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

Hi,
The steel goes through a phase transformation, it changes crystal 
structure.  As an example, in austenitic stainless steel, both austenite 
and martensite are present.  At the elevated temperature used to form the 
steel, the austenite is more stable and is the dominant component.  At 
lower temperatures, the martensite phase becomes more stable, and the steel 
transforms from austenite to martensite. The temperature at which the 
martensite transforms back into austenite is typically much higher than 
room temperature, so the steel remains martensitic after cooling.  The 
martensite is harder than the austenite, and so wear resistance is 
improved.

Bob Novak
Specialist - Process R&D
Carpenter Technology