Fire steels oxidise very quickly.This is even more so in a marine environment.Fire steels contain ferrous metal and will break down in moist climates
I have never seen this problem and live in a rain forest environment.
As I said before, my steel (3+ yrs old) is actually worn from use and shows no sign of corrosion or breakdown by any environmental means.
I suppose if I left the steel outside on the ground, in the raw elements for months at a time, then there may be some corrosion or breakdown...
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Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.
John Lubbock