JP2011214108A - Method for manufacturing ferrous sintered material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To economically provide a ferrous sintered material excellent in machinability in which diffusion of carbon is suppressed and graphite is dispersed, without adding an expensive boron oxide powder or boron nitride powder containing boron oxide.SOLUTION: This method for manufacturing the ferrous sintered material comprises: conducting compression molding of a powder obtained by adding, in compounding ratio, 0.05-1.5 mass% of aluminum salt of a higher fatty acid and 0.1-2.0 mass% of graphite powder with respect to an iron powder mixture that is a powder mixture for a ferrous sintered material from which the graphite powder is excluded, and exhibits a pearlite structure after sintering; and sintering the obtained green compact at a temperature equal to or higher than the diffusion temperature of carbon.

Description

  The present invention relates to a method for producing an iron-based sintered material, and more particularly to a technique for improving machinability by dispersing undiffused graphite in a sintered metal structure.

  Sintered materials by powder metallurgy can be shaped into a near net shape, and have the advantage of being able to produce a large number of products of the same shape once the stamping die is manufactured. Therefore, it is used in various fields. However, when applied to parts that require high accuracy, machining may be required after sintering, in which case good machinability is required.

  Therefore, from such a viewpoint, various techniques have been proposed for the purpose of improving the machinability of the iron-based sintered material. A method of using iron powder containing sulfur as a raw material powder, a method of adding and mixing sulfide to the raw material powder, a method of sulfiding a sintered body in a hydrogen sulfide gas atmosphere, etc. are adopted (Patent Document 1). Such).

  In addition, a technique for filling a resin or the like in the pores of a sintered alloy is also provided (Patent Document 2, etc.). In such a sintered alloy, the resin in the pores becomes the starting point of chip breaking during the cutting process, so that the chip breaking property is good.

  A material in which a green compact made of a raw material powder containing graphite powder is sintered at a temperature equal to or lower than the diffusion temperature of carbon and graphite is dispersed has been put to practical use (Patent Document 3, etc.). Graphite has an effect as a solid lubricant and is effective in improving machinability.

However, the method of dispersing sulfur, which is a free-cutting component, in the base of the sintered alloy has a limit in improving machinability. In addition, sulfur is an element that reduces the strength of the sintered alloy, and in particular, it causes a decrease in toughness and may promote corrosion of the sintered alloy, so that its use is limited.
Further, in the method of filling the pores of the sintered alloy with a resin or the like, the cost of the raw material for the resin or the like is increased and the number of processes is increased, so that the cost of the sintered material is increased.
In the method of dispersing graphite by performing sintering at a temperature equal to or lower than the carbon diffusion temperature, the sintering temperature is low, so the strength is low, and it cannot be applied to a member that requires strength.

  Therefore, the present applicant oxidized iron-based mixed powder containing 0.1 to 2.0% by mass of graphite powder as a material capable of dispersing graphite in the matrix even when sintered at a temperature higher than the diffusion temperature of carbon. An iron-based sintered material obtained by sintering a green compact composed of a mixed powder to which 0.01 to 1.0% by mass of boron is added, in which carbon diffusion is suppressed and graphite is dispersed in a base structure composed of ferrite and pearlite. It has been proposed (see Patent Document 4).

JP-A-5-179409 JP 2002-285293 A JP-A-61-243156 Japanese Patent Laid-Open No. 9-241701

  In the iron-based sintered material of Patent Document 4 described above, even when the sintering temperature is increased, the diffusion of carbon into the matrix is suppressed by boron oxide, and the hardness of the iron-based sintered alloy is reduced, thereby reducing the work. However, since expensive boron oxide powder or boron nitride powder containing boron oxide is added to the raw material powder, the raw material cost increases. Therefore, an inexpensive manufacturing method is required.

  Therefore, an object of the present invention is to economically provide an iron-based sintered material excellent in machinability in which graphite is dispersed by suppressing carbon diffusion.

  In order to achieve the above object, the present invention provides an aluminum salt of a higher fatty acid in a mixing ratio with respect to an iron-based powder mixture obtained by removing graphite powder from a powder mixture for an iron-based sintered material that exhibits a pearlite structure after sintering. By sintering a green compact made of a powder mixture to which 0.05 to 1.5% by mass of powder and 0.1 to 2.0% by mass of graphite powder are added at a temperature equal to or higher than the diffusion temperature of carbon. An iron-based sintered material is obtained.

  According to the present invention, an expensive boron oxide powder or boron nitride powder containing boron oxide is not added to the raw material powder, and the sintered metal structure has a structure in which undiffused graphite is dispersed. An iron-based sintered alloy having excellent machinability can be obtained.

  As a result of repeated investigations to obtain a sintered material in which graphite is dispersed by suppressing carbon diffusion, the present inventor has suppressed the diffusion of graphite by adding a higher fatty acid aluminum salt powder and graphite powder. It has been found that an iron-based sintered alloy having excellent machinability can be produced by forming a structure in which graphite is dispersed in a matrix structure composed of ferrite and pearlite.

