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Brinell Hardness Testing
- Reference Information and Standards -


Rockwell is the most common
type of hardness testing.

 

The Brinell method is primarily used to test forgings and castings made of steel and iron. The Indentor is usually a steel ball, 10mm in diameter. Standard loads range from 500 to 3,000 kilograms. The full load is applied for 10 to 15 seconds in the case of iron and steel, and for 30 seconds in the case of many other metals. The diameter of the impression is spherical, and its depth is proportional to the square of its diameter. This relationship is used to determine hardness.

                                                                2F
Brinell hardness number (BHN) =
                                                        D (D - √ D² - d²

To avoid the mathematics, tables such as Table I have been developed.

The Brinell number will be within one percent accuracy for high hardness if the indentation is measured to the nearest 0.01 mm. To obtain an accurate reading the test surface is filed and polished, and the impression is measured using a low-power microscope with a stage micrometer. Usually two readings are taken at right angles to determine the diameter of an indentation. However, certain materials tend to be elliptical in shape and require four diameter measurements taken 45 degrees apart. Some materials will present a poorly defined edge of the indentation. Cold worked alloys usually render an impression with a ridge extending above the original surface of the test piece. Annealed metals will often provide an impression that sinks below the surface. The indentation diameter must be measured with these effects in mind.

 

Another error factor may be introduced if the steel ball is flattened by testing a material harder than 500 BHN. For example, hardened steel cannot be tested with a hardened steel ball. Carbide balls are recommended for testing harder materials. (ASTM Specifications require that you use a carbide ball). Brinell hardness numbers determined with a steel ball are designated HBS; those determined with a carbide ball are termed HBW.

The amount of force applied to the Indentor should produce an indentation that is greater than 0.24 and less than 0.60 of the ball diameter. When a ratio is less than 0.24 the indentation is so small that errors in determining the diameter become a large portion of the total diameter. Further, the test loses sensitivity and small differences in hardness values can not be distinguished when the diameter of the impression exceeds .60 of the Indentor diameter. The following ranges are recommended to maintain an acceptable ratio with a 10mm ball Indentor:

  • 3,000 kilograms BHN 96 to 600
  • 1,500 kilograms for BHN 48 to 300
  • 500 kilograms for BHN 16 to 100

 

There are some general precautions that can be taken to promote an accurate Brinell test:

  • When indentations are made on a curved surface with a 10mm diameter ball, the radius should not be less than one inch.
  • Tests should not be made within two and one half times the diameter of indentation from each other or from the edge of the specimen. Also, an indentation will become asymmetrical if there is not adequate supporting material on each side.
  • The load should be applied perpendicular to the specimen to within two degrees.
  • The specimen should be thick enough to prevent the load from causing a bulge or marking on the side opposite of the indentation.
  • The surface to be indented should be ground and polished to provide a clearly defined indentation.
  • Test bars should be uniform in hardness and calibrated using equipment with traceable accuracy.

 

The limitation of the Standard Brinell Method is due to the optical reading of the indentation that may cause measurement errors due to the operator influence. Furthermore, an accurate specimen surface preparation is needed to obtain reliable results, and the Standard Brinell Method is not considered a quick test and is not suitable for high volume inspection.
To overcome some of these limitations with the Standard Brinell Method the Brinell Method modification is similar to a Rockwell test, as the test is based on the difference of penetration between the preload and load, using loads and Indentor’s required for the Brinell Testing Method.

The Brinell Principle Modification (Depth of Penetration) sequence is:
 


  • Activate test by push button, foot switch, or other method.
  • The Brinell Test Head moves towards the test piece, driven by a Hydraulic cylinder.

 

  • Indentor comes in contact with test surface.
  • Preload is applied.

 

  • Full Load is applied for the time specified in test procedure.
  • Test Head returns to preload position.

 

  • Brinell Hardness result is on a LCD display.

 


Rockwell Hardness Chart (+PDF)
(aka Hardness Scale Conversion Chart)

Round Correction Factor (+PDF)
Hardness Minimum Thickness (+PDF)

ASTM Hardness Test Methods (+PDF)
Rockwell Hardness Scales (+PDF)

Brinell Hardness Chart (+PDF)
Vickers Hardness Chart (+PDF)

Rockwell Hardness Testing
Brinell Hardness Testing
Microhardness Testing


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