Hardness measurements are critical for various industries in ascertaining the tensile force of materials to resist the impacts of other forces on them. However, there are different methods and techniques for measuring material hardness, including the Leeb and Rockwell hardness tests. These methods offer different measuring scales and sometimes have to be converted from one to the other using a chart. This article provides a practical way of converting between the Leeb and Rockwell hardness testing methods.
I. What is HL is Hardness?
The Leeb hardness measurement of material is done using a rebound testing method based on the loss of kinetic energy when the indenter impacts the sample object’s surface. A value is obtained from this impact which correlates with the Leeb hardness value. This value is designated as HL. It is the division of the velocity after impacting the object’s surface with the velocity before the impact on the material surface. HL = (Vr / Vi) x 1,000 The impact is often done by a ball indenter made from tungsten carbide.
II. What is HB in Hardness?
The Rockwell hardness is measured using a value designated with the RB. Just like in the preceding, the RB is an assigned number for the Rockwell hardness testing value measured on the B scale. For Rockwell testing, the B scale better represents metal materials with a hardness value below HRC 20. The test is often carried out using an indenter with a specified force-load impacting the material surface to cause an indentation. The indentation gives the hardness value after measuring the difference between an initial impact force and the final indentation caused by the last applied force.
III. Can you Convert between Hardness Scales?
Converting HRB to HRC is often done using tables with some interpolations. These charts are calculated based on specific formulas requiring high precision in input values to arrive at an accurate equivalent value. As such, these charts should be critically considered to ensure high accuracy.
IV. Leeb to Rockwell Hardness Conversion Table
Leeb (HLD; Type D Impact Device | Rockwell C (HRC; 120-degree cone, 150kg) | Rockwell B (HRB; 1/16″ ball 100 kg) |
856 | 72 | – |
850 | 71 | – |
843 | 70 | – |
837 | 68 | – |
829 | 67 | – |
824 | 66 | – |
812 | 65 | – |
806 | 64 | – |
799 | 63 | – |
787 | 62 | – |
782 | 61 | – |
776 | 60 | – |
770 | 59 | – |
763 | 57 | – |
751 | 56 | – |
748 | 55 | – |
739 | 54 | – |
731 | 53 | 120 |
724 | 52 | 119 |
719 | 51 | 119 |
709 | 49 | 118 |
699 | 48 | 117 |
693 | 47 | 117 |
688 | 46 | 116 |
677 | 45 | 115 |
669 | 44 | 115 |
660 | 43 | 114 |
650 | 42 | 114 |
640 | 41 | 113 |
635 | 40 | 112 |
630 | 39 | 111 |
621 | 38 | 111 |
617 | 37 | 110 |
613 | 37 | 110 |
605 | 36 | 109 |
599 | 35 | 109 |
588 | 34 | 108 |
579 | 33 | 107 |
572 | 32 | 106 |
Conclusion
In conclusion, converting one hardness test value to another is a fundamental process in manufacturing materials like steel and other metallic alloys. However, particular consideration must be given to the accuracy of the formulas and charts used in this conversion. Also, the hardness test will determine the hardness conversion charts to achieve better accuracy with the process.