Page 223 - Materials Science and Engineering An Introduction

6.10 Hardness • 195

Other hardness-testing techniques are frequently employed but will not be dis-
cussed here; these include ultrasonic microhardness, dynamic (Scleroscope), durometer
(for plastic and elastomeric materials), and scratch hardness tests. These are described
in references provided at the end of the chapter.

Hardness Conversion
The facility to convert the hardness measured on one scale to that of another is most de-
sirable. However, because hardness is not a well-defined material property, and because
of the experimental dissimilarities among the various techniques, a comprehensive con-
version scheme has not been devised. Hardness conversion data have been determined
experimentally and found to be dependent on material type and characteristics. The
most reliable conversion data exist for steels, some of which are presented in Figure 6.18
for Knoop, Brinell, and two Rockwell scales; the Mohs scale is also included. Detailed
conversion tables for various other metals and alloys are contained in ASTM Standard

10,000 Figure 6.18 Comparison of several
hardness scales.
10 Diamond (Adapted from G. F. Kinney, Engineering
Properties and Applications of Plastics,
5,000
p. 202. Copyright © 1957 by John Wiley & Sons,
New York. Reprinted by permission of John
Wiley & Sons, Inc.)
2,000
Corundum
or
9 sapphire
Nitrided steels
1,000 8 Topaz
80
1000
Cutting tools
800 60 7 Quartz
File hard
600 500 6 Orthoclase
110 40
400 5 Apatite
300 100 Easily
20 machined
200
200 steels
80 0 4 Fluorite
3 Calcite
Rockwell
100 60 C
100
40
Knoop 20 Brasses
hardness 0 and
aluminum
50
Rockwell alloys
B
2 Gypsum
20
Most
plastics
10
5
Brinell 1 Talc
hardness
Mohs
hardness