general, the bronze powder is pulverized until it has a particle size that can pass through a sieve having an opening of 75 μm to 350 μm.

  At this time, when the Sn component of the raw material bronze alloy powder is 40 to 50% by mass, heat treatment is performed at about 400 ° C., and the heat treatment temperature is increased as the Sn component of the bronze alloy powder to be used decreases. When using bronze alloy powder containing 10% by mass of Sn, the heat treatment temperature is preferably 750 to 800 ° C. In this way, Sn is diffused into the copper particles in the solid phase region without causing a liquid phase to appear during the heat treatment, and while the copper powder and the bronze alloy powder are diffusion-bonded, excessive Sn in the copper powder Diffusion can be prevented and the hardness of the Cu part can be kept low.

  The bronze powder according to the present invention thus obtained was confirmed to be bonded with copper powder and bronze alloy powder by structure observation with an optical microscope, and the Vickers hardness of the Cu part measured at a load of 10 g. It is a powder characterized by Hv of 50-100.

  This granulated powder has a separable segregation because the copper part and the bronze part are bonded together, and the soft copper part is deformed during press molding and adheres to the hard bronze part, so the formability is very good. . Furthermore, since a liquid phase does not appear during sintering, the rate of change in sinter dimensions is stable.

  Hereinafter, the present invention will be described in detail.

  In the present invention, the tin content of the entire bronze powder is set to 5 to 20% by mass. If the content is less than 5% by mass, the solid substrate of the sintered body is soft and the strength is low because the solid solution amount of Sn is small. For this reason, if it exceeds 20% by mass, there are too many Sn components and many brittle intermediate phases appear, leading to a decrease in strength.

  The reason why the Sn content of the raw material bronze alloy powder is 10 to 50% by mass is as follows. If the Sn content is less than 10% by mass, mixing this with copper powder to increase the total Sn content to 5% by mass or more will significantly reduce the amount of soft copper powder mixed, resulting in hard bronze particles. Since the ratio increases, the deformation of the particles at the time of molding is not sufficient, and a high molded body strength cannot be obtained. On the other hand, if it exceeds 50% by mass, a considerable amount of Cu-Sn liquid phase appears at the time of heat treatment even if the heat treatment temperature is set low, and this quickly wets the surface of the mixed Cu particles, and Sn is rapidly contained in the Cu particles. By diffusing, Cu particles are solid-hardened and formability is lowered.

The heat treatment temperature was 400-800 ° C, but when the Sn component of the raw material bronze alloy powder is 40-50 mass%, heat treatment is performed at a low temperature of about 400 ° C, and the heat treatment is performed as the Sn component of the bronze alloy powder used decreases. It is desirable to increase the temperature. When copper alloy powder containing 10% by mass of Sn is used, the heat treatment temperature is preferably 750 to 800 ° C. In this way, copper powder and bronze alloy powder can be diffusion-bonded in the solid phase sintering region without causing a liquid phase to appear during heat treatment, preventing excessive Sn from diffusing into the copper powder. The hardness of the Cu part can be kept low. Thereby, it is possible to obtain a bronze powder with good moldability and high mold strength while suppressing segregation of copper powder and bronze alloy powder. When the heat treatment temperature exceeds 800 ° C., the diffusion rate of Sn into the Cu is increased, the solid solution hardening of the Cu particles proceeds, the moldability is lowered, the cake becomes harder and the pulverization becomes difficult, and the productivity is increased. It drops significantly.
In the present invention, it is necessary to perform the above heat treatment in a non-oxidizing atmosphere. Generally, the heat treatment is performed in a reducing atmosphere such as an inert gas such as nitrogen or argon, hydrogen or a mixed gas of hydrogen and nitrogen. Done.

  The bronze powder according to the present invention thus obtained was confirmed to be bonded with copper powder and bronze alloy powder by microstructure observation with an optical microscope as shown in FIG. 1, and measured with a load of 10 g. It is a powder characterized in that the Vickers hardness Hv of the Cu part is 50 to 100.

  In addition, when using the bronze powder of the present invention, additives that are usually added to bronze by powder metallurgy, that is, single metal or alloy powder such as lead, zinc, bismuth, Cu-P, graphite, molybdenum disulfide, Solid lubricants such as manganese sulfide, hard particles such as carbides and nitrides, and molding lubricants such as metal soaps and waxes may be added and mixed.

