Hardness testing – overview of Brinell, Vickers and Rockwell

What is hardness testing and what is it used for?

Hardness is the resistance of a material to the penetration of a harder indenter. Depending on the standard method, hardness is calculated from an indentation area (measured optically), an indentation diagonal (measured optically) or a penetration depth (distance measured between minor and major load). Hardness values often correlate with strength properties, which is why standardised conversions exist. However, conversions depend on material and condition and do not replace direct strength testing.

Which applications require hardness testing?

• Incoming and in-process inspection in aerospace, automotive and medical engineering.
• Testing of heat treatments, coatings and surface layers (especially Vickers).
• Hardness profile measurements (Vickers at defined step distances).
• Failure analysis and microstructural assessment (revealing local differences).

How do the hardness testing methods work in detail?

Brinell hardness testing (DIN EN ISO 6506-1)

A hard-metal ball (HBW) is pressed into the prepared surface with a defined test force F. After unloading, two indentation diameters d at right angles are measured optically. The Brinell hardness HBW is calculated from this. Large ball diameters and test forces are suitable for coarse-grained microstructures; very high-strength materials are less suitable. The correct choice of ball diameter and test force ensures that the rim of the indentation neither piles up excessively (force too high) nor becomes ill-defined (force too low).

Vickers hardness testing (DIN EN ISO 6507-1)

A diamond pyramid (face angle 136°) produces a permanent indentation. The two diagonals are measured and the Vickers hardness HV is derived from them. The advantage: a wide force range down to the micro-load range (e.g. HV0.01) enables fine hardness profiles, surface layers and small components to be characterised. This requires appropriate surface preparation and reliable optical evaluation.

Rockwell hardness testing (DIN EN ISO 6508-1)

In Rockwell testing (e.g. HRC), the penetration depth of an indenter between minor and major load is measured. For HRC a diamond cone (120°) with a rounded tip is used. The method is robust, fast and well suited for automated serial testing. For very thin layers and very small spacing between indentations, Rockwell is less suitable than Vickers.

How are hardness values written correctly?

• HBW 2.5/187.5/10 – Brinell with ball Ø 2.5 mm, test force 187.5 kgf, dwell time 10 s.
• HV 30/10 – Vickers hardness with 30 kgf (≈ 294 N) and 10 s.
• HRC 62 – Rockwell hardness on the C scale (diamond cone), dimensionless.

Units: Brinell and Vickers are historically given without units (HBW, HV), but they are based on force/area relationships. Rockwell is a scale-specific number (HRA/HRB/HRC …).

Which method should I choose?

For serial testing with high throughput, Rockwell is popular; for fine microstructural differences and layer characterisation, Vickers offers the highest resolution. Brinell is particularly informative for coarse-grained or heterogeneous materials with sufficient thickness.

Which standards and conversion rules apply to hardness testing?

Brinell: DIN EN ISO 6506-1, Vickers: DIN EN ISO 6507-1, Rockwell: DIN EN ISO 6508-1. DIN EN ISO 18265 can be used for the conversion between hardness and tensile properties. Conversions are only valid within certain limits and depend on material and condition – for direct strength values, a tensile test or the Imprint Test (indentation plastometry) without conversion is preferable.