JPS5814482B2 - Manufacturing method of high-density high-alloy steel sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a high-density, high-alloy steel sintered body.

Conventionally, when manufacturing sintered bodies such as mechanical parts by powder metallurgy, ordinary powder metallurgy was used as a means to improve the mechanical properties such as wear resistance and strength of the sintered body. The sintered material formed by the sintered material is subjected to hot processing such as die forging, rolling, or extrusion in an atmospheric atmosphere to crush the pores in the sintered material and make it a non-porous body. .

However, in the conventional means for making the sintered material non-porous, (1) Generally, the upper and lower sintered materials are porous because they have a density ratio of 75 to 85%; In sintered materials such as high-speed steel and stainless steel, which contain large amounts of components such as Cr, V, Mn, and Sj, which are difficult to reduce, oxidation and decarburization reactions proceed to the inside of the material. An oxide film is formed on the particle surface, significantly deteriorating the mechanical properties, and insufficient densification.

Therefore, when heating these sintered materials before hot working, extremely difficult atmosphere adjustments must be made to prevent oxidation.

(2) As mentioned above, during hot processing of a porous sintered material formed by the normal powder metallurgy method, the porous nature has poor thermal conductivity, so it comes into contact with punches, molds, rolls, etc. The temperature at the periphery of the sintered material is much lower than that at the center, and the deformation resistance increases significantly. A large difference occurs in the sintered body, making it impossible to obtain a sintered body with uniform density.

Particularly in hot working of high-alloy steel sintered materials such as high-speed steel and stainless steel that have a high content of alloying components, the high-alloyed steel sintered materials are significantly Due to the property of increasing deformation resistance,
A considerably large density difference occurs compared to low alloy steel.

Problems such as this were occurring.

On the other hand, as a method for manufacturing a sintered body of high alloy steel such as high speed steel or stainless steel, extremely coarse raw material powder of the high alloy steel with an average particle size of 1 to 2 mm is manufactured by a cast atomization method, Packing the raw material powder into a metal container,
A method is also known in which the metal container containing the raw material powder is then compressed under cold and hot pressure, and a product of a desired shape is produced from a sintered billet with a density close to the theoretical density produced by this method. In order to manufacture the product, it is necessary to first roll the sintered billet into a material of a predetermined size, and then form the material into a final product of the desired shape by mechanical cutting or the like. It is not possible to improve yield and mass production, which are the major advantages of the gold method.

From the above-mentioned viewpoint, the present inventors have conducted research to apply powder metallurgy to produce sintered bodies of high-alloy steel such as extremely high-density high-speed steel and stainless steel in a simple process. As a result, if the density of the sintered material of the high alloy steel before hot working is 95% or more of the theoretical density, it is easy to adjust the heating atmosphere before hot working, and hot working in an atmospheric atmosphere is possible. This led to the discovery that a high-density, high-alloy steel sintered body with no difference in density between the central portion and the peripheral portion can be obtained with low processing pressure.

Next, in the method for producing a high-density high-alloy steel sintered body of the present invention, the reason why the density ratio of the sintered material before hot working is limited to a factor of 95 or more will be described.

In other words, since it is generally known that hot working a sintered material increases its density, little consideration is given to the density of the sintered material before hot working as mentioned above. At present, hot working is usually carried out at a density ratio of 75 to 85%.

There are not many problems when performing hot working of such porous sintered materials on low alloy steel, but when performing hot working on high alloy steel such as high speed steel and stainless steel, there are various problems. As mentioned above, problems occur, and in this invention, the problems that occur when manufacturing the high alloy steel sintered body are solved by changing the density ratio of the sintered material of the high alloy steel before hot working. As mentioned above, the problem was solved by increasing the ratio to 95 or higher.

