[TheForge] Re: Do you know if the normalizing differ substantially from the annealing

[Mike Spencer]

George Dixon wrote:

> Do you know if the normalizing differ substantially from the
> annealing
>
> Normalizing is using heat in a controlled manner to remove stress
> imposed by forging
>
> Annealing is using heat in a controlled manner to remove hardness,
> either from work hardening or heat treating


I recall once mentioning "annealing" something by heating it and
letting it cool in air to Sam Allen.  He corrected me, saying, "That's
normalizing."  Since Sam is a metallurgy professor at MIT, I reckoned
I hadda do some reading before I pontificated again. :-)

Looking at Mechanical Engineer's Handbook (Theodore Baumeister,
ed.,1958), I see that "annealing" is treated as a broad category of
processes used:

   (1) to remove stresses; (2) to induce softening; (3) to alter
   ductility,toughness, electrical, magnetic or other physical
   properties; (4) to refine the crystaline structure; (5) to remove
   gasses; or (6) to produce a definite microstructure....

Within that category are "fuel annealing" and "normalizing".

    Fuel annealing:

    Heating iron-base alloys above the critical range, holding above
    that range for a proper period of time, followed by slow cooling
    below that range. The annealing temperature is generally about 100
    F above the upper limit of the critical temperature range, and the
    time of holding is usually not less than 1 hr for each inch of
    section of the heaviest object being treated.  The objects being
    treated are ordinarily allowed to cool slowly in the furnace. They
    may, however, be removed from the furnace and cooled in some
    medium that will prolong the time of cooling AS COMPARED WITH
    UNRESTRICTED COOLING IN THE AIR. [Emphasis mine]

    Normalizing:

    Heating iron-base alloys to approximately 100 F above the critical
    temperature range followed by cooling to below that range in still
    air at ordinary temperatures.

Other sub-topics mentioned under the general rubric of annealing:
Process Annealing; Patenting; Spheroidizing.

I once made a (finger) ring by pattern-welding a piece of
off-the-shelf mild steel with a piece of Volkswagen beetle front
torsion spring.  Let it cool in air.  File glided off as if it were
glass.  Re-heated, allowed to cool more slowly in forge cinders. Still
like glass.  I finally threw it into my kitchen range where it
remained red hot all evening. I left it there over night so that it
cooled in the coals (later, the ashes) of a dying fire. Stove was cold
in the morning. Retrieved from the ashes, the ring could be filed
fairly easily, albeit noticably harder than mild steel.

So in the first two tries, I was normalizing it (consistent with Sam's
remark) and in the stove I was "fuel annealing" it, with a long hold
above critical followed by very slow and even cooling.

VW front torsion bars are, BTW, cool material.  They're compound units
of ca. 1/8" x 3/4" and 1/8" x 3/8" flat strips roughly a yard long.
You can clamp the end of one in the vise, bend it over 180 degrees and
(keeping your head well out of the way!) release it. Just whips back and
forth.  Heat one end to red, cool in air and try the same thing.
Snaps off as easily as, say, breaking a candy cane or a thin strip of
glass.


FWIW,
- Mike

-- 
Michael Spencer                  Nova Scotia, Canada       .~. 
                                                           /V\ 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^