Kathmandu University Civil Labs
ROCKWELL HARDNESS TESTThe 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
the resulting increase in penetration (Fig. 1B). When equilibrium has again been reached, 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 the 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)
Rockwell Hardness Test
Stanley P. Rockwell invented the Rockwell hardness test. He was a metallurgist for a large ball bearing
company and he wanted a fast non-destructive way to determine if the heat treatment process they were
doing on the bearing races was successful. The only hardness tests he had available at time were Vickers,
Brinell and Scleroscope. The Vickers test was too time consuming, Brinell indents were too big for his
parts and the Scleroscope was difficult to use, especially on his small parts.
To satisfy his needs he invented the Rockwell test method. This simple sequence of test force application
proved to be a major advance in the world of hardness testing. It enabled the user to perform an accurate
hardness test on a variety of sized parts in just a few seconds.
Rockwell test methods are defined in the following standards:
ASTM E18 Metals
ISO 6508 Metals
ASTM D785 Plastics
Types of the Rockwell Test
There are two types of Rockwell tests:
1. Rockwell: the minor load is 10 kgf, the major load is 60, 100, or 150 kgf.
2. Superficial Rockwell: the minor load is 3 kgf and major loads are 15, 30, or 45 kgf.
In both tests, the indenter may be either a diamond cone or steel ball, depending upon the characteristics
of the material being tested.
Rockwell Scales
Rockwell hardness values are expressed as a combination of a hardness number and a scale symbol
representing the indenter and the minor and major loads. The hardness number is expressed by the symbol
HR and the scale designation.
There are 30 different scales. The majority of applications are covered by the Rockwell C and B scales for
testing steel, brass, and other metals. However, the increasing use of materials other than steel and brass
as well as thin materials necessitates a basic knowledge of the factors that must be considered in choosing
the correct scale to ensure an accurate Rockwell test. The choice is not only between the regular hardness
test and superficial hardness test, with three different major loads for each, but also between the diamond
indenter and the 1/16, 1/8, 1/4 and 1/2 in. diameter steel ball indenters.
If no specification exists or there is doubt about the suitability of the specified scale, an analysis should be
made of the following factors that control scale selection:
Type of material
Specimen thickness
Test location
Scale limitations
Principle of the Rockwell Test
1. Select image to enlarge The indenter moves down into position on the part
surface
2. A minor load is applied and a zero reference position is established
3. The major load is applied for a specified time period (dwell time) beyond zero
4. The major load is released leaving the minor load applied
The resulting Rockwell number represents the difference in depth from the zero reference position as a
result of the application of the major load.
Reference
http://www.gordonengland.co.uk/hardness/rockwell.htm
Go through the above-mentioned drive link for clarity.
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