What is the Difference: between Rockwell, Brinell, and Vickers?

III. What is the Difference between Rockwell, Brinell, and Vickers Hardness?

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While hardness is essential, especially to metallurgists and engineers in the materials industry, it is worthy of note that it only describes the material&#;s resistance to a force or load application and does not determine some other functional properties. Also, the most common test methods offer several differences that ensure they are suitable for specific usages. 

• Rockwell

Description: 

The Rockwell hardness test method can easily pass as the most applied form of testing for material hardness majorly due to benefits like its fast-testing procedures and its high accuracy. According to ASTM E18, the applicable standard, the Rockwell hardness test often occurs in three phases. First, you apply an initial load, often called a preload, using either a ball or a diamond indenter for a short period. The preload is removed after the time elapses, the indentation caused by this load is measured, and the load increases. The increased load is applied to the material in the second phase, and the resulting indentation is measured. The difference in the resulting indentations from the preload and the final load gives the Rockwell value. The applied load for the Rockwell hardness test often ranges from 15kgf to 3,000kgf.

Advantages:

• This method does not require optical instruments like other hardness testing methods and is faster than most methods. 

• Imperfections and surface roughness do not affect its accuracies

• Circular-shaped materials like cones and cylinders are not a problem with the Rockwell test

• Measuring indentation is fast with the Rockwell test as it has a short measurement cycle

• It also tests plastic material accurately using a ball indenter. 

Disadvantages:

• It has a limited range of testing forces.

• Untreated steel and other materials with various irregularities might need additional tests using the Brinell test to ascertain their material hardness, as Rockwell alone will not suffice.

• For an accurate result, good contact is required between the indenter and the material surface. Where impurities are present on the material support surface, a deformation might occur on applying the test load, resulting in an inaccurate result.  

• The Rockwell hardness test is not the most accurate when used for hard materials.

Related Article: What is the Rockwell Scale?

Related Article: What are the Advantages and Disadvantages of the Rockwell Method?

• Brinell

Description:  

While the Brinell hardness test is widely used in the industry today, some features which make it unique are worth mentioning. Firstly, it enjoyed standardization before any other method was standardized which also accounts for why it is widely used. It is also the preferred accurate method for rough and coarse-grained surfaces that otherwise couldn&#;t be measured using other hardness tests. The test measures the indentation caused by a tungsten carbide ball of a diameter that ranges from between 1 to 10mm. More importantly, the load application can be as high as 3,000kgf which causes a permanent indentation where a low-powered optical instrument is used to check this impression. 

Advantages: 

• Brinell tests are most suitable for rough surfaces and materials as the first widely accepted hardness testing method.

• It utilizes a high load range for testing, which means it can test various hard materials. 

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• It has a wide range of hardness measurements.

• It is suitable for measuring the hardness of both ferrous and non-ferrous metals.

• Its spherical indenter makes the Brinell test more accurate than the Rockwell testing method, as it evenly distributes the load on the material surface. 

Disadvantages: 

• Using an optical instrument to measure the indentation made on the material surface poses opportunities for errors in the results.

• The time taken for equipment preparation also wastes a lot of time required for the actual test making the entire process very slow.

• The cost of carrying out a Brinell test is relatively high as you require an optical measuring instrument. 

• Vickers

Description: 

The Vickers hardness testing method is often considered a micro-hardness test as it is usually applied to small or thin objects and materials. Following the procedures given in ASTM E384 as the standard for micro-hardness testing, you&#;ll typically require a diamond indenter with an applicable load range of 10gf and 1kgf to produce an indentation on the material surface. Using an optical measuring instrument to measure the indentation is also required as the indentations are usually very small. It also means that the material surface must be well polished and smooth to achieve a highly accurate result. 

Advantages: 

• It has a wide material testing range for both hard and soft materials.

• The main test is straightforward to perform.

• The diamond indenter size is not considered in the calculations

• Materials of different hardness can employ the same diamond indenter for their measurement 

• It is very suitable for hardness testing in the laboratory 

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Disadvantages: 

• It takes a lot of time to execute as you&#;ll often require an optical measuring instrument which makes it slower than other testing methods

• The smooth and polished surface required can also be a source of inaccuracies when not adequately polished to achieve the necessary smooth surface.

• It also requires an extensive level of preparation which makes it laborious.

• Sometimes the test load is unevenly distributed across the material&#;s surface, making the indentation more apparent on the edges than on the sides of the material, which poses some inaccuracies in the results. 

Related Article: What are the Advantages and Disadvantages of the Brinell Method?

Related Article: What are the Advantages and Disadvantages of the Vickers Method?

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