CORROSION RESISTANCE

Porosity in PM parts significantly affects corrosion resistance due to possible entrapment of corrosive media. Higher density improves corrosion resistance, as it does most other properties. Stainless steel PM parts have relatively good corrosion resistance in the atmosphere and in weak acids. Nonferrous PM materials have corrosion-resistant properties similar to those of wrought forms.

SURFACE FINISH

Excellent surface finish is an inherent feature of PM parts. The overall smoothness and surface reflectivity depend on density, tool finish, and secondary operations. Conventional profilometer readings (RMS) take into account the peaks and valleys machines surfaces, while PM parts have a series of very smooth surfaces which are interrupted with pores of varying sizes. A chisel point stylus should be substituted for the more typical radius stylus when measuring the surface finish of PM parts with a profilometer (see figure). Effective surface finish of PM parts compares favorably with ground or ground-and-polished surfaces of wrought and cast components. Surface smoothness can be further improved by secondary operations such re-pressing, honing, burnishing, or grinding.

SOUND DAMPING

The porous nature of PM parts provides good sound damping. Ringing, common with wrought steel gears and other parts, is reduced due to the controllable density in PM products. This is an important benefit in business machines, air-conditioning blowers, and similar products where quiet operation highly desirable. Damping characteristics can be further improved by infiltration or impregnation with sound damping materials. The controllable density of PM parts is also used to dissipate and muffle noise of air-driven tools.

HARDENABILITY

The depth of hardening achievable in steel alloys is known as hardenability. The higher the hardenability rating, the more hardenable the steel. Hardenability data is provided in MPIF Standard 35, Material Standards for PM Structural Parts.