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Rockwell Hardness Test Scales

Many manufactured products are made of different types of metals and alloys varying in hardness, size, and thickness. To accommodate the testing of these diverse products, several different indenter types (as discussed in 3.3.8) were developed for the Rockwell test to be used in conjunction with a range of standard force levels. Each combination of indenter type and applied force levels has been designated as a distinct Rockwell hardness scale. The ASTM(2) defines thirty different Rockwell scales, as shown in Table 1. Rockwell hardness scales are divided into two categories: regular Rockwell scales and superficial Rockwell scales. Both categories of tests use the same types of indenters. The regular Rockwell scales employ the heavier force levels. For these scales, the preliminary force level is 98.07 N (10 kgf), and the standard total force levels may be 588.4 N (60 kgf), 980.7 N (100 kgf) or 1471 N (150 kgf). The superficial Rockwell scales employ lighter force levels, typically for use on thinner materials. For the superficial Rockwell scales, the preliminary force level is 29.42 N (3 kgf), and the standard total force levels may be 147.1 N (15 kgf), 294.2 N (30 kgf) or 441.3 N (45 kgf). Table 1 provides typical applications for the different Rockwell scales as recommended by ASTM(2) and it lists the appropriate type of indenter and force levels to be used with the particular scale.