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Yellowish Reflection on Steel

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gciriani

Materials
May 5, 2004
52
IT
I'm trying to comprehend the reason for an unwanted yellowish appearance on stainless steel, and a cure for it.

I work on a new treatment for stainless steel used for luxury accessories (high-end watch bands). The standard steel (Aisi 316L) has a nickel content (12%) which imparts the material a bright silver-white color when mirror polished. Unfortunately the treated material has a very slight yellowish appearance (invisible to the untrained eye), which is a no-no in the industry.

The treatment diffuses carbon under the surface, for 10-20 micrometers (depending on the treatment. According to the literature available, the carbon implants itself as FCC (face centered cubic lattice, i.e in the middle of the faces of each iron cube). A lab working on this asserts that the yellowish color is not superficial and appears at some depth. Would the FCC lattice explain the shift toward yellow? Is there a way of correcting this effect? Would a transparent thin coating have the effect of correcting the reflection by interference?
 
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