Brinell hardness is a measure of the hardness of a material, typically metal. It is determined by pressing a hardened steel or carbide sphere of a known diameter into the material under a known load, then measuring the diameter of the indentation left by the sphere. The Brinell hardness number (BHN) is calculated by dividing the load used, in kilograms, by the surface area of the indentation, in square millimetres.

The BHN is commonly used to determine the hardness of steels and other metals, as well as some ceramics and composites. The test is widely used because it is simple, inexpensive, and relatively insensitive to the size and shape of the specimen, but is not suitable for materials that are too hard or too soft, and it is not as accurate as other hardness tests such as Rockwell and Vickers.

What is Brinell Hardness Test

The Brinell hardness test is one of several standard methods for measuring the hardness of materials. The test uses a hardened steel or tungsten carbide ball that is pressed into the surface of the material under a known load. The ball is typically 10mm in diameter and the load applied can range from 500 to 3000 kgf. The diameter of the indentation left by the ball is then measured using a microscope. The Brinell hardness number (BHN) is calculated by dividing the load applied by the surface area of the indentation, which is calculated using the equation: BHN = Load (kgf) / (π/4) x (indentation diameter (mm))^2.

The Brinell hardness test is particularly useful for materials that have a relatively coarse grain structure, such as cast iron and some types of steel, as well as materials that have a surface that is not flat, such as forgings and rolled plates. The test is also commonly used for materials that are too large or too heavy to be tested using other methods. However, the test is not suitable for materials that are too hard or too soft, as the indentation left by the ball may not be visible or may be too large, respectively.

Procedure of Brinell Hardness Test

The procedure for performing a Brinell hardness test typically involves the following steps:

1. Prepare the specimen: The specimen should be cleaned and polished to remove any surface contaminants or defects. It should also be large enough and flat enough to accommodate the indentation made by the ball.
2. Select the ball and load: The ball used in the test should be made of hardened steel or tungsten carbide and should have a diameter of 10mm. The load applied should be within the range of 500 to 3000 kgf, depending on the type and hardness of the material being tested.
3. Apply the load: The ball is placed on the surface of the specimen and the load is applied to it using a loading device. The load should be applied for at least 10 to 15 seconds to ensure that the indentation is as deep as possible.
4. Measure the indentation: After the load is removed, the diameter of the indentation is measured using a microscope or a micrometer. It should be measured at the widest point of the indentation and be sure the measurements are taken at 90 degree to the diameter.
5. Calculate the Brinell hardness number: The BHN is calculated by dividing the load applied by the surface area of the indentation. The equation for this calculation is BHN = Load (kgf) / (π/4) x (indentation diameter (mm))^2
6. Record and Report: The results of the test are recorded and reported as the Brinell hardness number (BHN) or as the Brinell hardness number (HB) which is equivalent to BHN x 2.5. The test should be carried out by a skilled operator and measurements should be taken multiple times to ensure accuracy and consistency.

It’s important to note that the Brinell hardness test is not suitable for all materials and it should be used with caution on materials that are brittle, porous, or have a thin or irregular surface. Other hardness test methods may be more appropriate for these types of materials.

Brinell Hardness Test Formula

The formula for calculating the Brinell hardness number (BHN) is as follows:

BHN = Load (kgf) / (π/4) x (indentation diameter (mm))^2

Where:

• Load (kgf) is the load applied to the ball during the test, typically in the range of 500 to 3000 kgf.
• Indentation diameter (mm) is the diameter of the indentation left by the ball on the specimen, measured using a microscope or micrometer.
• π (pi) is a mathematical constant equal to approximately 3.14159
• The formula is based on the principle that the harder the material, the smaller the indentation will be for a given load.

Alternatively, the results can be reported as the Brinell hardness number (HB) which is equivalent to BHN x 2.5.

It’s important to note that the BHN is not a direct measurement of the hardness of the material, but rather an indirect measure of the resistance of the material to plastic deformation. Because the test involves pressing a ball into the surface of the material, it is influenced by factors such as the ductility of the material, the size and shape of the specimen, and the surface condition of the specimen.

