The Rockwell hardness test method consists of indenting the test
material with a diamond cone or hardened steel ball indenter. The
indenter is forced into the test material under a preliminary minor
load F0 (Fig. 1A) usually 10 kgf. When equilibrium has been
reached, an indicating device, which follows the movements of the
indenter and so responds to changes in depth of penetration of the
indenter is set to a datum position. While the preliminary minor load
is still applied an additional major load is applied with resulting
increase in penetration (Fig. 1B). When equilibrium has again been
reach, the additional major load is removed but the preliminary minor
load is still maintained. Removal of the additional major load allows a
partial recovery, so reducing the depth of penetration (Fig. 1C). The
permanent increase in depth of penetration, resulting from the
application and removal of the additional major load is used to
calculate the Rockwell hardness number.
HR = E - e
F0 = preliminary minor load in kgf F1 = additional major load in kgf F = total load in kgf e = permanent increase in depth of penetration due to major load
F1 measured in units of 0.002 mm E = a constant depending on form of indenter: 100 units for
diamond indenter, 130 units for steel ball indenter
HR = Rockwell hardness number D = diameter of steel ball
Fig. 1.Rockwell Principle
Rockwell Hardness Scales
Scale
Indenter
Minor Load F0
kgf
Major Load F1
kgf
Total Load F
kgf
Value of E
A
Diamond cone
10
50
60
100
B
1/16" steel ball
10
90
100
130
C
Diamond cone
10
140
150
100
D
Diamond cone
10
90
100
100
E
1/8" steel ball
10
90
100
130
F
1/16" steel ball
10
50
60
130
G
1/16" steel ball
10
140
150
130
H
1/8" steel ball
10
50
60
130
K
1/8" steel ball
10
140
150
130
L
1/4" steel ball
10
50
60
130
M
1/4" steel ball
10
90
100
130
P
1/4" steel ball
10
140
150
130
R
1/2" steel ball
10
50
60
130
S
1/2" steel ball
10
90
100
130
V
1/2" steel ball
10
140
150
130
Typical Application of Rockwell Hardness Scales
HRA . . . . Cemented carbides, thin steel and shallow case hardened
steel
HRB . . . . Copper alloys, soft steels, aluminium alloys, malleable
irons, etc.
HRC . . . . Steel, hard cast irons, case hardened steel and other
materials harder than 100 HRB
HRD . . . . Thin steel and medium case hardened steel and pearlitic
malleable iron
HRE . . . . Cast iron, aluminium and magnesium alloys, bearing metals
HRF . . . . Annealed copper alloys, thin soft sheet metals
HRG . . . . Phosphor bronze, beryllium copper, malleable irons HRH . .
. . Aluminium, zinc, lead
HRK . . . . }
HRL . . . . }
HRM . . . .} . . . . Soft bearing metals, plastics and other very soft
materials
HRP . . . . }
HRR . . . . }
HRS . . . . }
HRV . . . . }
Advantages of the Rockwell hardness method include the direct Rockwell
hardness number readout and rapid testing time. Disadvantages include
many arbitrary non-related scales and possible effects from the
specimen support anvil (try putting a cigarette paper under a test
block and take note of the effect on the hardness reading! Vickers and
Brinell methods don't suffer from this effect).
