Subject: How can you make steel harder by using ultra low temps.

I read a story awhile back that a Company in Cal. was freezeing steel 
products to make them harder.  The example they sited was a Bic razor 
blade.  The author was given one and he claimed it lasted ten times longer 
than a normal one.  Then I heard a crew cheif say that he had the pistons 
for his motors "cold hardened" to make them stronger.  I would like to 
understand how using ultra low temptures hardens steel.  

Thank You, E.F.Brewer

Re: How can you make steel harder by using ultra low temps.