JPH0629476B2 - Manufacturing method of sintered parts - Google Patents

Description

The present invention relates to a method for manufacturing a sintered part.

(Prior art) The main applications of ferrous sintered materials are structural parts and oil-free bearings with oil impregnated in the pores, which takes advantage of the cost advantage of mass production, but recently strength is required. It is also being adopted for the purpose of weight reduction and cost reduction. For this reason, in order to achieve high strength of iron-based sintered materials, pre-alloy (prealloy) powder to which alloying elements such as copper, nickel, molybdenum, and chromium are added is used as a sintered material. Is being attempted.

(Problems to be Solved by the Invention) However, the method using the above pre-alloyed powder cannot achieve sufficiently high strength at a normal sintering temperature, and therefore parts requiring particularly high strength, for example, for internal combustion engines In order to manufacture the connecting rods of sinter, strict control of the sintering atmosphere was required in order to prevent sintering of the strengthening elements such as Cr and Mn in the high temperature range of 1200 ° C or higher. . For this reason, new installation of equipment and a large increase in running cost cannot be avoided, and the expected cost reduction cannot be achieved, so it cannot be put to practical use, and parts such as connecting rods cannot be manufactured by the hot forging method. The current situation is unavoidable. A sintering method (Japanese Patent Application No. 60-99275), which comprises adding a sintering activation powder to sinter the prealloyed alloy powder at a low temperature, has also been attempted. Therefore, there is a demand for a method of manufacturing a sintered part that can achieve higher strength. Therefore, the present invention provides a sintered connecting rod which has strength equal to or higher than that of a connecting rod produced by hot forging of steel, which is currently the mainstream of connecting rods, and which has excellent durability and weight reduction. It is an object of the present invention to provide a manufacturing method without making a large change in conventional raw materials and processes.

(Means for Solving the Problems) In order to achieve the above object, the method for producing a sintered component according to the present invention is such that the iron-based alloy powder contains C: 0.5 to 6.7% and an unavoidable impurity, and the balance is Mixing step of adding and mixing 2% to 10% of sintering activated powder consisting essentially of Fe, 0.5 to 1.3% of graphite powder and a lubricant, and press-molding this to obtain an average density
6.8g / mm ³ ~7.4g / mm molding process for producing a green compact of ^3, the preheating step of heating and maintaining the 700 ° C. ~ 900 ° C. The piezoelectric powder in a vacuum or in a protective atmosphere, vacuum in this Alternatively, it is characterized by comprising a sintering step of heating and holding at 1140 ° C. to 1200 ° C. in a protective atmosphere, and a cooling step of cooling this to 200 ° C. at a cooling rate of 20 ° C./minute to 120 ° C./minute.

As the iron-based alloy powder, one containing an alloying element for strengthening, such as copper, nickel, molybdenum, or chromium, is used. Examples of such alloy powder include SA
E4100 (Cr 0.99%, Mn 0.78%, Mo 0.29%, O
0.16% and the commercially available balance Fe) may be used.

The sinter activated powder reduces and removes the oxide film on the surface of the base powder from a relatively low temperature and promotes the formation of a neck, but if the addition amount is less than 2%, the effect of improving the strength is insufficient. However, if the content exceeds 10%, the compressibility decreases, so the addition amount of the sintering activation powder is set to 2 to less than 10%.

If the amount of carbon in the sintering activated powder is less than 0.5%, the activation is insufficient, and if it exceeds 6.7%, the effect on activation becomes saturated and the productivity of the powder itself decreases. Therefore, the amount of carbon in the sintering activated powder is 0.5% ~
6.7%

As the lubricant, any of those usually used for this purpose may be used, and for example, zinc stearate may be used.

When manufacturing parts that require particularly high strength, such as sintered materials for connecting rods, it is necessary to increase the amount of carbon after sintering, but graphite is cheaper in terms of manufacturing costs. Therefore, it is preferable to supply graphite in terms of carbon exceeding the activation effect. In this case, the amount of carbon after sintering is
If it is less than 0.5%, the required strength cannot be achieved. On the other hand, if it exceeds 1.3%, carbides may be excessively precipitated to reduce the strength. Therefore, the amount of carbon after sintering is preferably in the range of 0.5% to 1.3%, and therefore, the graphite powder is contained in the range of 0.5% to 1.3%.
Is preferably added in an amount of.

