[TheForge] Ed- heat treating S-7

[theron]

rats!
I just bought a bag of foo foo dust off of e-bay
oh well
----- Original Message -----
From: <Hochewa@aol.com>
To: <theforge@mailman.qth.net>
Sent: Tuesday, September 02, 2003 5:05 PM
Subject: Re: [TheForge] Ed- heat treating S-7


> Yo Guys!
> Introducing the Rt. Rev. Hochewa of the Church of Orthodox Metallurgy.
> Transformation grain size is a funny thing.  It gets really funny when you
> try to control it in anything short of a pyrometer controlled heat
treating
> furnace.
> Grain size, whether it is the result of transformation or
recrystallization
> from the strained state, is a temperature controlled reaction.  As you
begin to
> get new structure or recrystallized grains, there is competition between
the
> energy of the volume of the grain and the energy of the grain surface.
When
> they are in equilibrium, you have the terminal grain size.  For a material
at a
> temperature with a certain thermo-mechanical history and chemistry, this
size
> is relatively fixed.  After the reaction is complete, time is no longer a
> factor.  Holding it forever at the temperature will have small effect on
the
> grain size.  If you increase the temperature of the work, you will get
grain
> growth but at a much slower rate.  Increasing deformation, hot or cold,
will create
> more sites for nucleation of new grains.
> As to the forge versus grind to shape question.
> The best condition that any material will be in is when you pick it up at
> your local neighborhood steel supply center.  The first time you heat it
in a
> forge, you screw it up.  The first time you hit it with a hammer you screw
it up
> more.  Without knowledge of working ranges, temperature control,
reductions
> between reheats, reduction rates, etc., we turn metallurgical jewels into
> costume jewelry.  This is not to say that what comes from our work is not
completely
> suitable for our purposes.  It is as sure as hell not in an optimum
condition!
> At my day job, the majority of the material I work with is better than 90%
> Platinum and it goes into biomedical devices for implantation.  There are
many
> times that I just have to walk away from watching an operator allegedly
follow
> the process sheet.  We do things that are not exactly right all the time
but
> we get away with it because metals tend to be forgiving.  Some are more
> forgiving than others.  Plain carbon steels are pretty hard to hurt.  The
more alloy
> that you put into a steel, the smaller the window is that you have to work
in
> without doing some damage.
> All tool steel suppliers have data sheets that go into some detail as to
how
> to work and heat treat their materials.  They are usually free or at least
> downloadable.  Read them. Try to understand what they are trying to tell
you.
> Following their recommendations may be a little tough unless you have the
> facilities.  Generous applications of black magic and foo-foo dust do not
replace
> knowledge or proper procedures.
>
> Regards,
>
> Hochewa
>
>
> In a message dated 9/2/2003 2:34:19 PM Eastern Standard Time,
> davesmucker@hotmail.com writes:
> The issue is not normalizing or annealing the steel per say.  (Let me say
> also, that I did not understand this for a long time myself.)  The issue
is
> that what give us smaller grain size is the action of going through the
> transformation point.  (in the cooling direction)  As the steel is
> transformed from the FCC form to the BCC form we get the formation of
> smaller grain size.  This is why Jim Batson goes through this step 3 times
> before heat treating his knife.  The only other thing we can change (the
> chemistry of the steel is already set) to get small grain size is forging
> itself.  This physical deformation also reduces grain size.  Only problem
is
> that every time we heat into the forging temperature range we are helping
> the formation of larger grain size.  This is one reason that fewer heats
are
> better as is the fact that fewer heats means more deformation per heat
which
> is good.
> This grain size issue is why some, George Dickson for example, suggest as
> much machining / grinding rather than forging for making tools.  Unlike
> George, I would never quench S-7 in anything faster than oil from a
cooling
> stand point.  I must say that George has made 100's of tools quenching in
> brine as have the many many students that have taken his classes.  The S-7
> we buy from the suppliers comes with a very fine grain size -- because
they
> have been very careful to obtain this fine grain size to aid in the end
use
> of their product.  The same can not be said for many of the non-tool
steels
> we might work with.
>
> Dave Smucker
>
>
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