Are All low carbons created magnetically equal

[BrassMonkey4]

I looking to hand build various loud speakers just for fun, both a subwoofer mag assembly and ribbion tweeter. I've found rod, bar and sheet 1008 low carbon steels in mcmaster.com but it doesen't say anything about their magnetic properties.

My question is can any 1008 low carbon steel be used for mag assemblies or do I need to look for more than just the carbon content to know if its usable? and if so what do I need to look for and where can I find a small quantity vendor? thank you

 

[MagMike]

The short answer to the question in your subject line is: No, not all low carbon steels are magnetically equal.

You won't find magnetic properties for the material from McMaster Carr because it is prettty rare for a steel mill (with the exception of Carpenter, but then you have to buy the entire melt) to process steel to optimize the magnetic properties. They are more focused on controlling chemical composition and/or mechanical properties. Most purchasers of steel aren't buying it for magnetic applications.

However, the differences between different grades/batches/lots will probably only be evident if you are pushing the envelope on a design. For hobbyist use, I doubt you'll see much of a difference. The 1008 should serve you well.

 

[EdStainless]

At this level of work the annealing probably makes more diff than minor chemistry variations.

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Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[sreid]

For your application as long as you keep the field strength at or below 1 Tesla, any low carbob steel will be OK. The reluctance of the steel is so low that compaired to the air gap the steel's reluctance is often assumed to be zero.

 

[BrassMonkey4]

Their in lies the problem. I'm trying to make a very high efficiency driver the efficiency of the driver is greatly dependant on field strength so I'm basically trying to build as strong of a field as possible with attainable materials. I'll be using Neo magnets and probably pushing near saturation of the steel I fear. Does anyone have a source for small quantity steels with a higher level of permeability. Or is their anything I can do to increase it in these materials from mcmaster, someone mentioned annealing is that’s something a hobbyist could take on?

Forgive me for my amateur knowledge

 

[EdStainless]

To all three questions, probably not. Sources of high perm material are not common. If you can find "enameling iron" or some low carbon ELI (extra low interstitial) or deep draw material you should be on your way.
Annealing takes high temp and very dry hydrogen atmosphere. It is an easy heat treatment, but not simple to do.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[dgallup]

If you are pushing the steel into saturation forget about high permeability. Relative permeability is approaching 1 as you reach saturation. That is the definition of saturation. What you need is high saturation flux density. The only things higher than pure iron are the iron cobalt alloys. Hyperco 50A will hit close to 2.4 Tesla. This is not hobbyist stuff.

 

[unclesyd]

You should look at the Silicon Steels for your core.

http://www.key-to-steel.com/Articles/Art101.htm

http://www.alleghenytechnologies.com/ludlum/pages/products/xq/asp/G.5/qx/ProductLine.html

 

[MagneticIronGuy]

Dear BrassMonkey4,

I have/do supplied/supply our CMI-C electrical core iron for audio speaker applications. Our Rod/Strip grades are specially melted with only "magnetics" in mind. Our Rod diameters fall in the .02% max. Carbon range and our strip is melted to a .008% max. Carbon level. I would use caution when thinking about IF steels and generic low carbon grades when you are trying to achive the lowest coercivity value that you can achieve in the Carbon family. ie. magnetic aging, fine grain structures, expensive decarb annealing without consistant results. Our core iron product has a great advantage in Low-Medium inductions of 15,000 - 18,500 gauss. In higher inductions our CMI-C has the ability to get to 21,500 gauss. SAE1008 would be in the area of 5,000 - 6,000 gauss due to a much finer grain structure coupled with a much higher Carbon/Nitrogen content. PS- I am a small and large quantity supplier of these grades.

Let me know if I can help!

lloyd@cmispecialty.com