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Chromating of zinc phosphate coated part

1) Is it possible to carry out trivalent chromating treatment over zinc phosphated surface (spring steel)? If so, what would be the corrosion protection?

2) Is it mandatory if a spring steel subjected to zinc phosphating treatment?

NARASIMHUN PARTHASARATHY
PROCESS DESIGNER - CHENNAI, TAMILNADU, INDIA
January 27, 2010

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1. Whether hydrogen de-embrittlement is required for a zinc phosphated spring steel component?

2. Is it possible to do chromate conversion coating directly on degreased, de-rusted steel part?

Narasimhun Parthasarathy
- CHENNAI, TAMILNADU, INDIA
January 28, 2010

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February 2, 2010

I don't know of a trivalent seal for zinc phosphate, I've only ever used a hexavalent version. You may want to ask your chemical suppliers about whether there is a trivalent option.

Spring steel will almost certainly need de-embrittlement. Steels greater that about 1100MPa are regarded as high strength steels and will require de-embrittlement as soon after treatment is completed as possible, preferably within 1 hour. Standard de-embrittlement would be at 195C (approx. 375 °F), the time would vary, dependent on the steel strength.

If you search the letters on this site you will find numerous threads relating to de-embrittlement of high strength steels.

Brian Terry
Aerospace - Yeovil, Somerset, UK