Stainless Steel and High Alloy Powders

E. Klar and P.K. Samal, OMG AMERICAS

Most stainless steel and other high-alloy powders are made by water atomization or by inert gas and centrifugal atomization. Information on these processes can be found in the article "Atomization" in this Volume. Water-atomized powders generally are of irregular particle shape and widely used for cold compaction and sintering. The densities of the resulting sintered parts are typically below about 95% of theoretical. It is for this reason that dynamic mechanical properties as well as a number of physical properties are below those of their fully dense counterparts. For the same reason, such parts often can tolerate greater levels of interstitials, although the tendency here is toward lower levels of interstitials in both powders and sintered parts.

Gas-atomized powders generally have spherical particle shape and require consolidation techniques such as hot isostatic pressing, extrusion, or metal injection molding. The properties of parts produced by these methods are generally equal and sometimes superior to their ingot metallurgy (I/M) counterparts. For these materials, the control of interstitials usually is very important. The superior properties derive from a more uniform and cleaner microstructure as a result of the rapid quenching inherent in the powder-making processes and from the careful control of contamination with ceramic and other materials during powder making and consolidation.

Three important classes of high-alloy powders are discussed in more detail in this section. They include stainless steel powders, tool steel powders, and superalloy powders. Aluminum alloy powders are discussed in a separate article in this Volume.

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