A Rockwell L scale hardness number is a number derived from the net increase in depth of impression as the load on a 6.3500 ± 0.0025-mm diameter steel-ball indenter is increased from a fixed 10-kg minor load to a 60-kg major load and then returned to the minor load.

A Rockwell hardness number is directly related to the indentation hardness of a material; the higher the Rockwell L scale reading, the harder the material. The test is useful in the evaluation and the manufacturing control of carbon and graphite materials.

1.1 This test method covers Rockwell L scale hardness testing of graphite materials with grain size less than 0.8 mm and a hardness range between 0 and 120.

1.2 Test Methods E18 shall be followed except where otherwise indicated.

1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.