FAILURE ANALYSIS
Corrosion pitting of stainless steel due to a lack of homogeneity in the material.

Cutting at corrosion's level
Breaking: due to a solicitation exceeding the resistance limit of the material.

Breaking up of a steel bar surface (important plastic deformation).
Fault on the surface: detected after polishing of the piece. Defect due to an inclusion in the metal base.

Rhenium inclusion in a precious metal causing a "comet" when polishing.