Cost-effective sinter-hardenable ferrous PM materials - Dr Brian James, Hoeganaes Corporation, USA
A ferrous PM material that has a microstructure consisting of more than fifty percent of martensite directly after sintering is said to be sinter hardened. The sinter-hardening process is gaining in popularity as it enables parts makers to eliminate an austenitizing and oil-quench hardening step when making PM parts that require heat treatment. Sinter hardening also reduces the distortion that sometimes arises during oil quenching. An additional benefit is that sinter-hardened parts do not contain retained quench oil; making subsequent tempering easier.
In order to sinter harden, a PM part needs to be made from a ferrous powder with sufficient hardenability; a material that will transform to a high percentage of martensite at the cooling rate available in the sintering furnace. For sintering furnaces that have just water-jacketed cooling this requires a material with a higher hardenability than for furnaces fitted with additional convective cooling.
