Differences Between Stainless Steel Hardness Scales: HB, HR, HV

                                                                                         Differences Between Stainless Steel Hardness Scales: HB, HR, HV

Introduction to Hardness 

Hardness refers to the ability of a material to resist indentation by a harder object. It is one of the key performance indicators for metallic materials. Generally speaking, the higher the hardness, the better the wear resistance. The commonly used hardness scales include Brinell Hardness, Rockwell Hardness and Vickers Hardness. 

1. Brinell Hardness (HB)

A hardened steel ball of a specified diameter (typically 10 mm) is pressed into the material surface under a defined load (usually 3000 kg). After holding for a period and removing the load, the Brinell Hardness value (HB) is calculated as the ratio of the applied load to the indentation area. Its unit is kgf/mm² (N/mm²). 

2. Rockwell Hardness (HR)

Brinell testing is not suitable when HB＞450 or the specimen size is too small; Rockwell Hardness measurement is adopted instead. A diamond cone with a vertex angle of 120°, or a steel ball with diameter of 1.59 mm / 3.18 mm, is pressed into the test material under a specified load. Hardness is determined based on the depth of the indentation. 

Three different scales are available for materials of different hardness ranges: 

HRA: Measured with a 60 kg load and diamond cone indenter, for extremely hard materials such as cemented carbide.

HRB: Measured with a 100 kg load and a 1.58 mm hardened steel ball indenter, for relatively soft materials such as annealed steel and cast iron.

HRC: Measured with a 150 kg load and diamond cone indenter, for high-hardness materials such as quenched steel. 

3. Vickers Hardness (HV)

A square-based diamond pyramid indenter with a vertex angle of 136° is pressed into the material surface under a load of no more than 120 kg. The Vickers Hardness value (HV, unit: kgf/mm²) is the load divided by the surface area of the indentation pit.