Brinell Hardness Test for Metals

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The Brinell hardness test is an optical testing method for samples with coarse or inhomogeneous grain structure. This is the best test method for achieving the bulk or macro-hardness of a material, particularly those materials with heterogeneous structures.

The difference between Vickers method and the Brinell method is that the Vickers use pyramid-shaped indenter, whereas the Brinell method uses a spherical indenter.

Brinell test methods are defined in the following standards-

• ASTM E10
• ISO 6506
• JIS Z 2243

Equipment Required

1. Brinell hardness tester RAB-250
2. Brinell microscope
3. Indentors (2.5mm and 5mm ball)

Brinell Test Machine Description

1. The Brinell Hardness Tester consists of a loading system, the main screw, and a dial gauge.
2. The loading system consisting of weights, leavers and a hydraulic dashpot and a plunger arrangement is enclosed in the cast iron body of the machine.
3. The main screw is also protected from extraneous elements by a rubber bellow.
4. It carries the test table on its top to hold the specimen and is actuated by a hand at the base.
5. The machine is provided with two ball indenters (of sizes 2.5mm&5mm) to transmit the test load on to the specimen.

Theory and Principle of Brinell Test

The test consists of forcing a steel ball of diameter 'D' under a load 'P' into the specimen for a known time and measuring the mean diameter 'd' of the impression left on the surface after removal of the load. The Brinell Hardness Number (BHN) is then calculated as load (in kg-f) dived by the surface area of indention (in mm²).

Depth of Indentation (h) is given by,

And therefore,

Where,
D = Diameter of Ball in mm
P = Applied load in kg-f, and
d = Diameter of indentation in mm.

The test load P, to be applied depends on the diameter D of the indenter and the material of the specimen. The table may be used for reference. The test surface should be machined smooth and even. The thickness of the specimen shall not be less than eight times the depth of indentation.

Test Procedure

1. The surface of the test specimen must be either machined, ground, lapped or polished.
2. Set the machine to the required stage of the test load.
3. Choose the indentor to be used and fasten it to the machine.
4. Place the specimen on the test table and, apply a minor load of 10-kg-f on it by turning the hand wheel and bringing both the pointers on the dial gauge to the 'set' positions.
5. Apply the major load (remaining part of the test load) on the specimen by turning the loading lever backward.
6. Maintain the load on the specimen exactly for the specified dwell time (15 seconds) and then release it by turning the loading lever forwards.
7. Take out the specimen and measure the diameter of the indentation formed on it by using the Brinell Microscope.

Observation and Calculation

The observations taken during the test are recorded as shown as in the figure below and the Brinell hardness value is calculated using the above-given formula.

Application of Brinell Hardness Test

1. Due to the wide number of ball sizes and loads available, it is possible to test a very wide range of hardness values using the Brinell method.
2. As the Brinell test uses relatively high loads, and therefore relatively large indent, it is frequently used to determine the hardness of the material which has undergone forgings or castings of large parts.

Read More: Vickers Hardness Test