Next, the present invention will be described in detail based on examples.
Examples 1 to 5 and Comparative Examples 6 to 12 shown below are a water atomized copper powder having an average particle size of 50 μm, and a water atomized bronze alloy having an Sn component content of 5 to 60% by mass and an average particle size of 40 to 50 μm. After mixing with powder and heat-treating for 20 minutes in a mixed gas of 75 vol% hydrogen and 25 vol% nitrogen at a specified temperature, the powder lump that has been sintered into a cake is disintegrated with a small grinder. This powder was crushed and made through a 100 mesh sieve (mesh size 150μm). Example 6 was produced in the same manner using electrolytic copper powder having an average particle size of 45 μm as copper powder.
Comparative Example 1 is a simple mixed powder obtained by mixing 90% by mass of water atomized copper powder having an average particle size of 50 μm and 10% by mass of water atomized tin powder having an average particle size of 25 μm by a mixer.
Comparative Example 2 is a mixture of 90% by mass of water atomized copper powder having an average particle size of 50 μm and 1% by mass of an aqueous solution of 5% by weight of polyvinylpyrrolidone added to the entire metal powder, and 10% by mass of water atomized tin powder having an average particle size of 25 μm. After mixing in a mold, pressurize with a pressure of 6 MPa , dry in an oven at 100 ° C for 1 hour, crush in a small pulverizer, and pass through a 100 mesh sieve. Segregation preventing treatment bronze powder.
In Comparative Example 3, 90% by mass of water atomized copper powder having an average particle size of 50 μm and 10% by mass of water atomized tin powder having an average particle size of 25 μm were mixed, and in a mixed gas of 75% by volume of hydrogen and 25% by volume of nitrogen. This is a partially alloyed bronze powder produced by heat treatment at 400 ° C for 20 minutes, and then pulverizing the powder lump that has been sintered into a cake shape with a small pulverizer and passing through a 100 mesh sieve.
Comparative Example 4 is a mixed powder obtained by mixing water atomized copper powder having an average particle size of 50 μm and water atomized bronze alloy powder having an Sn component content of 30% by mass and an average particle size of 45 μm.
Comparative Example 5 is a Cu-10 mass% Sn alloy powder having an average particle size of 48 μ and made by water atomization.

  With respect to these powders, the hardness of the Cu portion of the particle cross section, the green compact bending strength, the rate of change in the sinter dimensions and the variation thereof, and the sintered compact crushing strength were measured, and the appearance of the sintered compact was observed.

The hardness of the Cu part is filled with resin and polished, lightly etched to remove the strain caused by polishing, and then the V center hardness of 20 parts in the center of the Cu part shown in 1 of FIG. It is a value obtained by conducting an average test. The Vickers hardness Hv measured at a load of 10 g is about 50 for Cu that is well annealed and has few impurities, but becomes high when the crystal grains are fine or there are many impurities and alloy components. When the Hv value of the Cu part is low, it deforms well at the time of press forming and adheres to the hard bronze part, resulting in a powder having excellent formability, and the following green compact bending strength is improved. On the other hand, as the Hv value increases, the moldability deteriorates. Particularly, when the Hv value exceeds 100, the moldability deteriorates to some extent in practical use.
When the hardness of Cu is measured with a load of 10 g and the Vickers hardness is measured, the lowest value is about 50, which is not lower than that.

The green compact bending strength is a numerical value that evaluates the moldability of the powder, but it is 30 × 12 so that the powder density is 6.3 g / cm ³ by mixing the powder with a wax-based lubricant as a molding lubricant. It was molded into a 6 mm rectangular parallelepiped and its fracture strength was measured based on the ISO 3995 standard. This value is slightly different depending on the size and shape of the parts actually manufactured, but it is desirable that the strength is approximately 8.0 MPa or more.

During sintering, a wax-based lubricant was mixed with the powder as a molding lubricant, and the powder was molded into a cylindrical shape of φ14 × φ7 × 7 mm so that the green compact density was 6.3 g / cm ^3, and 75% by volume of hydrogen And in a mixed gas of 25% by volume of nitrogen at 780 ° C. for 20 minutes. Sintering was performed 10 times for each sample powder, the dimensional change rate before and after sintering was measured, and the crushing strength was measured based on JIS Z 2507 standard as the strength of the sintered body. In the measurement results shown in the following table, the standard deviation was described as the average value and the numerical value representing the variation in the dimensional change rate. When sintering is performed, the dimensions generally shrink and the dimensional change rate becomes negative. However, the magnitude of the value itself is not particularly problematic because the mold dimensions are determined in consideration of the dimensional change when forming the mold. However, if the value varies depending on the sample, there is a problem because the dimensional accuracy of the product decreases. The standard deviation value of the dimensional change rate is preferably as small as possible, but if it exceeds about 0.1, it is considered that there will be practical problems. A higher crushing strength of the sintered body is desirable, but if it is 200 MPa or more, there is no practical problem.

  The segregation state was determined by visually observing the side surface of the sintered body and determining whether or not the streaky pattern of the Sn rich portion was observed. The case where the streak pattern was observed was expressed as “segregation” and the case where the streak pattern was not observed was expressed as “none”.

In the following examples and comparative examples, these items are comprehensively evaluated, and the Vickers hardness Hv of the Cu part is 50 to 100, the green compact bending strength is 8.0 MPa or more, and the sintered dimensional change rate is A powder having a standard deviation of 0.1 or less, a sintered body crushing strength of 200 MPa or more, and no streaking segregation observed on the appearance of the sintered body was marked with ◯, and any item outside this range was marked with ×.

