Which material can the indenter used in the Rockwell hardness test be made from?

The indenter used in the Rockwell hardness test is typically made from hardened steel. This material is chosen because hardened steel has the necessary strength and durability to penetrate a variety of materials without wearing down or deforming during testing. The indenter must maintain its shape and hardness in order to produce accurate and consistent measurements of the material being tested.

Using softer materials like copper or aluminum would lead to indentation deformities during the testing process, which would compromise the accuracy of the hardness measurement. Additionally, a plastic indenter would not provide the necessary resistance and could easily deform, making it unsuitable for the rigidity required in Rockwell testing. Therefore, hardened steel is the most appropriate choice for ensuring reliable results in evaluating the hardness of different materials.