I think (as Ed said) you're going to have more issues with your HT
recipe than could be corrected by LN2.

Cryo is usually used to transform "retained austenite" (bad) to
martensite (good) and thus improve hardness. It is otherwise used to
refine structure and precipitate some useful carbides (often done by
24hr soak by "high end knife makers" in bulk).

The biggest culprits for retained austenite (non-magnetic soft molecule)
is too high a temp in austenitizing, or incorrect quench rate (too
fast), or both. If you screw up both and too much is retained (usually
near the surface) there will be visible cracks.

I would suspect that with a wood fire your HT temp would be too low,
steel at over 1400 is uncomfortably to look at for very long. Some
transformation will begin around 1300, but complete transformation needs
1425 (long soak) to 1475 (shorter soak). Cold punches (temporary or
short run) were often done with O/A and heated until they "looked wet"
then quenched. Both water hard and oil hard "do something" this way, but
are not nearly as good as they could be.

If your tools are just not wearing well but don't have visible surface
cracks then your temp is too low or the quench too slow.

BTW, "real heat treaters" will step on the time/temp numbers all the
time and make good working tools, it's an experience thing, that's why
they call it a "recipe"....

Matt


JoanD'arcRoast wrote:
I shape my wood lathe tools by hand, and then heat treat in a campfire
and quench in used motor oil.

I have access to LN2, but wonder if it would make a noticeable
improvement of the O-1.

I know I will encounter inefficiencies due to Leidenfrost effect, even
if I pre-chill the steel to minus 80 C. (Perhaps I can roto-vac to make
slush, I'll have to explore that.)

Opinions?

Do you think my methods are too primitive and hit-or-miss to achieve
better sharpness and edge retention on the lathe tool?

Am I barking up the wrong tree? Would the little extra hardness gained
not be desirable for this application?

Pointers? Links?

Thanks for taking the trouble to read this mess,
-j