Hardness tester and method for measuring the hardness of metallic materials

A method for determining the hardness of a metal sample by using a hardness tester provided with an indenter having an indenting tip of a hard and undeformable material and means for loading said indenter with a certain load for producing the penetration of said tip in the metallic sample, the depth of penetration and/or the width of the indentation produced under a given load providing a measure of the hardness of the material, characterized by comprising:

• utilizing an electrically conductive indenting tip and connecting said indenter and said metallic sample to the input terminals of an electric resistance measuring apparatus;
• loading said indenter up to a preset load on a reference metallic sample having a known hardness and detecting the contact resistance under said load;
• functionally setting the tester on a metallic sample to be tested and gradually loading the indenter until the same electrical contact resistance as detected on said reference sample is measured by said electrical resistance measuring apparatus and reading the load which is actually applied to the indenter;
• determining the hardness of the tested sample through a proportionality relationship between said preset load applied to the reference sample and the load applied to the tested sample for attaining the same electrical contact resistance on the reference sample and on the test sample.