Heat treating and inspection of metals Page: 24
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15-16 AIR CORPS
a. Annealing.-Nickel steel may be annealed or normalized by heat-
ing to a temperature of from 1,500 to 1,600 F. and cooling in still
b. Hardening.-In hardening nickel steel, the furnace temperature
should not exceed 1,100 F. when the parts are inserted; the tempera-
ure must then be gradually increased to from 1,430 to 1,500 F. This
steel should be quenched in oil.
c. Tempering.-Tempering for aircraft requirements may be accom-
plished at any of three different temperatures, each producing a
different ultimate strength. Regardless of the temperature used,
the parts should be held at the temperature indicated for at least 30
minutes, then removed, and allowed to cool in still air.
Tempering temperature Ultimate strength
(* F.) (pounds per square inch)
800 ------------------------------------150, 000
16. Chrome-molybdenum steel (SAE X-4130 and X-4135).-
Chrome-molybdenum steel is used extensively in aircraft construction
for tubular members, fittings, etc. It has excellent welding properties
as well as high strength and toughness.
a. Annealing and normalizing.-For annealing, the temperature of
the furnace should be held below 1,1000 F. when the parts are in-
serted, then gradually increased to between 1,600 and 1,7000 F.
After holding the parts at this temperature for a sufficient time to
allow full penetration of heat, the furnace should be shut down and
the parts allowed to cool to 1,100 F. At this temperature, they
should be removed, and allowed to cool in still air. The ultimate
strength of the fully annealed steel is approximately 78,000 pounds
per square inch. In normalizing, the parts are heated as described
above, but removed from the furnace directly after the "soaking"
period, and allowed to cool in still air. The ultimate strength ob-
tained in this case is approximately 90,000 pounds per square inch.
b. Hardening.-Hardening is accomplished by inserting the parts
in the furnace which has been preheated to not more than 1,1000 F.
After insertion, the temperature should be gradually increased to be-
tween 1,550 and 1,650 F. Parts having a thickness of less than
1/4 inch should be heated to the lower limit of the range. After the
soaking period the parts should be removed and quenched in oil.
c. Tenpering.--Hardened parts may be tempered for various ulti-
mate strengths.- In any case, the furnace temperature should be be-
low that of the tempering temperature when the parts are inserted,
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United States. War Department. Heat treating and inspection of metals, book, September 10, 1941; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc96657/m1/26/: accessed December 15, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.