National
Electronic Alloys Summary of Products
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THERMAL
TREATMENTS
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Although the nickel-iron low expansion
alloys are not hardenable, annealing and stress
relief thermal treatments are at times necessary
to promote structure uniformity and dimensional
stability. The relief of stresses introduced by
severe forming, bending, or machining, can be
accomplished by annealing at temperatures of approximately
1400 to 1800 F (760 to 982 C) for a time sufficient,
to thoroughly heat through the section. However,
the nickel-irons will oxidize readily at these
high temperatures. When annealing cannot be done
in a non-oxidizing enviroment (vacuum, dry hydrogen,
dissociated ammonia, etc.) sufficient material
must be allowed on work pieces to clean-up by
light grinding, pickling, etc., after annealing.
Stress relief for sections having light finishing
cuts or grinding performed after annealing is
accomplished by heating to 600 to 800 f (316 to
427 C), for a time to uniformly heat through the
work piece.
All of the nickel-iron controlled expansion alloys
can be hot forged, upset, formed, etc., at temperatures
between 1800 to 2100 F (982 to 1149 C). However,
heating for hot working must be done uniformly
at slow rates from relatively cold furnaces (black)
to minimize the potential for cracking through
large sections as a result of differential thermal
expansion stresses. Large forgings should be annealed
to promote uniformity after hot working. |
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