Manufacture of a green compact can be performed by using a molding die, a rubber die for static pressure, or the like to form a shape similar to the sintered part to be produced. If the average density of the manufactured sintered parts is less than 6.8 g / cm ³ , the strength required for sintered parts cannot be obtained, and if it exceeds 7.4 g / cm ³ , the effect of weight reduction becomes small, so the average density is preferably produced by molding a load such that ^{6.8g / cm 3 ~7.4g / cm 3} .

Then, the molded powder compact is heated in a vacuum or in a protective atmosphere to remove the oxide film on the surface. Reduction and removal of oxides on the surface of the base powder by the sintering activated powder occurs from around 600 ° C, but it is not sufficient in the temperature range of 700 ° C or lower and the effect for improving strength is insufficient.
On the contrary, in the temperature range of 900 ° C or higher, the reducing action of graphite is dominant, so that the formation and growth of the neck becomes insufficient.

Therefore, in order to reduce and remove the oxide on the surface of the base powder by the sintering activated powder, and to sufficiently perform the formation and growth of the neck, it is necessary to heat and hold at 700 ° C to 900 ° C. The heating and holding time depends on the size of the sintered part, but it is necessary to perform the heating for a sufficient time to obtain the effect of preheating. For example, in the case of a connecting rod of an internal combustion engine, it is 30 minutes or more.

Sintering is preferably carried out at temperatures in the range 1140 ° C to 1200 ° C under vacuum or protective atmosphere.

The vacuum in the preheating and sintering steps represents a degree of reduced pressure of 10 ³ orr or less, and the protective atmosphere is an atmosphere for protecting the sintered parts from oxidation, such as nitrogen and ammonia decomposition gas. , Butane modified gas, propane modified gas atmosphere.

Cooling after sintering is slower or slower than 20 ° C / min to 120 ° C / min, resulting in pearlite or martensite structure, and the strength required for sintered parts cannot be obtained. Therefore, the cooling rate is 20 ° C / min to 120 ° C / min.

(Operation) Since the sintered part manufactured according to the present invention is preheated under the conditions limited above, carbon in the sintering activated powder efficiently reduces the metal oxide film on the surface of the prealloy alloy powder. A sintered body made of a prealloy alloy can be obtained at a temperature of 1200 ° C or lower. In addition, high strength is achieved by limiting the conditions such as the composition of the sintered material and the cooling step as described above.

(Example) Example 1: SAE4100 powder (Cr 0.99) having a particle size of -100 mesh.
%, Mn 0.78%, Mo 0.29%, O 0.16% and balance Fe)
In addition, 8% of the sintering activated powder (Fe and 5%)
Of C), 0.5% of graphite powder (ACP) and 0.8% of lubricant (zinc stearate) are added and mixed by a V-type mixer, and 4.5t / cm ² ~ 7.2t by a die molding method. By applying a load of / cm ² , a connecting rod green compact having an average density of 6.8 g / cm ³ was produced. Next, in an ammonia decomposition gas atmosphere at 850 ° C
After heating for 30 minutes, sintering was also performed in the same ammonia decomposition gas atmosphere at 1150 ° C. for 60 minutes and cooled to 200 ° C. at a cooling rate of 30 ° C./minute to manufacture a sintered connecting rod. The carbon amount of the obtained sintered connecting rod was 0.77%, and the average density was
It was 6.8 g / cm ³ .

Examples 2 to 4: Sintered connecting rods were manufactured by the same method as in Example 1 based on the manufacturing conditions in the table below.

