Hardness Test - Rockwell hardness


Principle

 

Indentation with a hard metal ball or diamond cone with spherical cap of 200 µm radius in tree steps:
  1. Application of a preliminary test load F0 in maximum 2 s and holding the load for 3 s
  2. Application of the additional test load F1 in 3 s and holding the load for 5 s
  3. Unloading to the preliminary test load F0 and holding the load for 4 s. After 4 s reading of the remaining depth h at F0 as distance to the depth at preliminary test load
Somewhat different times are allowed (for details see standard). Currently only hard metal balls are allowed.


Formulas

 

F0 ... Preliminary test load
F1 ... Additional test load
h ... Remaining depth after unloading to the preliminary test load in mm
Rockwell - hardness = 130 - h / 0.002 mm for HRBW, HREW, HRFW, HRGW, HRHW, HRKW
Rockwell - hardness = 100 - h / 0.002 mm for HRA, HRC, HRD
Example: 70 HR30TW

Table 1 from DIN 6508

 

Rockwell
Hardness
scale
Hardness
symbol
 
Typ
of Indenter
 
Preliminary
test force
 Fo
Total
test force
  F
Field of application
(Rockwell
hardness range)
AHRADiamond cone98.07 N 588.4 N20 to 88 HRA
BHRBBall 1.5875 mm98.07 N 980.7 N20 to 100 HRB
CHRCDiamond cone98.07 N1.471 kN20 to 70 HRC
DHRDDiamond cone98.07 N 980.7 N40 to 77 HRD
EHREBall 3.175 mm98.07 N 980.7 N70 to 100 HRE
FHRFBall 1.5875 mm98.07 N 588.4 N60 to 100 HRF
GHRGBall 1.5875 mm98.07 N1.471 kN30 to 94 HRG
HHRHBall 3.175 mm98.07 N 588.4 N80 to 100 HRH
KHRKBall 3.175 mm98.07 N1.471 kN40 to 100 HRK

History

 

As suggested by Ludwik (1903), according to whom a reproducible hardness value can be deduced from a measured indentation depth, Rockwell presented the method developed in 1922. The major advantage of this method: the hardness value is easy to read directly on the testing machine (Indentation depth)


 

Valid standards

 

DIN EN ISO 6508 1 - 4 Metallic materials - Rockwell hardness test
Last revision 2014
ASTM E 18-07

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