[Woodcarver] performing cryogenics (freezing at 300* below zero) onwood carving tools.

[Mike Allen]

Hi:  A good example of cryogenic treatment is the Liberty ships in WW1.  As high-carbon steel is quenched, the high temperature phase, called austenite, transforms into a low (room temperature) phase called martensite, which is very hard and brittle.  If you temper martensite, you reduce the hardness slightly, but increase the toughness or ductility (decrease the brittleness). It's common for some of the austenite to not transform during cooling/quenching, because the final temperature was not low enough.  Later, in use, if the steel is cooled to a very low temperature, the retained austenite will transform to martensite, creating very hard and brittle areas.  The Victory ships broke up in the North Atlantic because the freezing water temperature was cold enough to cause this transformation.  This lead metallurgists to study the phenomenon, which we now know as the ductile/brittle transformation temperature.  For some steels, you have to go very low, cryogenic, to force this transformation.  Remember though, the new martensite isn't tempered and will be very brittle.  It would be better to force this complete transformation when the knife is first heat treated,  then tempering  would restore the toughness you need for a good edge tool.  Mike
  ----- Original Message ----- 
  From: Jeodea at aol.com 
  To: woodcarver at six.pairlist.net 
  Sent: Sunday, December 11, 2005 12:35 PM
  Subject: [Woodcarver] performing cryogenics (freezing at 300* below zero) onwood carving tools. 


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  A company in Omaha, NE is offering a service to perform  cryogenics (freezing at 300* below zero) on carving tools.  

  Has anyone tried this? Is there any metallurgists out there that could comment on the effect on our tools?

  I lived in Omaha for 4 years and well remember 4 weeks of -27 below zero weather - that didn't help my carving tools any!!

  you can check out a general description on cryogenics  at http://cvip.csufresno.edu/~rlk16/cryo.html

  Jim O'Dea


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