Standards for Brinell Hardness Test

Brinell hardness testing is governed by several international and national standards, including:

• ISO 6506-1:2005: This is the primary international standard for Brinell hardness testing, which outlines the procedures and requirements for performing the test on metallic materials. It includes specifications for the ball and load used in the test, as well as the measurement and calculation procedures for determining the Brinell hardness number.
• ASTM E10-18: This is the American Society for Testing and Materials (ASTM) standard for Brinell hardness testing of metallic materials. It is equivalent to ISO 6506-1 and covers the same procedures and requirements as the international standard.
• JIS Z2243: This is the Japanese Industrial Standard (JIS) for Brinell hardness testing. It is equivalent to ISO 6506-1 and ASTM E10-18 and covers the same procedures and requirements as the international and American standards.
• GB/T 231.2: This is the national standard for Brinell hardness testing in China, which covers the same procedures and requirements as the international and American standards.

These standards provide guidelines for the equipment and procedures used in Brinell hardness testing, as well as for the interpretation and reporting of test results. They are intended to ensure that the test is performed consistently and accurately, and that the results can be compared and correlated with other test results from different laboratories.

Requirements for Brinell Hardness Test

There are several requirements that must be met when performing a Brinell hardness test, as outlined in international standards such as ISO 6506-1, ASTM E10-18, and JIS Z2243. These include:

• Specimen preparation: The specimen should be cleaned and polished to remove any surface contaminants or defects. It should also be large enough and flat enough to accommodate the indentation made by the ball.
• Ball and load selection: The ball used in the test should be made of hardened steel or tungsten carbide and should have a diameter of 10mm. The load applied should be within the range of 500 to 3000 kgf, depending on the type and hardness of the material being tested.
• Loading procedure: The load should be applied for at least 10 to 15 seconds to ensure that the indentation is as deep as possible. The ball should be placed on the surface of the specimen and the load should be applied to it using a loading device.
• Indentation measurement: The diameter of the indentation should be measured at the widest point of the indentation using a microscope or a micrometer, and measurements should be taken at 90 degree to the diameter.
• Calculation of Brinell hardness number: The BHN should be calculated by dividing the load applied by the surface area of the indentation. The equation for this calculation is BHN = Load (kgf) / (π/4) x (indentation diameter (mm))^2
• Reporting of results: The results of the test should be recorded and reported as the Brinell hardness number (BHN) or as the Brinell hardness number (HB) which is equivalent to BHN x 2.5.
• Operator Qualification: The test should be carried out by a skilled operator who is trained to perform the test according to the appropriate standard and who is familiar with the equipment and procedures used.
• Repeatability: Measurements should be taken multiple times to ensure accuracy and consistency.

It’s important to note that these requirements are general and may vary depending on the specific application or the type of material being tested. For instance when measuring the hardness of castings or forging the requirements are different than for sheet metal or thin plates.

Advantages and Disadvantages of Brinell Hardness Test

Advantages of Brinell hardness testing

• Simplicity: The test is simple to perform and does not require any special equipment or training.
• Versatility: The test can be used on a wide range of materials, including metals, ceramics, and composites.
• Insensitivity to surface condition: The test is relatively insensitive to the surface condition of the specimen, making it useful for materials that have a surface that is not flat, such as forgings and rolled plates.
• Large indentation: The indentation left by the ball is large enough to be easily measured, even on materials that have a coarse grain structure.
• Inexpensive: The test is relatively inexpensive compared to other hardness testing methods

Disadvantages of Brinell hardness testing

• Inaccuracy: The test is not as accurate as other methods such as Rockwell and Vickers.
• Not suitable for brittle materials: The test is not suitable for brittle materials, as the indentation left by the ball may cause the material to crack or break.
• Not suitable for very soft or very hard materials: The test is not suitable for materials that are too soft or too hard, as the indentation left by the ball may not be visible or may be too large, respectively.
• Surface roughness: The roughness of the surface can affect the results.
• Indentation size: The size of the indentation can be affected by the surface hardness, which may lead to errors if a larger indentation is made.
• Operator dependence: The test is highly dependent on the operator’s skill and experience, which can lead to variations in results if the test is performed by different operators.
• Time-consuming: The test can be time-consuming, as multiple measurements may be needed to ensure accuracy and consistency.

The Brinell hardness test is a useful method for determining the hardness of materials, but it is not suitable for all materials and it should be used with caution on materials that are brittle, porous, or have a thin or irregular surface. Other hardness test methods may be more appropriate for these types of materials.