How does Discoloration occur during Sintering in MIM? How can it be resolved?

Date：2025-07-29   Views：1005

Mechanism:

During sintering, oxides or nitrides form on the surface of parts, causing discoloration. This is a clear indication of an issue with the sintering atmosphere. To prevent this, the metal surface must not react with the sintering atmosphere to form reaction products such as oxides or nitrides during sintering.

Causes:

High oxygen content in the sintering atmosphere → High-temperature reactive metal powders form metal oxides on their surfaces.

Sintering for seven minutes in an atmosphere containing nitrogen or ammonia → Reacts with chromium in stainless steel to form chromium oxide, reducing the corrosion resistance of stainless steel.

Vacuum sintering at too high a temperature → Chromium evaporates, reducing the corrosion resistance of stainless steel.

*Therefore, argon is commonly used as a protective atmosphere during high-temperature sintering of stainless steel.

Solutions:

• Inject ammonia as a protective atmosphere

• Install a gas dryer to prevent moisture oxidation

• Store raw materials in a light-proof and moisture-proof environment

• Use high-precision molds to prevent gas from entering gaps