Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

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)