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Corrosion of SS304 sheet metal

I am having a sheet metal sample for an automobile application. Material is SS304.The sample is buffed and used at 250 degrees C. I have observed some localized pitting corrosion on some areas ( flat areas, not bent ones).Please guide me to to understand why this corrosion has taken place within few hours of usage and how can I remove those corrosive spots as they damage the aesthetics of component ?

Can not be answered easily. It could have to do with how it was used/handled before polish or what contaminant it is around now. The high temperature certainly does not help as reaction rates roughly double with every 10 °C of temperature rise. You should have had it passivated after it was polished. If it was ever wire brushed, it will always fail!
Recovery- is not probable for the long term. It is very difficult to polish out pits and not have it look like a golf ball. Any residue left in the pit is a source of rapid renewed pitting. There are some chemical processes that will retard further pitting, but none that I am aware of will stop it once started.

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