Jon, if you want to "harden" a piece of steel because it lost its temper
from overgrinding and will no longer retain its sharpness, then the
process is more complicated than you think. You have to first anneal,
then harden, and lastly temper. Let me know, if you want more detail. I
delayed answering your question because I'm sure I"m one of the least
expert people on this group.


In article ,
says...
Jon Weaver wrote:

I want to harden a piece of steel, and from my school metal work days,
I think that I can simply heat it to red hot and then plung it into
'oil'

Is this the right? If so, what sort of oil should I use.. Are we
talking normal engine oil, or there there a special kind??

As you can tell, I havn't really got a clue what I am talking about,
so any info would be appreciated

Jon