Therefore, if the density of the high alloy steel sintered material before hot working is less than 95%, oxidation and decarburization reactions will proceed to the inside of the sintered material during heating before working, and in order to prevent this, Not only is quality control difficult due to the need for difficult atmosphere control, but the temperature decreases rapidly at the periphery of the sintered material that comes into contact with punches, molds, and rolls, and as a result, the deformation resistance of this area decreases. As the density increases significantly, it becomes difficult to eliminate the density difference between the center and the periphery, making it impossible to obtain a sintered body with a density close to the theoretical density. In this case, the processing pressure must be extremely high, which causes problems such as shortening the life of molds and rolls, so the density of the sintered material before hot processing must be reduced to 9.
It is desirable to have a density of 5% or more, preferably 97% or more.

Next, the present invention will be explained in detail with reference to Examples.

C: 0.86%, Si: 0.23%, Mn: 0.3
1%, P: 0.021%, S: 0.016%, Cr
: 4.1 3%, Mo: 4.9 5%, W: 6.
Composition consisting of 03%, V: 1.98%, Fe and other unavoidable impurities: remainder (JIS-SKHQ equivalent composition)
Carbon powder in an amount adjusted to the amount of oxygen contained in the high-speed steel powder was added to the high-speed steel powder and mixed and pulverized to prepare a raw material powder with a particle size of 100 mesh or less.

Next, a green compact with a diameter of 30 mmφ and a length of 30 mm is formed from the raw material powder, and the green compact is heated to 10-3 mmH.
The sintered material of the high-speed steel was manufactured by sintering in a vacuum of 100 g.

In addition, at the initial stage of the sintering process, oxygen in the green compact is reduced and removed by a gas reaction with the carbon powder added at the same time, and the pressure for compacting the green compact is increased;
By adjusting the sintering temperature, the density ratio was 78.0%,
90.0+%, 95.0%, 97.5%, and 99.
Sintered materials 1 to 5 with 0% were molded.

Next, each of the sintered materials having the above-mentioned density ratios is heated to 1100°C in an ordinary electric heating furnace, and then various forging pressures are applied in an atmospheric atmosphere to sinter the high-speed steel. A body was manufactured, and the density of the resulting sintered body was measured.

The results are shown in FIG. As shown in Figure 1, when the density ratio of the high-speed steel sintered material is 95.0% or more, the high-speed steel sintered material has a theoretical density (density ratio of 100%) with extremely low forging pressure. While a compact is obtained and oxidation does not occur during heating before forging, in high-speed steel sintered materials whose density ratio is less than 95.0%,
It is clear that a sintered body with the theoretical density cannot be obtained unless a considerably high forging pressure is applied, and furthermore, oxidation occurs to the inside during heating before forging.

In the above embodiment, a case was described in which a high-speed steel sintered body is manufactured by forging, but the present invention is not limited to this, and other high-alloy steel sintered bodies such as stainless steel can be manufactured by forging. It goes without saying that similar results can be obtained in the case of manufacturing, and also in the case of manufacturing these sintered bodies by rolling or extrusion.

As described above, according to the present invention, (1) When heating a high-alloy steel sintered material before hot working, oxidation and decarburization do not proceed to the inside of the material, making it easy to control the heating atmosphere.

(2) When hot working high-alloy steel sintered materials in the atmosphere, the working pressure is extremely low, which improves the life of molds, rolls, etc., and increases processing equipment with the same capacity. Enables hot processing of large sintered materials.

(3) There is no density difference between the center and the periphery, and it is industrially useful as it is possible to manufacture complex-shaped high-alloy steel sintered bodies with a uniform structure and a density close to the theoretical density through a simple process. This brings about a great effect.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between forging pressure and the density ratio of a high-speed steel sintered body after die forging, regarding high-speed steel sintered materials having various density ratios.

Claims (1)

[Claims] 1. A high alloy steel sintered material is formed from high alloy steel powder by a powder metallurgy method, and then the sintered material is subjected to hot working such as die forging, rolling, or extrusion to form a high alloy steel sintered material into a desired shape. In the method for producing a compact, the density of the high alloy steel sintered material before the hot working is 95% or more of the theoretical density,
And the sintered material is subjected to die forging, rolling,
Alternatively, a method for producing a high-density, high-alloy steel sintered body characterized by hot working by extrusion.