Heat treating and inspection of metals Page: 47
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HEAT TREATING AND INSPECTION OF METALS 45
produced, and opposite poles will be formed on the two sides of the
crack as shown at Q. In the conditions illustrated in and @, the
formation of new magnetic poles is caused either by a complete or
partial break in the path of the magnetic flux. This fact may be as-
sumed to include any discontinuity or abrupt change in the degree of
ease with which the magnetic flux is allowed to flow.
Q Field about a solid bar.
O Fields produced by breaking bar.
o Field produced by a crack in bar.
FIGURE 8.-Magnetic field about a steel bar.
b. The presence of these magnetic discontinuities may be detected by
the application of finely divided ferromagnetic particles. As the
particles are brought in the vicinity of the flaw they offer a better
path for the leaking magnetic flux and therefore tend to gather at
the point of leakage, outlining its boundaries. The ferromagnetic
particles may either be in the form of a dry powder or held in sus-
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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/m1/49/: accessed July 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.