From: jonathon (jemery@execpc.com)
Date: Sun Jun 20 2004 - 16:11:19 PDT
>... And on why do
>you heat the screw/bolt/nut instead of the surrounding area, it depend on
>what you want to save, when you get it that hot you temper the metal which
>makes it harder but it also makes it more fragile in most cases and if you
>are going to throw the screw/bolt/nut away.... Wayne
Right idea but wrong word, "temper" that is. To temper is to soften. When
one heat treats medium or high carbon steel, as in thru hardening (which
cannot be done to low carbon or mild steel), you heat it up beyond the
transition area, into the austenitic region, then quench it. At that point
it is as hard as you will ever get it, and in many cases it's to hard, as
you say it can seem to be almost fragile, to impact loads anyway. Normally
heat treated parts are then "tempered" after quenching to soften them some,
another term is "drawing back". And as you say, if you heat up a bolt red
and take the torch away, the surrounding metal will pull the heat away fast
enough that it has the net effect of quenching the bolt and thus it ends up
harder than it was. To leave a bolt soft after heating you must control the
cooling thru the red zone such that it goes from red to no red slowly, then
you would have effectively annealed it. Don't mean to be to picky, just
adding my two cents.
later,
je
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