Table 1 shows the results of bronze powder produced by various production methods. In the mixed powders of Comparative Examples 1 and 4, since the Cu component and the Sn component were not bonded, segregation occurred, and a streaky Sn-rich portion was observed on the side surface of the sintered body. In Comparative Example 2, segregation does not occur, but since the liquid phase sintering is performed in the same manner as Comparative Example 1, the variation in the dimensional change rate is large. The water-atomized copper powder used in Comparative Examples 1, 2, and 4 is rapidly solidified and the crystal grains are fine, so the particles are hard and have poor moldability. Although Comparative Example 3 has an annealing effect by heat treatment, it is also affected by solid solution hardening due to diffusion of Sn, and the particles are hard and have poor moldability. The alloy powder obtained by atomization in Comparative Example 5 has very high particle hardness and remarkably poor formability. On the other hand, the bronze powder according to the present invention shown in Example 1 was good in all of moldability, dimensional variation, sintered body strength, and segregation.

Table 2 shows the influence of the overall composition on the properties of the powder.
As shown in Comparative Example 6, when the total amount of Sn is less than 5% by mass, the solid solution amount of Sn is small, so that the substrate of the sintered body after sintering is soft and the strength is lowered. On the other hand, when it exceeds 20% by mass as in Comparative Example 7, there are too many Sn components and many brittle intermediate phases appear, causing a decrease in strength.

Table 3 shows the influence of the heat treatment temperature.
When the heat treatment temperature exceeds 800 ° C. as in Comparative Example 8, the diffusion of Sn into the Cu particles proceeds excessively, the hardness of the Cu portion increases, and the green compact bending strength decreases. In addition, when the heat treatment temperature is lower than 400 ° C. as in Comparative Example 10, even if a bronze alloy powder having a Cu-50 mass% Sn composition, which is easy to proceed at a relatively low temperature, is used as the raw material powder, the sintering is almost complete. It does not proceed and the bonding between the copper powder and the bronze alloy powder is insufficient, resulting in separation and segregation.
As shown in Examples 1 to 3, heat treatment was performed at 750 ° C. when the Sn component of the raw material bronze alloy powder was 10% by mass, 600 ° C. when 30% by mass, and 400 ° C. when 50% by mass. As a result, a bronze powder with low Cu part hardness and good formability and no segregation was obtained.

Table 4 shows the influence of the composition of the bronze alloy powder used as the raw material powder.
When the composition of the bronze alloy powder is 5% by mass as in Comparative Example 11, there is no room for adding copper powder in order to make the total composition 5% by mass or more, and only the bronze alloy powder is used. As a result, there is no Cu part and the hardness of the bronze part occupying the entire powder is as high as 134. For this reason, there was little deformation of the powder particles at the time of molding and moldability was lowered.
When the composition of the bronze alloy powder exceeds 50% by mass as in Comparative Example 12, a large amount of liquid phase appears even after heat treatment at 400 ° C., and Sn rapidly diffuses into the Cu particles. Hardness increased to 111 and formability decreased.
As shown in Examples 1 to 5, when the Sn content of the bronze alloy powder was 10 to 50% by mass, a good powder could be obtained by selecting an appropriate heat treatment temperature.

  Example 6 in Table 5 is a powder produced with the same composition and production conditions using electrolytic copper powder instead of the atomized copper powder of the raw material copper powder of Example 1, but the hardness of the Cu part is low. Good formability, no segregation, and high strength of the sintered body are obtained.

  The bronze powder according to the present invention can be used as a raw material powder for general copper-based powder metallurgy. In particular, since segregation does not occur and formability and sinterability are excellent, good characteristics can be obtained as a raw material powder for manufacturing precision, small, and complicated parts, which may be widely applied. .

It is a particle | grain cross-sectional photograph of the bronze powder of this invention manufactured by the method of this invention.

Explanation of symbols

1 Copper part 2 Bronze part

Claims (2)

  A bronze powder for powder metallurgy, in which the copper powder and a bronze alloy powder having a tin content of 10 to 50% by mass are diffusion-bonded, and the tin content of the entire bronze powder is Bronze powder for powder metallurgy, characterized in that the Vickers hardness Hv of the copper part measured at 5 to 20% by mass and a load of 10 g is 50 to 100.   A method for producing bronze powder for powder metallurgy, comprising copper powder and bronze alloy powder having a tin content of 10 to 50% by mass produced by an atomizing method, and a total tin content of 5 Bronze for powder metallurgy, characterized in that it is mixed so as to be ˜20% by mass, and the resulting mixture is heat treated at 400 to 800 ° C. in a non-oxidizing atmosphere, partially diffused and then crushed. Powder manufacturing method.