Stainless and Carbon Magnetism?

Question

Hello,

I recently received a katana as a gift from a friend. It's a handmade one and is really well done and is not a cheap $20 sword from a third rate shop. Anyways, I was experimenting with some advice my grandpa gave me and decided to stick a magnet to it to see if it was either stainless or carbon steel. To my delight the magnet stuck and it was in fact carbon (to me it just feels more authentic if it's made of carbon steel and not stainless even though carbon requires more care). Anyway (this is the part that makes me think I got my grandpa's instructions wrong) I grabbed a stainless steel short sword that I bought last year which is a cheap blade, and stuck a magnet to it. Surprisingly the magnet stuck even though the blade is labeled as stainless steel. I did the same with an old knife I received from my step brother that had some surface rust on it making it likely to be carbon too, and the magnet stuck. So I'm very confused. Katana had oil on it so it should be carbon.

Answer 1

From AZOM.com:

"Magnetic permeability is the ability of a material to carry magnetism, indicated by the degree to which it is attracted to a magnet. All stainless steels, with the exception of the austenitic group [300 series], are strongly attracted to a magnet.



Austenitic Grades

All austenitic grades have very low magnetic permeabilities and hence show almost no response to a magnet when in the annealed condition; the situation is, however, far less clear when these steels have been cold worked by wire drawing, rolling or even centreless grinding, shot blasting or heavy polishing. After substantial cold working Grade 304 may exhibit quite strong response to a magnet, whereas Grades 310 and 316 will in most instances still be almost totally non-responsive."

Almost all blades nowadays are one kind of stainless steel or another.  This is why they remain shiny with little or no care.