Machinery's Handbook, 31st Edition
506
Hardness Testing Table 5. Comparative Hardness Scales for Steel Table 5. (Continued) Comparative Hardness Scales for Steel
Rockwell Superficial Hardness Number Superficial Diamond Indenter
Rockwell Hardness Number
Brinell Hardness Number 10-mm Ball, 3000-kgf Load
Diamond Pyramid Hardness Number Vickers
A Scale 60-kgf Load Diamond Indenter
D Scale 100-kgf Load Diamond Indenter
Rockwell C Scale Hardness Number
15-N Scale 15-kgf Load
30-N Scale 30-kgf Load
45-N Scale 45-kgf Load
Tungsten Carbide Ball
Standard Ball
Hultgren Ball
21 20
243 238 230 222 213 204 196 188 180 173 166 160
231 226 219 212 203 194 187 179 171 165 158 152
231 226 219 212 203 194 187 179 171 165 158 152
231 226 219 212 203 194 187 179 171 165 158 152
61.0 60.5
40.9 40.1
69.9 42.3 20.7 69.4 41.5 19.6
35 34
(18) (16) (14) (12) (10) (8) (6) (4)
… … … … … 33 … … … … … 32 … … … … … 31 … … … … … 29 … … … … … 28 … … … … … 27 … … … … … 26 … … … … … 25 … … … … … 24
(2) (0)
… … … … … 24 Note: The values in this table shown in boldface type correspond to those shown in American Society for Testing and Materials Specification E140-67. Values in ( ) are beyond the normal range and are given for information only. Turner’s Sclerometer.— In making this test, a weighted diamond point is drawn once forward and once backward over the smooth surface of the material to be tested. The hard ness number is the weight in grams required to produce a standard scratch. Mohs’s Hardness Scale.— Hardness, in general, is determined by what is known as Mohs’s scale, a standard for hardness that is applied mainly to nonmetallic elements and minerals. In this hardness scale, there are ten degrees or steps, each designated by a min eral, the difference in hardness of the different steps being determined by the fact that any member in the series will scratch any of the preceding members. This scale is as follows: 1) talc; 2) gypsum; 3) calcite; 4) fluorspar; 5) apatite; 6) orthoclase; 7) quartz; 8) topaz; 9) sapphire or corundum; and 10) diamond. These minerals, arbitrarily selected as standards, are successively harder, from talc, the softest of all minerals, to diamond, the hardest. This scale, which is now universally used for nonmetallic minerals, is not applied to metals. Relation Between Hardness and Tensile Strength.— The approximate relationship between hardness and tensile strength is shown by the following formula: Tensile strength = BHN 3 515 (for Brinell Hardness Numbers up to 175). Tensile strength = BHN 3 490 (for Brinell Hardness Numbers larger than 175). The above formulas give the tensile strength in pounds per square inch for steels. These approximate relationships between hardness and tensile strength do not apply to nonfer rous metals, with the possible exception of certain aluminum alloys. Durometer Tests.— The durometer is a portable hardness tester for measuring hardness of rubber, plastics, and some soft metals. The instrument is designed to apply pressure to the specimen and the hardness is read from a scale while the pressure is maintained. Vari ous scales can be used by changing the indentor and the load applied.
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