  Next, the component composition of the present invention will be described. If the amount of the higher fatty acid aluminum salt powder is less than 0.05% by mass, the iron-based sintered alloy has a pearlite structure without suppressing the diffusion of graphite. Moreover, even if added over 1.5% by mass, not only the carbon diffusion suppression effect is not seen any more, but also the density of the green compact cannot be increased by lowering the theoretical density of the mixed powder. In order to reduce the strength and the fluidity of the mixed powder, the filling property into the mold is deteriorated. For this reason, the range of the optimal addition amount of the aluminum salt powder of the higher fatty acid was set to 0.05 to 1.5% by mass. In addition, this powder should just be a thing with the average particle diameter of about 1-30 micrometers normally used. When the average particle size is less than 1 μm, aggregation tends to occur, and when it exceeds 30 μm, uniform dispersion in the mixed powder becomes difficult.

  The higher fatty acid constituting the higher fatty acid aluminum salt is at least one of stearic acid, 12-hydroxystearic acid, lauric acid, myristic acid, palmitic acid, ricinoleic acid, and behenic acid. Since it also acts as a lubricant during molding, it is not necessary to add a molding lubricant separately, which is preferable in terms of both raw material cost and the theoretical density of the mixed powder. In addition, if the lubricity when extracting the green compact from the green compacting mold is insufficient, other lubricants may be added together, but the added amount because the theoretical density of the mixed powder decreases. Is preferably 1.5% by mass or less in total with the aluminum salt of the higher fatty acid.

  Further, if the amount of graphite powder added is less than 0.1% by mass, not only the amount of carbon diffusing into the matrix is small and the desired strength cannot be obtained, but also the amount of undiffused graphite is small and the effect of improving machinability. Less is. Moreover, when added over 2.0% by mass, it becomes a pearlite structure and the machinability is lowered, so it is necessary to increase the amount of aluminum salt powder of higher fatty acid, but this will improve the machinability. Since the effect is small, the range of the optimum addition amount of graphite is set to 0.1 to 2.0% by mass.

After preparing the raw material powder with the blending ratio shown in Table 1 and mixing it with a V-type mixer for 30 minutes, the mixed powder is compacted to a density of 6.8 Mg / m ^{3 and} has an outer diameter of 50 mm, an inner diameter of 30 mm, and a height. Five pieces of 25 mm green compacts were produced. Subsequently, each green compact was sintered by heating in a reducing gas (decomposed ammonia gas) atmosphere at 1130 ° C. for 30 minutes. Here, aluminum stearate (Al-St) was used as the aluminum salt of the higher fatty acid. Moreover, about the sample 1 and the sample 8 which do not contain aluminum stearate, zinc stearate (Zn-St) was added as a lubricant for compacting.

  A cutting test was performed on each sintered body, and the flank wear width of the tool edge was evaluated as the amount of tool wear. The cutting test was performed on an NC lathe using a diamond throwaway tip, the cutting speed was 300 mm / min, the feed was 0.03 mm / rev, the depth of cut was 0.10 mm, and water-soluble cutting oil was used to make 4000 m. Cut the distance. The tool flank face was observed with a scanning electron microscope (SEM) at cutting distances of 800 m, 1600 m, 2400 m, 3200 m, and 4000 m to measure the amount of tool wear. The measurement results are also shown in Table 1.

  From the results of Samples 1 to 8, it was found that the amount of tool wear was remarkably reduced by adding 0.05% by mass or more of aluminum stearate as compared with Sample 1 to which zinc stearate was added. Moreover, according to this invention, it was confirmed that the machinability equivalent to or more than the sample 8 which is a machinability improving material described in Patent Document 4 can be obtained. However, in Sample 7 in which the amount of aluminum stearate added exceeds 1.5 mass%, the machinability is good, but the theoretical density of the mixed powder is lowered, and the strength cannot be improved by increasing the density of the green compact. It was confirmed that the fluidity of the mixed powder was lowered and the filling property into the mold was deteriorated. From this, it was found that the addition amount of the higher fatty acid aluminum salt is preferably 0.05 to 1.5% by mass.

  Both aluminum stearate and zinc stearate are metal salts of stearic acid, but zinc stearate has no effect of suppressing the diffusion of graphite into the iron-based sintered alloy matrix. Therefore, although the mechanism is not yet elucidated, it is presumed that aluminum suppresses the diffusion of graphite to the iron-based sintered alloy matrix by some action.

  From the results of Samples 9 to 14, it was found that the amount of tool wear was remarkably reduced by adding 0.1% by mass or more of graphite as compared with Sample 9 to which no graphite was added. Further, in Sample 14 in which the amount of graphite added exceeds 2.0% by mass, tool wear increased because pearlite was generated. From this, it was found that the addition amount of graphite is preferably 0.1 to 2.0% by mass.

Claims (2)

  With respect to the iron-based powder mixture obtained by removing the graphite powder from the powder mixture for iron-based sintered material exhibiting a pearlite structure after sintering, 0.05 to 1.5 mass% of a higher fatty acid aluminum salt in a compounding ratio, A method for producing an iron-based sintered material, in which a powder obtained by adding 0.1 to 2.0% by mass of graphite powder is compression-molded, and the obtained green compact is sintered at a temperature equal to or higher than the diffusion temperature of carbon.   The higher fatty acid constituting the aluminum salt of the higher fatty acid is at least one of stearic acid, 12-hydroxystearic acid, lauric acid, myristic acid, palmitic acid, ricinoleic acid, and behenic acid. The manufacturing method of the iron-type sintered material as described in 2.