Rockwell hardness test

Rockwell test procedure

The Rockwell hardness test is a standardised depth difference method in which the permanent penetration depth of a test specimen into the material to be tested is determined under precisely defined test conditions. Unlike the optical hardness test methods, such as Brinell, Vickers or Knoop, which measure the size of the indentation, the Rockwell hardness test focuses on the depth of the permanent indentation. The following applies: If the indenter penetrates deeper into the workpiece surface at a constant test force, the material has a lower hardness. The Rockwell hardness HR is then calculated and specified from this measured indentation depth in conjunction with other parameters.

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

Rockwell testing is characterised by numerous advantages that make it particularly popular in industrial practice:

Complex sample preparation such as cutting, grinding or embedding is not required.
The determined hardness value can be read directly - there is no need for additional optical evaluation, as is necessary with Brinell, Vickers or Knoop methods.
The method impresses with its speed and cost-effectiveness: the test cycle is short and Rockwell hardness testers are more cost-effective than optical testers as no complex optics are required.

Despite its many advantages, Rockwell hardness testing also has some disadvantages:

The accuracy of the method can be compromised - even small measurement errors in the depth difference can lead to significant deviations in the determined hardness value.
The test site must be absolutely clean and free from contamination such as scale, oil or foreign bodies to ensure a reliable test result.
The condition of the indenter plays a decisive role: wear or deviations from the standard specifications influence the result. Therefore, only certified and calibrated indenters may be used.
With very hard materials, it is difficult to differentiate between differences in hardness using the Rockwell test method, even with an exact reading on the Rockwell scale.