Figure 3-59. Surface of a Steel Billet Showing a Lap.
Figure 3-60. Cross-Section of a Forging Lap (Magnified 100X).
h. Burning. Overheating of forgings, to the point of incipient melting, results in a condition which
renders the forging unusable in most cases, and is referred to as burning. However, the real source of
the damage is not oxidation, but the material becoming partially liquefied due to the heat at the grain
boundaries. Burning is a serious defect but is not generally shown by magnetic particle testing.
i. Flash Line Tears. Cracks or tears along the flash line (see Glossary) of forgings are usually caused by
improper trimming of the flash. If shallow they may "clean up" during machining. Otherwise they are
considered defects. Such cracks or tears can easily be found by magnetic particles. (See Figure 3-61.)