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This was quite a surprise to me: I went to my local ace hardware and bought some stainless steel button head screws for a high output pu I wanted to try. I realized tht they were probably hardened so I got out my torch and some ceramic blanket to anneal the screws, as well as a magnet to test for non magnetic. I tried the magnet on the screws before heating them up and I kid you not, they were non magnetic. The magnet I was using is a rare earth beast from a hard drive that will attract and hold anything with any iron in it (it will pick up chain from an inch away). The "Steel" screws that you can get from a hardware store aren't always very "steely" or ferrous, so test them before using. Maybe that's my new marketing scam "Non magnetic polepieces for quieter operation..."
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I'm thinking its normal for stainless steel to be non-magnetic.
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Most consumer grade stainless is non-magnetic...Comment
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You want your polepieces to be magnetically permeable or have the ability to carry magnetism. Generally C1018 or C1022 carbon steel is used most for screws, slugs and keepers. I bought some Cap Screws that are Alloy steel and they are magnetic...however the vendor doesn't give the mixture of alloys and their percentages. They were finished in Black Oxide.Originally posted by ShannonH View Post
Austenitic Grades of stainless steel (e.g., 18/10) have very low magnetic permeabilities and hence show almost no response to a magnet when in the annealed condition; however some steels in this category will show quite a strong response to a magnet, after substantial cold working e.g., Grade 304.Comment
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304 is magnetic after cold working? That I did not know. Do you by chance know what mechanism causes this?-MikeComment
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There are several types of Stainless steel. Most are non-magnetic, but there are som versions that are magnetic. The magnetic versions are either way more expensive (advance, super hard etc) or really cheep (because they have not used enough chrome and nickle. The most common version is often called 18-8 steel (18% chrome, 8% nickle, or the other way around, can't remember), found in decent quality kitchen zinks and that is not magnetic.Originally posted by dwhutchens View PostI'm thinking its normal for stainless steel to be non-magnetic.
Used to work quite a bit with stailess steel. I even used to know how to TIG-weld stailess...long time ago.Comment
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I'm used to working with
440C, so it was a surprise to me. 440C is magntic, but too hard for polepieces.Comment
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Fundamentally, there are three "kinds" of stainless steels: austenitic, ferritic, and martensitic, which each have a primary phase of austenitic, ferrite (which is what makes steel magnetic), and martensite. The microstructure is primarily determined by their composition. Of their composition, chrome and nickel are the two main ones that make a stainless steel "stainless". The 18-8 stainlesses (304 is the most common of them) that have been discussed in this thread are 18 wt% Cr and 8 wt% Ni. 440C is a ferritic stainless which has 18 wt% Cr and no nickel. 410 is a martensitic stainless which has 12.5 wt% Cr and 0.75 wt% Ni.
The stainless typically used for screws is 305, which is 17-19 wt% Cr and 10-13 wt% Ni. It's used for this because it has the lowest work and strain hardening rate of all the austenitic stainless steels.
That's intentional. Some grades of ferritic and martensitic stainless will rust, but it is only a light surface rust that doesn't completely doesn't completely destroy the metal over time like you would see with a common Cr-Mn steel. This is similar to what happens with bridge steels but they use Cu to get their corrosion resistance.because they have not used enough chrome and nickle
Article specifically about stainless steels and magnetism: http://www.mceproducts.com/knowledge...-dtl.asp?id=18Last edited by defaced; 05-10-2008, 05:37 PM.-MikeComment
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