Immaculate

March 27, 2010 1:08 PM

Why does stainless steel have such strange properties?

Its corrosion resistance has long been explained by the formation of a thin protective layer of chromium oxide, but it isn't the only weird feature of stainless steel. There's its thermal conductivity, which is surprisingly low for a metal alloy (16 W/mK, as opposed to 80 for iron, 94 for chromium or 91 for nickel), and also that curious "odor-eating" ability which is exploited in "stainless steel soap", and which seems quite real to me, but for which I can't find any convincing explanation online.
Does familiarity breed contempt? I have the feeling that if it wasn't such an ubiquitous material, its strange properties would get more scientific interest...

posted by Skeptic to science & nature (9 answers total)

It's mostly just the magic of metal alloying. Some types of SS (316 in particular) are even non-magnetic!
posted by ArgentCorvid at 1:32 PM on March 27, 2010

The thermal properties (as well as the lower electrical conductivity) which are explained by the mean free path of phonons (quantized particles of vibration) being shorter in alloys, because they're more disordered. More technical explanation here.

Fun fact: while diamond's superbly rigid lattice structure makes it by far the best solid conductor of heat, for very isotopically pure ¹²C diamond, its ability to conduct heat is much, much higher than even regular diamond.
posted by 7-7 at 1:38 PM on March 27, 2010

diamond's superbly rigid lattice structure makes it by far the best solid conductor of heat

At risk of repeating a folk etymology, I've heard that this is why diamonds are called "ice" (like metals, they tend to feel cold as they conduct heat away from your skin). And, you know, it probably has to do with how they look, too.
posted by pullayup at 1:44 PM on March 27, 2010 [2 favorites]

People who pay a lot for "stainless" steel appliances, are frequently dis-heartened when they find that "stainless" steels can be stained. Stainless steels, earlier known as "inox steel," gain their stain resistance properties, and some anti-magnetic properties, from particular alloying metals, or, the crystalline result of alloying some metals and carbon with iron, to produce a particular version of "stainless" steel.

There are, literally, tens of thousands of formulas for making steels. Only several hundred have proven economically valuable, and of those, only several dozen have been routinely described as "stainless" steels. Indeed, by annual tonnage produced, some highly "stainable" steels are much preferred, by modern society.
posted by paulsc at 2:19 PM on March 27, 2010

It works like anodized aluminum- the oxide layer provides a protective coating. Unlike aluminum (and titanium) anodizations, this oxide layer rebuilds itself when it is penetrated.

I'm not sure why the anger towards the word "stainless", it is pretty darned stainless compared to regular steel. Unless you treat it badly by letting it remain in contact with, say, poorly chosen cleaning chemicals.
posted by gjc at 3:56 PM on March 27, 2010

It's the change in the lattice structure due to the alloying with Chromium.

This is apparent in certain properties of stainless steel.

It is brittle and will crack where a steel bar would nicely bend. Stainless steel (303 comes to mind) is also difficult to mill, it does not cut nicely and tends to "gum."

If enough Chromium is added, stainless steel (as ArgentCorvald pointed out) becomes non-magnetic which for an alloy of iron is a really interesting and rather useful property.
posted by three blind mice at 4:55 PM on March 27, 2010 [1 favorite]

becomes non-magnetic which for an alloy of iron is a really interesting and rather useful property.

or a rather annoying property if my refrigerator doors are made out of it.
posted by alms at 6:16 PM on March 27, 2010

or a rather annoying property if my refrigerator doors are made out of it.

To each their own, I suppose. I just got my first "non-magnetic" ss refrigerator, and I'm kind of enjoying its lack of accumulating the bits of magnetic marketing fluff the old ones did.

Wish it repelled fingerprints as easily.
posted by nonliteral at 9:47 PM on March 27, 2010

303 machines like butter 304's a different story
posted by patnok at 7:04 PM on March 29, 2010