Limitations of Hardness Test

1) Hardness value alone cannot reflect the mechanical properties of different materials.

For different materials, if their tensile strength (σb), yield strength (σs, or 00.2), elongation (ε), cross-sectional shrinkage (ψ) and impact toughness (ak) or impact energy (Ak) and other mechanical performance indicators are the same, then in many cases, they can be considered to have the same mechanical behavior under various load conditions and are interchangeable.

2) Hardness value alone cannot explain the overall mechanical properties of the workpiece. Some parts with the same material grade can have the same hardness value, but due to different heat treatment processes, their overall mechanical properties may have a large difference.

3) Hardness lacks representativeness of mechanical properties under certain conditions. It is precisely because hardness alone cannot fully reflect other mechanical properties of the material, especially the overall mechanical properties. Therefore, under many working conditions, hardness alone is far from enough to characterize the quality of the material.

4) It is difficult to fully measure the quality of the material after heat treatment by hardness alone, and it is difficult to judge whether the heat treatment process is appropriate.

For example, the hardness of a hypoeutectoid steel part that has been overheated by quenching is the same as that of a part that has been quenched normally, but the impact toughness of the former is much lower than that of the latter.

This is because the hardness of the quenched part mainly depends on the carbon content of the martensite, and the impact toughness is closely related to the coarseness of the martensite structure.

The martensite of overheated steel is coarse, so its impact toughness is greatly reduced. Another example is that the hardness of hard aluminum that has been obviously overheated is the same as that of the same alloy that has not been overheated, but the strength (especially fatigue strength) and elongation, impact toughness, etc. of the former are significantly lower than those of the latter.

This is because the overheated hard aluminum has undergone boundary melting. Due to the above limitations of hardness testing, in the production and research of materials and their parts, in addition to hardness testing, other performance tests must be carried out according to specific circumstances. Of course, this does not affect the widespread application of hardness testing.

Optical Brinell Rockwell Vickers Multi-functional Hardness Tester HBRV-187.5 with 40x Reading Microscope

Main Parameters: