Stainless steel hardness is one of the most important characteristics when choosing the material for a specific application. Of course, stainless steels are well known for their resistance to corrosion, but these steel can also be considerably strong depending on how they are produced.

What is stainless steel hardness?

Stainless steel hardness is usually defined as a property of the surface that represents how resistant the material is to indentation, scratch or wear. A higher hardness means a higher resistance and a higher difficulty to perform machining or any other similar operations on the material.

In addition, hardness is an indication of its mechanical behavior during operation, and also an indication of how they can be formed or machined into an end product.

How is stainless steel hardness tested?

There are different methods to test materials hardness. When it comes to steels, the most common ones involve indentation resistance, which is tested by using specific materials and shapes such as diamond ball or cone among others.

There are three methods which are the most common ones to test steels hardness. They are Vickers, Brinell and Rockwell.

The Vickers test uses a diamond pyramid as indenter, and a load that ranges from 1 to 100 kgf is applied on the material. Generally, the full load is applied for 10 seconds approximately. Then, the area of the indentation mark is calculated by means of a microscope. Finally, the load is divided by the square millimeters of the area to obtain the Vickers hardness number of the material.

The Brinell test uses a hardened steel or carbide ball with a diameter of 10 mm as an indenter with a load of 3000 kgf to be applied on the material. Due to the high load applied, this test is often used to test hardened steels, although for softer materials the load can be reduced to avoid excessive indentation. In the case of testing iron or steel, the load is applied for 10 to 15 seconds, and for other type of metals is applied for about 30 seconds. As well as in the Vickers test, a microscope is used to measure the diameter of the indentation in order to calculate its area to divide the load applied, thus obtaining the Brinell hardness number of the material.

The Rockwell test is a little more complex. It involves different scales identified with capital letters. The most common scales used to test stainless steel hardness are the B and C scales, the latter usually used for hardened stainless steels. In this test (C scale) a diamond cone is used as an indenter and the measure considered to calculate the hardness number is the penetration of the indenter.

Conclusion

There are different tests for different types of materials. It is important to know which one is the most adequate according to the characteristics of the material.

Something important to keep in mind is that all of these tests give a number without units. In order to understand what this number represents in terms of units, there are different conversion systems to be used, such as ASTM E140.

The following table gives an idea on the relation among these numbers and an approximation to the tensile strength they represent. Please be aware that this values are only for reference and that there is no exact equivalence. In any case, the values obtained from actual testing should be the ones used.

Tensile Strength Vickers Brinell Rockwell
N/mm2 HV HB HRC
250 80 76
270 85 80.7
285 90 85.2
305 95 90.2
320 100 95
335 105 99.8
350 110 105
370 115 109
380 120 114
400 125 119
415 130 124
430 135 128
450 140 133
465 145 138
480 150 143
490 155 147
510 160 152
530 165 156
545 170 162
560 175 166
575 180 171
595 185 176
610 190 181
625 195 185
640 200 190
660 205 195
675 210 199
690 215 204
705 220 209
720 225 214
740 230 219
755 235 223
770 240 228 20.3
785 245 233 21.3
800 250 238 22.2
820 255 242 23.1
835 260 247 24
850 265 252 24.8
865 270 257 25.6
880 275 261 26.4
900 280 266 27.1
915 285 271 27.8
930 290 276 28.5
950 295 280 29.2
965 300 285 29.8
995 310 295 31
1030 320 304 32.2
1060 330 314 33.3
1095 340 323 34.4
1125 350 333 35.5
1115 360 342 36.6
1190 370 352 37.7
1220 380 361 38.8
1255 390 371 39.8
1290 400 380 40.8
1320 410 390 41.8
1350 420 399 42.7
1385 430 409 43.6
1420 440 418 44.5
1455 450 428 45.3
1485 460 437 46.1
1520 470 447 46.9
1555 480 456 47.7
1595 490 466 48.4
1630 500 475 49.1
1665 510 485 49.8
1700 520 494 50.5
1740 530 504 51.1
1775 540 513 51.7
1810 550 523 52.3
1845 560 532 53
1880 570 542 53.6
1920 580 551 54.1
1955 590 561 54.7
1995 600 570 55.2
2030 610 580 55.7
2070 620 589 56.3
2105 630 599 56.8
2145 640 608 57.3
2180 650 618 57.8
660 58.3
670 58.8
680 59.2
690 59.7
700 60.1
720 61
740 61.8
760 62.5
780 63.3
800 64
820 64.7
840 65.3
860 65.9
880 66.4
900 67
920 67.5
940 68