How to read and represent a Rockwell hardness value

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A Rockwell hardness value consists of three components:

1. A numeric hardness value
2. The two letters "HR", standing for "Hardness according to Rockwell"
3. The Rockwell scale designation, defining the combination of main load (total test force) and type of indenter used in the corresponding Rockwell method.

Note: Test methods using a spherical indenter must also be identified with a "W" since the standard amendment in March 2015 in the ISO 6508. The "W" provides information about the ball material (tungsten (=wolfram) carbide).

Examples of how to represent and read a Rockwell hardness value according to

a. "regular" Rockwell procedure, method HRC:

45 HRC

  • 45 …hardness value 
  • HR …as per Rockwell 
  • C …with 150 kgf main load and diamond 120° indenter


b. Super Rockwell procedure (Superficial Rockwell), method HR30T:

80 HR30TW

  • 80 …hardness value 
  • HR …as per Rockwell 
  • 30 …with main load 30 kgf 
  • TW …and 1/16-inch ball indenter made of tungsten carbide
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