Rockwell C Hardness Scale

The Rockwell method is a static hardness testing method, which has the following characteristics:·

• It is a hardness measurement method specified by the ISO 6508, ASTM E18 standards.·
• It is used for hardness testing in the macro range (test force≥49.03 N), more specifically with a test force of 29.42 to 1471 N.·
• Indenter shape and material: Depending on the specific Rockwell method used, the indenter is either a diamond cone (with a cone angle of 120 °) or a hard metal ball (with a 1⁄16-inch radius).

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Operating principle

In the Rockwell method, the total test force is applied in two phases. In the first phase, a preload force is applied so that the indenter reaches a depth h0 into the material; in the second phase, the additional force is applied, resulting in the indenter reaching a depth h1. The initial preload force plus the additional test force gives the total test force (also referred to as total force or major load). The total force is applied to the specimen for a specific period of time, after which the additional force is removed, causing the indenter to move upward to a higher level at depth h2 (Figure 2).

The Rockwell hardness (HR) can now be calculated using the residual depth h= h2.- h1 of the indentation.

Figure 2: Operating principle of Rockwell hardness measurement.

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Abbreviation explanation

1. Numerical hardness value

2. The two letters "HR" indicate the Hardness Rockwell method.

3. The designation of the Rockwell scale is defined by the combination of the major load (total test force) and the type of indenter used.