Hi Gene & even-tempered Galoots !

Gene remarked on the brittleness of a Disston saw
whose hardness was in the neighborhood of Rc52.

Small wonder.  Except for the shock-resisting
tool steels (the S series) one should never
harden & temper a tool steel in the temperature
range that gives a Rockwell C hardness in the
mid-fifties.  That's because the steel will have
its worst possible combination of hardness and
ductility.  In other words, it will be brittle.

Therefore, tools which have to end up in the mid fifty
Rockwell C range must be made from S series tool steels,
or they must be lower in carbon so that they end up
in that range after tempering at lower temperatures.

The so-called temper-embrittlement range is around
500 degrees Fahrenheit.  The S series tool steels
don't drop to the mid-fifties in hardness unless
they're tempered considerably hotter than that, so
they don't get brittle.

Saw steel will therefore perform better if tempered
into the mid forties on the Rockwell C scale.

Galoots whose saws become brittle after electrolysis
can prevent that by baking the saws around 300 F for
several hours immediately after the electrolysis to
drive off the hydrogen that causes the embrittlement
(actually, delayed cracking due to residual stress).

A saw whose teeth have already cracked due to omission
of the post-electrolysis baking step will have to have
all those teeth "pulled" and replaced with new ones
filed from the solid.

Without seeing the broken teeth first-hand, I can't say
which malady did in that Disston, so I've given both of
the sad explanations.

Best regards,
George Langford
amenex@a...