There are numerous appropriate procedures to measure the load that a material resists under certain conditions. Among the various scales such as the Vickers scale, Brinell scale; Rockwell hardness scale stands out, whose usefulness, after almost a century, continues to be required. That is the reason why Rockwell is the most commonly used scale. The procedure is simple: establish the force of an element, subjected to penetration, and calculate the depth of the mark it leaves on its surface, but it has some limitations too.
Below, we will discuss what is the Rockwell scale, its differences, and factors which are affecting the results? Let’s get started!
I. Why Different Scales are Used in Rockwell Hardness Testing?
Different scales can be used which come from using different combinations of indenters and test force, allowing virtually any metal or alloy to be tested. Different Rockwell hardness scales are used for different sample objects since it is not the same to analyze such as copper as steel or another element. Various scales are used so as not to damage the machine or the indenter, which is often very expensive.
II. Which Scale is Used in Rockwell Scale?
The Rockwell hardness scale consists of applying a load on the object under measurement mediated by an indenter (it can be a spheroconical diamond indenter or a steel or hard metal sphere), and it is measured how much that indenter penetrates the object to be measured. For normal scales, each unit of Rockwell hardness is equivalent to 0.002 mm in depth, and for Superficial Rockwell hardness scales, each unit of hardness is equivalent to 0.001 mm in depth.
III. What are B Scale and C Scale in Rockwell Hardness?
There are 11 basic scales for determining hardness (A, B, C, D, E, F, G, H, K, N, T), which are designed to work in various combinations of “intended – load”. But the most common scales are
- HRB – with a ball Ø 1.588 and a total force on the measuring head of 100 kgf. It is used for unhardened steel and non-ferrous metals.
- HRC – with a cone and a total force on the measuring head of 150 kgf. It is used for hardened steel.
IV. How do you Choose a Rockwell Hardness Scale?
Types of Test Material
While performing the Rockwell hardness test, the type of testing material should be first known. Different types of materials have different testing scales for reliable outcomes. You can choose a scale from standard tables of Rockwell hardness scale which is given in the literature. Mostly, softer material has bigger scal value. If you do not take care of this factor, then it is not possible to apply an accurate Rockwell hardness procedure and get reliable results.
Test Material Area
Deformation of the material not only flows below indentation but also flows outside of the material. This not only makes the thickness of the material crucial but also limits the width of the material also. Keep in mind to place the test material in the middle of the testing surface. If you process the Rockwell testing at the end or corner of the testing surface, then the material can push out of the testing area at the time of deformation around the indentation. This can provide less hardness value than actual. This is more common when measuring soft objects.
Generally, according to the Rockwell ISO standard, the distance should be more than 1mm.
Many Rockwell test standards also stated that while processing the test, there should be a distance of more than 2.5 times the diameter of the indentation between mid of an indentation and the periphery of the material.
Thickness of Test Material
In the Rockwell hardness test, indentation depth depends on the thickness of the material. In the process of the test, material present near indentation is deformed in plastic. This deformation is actually creating depth of indentation. If the thickness of the material is thin for the specific test, then the whole material will be deformed and will flow on the test surface with the hanging anvil, and indentation depth will not be created. This affects the procedure of deformation in a negative way which can lead to flawed hardness outcomes.
To avoid this and to get Rockwell test outcomes, the testing material should have an adequate thickness. You can choose a Rockwell hardness scale with suitable test forces (load) and indenter size according to the material thickness that must be used in the procedure.
The thickness can also be selected from the Rockwell scale table.
First, find the estimated value of the hardness of the test material. The approximate Rockwell measurement of the thickness can be checked from graphs or tables (which can be found in the literature on the Rockwell hardness test). Some of the examples of this data are available in ASTM standards.
Test Material Homogeneity
Material size and its location should show homogeneity while processing the hardness test. Also these Features should keep in mind while choosing the scale in performing the Rockwell hardness. But if these two features are not homogeneous then alternatively you can adopt other measures for reliable outcomes of results.
If the size of testing material is not large enough then you can choose a scale that can create an appropriately large indentation to cover the whole test surface. Surrounding area of the Rockwell indentation should be adjusted in a way that testing material should come in the middle to avoid deformation of the material out of the testing area.
Scale Limitations
It is theoretically defined that Rockwell has a wide range of different scales starting from 0 to 100 which covers specific hardness values, and all the scales can be used for testing.
But there are the practical limitations in material testing with low hardness, these limitations can cause the material to reach the place of the indenter cap for the intender ball. This is due to the deep penetration of the indenter in the material
V. Other Important Factors to Consider
Scales are employed to test the hardness of metals with various methods for the static application of the loads, No matter whether you are measuring depth caused by penetration or the size of the indentation.
Different methods with static hardness are:
- Depth measurement methods
Scales are applied while measuring the value of residual depth of indentation caused by the indenter used in the test. The Rockwell method has the advantage to be the only standardized method by the ASTM 18 and ISO 6508. There are two not standardized methods for depth measurement called the Brinell(HBT) and the Vickers(HVT).
- Optical measurement methods
These types of methods are also used to measure the value of the residual size of indentation caused by the indenter in the test. All three common methods are standardized in this case of optical measurement by ISO and ASTM.
- Leeb rebound method
This is the alternate method which involves application of dynamic force. In this method the value of the height of a ball rebound is calculated to analyze the hardness of the testing material.
VI. Rockwell Hardness Scale Chart
Hardness Conversion for Rockwell B scale:
B | A | E | 15T | 30T | 45T | HV | HK | HB | HB |
30 kgf | 60 kgf | 100 kgf | 15 kgf | 30 kgf | 45 kgf | Vickers | Knoop | Brinell | Brinell |
1/16 Ball | Diamond | 1/8 Ball | 1/16 Ball | 1/16 Ball | 1/16 Ball | Scale | >500 gf | 10/3000 | 10/500 |
100 | 61.5 | – | 93.1 | 83.1 | 72.9 | 240 | 251 | 240 | 201 |
99 | 60.9 | – | 92.8 | 82.5 | 71.9 | 234 | 246 | 234 | 195 |
98 | 60.2 | – | 92.5 | 81.8 | 70.9 | 228 | 241 | 228 | 189 |
