The Brinell hardness test consists in indenting the metal surface with a 10-mm diameter steel ball at a load of 3,000 kg.
For soft metals the load is reduced to 500 kg to avoid too deep an impression. For very hard metals Tungsten carbide ball can be used to minimize distortion of the indenter. The surface on which the indentation is made should be relatively smooth and free from dirt or scale.
Brinell Test Method
- Sample is prepared first. The sample preparation includes grinding, polishing & etching.
- The indenter is pressed into the sample by an accurately controlled test force.
- It is important to choose the combination of load and ball size carefully so that the indentation is free from distortion and suitable for measurement.
- The force is maintained for a specific time (max 30Sec.).
- After this time period, 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 a optical microscope.
- The Brinell hardness number is a function of the test force divided by the curved surface area of the indent.
HB = The Brinell hardness number
F = Applied load in kg
D = Diameter of the spherical indenter in mm
d = Diameter of the resulting indenter
impression in mm.
Load & Time For Brinell Test
In Brinell test, the load applied (P) is directly proportional to the ball diameter (D).
P ∝ D²
P= K D²
Where K is the Load factor.
|Material||Value of K||Load in Kg||Time of load (sec.)|
|Steel & Cast Iron||30||3000||10-15|
|Copper & it’s alloys and Al alloys||10||1000||30|
|Lead & it’s alloys||1||100||60|
|Spherical Steel Ball||Minimum hardness 800 Kgf/mm^2 on Vicker Scale|
Indenter choice based on specimen tested
|For Material upto 450 BHN||High Carbon Steel|
|Greater than 450 BHN||WC Ball|
d/D For Brinell
The d/D ratio ensures the impression is reasonably similar. it’s value is 0.25- 0.50. it’s ideal value is 0.375.
Brinell hardness test depends on the load. it is best suited for measurement of hardness upto 450 BHN.
1. The greatest error found in Brinell hardness test is deviation in the measured diameter of impression from the actual one . This is found due to localized deformation of metal at the rim of impression. Ridging (d’>d) & sinking (d'<d), these two irregularities found due to localized deformation.
2. Flattening Of Indenter- The minimum hardness of Brinell ball should be 800Kgf/mm² on Vicker scale. Although indenter choice is based on the material tested.
- Testing Surface should be clean.
- Specimen should be flat and normal to indenter.
- Minimum thickness of workpiece should be 10 times of depth of impression.
- Distance between two indentation should be 2 or 3 times of dia of indentation.
- Thin hard component should not be tested on Brinell hardness.
- it is Easy to perform
- It can measure hardness of heterogeneous material such as grey cast iron containing very soft graphite flakes in the hard matrix due to large indenter (10mm).
- Brinell hardness is function of carbon content in steel. Therefore this method provide a rapid estimation of approximate carbon content in steel.
- Brinell hardness number is dependent on load.
- Hardened steel and surface hardened steel can not be tested by this method.
- It has large size of indentation.
Question For You
- Why Hardness of Grey Cast Iron is measured by Brinell hardness test?
- What is the unit of BHN?
- What is the standard time of loading in measuring hardness of steel by Brinell hardness test?