Sintering
Sintering is a heat treatment process where metal or ceramic powder is heated below the melting point so that the powder grains weld together at their contact points. A solid but often porous body is formed – the basic process of powder metallurgy.
What Is Sintering
Sintering is a heat process where fine powder – metal or ceramic – is heated under pressure to a temperature below the melting point. The powder grains bond at their contact points: first small sinter necks grow, then the grains increasingly weld together into a solid body.
The Difference from Melting
When melting, the material becomes completely liquid. During sintering it stays solid, only the surfaces of the grains bond. That's why a sintered part often remains slightly porous if it isn't additionally compacted – for example by hot isostatic pressing (HIP).
Where Sintering Is Used
Sintering is the basic process of powder metallurgy. It produces sintered bronze bearings, formed parts from metal powder, but also high-performance materials like PM tool steels. The same principle is behind 3D-printing of metal (laser sintering).
Sintering and Welding
Sintered parts are demanding to weld: residual porosity and possible binder residues disturb the weld, and the fine structure tailored for sintering is altered in the heat-affected zone. This explains why PM steels – made from sintered powder – are so hard to weld.