What is the Rockwell Scale?
The Rockwell scale is a hardness scale, which means, how much pressure needs to be applied before a mark or indentation is left on the material. Another way would be how resistant a steel is to deformation from another material. The Rockwell test will determine how hard any alloy is used in knife making.
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. The newest powdered steels can reach the mid 60’s.
Generally harder steels are preferred with knives, as the blade will hold its edge, i.e. stay sharper for longer. A knife with a higher HRC should have a better blade, simple?
Hardness, however, comes at the cost of the malleability of the steel. The harder a steel becomes the more brittle it is. High hardness steels with a Rockwell HRC hardness of above 60 are usually too fragile to be used reliably in the kitchen, they will break, the blade edges will chip. Most knives with a high hardness rating must be made with a 3 Ply or Damascus construction and protected by a softer steel.
Harder steels are also harder to sharpen and will require more skill to resharpen blades to their full potential with expensive Japanese whetstones.
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; if a knife is going to be used for a lot of heavy chopping, a knife will a lower HRC that has more toughness 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 have a Rockwell HRC level of ~60, getting to this hardness level will be down to the skill of the factory in hardening the steel to the required level, just because a brand says the blade is made from VG-10 does not mean that it will have been hardened correctly.