97 | 59.5 | – | 92.1 | 81.1 | 69.9 | 222 | 236 | 222 | 184 |
96 | 58.9 | – | 91.8 | 80.4 | 68.9 | 216 | 231 | 216 | 179 |
95 | 58.3 | – | 91.5 | 79.8 | 67.9 | 210 | 226 | 210 | 175 |
94 | 57.6 | – | 91.2 | 79.1 | 66.9 | 205 | 221 | 205 | 171 |
93 | 57 | – | 90.8 | 78.4 | 65.9 | 200 | 216 | 200 | 167 |
92 | 56.4 | – | 90.5 | 77.8 | 64.8 | 195 | 211 | 195 | 163 |
91 | 55.8 | – | 90.2 | 77.1 | 63.8 | 190 | 206 | 190 | 160 |
90 | 55.2 | – | 89.9 | 76.4 | 62.8 | 185 | 201 | 185 | 157 |
89 | 54.6 | – | 89.5 | 75.8 | 61.8 | 180 | 196 | 180 | 154 |
88 | 54 | – | 89.2 | 75.1 | 60.8 | 176 | 192 | 176 | 151 |
87 | 53.4 | – | 88.9 | 74.4 | 59.8 | 172 | 188 | 172 | 148 |
86 | 52.8 | – | 88.6 | 73.8 | 58.8 | 169 | 184 | 169 | 145 |
85 | 52.3 | – | 88.2 | 73.1 | 57.8 | 165 | 180 | 165 | 142 |
84 | 51.7 | – | 87.9 | 72.4 | 56.8 | 162 | 176 | 162 | 140 |
83 | 51.1 | – | 87.6 | 71.8 | 55.8 | 159 | 173 | 159 | 137 |
82 | 50.6 | – | 87.3 | 71.1 | 54.8 | 156 | 170 | 156 | 135 |
81 | 50 | – | 86.9 | 70.4 | 53.8 | 153 | 167 | 153 | 133 |
80 | 49.5 | – | 86.6 | 69.7 | 52.8 | 150 | 164 | 150 | 130 |
79 | 48.9 | – | 86.3 | 69.1 | 51.8 | 147 | 161 | 147 | 128 |
78 | 48.4 | – | 86 | 68.4 | 50.8 | 144 | 158 | 144 | 126 |
77 | 47.9 | – | 85.6 | 67.7 | 49.8 | 141 | 155 | 141 | 124 |
76 | 47.3 | – | 85.3 | 67.1 | 48.8 | 139 | 152 | 139 | 122 |
75 | 46.8 | – | 85 | 66.4 | 47.8 | 137 | 150 | 137 | 120 |
74 | 46.3 | – | 84.7 | 65.7 | 46.8 | 135 | 147 | 135 | 118 |
73 | 45.8 | – | 84.3 | 65.1 | 45.8 | 132 | 145 | 132 | 116 |
72 | 45.3 | – | 84 | 64.4 | 44.8 | 130 | 143 | 130 | 114 |
71 | 44.8 | 100 | 83.7 | 63.7 | 43.8 | 127 | 141 | 127 | 112 |
70 | 44.3 | 99.5 | 83.4 | 63.1 | 42.8 | 125 | 139 | 125 | 110 |
69 | 43.8 | 99 | 83 | 62.4 | 41.8 | 123 | 137 | 123 | 109 |
68 | 43.3 | 98 | 82.7 | 61.7 | 40.8 | 121 | 135 | 121 | 108 |
67 | 42.8 | 97.5 | 82.4 | 61 | 39.8 | 119 | 133 | 119 | 106 |
66 | 42.3 | 97 | 82.1 | 60.4 | 38.7 | 117 | 131 | 117 | 104 |
65 | 41.8 | 96 | 81.8 | 59.7 | 37.7 | 116 | 129 | 116 | 102 |
64 | 41.4 | 95.5 | 81.4 | 59 | 36.7 | 114 | 127 | 114 | 100 |
63 | 40.9 | 95.1 | 81.1 | 58.4 | 35.7 | 112 | 125 | 112 | 99 |
62 | 40.4 | 94.5 | 80.8 | 57.7 | 34.7 | 110 | 124 | 110 | 98 |
61 | 40 | 93.5 | 80.5 | 57 | 33.7 | 108 | 122 | 108 | 96 |
60 | 39.5 | 93 | 80.1 | 56.4 | 32.7 | 107 | 120 | 107 | 95 |
59 | 39 | 92.5 | 79.8 | 55.7 | 31.7 | 106 | 117 | 106 | 94 |
58 | 38.6 | 92 | 79.5 | 55 | 30.7 | 104 | 117 | 104 | 92 |
