The indentation hardness test is the most common method for evaluating the mechanical properties of beryllium copper components. The method is low cost, fast, and easy to operate, while requiring a small amount of material to be inspected. Hardness testing is used to monitor process operations. For example; cold working, solution annealing, quenching and hardening.
The selection of hardness test methods for strip and sheet products has a set of hardness test methods (Table 1) for beryllium copper. Based on the type of alloy, the thickness of the state (hardness) and parts may be, can be found in the corresponding ASTM standards and equipment and detailed information on the corresponding verification step.
Rockwell test The Rockwell hardness test consists of thirty different methods (scales) depending on the shape of the load and the indentation. The most commonly used Rockwell scales B and C are generally not used to detect beryllium copper alloys unless the thickness of the part is above 1 m.m. The hardness values ​​for the B and C scales are for reference only. As a technical condition of the material and inspection of the sheet product, it is necessary to carry out the inspection using a suitable surface scale (N and T) or a microhardness scale.
Table 1. Hardness test method for beryllium copper Hardness test method ASTM standard Rockwell E18
Vickers E29
Knoop E348
The surface Rockwell hardness test uses a N and T scale and can apply a load of 15 or 30 g. The surface calibration method allows the minimum thickness of the specimen to depend on the hardness of the material. See ASTM Standard E18. As an approximation, a load of 30 g is used for a sample having a thickness of 0.6 mm or more, and a load of 15 g is used for a sample of 0.4 mm thick, and a thinner material (Wicks and Knoop) is used for a thinner material. [next]
Wilhelm and Knoop test
The standard Vickers hardness test can also be used as a diamond cone hardness (DPH) test. The load is between 1 and 120 kg. When the load is less than 1000g, it is regarded as the Vickers microhardness test. The principle of load selection is that the diagonal of the Vickers indentation is less than 20% of the thickness of the part.
The Knoop test is a special microhardness using a long indentation (compared to the Vickers square indentation). Its long axis is equivalent to 7 times the short axis. Due to the anisotropy of cold-worked parts and the directionality of the test indentations, it is often necessary to repeat the Knoop readings multiple times to obtain accurate test data. If possible, for each test, the average of the Knoop readings at 90o should be taken. The loading range of the Knoop test is 1-1000 g. When testing the thin material with Vickers hardness, the hardness should be hardness on the cross-section of the sample. The thickness of the metallographic polished sample is at least 0.05 mm.
The interpretation of the test results is due to the small volume of material affected during the hardness test. It is necessary to carefully obtain representative test values. Multiple measurements should be taken to avoid unevenness, such as hard bismuth or grain boundaries. The resulting error reading. When uneven cold working causes the surface hardness to be high, the hardness of the cross section should be checked. The penetration depth of the indentation must be less than 10% of the thickness of the metal, and at least two indentation radii are taken from one corner. The reading.
When the hardness test value indicates the strength of the material, it cannot replace the tensile strength. When the tensile strength and hardness value are given at the same time, the tensile value is given priority. The hardness value is only used as a reference. For convenience, the hardness is often used. The conversion value of the scale. However, ASTM does not allow the conversion value of this scale to be used in the certificate of the material.
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