JPS60162701A - Production of sintered and forged parts - Google Patents

Abstract

PURPOSE:To obtain sintered and forged parts having decreased defects in the surface part in a method for molding compressively a powdery raw material of a metal to be sintered to a compression molding and forging the molding after sintering by bringing solid particles into collision against the surface of the compression molding. CONSTITUTION:A powdery raw material of a metal to be sintered is pressurized in compression molding dies and is compacted under pressurizing force to obtain a compression molding having a specified shape. Solid particles are brought into collision against the surface of the resulting compression molding to compact at least the surface part of the compression molding. Shot blasting is usable as a method for bringing the solid particles into collision against said part. Such compression molding is thereafter heated in a non-oxidative atmosphere to sinter and is formed a solid solution. The resulting sintered body is forged at a high temp. and the sintered and forged parts are thus obtd.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a method for manufacturing a sintered forged product.

As a method for manufacturing resource-saving and energy-saving metal molded products, the sinter-forging method, in which #1 is formed after sintering metal powder, is attracting attention. In particular, in recent years, metal parts such as automobile parts, industrial machine parts, and agricultural machine parts have been manufactured by the sintering and forging method.

[Prior art] 1. A conventional method for producing a sintered forged product includes a step of compression molding a sintered metal powder raw material to obtain a compression molded body, a step of heating and sintering the compressed molded body, and a heating process. It is manufactured by a method that includes the step of forging a sintered compact under high temperature to obtain a sintered product.

'In this conventional manufacturing method of sintered forged products, the density of the compression molded body obtained by compression molding is 5°5 to 7.5.
0/Crt13 and is extremely porous. For this reason, when a sintered compact is taken out of a non-oxidizing heating sintering furnace, air enters from the surface to the inside through the pores of the compact, causing the surface area to deteriorate. oxidized or decarburized. Furthermore, since the surface portion is in direct contact with the forging die, the surface portion of the sintered body, which has been heated to 'ISm' by heating and sintering, is cooled by the forging die. This cooled surface portion is less likely to be consolidated by forging than the uncooled interior, and therefore residual pores are likely to remain in the surface portion. For these reasons, in the conventional wJ manufacturing method for sintered forged products, defects such as the presence of an oxidized layer or decarburized layer or a large number of pores are likely to occur on the surface of the obtained molded product. Therefore, the obtained sintered forged products had problems such as low mechanical properties such as fatigue strength and tensile strength.

[Object of the Invention] The present invention overcomes the above-mentioned problems, and aims to provide a method for manufacturing a sintered forged product with fewer defects on the surface.

[Summary of the Invention] The method for producing a sintered forged product of the present invention includes colliding solid particles onto the surface of the compression molded product after the step of obtaining the compression molded product and before the sintering step, thereby reducing the temperature of the compression molded product. The special feature lies in the addition of a consolidation process to consolidate the surface area.

In the method for producing a sintered forged product of the present invention, the surface of the compression molded body used in the sintering step is consolidated, and the pores on the surface of the molded body are closed. For this reason, the heated and sintered compact obtained in the sintering process also has closed pores on its surface. Therefore, even if a sintered compact at a temperature of less likely to. This makes it difficult to form oxides or a decarburized layer on the surface of the sintered compact. In addition, the surface area is consolidated during forging, so even if the surface area is cooled in the forging die, the degree of consolidation of the surface area by forging is comparable to that of the inside. . As a result, sintered forged products with excellent fatigue strength and tensile strength properties can be manufactured.

[Detailed explanation of the structure of the invention]

The method for producing a sintered forged product of the present invention includes a step of obtaining a compression molded product, a step of consolidating the surface of the compression molded product, a step of sintering the compression molded product, and a step of heating the sintered molded product at a high temperature. Including the process of forging.

The process of obtaining a compression molded body is a process of compressing the sintered metal powder raw material in a compression mold and compacting it by applying pressure to obtain a compression molded body having a certain shape.

