Stainless steel, a kind of high-alloy steel, is widely used in various industries with neat and beautiful appearance. Representative stainless steels include 13 chrome steel, 18/8 chrome-nickel steel, and so on. In the light of metallography, stainless steel with over 12% chromium can form chromium film that prevents corrosion when exposed to air or corrosive chemicals. However, there are some exceptions.
1. Stainless steel will rust rapidly when exposed to chlorides which exist in salt, seawater, soil, and so forth. So stainless steel products are supposed to be used in non-chloride environments and cleaned frequently. For instance, an American company has accommodated chloride-containing liquid in an oak container for nearly 100 years. Later they decided to use a stainless steel container instead. To their surprise, it leaked after 16 days because of corrosion.
2. Stainless steel without solid solution treatment may fail to resist corrosion effectively because it is a low-alloy compound rather than a solution.
3. Stainless steel with low carbon content will dissolve out a few carbides when welded, which may cause intergranular corrosion, also called weld decay. The phenomenon can be avoided if titanium and niobium are added to the metal and stabilize it.