Understanding the Brinell Hardness Scale

Developed in 1900 by Swedish engineer Johan August Brinell, the Brinell hardness scale is used to test the hardness of metal. The Brinell test is one of the main three tests of hardness in the steel industry, along with the Vickers and the Rockwell hardness tests. The method involves indenting a test material with a hardened steel or carbide ball that is 10 mm in diameter with a load of 3000 kilograms. Be glad you only had to take your SAT, because this test sounds like it'd be pretty painful to pass.

For softer surfaces, the load can be cut down as low as 500 kg to prevent excess indentation. The load is normally applied for 10 to 15 seconds in the case of iron and steel and for at least 30 seconds with other metals. A microscope set to low power is then used to measure the diameter of the indentation caused by the test material. You should use the average of two readings of the diameter of the impression at right angles to enhance the accuracy of the results. The Brinell harness number is calculated by dividing the load by the surface area of the indentation.

When quoting a Brinell hardness number, abbreviated to BHN or HB, the load number must be specified as well as the material the ball was made of. For example, HBS 20/3000 would mean that a hardened steel ball indenter was used. The 20 is the ball's diameter in millimeters, and the 3000 is the force in kilograms.

The Brinell hardness number of different types of steel varies considerably based on several factors. Heat treatments are a common way to change the BHN of the various kinds of steel. Heat treatment is the controlled heating and cooling of metals to alter their physical and mechanical properties without changing the shape of the product. It is often associated with increasing the strength of material, but it can also be used to alter certain manufacturing objectives such as improving machining, adjusting formability and restoring ductility after a cold working operation. It helps with the manufacturing process, and it also improves product performance by increasing strength and other positive features.

Strangely enough, though, hot rolled steel is usually relatively soft when compared to cold rolled steel. Hot rolled steel is made when steel is forced through a set of work rolls at a high temperature. Cold rolled steel is produced when it is forced through at a lower temperature, below its re-crystallization temperature. Hot rolled steel sheets are often used for framing and general structural purposes in order to provide strength and stability and in instances when rust proofing isn't necessary.

Cold rolled steel sheets and cold rolled steel coils are used often in refrigerators and cars. Cold rolled steel is actually formed after the hot rolled steel process. The cold rolled steel sheet minimizes the thickness of the hot rolled steel and it also increases its durability.

Brinell and Rockwell Hardness Scales are used as a quality control indicator on all types of steel sheeting and plate during the manufacturing process. It assists in assuring the customer and end-user get the right grade of material for the job at hand.

The Brinell hardness scale determines more than just the hardness of hot rolled steel and cold rolled steel. It is used to test a variety of different materials. Along with the Vickers test and the Rockwell test, it is one of the main techniques to measure the hardness of various metallic materials.

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