This international standard was deyeloped in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. Designation:C748-20 An American National Standard INTERNATIONAL StandardTestMethodfor Rockwell Hardness of Graphite Materials1 This standard is issued under the fixed designation C748; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval. 1. Scope* 4. Significance and Use 1.1 This test method covers Rockwell L scale hardness 4.1ARockwell L scalehardness number is a number testingofgraphitematerialswithgrainsizelessthan0.8mm derived from the net increase in depthof impression as the load and a hardness range between 0 and 120. on a 6.3500 mm ± 0.0025 mm diameter steel-ball indenter is 1.2 Test Methods E18 shall be followed except where increased from a fixed 10 kg minor load to a 60 kg major load and then returned to the minor load. otherwise indicated. 4.2 A Rockwell hardness number is directly related to the 1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this indentation hardness of a material; the higher the Rockwell L standard. scale reading, the harder the material. The test is useful in the evaluation and the manufacturing control of carbon and graph- 1.4 This standard does not purport to address all of the ite materials. safety concerms, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- 5.Apparatus priate safety, health, and environmental practices and deter- 5.1 Rockwell Hardness Tester, calibrated in accordance with minetheapplicabilityof regulatorylimitationspriorto use. 1.5 This international standard was developed in accor- the requirements of Section 7. dance with internationally recognized principles on standard- 5.2Rockwell Hardness Tester Anvil, appropriate for the ization established in the Decision on Principles for the material shall be used as the specimen base plate. Developmentof International Standards,Guides and Recom- 6. Test Specimen mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. 6.1 The recommended test specimen shall be flat, rectangular, have a minimum thickness of 6.35 mm, and a 2. Referenced Documents minimumwidthandlengthof12.7mm. 2.1 ASTM Standards:2 6.2 The test surface roughness shall not exceed 3.2 μm E18 Test Methods for Rockwell Hardness of Metallic Ma- arithmetical average. terials 6.3 The test surface to opposite face parallelism for flat E171 Practice for Conditioning and Testing Flexible Barrier specimens shall be within 1 %. For all other specimen shapes, Packaging the test surface must be maintained normal to the direction of load application. 3. Summary of Test Method 3.1 The specimen is held in position and the load is applied. 7. Verification of Calibration Final position of the indicator on the scale is observed and 7.1 Level the Rockwell hardness tester in accordance with recorded as the hardness number. the manufacturer's instructions. 7.2 The adjustment of speed-of-load application is of great importance. Adjust the dashpot on the Rockwell tester so that 'This test method is under the jurisdiction of ASTM Committee D02 on the operating handle completes its travel in 4 s to 7 s with no Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of specimenonthemachineornoloadappliedbytheindenterto Subcommittee D02.FO on Manufactured Carbon and Graphite Products Current edition approved May 1, 2020. Published May 2020. Originally the