Rockwell hardness test

Rockwell test procedure

In the Rockwell hardness test, a differential-depth method, the residual depth of the indent made by the indenter is measured. In contrast, the indentation size is measured in the Brinell, Vickers and Knoop optical test methods.
The deeper a defined indenter penetrates at a defined test force into the surface of a workpiece (specimen), the softer the tested material.

Categorisation of the Rockwell method

The Rockwell method is a static hardness testing method, which can be further characterised as follows:

It is one of the standardised procedures (ISO 6508, ASTM E18).
The process is used to test hardness in the macro range (test force >= 49.03 N), more precisely with a test force of 29.42 to 1471 N.
It is a differential-depth method. This means that the residual depth of indentation left by the indenter is measured to determine the hardness value of a test specimen.
Indenter shape and material: Depending upon the specific Rockwell method employed, the indenter is either a diamond cone (with a cone angle of 120°) or a hard metal ball (with various diameters depending on the method).

Distinction between Rockwell and Super Rockwell

Rockwell methods and applications

How to read and represent a Rockwell hardness value

Advantages and disadvantages of the Rockwell method

The Rockwell method has the following advantages:

no specimen preparation required (separation, grinding, embedding)
hardness value directly readable, no optical evaluation required (measurement of diagonals as in the optical methods)
quick (short test cycle) and cost-effective process (the relevant hardness testers are relatively inexpensive, as they do not need to be equipped with elaborate optical systems, such as those used in Brinell, Vickers and Knoop machines)
non-destructive testing; the test specimen can be used for other purposes.

The Rockwell method has the following disadvantages:

It is not always the most accurate hardness testing method, as even a slight error in measuring the depth difference can result in a significant error in the calculated hardness value.
The test location must be completely free of all contamination (e.g. scale, foreign bodies or oil) in order to achieve a meaningful test result.
The indenter has unknown effects on the test results, e.g. if the indenter is worn and the point of the tip is no longer sufficiently acute (only use certified and calibrated indenters in order to minimise such effects!).
With increasing hardness, it becomes increasingly difficult to distinguish between materials.