Rockwell Scale Hardness of Knives

It seems a lot of importance and confusion has been given to this topic recently. I can see this term easily falling into the same consumer buzzword hell as “megapixels” for cameras and “bits” for video gaming consoles. Before I go into the relevance of the Rockwell system I want to first talk about steel.

A knife maker will buy steel from a company that processes it from iron ore and other materials to create a specific alloy. A high-quality steel for kitchen knives has specific metallurgical properties and can be expensive to produce. If the knife maker buys a cheaper - lower quality steel, it will make no difference how hard it is in Rockwell terms or how it is processed by the knifemaker - it will simply be a bad knife. A good example is the Global brand, which I like very much. Many of these knives are not forged to create a lighter knife. Because of the alternative techniques used, and the high-quality steel, they are able to create a great lightweight knife without the forging process so valued among knife consumers.

Hardness of knives is very important. A softer steel will be more durable but not retain an edge the way a hard steel will. On the flipside a hard steel will be sharper and have better edge retention, but will be much more delicate and likely to chip or break. This is the idea behind ceramic knives, they are so hard that they almost never need to be sharpened, but even dropping them onto a marble counter can damage or destroy it. Blades made for axes, chisels and swords must be made from a softer steel because they must endure high impact that would break a blade from a harder steel. On the other hand, pocket knives and hunting knives don’t have this problem and are often made from very hard steels.

A cheap knife or blade from a softer steel is extremely hard to sharpen and will never take on the edge of a harder steel blade.

The Rockwell scale is a measurement system used by commercial manufacturers to determine the relative hardness of objects based on the depth of indentation from a heavy object. In other words, they drop a heavy ball or diamond cone onto the steel and measure the size of indentation. For knives they use the “C” scale in units labeled “HRC.” High carbon steel kitchen knives generally run from HRC 56-58. HRC 62 is a very hard knife.

Initially I spent a great deal of time comparing Rockwell ratings for different brands. For the most part it seems these companies list a very generic and apocryphal range. In my opinion there are many other factors that are more important in buying a knife, among which is cosmetic appeal. Obviously I am concerned with a high quality knife, but a good knife is a good knife. You don’t have to call the steel company to confirm the alloy.

High carbon steel is an alloy where carbon is added to increase hardness. The difference between “Carbon steel” and “high carbon steel” is with high carbon steel or HCS, other elements have been added to prevent rust and tarnish and increase durability. These additional elements effectively decrease the hardness of the knife which makes HCS a compromise between the two types of steel.

Hardness is important when buying a knife but only to an extent. A professional chef will invest the money is a very hard Japanese knife because it will not need to be sharpened as often even with extensive daily use. These knives can break or chip if they are dropped on a hard floor or even handled carelessly. They require greater attention and care. Wusthof knives are very durable and have comparable edge retention. The represent a good value.

7 comments:

Jo said...

It is interesting topic. From my knowledge “carbon steel” is steel containing 0.05% carbon or more, if containing more than 0.6% it will be called high carbon steel. If steel is containing carbon, it will rust, more carbon to it, it will rust easier and faster. So actually high carbon stainless steel is misleading. Some Japanese high carbon steel knife when it is covered with wet towel it will rust within 30 seconds. So when you use this kind of knife you should have to be very careful otherwise you will be hurting yourself. This is why hard to find “High carbon steel” knives in the market nowadays.

HRC 55 steel may be brittle than HRC 60, it is all depend on the heat treatment. Most of pocket knives are made from 420 steel, it is not a very hard steel (general speak 440 steel is harder than 420 steel). Ceramic knife’s blade is very hard but not necessarily brittle it depends on the temperature control.

Don’t be fooled with most of name brands or expensive knives, they usually turn out are not good knives but only over price. For example many, Japanese knives are very expensive and GOOD LOOKING but not so easy to handle and use, so actually, they are not qualified to be called as “good knives” may be you can call them “GOOD LOOKING” knives.

Akki Katakol said...

Very interesting info. Right now I am obsessed with finding a good kitchen knife and that's how I stumbled across your blog. I was about to send the knife I ordered because the seller could not give me its HRC. After reading your post, the knife might have a chance of stay in the kitchen. Now that the HRC is out of the way I'm off to finding out more about 14Cr14MoV steel. Thanks for the info and keep up the good work (read crazy! :).

lizzybee said...

How can I find out what the rating of different makes of knives is exactly? I looked on the manufacturer's site and there is nothing to tell me what the hardness is. I am trying to get the best sharpening rods to match these knives (Global, and Messermeister for example) and I cannot find this info... any suggestions? Thank you in advance. Beth

T Taylor said...

@lizzybee... Generally speaking, most of the Global range is in the 60HRC range. However, IMHO what your are asking for has less importance than you might think. The type of blade you are sharpening is at least equally relevant. Using your examples, (which are perfect for this explanation, I might add!), if you have a Global that needs sharpening, you would want to use a ceramic rod - regardless of the hardness of the metal. This is due to the inherent nature of the style of blade it is - Japanese blades are thinner than German style blades. The angle of the edge is also different. If you use a metal sharpener against a Japanese blade, you will "grind", rather than "hone" the edge. Conversely, using a diamond steel on the Messemeister, with its heaver gauge and greater blade angle, (20 deg. as opposed to 12 - 15 on Japanese knives), is the way to go. Same logic applies to stones - softer stones for the Japanese blades... harder for German. Hope this helps.

SpecialTChef

lizzybee said...

Great help, and many thanks. It clears up a lot for me. I really appreciate your advice!

Naifujitsu said...

Thanks for this concise explanation. I've recently purchased and have been using on a daily basis two damascus 33 layer VG-10 Japanese chef's and utility knives. I work in the restaurant industry and am an avid home cook so they see a lot of use, though not quite as much as a professional chef. These knives have phenomenal edge retention. Paired with a ceramic honer I don't see myself taking them to a Japanese whetstone for a full year. That being said, they do require and incredibly meticulous care routine. I've noticed that most people simply don't have the mentality, or possibly the desire, to wipe, hand wash, hone, and handle carefully their knives with every use. The few times I've allowed others to use these knives with explicit instructions they were never followed. For this reason, no one touches these knives except for me. Buyer beware, if you invest in a gorgeous handmade masterpiece, stash it in a drawer somewhere and keep the more durable knives out for guests and family.
Also, I've heard excellent things about Wustof knives but never that they retain an edge comparably to Japanese knives. This will almost certainly be my next purchase. Thank you.

vanya said...

Great post! ty