Stainless steel magnetism

E

elementfe

Joined
May 3, 2008
Messages
1,436
Curious- what makes certain stainless steels magnetic? I have a few pieces in a drawer that I neglected to mark, mix of heat treated and not, either CPM154 or 440c...some are magnetic and some aren't.
Is that a useful tool, failing proper identification to tell the two apart, or is there a whole lot more going on?
All the pieces and blades that I KNOW are 440c are very attractive to magnets.

Thanks!
 
Its not the iron, its the alloys. 300 stainless has nickel as well as chromium. It is not magnetic because of the structure. 400 Stainless has no nickel, and is magnetic.
In any case, stainless is not nearly as magnetic as carbon steel.
 
Very interesting article, thanks!
I just tested a few finished blades, out of curiosity- again, mix of 440c and CPM154. All are attracted to magnets except one of the CPMs...and this one was treated just like the other, with a subzero quench...so it's hardly austentitic.
Lots of mystery here, thanks for the responses.

edit: In case anyone is interested, this article http://www.mceproducts.com/knowledge-base/article/article-dtl.asp?id=18 implies that martensitic stainless steel is easy to magnetize but very difficult to demagnetize...and that it should be attracted to a magnet.

Stacy, thanks for your response, I think I get how that works...a little- that's why I think it's odd that a blade wouldn't be magnetic. It's hard (file test) and unless someone pulled a fast one on me I know the history of it. How could 154 NOT be magnetic, given the alloy?
 
Last edited:
CPM 154 is essentially 440C with added molybdenum for enhanced edge-holding and through-hardening.
Both are martensitic, and should be ferromagnetic at room temperature.
I'd guess either one of your steels is 300 series (or aluminum, or something else entirley) or something untoward happened in the heat treat.
Martensitic steels do often go non-magnetic when heated (to red, I believe. Properties of Materials was a few years ago now.) But, these typically return to ferromagnetic as they cool down.
 
Austenite, ferrite , and martensite are the three structures you find in steel. Austenite is non-magnetic but ferrite and martensite are magnetic.But it's really a physics question not metallurgy. Confusing since ferrite is magnetic at RT but non-magnetic at higher temperatures but magnetic again at higher still higher temperatures [Delta Ferrite ] .We sometimes use temperature to help us HT , the conversion is the Curie temperature of 1440 F [?]
 
The Curie point, above which steel becomes non-magnetic, is around 1414 deg. F. The addition of nickel lowers both the Curie point and the temperaure at which austenite becomes stable. Enough nickel to make austenite stable at room temperature, as in 3xx stainless steels, is enough to lower the Curie point to below room temperature. It is also related to the structure. 301 stainless is austenitic at room temperature, and non-magnetic in the annealed conditon. However, cold work hardens it and the structure changes to martensite, and it becomes magnetic again. It is also possible to have magnetic austenite with the right combination of temperature and steel chemistry. 1080 (or close) will fully harden (HRc 66-68) when quenched from 1350-1375 deg. F.
 
You must log in or register to reply here.
Back
Top