From: GwH611@netscape.net
Sent: Monday, May 07, 2001 12:02 PM
To: 928
Subject: [928] Re: cryogenically treating rotors?

Hi Mike,

I'll try this again.  The software Netscape uses is obviously written
by some high-school kid, and it doesn't like people that have to think
when replying to a message.

I'll share what knowledge I retained after car-pooling with a Russian
Metalurgist for a couple of years.  His speciality was "Designer Steels";
he designed the steel used in the trans-Siberian pipeline.  He said the
toughest part was designing it so it wouldn't shatter from the cold, but
could still be welded.

Anyway ...  A metalurgist views steel as a super-saturated soloution of
carbon in iron.  There's carbon that has associated with an iron molecule,
but there's a fair amount of it "just floating" in there.  The various
quenching methods are attempts to control the free carbon.

When you get steel very, very, (not-a-lot-of-degrees-kelvin) cold, the
free carbon is forced to associate with an iron molecule.  And it (they)
will stay associated even after the steel is brought back to room
temperature.

But you need to get it there slowly.  If you just toss a rotor into an LN
bath, it will crack.  The commercial places ( http://www.frozenrotor.com 
for one.) chill at about 1-deg-C/Minute.  But once you get it cold, it
doesn't have to stay cold for long.  The warming process is about the
same as the chilling process.

I want to do this to my rotors, but SWMBO is unconvinced about the
necessity of the added expense.

And I asked about cryogenic treatment of non-ferrous alloys.  The answer
I got was "Nyet.  They don't work that way."

HTH,
Gary