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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
1999

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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.

Larry Hanke
Minneapolis, Minnesota
1999

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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 °F) phosphate coatings can be compromised.

  
Craig Burkart
- Naperville, Illinois
1999