Magnifer 7904 heat treatment

[marcus4]

Hello. Please help me understand the detail about the "Take-out-temperature " of the soft magnetics 7904 material. I don't fully understand the therm "Service temperature" at figure 7&8 site 7 of the data sheet

https://files.engineering.com/getfi...d2d9f11177ef&file=Data_Sheet_VDM_MAG_7904.pdf

I understand that it's very important for the final permeability but can't figure out exact procedure.
Thanks

 

[EdStainless]

Use figure 7&8.
What is your service temp?
Does your service depend more on initial perm or max perm?
Find the take out temp that matches your needs.
Then anneal at 1200C for 4 hrs, allow to cool in the furnace at a rate of 0.9C/min
And then remove and force air cool when you reach the desired take out temp.


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[IRstuff]

From the same datasheet, which is pretty much what I thought from the figures

Different chemical compositions, especially in terms of the contents of the elements Ni and Mo, influence the most favourable annealing parameters such as the cooling rate and the take-out or tempering temperature in order to obtain optimum magnetic properties.

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[marcus4]

Please correct me if I'm wrong."Service temperature" is nothing else but operating temperature?

 

[EdStainless]

exactly right about the temp

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[marcus4]

So, if the part will operate at the service temperature 20-30c I should proceed with the take out @ 490-500c for the best magnetics properties?

 

[EdStainless]

Using 495C will give you the highest initial perm at your use temp.
And it is very close to the peek of the max perm also.

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[marcus4]

495c, thanks, clear. But looking at the cooling rate of 0.9k/min (4c/secomd, right?) it can be really tricky. Or I miss something here again?

 

[EdStainless]

You are correct, that is tricky.
At high temps that will require a programed ramp to not cool faster.
At low temps you may need to assist the cooling a little.

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[IRstuff]

Even trickier, that temperature presumably relates to the bulk material temperature, and not just the environmental temperature

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[marcus4]

All clear. Thanks guys

 

[EdStainless]

When we did alloys like this we always used forced convection furnaces.
Better uniformity and control.

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