Difference Between Brinell and Rockwell Hardness

Hardness is a measure of a material's ability to resist indentation or deformation. It is a crucial property in engineering and manufacturing applications, as it determines a material's suitability for specific tasks. There are many methods to measure the hardness of a material, including Brinell and Rockwell hardness tests. In this essay, we will explore the differences between these two methods.

What is Brinell Hardness?

Brinell hardness (HBW) is the ratio between the applied force and the surface of the print. Indenter is a hard metal ball, with a diameter D that is imprinted by force F into the surface layers of the material. The diameter of the ball is standardized and amounts to: 10; 5; 2.5; 1mm.

By imprinting the test material, a print of the shape of the cubic diameter of the base diameter dB and the depth hB is generated. The Brinell hardness meter uses an impulse force of 9.807N to 29420N depending on the test material and the diameter of the impeller ball

The load is usually applied for 10 to 15 seconds in the case of testing steel or steel materials, and for other softer materials the load must be applied at least 30 seconds. The subject to be tested must be purified and defatted, and the surface smooth so as the measurement to be as precise as possible in order to determine the diameter of the bowl of the calotte.

During the measurement, there must be no vibration, because they could unduly influence the values of the measured hardness. Brinell’s hardness is a dimensionless size. In comparison with other hardness testing methods, Brinell’s ball leaves the deepest and largest print, and thus functionally and/or aesthetically disfigures the surface (if the hardness is measured on the product rather than on the sample).

What is Rockwell Hardness?

Unlike Brinell’s and Vickers’s methods, Rockwell’s method does not measure the size of the imprint, but the depth of penetration of the indenter. That is why in case of Rockwell the hardness is read on the hardness scale, after it has been released.

Inductors are made of a diamond stem or ball of acacia. The stem diamonds have a peak angle of 1200 and a radius of 0.2mm round, while the ball diameter is 1/16″ and 1/8″. HRB (ball) test is used for soft and medium hard metals while HRC (cone) is used for hardwoods and typically heat-treated materials.

The total possible penetration depth of the indenters is 0.2mm (HRC) or 0.26mm (HRB) and is divided into 100 parts by HRC method or 130 for the HRB method, so hardness at Rockwell’s method is: 1e=0.002m. In the HRC method the indenter has a form of a diamond trunk, which is loaded with pre-load F0=98.07 N for a period of 3 seconds, thus obtaining a starting point from which the penetration depth is measured.

The total load F follows, by adding the main load F1=1373N, for a duration of 4±2 seconds, and the amount of hardness defines the depth of penetration of indenter hR, after removal of main load F1, when backfilling occurs due to material elasticity. For the HRB method, the principle of measurement is the same, except that the steel ball is imprinted with a preload of F0=98.07N or main load F1=882.6N so that the total load is F=980.7N.

Differences: Brinell and Rockwell Hardness

There are several differences between the Brinell and Rockwell hardness tests. One of the most significant differences is the type of indenter used. The Brinell test uses a hardened steel ball, while the Rockwell test uses either a diamond cone or a hardened steel ball. The choice of indenter depends on the material being tested and the desired level of precision. The diamond cone is generally used for harder materials, while the hardened steel ball is used for softer materials.

Another difference between the two tests is the method of measurement. The Brinell test measures the diameter of the indentation, while the Rockwell test measures the depth of the indentation. This can affect the accuracy of the results, as measuring the diameter of an indentation can be more challenging than measuring its depth.

The units of measurement used in the two tests are also different. The Brinell hardness number is expressed in kilograms per square millimeter (kg/mm²), while the Rockwell hardness number is expressed in arbitrary units (HRA, HRB, etc.). This can make it more difficult to compare results between the two tests.

The testing procedures for the two tests also differ. The Brinell test involves applying a constant force for a specified period, while the Rockwell test involves applying an initial force followed by a secondary force. This can affect the accuracy of the results, as the application of two forces can introduce more variables into the test.

Finally, the materials that can be tested using the two methods differ. The Brinell test is better suited for softer materials, such as aluminum, copper, and brass. The Rockwell test, on the other hand, is better suited for harder materials, such as steel and titanium.

The following table highlights the major differences between Brinell Hardness and Rockwell Hardness −

Conclusion

In conclusion, both the Brinell and Rockwell hardness tests are widely used methods for measuring the hardness of materials. They differ in the type of indenter used, the method of measurement, the units of measurement, the testing procedures, and the materials that can be tested.

Choosing the right test for a specific application depends on the material being tested, the desired level of precision, and the availability of equipment. It is essential to select the appropriate method to ensure accurate and reliable results.

Vineet Nanda

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Updated on: 21-Aug-2023

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