Phosphate coated steel after excessive temperature exposure
Phosphate coated (Keyphos) steel to AISI/SAE 4130 has been exposed (in service) to excessive temperature, sufficient to locally burn off the coating. I need to establish that the elevated temp has not caused a reaction between coating and steel (as cadmium would of done). Your comments would be appreciated.Andy Wymer
- Banbury Oxfordshire England
Depending on the temperature of exposure, there may be a possibility of iron phosphide formation at the surface. Metallographic examination, either by destructive testing of a typical part or in situ examination, could confirm any damaging conditions.
Our colleague is correct. Phosphate coatings are hydrated crystals and the first thing to leave will be water. Even in very short times (hours) at relatively low temperatures (250 deg F) phosphate coatings can be compromised.
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