Rockwell hardness

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Definition: Leeb hardness is a dynamic hardness testing method. It is a hardness value calculated by having an impact body of specified mass strike the surface of the specimen at a certain speed under the action of elasticity; this value is determined from the ratio of the rebound velocity of the indenter at a distance of 1 mm from the specimen surface to the impact velocity. Multiplying this ratio by 1000 gives the Richter hardness value, measured in HL. II. Principle: The working principle of the Rockwell hardness tester is based on elastic impact. When the impact body strikes the surface of the material under test, elastic deformation occurs. Materials with different hardnesses exhibit varying degrees of elastic deformation. Harder materials exhibit less elastic deformation, and the impact body rebounds more quickly ； Softer materials undergo greater elastic deformation, and the impact body rebounds at a slower speed. By measuring the rebound velocity and impact velocity of the indenter, the Leeb hardness of the material can be calculated. III. Calculation formula: The basic calculation formula for Rockwell hardness (HL) is obtained by multiplying the ratio of the rebound velocity of the impact body (vR) to the impact velocity (vA) by 1000; thus, the basic formula is: HL = 1000×(vR/vA). For example, when the rebound speed of the impact body is 2 m/s and the impact speed is 3 m/s, the Rockwell hardness HL is calculated using the formula as HL = 1000×(2/3)≈667 HL. Formulas for converting hardness values (conversion to other types of hardness). For example, in the case of certain metal materials, HV = e×HL + f (where e and f are coefficients). These coefficients are usually determined based on tests and research on specific materials. In practical applications, if accurate conversion is required, it is necessary to refer to relevant standards or determine appropriate coefficients through experiments. Similarly, for steel materials, there are approximate conversion formulas. For example, HRC = c×HL + d (where c and d are coefficients determined based on factors such as the material). However, these conversion formulas vary depending on the type of material and its hardness range. This is because different materials have varying physical properties, such as elastic modulus, which affects the relationship between different hardness values. For steel and cast steel, the empirical formula is generally HBW = a×HL + b (where a and b are coefficients, which vary for different materials). Within a certain range, a = 0.108 and b = -8.7; this conversion relationship is obtained by fitting a large amount of experimental data. Conversion between Rockwell hardness and Brinell hardness (HBW); conversion between Rockwell hardness and Rockwell hardness (HRC); conversion between Rockwell hardness and Vickers hardness (HV). It should be noted that due to the diversity and complexity of materials, these conversion formulas are only approximate. When high precision in measuring hardness is required, it is best to determine the accurate hardness value using standard hardness testing methods. IV. Domestic standard: GB/T 17394.1-2014: \"Metallic materials – Rockwell hardness test – Part 1: Test methods\", which specifies the methods for conducting Rockwell hardness tests on metallic materials, including the test principle, symbols and explanations, test specimens, testing equipment, test procedures, and the processing of test results. GB/T 17394.2-2022: “Metallic materials – Leeb hardness test – Part 2: Inspection and calibration of hardness testers” specifies the requirements and methods for inspecting and calibrating Leeb hardness testers, thereby ensuring the accuracy and reliability of their measurements. GB/T 17394.3-2022: “Metallic materials – Leeb hardness test – Part 3: Calibration of standard hardness blocks” defines the procedures and requirements for calibrating standard hardness blocks used in Leeb hardness testing, thus guaranteeing their accuracy and consistency. GB/T 17394.4-2014: “Metallic materials – Leeb hardness test – Part 4: Conversion tables for hardness values” provides conversion relationships between Leeb hardness and other common hardness scales (such as Brinell, Rockwell, and Vickers hardness), facilitating comparison and conversion between different hardness values.

JJG 747: “Verification regulations for Leeb hardness testers” serves as the basis for metrological verification of Leeb hardness testers. It outlines the verification items, methods, conditions, intervals, and criteria for determining compliance, ensuring that these testers meet required metrological performance standards. JB/T 9378: “Leeb hardness testers” specifies the technical requirements, test methods, inspection rules, as well as labeling, packaging, transportation, and storage provisions applicable to both portable and stationary Leeb hardness testers.

DL/T 1845-2018: “Test method for Leeb hardness of high-alloy steels used in electrical equipment” establishes a test method for determining the Leeb hardness of high-alloy steel materials utilized in electrical equipment, providing a standardized basis for hardness assessment within the power industry. T/SHZSAQS 00119-2022: “Operating technical specifications for Leeb hardness testers” details operational procedures, precautions, maintenance requirements, etc., aiding operators in proper usage and upkeep of such testers while enhancing measurement accuracy and reliability. T/CFA 010604.3-2017: “Method for transverse Leeb hardness testing of welded zones in cast steel components” offers specific procedures and criteria for conducting Leeb hardness tests on welded areas of cast steel parts; this is crucial for evaluating weld quality. T/ZS 0336-2022: “Technical specifications for on-site determination of tensile strength of constructional steels via Leeb hardness method” explains how to utilize the Leeb hardness method to determine the tensile strength of constructional steels at job sites, thereby offering technical support for on-site quality assessment of such steels. T/ZJBX 03-2019: “On-site method for hardness testing of metallic materials using portable D-type Leeb hardness testers” sets forth the procedures and requirements for employing D-type portable Leeb hardness testers to assess material hardness in situ.

V. International Standards
ISO 16859-1:2015: “Metallic materials – Leeb hardness test – Part 1: Test method” is an international standard developed by the International Organization for Standardization regarding Leeb hardness testing of metallic materials. Similar to China’s GB/T 17394.1-2014, it describes fundamental principles and operational steps involved in testing; this standard enjoys widespread application worldwide. ISO 16859-2:2015: “Metallic materials – Leeb hardness test – Part 2: Verification and calibration of testing equipment” stipulates requirements concerning verification and calibration processes for Leeb hardness testing devices, ensuring measurement accuracy and consistency across devices manufactured by various companies or over time; this aligns with China’s GB/T 17394.2-2022. ISO 16859-3:2015: “Metallic materials – Leeb hardness test – Part 3: Calibration of reference test blocks” outlines methods and criteria for calibrating reference test blocks employed in Leeb hardness testing, ensuring reliable hardness values; this corresponds to China’s GB/T 17394.3-2022.

Other foreign standards:
ASTM A956/A956M-22: “Standard test method for Leeb hardness of steel products” was formulated by the American Society for Testing and Materials. It details procedures for testing Leeb hardness of steel products, including specimen preparation, equipment specifications, testing steps, and reporting formats; this standard finds application in hardness evaluation of diverse steel products