On Sun, 3 Apr 2005 14:48:33 -0400, "Proctologically Violated©®"
wrote:

Dizzying, but clear--I think!
Where'd you learn alladis?? Sounds like you were a heat treater in a
former life! Dat is a tough job!! Esp. in the summer...

But, the diff. between the SS tubing I have and CR is like night and day:
SS is clearly stiffer. Sometimes, depending on finishes, you can't tell by
looking at it, but you can tell by banging it/tugging on it. Also much
harder! which mebbe is the flip side of stiffness?

The sears blades: Yeah, I couldn't vouch for the edge (did seem crappy, in
retrospect), but tryna bend a bent blade back into shape (roots,
donchaknow), was pert near impossible. Needed O/A.
Mebbe not hard, but incredibly tough--which, IIUC, has its own measure of
sorts.

I made my mower blade out of P-20 on the recommendations of a mould
and die guy.

Seems to work pretty well, edge holding is so so. But I dont have many
big rocks.

Gunner

----------------------------
Mr. P.V.'d
formerly Droll Troll
"Ed Huntress" wrote in message
...
"Proctologically Violated©®" wrote in message
...
Great links.

But, I'm curious about your comments on SS/chrome. SS is less stiff??
Not
the stuff I deal with, esp. tubing. Or sheet.

Yes. It's a little less stiff than mild steel. I'll see if I can find some
Young's Modulus figures for common materials and post them. The
"springiness" of a material -- that is, its stiffness up to the point
where
it breaks or takes a permanent bend -- is measured by Young's Modulus, or
the Modulus of Elasticity.

Chrome aids hardening?

Yes. I'd have to go back to my texts, but my recollection is that, up to
some moderate percentage, it *slightly* improves superficial hardness, but
that it *greatly* increases depth of hardening. The air-hardening steels,
which through-harden to great depth, get their through-hardening
properties
from chromium. It's all but impossible to through-harden a thick piece of
plain, high-carbon steel, such as AISI 1095.

Then why is hardenable SS so rare?? I think a rel
recent development, as well.

Common grades of stainless, the 300-Series, can't be quench-hardened
because
the high chromium content (and maybe the nickel contributes; I forget)
prevent the steel from transforming into the hard phase, which is called
martensite. 300-Series stainless remains in the austenitic phase at room
temperature.

When you heat-treat a piece of high-carbon steel, heating it above the
transformation temperature (say, 1400 - 1650 deg F) converts the steel
phase
to austenite, where it remains as long as you keep it above the
transformation temperature. Austenite is soft. If you cool the steel
slowly,
it transforms into another soft phase, called ferrite. If you quench it
quickly, faster than the rate known as its "critical quench rate," it
transforms into martensite, instead of ferrite. Martensite is hard.

Plain carbon steels have a very fast critical quench rate. That's why you
have to quench them in water. Certain alloy ingredients slow that rate
down.
That's "oil-hardening" steel. You don't necessarily quench it in oil
(whether you do depends on the piece's thickness, and the result you
want),
but the suggestion is that you can quench it a little slower and the
austenite will still convert to martensite.

High-alloy steels that can be quenched even more slowly are the
air-hardening steels. In very thin sections, even 4130 is more-or-less
air-hardening. The A-Series tool steels will fully harden in air, up to
substantial thicknesses.

I hope this is clear. I hate to have to re-edit these things. g

--
Ed Huntress




Rule #35
"That which does not kill you,
has made a huge tactical error"