What are the requirements for samples when testing metal Rockwell hardness?

When testing the Rockwell hardness of metals, the following requirements are imposed on the test specimens:

1. The surface of the specimen should be smooth and flat, free of scale and foreign contaminants, especially grease. It is recommended that the surface roughness Ra of the specimen should not be greater than 0.8um, unless otherwise specified in the product or material standards.

2. The preparation of the specimen should reduce the influence of factors such as heating or cold working on the surface hardness.

3. There should be no visible deformation on the back of the specimen after the test.

For tests conducted with a diamond cone indenter, the thickness of the specimen or test layer should not be less than 10 times the residual indentation depth; for use tests conducted with a ball indenter, the thickness of the specimen or test layer should not be less than 15 times the residual indentation depth.