Stainless Steel Sintering

Sintering is defined as “The thermal treatment of a powder or compact at a temperature below the melting point of the main constituent, for the purpose of increasing its strength by bonding together of the particles.” In a specially designed furnace with a controlled atmosphere, “green” parts molded from a powdered metal mixture are brought to a temperature just below the alloy’s melting temperature.

In the first stage of sintering, impurities and binder materials are off gassed leaving only small traces of carbon in the metal powder. To prevent oxidation of the metal powders, an oxygen-free atmosphere is created within the furnace. In the case of stainless steel, this is most often a vacuum. So stainless steel sintering is usually use the vacuum sintering furnace.

As the part approaches the alloy’s melting temperature a process called solid state bonding occurs forming a solid metal part. It is critical that the temperature not go above this point or the part may collapse. This back-down temperature becomes extremely critical when hollow parts such as stainless steel hose fittings are being produced. The physical changes that take place in a sintering furnace are fairly complex. In general, the welded areas formed during compaction grow as a result of solid-state diffusion; grain growth and Re-crystallization often follow decreasing the total porosity as a percentage of volume. These changes, if properly controlled, result in a part that resembles a cast or forged metal part.