Hardness testing is performed to determine a material’s resistance to plastic (permanent) deformation, and is generally useful in realizing a material’s response to a heat treatment process. A hardness test does leave a permanent mark on the test sample. The affected area is usually small enough to be of no concern, however, a hardness test is still classified as a destructive test. Therefore, finished machined parts could be damaged due to this test. In cases such as these, the customer should either mark non-critical areas or supply test pieces that represent the finished part material heat lot and geometry.