ASTM C748
ASTM C748 – Standard Test Method for Rockwell Hardness of Graphite Materials Description: Significance and Use 4.1 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 mm ± 0.0025 mm diameter steel-ball indenter is increased from a fixed 10 kg minor load to a …