Comparative Example 1: Using a commercially available JIS S55L material, it was processed into a connecting rod shape by a hot forging method, heated and held at 830 ° C for 30 minutes, then oil-quenched (oil temperature 60 ° C), and 550 ° C x 60 minutes. A connecting rod was manufactured by tempering the. The average density of the obtained connecting rods was 7.86 g / cm ³ and was uniform. It should be noted that this comparative example shows an example of a rod manufacturing method which is actually performed at present.

Comparative Examples 2 to 9: In the same manner as in Example 1, sintered connecting rods were manufactured under the manufacturing conditions shown in Table 1 below. In each comparative example, at least one of the manufacturing conditions such as the composition of the sintered material, the preheating conditions, the sintering conditions, and the cooling rate is different from the manufacturing conditions of the present invention.

Test Example 1: A fatigue tester was used to measure the fatigue strength of the connecting rods manufactured in the above Examples and Comparative Examples. The results are shown in Table 1 below and the graph in FIG.

As is clear from Table 1 and the graph of FIG.
The fatigue strength of the sintered connecting rods manufactured according to Nos. 4 to 4 is comparable to or higher than that of the hot forged connecting rod of Comparative Example 1. On the other hand, Comparative Examples 3 to 9 are methods of sintering the pre-alloyed alloy powder that has been conventionally developed, without depending on the manufacturing conditions according to the present invention, and the fatigue of the sintered connecting rod manufactured by this method. The strength is lower than that of the connecting rods of Examples 1 to 4 and Comparative Example 1. Further, Comparative Example 2 is a method similar to the methods of Comparative Examples 3 to 9 which consists of sintering the prealloy alloy powder without depending on the production conditions according to the present invention, but the sintering is carried out at a high temperature (1300 ° C.). Therefore, the fatigue strength comparable to that of Comparative Example 1 is achieved. However, since this method sinters at a high temperature, it requires special equipment and strict control of the sintering atmosphere.

Test Example 2: A bench endurance test was performed on the connecting rods manufactured in Examples 1 to 4 and Comparative Example 2 under the following conditions.

E / G used: 4 cylinders, 1600cc, gasoline E / GE / G rotation speed: 6000 rpm Load: full load time: 300 hr In this test, the connecting rods manufactured in Examples 1 to 4 and Comparative Example 2 had no problem. Did not happen.

Test Example 3: The weight of all the above Examples and Comparative Examples was measured, and the achievement degree (%) of weight reduction with respect to Comparative Example 1 was examined. The results are shown in the above table and the graph of FIG. As is clear from the table and the graph, the sintered connecting rods of Examples 1 to 4 were 9.7% to 13.5% as compared with the hot forged connecting rod of Comparative Example 1.
% Weight reduction has been achieved.

(Effect of the Invention) A sintered part produced by sintering the prealloy alloy powder, the sintering activation powder and the graphite by the method of the present invention and cooling at an appropriate rate is produced by the conventional hot forging method. It has higher strength and lighter weight than the sintered parts. Furthermore, special equipment is required because there is no need to perform strict control of sintering and manufacturing conditions at a high temperature of 1200 ° C or higher as in the conventional sintering method using pre-alloyed alloy powder. In addition, mass production is easy, and cost reduction can be achieved.

[Brief description of drawings]

FIG. 1 is a graph showing the fatigue strength of connecting rods manufactured according to Examples and Comparative Examples of the present invention, and FIG. 2 is a graph showing the weight of the connecting rods.

Claims (1)

[Claims] 1. An iron-based alloy powder, C: 0.5 to 6.7%, sinter activated powder 2% to 10% containing unavoidable impurities and the balance being essentially Fe, graphite powder 0.5 to 1.3% and lubrication. mixing step, the molding step of producing a powder having an average density of 6.8g / mm ³ ~7.4g / mm ³ which was pressure-formed added to and mixed agent,
700 ℃ ~ 900 in the green compact or in a protective atmosphere
Pre-heating process to heat and hold at ℃, sintering process to heat and hold at 1140 ℃ to 1200 ℃ in vacuum or protective atmosphere, and further to 200 ℃ at cooling rate of 20 ℃ / min to 120 ℃ / min A method of manufacturing a sintered part, which comprises a cooling step of cooling.