Stainless Steel

Figures 1 through 4 are photomicrographs of the microstructure of the bolt in an area where the 304 stainless steel is in the annealed state, i.e. there appears to be little evidence of plastic deformation in the twinned grains of the microstructure.

The threads on the bolt were evidently produced by thread rolling as shown by cold-worked structure of the stainless steel in the vicinity of the threads. See Figures 5 through 8.

Figures 1 and 2 show a series of horizontal, parallel bands that pass without interruption or displacement from one grain to another. This prominent aspect of the microstructure is called "veining" and is caused by segregation of alloying elements. In this case the segregation is likely carried over from the original ingot structure.