Stress relieving 316L 1

[machining pro]

My company is currently buying sheet material. Our parts are 13.00Long x 6.5 wide X.031 thick. Because they are blanked out of coil material, they have a curve in them. This makes our machining process difficult to have consistent dimensions. My though was to stress relieve them flat. Is this possible and does anyone have furnace parameters to do this. We do have a SECO vacuum furnace if that even matters.

Thanks

 

[3DDave]

Normally there are flatteners to remove the curve from the coil. Vacuum holding fixtures are used to hold non-flat material flat during machining.

I don't think you can stress relieve your way to flatness; stretching is one method when a flattener isn't used. It certainly works for small diameter wire.

For anyone who hasn't seen them:

https://www.thefabricator.com/thefa...eners-and-levelers-for-coil-processing-part-3

 

[EdStainless]

Coil stock is commonly mechanically flattened.
It involves a set of top and bottom rolls in the offtake.
Thermal treatment is a poor option.
Any temp above 800F (425C) is prone to cause damage to the microstructure.
And those temps are too low for good strain relief.

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P.E. Metallurgy, consulting work welcomed

 

[geesaman.d]

Stress relief will relieve uneven stresses. Coil sheet has very even stresses that make its natural shape - a coil. So I agree you need a flatting or slight reverse roll operation to make the natural shape flat again.

Also, 300 series can be very difficult to stress relieve. So perhaps you can be thankful you don't have a reason to wade into that muck.

 

[machining pro]

Thanks for the advice. We are planning to build a vacuum chuck for our process. Does anyone have any knowledge of a hand roll/flattening machines for testing purposes?

 

[geesaman.d]

We are using something like a McMaster-Carr 23815A11, which is fully manual but easy to use. In our case we're taking flat sheets and curving them into 350 degree pieces of a varying diameters and we have full-scale printed template taped to the machine so the operator knows when they have it curved to the correct diameter. I imagine this will allow you to straighten and manage the variation in roll diameter. I couldn't find a brand name or model on our unit.

 

[EdStainless]

You could try looking at people that supply tools for forming sheet metal.
You should also go back to your supplier (and others) and tell them that you need it flatter.
I find it hard to believe that someone that uncoils metal for a living doesn't have a flattener.

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P.E. Metallurgy, consulting work welcomed

 

[MagBen]

The machine is called SBL (stretch bench lever). I think any strip manufacturer has such machine to flatten the strip. you can often request to have a coil set requirement. you will have a more or less coil set for any strip product, the softer the higher coil set. increasing the core diameter can decrease coil set when coiling. or just simply ask for straight and cut operation, instead of coiled strip product.

stress relief 316 can ruin your material. i saw hardness clearly increase at low temp anneal, you are not softening but actually "harden" material.

 

[EdStainless]

There are also roll levelers that used multiple top and bottom rolls to gently flex the material and even it out.
These usually require continuous feed material such as straight off of the coil.
Bigger ones are motor driven (think 500hp to flatten 0.75" coiled SS)

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P.E. Metallurgy, consulting work welcomed