Hardness test methods and hardness conversion tables

Introduction

Hardness is a surface property where indentation, scratching or wear is resisted.
The higher the hardness the more resistant the surface and the more difficult surface operations such as cutting and machining are.
Testing the hardness of steels can be used an indication of how they can be manipulated (formed, machined etc.) and how they will perform mechanically.

Hardness test methods

Common tests for hardness in metals involve measuring the resistance to indentation by a hardened steel or diamond ball, cone or pyramid.

The common test methods include: -

    Brinell
    Vickers
    Rockwell

The hardness figures do not have units. They are an index, based on either the cross-section of the indentation made, measured after the test, or the depth of indentor travel into the metal surface.
The hardness figure is followed by a code indicating the test method.

The Brinell and Vickers methods have been used historically in the UK, the Brinell method for softened steels and Vickers method for either softened or hardened steels.
In these tests the 'diameter' of the impression is measured.

The Rockwell method was first introduced in the US.
These methods assess the hardness by measuring the depth of indentor penetration.

The B scale is used for softened steels and the C scale for hardened steels.
Other scales are also available. These include scales A, D, E, F, G H, K, as well as 'superficial test' scales HR15N, HR30N, HR45N (cone indentor) and HR15T, HR30T, HR45T (ball indentor).
Normally the B and C scales are used on stainless steels, B for softened steel and C for hardened steel.

Hardness conversions between different scales

There are several hardness scale conversion systems, including BS 860 and ASTM E140.
The table shows a set of values that has been used for stainless steels and also includes a tensile strength (UTS) comparison. The Rockwell B values are superimposed on this table using an approximation from ASTM E140 Table5, which compares Rockwell B and Brinell.

Comparison tables should only be used as a guide. The figures shown are not equivalents and BSSA accepts no responsibility of the accuracy of the data. In any case of doubt or dispute values using the actual test methods should be used rather than converted table values.

Hardness conversion table

Brinell Hardness (HB) Vickers Hardness (HV) Rockwell (HRB) Rockwell (HRC) UTS (N/mm2)
- 640 - 57 -
- 615 - 56 -
- 591 - 54.5 -
- 569 - 53.5 -
- 547 - 52 -
- 528 - 51 -
- 508 - 49.5 -
- 491 - 48.5 1539
444 474 - 47 1520
429 455 - 45.5 1471
415 440 - 44.5 1422
401 425 - 43 1363
388 410 - 42 1314
375 396 - 40.5 1265
363 383 - 39 1236
352 372 - 38 1187
341 360 - 36.5 1157
331 350 - 35.5 1118
321 339 - 34.5 1089
311 328 - 33 1049
302 319 - 32 1020
293 309 - 31 990
285 301 - 30 971
277 292 - 29 941
269 284 - 27.5 912
262 276 - 26.5 892
255 269 100 25.5 873
248 261 99 24 853
241 253 98 23 824
235 247 97 22 794
229 241 96 20.5 775
223 235 - - 755
217 228 95 - 745
212 223 94 - 716
207 218 93 - 696
197 208 91 - 667
187 197 89 - 637
179 189 87 - 608
170 179 85 - 559
163 172 83 - 539
156 165 81 - 530
149 157 79 - 500
143 150 77 - 481
137 144 74 - 471
131 138 72 - 461
126 133 69 - 451
121 127 67 - 431
116 122 64 - 422
111 117 61 - 402
107 113 - - 382
103 108 - - 373

Other sources of hardness equivalent tables are:

Corrosion Source

Carbide Depot

Gordon England

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