Steel Hardness

Note that hardness conversions are approximate only as the different scales use different methods of testing

Brinell Vickers Rockwell

Impression Hardness hardness Hardness Hardness Equiv Rm Equiv Rm Equiv Rm
Dia. mm HB HV B C tonf/in² kgf/mm² N/mm²
2.50 601 640 - 57.0 - - -
2.55 578 615 - 56.0 - - -
2.60 555 591 120 54.5 - - -
2.65 534 569 119 53.5 - - -
2.70 514 547 119 52.0 - - -
2.75 495 528 117 51.0 - - -
2.80 477 508 117 49.5 - - -
2.85 461 491 116 48.5 101 160 1569
2.90 444 474 115 47.0 98 155 1520
2.95 429 455 115 45.5 95 150 1471
3.00 415 440 114 44.5 92 145 1422
3.05 401 425 113 43.0 88 139 1363
3.10 388 410 112 42.0 85 134 1314
3.15 375 396 112 40.5 82 129 1265
3.20 363 383 110 39.0 80 126 1236
3.25 352 372 110 38.0 77 121 1187
3.30 341 360 109 36.5 75 118 1157
3.35 331 350 109 35.5 73 114 1118
3.40 321 339 108 34.5 71 111 1089
3.45 311 328 108 33.0 68 107 1049
3.50 302 319 107 32.0 66 104 1020
3.55 293 309 106 31.0 64 101 990
3.60 285 301 105 30.0 63 99 971
3.65 277 292 104 29.0 61 96 941
3.70 269 284 104 27.5 59 93 912
3.75 262 276 103 26.5 58 91 892
3.80 255 269 102 25.5 56 89 873
3.85 248 261 102 24.0 55 87 853
3.90 241 253 100 23.0 53 84 824
3.95 235 247 99 22.0 51 81 794
4.00 229 241 98 20.5 50 79 775
4.05 223 235 97 - 49 77 755
4.10 217 228 96 - 48 76 745
4.15 212 223 96 - 46 73 716
4.20 207 218 95 - 45 71 696
4.30 197 208 93 - 43 68 667
4.40 187 197 91 - 41 65 637
4.50 179 189 89 - 39 62 608
4.60 170 179 87 - 36 57 559
4.70 163 172 85 - 35 55 539
4.80 156 165 83 - 34 54 530
4.90 149 157 81 - 32 51 500
5.00 143 150 79 - 31 49 481
5.10 137 144 77 - 31 49 481
5.20 131 138 74 - 30 47 461
5.30 126 133 72 - 29 46 451
5.40 121 127 70 - 28 44 431
5.50 116 122 68 - 27 43 422
5.60 111 117 66 - 26 41 402
5.70 107 113 64 - 25 39 382
5.80 103 108 61 - 24 38 373

Brinell Hardness

The Brinell hardness test consists in indenting the metal surface with a 10-mm-diameter steel ball at a load of 3,000 kg mass (∼29400 N). For soft metals the load is reduced to 500 kg to avoid too deep an impression, and for very hard metals a tungsten carbide ball is used to minimize distortion of the indenter. The load is applied for a standard time, usually 30 s, and the diameter of the indentation is measured with a low-power microscope after removal of the load. The average of two readings of the diameter of the impression at right angles should be made.

Vickers Hardness

The Vickers hardness test uses a square-base diamond pyramid as the indenter. The included angle between opposite faces of the pyramid is 136°. This angle was chosen because it approximates the most desirable ratio of indentation diameter to ball diameter in the Brinell hardness test. Because of the shape of the indenter, this is frequently called the diamond-pyramid hardness test. The diamond-pyramid hardness number (DPH), or Vickers hardness number (VHN, or VPH), is defined as the load divided by the surface area of the indentation. In practice, this area is calculated from microscopic measurements of the lengths of the diagonals of the impression

Rockwell Hardness Test

The most widely used hardness test is the Rockwell hardness test. Its general acceptance is due to its speed, freedom from personal error, ability to distinguish small hardness differences in hardened steel, and the small size of the indentation, so that finished heat-treated parts can be tested without damage. This test utilizes the depth of indentation, under constant load, as a measure of hardness. A minor load of 10 kg is first applied to seat the specimen. This minimizes the amount of surface preparation needed and reduces the tendency for ridging or sinking in by the indenter. The major load is then applied, and the depth of indentation is automatically recorded on a dial gage in terms of arbitrary hardness numbers.
  
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