"Dar" wrote in message
...
On Apr 4, 10:03 pm, "Ed Huntress" wrote:
"Dar" wrote in message

...





Howdy folks,
Anybody familiar with annealing 0-1 ?. Lately the flat stock I've been
getting is harder than normal , so to test my theory about that being
caused at least significantly by the condition of the steel as opposed
to alloying variances, I annealed a batch of die plates the other
day .
I was right about that and my guess is that the mill is cutting mfg
costs by not fully annealing the stock that the flat-grinders are
being supplied with. According to data from Diehl Steel, the slow
cooling should take place at 35 deg F max . per hour from 1475 deg to
1110 deg, which takes roughly... a whole freakin day !. Regardless of
why the steel is harder than normal, my concern is about degradation
that may occur from the steel spending so much time at elevated
temps. I wrapped my parts in ss foil and that did keep them clean, and
I am assuming that since these are the directions given for annealing,
that it's safe to actually do it; that the steel does maintain it's
"hardenability integrity " through the process of annealing and
subsequent hardening after cold working.

Input?.

Thanks,

DS

The steel should harden with no problem. Some may question whether you'll
have grain growth as a result of the slow cooling, but, IIRC, that
shouldn't
be a problem because it's below the transition temperature for the entire
time. Grain growth wouldn't harm hardenability, but it would harm
toughness.

In any case, I think anything that happens to the grain is going to be
upset
when you heat it above the transition temp again to re-harden it, anyway.
Considering how careful you're being with the annealing, it ought to be
OK.

I've hardened plenty of oil-hardening stock but I don't recall ever
annealing it, so I'm speaking from theory rather than experience.

--
Ed Huntress- Hide quoted text -

- Show quoted text -

The thing in the back of my mind I read somewhere is that carbon can
leach
out at high temps , and it might detriorate the steel and leave it
less tough
or more fragile than it otherwise would after hardening and
tempering . But
it sounds like I'll be ok. Thanks,
DS

Carbon can indeed oxidize at the surface, but it's slightly less of a
problem with oil-hardening than with water-hardening. It actually
decarburizes, leaving the steel soft on the surface (called "bark").
However, you want to protect it with a carbon-rich atmosphere. The SS foil
will minimize oxidizing. Throwing in some graphite powder, charcoal, or a
big pinch of Kasenit will add more security by creating a sacrificial
atmosphere of carbon monoxide, should any oxygen get through the foil seams.

Someone mentioned throwing in a piece of tissue. I've never heard of that,
but it probably would do it , except for the length of time the piece will
be heated. Some people wrap the parts in heavy kraft paper. Bone meal is
another traditional source of carbon. It doesn't take anything fancy but you
have to keep that atmosphere for hours, so make it something that will last.

This is why they use graphite boats in traditional tool-hardening
applications. With SS foil, the boat isn't necessary. But you still want a
source of carbon in there.

I don't know the temperature at which you'll be safe from decarb but it's
certainly no lower than 700 or 800 deg. F. So it's only a problem in the
early stage of the process, if at all. The issue usually comes up in
relation to temperatures above transition, and you're *starting* at around
the transition temperature.

If you get bark, you probably won't know it until after you re-heat-treat
the piece. If you've machined the surface off of it (say, 0.010" or more)
before heat treatment, the bark will go away and you won't even know you had
bark in the first place.

--
Ed Huntress