slowly kiln heating the item to about 1300F and alowing the
piece to slowly cool in the kiln, or in the air. quenching the
piece would make it brittle. a local toolmaker i know, would
quench his steel in oil when annealing and water when
When steel is heated, there is a temperature at which the iron
in the steels transforms to a different structure. This
temperature, the transformation temperature, is about 1360F for
plain carbon steels and may be up to 1500F for higher alloys.
When cooling from above the transformation temperature, the
structure again changes, but the new structure is determined by
the cooling rate. By definition, annealing is the slow cooling
from above the transformation temperature and hardening is rapid
The rate of cooling is critical. Since a plain carbon steel
requires a very rapid cooling to harden - in agitated water - air
cooling would be considered a “slow” cool. Remember too that the
size of the piece greatly affects the cooling rate.
In regard to your question about water vs oil quenching, if the
steel were heated over the transformation temperature, quenching
in either would develop hardness in the steel; a small amount in
plain carbon to full hardness in many other steels. Except for
the plain carbon steels, most other steels would become hard if
quenched in oil from over the transformation temperature.
In addition to annealing and hardening there is another process
that is used to soften steel. This is called “tempering” or
"drawing" and consists of reheating the steel after hardening,
the higher the temperature used ( but below the transformation
temperature ) the softer the steel will become. Tempering is used
to remove brittleness from a hardened steel and to adjust the
hardness to a required range. Heating to 1300F as in your
question, would not transform the steel, but would soften it by
tempering. In this case, the cooling rate is not critical and
even if water quenched, no hardening will result. This process is
sometimes referred to as a “subcritical anneal”.
The above also apply to cold worked steels that require
There are many books on steels put out by the steel companies
and your local steel service center (distributor) may give you
some of these.
I hope the above answers your questions, if not, try again.