Heat treatment of soft magnetic materials
Heat treatment of soft magnetic materials
(OP)
Does anyone have recommended sources for low volume heat treatment of soft magnetic materials that would include magnetic bias during the thermal process schedule? The objects may be up to 5 feet in length.





RE: Heat treatment of soft magnetic materials
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Plymouth Tube
RE: Heat treatment of soft magnetic materials
RE: Heat treatment of soft magnetic materials
RE: Heat treatment of soft magnetic materials
The bigger problem is you want to apply a transverse field, i can hardly imagine any one has such huge unit. Are you trying to have a linear B-H curve, so a stable permeability at varying H? Not all soft magnets can be induced magnetic anisotropy by HT at the presence of a magnetic field.
as for Fe-Ni50, you donot want to HT with a field at 447C, which is too high, very close to its curie temperature. The bias field has no use at all at 1180C
RE: Heat treatment of soft magnetic materials
But then I also thought that this was only done with special alloys.
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Plymouth Tube
RE: Heat treatment of soft magnetic materials
Thank you for your advise. As I review the HT instructions for soft magnetic materials I think I am gaining an understanding of the process. The HT at 1180C (1177C upon further review) is an anneal/stress relief step and applied bias has no effect. The anneal is combined with dry H2 which acts as a reducing agent to prevent surface corrosion/oxidation and remove impurities from the material if the anneal temp is held long enough. This is diffusion process which explains why the extended dwell time is required. Then the temp is lowered to something less than the Curie temp and a magnetic field is applied. Your comment on the dwell at 447C being too close to the Curie temp is well advised. Upon further review the recommended temperature for gain growth is 427C for either Permalloy 50 or 430FR. There are similar but lower numbers for Cobalt alloys. At this stage apparently the grain structure of the alloy grows resulting large grains. Now this will also occur in the absence of an applied field or the ambient Earth's field. I don't think the grain size is a strong function of magnetic bias. So the bias must act to align the domain axis(?). The intent is to linearize the B-H curve (i.e. minimize the internal area of the B-H loop) so the remanence is minimized. I believe there is a facility in FRG that can perform biased HT on medium sized objects however I was hoping a domestic capability was present. It has also been suggested that HT without bias may be enough to linearize the B-H curve. So does it make sense that large grain material would result in lower remanence (with or without magnetic bias during HT)? Please keep I mind that the object is not a thin film and is bar/rod in form. Again, thank you for your advise.
RE: Heat treatment of soft magnetic materials
A magnetic bias annealing has nothing to do with grain size ro grian growth. Actually as for Fe-Ni, at 400-500C, there is no grain growth, since the temperature is too low. The bias magnetic field is to help form a preferential alginment of like-atom pairs. due to low temperature, the hold time is long for a slow atom diffusion.
the bigger the grain, the smaller the coercivity, so the smaller the BH area (only apply to traditional materials, not for nanostructured materials). however, the grain size doesnot have much relationship with remanence, the shape of BH does. Low remanence doesnot necessarily mean small BH area.
Annealing in an H2 to Remove impurities (C, S etc) is not effective for bar/rod products, while it is one of main purposes for strip products.