Plain, Low Carbon Steel
As shown by the micrograph in Figure 1, this nut has been fabricated in part by a cold-forming process. Slip bands and serrated grain boundaries are revealed by the ferrite grains. The steel in this particular region of the nut has undergone a plastic strain of approximately 20% to 40%. Evidence of the slip bands in the ferrite grains also can be seen in Figure 2.
Figures 3 through 6 are SEM micrographs of the microstructure of the nut. The fine lamellar structure of a small pearlite colony is shown in the high-magnification micrographs found in Figures 5 and 6.