Introduction
In metal stamping processes, the hardness of the materials affects the success of the stamping operations. Depending on the product and the operations, the material of the die must possess adequate strength and ductility to ensure the proper product characteristics. Hardness is a property of a metal that reflects its resistance to wear and deformation and is often stated in either the Rockwell, Brinell, Vickers scale. It is important to understand the relationship between these three widely used scales to make sure the correct material is selected for the application.
Relationship between the Rockwell, Brinell, and Vickers Hardness Scales
The Rockwell, Brinell, and Vickers hardness scales are all used to measure the hardness of materials. Rockwell hardness is one of the most common types of hardness tests used in metal-forming industries. It is an indentation hardness test that is fast, nondestructive, and highly repeatable. Brinell hardness is a measure of the resistance to permanent indentation of a material. The Vickers hardness test also uses an indentation test method to measure the hardness of materials. Each of these scales has been found to correlate to one another.
The Rockwell scale is generally expressed with a letter-number combination, such as “HRC60”. It is used to measure the hardness of non-austenitic steels, medium and high carbon steels, hard cast irons, and titanium alloys. The Rockwell hardness is calculated by taking the applied load and subtracting it from the depth of the resulting impression.
The Brinell scale is expressed as “HB” and is commonly used to measure the hardness of ductile and cast irons, stainless steels, and other higher alloy steels and non-ferrous alloys. Brinell hardness is calculated by dividing the applied load by the area of the resulting indentation.
The Vickers scale is usually expressed as “HV” and is used to measure the hardness of a variety of materials, including metals, plastics, ceramics, and composites. Vickers hardness is calculated by dividing the applied load by the surface area of the indentation.
Correlation between the Rockwell, Brinell, and Vickers Hardness Scales
The Rockwell, Brinell, and Vickers hardness scales are all interrelated, with each scale displaying a different degree of hardness when compared to the others. To help ensure consistency between the scales, conversion tables have been developed which give a direct conversion of values on one scale to another. While most conversions are approximate, they are largely in agreement with material and grease penetration tests.
For example, a material with a Rockwell hardness of HRC60 would generally have a Brinell hardness of around HB292, and a Vickers hardness of HV450. While this is only one example, it shows the approximate conversion between these three scales and illustrates how any hardness value on one scale can be converted to another.
Conclusion
The Rockwell, Brinell, and Vickers hardness scales are widely used to measure the hardness of metal components. Each of these scales measure hardness in a different way, but their values tend to correlate to one another. Conversion tables can be used to convert a hardness value from one scale to another, allowing for consistent results when comparing different materials. Understanding the correlation between these scales is essential in order to select the correct material for any metal-forming process.
