Understanding Material Hardness: Brinell, Rockwell, and Vickers Methods

Hardness refers to a material's ability to resist localized deformation, especially plastic deformation, indentation, or scratches. It is an indicator of a material's softness or hardness and is one of the key performance metrics for metals. The commonly used hardness indicators include Brinell Hardness, Rockwell Hardness, and Vickers Hardness. 

1. Brinell Hardness (HB) 

Brinell Hardness (HB) is determined by pressing a hardened steel ball or a carbide ball with a specified diameter D  (in millimeters) into the surface of the material under a specific test force F (measured in Newtons, 1 kgf=9.8 N ), holding it for a specified duration, and then removing the force. The average diameter of the indentation d (in millimeters) is measured using a reading microscope. The Brinell Hardness value HB can then be calculated using a formula or obtained directly from a Brinell Hardness table based on d. 

• Symbol: HBS or HBW  

• HBS: Represents a hardened steel ball indenter, used for materials with a hardness value below 450, such as mild steel, gray cast iron, and non-ferrous metals. 

• HBW: Represents a carbide ball indenter, used for materials with hardness values below 650. 

General Principle: 

• The smaller the Brinell Hardness value, the softer the material, and the larger the indentation diameter. 

• Conversely, the larger the Brinell Hardness value, the harder the material, and the smaller the indentation diameter. 

 Range: 8–650 HBW 

2. Rockwell Hardness (HR) 

Rockwell Hardness (HR) is determined based on the depth of the plastic deformation (indentation depth) caused by an indenter, with 0.002 mm as one unit of hardness. By using different indenters and test forces, various combinations can be created, corresponding to different Rockwell hardness scales. 

Usage: 

• When the sample is too small or the Brinell Hardness (HB) exceeds 450, Rockwell Hardness testing is used. 

• The test involves pressing either a 120° diamond cone or a steel ball with diameters of 1.5875 mm, 3.175 mm, 6.35 mm, or 12.7 mm into the material surface under a specific load. The depth of the indentation determines the material's hardness. 

Common Scales: 

• HRA: Uses a 60 kg load and a diamond cone indenter. Applicable to extremely hard materials, e.g., thin steel sheets, cemented carbide.  

• HRB: Uses a 100 kg load and a 1.5875 mm hardened steel ball. Suitable for softer materials, e.g., mild steel, non-ferrous metals, annealed steel. 

• HRC: Uses a 150 kg load and a diamond cone indenter. Suitable for harder materials, e.g., quenched steel, cast iron. 

Usage Ranges for Different Scales: 

3. Vickers Hardness (HV) 

Vickers Hardness (HV) is particularly suitable for microscopic analysis. It is measured by pressing a square-based diamond pyramid indenter with a 136° angle into the material under a test load not exceeding 120 kg. The Vickers Hardness value HVHV is obtained by dividing the applied load by the surface area of the indentation. 

Features: 

• Wide measurement range: 10–1000 HV. 

• Small indentations: Suitable for thin materials and surface-hardened layers like carburized and nitrided layers. 

Applications: 

 Vickers Hardness testing is widely used for measuring thin materials or surface layers due to its precise small indentations.