Bending stainless - hot or cold?

[srp]

I want to make a couple of bracing straps from 316 stainless strip, 400mm long x 30mm x 3mm. Each strap will have two bends in it, one around 75 degrees and the other 15, ideally with a tight radius, say 6mm.
Is it best done hot or cold? If hot, does it need any special treatment to prevent brittleness, like annealing or stress relief?

 

[Clyde_Wanderer]

Stainless can be bent cold without weakening it, and it can be bent heated too, but takes a lot of heat and makes for more work polishing it up after if you want it polished.
I am just after makink a new deck plate for the rear stay, which the old one was 3mmx40mmx500 long, the new one I made is 6mmx same demns as above, I had to bend it at the top end, just put it in the vice with cardboard to protect it fron getting marked and used a mallet, bent no bother.
I also made new bow roller plates which were 8mm thick, and had to bent the front leading edges of them, heated it with an oxyacetlene kit, it did take a lot of heat as the bend was close to the edge so not a lot of leaverage.
Will put on a pic later if I can.
To polish, use a linisher wheel and phenol saop.

 

[roger]

I've bent 4- 5 mm. SS strip using a butane blow torch. You need to get it glowing a bit. This is not too difficult as Stainless is a relatively poor conductor of heat.
The main problem is bending something very hot without it cooling too much or burning you.
Its a case of heat it up, slam it in the vice, tighten vice and bend it at once. Sacrifical bits of wood in the vice keep it warmer but beware fire.
With strip the edges can "lag" behind the rest of the bend (i.e. larger radius and you may need to do some filing to finish the job off.

 

[Avocet]

What sort of equipment do you have at your disposal for bending it? If you were going to put it in a vice and bash it with a hammer, be really careful about leaving vice marks in it which could subsequently start fatigue cracks (depending on how it is loaded). The best way would be in a proper "press brake" and I'd prefer to do it cold so that I (a) don't have to re-polish, and (b) work harden the material so it ends up even stronger in the vicinity of the bend.

 

[Norman_E]

If you do bend it in a vice remember that a sharp bend will be a stress raiser. I have a proper metal bending tool but it does not quite accept 30mm wide strip.

Without such a tool the best method is to do it cold but to as big a radius as you can accept, bending it by placing it between a steel engineer's vee block and a piece of round bar, and squeezing the assembly in a big vice. You can protect the steel from being marked by the corners of the vee block by inserting a piece of thin aluminium between the steel and the vee block.