Back to Ganoksin | FAQ | Contact

Troubleshooting annealing of stainless steel


#1

Dear all,

I have gone through the archives to search for advice on annealing
stainless steel, but unfortunately have found no joy. I have some
old inox steel forks which I want to bend (and Uri Geller is not at
hand). I’ve tried the cherry red torching and quenching?

Any tips? Please?

Many thanks,
Zee


#2

Hello Zee, Let the steel cool slowly until it is room temp. It will
probably be soft.

Have fun.
Tom Arnold


#3

Ferrous metals are annealed by heating to red and then cooling VERY
slowly. They must NOT be quenched. The traditional method of
annealing steel or cast iron was to heat to red in a coal fire and
leave overnight to cool when the fire went out.

Carbon steels are hardened by quenching; that’s how cutting tools are
hardened.

Regards, Gary Wooding


#4

Hi Zee,

Ultimate softness depends on finding the right cycle for the exact
alloy of stainless they’re made of. Good luck figuring that out.

Meanwhile, a good ‘off the cuff’ process would be to heat them red
hot on a surface of sand or pumice rocks, then dump a bunch more sand
or pumice on top of them, and come back in the morning. The goal is
to cool them as slowly as possible. Putting them into a hot burnout
kiln, and letting them cool overnight with the kiln would be another
easy answer.

Compared to normal jewelry metals, steels (and especially stainless)
are very screwy materials. They’re bass-ackward of everything you’re
used to when it comes to heat, and how to handle them. Heating and
quenching as you would for silver actually makes steel harder.

Regards,
Brian.


#5

Not hot enough probably, you need to exceed 1750F to anneal most
stainless.

James Binnion
James Binnion Metal Arts


#6
Ferrous metals are annealed by heating to red and then cooling
VERY slowly. They must NOT be quenched. The traditional method of
annealing steel or cast iron was to heat to red in a coal fire and
leave overnight to cool when the fire went out. Carbon steels are
hardened by quenching; that's how cutting tools are hardened. 

I’ll back this up, and add that to anneal properly the steel has to
cool slowly, so putting the steel into vermiculite is a good thing to
do if you want to anneal steel.

The problem comes if the steel is air hardening steel, then it has
to be treated very differently.

Regards Charles


#7
Let the steel cool slowly until it is room temp. It will probably
be soft. 

You want to quench austenitic stainless (300 series) to avoid
chromium carbide precipitation which can lead to cracking. As it is
not heat treatable to harden it really doesn’t matter if you quench
it.

James Binnion
James Binnion Metal Arts


#8

Alberic wrote:

Meanwhile, a good 'off the cuff' process would be to heat them red
hot on a surface of sand or pumice rocks, then dump a bunch more
sand or pumice on top of them, and come back in the morning. The
goal is to cool them as slowly as possible. Putting them into a hot
burnout kiln, and letting them cool overnight with the kiln would
be another easy answer. 

Gary wrote:

Ferrous metals are annealed by heating to red and then cooling
VERY slowly. They must NOT be quenched. The traditional method of
annealing steel or cast iron was to heat to red in a coal fire and
leave overnight to cool when the fire went out. 

While both the above answers would be good for simple carbon tool
steel they will not have the desired results for Autistic stainless
which is by far the most common type. You must heat quite a bit
hotter than you would for carbon steel, at least 1750 -1850 F and
then quench to avoid the formation of chromium carbides that
precipitate out of the matrix if allowed to cool slowly. The chromium
carbides cause two problems, cracking and loss of corrosion
resistance. But even when fully annealed they will not be much
softer. It is a tough, difficult to work material even when fully
annealed.

James Binnion
James Binnion Metal Arts


#9

Hi Jim.

While both the above answers would be good for simple carbon tool
steel they will not have the desired results for Autistic
stainless which is by far the most common type. 

Interesting. I normally only mess around with 400 series, if I’m
using it at all. So this is useful to know.

Regards,
Brian.


#10
You want to quench austenitic stainless (300 series) to avoid
chromium carbide precipitation which can lead to cracking. As it
is not heat treatable to harden it really doesn't matter if you
quench it. 

for this very reason. In the article I read they suggested ice cold
water.

Chris Gravenor


#11
While both the above answers would be good for simple carbon tool
steel they will not have the desired results for Autistic stainless
which is by far the most common type. 

