Heat treating and inspection of metals Page: 13
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HEAT TREATING AND INSPECTION OF METALS 6
be judged approximately by its color. The temperatures correspond-
ing to various colors are given in table I; however, the accuracy with
which temperatures may be judged by color depends on the experience
of the workman and on the light in which the work is being done.
TABLE I.-Color chart for steel at various temperatures
Color F. Color F.
Faint red-------------- 900 Salmon _ 1, 650
Blood red----------------- 1,050 Orange _ 1, 725
Dark cherry_ 1, 075 Lemon-_ 1, 825
Medium cherry ------------ 1, 250 Light yellow_ --------------- 1,975
Cherry or full red 1,375 White -------------------- 2, 200
Bright red________________ 1, 550 Dazzling white_ 2, 350
e. A number of liquids may be used for quenching steel. Both the
media and the form of the bath depends largely on the nature of the
work to be cooled. It is important that a sufficient quantity of the
media be provided to allow the metal to be quenched without causing
an appreciable change in the temperature of the bath. This is par-
ticularly important where many articles are to be quenched in
(1) Quenching procedure.-The tendency of steel to warp and
crack during the quenching process is difficult to overcome, and is due
to the fact that certain parts of the article cool more rapidly than
others. Whenever the transformation of temperature is not uniform,
internal strains are set up in the metal which result in warpage or
cracking, depending on the severity of the strains. Irregularly shaped
.parts are particularly susceptible to these conditions although parts
of even section are often affected in a similar manner. Operations
such as forging and machining may set up internal strains in steel
parts and it is therefore advisable to normalize articles before at-
tempting the hardening process. The following recommendations
will greatly reduce the warping tendency and should be carefully
(a) An article should never be thrown into the bath. By permit-
ting it to lie on the bottom of the bath it is apt to cool faster on the top
side than on the bottom side, thus causing it to warp or crack.
(b) The article should be slightly agitated in the bath to destroy
the coating of vapor, which might prevent it from cooling rapidly.
This allows the bath to rapidly convey its heat to the atmosphere.
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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/m1/15/: accessed July 26, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.