Annealing stainless steel

[Glyn DaviesParticipant @glyndavies49417]

[Glyn DaviesParticipant @glyndavies49417]

I have some 3mm thick stainless steel that I bought from an autojumble. It is non magnetic. I need to saw, drill and file it into a large key shape. Is there any way to anneal it so it won't wreck my bandsaw blade?

[SillyOldDufferModerator @sillyoldduffer]

No one knows! Pretty much any steel that resists corrosion is called 'Stainless', irrespective of which of the 5 or 6 main families it's actually in. Some can be annealed, some are magnetic, some work-harden, others not. Some is extremely hard, other types machine reasonably well. As it was bought from an auto-jumble, the alloy is unknown, as is whether it's hot or cold rolled, or already annealed. I'd cut a bit off and experiment.

Generally I avoid stainless, but where I have used it the trick seems to be to keep cutting at all costs, applying plenty of force and cooling lubrication. If the stainless is the type that work-hardens, and the scrap I've picked up usually is – then any rubbing instantly makes the steel as hard as HSS and blunts the tool. If this isn't immediately noticed, the blunt tool causes work-hardening to go deeper making it difficult to restart; newly sharpened tools can be defeated at the get go.

Advice in my books about annealing Stainless varies considerably depending on the alloy, but they all require the temperature to be held for an hour and then call for rapid cooling. The lowest temperature I've seen for annealing a stainless is 270C, the highest – for a different alloy – 1100C. This is to fully anneal the metal; might get away with less heating because it only needs to be softened enough to cut. Which it might be already?

Not a fan of stainless in my workshop!

Dave

[Clive Brown 1Participant @clivebrown1]

If it's non-magnetic, then it's almost certainly an austenitic 300 series. This a tough material but not hard in the usual sense. It work-hardens locally when distorted by bending or cutting but can normally be drilled, turned without too much of a problem if lowish speeds and fairly deep cuts are employed, taking care not to allow rubbing.

Heat treatment to anneal work hardened areas would involve heating to 800+ degrees c. for a period.

As for a typical small bandsaw, I'd see it as bad news.

[OldironParticipant @oldiron]

I have found the best way to cut stainless plate is to use a 1mm thick cutting disc made for stainless steel in an angle grinder.. Cut as close to the line as you dare then use a sharp file to get to final shape.

regards

[VicParticipant @vic]

I had to drill and mill some slots into some 5mm thick stainless plate. The slots went ok but I let the drill rub on one of the holes. I had to heat part of the plate to cherry red before I could continue to drill it.

[SteviegtrParticipant @steviegtr]

I recently fitted a new 18tpi bi-metal blade in my band saw. Then made the mistake of cutting some stainless, pretty much wrecked it in no time. Not sure if it was a bad quality blade, the user or the stainless. The make of the blade is Morse from Ohio. I used to work a lot with Stainless for my work in the Food industry. Soft as butter to drill, but once it heats up due to drill rubbing, the jobs over. Even with a new bit, the part drilled hole was too hardened to get going again. 

Steve.

Edited By Steviegtr on 27/02/2020 18:43:24

[old martParticipant @oldmart]

For the type of SS which work hardens, a sharp drill, low speed and high rate of feed will usually get the best results. Never let the drill dwell, or the rubbing will harden the surface. I burned up a cobalt hss drill on a stainless digital scale (like the calipers have) and had to resort to solid carbide.

[Glyn DaviesParticipant @glyndavies49417]

Thanks for the replies. This is what I want to make (a means of attaching the dog to a seat belt socket!):

I think I'll cut a rectangle out with an angle grinder and put it on the gas ring for a while, quench and see how it cuts with a saw. The square of 3mm plate I bought from the autojumble had been cut with a press brake, so it's obviously cuttable with HSS.

As an aside, I am surprised to find that my Draftsight is still working – they said unless I paid a subscription it would be gone by Christmas.

Edited By Glyn Davies on 27/02/2020 22:39:59

[Neil WyattModerator @neilwyatt]

I know we all love making things ourselves, but you can buy these with a short starp and a quick release clip for £1.99 on eBay, UK stock… cheap enough to bin if it's no good, but you could always keep the 'key' part.

I'm not sure I would trust a cheap child restraint from eBay but if it's just to stop the dog from taking over the driving…

Neil

[Glyn DaviesParticipant @glyndavies49417]

Thanks Neil. I've ordered one of the ebay straps but the tongue part comes with a slot and I want a ring. And if I don't have a go at making it, that square of stainless will just sit their until I've shuffled off..

This was prompted, by the way, by Cheshire Police announcing that any drivers caught with unrestrained dogs will get done for driving without due care. Despite the fact that our Stanley sits happily behind the rear seats of the Focus either looking out of the back window or dozing on his bed.

[Glyn DaviesParticipant @glyndavies49417]

Just to wrap up. I used a hacksaw to cut out a rectangle from the 3mm plate, heated it to red on fire bricks and quenched. Result – no softening. I then reheated it and let it cool naturally. Result – no softening. So then it was a couple of hours with the angle grinder with a 1mm cutting disk, disk sander and files and voila – job done. I put it in the 4 jaw in the lathe to drill and bore the 25mm hole. But no more stainless for me, thank you!

[Nick HulmeParticipant @nickhulme30114]

Stainless has nothing to do with this sad story.
The cheerful purchase of Mystery Metal because it is seen as cheap is the story here.
If you buy known materials you can look up heat treatment and cutting speeds, this saves you looking like the chump who has bought Scrapbinium cheaply and now cannot do anything with it.

[Glyn DaviesParticipant @glyndavies49417]

Who said it was cheap?

[Neil WyattModerator @neilwyatt]

I confess, when I have the dog in the car I just tie her lead to the headrest's leg (she wears a harness not a collar).

Neil

[Nigel BennettParticipant @nigelbennett69913]

I recall a chap who used to take his dog "Badger" out in the car. He just used to fling the poor thing in the boot of his Mini. He told me he found pawmarks on the underside of the rear parcel shelf after an enthusiastic drive to the walkies area. Dog must have been daft as a brush, as it apparently jumped into the boot of its own accord quite happily when a walk was in prospect. So no restraint needed!

[Alan JacksonParticipant @alanjackson47790]

The problem with stainless steel is that carbon carbide and chromium like each other too much and at high temperatures form austenite which is a solid solution of one mix. The affinity is so strong that it does not come out of solution very easily. This is the very fact that makes stainless steel stainless, Its the dissimilar mix of ferrite and iron that make carbon steel go rusty.

Alan

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