On Mon, 22 Dec 2008 13:59:47 -0500, Alan Browne, who is determined
to show that he knows all of the answers, wrote:
Then it's not stainless steel.
Some grades of stainless steel aren't magnetic. Depends on how much
nickel is in it, I gather.
Yes, you're right there is type of stainless called "Austenitic" that,
in the right conditions, is non magnetic. Slap it with a hammer (or
other tooling) and it becomes quite attracted to magnets, however.
I've an old KitchenAid pot that's been knocked around and banged
up for years. "Stainless Steel" is stamped on the bottom and
there's no noticeable attraction by strong magnets. Did you just
google "Stainless Steel" and discover the word "Austenitic"?
In general, the higher the proportion of chromium, the stronger the
corrosion resistance of the steel. In addition to chromium, other
metals are added to give the steel particular properties such as
strength and malleability. Specifically nickel is used to strengthen
the oxide layer.
As for whether they are magnetic, the answer is that it depends.
There are several families of stainless steels with different physical
properties. A basic stainless steel has a 'ferritic' structure and is
magnetic. These are formed from the addition of chromium and
can be hardened through the addition of carbon (making them
'martensitic') and are often used in cutlery. However, the most
common stainless steels are 'austenitic' - these have a higher
chromium content and nickel is also added. It is the nickel which
modifies the physical structure of the steel and makes it non-magnetic.
So the answer is yes, the magnetic properties of stainless steel are
very dependent on the elements added into the alloy, and specifically
the addition of nickel can change the structure from magnetic to non-magnetic.
If you have non-magnetic stainless steel and you "Slap it with a
hammer", does that knock the nickel out of the steel, leaving a
powdery residue? Is this the famous "plugged nickel" that is used
to measure your theories' values? How hard does a pot have to be
slapped to change the steel's structure and make it non-magnetic?
Can it be done easily in a kitchen or is a machine shop's equipment
sufficient? Reheating the pot to a very high temperature will
return it to its non-magnetic state. Isn't the internet great?