Re: New guy with questions

Jan,

Well, I've never heard martensite described as "skruntchy", but
that is probably as good a description as one gets. I agree with
Smoke; find a good book and an comfortable desk for learning about
the iron-carbon system. It's anything but simple, and there are a
few things yet to discover within it. Besides, it's kind of OT.

I'll give this a shot though. Apologies for the long-ish post.

It wouldn't be too wrong to think of the hardening process as an
atomic game of "musical chairs". When the steel is hot, the carbon
atoms can get up and dance around.

But when the music stops (cooling), they had better get back in
their places! Otherwise they're stuck outside, which distorts the
matrix and makes the steel harder/stronger. The atoms to chairs
ratio is fixed by the carbon content. So a higher carbon steel
responds better to quenching since there are fewer "chairs" available
for the carbon. Cooling it faster enhances the effect as well.

Now throw a few large atoms like molybdenum, chromium, & nickel
into the game. These guys interfere with the getting into the chairs
process (diffusion), and so this alloy steel responds even more to
readily to quenching. So well, in fact, that it needs a slower
quench medium. That's the oil hardening steel; good for heavy
sections and tools where you want minimal warping from the quench
cycle.

More carbon, more heavy alloying ingredients, and you've got air-
hardening steel. That's the "magic".

I don't want to carry that analogy further, since it's not quite
the whole story. But here are a few bullet items to carry back into
the shop:

- Always temper after hardening.

- For the blowtorch folks: when it loses its magnetism, it's ready
to quench.

- Get the hardening recipe if you can, since there are some "trick"
steels out there that perform better with multi stage quench
processes.

Again, sorry about the off topic-ness.

Dave Kowalczyk
Seattle WA
annoying web plug --> http://www.dakeng.com

--- In CAD_CAM_EDM_DRO@y..., JanRwl@A... wrote:
> In a message dated 12-Oct-01 10:46:02 Central Daylight Time,
> johnhe@s... writes:
>
>
> > How does oil hardening tool steel work chemically? I know you can
heat and
> > dunk in oils instead of water for less harsh tempering.
> >
> >
>
> John: It's not "chemically", but "physically". The alloy-
molecules
> "skruntch up" upon rapid-cooling, making alloy-bonds (whatever you
call 'emâ€"I
> am not an eddikatid metul urge ist!) happen. Since the "oil hard"
steel is
> more expensive (to buy in rods and bars), it must have more magic
in it than
> "water hard". There is also "air-hard", but I don't know how it
compares.
>
> I THINK the oil-hard is more or less "ready to use" after quenching
in oil,
> whereas the water-hard is so brittle it must be
carefully "tempered"
> (re-heated a special controlled amount that takes years of skill
at "reading"
> color (redness) of metal, knowing when to stop re-heating, and HOW
to
> cool-down, properly. But I am NOT sure. When I need a "one-time"
tool of
> some kind, I often don't even pay much attention to which is which,
and just
> plunge the orange-hot tool in whatever's handy (my oil-bucket for
this
> doesn't evaporate as does water, so, often it's "just oil". This
works, at
> least for one-time, non-professional tools, so I retain ignorance!
>
> Some metallurgist/tool-maker should answer this question for us
all!
> Well?????
>
> Jan Rowland
>
>
> [Non-text portions of this message have been removed]