JPS63250405A - Production of high strength product of powder - Google Patents

Abstract

PURPOSE:To economically produce a small-sized high strength product by heating and hot forging a cold compacted body of metal powder to increase the density and by subjecting the forged product to hot isostatic press forming. CONSTITUTION:Metal powder as starting material is cold compacted and the compacted body is heated and hot forged in closed dies so that the forged product has >=96% density ratio. The compacted body may be heated, cooled and reheated before the hot forging. The forged product is then subjected to hot isostatic press forming to eliminate the residual voids. Thus, the wear of the dies can be suppressed, compression to true density is enabled and a high density and high strength product can be produced at a low cost.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for manufacturing powder metallurgy products, which comprises a process of manufacturing metal powder by compression molding and then sintering, and particularly relates to a method for manufacturing powder metallurgy products, particularly high-strength powder metallurgy products. The present invention relates to a method for economically producing .

[Prior art] The powder metallurgy method, which can produce large quantities of mechanical parts of the same size and shape by compression molding raw metal powder in a mold and then sintering it continuously, is a method that enables production from raw materials to products. Powder metallurgy products have the advantage of being short, can be easily molded even into complex shapes, and have high dimensional accuracy, reducing the need for machining in subsequent processes. Demand is steadily increasing.

By the way, while powder metallurgy products have the above-mentioned advantages, voids remain between the powder during the compression molding stage, and shrinkage during sintering is kept as small as possible to improve dimensional accuracy, so the porosity is low. generally ranges from 10 to 20%. Therefore, in terms of mechanical strength, it has low elongation and low toughness, with a tensile strength of 10 to 50 kg.
It remains at f/m+n2.

Therefore, in order to manufacture powder metallurgy products with higher strength, for example, Ni and MO are added in the form of powder to improve the mutual sliding of the powders, making the powder highly compressible.
Measures have been taken to increase the density by stage compression.

[Problems to be solved by the invention] Although various high-density technologies have been proposed, none of them has been able to sufficiently eliminate internal voids, and it has not been possible to sufficiently eliminate internal voids, and Products with high strength and high toughness have not been obtained, and in order to achieve high strength and high toughness, it is necessary to increase the true density.

However, since it is difficult to achieve true density through cold working, various studies have been conducted, and it has been found that high density can be achieved by hot forging.
A powder forging technique has been proposed in which hot die forging is performed after compression molding and sintering according to the usual powder metallurgy method. In other words, when powder forging technology is adopted, the voids remaining in the sintered product can be eliminated and densified by hot die forging after sintering is completed, so even powder metallurgy can achieve high strength and high toughness. Now you can get the following products. Furthermore, since this powder forging technology enables high-precision forging, it was expected that post-processing could be omitted and manufacturing costs could be reduced, similar to conventional powder metallurgy.

However, when powder forging technology was put into practical use, although improvements in strength and toughness through true densification yielded almost satisfactory results, the short lifespan of hot forging dies led to high mold costs, and When comparing the costs, it becomes clear that it is not that advantageous. Therefore, at present, there has been little progress in practical use except for special uses.

Another disadvantage of the powder forging method is that it is not suitable for manufacturing small-scale products.

In other words, in the conventional powder forging method, pre-sintered crystals in a high temperature state are quickly sieved into a forging die and hot forged, but when the product size is small, the thermal profile of the product is small. As a result, the product was cooled during the 8th feeding process, making it difficult to sufficiently increase the density inside the product using normal forging pressure.

Further, if the forging pressure is increased too much, the mold may be damaged, or even if the mold does not break, the life of the mold will be further shortened.

The present invention has been made with attention to these circumstances, and it takes advantage of the features of powder forging technology to solve problems that lead to a rise in mold costs, such as mold breakage and shortened mold life, and achieves high strength. The object is to provide a method by which products, especially small, high-strength products, can be manufactured economically.

[Means for Solving the Problems] The method of the present invention that achieves the above object cold-forms metal powder, further heats it, or heats it, cools it, reheats it, and then hot forges it, The gist is that hot isostatic press forming is performed after the density ratio of the forged product is at least 96%.

