Unformatted text preview: 7.16 Hardness ● 179 Table 7.5a Rockwell Hardness Scales
Scale Symbol A B C D E F G H K Indenter Diamond in. ball Diamond Diamond in. ball in. ball in. ball in. ball in. ball Major Load (kg) 60 100 150 100 100 60 150 60 150 Table 7.5b Superﬁcial Rockwell Hardness Scales
Scale Symbol 15N 30N 45N 15T 30T 45T 15W 30W 45W Indenter Diamond Diamond Diamond in. ball in. ball in. ball in. ball in. ball in. ball Major Load (kg) 15 30 45 15 30 45 15 30 45 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 application. This variable must also be considered in interpreting hardness data. BRINELL HARDNESS TESTS15
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 7.4).16 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. Maximum specimen thickness as well as indentation position (relative to specimen edges) and minimum indentation spacing requirements are the same as for Rockwell tests. In addition, a well-deﬁned indentation is required; this necessitates a smooth ﬂat surface in which the indentation is made.
15 16 ASTM Standard E 10, ‘‘Standard Test Method for Brinell Hardness of Metallic Materials.’’ The Brinell hardness number is also represented by BHN. ...
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