Differences and Comparison Table of Rockwell Hardness, Brinell Hardness, and Vickers Hardness

I. Introduction to Hardness

Hardness represents the ability of a material to resist the indentation of a hard object into its surfaCE. It is one of the important performance indicators of metallic materials. Generally, the higher the hardness, the better the wear resistance. The commonly used hardness indicators are Brinell hardness, Rockwell hardness, and Vickers hardness.

1. Brinell Hardness (HBW)

A hard alloy ball of a certain diameter (usually 10mm) is pressed into the surface of the specimen under a testing load (usually 29.42KN). After maintaining the load for a specified time, the load is removed, and the diameter of the indentation on the specimen surface is measured (see Figure 1). The ratio of the load to the surface area of the indentation is the Brinell hardness value (HBW).

2. Rockwell Hardness (HR)

When the hardness is too high or the specimen is too small to perform the Brinell hardness test, the Rockwell hardness test is used instead. A diamond cone indenter with an apex angle of 120° or a hard alloy ball indenter with a diameter of 1.5875mm or 3.175mm is pressed into the surface of the test material under a certain load. The hardness value is obtained from the depth of the indentation. According to different hardness levels of the test materials, there are several Rockwell scales commonly used as follows:

• HRA: Hardness obtained by using a diamond cone indenter and a 60kgf load. It is used for materials with extremely high hardness (such as hard alloys).

• HRB:Hardness obtained by using a hardened Steel ball indenter of 1.5875mm diameter and a 100kgf load. It is used for materials with relatively low hardness (such as annealed steels and cast iron).

• HRC: Hardness obtained by using a diamond cone indenter and a 150kgf load. It is used for materials with very high hardness (such as quenched steels).

3. Vickers Hardness (HV)

Under a load not exceeding 120kg, a diamond square pyramid indenter with an apex angle of 136° is pressed into the surface of the material. The Vickers hardness value (HV) is the quotient obtained by dividing the load value by the surface area of the indentation (expressed in kgf/mm²).

Practical Relationship

In practice, there is an approximate corresponding relationship among various hardness values of metallic materials, as well as between hardness values and strength values. Since hardness is determined by the resistance to initial and continued plastic deformation, the higher the material’s strength, the higher its resistance to plastic deformation, and the higher its hardness value. However, the conversion relationships differ among materials.

II. Hardness Comparison Table

According to the German standard DIN 50150, the following table shows the approximate correspondence between the tensile strength of steel and the Vickers hardness, Brinell hardness, and Rockwell hardness within commonly used ranges.