Brinell Hardness Test for Metals

Brinell Hardness Test for Metals

A carbide ball is pushed into the material during the Brinell hardness test. The indentation surface is used to determine the hardness of the material!

Introduction

Components must not only be strong but also resistant to wear in a variety of applications. This is usually true anytime two or more components are in motion relative to one another. These include, but are not limited to, gears, shafts, bolts, and pins.

High wear resistance eventually equates to a hard surface, which prevents the surface from being harmed when it comes into touch with neighboring components, thus minimizing wear. As a result, characteristic values are needed to describe a material’s hardness. To get such parameters, one needs first define hardness:

The indentation hardness of a material is proportional to its resistance to penetration by an indenter (indentation resistance)!

All hardness testing techniques, under this definition, are ultimately based on the same concept. An indenter (e.g., a ball, cone, or pyramid) is pushed into the material surface to be tested with a specific force. The hardness of the indentation is dictated by the indentation left behind.

Depending on the material being tested and the boundary circumstances, several hardness tests have evolved, the results of which are usually incomparable. As a result, hardness levels may be compared only if they were determined using similar test methods. The following sections describe the most critical processes and their associated benefits and drawbacks:

• Brinell hardness test (explained in this article)
• Vickers hardness test
• Rockwell hardness test

Hardness testing may be performed on specially produced specimens or actual components, provided their functioning is not compromised by the depression left behind.

Brinell Hardness Test

Brinell hardness testing is an optical procedure used to determine the hardness of materials having a coarse or inhomogeneous grain structure. This is the optimal test technique for determining a material’s bulk or macro-hardness, especially for materials with heterogeneous structures.

The Vickers technique is distinguished from the Brinell method by the fact that the Vickers method employs a pyramid-shaped indenter, while the Brinell method employs a spherical indenter.

The following standards describe the Brinell test methods:

• ASTM E10
• ISO 6506
• JIS Z 2243

Required Equipment

1. Brinell hardness tester
2. Brinell microscope
3. Indenters (2.5mm and 5mm ball)

Brinell Test Machine

1. A loading mechanism, a main screw, and a dial gauge comprise the Brinell Hardness Tester.
2. The loading system, which consists of weights, leavers, a hydraulic dashpot, and a plunger arrangement, is contained inside the machine’s cast iron body.
3. Additionally, a rubber bellow protects the main screw from external influences.
4. It is operated by a hand at the base and carries the test table on its top to hold the specimen.
5. The machine is equipped with two ball indenters (2.5mm and 5mm in diameter) for transmitting the test load to the specimen.

Brinell Test Theory and Principle

The test is performed by pushing a steel ball of diameter ‘D’ into the specimen under a known force ‘P’ for a certain period and then measuring the mean diameter ‘d’ of the imprint left on the surface when the pressure is removed. The Brinell Hardness Number (BHN) is then determined by multiplying the load (in kg-f) by the indentation’s surface area (in mm²).

The depth of the indentation (h) is defined as,

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 that must be applied is dependent on the indenter’s diameter D and the specimen’s material. The table may be used as a guide. The test surface should be smooth and uniformly machined. The specimen’s thickness must be at least eight times the depth of the depression.

Procedure for Testing

1. The test specimen’s surface must be machined, ground, lapped, or polished.
2. Adjust the machine to the stage of the test load that is needed.
3. Select the appropriate indentor and secure it to the machine.
4. Place the specimen on the test table and apply a 10-kg-f minor load to it by rotating the hand wheel and bringing both dial gauge pointers to the’set’ positions.
5. By reversing the loading lever, apply the major load (the remainder of the test load) to the specimen.
6. Maintain the weight on the specimen for the prescribed dwell period (15 seconds) and then release it by forward rotation of the loading lever.
7. Remove the specimen and, using the Brinell Microscope, determine the diameter of the depression.

Observation and Calculation

The test results are recorded as indicated in the figure below, and the Brinell hardness value is computed using the procedure above.

Brinell Hardness Test Application

1. Due to the broad variety of ball sizes and loads available, the Brinell technique is capable of testing a very wide range of hardness values.
2. Due to the fact that the Brinell test employs very high loads and therefore a relatively big imprint, it is often employed to evaluate the hardness of material used in large forgings or castings.

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