When you look at the specifications of knives, you can often notice a certain number with the designations “RC” or “HRC” after it. This number represents the values of the Rockwell rating.
The definition of Rockwell
The Rockwell rating is a scale used to measure the hardness of a material. The Rockwell hardness test is the industry standard for knives. For example, in stainless steel AUS-8, this indicator is 57-59RC. Usually a range is specified, which means that any change in the hardening process will fall within this range. The range should never exceed two points with reliable quality control. Testing practically does not damage the tested material and provides important information about the hardness and durability of steel.
Why HRC? There are quite a large number of scales by which the measurement takes place: A; B; C; D; E; F; G; H; K; N; T. But the most suitable for measuring the hardness of the knife is the C scale (load 150 kg/c, diamond tip with an angle of 120 degrees). Hence the abbreviation HRC.
How does Rockwell testing works? The test is performed by measuring the penetration depth of the diamond-tipped indenter at high load compared to the penetration caused by preload. It is important that the measured surface is flat. One small drawback when testing the knife is that there is a small dot dent at the point of contact with the identifier. This can be avoided if testing is carried out in an area that is hidden under the handle.
What do these numbers mean in practice?
The same steel can have both a low and a high HRC index. However, each steel has its own range in which steel will work best. The higher the number, the harder the steel. The harder the steel, the better the edge retention. The better the edge is held, the less often you have to sharpen it. On the other hand, the harder the steel, the more brittle it is. In the end, it all comes down to preferences in using a custom knife. How often do you want to hone it and for what purposes do you want to use it. Many users judge the quality of steel based on the Rockwell number, while it is believed that higher numbers indicate a higher quality of steel. Sometimes it is, but not always.
Some people like softer steel in the range of 54-56 HRC. Softer steels require sharpening more often, but they are much easier to sharpen than harder ones. They are also less prone to chipping. The edge is likely to be doubted rather than chipped, which is much easier to fix.
The Rockwell test is very important for manufacturers as an additional quality control, but also works as one of the parameters of choice for the consumer. Knowing the Rockwell number will help you predict how well the blade will work, and possibly prevent unsuccessful purchases. If you see that an ordinary folding knife has a 50+ index, it can be sharpened against a curb or wall. If you need a knife of greater hardness, aim for the 57-59 range. And finally there are knives with a fantastic range of 60-63.