The sintered metal powder raw material is not particularly limited, and conventional sintered metal powder raw materials used for ordinary sintered forged products can be used. In particular, iron-based sintered metal powder raw materials are suitable for the production method of the present invention. More specifically, a mixed powder consisting of iron powder, copper powder, and graphite powder is often used as a raw material for sintered metal powder. The blending ratio of copper powder is 1.0 to 71.0% by weight (hereinafter % means mm%).
%, and the blend m of graphite powder is generally 0.2 to 1.0%, with the balance being iron powder. To this, 0.5 to 1.0% of zinc stearate, which is a lubricant, is added and mixed.

Here, the copper powder and graphite powder are dissolved in the iron powder during the sintering process, and play the role of improving the rigidity, strength, etc. of the obtained forged product. ' Of the compression molded product obtained in the process of obtaining the compression molded product! degree 5
．． It is preferable to compact it to about 0 to 7.50/cm3. If the density of the compression molded product is less than 5.0 g/CrTl'3, the strength of the compression molded product may not be sufficient and the surface portion may peel off when performing Shot Plus 1 or air blasting in the next process. , corners and corners are often chipped. Conversely, the density of the compression molded body was set to 7.5 (J/Cm
If it exceeds 3, an extremely large compression force is required during compression molding. This makes it difficult to obtain compression molded products with extremely high density.

For practical purposes, it is sufficient that the compression molded body has a density of 7.50 g/am3 or less.

The step of consolidating the surface portion of the compression molded article is a step of colliding solid particles against the surface of the compression molded article obtained in the step of obtaining the compression molded article, thereby consolidating at least the surface portion of the compression molded article. As a method of colliding solid particles, shot blasting and air blasting can be used. Note that shot blasting also includes shot peening. The material of the shot grains may be steel, glass, alumina, etc., and the material is not particularly selected. Alternatively, iron powder for powder metallurgy may be used. Tests conducted by the inventors have revealed that the particle size of the shot grains is preferably a diameter Q of 5 mm or less, more preferably 0.2 mm or less. The degree of compaction is determined by the density of the compression molded product obtained by compression molding and the density of 0.5 to 1.5 (1
-/C1 is preferably as high as possible. Further, the thickness of the surface portion to be consolidated is preferably about 50 to 500 .mu.C.

The sintering step is a step of heating the compression molded body whose surface portion has been consolidated in a non-oxidizing atmosphere to turn the raw material powder particles into a sintered solid solution and integrate them.

Conditions such as sintering temperature and sintering atmosphere can be arbitrarily selected depending on the type of sintered metal powder raw material used. When the powder raw material is an iron-based powder raw material, the atmospheric gas is preferably an endothermic gas commonly known as RX gas. Sintering temperature is about 1150 degrees 1 sintering time is 2
About 0 minutes is good.

When the sintered metal powder raw materials are made of iron, copper, and graphite powder, the iron powders are sintered together by this sintering, and the copper and graphite are diffused into the sintered iron metal to form a solid solution.

The process of obtaining a sintered forged product by forging at high temperatures is a process in which the sintered crystals obtained in the sintering process are placed in a forging die, and hot forging is performed in the forging die. This process is basically the same as the conventional sinter forging process, and when iron-based materials such as powder raw materials are used, a die made of alloy tool steel is used as the forging die. The pressure is approximately 8000 kQ/cm2.

The sintered forged product manufactured by the manufacturing method of the present invention has a porosity of about 1.0% in the surface portion.

When iron-based metal is used as the powder raw material, the density is 780.
g/cm3 can be obtained. Note that the forged product obtained after the sintering and forging process can be subjected to heat treatment or mechanical processing if necessary.

(Effects of the Invention) In the method for producing a sintered forged product of the present invention, the surface of the compression molded body that is heated and sintered in the sintering process is consolidated and the pores on the surface are crushed. If the sintered compact is removed from the high temperature after the sintering process, the iJ
3, it is difficult for air to penetrate inside through the pores in the surface rM section. Therefore, an oxide layer or a decarburized layer is less likely to form inside the molded body. In addition, even if the surface part of the sintered compact is cooled by the forging die during forging and becomes difficult to consolidate because the surface part is more consolidated than the inside, the degree of consolidation of the surface part is relatively small. It gets expensive.

