Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: chris on 06/11/2008 04:11:47
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Why is stainless steel stainless? What stops it going rusty? What is the "cost" of this corrosion-resistance in terms of other physical characteristics that might be lost?
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Why is stainless steel stainless? What stops it going rusty? What is the "cost" of this corrosion-resistance in terms of other physical characteristics that might be lost?
About being stainless, I think to remember it depends on the thin layer of chromium oxide on the surface of the steel (which also cause it not being easily solded with other metals).
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I hear it's not too good under anaerobic conditions - like when you cover marine bolts with fibreglass.
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Modern stainless steel is a chromium alloy which includes tungsten and chrome and because of the chrome content it does not rust easily. As lightarrow said when exposed to air/oxygen a microscopic layer of chromium oxide is formed on the surface. This inhibits the rusting process.
You can get different grades depending on the amount of chromium included however, despite its name it can stain. It has a higher tensile strength than normal steel and is used a lot in Nuclear power plants because of its anti corrosion properties.
I live in Sheffield UK said to be where it was discovered and was told the discovery was an accident. A wrong batch was made and the bars were then discarded outside in the open when many months later it was noticed that the bars had not rusted.
Years ago I went to the steelworks and saw it being made and was given a chunk of chrome and tungsten to take home as a souvenir.
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I thought most SS used nickel not chrome?
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I thought most SS used nickel not chrome?
Some types can include a percentage of nickel and also other metals but its mainly the chrome content that gives it it rustproof quality.
Lots of specialist stainless steels are made which are graded by number as an indication of their content. For instance, too much chrome content can make the steel brittle which is no good for some uses.
Sorry, off topic. Just thought of controversy of the alleged Iraq Super-Gun barrels that were produced here several years ago. Even so, I think Sheffield still has a big market in the "specialist" steels department.