In the fabrication of chasing tools, the steel is first
annealled, then shaped, and finally, hardened and tempered.
Annealing, hardening and tempering each have a definite purpose.
Annealing does more than just make the steel soft enough to work
cold. It also affects the grain structure. If steel is reheated
for hardening, without going through the annealing phase, the
grain structure may enlarge, making the final product brittle, and
coarse. Some steels, although they may have become brittle
without proper annealing, may not reach sufficient hardness.
My question/confusion concerns the tempering step. I do not
understand what one should do if one quenches the steel at the
incorrect temperature ie. misses that change to a light straw
Yes, steel should go through all three steps: annealing,
hardening, then tempering. These three are part of a single
process, and not separate processes. Some steels are forgiving
enough to allow reheating to critical temperature (the point where
the steel loses it’s magnetic nature, but not beyond) and quenching
to make them hard without annealing. I’ve never been absolutely
sure which steels will let you do this, so I go through all three
steps. Someone else seems to have suggested that some tools should
be hardened, and some tempered. This is not quite right; I may
have misread their message. Unless you want to use the tool in the
annealed state, it should be hardened. This will likely make it
too hard, so this hardness should be modified, or tempered, to the
point where the tool is still properly hard for the task, but not
so hard as to be fragile, and shatter when working. Some tools are
tempered less than others. Scribes, etc., are left with a lot of
hardness. Punches and chisels are tempered more, i.e. heated
more, so they will not be as hard, and not shatter in use.
Hammers, etc., are tempered more still.
Some publications suggest that you should repeat the entire
annealling-hardening- tempering process, while at least one
other, Marcia Lewis' book (Chasing), suggests that one should
only repeat the hardening and tempering steps. It makes sense to
repeat the hardening step to remove the structural
inconsistencies caused by the previous tempering attempt, but
reannealling does not seem necessary.
Without going all the way back to the annealed state, some of
these “inconsistencies” may remain – primarily large grain
structure. Large grain structure is not good! To make the grain
structure smaller, you should anneal.
What’s the big deal? Simply heat to critical (non-magnetic) and
cool as slowly as possible. Bury the hot tool in a pan of wood
ashes, or sand, or kaowool, or lime, or the pumice of your
annealing pan, and let cool slowly. If you have a burnout oven,
or an enameling kiln, get it hot (but not hotter than the steel),
and put the hot, non-magnetic steel into it. Turn the oven off
immediately, or even perhaps before you put the steel into it, and
let the whole thing cool.
When the steel is cooler than about 150-200 degrees, or cooled all
the way down to room temperature, you can reheat to critical, then
harden by quenching in the appropriate medium for the steel. This
is usually oil or water, depending on the steel. There are other
quenching mediums, but these are the most common. Once hardened,
polish the steel, and heat the tool an inch or so above the
working face. When the ‘colors begin to run’, pull the torch.
When they slow, give a little more heat. As long as you don’t
exceed the tempering color (temperature) you can go back and temper
(or soften) the hardness by heating until the face of the tool just
reaches the color you want. Some people heat the tool all the way
back at the striking surface, and let the colors run. This will
partially anneal the striking face, minimizing chipping.
Find a copy of Richard Wegar’s (sp?) “The Making of Tools”. Wegar
gives a very good description of tool making, describing the
hardening of many tools, complete with pictures, including chasing
tools and stone worker’s tools. Several other books on
blacksmithing also give good descriptions.