GTBL042-07 GTBL042-Callister-v2 August 6, 2007 12:43
7.16 Hardness • 227
1000
800
600
200
300
400
100
80
60
40
20
Diamond
0
10
1
2
3
4
5
6
7
8
9
Talc
Gypsum
Calcite
Fluorite
Apatite
Orthoclase
Quartz
Topaz
Corundum
or
sapphire
10
5
20
50
100
200
500
1,000
2,000
5,000
10,000
Knoop
hardness
Brinell
hardness
Mohs
hardness
Rockwell
C
110
0
20
40
60
80
100
Rockwell
B
Easily
machined
steels
Nitrided steels
File hard
Cutting tools
Most
plastics
Brasses
and
aluminum
alloys
Figure 7.30
Comparison of
several hardness
scales. (Adapted
from G. F. Kinney,
Engineering
Properties and
Applications of
Plastics,p. 202.
Copyright©c1957 by
John Wiley & Sons,
New York.
Reprinted by
permission of John
Wiley & Sons, Inc.)
Metals.” In light of the preceding discussion, care should be exercised in extrapolation
of conversion data from one alloy system to another.
Correlation Between Hardness and Tensile Strength
Both tensile strength and hardness are indicators of a metal’s resistance to plastic
deformation. Consequently, they are roughly proportional, as shown in Figure 7.31,
for tensile strength as a function of the HB for cast iron, steel, and brass. The same
proportionality relationship does not hold for all metals, as Figure 7.31 indicates.
As a rule of thumb for most steels, the HB and the tensile strength are related accor-
ding to
TS(MPa)= 3. 45 ×HB (7.25a)
For steel alloys,
conversion of Brinell
hardness to tensile
strength
TS(psi)= 500 ×HB (7.25b)