[Function] As mentioned above, the powder forging method has been developed because it is possible to obtain products with true density, but even though it is hot, it is necessary to forge until the true density (density ratio: 100%) is reached. As a result, the forging pressure becomes considerably high, and an excessive load is placed on the mold that supports the forging pressure, reducing the life of the mold.

On the other hand, in the present invention, we stop forced forging that causes a reduction in die life, and the density ratio reached in hot die forging is kept slightly before the true density. By leaving it to the press (HIP), wear and tear on the hot forging die is prevented. In other words, if hot die forging is completed with some voids left inside the product, the required forging pressure will be considerably smaller, and the voids will act as a pressure buffer, greatly reducing the load on the mold. , damage to the mold is almost completely prevented, and wear and tear on the mold is significantly reduced. However, hot forging must be carried out to a density ratio of at least 96%, and the density ratio at the end of hot forging must be 9.
If it is less than 6%, the density ratio will not increase sufficiently even if the hot isostatic pressing treatment described below is performed, and the true density will not be reached at all.

As mentioned above, by leaving a margin of up to 4%, the pores remaining in the hot die forged product can be removed without the need for a die.
Emitted to the outside by IP law. In other words, in HIP, it is possible to compress hot die forged products at high pressure using a fluid as a medium, without putting them in a capsule or in general, so it is possible to increase the density ratio and improve the true quality without fear of die wear. Density products can be manufactured. In addition, the method of placing hot forged products one by one into capsules during HIP processing would complicate the process and increase production costs.
It is desirable to directly insert the hot forged product into a pressure medium and embed it in HIP% without using a capsule.

Further, in the process of the present invention, as shown in the above structure, powder forging is followed by HIP treatment, but operations up to powder forging may follow conventional powder forging processes. In other words, after cold forming metal powder, the molded product is heated to sinter, and after sintering, hot forging is subsequently performed, or the sintered crystal is once cooled and then reheated for hot forging. All you have to do is There are no particular restrictions on the methods and conditions of cold forming, sintering, and hot forging in these steps, and conventional methods may be followed.

[Example] Equivalent to S A E 4840 (2%N i -0,5Mo
%-0.4%C-Fe) by the water spray method was sieved into 180 meshes (175 μm or less) with an outer diameter of 6
It was cold compression molded into a cylindrical shape with a diameter of 5 mm, an inner diameter of 34 mm, and a height of 50 mm. And in H,X surrounding gas, 1120℃,
After heating for 30 minutes, immediately reduce the outer diameter to 67 mm and the inner diameter to 3.
Forged in a 2mm closed mold.

The horizontal axis in FIG. 1 shows the measured density of forged materials obtained by varying the forging pressure at this time. and 6 from 7.23g/cm3 to 7.89g/cm3 shown in Figure 1.
Each type of product was subjected to HIP treatment in its as-forged state. HIP conditions are 1100℃, 1500kg/ctn2
．． It is one hour. The vertical axis of FIG. 1 is the result of measuring the density of each product again after the HIP treatment. As a result, the first
As shown in the figure, A was divided into 82 groups.

In other words, for the A group, the density before HIP is
This has not changed since then. On the other hand, those in group B with an initial density of 7.58 g/cm' or higher are HI.
The PIA process gave a density of 7.89g/c+n3, and when the internal structure of the product was examined in detail using a microscope, there were no pores at all, and the density ratio was completely 100%. The effect of HIP will not appear on A group with less than 100%, Qjl Do you get it. Similar results are F2-2%Cu-0,6%
It is also recognized in powder forged materials made from C, Fe-3% Si, and AI powders, and if they have an initial density of 96% or more in terms of density ratio at the end of hot forging, by HIP, It was confirmed that most metal powder materials can be easily made to have a density of 100%.

