The Brinell hardness test is an empirical indentation hardness test that can provide useful information about metallic materials. This information may correlate to tensile strength, wear resistance, ductility, and other physical characteristics of metallic materials, and may be useful in quality control and selection of materials.
PRINCIPLE OF THE BRINELL HARDNESS TEST
An indentation hardness test using a verified machine to force an indenter (tungsten carbide ball with diameter), under specified conditions, into the surface of the material under test. The diameter of the resulting indentation is measured after the removal of the force. The general principle of the Brinell indentation hardness test consists of two steps:
- The indenter is brought into contact with the test specimen in a direction perpendicular to the surface, and the test force is applied (Apply the test force within 1 to 8 s). The test force is held for a specified dwell time and then removed (Maintain the fully applied test force for 10 s to 15 s).
- The diameter of the indentation is measured in at least two directions perpendicular to each other. The Brinell hardness value is derived from the mean of the diameter measurements.
REPRESENTATION OF THE BRINELL HARDNESS VALUE
Brinell hardness values shall not be designated by a number alone because it is necessary to indicate which indenter and forces have been employed in making the test. Brinell hardness numbers shall be followed by the symbol HBW, and be supplemented by an index indicating the test conditions in the following order: Diameter of the ball (mm) and a value representing the test force (kgf). Examples: 450 HB10/3000 = Brinell hardness number of 450 obtained with a ball diameter of 10mm and a test force of 3000 kgf, 150 HB2.5/62.5 = Brinell hardness number of 150 obtained with a ball diameter of 2.5mm and a test force of 62.5 kgf.
SAMPLE SURFACE PREPARATION
When necessary, the surface on which the indentation is to be made should be filed, ground, machined or polished flat with abrasive material so that the edge of the indentation can be clearly defined to permit the measurement of the diameter to the specified accuracy. Preparation shall be carried out in such a way that any alteration of the surface hardness of the test surface (for example, due to overheating or cold-working) is minimized.
MEASUREMENT OF THE BRINELL INDENTATION
Measure the diameter of each indentation in two directions, perpendicular (90°) to each other. Additional measurements of the indentation diameter may also be made. The arithmetic mean of the measurements shall be used for the calculation of the Brinell hardness number.
For tests on flat surfaces, the difference between the largest and smallest measured diameters for the same indentation shall not exceed 1% of the indenter ball diameter unless it is specified in the product specification, such as for an anisotropic grain structure.
When indentations are made on a curved surface, the minimum radius of curvature of the surface shall be two and a half times the diameter of the ball. Indentations made on curved surfaces may be slightly elliptical rather than circular in shape. The measurements of the indentation shall be taken as the mean of the major and minor axes.
The distance between the centers of two adjacent indentations shall be at least three times the diameter of the mean indentation. The distance from the center of any indentation to an edge of the test piece shall be at least two and a half times the diameter of the mean indentation.
TESTING OF THE AMBIENT TEMPERATURE
Brinell hardness tests should be carried out at an ambient temperature within the limits of 10 to 35°C (50 to 95°F). Users of the Brinell test are cautioned that the temperature of the test material and the temperature of the hardness tester may affect the test results. Consequently, users should ensure that the test temperature does not adversely affect the hardness measurement.
PRINCIPLE OF THE BRINELL HARDNESS TEST
Tungsten carbide balls of four allowed diameters: 1, 2.5, 5 and 10 mm.
The test consists of imprinting a ball of diameter D, with load F, on the specimen to be examined and measuring the diameter d of the imprint left on the surface, after the load has been removed. The Brinell HB hardness is a value equal to a quotient of the test load F of the imprint (expressed in kg f) for the area (in mm2), considered to be a segment of a sphere, with the ball diameter D.
BRINELL HARDNESS SCALES
The combinations of indenters and test forces define the Brinell hardness scales. The standard Brinell hardness scales and test forces correspond to force-diameter ratios of 1, 1.25, 2.5, 5, 10 and 30.
