Rockwell Hardness testing measures the hardness of the tested material via a differential depth measurement. The Rockwell test determines the hardness of the material by comparing the depth of the indentation created by a large test load, and that created by a preload.
To perform the test the specimen is prepared, and an indenter is pressed into the material under a preload. The depth of the indentation is measured. Next the indenter is brought down at a set force for specific dwell time and released. The depth of the new indent is measured and compared to the preload indentation to determine the Rockwell Hardness.
The forces used in testing vary according to the test type, whether it is a full Rockwell test or a superficial test, and the specification requirements. Forces used are as follows:
- Rockwell testing is done under 100kgf and 150kgf loads.
- Superficial testing is done under 15kgf, 30kgf and 45kgf loads.
Superficial testing is generally done to check surface hardness, and or variation in surface hardness. It is used to measure case hardened surface hardness without penetrating the case layer. It is also used to verify case depth of material. On the other hand, full Rockwell testing generally penetrates case depth into the core of the material.
The advantage of Rockwell testing over Brinell testing is the smaller size of the indenters. Brinell indentations are often too large to be considered non-destructive, while Rockwell indentations are often small enough to go unnoticed.
Rockwell Testing may be performed on any metallic material.
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Rockwell Testing is performed per ASTM E18 Rockwell Hardness Testing of Metallic Materials.