ASTM E18 test method determines the Rockwell hardness of metallic materials by the Rockwell indentation hardness principle. This test method provides information on metallic materials related to their tensile strength, wear resistance, and ductility. This test is useful in quality control and the selection of materials.
The ASTM E18 Rockwell hardness test is an empirical indentation hardness test that can provide useful information about metallic materials. Rockwell hardness (HRC) is generally used for high hardness materials and determination of the hardness after heat treatment. The standard is used to determine related physical characteristics of the metallic materials undergoing testing, as well as meeting acceptance testing of commercial shipments and can be useful in quality control and selection of materials.
For ASTM E18, the indenter is brought into contact with the test specimen, and the preliminary test force F is applied. After holding the preliminary test force for a specified dwell time, the baseline depth of indentation is measured. The force on the indenter is increased at a controlled rate by the additional test force F₁ to achieve the total test force F. The total test force is held for a specified dwell time. The additional test force is removed returning to the preliminary test force. After holding the preliminary test force for a specified dwell time, the final depth of indentation is measured. Then, the measurement is converted into a hardness number using the appropriate Rockwell scale. The preliminary test force is removed and the indenter is removed from the test specimen. Rockwell hardness test should be carried out at an ambient temperature within the limits of 10°C to 35°C.
The thickness of the specimen tested should exceed 10 times the depth of indentation according to ASTM E18.
The standard Rockwell indenters used are either diamond spheroconical indenters or tungsten carbide balls of 1.588 mm, 3.175 mm, 6.350 mm, or 12.70 mm in diameter.
Rockwell hardness number is calculated as:
For scales using a diamond spheroconical indenter: Rockwell Hardness = 100 – (h/0.002)
For scales using a ball indenter: Rockwell hardness = 130 – (h/0.002)
where, h = indentation depth caused by major load in mm.