Knife Sharpening Using Traditional Methods: Hardness

The YouTube video here really helped me understand how the process works and the key thing to realize is that in many cases, this is an automated process.

Rockwell Hardness Test

Basically, kitchen knives vary in hardness from 54 to 67 with the most common knives, the ones most of us own such most Henckels, Wusthoff, Grohmann are in the 56-58 range. It should be noted that even one number represents a significant variance in hardness, so a knife with a hardness of 60 is much harder that a 58.

Of the knives I have sharpened, 60 seems to be the perfect number in terms of holding edges and ease of sharpening. Remember, there are other factors involved that can have an impact on the quality of knife. Just because a knife has a hardness of 60 does not necessarily mean it is better than one with 58.

Rockwell hardness testing is an indentation testing method. The indenter is either a conical diamond (brale) or a hard steel ball. Different indenter ball diameters from 1/16 to 1/2 in. are used depending on the test scale.

To start the test, the indenter is “set” into the sample at a prescribed minor load. A major load is then applied and held for a set time period. The force on the indenter is then decreased back to the minor load. The Rockwell hardness number is calculated from the depth of permanent deformation of the indenter into the sample, i.e. the difference in indenter position before and after application of the major load. The minor and major loads can be applied using dead weights or springs. The indenter position is measured using an analog dial indicator or an electronic device with digital readout

I think we have the basic idea now, metal is tested using a indentation process and for knives it is the "C" Scale so the letters HRC I believe stand for Hardness Rockwell C scale, (kitchen knives, or just knives)

I think like other things in our lives that we buy, this hardness scale is used by knife makers/sellers as hype.

Not many people purchase their knives based on this scale, they won't not purchase a good knife just because it has an HRC of 58 and not 60. That is my opinion.

Here are some of the common knife brands and their HRC rating:

Note that a single digit increase denotes a 10% increase in hardness and therefore a 10% increase in edge retention.......but we all know that despite the level of hardness, all knives get dull sooner that we would like them too.

Global - 56-58
Shun 60-61 or 61-62 for the SG2 steels in the Shun line.
Grohmann - 54-56 (Grohmann knives are made in Nova Scotia and very popular here)

Carbon knives, the Japanese Hand Made wonders are harder of course.

Moritaka is up around 64-65 and Masakage knife hardness varies but definitely up there above 61.

You see a lot of knives with HRC or High Carbon Content, this means that along with the Carbon, other elements such as Vanadium, or Chromium are added but the % of carbon is higher, at least 5%.

(Axes are generally around the 40 to 45 range)

Again, there are some very hard knives that are not hand made and made of carbon, the Henckels Twin Cermax for example is a staggering 66, it's an awesome knife.