When looking for a new knife, you might have noticed the term Rockwell hardness (or its abbreviation “HRC” or “RC”) in different knife descriptions. This simply denotes the hardness of the steel used for the knife blade. Hardness is an important attribute that affects knife performance.
This post will get deeper into everything you need to know Rockwell hardness for knives. You’ll learn what exactly is Rockwell hardness and how it’s tested and how to interpret Rockwell hardness numbers like a pro metallurgist. You’ll also get to know the best Rockwell hardness for a knife.
What is the Rockwell Hardness?
Rockwell hardness is a scale used to describe the hardness of a steel alloy. For starters, the term hardness describes a metal’s ability to resist penetration and permanent deformation by another material. The Rockwell Hardness, therefore, gives you an idea how hard a blade is to resist deformation when it comes into contact with other media.
The hardness can also be expressed as a range. For instance, 52100 carbon steel has a range of 62-64 HRC. This means that the hardness of the steel will fall between these two values, depending on the tempering method. The range should, however, not be greater than two in a well-controlled quality setting.
Though there are many different Rockwell hardness scales, the Rockwell hardness scale C is the industry standard for knives and is usually abbreviated as HRC or RC.
How is Rockwell hardness measured?
The Rockwell hardness test involves measuring the depth of penetration of a diamond-tipped indenter under a large load compared to penetration made by a pre-load.
This is how you carry out the hardness measurement:
The first part involves applying a small pressure to determine the steel hardness/resistance under light, precisely controlled amount of load. The diamond indenter, also referred to as the indentation tool, will make a slight impression on the knife steel you’re testing. You can then measure this impression or depth and record it as value A.
In the second part, you apply a much heavier load to the same spot on the steel you’re testing. Measure the new penetration level and record it as value B.
Now deduct the light penetration value A from the deep penetration value B (i.e., Value A minus Value B) and transfer the difference you get to the Rockwell C scale. The corresponding value display on the Rockwell scale becomes the Rockwell hardness of your steel.
What do Rockwell hardness numbers mean?
Understanding the Rockwell numbers will help you easily choose a knife with a performance that matches your standards and personal preferences.
FIRST…let’s burst the misconception that higher RC numbers mean higher quality steel. While this might prove true in some cases, it doesn’t always hold true for most steels used for knives.
HRC Rule of Thumb: The higher the hardness number, the harder a knife steel is. And the lower the RC number, the softer the steel becomes. In simpler words, a steel with 45 HRC is considered soft while a steel featuring 60HRC is hard steel. A real-life example: 440C stainless steel has 57HRC hardness which means it’s less hard compared to AUS-8 stainless steel with 59 HRC hardness.
Higher hardness also means that a knife has better edge/sharpness retention. And good edge retention means you’ll spend less time sharpening it. That is, you’ll be using your knife for long periods of time for hard tasks without losing its sharpness.
BUT…high hardness comes with a downside which is increased brittleness. High hardness knives sacrifice toughness and are at a greater risk of chipping, cracking, or beddings under stress or impact.
What is the best Rockwell hardness for a knife?
It depends. Most steel alloys used for knives range from 45 RC all the way up to 60 HRC. But there’s really no specific value set as the “best HRC for knives.” Instead, the best Rockwell hardness for a knife depends on what type of knife you want and your personal preferences.
This is where the Rockwell hardness scale C hardness can further be put into softer steel and harder grades of steel:
Softer steels (54-56 RC hardness)
This category features low hardness steels—around 54-56 HRC— and usually lose their edge quickly, so they need frequent sharpening. However, they’re super-easy to sharpen. They also offer better toughness and they’re less likely to chip or break.
Knives intended for harder everyday use should feature a softer steel grades which offer high toughness to enable them to withstand tough use without fracturing or breaking. Examples include Ontario machetes, axes, larger knives, and generally all knives intended for field work.
Other tools such as throwing knives and throwing axes should be made of even softer steel as they require even greater toughness to enable them to withstand the throwing action without shattering.
Harder steels (59-66 RC hardness)
Steels in this category display higher hardness—in the 59-66 HRC range. As we mentioned earlier, these steels have better edge holding ability than softer steels. They’re, however, harder to sharpen and offer low toughness. They can easily chip or break under impact.
Pocket knives designed for everyday use should be made of steel with a hardness of 57-59 HRC. This is a good hardness with some good quality to it to withstand daily use without chipping or breaking.
Most of the premium knife steels such as CPM S30V, CPM S110V, VG10, Elmax, ZDP-189, etc., offer a hardness revolving around 59-64 RC range. This is high 50s and low 60s and is often referred to as the “Sweet Spot” for knife Rockwell hardness. If you go further than this, the steel becomes brittle.
Steel hardness, usually expressed in Rockwell hardness scale C, is an important factor to consider when looking for a knife. This knife Rockwell hardness guide has walked you through all the basics and crucial info you need to know about Rockwell hardness for knives to help you understand what those numbers followed by “HRC” or “RC” are all about.
We hope that after reading this guide, you can now easily understand how low and high hardness ratings impacts the performance of a knife and how to pick the best Rockwell hardness for your next knife.