Users of a Rockwell hardness conversion chart must know the material’s testing results in at least one of the commonly-used hardness scales. The four standard hardness testing methods are Rockwell, Brinell, Vickers and Leeb. The conversion chart compares hardness testing results across each of these methods.
One starts by finding the known result in the column corresponding to the testing method. One then looks across the other columns to find the equivalent hardness under each method. For example, a material with a score of 552 on the Brinell scale corresponds to a score of 56 on the Rockwell C scale.
The Rockwell method estimates a material’s tensile strength based on the depth of indentation. The type of indenter corresponds to a specific letter and hardness scale. For example, a 1/16-inch-diameter steel sphere indenter produces results on the Rockwell B scale.
The Vickers method uses a pyramid-shaped indenter to apply force to the material. The size of the resulting indentation determines the material’s hardness rating. The Brinell method also measures hardness by the scope of an indentation. The Leeb rebound test bounces a projectile against the material and measures the amount of energy lost. Hard materials result in a faster rebound than soft materials.]
When conducting a Rockwell hardness test, scientists choose the combination with the largest force and smallest indenter appropriate for the material type and operation conditions. For brittle or very thin materials, a superficial Rockwell hardness test can be conducted that uses shallower indenters and smaller forces.