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According to the principle of the Leeb hardness test, as long as the material has a certain rigidity and can form a rebound, an accurate Leeb hardness value can be obtained. However, there is no corresponding conversion relationship between the Leeb hardness and other hardness standards for many materials. The Leeb hardness tester is only equipped with conversion tables for 9 materials, specific materials are as follows: steel and cast steel, alloy tool steel, gray cast iron, nodular cast iron, cast aluminum alloy, brass, bronze, pure copper, and stainless copper. For some special material samples, users can use the fitting curve software provided by the company to make special conversion tables. In actual production, a variety of metal materials are used. Since the Leeb hardness tester is sensitive to the processing method and the alloy composition of the material, and the hardness conversion tables stored in the Leeb hardness tester chip cannot meet all users' needs, users can use fitting software to make their own special hardness conversion tables during testing.
The error of converting Leeb hardness to other hardness includes two aspects: one is the measurement error of Leeb hardness itself, which involves the dispersion when the test is conducted according to the method and the measurement error of multiple Leeb hardness testers of the same model. The other aspect is the error generated by comparing the hardness measured by different hardness test methods. This is because there is no clear physical relationship between various hardness test methods, and it is affected by measurement unreliability during mutual comparison.
The conversion table in the Leeb tester may produce deviations for the following steel types: all austenitic steel heat-resistant tool steel and martensitic chromium steel (tool steel); hard materials will cause an increase in elastic modulus, resulting in lower L values. This type of steel should be tested on the cross-section. Local quenching will cause higher L values. Magnetic steel will cause lower L values due to the influence of the magnetic field. Surface-hardened steel with a soft matrix will cause lower L values, but it does not affect the L value when the hardened layer is greater than 0.8mm.
Generally, due to the small size of the tooth surface, the testing error is relatively large. Users can design corresponding fixtures according to the situation to help reduce the error.
The Leeb hardness value is not only related to hardness and strength but also to the elastic modulus. The hardness value is a characteristic parameter of material hardness and plasticity, and the components of both must be measured simultaneously. In the elastic part, the L value is first affected by the E modulus. In this respect, when the static hardness is the same and the E value is different, the material with a lower E value has a larger L value.
When the measured workpiece is formed by hot rolling process, if the testing direction is consistent with the rolling direction, the test value will be lower due to the larger elastic modulus E. Therefore, the testing direction should be perpendicular to the hot rolling direction. For example, when measuring the hardness of cylindrical sections, it is better to test in the radial direction (generally, the hot rolling direction of the cylinder is axial).
When measuring the hardness of pipe fittings with the Leeb hardness tester, please pay attention to: make sure the pipe fittings are securely supported, the testing point should be close to the support point and parallel to the support force, and place an appropriate core inside the thin-walled pipe.