Is Stainless Steel a non ferrous metal?

  • #1
rollingstein
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Main Question or Discussion Point

Read this quote on a major recycler's website:

"During this processing, we separate ferrous materials from nonferrous and further separate the copper, aluminum, brass, stainless steel, and other metals from the stream of nonferrous metals. "


Is Stainless considered non-ferrous? Why? Isn't it mostly iron?

Or am I misreading what they mean here.

http://www.omnisource.com/buy/?p=our_products
 

Answers and Replies

  • #2
tiny-tim
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hi rollingstein! :smile:

from the british stainless steel association (http://www.bssa.org.uk/faq.php?id=24) …

(motto: "making the most of stainless steel" … wow! who'd have guessed that? :rolleyes:)

Is stainless steel non-magnetic?

It is commonly stated that “stainless steel is non-magnetic”. This is not strictly true and the real situation is rather more complicated. The degree of magnetic response or magnetic permeability is derived from the microstructure of the steel. A totally non-magnetic material has a relative magnetic permeability of 1. Austenitic structures are totally non-magnetic and so a 100% austenitic stainless steel would have a permeability of 1. In practice this is not achieved. There is always a small amount of ferrite and/or martensite in the steel and so permeability values are always above 1. Typical values for standard austenitic stainless steels can be in the order of 1.05 – 1.1. See Composition effects on the magnetic permeability of austenitic stainless steels

It is possible for the magnetic permeability of austenitic steels to be changed during processing. For example, cold work and welding are liable to increase the amount of martensite and ferrite respectively in the steel. A familiar example is in a stainless steel sink where the flat drainer has little magnetic response whereas the pressed bowl has a higher response due to the formation of martensite particularly in the corners.

In practical terms, austenitic stainless steels are used for “non-magnetic” applications, for example magnetic resonance imaging (MRI). In these cases, it is often necessary to agree a maximum magnetic permeability between customer and supplier. It can be as low as 1.004.​
(se also http://en.wikipedia.org/wiki/Stainless_steel#Properties)
 
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  • #3
SteamKing
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Stainless steels contain a large percentage of alloying elements, chiefly chromium, which makes it prudent to separate this material from mild steel for recycling.
 
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  • #4
Chronos
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Strictly speaking, any alloy that includes iron is a ferrous material. For handling purposes, alloys that are non-magnetic are often considered non-ferrous.
 
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  • #5
rollingstein
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Gotcha! Thanks everyone!
 

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