Hardness Calculator

Convert Hardness between HB, HV, HRC, and HRB

What is Hardness?

Hardness is a measurement of the resistance to localized plastic deformation caused by force or abrasion. Materials with high hardness would generally be stronger and more wear-resistant, but on the other hand, more brittle and sensitive to fracture. Hardness is a broad topic, that well covered. In this post, we will cover it from the machining perspective.

Hardness measurement and units

Hardness is measured in several methods and units. The standard units used in the machining space are:

Hardness measurment device

Rockwell [HRC/HRB/HRA] is one of the most common units used for listing the hardness of machined materials. the test is done by measuring the depth of penetration of a sphere under a large load compared to the penetration made by a reference preload. The Rockwell scale is divided into 9 sub-scales marked by letters A-K. Each scale uses a different reference load and different sphere sizes. In machining, the most common is the C scale (HRc]. Machined metal is usually between 10-65 HRC.

Brinnel Hardness Testing
By Lokilechderivative work: Nerdture

Brinell [HB] is one of the most common units used for listing the hardness of steel materials. the test is done with a 10 mm steel ball pressed with 3000 Kgf (6,614 Lbf). Common values for machined materials range from 100 HB for very soft materials up to 650 HB for heat-treated steels.

The advantage of Brinell [HB] over Rockwell [HRC/HRB], is that the whole range is covered on the scale, whereas in Rockwell C scale when the hardness is below 180 HB, you must switch to Rockwell B.

Vickers hardness test
By User A1 (Wikipedia)

Vickers [HV] is a common unit used for listing the hardness of carbide grades and other hard cutting materials such as Ceramics, CBN, and PCD. The test is done by measuring the surface area of the indentation created by a diamond in the shape of a square-based pyramid. The HV number is equal to the force divided by the area (F/a). Carbide grades are usually in the range of 1,300-1,900 HV. Ceramics can reach a hardness of 2,000 HV, CBN up to 3,000 HV, and PCD up to 6,000 HV

Hardness in Machining

Hardness is one of the most critical parameters when it comes to any machining discussion. It is the primary parameter to know for both the raw materials and the cutting materials.

Raw Materials

Although counter-intuitive, it is not ideal to machine very soft material. It is impossible to break chips below a certain hardness, and the raw material tends to stick on the cutting edge causing BUE. From a certain hardness point, increasing the hardness further increases the wear and will either require you to reduce the cutting speed or settle for lower tool-life. Above a certain threshold, it will become impossible to machine the material with a conventional carbide insert, and advanced materials such as Ceramics and CBN will be mandatory.

Material Groups Hardness Range

Material GroupHBHRC
Steel (Annealed)70-270<28
Steel (Quenched and tempered)270-35029-38
Steel (Hardened)350-75039-68
Stainless Steel (Austenitic)70-180<10
Cast Iron180-30010-32
Aluminum60-100
Heat resistance superalloys (Inconel)130-450<46
Titanium70-370<40

Tungsten Carbide

Most cutting tools are made from Tungsten Carbide. Steel can reach after heat treatment a hardness of up to 1,000 [HV]. Tungesten Carbide Grades range between1300 and 2000 HV, and therefore are suitable to cut metals. The high hardness comes hand in hand with lower toughness and brittleness. Choosing a too hard grade can cause catastrophic failure from inserts breakage or lower tool-life due to the cutting edge’s chipping.

Carbide inserts recommended hardness per application

Grade HardnessHardness [Hv] Application
Hard1700-1900Continuous turning in stable conditions
Balanced1500-1700Turning at less favorable conditions and Grooving
Tough1300-1500Milling, parting off or Turning with interrupted cut

Hardness Conversion Chart

BRINELL [HB] ROCKWELL-C [HRC] ROCKWELL-B [HRB] VICKERS [HV] STRENGTH [N/mm^2]
800 72    
780 71    
760 70    
752 69    
745 68    
746 67    
735 66    
711 65    
695 64    
681 63    
658 62    
642 61    
627 60    
613 59    
601 58   746
592 57   727
572 56   694
552 55   649
534 54 120 589
513 53 119 567
504 52 118 549
486 51 118 531
469 50 117 505
468 49 117 497
456 48 116 490 1569
445 47 115 474 1520
430 46 115 458 1471
419 45 114 448 1447
415 44 114 438 1422
402 43 114 424 1390
388 42 113 406 1363
375 41 112 393 1314
373 40 111 388 1265
360 39 111 376 1236
348 38 110 361 1187
341 37 109 351 1157
331 36 109 342 1118
322 35 108 332 1089
314 34 108 320 1049
308 33 107 311 1035
300 32 107 303 1020
290 31 106 292 990
277 30 105 285 971
271 29 104 277 941
264 28 103 271 892
262 27 103 262 880
255 26 102 258 870
250 25 101 255 853
245 24 100 252 838
240 23 100 247 824
233 22 99 241 794
229 21 98 235 775
223 20 97 227 755
216 19 96 222 716
212 18 95 218 706
208 17 95 210 696
203 16 94 201 680
199 15 93 199 667
191 14 92 197 657
190 13 92 186 648
186 12 91 184 637
183 11 90 183 617
180 10 89 180 608
175 9 88 178 685
170 7 87 175 559
167 6 86 172 555
166 5 86 168 549
163 4 85 162 539
160 3 84 160 535
156 2 83 158 530
154 1 82 152 515
149   81 149 500
147   80 147 490
143   79 146 482
141   78 144 481
139   77 142 480
137   76 140 475
135   75 137 467
131   74 134 461
127   72 129 451
121   70 127 431
116   68 124 422
114   67 121 412
111   66 118 402
107   64 115 382
105   62 112 378
103   61 108 373
95   56 104
90   52 95
81   41 85
76   37 80
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