Rockwell Hardness Test

Definition - What does Rockwell Hardness Test mean?

The Rockwell hardness test is the most employed hardness test method. It is used on all kinds of metals, except in situations where the surface conditions and metal structure would produce high variations.

This test takes measurements of the permanent depth indentation caused by a load or force on a particular indenter.

Corrosionpedia explains Rockwell Hardness Test

The Rockwell hardness test is performed primarily through a test force, more commonly known as a minor load or preload. This is applied to a specific sample with the help of an indenter. This reflects the reference, or zero, finish. Once the minor load step is finished, the application of extra load is applied in order to achieve the necessary test load.

After the force has been applied, it is withheld at a pre-determined period to permit elastic recovery. Then, the major load undergoes release and the resulting position is measured against the preload position. The depth indentation variance is also measured between the values of the major load and preload. The distance obtained is then transformed into a hardness digit. There are many scales symbolized by one letter and this utilizes various indenters or loads. The result appears like "HRA," where A is regarded as the scale. Essentially, a harder substance is indicated by a higher letter.

The most widely used indenter is the diamond cone, which can measure the hardness of carbides and steel at 120 degrees. Other materials, especially softer ones, are gauged with the use of tungsten carbide rounds. The test force and indenter together account for the Rockwell scale.

The main advantage of the Rockwell hardness test is that it can display direct hardness values. This prevents tiresome calculations that may be encountered in other techniques used to measure hardness. This method is commonly used in metallurgy and engineering. This test is widely used because of its:

  • Reliability
  • Speed
  • Resolution
  • Robustness
  • Small indentation area

In order to obtain accurate readings, the test material should have a thickness that is 10 times the indentation depth. Readings should also occur at a perpendicular or flat surface, since convex surfaces may result in lower readings. In such cases, correction factors for convex surfaces may be used.

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