Sponge-iron powder

Details Sponge-iron powder Sponge-iron powder

1995-08-29

1999-05-11

Wyszomierski, George

Specialized metallurgical processes, compositions for use therei

Processes

Producing or purifying free metal powder or producing or...

75354, 241 2413, 241 2425, B22F9/04

Patent

active

059023732

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to iron-based powder compositions containing hard-phase material. More specifically, the invention relates to powder compositions based on sponge iron.
According to the invention, a finely divided powder material is prepared which can be used for making compacted and sintered products. The desired properties of the finished product are determined e.g. by the hard-phase materials selected. The properties of the sintered product can also be affected by alloying additivies which may be included in the powder composition of the invention.
Iron-based powder materials containing hard-phase material are described e.g. in an article by Thummler et al (Powder Metallurgy International, Vol. 23, No. 5, 1991, pp 285-290). For making such iron-based materials, the iron-containing starting material used has been atomised iron powder or carbonyl iron which when ground with hard-phase material is stated to provide a mechanically alloyed powder that can be used for making sintered products having high abrasion resistance.
It has now been found that if atomised iron or carbonyl iron is replaced by sponge iron as starting material in grinding together with hard-phase materials, it is possible to produce a powder of potentially equally useful properties as the known powder. Apart from the advantage of sponge iron being essentially cheaper than atomised iron and carbonyl iron, the powder composition of the present invention can be produced by significantly less energy-intensive and less complicated grinding procedures than when producing the above-mentioned known powder compositions.
In the method of the present invention, sponge-iron powder, powder of hard-phase material and optionally alloying substances are mixed in a milling device, such as a ball mill containing balls of steel or ceramic material. The mill vessel, containing powder and balls, is filled with liquid, such as heptane, alchol, cyclohexane or water, and a dispersing agent is also optionally added to the liquid, whereupon the vessel is sealed after it has been filled with nitrogen gas or any other inert gas. The mill vessel is thereafter rotated as long as the desired particle size and particle size distribution is obtained. Examples of other types of milling devices are attrition mills or vibratory mills.
Grinding methods of the type used according to the present invention are described in German Patent Publication 1,905,764. However, this publication is concerned with the grinding of only a metal, without the addition of hard-phase material, thus yielding a type of particles having a powder density of less than 1 g/cm.sup.3 and a surface area of at least 1 m.sup.2 /g. In the conception of the present invention, it has however been found that if these particles are mixed with particles of hard-phase material, a powder of inadequate compressibility is obtained. If, on the other hand, grinding of sponge-iron powder takes place in the presence of hard-phase powder, a fine powder is obtained which, optionally after conventional agglomeration, is well suited for the production of compacted and sintered products, which are expected to have desirable properties because of the presence of hard-phase material. Also in respect of the sintering process itself, the new powders are expected to yield valuable advantages as compared with conventional powder compositions.
The sponge-iron powder used as starting material suitably is a commercially available, annealed or non-annealed sponge-iron powder, such as NC 100.24 or M 100 having an average particle size of 90 .mu.m. These powders are commercially available from Hoganas AB. The invention is however not restricted to powders having such average particle sizes but also larger and smaller sizes can be used.
The degree of grinding varies depending on the type and the particle size of the starting materials, and is suitably determined in each particular case. When using e.g. NC 100.24 or M 100 having an average particle size of about 90 .mu.m, favourable results have been obtained when grinding t

REFERENCES:
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patent: 4518427 (1985-05-01), Tengzelius et al.
patent: 4647304 (1987-03-01), Petrovic-Loton et al.
patent: 4787561 (1988-11-01), Kemp et al.
"Sintered Steels With High Content of Hard Phases: A New Class of Wear Resistant Materials", F. Thummler et al., Powder Metallurgy International, vol. 23, No. 5, 1991, pp. 285-290.

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