Stainless Steel - heat treating

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Shaftoflame · #1 Post by **Shaftoflame** » Tue May 02, 2006 5:59 am

Hi There
I have some stainless spring stock, sent to me as a sample years ago so I could set the carb slide heights on the RD (have 1.0mm nad 0.7mm) I was expecting about 10cm of each but they sent me about 30M of each... Have been using it off and on for small pointy tools - and a set of feelers for the RD carbs. However have just tried using some for its purpose - making a small compression spring. I think the stock is half hard, and does not wind tight to a former, so I tried heating to cherry red and air cooling to anneal it. made a difference amd wound the spring, cut to length etc - lovely. However in what I would guess id full soft, the spring quickly takes on a compression set (why are we surprised?) Tried to re harden by heating to cheery red and quenching in water - seemed reasonable being as annealing worked. I have a now even softer stock, which has a distinct black crust. Any suggestions from those with some 'real' knowledge as to how to re-harden? I cannot ring and ask either the supplier - forgotten who it was, do not remember the spec of the stock etc, nor the company I worked for when I got it as they have gone bust....

Thanks

R

Jeff B · #2 Post by **Jeff B** » Tue May 02, 2006 6:00 pm

Without knowing what the material is it's difficult. I'd suggest finding a book about heat treating stainless and try the different recipies that the different kinds of stainless use. Are you sure it's spring stock? Hardenable stainless steel is quite expensive. For instance I've heard 420 and 440 air hardening stainless steel is twice as expensive as 304. Comparing what you paid for it to equilivant size and length in a new material cataloge might help you figure out what it is and what to try for hardening it.

#3 Post by **hybrid** » Tue May 02, 2006 8:36 pm

Quenching in water always makes the metal softer! Thats what annealing is.
The slower it cools, the harder the metal should be.

You could try burying it in cement powder, or limestone powder or something like that after its heated. That should cool it slower than air.

#4 Post by **smurph** » Wed May 03, 2006 2:21 am

If your work piece softened up after quenching in water, then the stainless steel is probably of the austenitic variety. This type of stainless cannot be hardened with heat treatments with high temperatures. Only Martensitic stainless steels respond to heat treatment hardening of the variety that we are used to (heat and quench).

The way to tell what if it's austenitic or some other type of alloy is by seeing if a magnet will stick to it. Use your newly softened (anneald) piece to test. If it has no ferromagnetic properties in the annealed state, the magnet will not stick and it's most likely of the austenitic type. If a magnet sticks, it is of either martensitic or ferritic type. If a magnet will not stick to your hardened samples, it is most definitely of an austenitic type.

About the only way to harden purely austenitic type stainless steels is to cold work it, also know as work hardening. Try taking the soft piece you created and pound it with a hammer. It may harden up pretty quickly. But this could be a set back to the desired shape!

It could be a precipitation hardening alloy variety, even if the metal has austenitic properties in the annealed state. In which case, heating to 650-750 degrees F (relatively low heat) will cause it to age harden. Depending on what type of alloy it is, magnets may or may not stick to the metal in the hardened state.

I hope this helps you find out a little more about what you have, at the least.

Steve

Shaftoflame · #5 Post by **Shaftoflame** » Wed May 03, 2006 1:39 pm

Hi Guys - thanks for the assistance.

Is it spring stock - yup know that one.
Compare price - well it was a free sample and I have had it aboiut 15 years....

Bash it up with a hammer - thought about it.

Have been playing though... forming the spring onto a 6mm mandrel (? right term?) it would spring out to about 9 to 10 mm ID when released. However, running it onto a 2.5mm mandrel casued it to hold on tight and I had to twist it off, so used 4mm and it released just nice to fit a 7.5mm hole. Now need to have a play and see if I can get the right amount of pressure from it.

Oh it is magnetic in its 'untreated' state.

Thanks again

R