JPS63213601A - Production of low oxygen tool steel powder - Google Patents

Abstract

PURPOSE:To easily obtain low oxygen tool steel powder having satisfactory formability by crushing oxide on the surface of water atomized tool steel powder of a specified particle size by a mechanical means and by separating and removing the crushed oxide. CONSTITUTION:Oxide on the surface of tool steel powder of <=350 mesh produced by water atomization is crushed by a wet mechanical crushing means such as an attriter or a ball mill. The oxide crushed and peeled from the surface of the powder is separated and removed by a proper means such as flotation or air elutriation to produce the titled powder. The low oxygen content of the powder can be easily and effectively attained and the recrushing or classification of sintered particles formed by reduction is made unnecessary. The powder is uniformly miscible with hard powder, is easily formable and can give a sound sintered body.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to the production of low-oxygen tool steel powder suitable as a raw material powder for sintering cutting tools, molds, rolling rolls, and other wear-resistant parts. Regarding the method.

(Prior art and its problems) As is well known, the atomization method among metal powder manufacturing methods involves applying a jet stream of liquid or gas to the molten metal flowing down a molten metal nozzle to pulverize the molten metal stream and rapidly solidifying it. This is a method to obtain metal powder.

Water is mainly used as a liquid jet, but
Since the metal powder produced by this water atomization method is inevitably oxidized, the oxides adhering to the powder surface after atomization are usually reduced before use.

On the other hand, with gas jets, a low-oxygen powder can be obtained by using a non-oxidizing gas as the atomizing medium gas, but the powder is spherical and cold-open molding is difficult.

Note that the shape of the water atomized powder is irregular.

By the way, in recent years, as processing becomes more precise, tool materials that have both high hardness and high toughness and are easy to machine are required. Although high speed tools are used,
The most suitable material for these tools is high-speed steel material made by powder metallurgy (powdered high-speed steel), which has high performance and can be hardened.

In other words, unlike melted HSS, which has problems associated with melting, such as the segregation of carbides that are added in large amounts to give it high hardness, and restrictions on the composition from the melting process, powdered HSS has problems with high alloying. It is relatively easy to manufacture, and it can be manufactured in terms of toughness, heat resistance, abrasion resistance, etc. that are better than melted high speed steel. Furthermore, it is possible to strengthen or impart properties that are insufficient or not possessed by one type of raw material powder by mixing multiple types of powder. For example, Ti
N.

Attempts have also been made to produce highly wear-resistant sintered high speed steel by adding and sintering nitride or carbide powder such as VC.

The above-mentioned high speed steel compensates for the wear resistance of conventional powdered high speed steel compared to cemented carbide, has wear resistance comparable to lower grade cemented carbide, and has toughness superior to cemented carbide. It is a tool material that enables machining that cannot be performed on other machines.

In addition to the wear resistance of the cemented carbide plate mentioned above, it has excellent toughness,
The reason why fine HSS powder with a mesh size of 350 mesh or less is used in sintered high speed steel that can be machined is because if the mesh size is 350 mesh or more, even if hard particles such as TiN are mixed, it is difficult to uniformly disperse the powder.

The suitable powder to use for this is high-speed steel powder produced by the water atomization method, which has good moldability, but as mentioned above, powder produced by the water atomization method has a lot of oxides attached to the surface, which must be reduced and removed. In particular, when reducing fine powder of 350 mesh or less, which is suitable for the hard particle mixing, the problem is that the powder aggregates and disintegration becomes difficult.

In view of these problems, the present invention is aimed at producing not only the above-mentioned high speed steel powder but also a wide range of tool steel powders including high speed steel. This was done with the purpose of easily obtaining the following.

(Means for solving the problem) That is, in order to achieve the above object, in the present invention, the surface oxide of water atomized tool steel powder of 350 mesh or less is
They adopted a method of pulverizing by mechanical pulverizing means and then separating and removing the powdered oxide.

(Example) The present invention will be explained below along with examples.

The tool steel powder targeted by the present invention is a water atomized powder in order to obtain a powder with good formability, and from the standpoint of mixing and dispersibility with hard powder, it is already known that it is a fine powder of 350 mm.7 or less. As mentioned above, powder of 350 mesh or less is 3
They discovered that it is easy to crush surface oxides in powders with a mesh size of 50 or more, and utilized this knowledge.

