Bending stainless steel

[Joe_Cole]

I want to bend some stainless steel.

What is the best way of heating it to avoid discolouring it? Alternatively how best to repolish it after heating?

Or should I bend it cold (which will be difficult)?

Joe


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[charles_reed]

Don't heat it, stainless is always bent cold.

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[JSB]

Hi Joe

I had a S/S guardrail bent by a passing fishing boat, took it off put it into the vice, put a length of scaffold pipe over it and tried to bend it straight, waste of time, no movement. Went round to a friend who heated it red hot with a calor flame torch (fearsome tool) straightened it easily. Polished up without a problem but I do not know what grade S/S it was.

John

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[ongolo]

Depends what you want to bend, heating it might be the only way. Heat to dull red. Anything over 200Cel will begin to discolour steel, stainless will begin to color a little later.

Best way to polish is electro polish. Depends on the quantity and part size, it can be done quite easily. The setup is similar to electroplating, but the process is different and so are the chemicals used.

I do not have the exact concotion with me on the boat now, but Nigel Calder's book about corrosion has the method and formulae.

There is also a paste available that removes the stains and discouloring.

regards ongolo


<hr width=100% size=1>1000 dream about it, 100 talk about it, 10 start and 1 completes it

 

[ongolo]

When you heat stainless, make sure that your flame has excess oxygen that is an almost transparent light blue sharp flame.

Avoid excess acetylene or other heating gas excess indicated by a silvery whitish feathery soft flame. The latter carbonizes the stainless steel leading to a number of problems.

regards ongolo


<hr width=100% size=1>1000 dream about it, 100 talk about it, 10 start and 1 completes it

 

[Birdseye]

if you can bend it cold, then do so. otherwise heat with a torch as little as you can get away with and as quickly as you can. any discolouring will only be surface and can be removed with a polishing mop and the correct soap (any difficulty with supplies, try one of the custom motorbike mags - they use these materials)

risk is not just discolouration, but grain growth and subsequent rusting ie as bad as mild steel.

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[Avocet]

Is it tube you're thinking of bending or sheet? If its tube (e.g. for a pulpit) you could try "sand bending". You get the length of tube and weld a cap on one end then fill it with dry sand. you'll need to tap it down well several times until you can get no more in. When it is completely full, weld a cap on to the other end. You should now be able to bend it without reducing the diameter at the bend or ovalising the tube. You can then cut the caps off and empty the sand out when you're happy with it. Note that you only get one go. Stainless work hardens like you wouldn't believe so it's almost impossible to straighten out an incorrect bend - even slightly! I'm told you can polish the discolouration out of it if you end up heating it but I don't know what's best to use - probably something like "Solvol autosol" but it might take a while!

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[Gunfleet]

Machine mart make a device for bending it, basically a haydraulic pump and a set of dies. It's not too expensive and does the job perfectly in a minute or two.

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[PeteMcK]

Because..

the most commonly used marine stainless alloys attain most of their strength through having been cold-worked. Heating sufficiently to make the metal easy to work will anneal it, making it permanently soft, and will reduce its yield strength by about 2/3. Other than by cold-working (practically impossible for a finished component) there's no way this strength can be regained.

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[Joe_Cole]

Re: Because..

Thanks for you help everyone. It's more complicated than I had hoped! Ah well, that's boating!

Regards

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[ongolo]

Re: Because..

It would be fantastic if that were so, then it would be possible to at least eradicate two of the reasons of stainless steel failure, namely the results of brittleness by work hardening and stress corrosion, both caused by s.steel becoming too hard.

I have never noticed any difference that ss gets ever softer due to welding with one of the three methods available to me. Machining it after wards (milling/turning/drilling or grinding), I would certainly notice that only 33% of its strength or hardness remains. Bening cold introduces much unwanted stress to begin with.

Sheet metal gets bend cold here, roundbar and flat gets warmed up. If anealing would work to make it soft, one could actually use s.steel for black smithing, which is totally impossible. Black smithing being one of my many hobbies.

Are you sure you dont get mixed up with carbon or tool steel?

<hr width=100% size=1>1000 dream about it, 100 talk about it, 10 start and 1 completes it

 

[30boat]

Re: Because..

I was thinking along the same lines...

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