On 15/12/2019 21:10, Vir Campestris wrote:
On 15/12/2019 12:23, Brian Reay wrote:

Ah, I vaguely recall something similar but haven't tried it. I expect
there are many 'old fashioned' methods which work after a fashion.

Maybe I've missed, but the one I recall was dunking the hot object in oil.

Andy

That is to cool it more quickly than you can in water, because the steam
bubbles provide insulation. There would be hardly any time for carbon to
diffuse deep enough into the structure before it cooled down. IIRC case
hardening compounds contain plenty of heavy oil / pitch etc which will
convert fairly quickly to carbon. You would typically be heating for
several hours to get the carbon to diffuse in to a depth of a millimetre
or so.