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Hardness Conversion Chart *

Comparison of Hardness Scales approx.** and Tensile Stress
Equivalents approx. (maximum value) in imperial and metric units.
Rockwell 'C' Scale Diamond Pyramid Scale
HV10 HV30		 Brinell Tensile Stress
Equivalents		 Scler Scope
Hardness Number		 Rockwell Diamond Pyramid
Scale HV10 HV30
    Dia. Imp. for
10mm Ball		 Carbide Ball Standard Ball Tons/in2 1000lb/in2 kg/mm2 MPa
{N/mm2}		        
67.7 900               96 85.6 67.7 900
67.0 880               95 85.0 67.0 880
66.3 860               93 84.7 66.3 860
65.5 840               92 84.2 65.5 840
64.8 820               90 83.8 64.8 820
64.0 800               88 83.4 64.0 800
63.3 780               87 83.0 63.3 780
62.5 760               86 82.6 62.5 760
61.7 740               84 82.2 61.7 740
61.0 725 2.44 630 - - - - - 82 81.8 61.0 725
60.5 710 2.45 627 - - - - - - 81.5 60.5 710
60.0 698 2.50 601 - 132 295 208 2039 81 81.2 60.0 698
58.9 670 2.55 578 - 127 284 200 1961 78 80.6 58.9 670
57.1 630 2.60 555 - 122 273 192 1884 75 79.6 57.1 630
56.1 609 2.65 534 - 117 262 184 1807 73 79.0 56.1 609
54.4 572 2.70 514 - 112 250 176 1729 71 78.2 54.4 572
51.9 532 2.75 495 495 108 241 170 1668 68 76.9 51.9 532
50.7 517 2.80 477 477 105 235 165 1621 66 76.3 50.7 517
49.5 497 2.85 461 461 101 226 160 1559 64 75.5 49.5 497
47.5 470 2.90 444 444 98 219 155 1513 62 74.2 47.5 470
46.0 452 2.95 429 429 95 212 150 1467 60 73.5 46.0 452
44.8 437 3.00 415 415 92 206 145 1420 58 73.0 44.8 437
43.7 422 3.05 401 401 88 197 139 1359 56 72.5 43.7 422
42.4 408 3.10 388 388 85 190 134 1312 54 71.5 42.4 408
41.3 395 3.15 375 375 82 183 129 1266 52 71.0 41.3 395
39.9 381 3.20 363 363 80 179 126 1235 51 70.3 39.9 381
38.8 370 3.25 352 352 77 172 121 1189 49 69.8 38.8 370
37.7 359 3.30 341 341 75 168 118 1158 48 69.2 37.7 359
36.7 349 3.35 331 331 73 163 114 1127 46 68.8 36.7 349
35.0 337 3.40 321 321 71 159 111 1096 45 68.0 35.0 337
34.0 327 3.45 311 311 68 152 107 1050 43 67.5 34.0 327
33.0 318 3.50 302 302 66 147 104 1019 42 66.8 33.0 318
32.0 308 3.55 293 293 64 143 101 988 41 66.2 32.0 308
30.9 300 3.60 285 285 63 141 99 973 40 65.7 30.9 300
29.8 292 3.65 277 277 61 136 96 942 38 65.2 29.8 292
29.0 284 3.70 269 269 59 132 93 911 37 64.6 29.0 284
27.5 275 3.75 262 262 58 130 91 895 36 64.0 27.5 275
26.6 269 3.80 255 255 56 125 89 865 35 63.6 26.6 269
25.2 261 3.85 248 248 55 123 87 849 34 62.9 25.2 261
24.3 255 3.90 241 241 53 118 84 818 33 62.6 24.3 255
23.0 247 3.95 235 235 51 114 81 787 32 62.0 23.0 247
22.0 241 4.00 229 229 50 112 79 772 31 61.6 22.0 241
20.8 234 4.05 223 223 49 110 77 756 30 60.7 20.8 234
  228 4.10 217 217 48 107 76 741 - - - 228
Hardness
'B' Scale		                     Hardness
'B' Scale		  
98 222 4.15 212 212 46 103 73 710 29 - 98 222
97 218 4.20 207 207 45 101 71 695 28 - 97 218
96 212 4.30 197 197 43 97 68 664 27 - 96 212
93 196 4.40 187 187 41 92 65 632 25 - 93 196
91 188 4.50 179 179 39 88 62 602 - - 91 188
88.5 178 4.60 170 170 36 81 57 556 24 - 88.5 178
86 171 4.70 163 163 35 78 55 540 - - 86 171
84.2 163 4.80 156 156 34 76 54 525 23 - 84.2 163
82 156 4.90 149 149 32 72 51 494 - - 82 156
80 150 5.00 143 143 3t 69 49 479 22 - 80 150
77 143 5.10 137 137 30 67 48 463 21 - 77 143
75 137 5.20 131 131 29.5 66 47 455 20.5 - 75 137
72.5 132 5.30 126 126 29 65 46 448 20 - 72.5 132
70 127 5.40 121 121 28 63 44 432 - - 70 127
67 122 5.50 116 116 26 58 42 401 15 - 67 122
*These charts were prepared using information contained in B.S.860/1967. This standard differs significantly from the superseded standard B.S. 860/1939, and differs slightly from the conversion scales adopted by SAE and ASTM sources.
** Where hardness acceptance values are specified and a conversion from one scale to another is necessary the source of the conversion data should be stated and understood by the parties involved.

Hardness

Hardness is the property of a material that enables it to resist plastic deformation, penetration, indentation, and scratching. Therefore, hardness is important from an engineering standpoint because resistance to wear by either friction or erosion by steam, oil, and water generally increases with hardness.

Hardness tests serve an important need in industry even though they do not measure a unique quality that can be termed hardness. The tests are empirical, based on experiments and observation, rather than fundamental theory. Its chief value is as an inspection device, able to detect certain differences in material when they arise even though these differences may be undefinable. For example, two lots of material that have the same hardness may or may not be alike, but if their hardness is different, the materials certainly are not alike.

Several methods have been developed for hardness testing. Those most often used are Brinell, Rockwell, Vickers, Tukon, Sclerscope, and the files test. The first four are based on indentation tests and the fifth on the rebound height of a diamond-tipped metallic hammer. The file test establishes the characteristics of how well a file takes a bite on the material.

As a result of many tests, comparisons have been prepared using formulas, tables, and graphs that show the relationships between the results of various hardness tests of specific alloys. There is, however, no exact mathematical relation between any two of the methods. For this reason, the result of one type of hardness test converted to readings of another type should carry the notation "____ converted from ____" (for example "352 Brinell converted from Rockwell C-38").

Another convenient conversion is that of Brinell hardness to ultimate tensile strength. For quenched and tempered steel, the tensile strength (psi) is about 500 times the Brinell hardness number (provided the strength is not over 200,000 psi).

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