A Hardness-test of any standard type will correctly express an acceptable result, if performed within the established conditions (minimum thickness, surface preparation, suitable hardness) using:
- a specific indenter (defined by fixed shape, dimensions, material and properties),
- under the application of a certain static force ,
- for a definite time ,
- following precise measuring procedures.
It must be stressed at once that hardness is not a physical property like density or melting point.
It is indeed a structural property reflecting the quality of the specific microstructure of the specimen.
This depends on the material, on the fabrication processes and on the thermal history at the time and in the condition it is when presented to Hardness-test.
The popularity and the common use of Hardness-test for routine acceptance of materials and parts, for process control (i.e. heat treatments, welding etc.), or as an essential element of any metallurgical investigation , derives from its advantages :
- It is non destructive , in that it leaves only a small mark on the surface,
- It is inexpensive and gives an immediate result,
- It is reliable and repeatable in the hands of knowledgeable inspectors