Figures 1 to 3 are metallographic photographs (xlOO) of examples of water atomized tool steel powder, and Figure 1 shows particle size of 10 (~150).
The mesh size is 200 to 300 meshes in FIG. 2, and 350 meshes or less in FIG. 3. Powders coarser than 350 meshes have a grape cluster-like surface, making it difficult to crush surface oxides.

As the mechanical crushing means for the surface oxide, wet crushing means such as an attritor or a ball mill can be used.

Next, the pulverized oxides flaked off from the powder surface by the above-mentioned pulverization can be separated and removed by appropriate means such as flotation or air separation.

Further specific examples will be described below.

Table 1 below shows the chemical composition of the raw material powder (water atomized tool steel powder, 350 mesh or less) made into low-oxygen tool steel powder by the method of the present invention. Put it in the attritor as .7kg,
Mixed in alcohol for 10 minutes. In other words, the intense mixing causes the powders to rub against each other and pulverize the surface oxides.

' , 1 - The thus pulverized powder is taken out of the attritor,
Further alcohol was added and the suspended mixture was allowed to stand and settle.

This results in copper powder with large specific gravity and particle size (specific gravity approximately 8g/
cc, particle size of about 5 μm or more) sank first, and a large amount of oxides with small specific gravity and particle size (specific gravity of about 3 g/cc, particle size of about 1 μm or less) remained in suspension in the liquid. By separating the liquid, much of the oxide could be removed.

Table 2 shows the status of oxide removal by the above means, as a function of changes in the amount of oxygen.

Table 2 Unit wt, χ Next, among the above sample powders, for steel type A powder, a powder subjected to the low oxygen treatment of the present invention and an untreated powder were prepared,
Both were made into sintered bodies (sintered high speed steel materials) in the following manner.

That is, in both of the above, 10χTiN powder, 6
．． After adding 5χ VC powder and mixing them in alcohol using an attritor for 5 hours, the mixed powder was dried, and 4χ of paraffin was added to the dry mixed powder and kneaded well.

The above-mentioned kneaded product was molded into a round bar shape of 25φ×100(n) using a cold isostatic press applying a pressure of 3 t/cm 2 , and then the molded product was heated to 1150° C. in a vacuum to perform a reduction treatment. However, the reduction treatment time was as follows: Low-oxygen treated powder compact: -2 hours; Untreated powder compact: -1:4 hours.

Next, each molded body after the above treatment was heated at 1290°C for 1 hour and sintered to produce a sintered body (sintered high speed steel material).When the oxygen content of each sintered body was investigated, it was found that the oxygen content was low. Oxygen content in treated powder sintered body - 0,043χ Oxygen content in untreated powder sintered body ----m=----...
-・-0,082Z.

(Effects of the Invention) As described above, in the present invention, the surface oxide of water atomized tool steel powder of 350 mesos or less is crushed by mechanical crushing means, and the crushed oxide is separated and removed. Compared to low oxygen reduction through reduction, it was possible to achieve low oxygen reduction easily and effectively, and there was no need to re-grind or classify the sintered particles associated with reduction. .

In addition, the effect of reducing oxygen is excellent as shown in the above-mentioned specific examples, and therefore, the sintered body using powder according to the present invention can shorten the reduction process during its production, and can also achieve sound sintering. You will gain a body.

The powder according to the present invention has a particle size of 350 mesosius or less and is based on a water atomized powder with good moldability, so it has good uniformity in mixing with hard powder, is easy to mold, and is healthy from this point of view. A sintered body can be obtained, and the industrial value of the present invention is significant.

[Brief explanation of the drawing]

Figures 1 to 3 are metallographic photographs (xloo) of examples of water atomized tool steel powder, and Figure 1 has a grain size of 100 to 150.
Figure 2 shows powders of 200 to 300 mesh, and Figure 3 shows powders of 350 mesh or less. Figure 3 (x TOO) Figure 2 Figure 1

Claims (1)

[Claims] (1) A method for producing low-oxygen tool steel powder, which comprises pulverizing surface oxides of water atomized tool steel powder with a size of 350 mesh or less by mechanical pulverization means, and then separating and removing the pulverized oxides.