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Posted by on March 11, 2006, 11:25 am
Please log in for more thread options > >> ...wondering about the differences in differential quenching
> >> and differential tempering and... [partial austenitizing too?;]
> > BTDT by accident one time :) the thin part was ready to quench
> > and the thick back wasn't, but was real close so went for it and
> > quenched it anyway.
> > That knife couldn't be broken if you wanted to. It bent back and
> > forth like steel shipment strapping ("tie banding" -RR lingo;) but
> > the edge cracked right away since it was "dead hard" (untempered).
> Once properly tempered though it should have been an outstanding
> blade don't you think?
Like Chas sez, "yes for certain uses, but not for others".
So far, I haven't found a need for other than an all-hard knife.
> >> ...which results in a tougher knife all else being equal?
> > I sure as heck don't know. :(
> >> As I understand it, differential quenching, either clay-coat or
> >> edge quench, will give a hard martenistic edge with a soft perlite
> >> spine. (I suppose the spine may be some combination of
> >> perlite/martensite and perhaps with a little bainite). A
> >> differential temper on the other hand will still have the hard
> >> martensite edge with a softened marteniste spine.
> > That all sounds right to me. :)
> >> So if someone was chasing that elusive ideal knife, which would
> >> be a better choice and if you can why?
> >> Ron
> > Cool question. :)
> So let's review a couple of things. Tempering over a metal's
> ideal temperture - say over 400F and up to 800F I've been hearing
> all kinds of information lately that says you loose grain cohesion
> and strength.
Yeah, "temper embrittlement". :)
> On the other hand, if the steel has a good grain structure to
> begin with and you never actually harden it in the quench, it
> gets left out of the temper equation to a large degree.
Yes, since it'll remain pearlite.
That's what my blade did. (above)
> So you have a hard tempered edge and a dead soft backing... or
> maybe a slightly hardened backing (I would think this would be
> better). Seems to me this would be ideal. Of course the best bet
> is to do the same knife both ways and beat the hell out of them to
> see :-).
At least it'd be ideal to pass some sort of artificial "knife guild
type" test. ;) Or survive Cliff. ;)
> Then there is also pulling the knife out of the quench while it is
> still around 700F. I did this to a sword blade that once cool was
> plenty hard. I could'nt find a local shop that would hardness
> test it for me but the blade had a nice springy feel to it after
> temper. Too subjective for this discussion really but it's an
> idea to play around with.
> GA
Yeah, that sucker prob'ly still became mostly martensite anyway,
just the same if it hadn't been pulled from the quench. (as long
as you got it under that "nose";)
I tend to do my butcher knives that way too. They usually need some
sort of "warp straightening" operation :/ and that's a good time to
do it since the martensite isn't fully formed. :)
Alvin in AZ
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