T.O. 33B-1-13-101e. HydrogenFlakes. Flakes are internal ruptures that may occur in steel as the result of internal stressesfrom metallurgical changes and decreased solubility of hydrogen from excessively rapid cooling. Flakesusually occurring in fairly heavy sections and certain alloys are more susceptible than others. Figure 3-57 shows magnetic particle indications of flakes that have been exposed on a machined surface. Sincethese ruptures are deep in the metal - usually half way and more from the surface to the center of thesection they will not be shown by magnetic particle testing on the original surface of the part.Figure 3-57. Magnetic Particle Indications of Flakes in a Bore of a Large Hollow Shaft.f. ForgingBursts. When steel is worked at too high a temperature it is subject to cracking or rupturing.Too rapid or too severe a reduction of section can also causebursts or cracks. Such ruptures may beinternal bursts, or they may be cracks at the surface. Cracks at the surface are readily found bymagnetic particle testing. If interior, they are usually not shown except when they have been exposed bymachining. (See Figure 3-58.)Figure 3-58. Magnetic Particle Indications of Forging Cracksor Bursts in an Upset Section Severe Case.g. ForgingLaps. As the name implies, forging laps or folds are formed when, in the forging operation,improper handling of the blank in the die causes the metal to flow so as to form a lap, which is latersqueezed tight. Since it is on the surface and is oxidized, this lap does not weld shut. This type ofdiscontinuity is sometimes difficult to locate, because it may be open at the surface and fairly shallow,and often may lie at only a very slight angle to the surface. In some unusual cases it also may be solidlyfilled with magnetic oxides. (See Figure 3-59 and Figure 3-60.)
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