57 | 38.1 | 91 | 79.2 | 54.4 | 29.7 | 103 | 115 | 103 | 91 |
56 | 37.7 | 90.5 | 78.8 | 53.7 | 28.7 | 101 | 114 | 101 | 90 |
55 | 37.2 | 90 | 78.5 | 53 | 27.7 | 100 | 112 | 100 | 89 |
54 | 36.8 | 89.5 | 78.2 | 52.4 | 26.7 | – | 111 | – | 87 |
53 | 36.3 | 89 | 77.9 | 51.7 | 25.7 | – | 110 | – | 86 |
52 | 35.9 | 88 | 77.5 | 51 | 24.7 | – | 109 | – | 85 |
51 | 35.5 | 87.5 | 77.2 | 50.3 | 23.7 | – | 108 | – | 84 |
50 | 35 | 87 | 76.9 | 49.7 | 22.7 | – | 107 | – | 83 |
49 | 34.6 | 86.5 | 76.6 | 49 | 21.7 | – | 106 | – | 82 |
48 | 34.1 | 85.5 | 76.2 | 48.3 | 20.7 | – | 105 | – | 81 |
47 | 33.7 | 85 | 75.9 | 47.7 | 19.7 | – | 104 | – | 80 |
46 | 33.3 | 84.5 | 75.6 | 47 | 18.7 | – | 103 | – | 80 |
45 | 32.9 | 84 | 75.3 | 46.3 | 17.7 | – | 102 | – | 79 |
44 | 32.4 | 83.5 | 74.9 | 45.7 | 16.7 | – | 101 | – | 78 |
43 | 32 | 82.5 | 74.6 | 45 | 15.7 | – | 100 | – | 77 |
42 | 31.6 | 82 | 74.3 | 44.3 | 14.7 | – | 99 | – | 76 |
41 | 31.2 | 81.5 | 74 | 43.7 | 13.6 | – | 98 | – | 75 |
40 | 30.7 | 81 | 73.6 | 43 | 12.6 | – | 97 | – | 75 |
39 | 30.3 | 80 | 73.3 | 42.3 | 11.6 | – | 96 | – | 74 |
38 | 29.9 | 79.5 | 73 | 41.6 | 10.6 | – | 95 | – | 73 |
37 | 29.5 | 79 | 72.7 | 41 | 9.6 | – | 94 | – | 72 |
36 | 29.1 | 78.5 | 72.3 | 40.3 | 8.6 | – | 93 | – | 72 |
35 | 28.7 | 78 | 72 | 39.6 | 7.6 | – | 92 | – | 71 |
34 | 28.2 | 77 | 71.7 | 39 | 6.6 | – | 91 | – | 70 |
33 | 27.8 | 76.5 | 71.4 | 38.3 | 5.6 | – | 90 | – | 69 |
32 | 27.4 | 76 | 71 | 37.6 | 4.6 | – | 89 | – | 69 |
31 | 27 | 75.5 | 70.7 | 37 | 3.6 | – | 88 | – | 68 |
30 | 26.6 | 75 | 70.4 | 36.3 | 2.6 | – | 87 | – | 67 |
Hardness Conversion for Rockwell C scale:
Rockwell | Superficial Rockwell | Brinell | Vickers | Knoop | Tensile Strength | ||||
Diamond Penetrator |
Diamond Penetrator | 10 mm Carbide Ball | Diamond Pyramid | Diamond Penetrator | Steel | ||||
C | D | A | 15N | 30N | 45N | 3000 |
10 kgf | 500 gf & over | Equil. |
68 | 77 | 86 | 93 | 84 | 75 | – | 940 | 920 | – |
67 | 76 | 85 | 93 | 84 | 74 | – | 900 | 895 | – |
66 | 76 | 85 | 93 | 83 | 73 | – | 865 | 870 | – |
65 | 75 | 84 | 92 | 82 | 72 | – | 832 | 846 | – |
64 | 74 | 84 | 92 | 81 | 71 | – | 800 | 822 | – |
63 | 73 | 83 | 91 | 80 | 70 | – | 772 | 799 | – |
62 | 73 | 83 | 91 | 79 | 69 | – | 746 | 776 | – |
61 | 72 | 82 | 91 | 79 | 68 | – | 720 | 754 | – |
60 | 71 | 81 | 90 | 78 | 67 | – | 697 | 732 | – |
59 | 70 | 81 | 90 | 77 | 66 | 634 | 674 | 710 | – |
58 | 69 | 80 | 89 | 76 | 64 | 615 | 653 | 690 | – |
57 | 69 | 80 | 89 | 75 | 63 | 595 | 633 | 670 | – |
