Sometimes it’s interesting to see what happens when you cut a material. For thin sheet metal, shearing is a common operation to get to a net or near net geometry. Shearing applies a shear force to the sheet metal being cut by way of two metallic blades which then cause the sheet metal to fail and be cut.
However, the forces applied can also cause cold work to occur. This is particularly interesting in austenitic stainless steels. Austenitic stainless steels are alloyed with chromium and nickel to stabilize the austenite phase. However, when strain is applied, martensite can be formed.
In the below photomicrograph, one can see the shear bands within the austinite grains forming and the transformation to martensite (black instead of white) within the grain boundary. Additionally, the direction of searing can be determined based on the direction of the cold work.
The etchant used in this case, Marbles reagent, is very effective at showing this transformation from cold work.