|Brinell scale (Ball diameter mm / Test force kgf)||Force-diameter ratio||Test force (N)||Hardness range|
|HBW 10/3000||30||29420||95.5 to 650|
|HBW 10/1500||15||14710||47.7 to 327|
|HBW 10/1000||10||9807||31.8 to 218|
|HBW 10/500||5||4903||15.9 to 109|
|HBW 10/250||2.5||2452||7.96 to 54.5|
|HBW 10/125||1.25||1226||3.98 to 27.2|
|HBW 10/100||1||980.7||3.18 to 21.8|
|HBW 5/750||30||7355||95.5 to 650|
|HBW 5/250||10||2452||31.8 to 218|
|HBW 5/125||5||1226||15.9 to 109|
|HBW 5/62.5||2.5||612.9||7.96 to 54.5|
|HBW 5/31.25||1.25||306.5||3.98 to 27.2|
|HBW 5/25||1||245.1||3.18 to 21.8|
|HBW 2.5/187.5||30||1839||95.5 to 650|
|HBW 2.5/62.5||10||612.9||31.8 to 218|
|HBW 2.5/31.25||5||306.5||15.9 to 109|
|HBW 2.5/15.625||2.5||153.2||7.96 to 54.5|
|HBW 2.5/7.8125||1.25||77.01.00||3.98 to 27.2|
|HBW 2.5/6.25||1||61.29.00||3.18 to 21.8|
|HBW 1/30||30||294.2||95.5 to 650|
|HBW 1/10||10||98.07.00||31.8 to 218|
|HBW 1/5||5||49.03.00||15.9 to 109|
|HBW 1/2.5||2.5||24.52.00||7.96 to 54.5|
|HBW 1/1.25||1.25||12.26||3.98 to 27.2|
|HBW 1/1||1||22.27||3.18 to 21.8|
BRINELL MINIMUM THICKNESS (mm)
MINIMUM THICKNESS MEASURABLE
The thickness of the specimen tested shall be such that no bulge or other marking showing the effect of the test force appears on the side of the piece opposite the indentation. The thickness of the material under test should be at least ten times the depth of the indentation.
CAUTION: Under certain conditions of testing a relatively thin material or coating on a material with high hardness, there is a potential for the test material to break or shatter under load resulting in serious personal injury or damage to equipment. Users are strongly cautioned to exercise extreme care when testing a material that could potentially fail under load. If there is a concern or doubt, do not test the material.
|Diameter of indentation mm||Ball 10 mm||Ball 5 mm||Ball 2.5 mm||Ball 1 mm|
BRINELL MAXIMUM ALLOWABLE REPEATABILITY AND ERROR
|Reference Block Hardness||Maximum Repeatability R|
(% of d)
|Maximum Error E|
(% of H)
|HBW <= 125||3.0||3.0|
|125 < HBW <= 225||2.5||3.0|
|HBW > 225||3.0||3.0|
TERMINOLOGY & TIPS
Determination of the values of the significant parameters by comparison with values indicated by a reference instrument or by a set of reference standards.
Indenters for the Brinell hardness test shall be tungsten carbide balls of four allowed diameters (1, 2.5, 5 and 10 mm). Dust, dirt, or other foreign materials shall not be allowed to accumulate on the indenter, as this will affect the test results.
Portable Brinell hardness testing machine
A Brinell hardness testing machine that is designed to be transported, carried, set up, and operated by the users, and that measures Brinell hardness by the Brinell indentation hardness test principle.
Brinell hardness machine
Equipment for Brinell hard- ness testing usually consists of a testing machine, which supports the test specimen and applies an indenting force to a ball in contact with the specimen, and a system for measuring the mean diameter of the indentation in accordance with the Brinell hardness test principle. The design of the testing machine shall be such that no rocking or lateral movement of the indenter or specimen occurs while the force is being applied. The design of the testing machine shall ensure that the force to the indenter is applied smoothly and without impact forces.
A specimen support or “anvil” shall be used that is suitable for supporting the specimen to be tested. The seating and supporting surfaces of all anvils shall be clean and smooth and shall be free from pits, deep scratches, and foreign material. If the anvil is damaged from any cause, it shall be repaired or replaced. Common specimen support anvils should have a minimum hardness of 58 HRC.
Flat pieces should be tested on a flat anvil that has a smooth, flat bearing surface whose plane is perpendicular to the axis of the indenter.
Small diameter cylindrical pieces shall be tested with a hard V-grooved anvil with the axis of the V-groove directly under the indenter, or on hard, parallel, twin cylinders properly positioned and clamped in their base.
Special anvils or fixtures, including clamping fixtures, may be required for testing pieces or parts that cannot be supported by standard anvils.
To bring in conformance to a known standard through verification or calibration.
For best results, both the test surface and the bottom surface of the test piece should be smooth, even and free from oxide scale, foreign matter, and lubricants. An exception is made for certain materials such as reactive metals that may adhere to the indenter. In such situations, a suitable lubricant such as kerosene may be used. The use of a lubricant shall be defined on the test report.
Preparation shall be carried out in such a way that any alteration of the surface hardness of the test surface (for example, due to heat or cold-working) is minimized.
The error E
The error in the performance of a Brinell hardness machine at each hardness level, under the particular verification conditions, is estimated by the percent error of the average of n indentation measurements made on a standardized test block as part of a performance verification relative to the certified average hardness value of the standardized test block.
Indenters – Indenters for the Brinell hardness test shall be tungsten carbide balls of four allowed diameters (1, 2.5, 5 and 10 mm). Dust, dirt, or other foreign materials shall not be allowed to accumulate on the indenter, as this will affect the test results.
The repeatability R
The repeatability R in the performance of a Brinell hardness machine at each hardness level, under the particular verification conditions, is estimated by the percent range of diameter values of n indentations made on a standardized test block as part of a performance verification, relative to the average of the n measured diameter values.
Checking or testing to assure conformance with the specification. Brinell testing machines shall be verified periodically using test blocks.