Example I SAE 4120 equivalent (1%Cr-0,2%Mo-
0,6%Mn-0,2%C-Fe) water spray powder
Sieve into mesh (175 μm or less), outer diameter 52.
Cold mold compression molding was carried out into a disc having a diameter of 5 mm and a height of 15.5 mm. Then, at 1120°C in an H2 gas atmosphere.

It was heated for 30 minutes and then forged into a gear shape with an outer diameter of 54.85 mm as shown in FIG. 2 using a closed mold. At this time, three identical molds were prepared, and the forging pressure was changed to three different types, and forging was carried out until the life of the mold. Forging pressure is 6
The average density of the forged body at t/cm' was 98%. In this case, 45,000 products could be forged before the mold life expired. Also, the forging pressure is 10 t/cm2
When , a product with a density ratio of 99% is obtained, and the mold life is 1.
It was 5,000 shots. On the other hand, in order to obtain a product with a density ratio of 100%, a forging pressure of 12 t/cm"' was required, and the mold life at this time was 9000 shots.

Next, products with a density ratio of 98% and 99% were directly charged into a HIP device and heated to 1100°C.

Heating at 1500 kg/cm' for 1 hour,
Pressurization was applied to completely remove remaining pores. density ratio 1
00% was confirmed by measuring the density of the product after HIP.

As mentioned above, finished products with a density ratio of 100% were finally obtained for each of the products that went through the above three types of processes, but the total cost of forging molds and HIP processing costs differed as shown in Figure 3. As described in the present invention, powder forging is performed with some pores left to the extent that HIP treatment is possible, and then HIP treatment is performed.
It was confirmed that P treatment is more economical. Also, the material used in this example (SAE 412
0), there is no economic advantage if the forging density ratio is 99%, and if it is less than 98% and the HI PIA process is effective.
It was found that forging at % or higher is economically superior. Here, the upper limit of the economically advantageous forging material density ratio is less than 99% in this example, but as a result of studying various materials and product shapes, it was found that this value varies in various ways. However, it has been confirmed that if the HIP treatment is performed continuously at a density ratio of at least 96%, compression to the true density is possible and the cost is lower than that of the conventional method.

Example 2 -100 mesh (147 μm or less) pure iron powder was added with -3
25 meshes (44 μm or less) of Fe-3i alloy powder were mixed to give a composition of Fe-3%Si. This mixed powder was formed into a columnar shape with an outer diameter of 10 mm and a height of 8 mm by cold press molding. This was heated in H2 for 30 minutes and then immediately sealed and forged in a mold. At this time, even though it was forged at 20 t/cm2, which is the upper limit of the allowable pressure of the die, the density ratio of the forged product was 99%, and it was impossible to obtain 100% production with the conventional powder forging method. I couldn't do it. The reason for this is firstly that the material is hard, Fe-3%Si, and because the product shape is small with an outer diameter of 10 mm, the temperature drops during transfer from the heating furnace to the forging press, increasing deformation resistance. These have been the fate of conventional powder forging technology. Therefore, the powder forged product with a density ratio of 99% was immediately put into a HIP machine and heated at 1000°C and 1500°C.
kg/cm2. After 1 hour of treatment, density measurement revealed that the density ratio was 100%. When the maximum magnetic permeability μm was measured as the direct current magnetic property of the conventional powder forged material and the product of the present invention, the results shown in Table 1 were obtained, confirming that the material of the present invention is superior.

Table 1 [Effects of the Invention] The present invention is configured as described above, and since powder forging is stopped slightly before the true density and HIPIA filling is performed, wear and tear on the mold can be reduced, and high-density, high-density It is important to obtain strong products economically.

[Brief explanation of drawings]

Figure 1 shows the density before HIP treatment and HI
A graph showing the density relationship after P treatment, Figure 2 is Example 1
FIG. 3 is an explanatory cross-sectional view showing the shape of a powder forged product (gear) in Embodiment 2, and FIG. Figure 3

Claims (1)

[Claims] After cold forming metal powder and further heating or
A method for producing a high-strength powder product, which comprises cooling and reheating, hot forging to a density ratio of at least 96%, and then hot isostatic pressing.