I’m working temp in an Architecture firm. One of the designers is using a stainless steel wall in a kitchen. I said something like, “Cool! magnets!” She said that stainless steel is nonmagnetic. I told her she was crazy. She insisted that some stainless steel is nonmagnetic. I said steel is made of iron, end of story. She said nuh uh.
Am I gonna hafta admit I’m wrong? or is she nuts, like I said?
You are wrong. Many varieties of stainless steel are nonmagnetic. Stainless steel contains iron, but it also contains chromium and nickle - apparantly enough to render it nonmagentic.
Of course, as long as there is some reasonable % of iron, there will be some detectable magnetic properties- but not enough for a typical refrigerator magnet to stick to. There are many many “stainless steel” alloys- and some will rust, note.
Some of the el-cheapo stainless steel flatware in my utensil drawer at home sticks to refrigerator magnets (and tends to rust a tiny bit if it stays wet for a long time). The better stuff doesn’t stick to magnets (and never rusts, either). Maybe you could try this experiment and see firsthand?
So how much iron does steel need to contain to be called steel?
How much iron does steel need to be magnetic?
What’s the overlap or gap?
I don’t think it’s so much the dilution of the iron content by the other constituents of the alloy, that renders it nonmagnetic (after all, you could mix 30% iron filings with 70% candle wax and I think it would still be attracted quite strongly to a magnet - I think it’s the effect they (the other components of the alloy) have on the crystal structure (or something like that) of the metal.
It depends on the alloy and how it’s been worked. Most stainless will be nonmagnetic if annealed.
304 is the most common alloy, and would likely be the material used in a kitchen. Its magnetic properties are very dependant on how it’s been worked.
Bingo.
Iron, carbon steel, alloy steel, and ferritic stainless steels (like automotive exhaust pipes or cheap stainless silverware) form body-centered cubic structures at temperatures below 727 degrees C. In iron-containing alloys, this composition is known as ferrite, and behaves ferromagnetically; i.e., magnets stick to it.
If the temperature of any of these materials is raised above 727 C, the material will undergo a solid phase transition, forming a face-centered cubic (also known as cubic close packed) structure. Iron arranged in this formation is known as austenite, and loses its ferromagnetic properties.
Now, if you have a stainless steel with a sufficient amount of chromium, say 16-25% by weight, plus some nickel or manganese, it will stay austenitic even at low temperatures. Hence, nonmagnetic austenitic stainless steels, such as you might make a kitchen sink or coffee mug from.
Also, aren’t US Navy ships degaussed to make their steel hulls non-magnetic?
Again, this would have nothing to do with the steel composition but rather the arrangement of the steel at the molecular level.
Degaussing will remove stray residual magnetic stresses (the ship won’t act as a permanent magnet after degaussing), but it won’t affect its molecular structure; a ship made of HSLA-65, will still have a ferritic microstructure, and will still react ferromagnetically to an external magnet.