Have you ever wondered about the importance of hardness testing on a metallic material? The various testing techniques are designed as a quality control standard to understand a material’s strength and effects of indentation on the steel. This has commonly been practiced for a long time spanning over centuries, and with results garnered, conversion to other measuring scales can result in a different scaling outcome compared to the expected outcome. However, delving further into the subject matter gets more interesting. Let’s find out more if your curiosity has been aroused.
I. What is the Rockwell Hardness Test?
Rockwell hardness test is a hardness scale that estimates the level of penetration from the pressure applied by an indenter with a huge load and compared with the indentation caused by a small load. This hardness test can be executed on numerous hardness testers, but all hardness testers can be categorized into three. They include the Analog model, the Digital model, and the Bench model. The Rockwell hardness test is certified by the International Standards Organization (ISO) and the US Standard (ASTM).
II. What is the Vickers Hardness Test?
The Vickers hardness test is a replacement method for the Brinell hardness test. It was developed by R.L. Smith and G.E. Sandland for Vickers LTD. The Vickers hardness test is less difficult to operate when compared to other testing methods as its estimations are not determinant of the size of the indenter. This hardness test applies to all materials regardless of hardness. Like the Rockwell hardness test method, it is also certified by the ISO and ASTM standard regulatory board.
III. What is the Difference between Rockwell and Vickers Hardness Test?
The Rockwell hardness test is quite similar to the Vickers hardness test, but let’s examine their differences. The Rockwell method requires no material prep, and it is one of the most deployed metal hardness tests due to its easy readability of hardness value and cheaper to execute. The Vickers method, on the other hand, requires material prepping and incurs a higher cost of operation. But the Vickers method offers less force and better accuracy than the Rockwell method.
IV. Can you Convert between Hardness Scales?
As earlier mentioned, heat treatment practitioners have employed the conversion of hardness scales from one method to another in the past. Efforts are being embarked on to reduce hardness testing into comprehensive and elementary testing, hence the need for conversion. But it may vary in results after conversion as it is not mathematically accurate. But is the conversion between hardness scales possible? Your definite answer is yes.
V. Rockwell to Vickers Hardness Conversion Chart
Rockwell C (HRC) 150kg | Rockwell A (HRA) 60kg | Rockwell D (HRD) 100KG | Vickers (HV) |
80 | 92.0 | 86.5 | 1865 |
79 | 91.5 | 85.5 | 1787 |
78 | 91.0 | 84.5 | 1710 |
77 | 90.5 | 84.0 | 1633 |
76 | 90.0 | 83.0 | 1556 |
75 | 89.5 | 82.5 | 1478 |
74 | 89.0 | 81.5 | 1400 |
73 | 88.5 | 81.0 | 1323 |
72 | 88.0 | 80.0 | 1245 |
71 | 87.0 | 79.5 | 1160 |
70 | 86.5 | 78.5 | 1076 |
69 | 86.0 | 78.0 | 1004 |
68 | 85.6 | 76.9 | 940 |
67 | 85.0 | 76.1 | 900 |
66 | 84.5 | 75.4 | 865 |
65 | 83.9 | 74.5 | 832 |
64 | 83.4 | 73.8 | 800 |
63 | 82.8 | 73.0 | 772 |
62 | 82.3 | 72.2 | 746 |
61 | 81.8 | 71.5 | 720 |
60 | 81.2 | 70.7 | 697 |
59 | 80.7 | 69.9 | 674 |
58 | 80.1 | 69.2 | 653 |
57 | 79.6 | 68.5 | 633 |
56 | 79.0 | 67.7 | 613 |
55 | 78.5 | 66.9 | 595 |
54 | 78.0 | 66.1 | 577 |
53 | 77.4 | 65.4 | 560 |
52 | 76.8 | 64.6 | 544 |
51 | 76.3 | 63.8 | 528 |
50 | 75.9 | 63.1 | 513 |
49 | 75.2 | 62.1 | 498 |
48 | 74.7 | 61.4 | 484 |
47 | 74.1 | 60.8 | 471 |
46 | 73.6 | 60.0 | 458 |
45 | 73.1 | 59.2 | 446 |
44 | 72.5 | 58.5 | 434 |
43 | 72.0 | 57.7 | 423 |
42 | 71.5 | 56.9 | 412 |
41 | 70.9 | 56.2 | 402 |
40 | 70.4 | 55.4 | 392 |
39 | 69.9 | 54.6 | 382 |
38 | 69.4 | 53.8 | 372 |
37 | 68.9 | 53.1 | 363 |
36 | 68.4 | 52.3 | 354 |
35 | 67.9 | 51.5 | 345 |
34 | 67.4 | 50.8 | 336 |
33 | 66.8 | 50.0 | 327 |
32 | 66.3 | 49.2 | 318 |
31 | 65.8 | 48.4 | 310 |
30 | 65.3 | 47.7 | 302 |
29 | 64.6 | 47.0 | 294 |
28 | 64.3 | 46.1 | 286 |
27 | 63.8 | 45.2 | 279 |
26 | 63.3 | 44.6 | 272 |
25 | 62.8 | 43.8 | 266 |
24 | 62.4 | 43.1 | 260 |
23 | 62.0 | 42.1 | 254 |
22 | 61.5 | 41.6 | 248 |
21 | 61.0 | 40.9 | 243 |
20 | 60.5 | 40.1 | 238 |
Conclusion
So, what does all this mean? Both the Rockwell hardness testing method and the Vickers hardness testing method have their respective strengths and drawbacks, which is the reason why conversion was adopted. Although mathematically, the conversions are not exact, thermal treatment operators find it resourceful. The Rockwell to Vickers conversion chart shows an illustration of how the conversion values are represented. Finally, the conversions are also ASTM E-140 and A-170 standards, which identify that it is safe to adopt.