Magnetic Permeability: 1008 vs 1018

[Rachel_CleanEnergy1]

Hi All,

I'm trying to find out the difference in the magnetic permeability between 1008 and 1018.

I have been trying to find the BH curves for these materials and also been reading some relevant threads. I understand that cold work and heat treatment play a very important role for such materials and permeability can vary vastly from supplier to supplier. Let's assume the cold work and heat treatment are the same for 1008 and 1018. Will there be a large discrepancy in the permeability between these two grades of carbon steel?

Thanks!

 

[EdStainless]

There will be a big difference.
The 1008 has lower C and lower Mn, which will increase max perm.
The Si level could also be a significant factor, lower is better for soft properties.
Find a copy of Ferromagnetism by Bozorth, it has curves for commercial steels and high purity Fe.

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

For a magnetic application, you 'd better full anneal them. And in this case, the difference is big.
But if both materials are cold worked, there will be less difference, since the magnetism now is controlled by stains, defects etc.

 

[EdStainless]

And by anneal we mean at 2500F in dry hydrogen, it will remove strain and lower the C levels.

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P.E. Metallurgy, Plymouth Tube

 

[Rachel_CleanEnergy1]

Thank you so much!

I just got a copy of the book Ferromagnetism. After a quick scan, I found the second chapter, Magnetic properties of materials most relevant. I noticed from the graphs that permeability is strongly influenced by carbon content and heat treatment.

However the book discusses about magnetic properties of pure iron and a variety of alloys(Iron-silicon, Iron-nickel, etc. Since 1008 Steel has Iron, C, Mn, Nickel and some other contents in it, I'm wondering what kind of alloy is 1008 or 1018 grade steel defined as? Should it be Iron-carbon alloy?

 

[EdStainless]

Make sure that you are in a chapter on soft magnetic material and not permanent magnets.
These are basic Fe-C alloys, there is little else in them. Everything else added together is <1% total (or it should be).

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P.E. Metallurgy, Plymouth Tube

 

[hacksaw]

what is your design intended to do? otherwise you are only dealing in the abstract...

 

[Rachel_CleanEnergy1]

Thanks for the reply!

We primarily use the material in heat exchanging systems and we want the permeability to be as high as possible. However when I called up the suppliers of 1008 or 1018, most of them don't anneal the material in their production.

For those who are familiar with the industry, is it possible to get well-annealed 1008 at all or it's common to buy the material and send it for annealing in another workshop?

 

[EdStainless]

If you are concerned you will want to handle the annealing.
The process heat treatment is usually a normalize or a stress relief.
Just be warned that if you actually anneal the material likely won't meet the original specification, it will have significantly lower mechanical properties.

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

Normally you will get mill annealed product, if the finish part does not experience much cold work, people sometime use as-is. However, for the best magnetic properties, finish fabricated arts must be full-heat treated. To achieve the most magnetic permeability, relatively low temperature at wet Hydrogen can be used to effectively remove carbon; when annealing at temperature above 950C to maximize permeabilities, use dry H2. the higher temperature the better, say 1100-1200C. 2500F Ed mentioned above is too high for most heat-treaters.

 

[dgallup]

Please explain to me the importance of magnetic permeability in a heat exchanger system. I must be missing something.

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[Rachel_CleanEnergy1]

Thanks for your insights on annealing. We develop energy-saving technology for conventional heat exchanging devices and that requires high magnetic permeability of the material.

On a side note, while I found most metal suppliers unable to anneal 1008 sheets(for fear of warping the sheet as we are looking for 24 gauge or thinner), tube suppliers do anneal their products as a common practice(the wall thickness of the tube is equally thin,0.3-0.5mm). My question is, does annealing or relevant thermal process affect the shape of the material(could be sheet or tube) if it is very thin?

Thanks!

 

[dgallup]

What possible connection is there between magnetic permeability and heat transfer???? Please explain the physics.

EDIT: Found it, new to me.

The magnetocaloric effect can be quantified with the equation below:

where T is the temperature, H is the applied magnetic field, C is the heat capacity of the working magnet (refrigerant) and M is the magnetization of the refrigerant.

From the equation we can see that magnetocaloric effect can be enhanced by:

applying a large field
using a magnet with a small heat capacity
using a magnet with a large change in magnetization vs. temperature, at a constant magnetic field

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[dgallup]

If you want to maximize permeability, there are a lot of far better materials.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[EdStainless]

But mild steel is the only one that he will find commercial tubing in.
Fro a realistic anneal Ben is right, 1150-1200C in very dry hydrogen is a realistic treatment.


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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

I, too, am interested in the physics behind. I think it unlikely be magnetocaloric, but maybe simply the induction heat? because 1008 is tube form, it is not used as the core, but used as the portion to be heated up from AC field. If all these assumptions are correct, a big advantage of a high permeability is to decrease the skinning depth, so lower frequency can be applied to increase heat exchange efficiency. The contribution to heat from hysteresis losses due to ferromagnetism is relatively low, compared with eddy current heat. And also, higher permeability does not necessarily mean higher magnetic hysteresis heat.

on a side note, except for the availability of form (tube), mild steel is much cheaper than other materials. E.g., 1008 could be sold at $1 per lb vs electrical(pure) iron at $15 per lb.

 

[hacksaw]

Certainly an interesting discussion, by the way what temperatures are involved in the heat transfer product?

 

[Rachel_CleanEnergy1]

Thank you everyone for the kind replies. They are very helpful.

For the physics involved this application, what Ben pointed out is most relevant; we take advantage of the fact that high frequency alternating current flows through the outer layer of the conductive tube, decreasing the skin depth and eventually promoting the thermal performance of the system. Therefore the higher the magnetic permeability of the material, the better the performance. But still, as Ed and Ben mentioned, we have to take into account of the cost and availability of the material. At this stage, we are trying to find the best option that has good magnetic properties and also affordable price and market availability.

Again really appreciated your help. Your suggestions and insights will guide me in my further research and tests.

 

[hacksaw]

Puzzled that skin-depth should affect thermal performance in any meaningful way.

Does the group have any insight into what the OP is trying to accomplish?