Rockwell hardness testing is a general method for measuring the bulk hardness of metallic and polymer
materials. Although hardness testing does not give a direct measurement of any performance
properties, hardness of a material correlates directly with its strength, wear resistance, and other
Rockwell hardness testing is an indentation testing method. The indenter is either a conical diamond (brale) or a hard steel ball. Different indenter ball diameters from 1/16 to 1/2 in. are used depending on the test scale.
To start the test, the indenter is “set” into the sample at a prescribed minor load. A major load is then applied and held for a set time period. The force on the indenter is then decreased back to the minor load. The Rockwell hardness number is calculated from the depth of permanent deformation of the indenter into the sample, i.e. the difference in indenter position before and after application of the major load. The minor and major loads can be applied using dead weights or springs. The indenter position is measured using an analog dial indicator or an electronic device with digital readout.
The various indenter types combined with a range of test
loads form a matrix of Rockwell hardness scales that are
applicable to a wide variety of materials. Each Rockwell
hardness scale is identified by a letter designation indicative
of the indenter type and the major and minor loads used for
the test. The Rockwell hardness number is expressed as a
combination of the measured numerical hardness value and
the scale letter preceded by the letters, HR. For example, a
Regular Rockwell Hardness Testing - Measures the bulk hardness of the material. There are separate scales for ferrous metals, nonferrous metals, and plastics. Common Rockwell hardness scales include A, B,C and F for metals and M and R for polymers.
Superficial Rockwell Hardness Testing - A more surface-sensitive measurement of hardness than regular Rockwell scales. This technique is useful for testing thin samples, samples with hardness gradients at the surface, and small areas. Superficial Rockwell hardness scales are N and T for metals and W, X and Y for nonmetallic materials and soft coatings.
Testing is typically performed on flat or cylindrical