[TheForge] (no subject)

[jim wallbridge]

Frosty said:
I never thought of using an air hardening steel till now. What I wonder is.
Air hardening means air quenching. It comes to full hardness cooling at the
rate air chills it. As an anvil face, it'll cool much more slowly as it has
the large thermal mass of the cast iron body. I think it'll take a more
agressive quench than air in this case. Still not having to worry about
tempering is pretty attractive and worth thinking about.
-- 
The terms water hardening, oil hardening and air hardening are 
relatively inprecise and refer to alloy which have sufficient 
hardenability to harden when typical section sizes are quenched by 
the stated method.  As an example  very thin (e.g. 1/16" dia) water 
hardening grades can and probably should be quenched in oil.  Very 
thick sections of oil hardening steel may require a water quench to 
reach maximum hardness.  In general the more severe the quench the 
more likely that cracks and distortion will appear.  There are 
quenching methods between those three as regards severity of 
quenching (i.e. cooling rate).  For the specific case under 
consideration, of a steel plate brazed to a cast iron anvil,  whether 
air cooling will be sufficient for a particular alloy will depend on 
its hardenability (of which there is a wide range in the air 
hardening steels).   Use of steels of marginal hardenability would 
suggest the use of fans perhaps with a fine mist of water. 
Alternately there is probably only a low risk of cracking if the 
assembly were to be quenched in a large shallow pan of moving oil 
(approximate depth of oil equal to 1/2 of the thickness of the 
steel).    Oil depths approximately equal to the thickness of the 
steel should be avoided as there result in high stress in the 
vicinity of the braze which already will be under high stress.

jim
(James ME Wallbridge P. Eng.) Libertarian, Metallurgist, Wood & Metal 
Worker, Fly Fisher,  Resident of Calgary,  Canada's new head office 
location of choice.   Permission is hereby given to use any or all 
information herein, as an attributed quote, unless the body of the 
message states otherwise.