The Brinell hardness tester is a precision instrument used to test the Brinell hardness of metals. It is primarily employed to determine the hardness of materials such as cast iron, steel, non-ferrous metals, and soft alloys. The Brinell hardness test produces the largest indentation among all hardness testing methods; because it reflects the material’s overall properties and remains unaffected by micro-segregation of the microstructure or compositional non-uniformity, it is considered a high-precision hardness testing method.
Target Materials
Forged steel and cast iron with non-uniform structures
Principle
Measurement based on indentation diameter
Application
Metallurgy, forging, unquenched steel, etc.
Introduction
Brinell hardness testers are used to test castings, forgings, steel in its as-supplied state, non-ferrous metals, and semi-finished steel components that have undergone quenched-and-tempered heat treatment. As a portable instrument suitable for workshop use, it is easy to operate and carry; it enables on-site testing of large workpieces without the need for sampling, allowing for piece-by-piece inspection.
Brinell hardness testers are primarily used for testing the hardness of forged steel and cast iron, which often possess non-uniform microstructures; there is a strong correlation between Brinell hardness and tensile test results for forged steel and gray cast iron. The Brinell test is also applicable to non-ferrous metals and mild steel, and the use of small-diameter ball indenters allows for the testing of small or thin materials. These testers are predominantly used for inspecting raw materials and semi-finished products; due to the large size of the resulting indentation, they are generally not used for inspecting finished products.
Selecting test conditions for the Brinell test—specifically the test force (F) and the indenter ball diameter (D)—involves considerations similar to choosing a scale for the Rockwell test. These choices cannot be made arbitrarily but must adhere to specific rules regarding the appropriate combination of test force and ball diameter; consequently, the application process is slightly more complex than that of the Rockwell test.
Brinell Test Principle
The working principle of the Brinell hardness tester involves pressing a steel ball of a specific diameter into the surface of a test specimen at a controlled speed and under a specified test force; the force is then removed after a prescribed dwell time. The Brinell hardness value of the metal is expressed as the average pressure exerted over the spherical surface area of the indentation.
Technical Requirement
The Brinell hardness tester is a precision instrument used to measure the Brinell hardness of metals. Although there are various types of Brinell hardness testers with differing designs, they must all meet the following technical requirements:
1. The structure of the Brinell hardness tester must satisfy the testing specifications outlined in the national standard “Metallic Materials—Brinell Hardness Test.”
(1) The Brinell hardness tester must be equipped with spherical indenters of the various specifications required by the aforementioned standard. Refer to the table for the permissible diameter tolerances, surface quality, and hardness requirements for the spheres.
Requirements for Brinell hardness indenters<br> | ||||
Diameter /mm | Tolerance/mm | Surface RoughnessRa/μm | Steel Ball HV10 | Carbide Ball HV |
10 5 2.5 2 1 | ±0.005 ±0.004 ±0.003 ±0.003 ±0.003 | ≤0.2 | ≥850 | ≥1500 |
(2) During testing, it shall be possible to apply a predetermined test force or a test force within the range of 9.807 to 29,420 N (1 to 3,000 kgf) as required.
(3) The test force shall be applied uniformly and smoothly, without impact or vibration. The application time for the test force shall be 2 to 8 seconds, and the dwell time of the test force shall be selectable and controllable based on the properties of the material being tested.
2. The Brinell hardness tester shall meet the requirements of the verification regulations.
(1) The allowable error of the test force of the Brinell hardness tester should not be greater than ±1.0%, and the variation should not be greater than 1.0%.
(2) Regarding the display error and repeatability of the Brinell hardness tester, the display error of the Brinell hardness tester refers to the relative error between the hardness value displayed by the tested hardness tester and the standard value. During the inspection, measure 5 points evenly distributed on the standard block, and use the arithmetic mean of the 5 points to calculate the indication error according to the following formula.
——Arithmetic mean of five hardness measurements；
H——Hardness value of a standard hardness block.
Requirements regarding the repeatability of Brinell hardness readings are intended to ensure the operational stability of the hardness tester and minimize the scatter of test data. Factors such as excessive friction in the tester’s moving parts, looseness or wear of the knife-edge or knife-seat, and insecure mounting of the ball within the indenter sleeve can all lead to increased variation in readings. Additionally, repeatability is influenced by the non-uniformity of the standard test block.
The requirements for the indication error and repeatability of the hardness tester are given in the table:
Hardness of the standard blockHBS(HBW) | Indication error δ (%) | Repeatability of indication HBS(HBW) |
≤225 >225 | ±3 | 0.06 0.03 |
Feature
(1)Permanent Indentation
Using a 3,000 kg test force and a 10 mm ball, the resulting indentation accurately reflects the true hardness of materials with coarse grain structures, such as cast iron, cast steel, and forgings. The permanent indentation left after testing allows for re-examination at any time.
(2)True and Accurate
Testing follows the authentic Brinell hardness test principle—identical to that of benchtop Brinell testers—rather than relying on the significantly distorted converted values often produced by other portable instruments (such as Leeb hardness testers).
(3)Precise Testing
The test force calibration accuracy is within 0.5% of the load, and the hardness testing precision matches that of benchtop models.
(4)Any Orientation
There are no directional limitations; measurements can be performed in any orientation, including overhead, underneath, sideways, or inverted positions.
Advantages
The advantage of the Brinell hardness test lies in the representativeness of the hardness value. Typically employing a 10 mm diameter ball indenter and a 3000 kg test force, the test creates a large indentation area. This reflects the average value of the combined effects of various constituent phases across a significant area of the metal, minimizing the influence of individual phases or minor local inhomogeneities. Consequently, it is particularly suitable for testing materials with coarse grains, such as gray cast iron, bearing alloys, and certain metallic materials. The test data is stable and reproducible, with precision higher than that of the Rockwell test but lower than that of the Vickers test. Furthermore, there is a strong correlation between Brinell hardness values and tensile strength values.
The Brinell hardness test offers excellent representativeness regarding hardness. It generally utilizes a large-diameter cemented carbide ball indenter and test forces up to 3000 kg. The resulting large indentation area eliminates the influence of micro-scale phase variations, providing a comprehensive average of the properties of polycrystalline metallic materials. This makes it especially suitable for testing coarse-grained materials such as gray cast iron, annealed steel, and bearing alloys, yielding good repeatability and stable results. Additionally, research indicates a strong correlation between Brinell hardness values and tensile strength values.
Disadvantages
The disadvantages of the Brinell hardness test include large indentation sizes, which complicate the inspection of finished products; a more complex testing process compared to the Rockwell hardness test; and time-consuming measurement operations and indentation readings. Furthermore, phenomena such as ridging, sinking, or smooth transitions at the indentation edges can lead to significant errors in measuring the indentation diameter; consequently, the test requires operators with skilled technique and extensive experience, and is typically performed by specialized laboratory personnel.
Indentors
Indentors generally come in four sizes: Φ2.5 mm, Φ5 mm, Φ10 mm, and Φ1 mm.
