Abstract
If not used within a few days of the last skin pass, low- and extra-low-carbon steel coils often give formed parts with stretcher-strain markings. These defects are caused by the phenomenon of strain aging occurring within the metal. By the use of mechanical tests, such as hardness and tensile tests, it is possible to follow the way in which the strength and ductility of the steel vary with time. X-ray diffraction studies were also conducted and gave results that do not appear to be influenced by the displacement of interstitial elements, but reveal compressive strains perpendicular to the sheet, and enable an average root mean square displacement of the atomic planes in question and an average dislocation density to he estimated. By considering the absolute plastic deformation imposed on the individual steel grains, it might be possible to link the random variation of the stresses with the distribution of dislocations. There may also be a connection between the stored plastic energy and the absolute plastic deformation.
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