56 | 68 | 79 | 88 | 74 | 62 | 577 | 613 | 650 | – |
55 | 67 | 79 | 88 | 73 | 61 | 560 | 595 | 630 | – |
54 | 66 | 78 | 87 | 72 | 60 | 543 | 577 | 612 | – |
53 | 65 | 77 | 87 | 71 | 59 | 525 | 560 | 594 | – |
52 | 65 | 77 | 86 | 70 | 57 | 512 | 544 | 576 | – |
51 | 64 | 76 | 86 | 69 | 56 | 496 | 528 | 558 | – |
50 | 63 | 76 | 86 | 69 | 55 | 481 | 513 | 542 | – |
49 | 62 | 75 | 85 | 68 | 54 | 469 | 498 | 526 | – |
48 | 61 | 75 | 85 | 67 | 53 | 455 | 484 | 510 | – |
47 | 61 | 74 | 84 | 66 | 51 | 443 | 471 | 495 | – |
46 | 60 | 73 | 84 | 65 | 50 | 432 | 458 | 480 | – |
45 | 59 | 73 | 83 | 64 | 49 | 421 | 446 | 466 | – |
44 | 59 | 73 | 83 | 63 | 48 | 409 | 434 | 452 | – |
43 | 58 | 72 | 82 | 62 | 47 | 400 | 423 | 438 | – |
42 | 57 | 72 | 82 | 61 | 46 | 390 | 412 | 426 | – |
41 | 56 | 71 | 81 | 60 | 44 | 381 | 402 | 414 | – |
40 | 55 | 70 | 80 | 60 | 43 | 371 | 392 | 402 | – |
39 | 55 | 70 | 80 | 59 | 42 | 362 | 382 | 391 | – |
38 | 54 | 69 | 79 | 58 | 41 | 353 | 372 | 380 | – |
37 | 53 | 69 | 79 | 57 | 40 | 344 | 363 | 370 | – |
36 | 52 | 68 | 78 | 56 | 38 | 336 | 354 | 360 | – |
35 | 52 | 68 | 78 | 55 | 37 | 327 | 345 | 351 | – |
34 | 51 | 67 | 77 | 54 | 36 | 319 | 336 | 342 | – |
33 | 50 | 67 | 77 | 53 | 38 | 311 | 327 | 334 | – |
32 | 49 | 66 | 76 | 52 | 34 | 301 | 318 | 326 | – |
31 | 48 | 66 | 76 | 51 | 33 | 294 | 310 | 318 | – |
30 | 48 | 65 | 75 | 50 | 31 | 286 | 302 | 311 | – |
29 | 47 | 65 | 75 | 50 | 30 | 279 | 294 | 304 | – |
28 | 46 | 64 | 74 | 49 | 29 | 271 | 286 | 297 | – |
27 | 45 | 64 | 73 | 48 | 28 | 264 | 279 | 290 | – |
26 | 45 | 63 | 73 | 47 | 27 | 258 | 272 | 284 | – |
25 | 44 | 63 | 72 | 46 | 26 | 253 | 266 | 278 | – |
24 | 43 | 62 | 72 | 45 | 24 | 247 | 260 | 272 | – |
23 | 42 | 62 | 71 | 44 | 23 | 243 | 254 | 266 | – |
22 | 42 | 62 | 71 | 43 | 22 | 237 | 248 | 261 | – |
21 | 41 | 61 | 70 | 42 | 21 | 231 | 243 | 256 | – |
20 | 40 | 61 | 69 | 42 | 20 | 226 | 238 | 251 | – |
Conclusion
No wonder, Rockwell hardness testing scales are globally used and are the most popular ones. It is used for static hardness testing of the material. We have described thoroughly in this article the scales of the hardness test. Just follow the standard scale tables and rules to get the accurate values of the hardness of your test material. Want to learn more about the scales of different hardness testing or other factors of hardness testing by visiting our website hardnessgauge.com.