Hardness Test - Rockwell hardness

Principle

Indentation with a hard metal ball or diamond cone with spherical cap of 200 µm radius in tree steps:

Application of a preliminary test load F₀ in maximum 2 s and holding the load for 3 s
Application of the additional test load F₁ in 3 s and holding the load for 5 s
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 F_o	Total test force F	Field of application (Rockwell hardness range)
A	HRA	Diamond cone	98.07 N	588.4 N	20 to 88 HRA
B	HRB	Ball 1.5875 mm	98.07 N	980.7 N	20 to 100 HRB
C	HRC	Diamond cone	98.07 N	1.471 kN	20 to 70 HRC
D	HRD	Diamond cone	98.07 N	980.7 N	40 to 77 HRD
E	HRE	Ball 3.175 mm	98.07 N	980.7 N	70 to 100 HRE
F	HRF	Ball 1.5875 mm	98.07 N	588.4 N	60 to 100 HRF
G	HRG	Ball 1.5875 mm	98.07 N	1.471 kN	30 to 94 HRG
H	HRH	Ball 3.175 mm	98.07 N	588.4 N	80 to 100 HRH
K	HRK	Ball 3.175 mm	98.07 N	1.471 kN	40 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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