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

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7.16 Hardness • 225

Table 7.6a Rockwell Hardness Scales

Scale Symbol Indenter Major Load(kg)

A Diamond 60

B 161 -in.ball 100

C Diamond 150

D Diamond 100

E^18 -in.ball 100

F 161 -in.ball 60

G 161 -in.ball 150

H^18 -in.ball 60

K^18 -in.ball 150

Table 7.6b Superficial Rockwell Hardness Scales

Scale Symbol Indenter Major Load(kg)

15N Diamond 15

30N Diamond 30

45N Diamond 45

15T 161 -in.ball 15

30T 161 -in.ball 30

45T 161 -in.ball 45

15W^18 -in.ball 15

30W^18 -in.ball 30

45W^18 -in.ball 45

of one indentation and the specimen edge, or to the center of a second indenta-

tion. Furthermore, testing of specimens stacked one on top of another is not recom-

mended. Also, accuracy is dependent on making the indentation into a smooth flat

surface.

The modern apparatus for making Rockwell hardness measurements (see the

chapter-opening photograph for this chapter) is automated and very simple to use;

hardness is read directly, and each measurement requires only a few seconds.

The modern testing apparatus also permits a variation in the time of load appli-

cation. This variable must also be considered in interpreting hardness data.

Brinell Hardness Tests^16

In Brinell tests, as in Rockwell measurements, a hard, spherical indenter is forced

into the surface of the metal to be tested. The diameter of the hardened steel (or

tungsten carbide) indenter is 10.00 mm (0.394 in.). Standard loads range between

500 and 3000 kg in 500-kg increments; during a test, the load is maintained constant

for a specified time (between 10 and 30 s). Harder materials require greater applied

loads. The Brinell hardness number, HB, is a function of both the magnitude of the

load and the diameter of the resulting indentation (see Table 7.5).^17 This diameter is

measured with a special low-power microscope, utilizing a scale that is etched on the

eyepiece. The measured diameter is then converted to the appropriate HB number

using a chart; only one scale is employed with this technique.

(^16) ASTM Standard E 10, “Standard Test Method for Brinell Hardness of Metallic Materials.”
(^17) The Brinell hardness number is also represented by BHN.