Interesting. I normally only mess around with 400 series, if I’m
using it at all. So this is useful to know.

I am guessing you mean the Martensitic steels in the 400 series like
440C. They act a lot more like a an air hardening tool steel so to
anneal 440C you want to heat to 1562-1652 F, then slow furnace cool
to about 1100 F and then air cool. So a bit cooler than the 300
series for annealing temps

James Binnion
James Binnion Metal Arts


#12

This is such a wide open question. It depends on the alloy, whether
it’s air, oil, or water hardening, the amount of carbon in it, etc.

Michael
www.radharcknives.com


#13
From my research you in fact have to cool it as quickly as
possible for this very reason. In the article I read they suggested
ice cold water. 

Are you talking about a sub-zero quench? That’s the best way to
harden stainless steel.

Regards Charles


#14
This is such a wide open question. It depends on the alloy,
whether it's air, oil, or water hardening, the amount of carbon in
it, etc. 

Sure is. When you deal with mystery metal that’s what you get. It’s
best to buy your alloys (or make them), then you’ll know how they
will perform.

Regards Charles


#15

Hi Jim,

I am guessing you mean the Martensitic steels in the 400 series
like 440C. They act a lot more like a an air hardening tool steel
so to anneal 440C you want to heat to 1562-1652 F, then slow
furnace cool to about 1100 F and then air cool. So a bit cooler
than the 300 series for annealing temps 

Yeah, specifically 440C, and I only ever work that hot (blades) so
annealing isn’t really a concern. Wow…I just stopped to think when
the last time I forged a stainless blade was. Yikes! My forge has
been mothballed for 12 years now. Funny how time creeps up on you.
The good news is that I’m moving in the next few months, with the
goal of getting enough space to actually get all my gear into one
state, and uncrated, for the first time in years. Now all I have to
do is rent a crane…

Cheers-
Brian.


#16
Are you talking about a sub-zero quench? That's the best way to
harden stainless steel. 

Its my understanding (and an earlier post from James stated as such)
that you can’t heat harden Stainless. As stated in earlier posts,
the problem with annealing stainless is that with slow cooling the
chromium tends to crack etc. My research confirmed what earlier
posters have stated And one source that I encountered stated the
importance of cooling rapidly that ice water should be used. I took
it to mean as cold as you could get it.

Having said all that we have to also realize that there are many
types of stainless and each type has its own properties.


#17
Its my understanding (and an earlier post from James stated as
such) that you can't heat harden Stainless. As stated in earlier
posts, the problem with annealing stainless is that with slow
cooling the chromium tends to crack etc. My research confirmed what
earlier posters have stated And one source that I encountered
stated the importance of cooling rapidly that ice water should be
used. I took it to mean as cold as you could get it. 

Stainless steel has a tendency to build up stress, and to warp.
Heating needs to be an even heat.

Most stainless steel will harden in a light oil, some are air
hardening, it’s possible.

The tempering process “must” occur pretty much straight away. Either
a traditional temper or a sub-zero quench, depending on the stainless
alloy. A data sheet is handy. If you have mystery stainless, then
you have to do a trial, or sell the stainless and a know alloy.

Acetone and dry ice, or liquid nitrogen. Plunge the blade into the
liquid for 20-30 seconds, that’ll do it.

Chilly work :wink:

Regards Charles


#18
Most stainless steel will harden in a light oil, some are air
hardening, it's possible. 

There are dozens of stainless steel alloys with widely varying
properties… Austenitic stainless the most common(300 series) the
most common type of stainless steels are in this category, they will
not harden with any heat treatment period. Martensitic stainless
(some but not all of the 400 series) will harden with appropriate
heat treatment for the particular alloy.

James Binnion
James Binnion Metal Arts


#19
Austenitic stainless the most common (300 series) the most common
type of stainless steels are in this category, they will not harden
with any heat treatment period. 

Yeah, and it will also not roll cold either. I am working with some
and I thought, “AHA! Lets see if I can roll this down instead of
filing it flat” ( Hans in shortcut mode) Well, it was no more that
5% reduction when it went “POP” and it cracked. Admittedly, I did not
know its state of annealment.

I decided to file instead…
Cheers, Hans