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The Vickers hardness test method, also referred to as a microhardness test method (ASTM E-384, E92 and ISO 6507), consists of indenting the test material with a diamond indenter. This indenter has the form of a pyramid with a square base and an angle of 136 degrees between opposite faces subjected to a load of 1g to 120 Kgf. The method is mostly used for small parts, thin sections, or case depth work. The microhardness methods are used to test on almost any type of material. The Vickers test is useful for a variety of applications, for instance for testing thin materials like foils, or measuring individual microstructures.
The Vickers test is easy to use, since the size of the identer isn't of interest for the required calculations, and the indenter can be used for all materials, no matter the hardness. The Vickers hardness test has one of the widest scales, known as the Vickers Pyramid Number (HV) or Diamond Pyramid Hardness (DPH).
The Rockwell hardness test method, as defined in ISO 6508 & ASTM E-18, is the most commonly used method to determine a material's hardness and is suitable for almost all metals. It measures the permanent depth of indentation produced by a force/load on an indenter. The Rockwell test is generally easier to perform, and quicker than other types of hardness testing methods. The method is also more accurate than other types of hardness testing methods. The main advantage of Rockwell hardness is its ability to display hardness values directly.
The Rockwell scale is based on the indentation hardness of a material. There are different scales, denoted by a single letter, that use different loads or indenters. When testing, indentation hardness correlates linearly with tensile strength.
The Brinell hardness test method (as defined in ASTM E10 and ISO 6506) is mostly used when another test method isn't an option. This is when test materials have a structure that is too coarse or a surface that is too rough to be tested using another test method, e.g. castings and forgings. Brinell testing often uses a very high test load (from 500 to 3000 Kgf) and a 10mm ball indenter so that the resulting indentation averages out most surface and sub-surface inconsistencies.
The greatest source of error in Brinell testing is the indentation measurement. Due to disparities in operators making the measurements, the results will vary even under perfect conditions. Less than perfect conditions can cause the variation to increase greatly. Jagged edges make interpretation of the indentation difficult. Frequently the test surface is prepared to remove surface conditions. Automatic optical Brinell scopes use computers and image analysis to read the indentations consistently. This standardization helps eliminate operator subjectivity.
Universal hardness testers are in fact hybrid instruments allowing the user to make Rockwell, Vickers, Knoop, and Brinell hardness tests according to the applicable ISO, ASTM and JIS standards, with one single machine. Universal hardness systems do not convert hardness values, but apply tests according to standard procedures.
While most hardness testers in particular measure only one kind of scale (either Rockwell or Vickers or Brinell), the universal testers cover a wide range of testloads and measurement procedures. Today’s state-of-the-art universal hardness testing machines use innovative technology. This means testing in a wide range of applications, with a high-precision level.