JPH0723481B2 - Stainless steel powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a stainless steel powder, and more particularly to a stainless steel powder suitable for powder metallurgy which can improve the compression density and the sintering density.

(Prior art and problems to be solved) There are Ni-based and Cr-based stainless steel powders, but Ni-based stainless steel powders are sintering machines that utilize the characteristics of stainless steel such as corrosion resistance, heat resistance, and non-magnetism. Suitable for parts and various filters, Cr-based stainless steel powder is suitable for high-strength, wear-resistant sintered materials.

Such stainless steel powder is generally manufactured by melting and refining the raw material in a melting furnace such as a high frequency induction furnace, and then atomizing the molten metal by a water spray method, but since the impurity level is high and it is easy to harden, Compressed density and sintered density do not increase,
There is a problem that the characteristics of the sintered body are deteriorated.

Therefore, various methods for improving these densities have been studied, and they are softened by annealing, or, for example, as shown in JP-A-61-30604, a so-called AOD furnace ( Nitrogen content is 150ppm or less, oxygen content is 1000pp using an argon / oxygen refining furnace)
Attempts have been made to reduce the nitrogen content, such as m or less. However, softening due to annealing causes a cost increase. On the other hand, although the compression density and the sintering density are improved for the time being due to the reduction of the amount of such impurities, a significant improvement cannot be expected at present.

(Object of the Invention) It is an object of the present invention to provide a stainless steel powder capable of solving the above-mentioned drawbacks of the prior art and significantly improving the compression density and the sintering density.

(Structure of the invention) In order to achieve the above object, the present inventor has made various studies on conventional methods for reducing impurities in stainless steel powder, and as a result of simply reducing the contents of oxygen and nitrogen as impurities, It was found that hardening of steel powder could not be effectively prevented. Therefore, as a result of researching reduction measures for other impurities, if oxygen, nitrogen, and especially nitrides such as AlN and TiN are reduced, the hardness of stainless steel powder,
In particular, it has been found that the hardness of the chromium-based stainless steel powder can be reduced, and therefore the compression density and the sintering density can be further improved.

That is, the stainless steel powder according to the present invention, TotalAl ≦ 4
0ppm, TotalTi ≦ 150ppm, TotalO ≦ 2000ppm, TotalN ≦ 15
It is characterized by being regulated to 0 ppm.

Next, the reasons for limiting the chemical components in the stainless steel powder of the present invention will be described.

The reason why TotalAl is limited to 40 ppm or less is that if the content exceeds 40 ppm, the amount of AlN produced increases and the hardness of the stainless steel powder becomes too high, thus improving the compression density and the sintering density. Because I cannot do it.

The limitation of TotalTi to 150ppm or less is that when it is contained in excess of 150ppm, the amount of TiN produced increases and the hardness of the stainless steel powder becomes too high, thus improving the compression density and the sintering density. Because I cannot do it.

The limitation of TotalO to 2000ppm or less is that when it is contained in excess of 2000ppm, the amount of oxides produced increases, the hardness of stainless steel powder becomes high, and it becomes difficult to bond it. This is because not only the sintering density cannot be improved but also the sintering strength cannot be improved.

Further, the total N is limited to 150 ppm or less, exceeding 150 ppm, if included, the amount of nitrides such as AlN and TiN produced increases, and the hardness of the stainless steel powder becomes too high, therefore, This is because the compression density and the sintering density cannot be improved.

The present invention will be described in detail below based on examples.

The stainless steel powder of the present invention is manufactured by first reducing nitrogen and oxygen in molten steel by using an AOD furnace, then remelting the raw material by a melting furnace such as a high frequency induction furnace, and then atomizing by a water spray method. To do. In this case, AO obtained by normal operation
Material D contains 150 to 200 ppm of nitrogen, but if Ar gas is used to prevent nitrogen pickup due to the use of nitrogen gas, it is reduced to 100 to 150 ppm, and the oxygen content is 2
Reduced to 000ppm or less.

However, the content level of Ti and Al is usually 50-60 pp for Al.
Since m and Ti are as high as about 200 ppm, and there are many nitrides such as AlN and TiN in the steel, hardness reduction cannot be expected. This is due to the chromium source used as a raw material in the case of melting stainless steel.
This is because impurities such as Ti are mixed in, and it is impossible to reduce the amount of such impurities even if an AOD furnace is used.

Therefore, even in the normal melting and refining process, Ti
To reduce the amount of nitrides such as N and AlN, use a raw material with a small amount of Ti and Al.
i and Al may be used.

The stainless steel melt thus obtained had Al and Ti lower than the conventional content levels, Al 40ppm or less, and Ti 150ppm.
Since it has been reduced to the following, if it is atomized by a water spraying method as in the conventional case, a stainless steel powder having a low hardness can be obtained.

(Example) A raw material using a Fe-Cr alloy of low Al and Ti as a chromium source is Ar.
Refining in an AOD furnace using gas, then remelting in a 1 ton high frequency induction melting furnace, atomizing the resulting melt by a water atomization method, and various stainless steels having the chemical composition (wt%) shown in Table 1. Obtained steel powder.

Further, for comparison, a normal Fe-Cr alloy was used as a chromium source, melted and refined in the same manner, and stainless steel powder was obtained by a water atomization method.

These stainless steel powders were used for molding and sintering by a conventional method, and the densities of the obtained molded body and sintered body were examined. The results are shown in Table 2.

As is clear from Table 2, when the stainless steel powder of the present invention is used, both the compression density and the sintered density are improved, and especially the sintered density is greatly improved. Also,
If the Al and Ti contents are reduced, the improvement effect is not diminished even if the oxygen content is relatively large.

Next, in the 410 system, as an example of the present invention, Ti content is 100 ppm, molten metal with Al content regulated to 10 ppm, as a conventional example, Ti content is 200 ppm, Al content is 60 ppm, with respect to molten metal, carbon Refining was performed by changing the equivalent weight (C + aN) (a: constant), stainless steel powder was produced by the water atomization method, and this was molded to examine the compression density. As shown in FIG. 1, the result shows that the compression density can be increased by lowering the carbon equivalent (particularly the nitrogen content), but the present invention example having a smaller Ti and Al content than the conventional example. The effect of improving the compressed density is large, and therefore the effect of improving the sintered density is also large.

(Effects of the Invention) As described in detail above, according to the present invention, not only oxygen and nitrogen as impurities in steel, but also stainless steel powder with a reduced amount of nitrides such as TiN and AlN can be provided. Therefore, it is possible to significantly improve the compression density and the sintered density, and it is possible to manufacture a sintered product having excellent characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the carbon equivalent of stainless steel powder and the compression density.

Claims (1)

[Claims] [Claim 1] Total Al ≤ 40 ppm, Total Ti ≤ 150 ppm, Total
A stainless steel powder characterized by being regulated to O ≦ 2000 ppm and Total N ≦ 150 ppm.