Scope:

ASTM E18 test method provides information about the physical properties of metals such as tensile strength, wear resistance, ductility, and so on, and is useful in the quality control and selection process of metals. Large quantity shipments are often tested to determine if the requirements of the products are met. This is called acceptance testing. Rockwell hardness tests are used extensively in the acceptance testing of metallic materials. 

Test Procedure:

First, an indenter applies a minor load on the metal, causing a dent for ASTM E18 test method. The depth of the dent establishes the baseline depth. Without removing the minor load, a major load is applied for a specific time, and the depth of the indentation produced by it is measured. The harder the metal, the shallower the penetration, and vice versa. The Rockwell hardness value is derived from the difference in the two depths: the baseline depth and final depth. This distance is converted to a hardness number. 

Video 01: Rockwell hardness test

Specimen size:

For ASTM E18, the hardness of the sample’s test surface should not alter during the preparation of the sample. For instance, heat or cold-working alters the hardness of the sample. The test surface and the bottom surface of the sample must be smooth, and free from foreign matter, oxide scale, and lubricants. Certain reactive metals get stuck to the indenter. In such cases, a suitable lubricant is used.

Data:

Rockwell hardness calculation in ASTM E18 testing:   

HR = N – hd 

Where d is the depth in mm (from the zero load point), and N and h are scale factors that depend on the scale of the test being used. 

Conclusion:

ASTM E18 test method provides information about the physical properties of metals such as tensile strength, wear resistance, ductility, and so on, and is useful in the quality control and selection process of metals.