Heat treating and inspection of metals Page: 14
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6-7 AIR CORPS
(c) An article should be quenched in such a manner that all parts
will be cooled uniformly and with the least possible distortion. For
example, a gear wheel or shaft should be quenched in a vertical
(d) Irregularly shaped section should be immersed in such a man-
ner that the parts of the greatest section enter the bath first.
(2) Quenching media.-(a) Water is used more than any other
medium in the quenching of steel during the hardening process. The
water bath should be maintained at 700 F., as extremely cold water is
apt to warp or crack the steel, and water above this temperature will
not produce the required hardness.
(b) Salt brine is used where higher heating capacity is necessary.
The mixture is made by dissolving ordinary salt in water until a 10
percent solution is obtained.
(c) Oil is much slower in action than water and the tendency of
heated steel to warp or crack when quenched may be greatly reduced
by its use. Unfortunately, parts made from high carbon steel will
not develop maximum hardness when quenched in oil unless they are
quite thin in cross section. Its use is, however, recommended in all
cases where it will produce the desired degree of hardness.
(d) For many articles such as milling cutters and similar tools, a
bath of water covered by a film of oil is occasionally used. When the
steel is plunged through this oil film a thin coating will adhere to it,
retarding the cooling action of the water slightly, thus reducing the
tendency to crack, due to contraction.
(3) Straightening of parts warped in quenching.-Warped parts
must be straightened by heating first, and then applying pres-
sure. This pressure should be gradual and must continue until the
piece is cooled. If the article is not too large in cross section it may
be placed between the centers of a lathe, then heated by some means
until lard oil, applied to the surface, begins to smoke. At this point,
pressure should be applied to the convex side by means of a tool
shank held in the tool post. The pressure should be sufficient to spring
the part slightly in the opposite direction from which it is bent. An
article thus straightened may be cooled by applying wet cloths uni-
formly to the entire surface, or left between the centers until cooled by
air. No attempt should be made to spring hardened steel without
heating, regardless of the number of times it has been previously
heated, as steel in its hardened condition cannot be bent or sprung cold
with any degree of safety.
7. Tempering.-a. Steel in the hardened state may be considered
in an unstable condition at atmospheric temperature. Tempering of
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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/m1/16/: accessed March 28, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.