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Bright annealed stainless ... different shades? Why do they go brown?

HI ALL

My name's Lee, and my company
builds all ranges of road tankers from liquid nitrogen to food prod products and wastes.

My question is regarding the " bright annealed finish " , are there different shades ? as we have just skinned 15 tankers in 0.7mm bright annealed and the finish is of a milky grain and not a shinny mirror finish - also when we have " T-cutted " & "glass polished " by hand the marks out of the sheets on the tanker - once outside there seems to be a brown colour and streaking gradually appearing on the sheets when left to the elements ?

please can anyone explain this and why it happens ?

many thanks and kind regards,

Lee Barrett
road tanker builders - Lancashire, United Kingdom
July 3, 2008

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Hi Lee,
First, it should be mentioned that the SS surface should be cleaned prior to annealing. If not, you may see any one of colors of rain bow due to type of soil on your metal. Then, it also should be mentioned, if you want to have mirror finish, past treatment after annealing may be needed, such as pickling or/and de-scaling. Furthermore, all after, a passivation may also be needed.

Jun Zhang
- Cincinnati, Ohio
July 7, 2008