Brinell Hardness Test

Brinell Hardness Test

Austempered ductile iron castings, or more commonly ADI castings, is a ductile iron casting which is processed by a special heat treatment. The austempering process, with ductile iron’s superior castability, results in a material which can be used to cast complex shapes, with a greater consistency of quality, and often at less cost.  The heat treatment requires an interrupted quench, usually into a salt bath, to cool the cast part at a planned rate and then held isothermally for long enough to convert the microstructure to Ausferrite. The resulting material has a combination of exceptional strength and toughness, meeting and often exceeding those of alloy steels.

Standards

Brinell Test methods are defined in the following standards:  ASTM E10 ; ISO 6506

Brinell Test Method

All Brinell tests use a carbide ball indenter. The test procedure is as follows:

  • The indenter is pressed into the sample by an accurately controlled test force.
  • The force is maintained for a specific dwell time, normally 10 – 15 seconds.
  • After the dwell time is complete, the indenter is removed leaving a round indent in the sample.
  • The size of the indent is determined optically by measuring two diagonals of the round indent using either a portable microscope or one that is integrated with the load application device.
  • The Brinell hardness number is a function of the test force divided by the curved surface area of the indent.
  • The indentation is considered to be spherical with a radius equal to half the diameter of the ball. The average of the two diagonals is used in the following formula to calculate the Brinell hardness.

Application

Because of the wide test force range the Brinell test can be used on almost any metallic material. The part size is only limited by the testing instrument’s capacity.

Strengths

  • One scale covers the entire hardness range, although comparable results can only be obtained if the ball size and test force relationship is the same.
  • A wide range of test forces and ball sizes to suit every application.
  • “Nondestructive”, sample can normally be reused.

Weaknesses

  • The main drawback of the Brinell test is the need to optically measure the indent size. This requires that the test point be finished well enough to make an accurate measurement.
  • It is slow as testing can take 30 seconds not counting the sample preparation time.

Below is a schematic of a Brinell Hardness Test:-