What is the Rockwell Scale?
The Rockwell scale is a hardness scale defined by how much pressure needs to be applied before a mark or indentation is left on the material. When it comes to knives, it is determined by the indentation left in the heat treated and tempered blade using a much harder material, usually diamond but can be a hardened steel ball. For some hobbyist makers it is determined by how much a file bites into the steel after heat treatment.
Whilst there are many different hardness tests, knife manufacturers have come to use the Rockwell scale, as an industry standard and it is widely understood. This is due to the accuracy, low costs, and ease of testing materials.
A high Rockwell rating means that the steel has high strength. Knife steels typically start in the mid 40’s, any rating above 55 is considered ‘hard’. The top Japanese steels have hardness ratings of around 60 HRC however the newest powdered steels can reach the mid 60’s.
Generally harder steels are preferred with knives, as the blade will hold its edge and stay sharper for longer.
A knife with a higher HRC should have a better blade, right?
Not exactly, Hardness comes at the cost of the malleability of the steel. The harder a steel becomes the more brittle it is. High hardness steels are ones with a Rockwell HRC hardness of above 60 and are usually too fragile to be used on their own in a knife, they can break and chip. As a result most knives with a high hardness rating must be made with a 3 Ply or Damascus construction and protected by a softer steel cladding.
Harder steels are also harder to sharpen and will require more skill to resharpen blades to their full potential, we always recommend using Japanese whetstones to get the most out of your knives.
So, a high Rockwell HRC does not necessarily mean that a knife will outperform a knife with a lower HRC rating. There are other factors involved. If a knife is going to be used for a lot of heavy chopping, a knife with a lower HRC might be preferred. In addition, the actual blade grind, convex, concave, straight will make a major difference on how the knife performs.
One final note is that, whilst certain steel alloys, VG-10 for example can have a Rockwell HRC level of 60, getting to this hardness level will be down to the skill of the factory and the processes used in hardening the steel to the required level.
