From: Michael Gunter 26/05/99 23:09:13 Subject: Metallurgy post id: 13910 When there is so much iron in stainless steel and austenitic steel (train tracks, I think), how come magnets don't stick to them? How can any smallish proportion of other elements in the alloy "hide" the iron dipoles from the external magnetic field? From: Di 26/05/99 23:27:06 Subject: re: Metallurgy post id: 13915 The main reason why most stuff is not magnetic i think is because the magnetic moment of one electron in an atom is cancelled by another in an atom orbiting in the opposite direction. From: Di 27/05/99 0:41:21 Subject: re: Metallurgy post id: 13924 Just looking up the composition by mass of Stainless steel. Find that there is a hell of alot Cr (4-27) and even Ni (1-22)in it. From: Alan 27/05/99 15:36:38 Subject: re: Metallurgy post id: 14181 Basically Michael your right. There is a change in the phase from ferritic to austenitic and hence the metal crystal structure from Body Centred Cubic to Face Centred Cubic, which hides the presence of the iron. Most of the commercial stainless steels are austenitic. But some are ferritic some are both (duplex) and some are martensitic. When I get home I'll try to post something which is a bit more complete. From: Alan 27/05/99 22:37:42 Subject: re: Metallurgy post id: 14286 Back again. Lots of posts today ... Thursday...mmm The martensitic & ferritic stainless steels are both magnetic. Even though the martensitic structure will not be BCC. If you remember back a month or two there was a discussion of freezing water water and I think Cam originally mentioned the Eutectic temperature. Well there are 3 other types of phase changes I'm aware of. Eutectoid which is effectively the same as a Eutectic except that it instead of a liquid transforming into two solid phases. It's a solid phase changing to 2 solid phases. A peritectic transformation involves a liquid and a solid changing to another solid phase. Similarly the peritectoid has 2 solid phases changing to a 3rd solid phase. The eutectoid transformation is important in producing stable austenitic phases / structures as the addition of small amounts of Nickel lowers the eutectoid transformation temperature significantly. The result is the at room temperature the austenite may be stable (or atleast unable (metastable)) to change into the ferritic structure. I should stay that Chromium actually contracts the austenic region but the Nickel has a much more significant effect causing its expansion. I'm calling it a region because the carbon content is important, think of a diagram show carbon content on the X axis and temperature on the Y axis. Then place a diamond shape in it which represents the austenitic phase. Chromium goes up the diamond gets smaller, nickel goes up the diamond gets bigger. Mangenese has a similar effect to Nickel in being a austenite stablising element. I hope this answers the question. It probablyt opens up a few others though. Ask quickly, I'm going away for a week, Saturday. From: Michael Gunter 28/05/99 11:24:32 Subject: re: Metallurgy post id: 14369 Thanks for that. I think I need to get more background info elsewhere before asking secondary questions on this one! No wonder stainless steel remained a holy grail for so long. It's obviously quite complex. From: Alan 28/05/99 20:06:34 Subject: re: Metallurgy post id: 14457 Michael Where did I loose you, so I cover it more concisely. As I said I'm away from tomorrow afternoon for a week. So better to ask today. Metallurgy in general is harder than most people think, it's also fairly logical and things fall into place after a while. I had friends doing Medicine who couldn't believe our work load or the subjects covered. I've done heaps of X-Ray work, ultrasonics, photography in general, sub atomic partical theory, electrical engineering, geology etc etc etc. Everything ends up being related both within metallurgy and all other sciences and engineering fields. This forum is un-moderated. The views and opinions expressed are those of the individual poster and not the ABC. The ABC reserves the right to remove offensive or inappropriate messages.