For this reason, sintered products with high fatigue strength and tensile strength are produced.

〔Example〕

For 100 parts by weight of pure iron powder with a particle size of approximately 80 microns, 211 mM of copper powder with a particle size of approximately 20 microns, 0.6 part by weight of graphite powder with a particle size of approximately 10 microns, and 0.8 parts by weight of zinc stearate, which is a lubricant. parts were blended and thoroughly mixed using a V-type mixer. Next, the plate thickness is 5IIIll, and the length of the parallel part is 20mg+
A compression molded body for the plate bending test was manufactured. The pressure during compression molding is 5000 kg/Cm2. The density of the compression molded product obtained was approximately 6.8 g/C-3.

Next, air blasting was performed on the surface of the compression molded body using iron powder for powder metallurgy with a diameter Q of 2 mm or less. After that, the air-plast compression molded body was heated and sintered at 1150 degrees for 20 minutes in an endothermic gas, and then taken out of the furnace and transferred to a forging mold in the atmosphere, and immediately produced with a weight of 8000 kg/a.
Hot forging was carried out at a pressure of 1. Then, it was left to cool in the atmosphere. It should be noted that it took about 10 seconds from the time the product was taken out of the sintering furnace to the time it was pressurized with the forge die.

In order to examine the characteristics of the obtained sintered forged product, the forged product was cut and the maximum oxide layer depth, surface layer porosity, and decarburization depth were measured. In addition, the internal Vickers hardness was measured. Furthermore, the tensile strength and fatigue strength of the obtained tJl product were measured 107 times. Results not shown in table.

As a comparative example, the manufacturing method described above was carried out in the same manner as in Example 2, except for the surface consolidation step of the compression molded body by air blasting, and the other steps were the same as those in Example 2. I did a good job. The properties of the obtained forged product were measured in the same manner as in the examples.

The results are also shown in the table.

As is clear from the table, the maximum oxide layer depth was 95% in the conventional method.
μ, whereas in the method of the present invention, the depth of 112 coals is 40 μm.In the method of the present invention, the depth of coal is 0.231111, whereas in the method of the present invention, the depth is 0.231111.
．． 12+11111. The porosity of the outermost layer is 3 in the conventional method.
．． It can be seen that the number of defects in the surface layer is 1.0% compared to 2% in the method of the present invention. Incidentally, the internal hard grain was 1-1V 240 to 260 for both the method of the present invention and the conventional method, with no difference. The tensile strength of the conventional method was 74.6 kg/mm2, whereas the method of the present invention had a tensile strength of 75.3 kg/l111, and the fatigue strength of the conventional method was 2.
3,2 ko/mm2, whereas the method of the present invention has 27,8 ko/mm2.
It was confirmed that the kl/l was as high as 111.

Patent applicant: Toyota Motor Corporation Agent: Patent Attorney Hiroshi Okawa Patent attorney Osamu Fujitani Same patent attorney Akio Maruyama

Claims (4)

[Claims] (1) A step of compression molding a sintered metal powder raw material to obtain a compression molded body, a step of heating and sintering the obtained compression molded body, a process of forging the heated and sintered molded body at a high temperature and sintering it. In the method for manufacturing a sintered forged product, the method includes a step of colliding solid particles against the surface of the compression molded product to compact the surface part of the compression molded product, The method for manufacturing a sintered forged product is characterized in that the above-mentioned sintering step is then carried out. (2) Density is 5.0-7.5g/cm3 due to compression molding
The manufacturing method according to claim 1, for obtaining a compression molded product. (3) The IllI manufacturing method according to claim 1, wherein the step of compacting is performed by shot blasting, air blasting, etc. (4) The manufacturing method according to claim 1, wherein the sintered metal powder raw material is made of iron powder, copper powder, graphite powder, or the like.