Rockwell Hardness Scale 101: Using It on Your Knives
by HexClad Cookware
To determine where your knives fall on the quality and durability scale, you’ll need to know where it falls on the Rockwell hardness scale. This test method helps you determine your knife's strength, and we will dive deep to tell you all about it.
We’re going to break down this scale, and discuss where it came from and why.
Finally, we will give you a little play-by-play if you want to test your own knives against the Rockwell scale at home (and why you should avoid this method if you can help it).
By the end of this read, you should have everything you need to know and will better understand why our chef’s knives outshine the competition.
What Is a Rockwell Hardness Value?
The Rockwell hardness scale, named after Hugh and Stanley P. Rockwell, is a scale-based indentation system used to determine the strength of plastics and metallic materials. It’s sometimes referred to as the American Standard Test Method for Rockwell Hardness (or ASTM E 18).
Knives are given a designation or number following the penetration of the indentation tool. The goal is to see how much the material resists when pressed. The indent left behind is measured. This designation is called a Rockwell hardness number.
One of the most common uses for Rockwell hardness numbers (and other similar hardness test methods) is rating hard steel. The hardness factor depends upon the indentation’s depth during testing. Depending on the type of blade used for your knives, the rating will be from 45, relatively soft, through a 60, the hardest and most durable option.
A 60 on the hardness scale will designate that your knife’s blade can last longer and that the type of steel used to make your knife is of the hardest quality. But, these two factors aren’t enough on their own to determine the quality of the knife itself.
Even the hardest blades can be brittle, depending on the quality or the company. That’s why we take so much care in crafting our Japanese Damascus Steel knives.
Japanese Damascus Steel is formed by folding the steel during the pliable phase on top of each other to create layers and veins naturally in the metal. The steel is made from a combination of alloys.
The layering process also refers to the mixture of metals layered together to create strong, durable, and flexible metal. Not only does the technique produce an aesthetically pleasing blade, but also the strongest and most durable knife you could hope to chop onions with.
Even though the Rockwell hardness scale is the most straightforward answer to the strength of metal, some different scales and measurements can be used to get test results that measure the hardness of a material.
One example is the Brinell hardness test, used to rate and measure metals too coarse to capture a proper reading on the Rockwell system. Another example is the Vickers hardness test, a method crucial for testing and measuring thin metals, ceramics, and soft steels.
Lastly, there’s also the Knoop method, which uses a conical diamond tool that measures the thin tips of softer materials.
However, the Rockwell hardness scale is reliable and quick to use on harder materials. Thus, it is the most popular option for quality control on knives.
Who Created the Rockwell Hardness Scale?
Two men worked together to receive a patent for the Rockwell hardness scale in 1919. Metallurgists Stanley Rockwell and Hugh Rockwell worked for a manufacturing company in Bristol, Connecticut.
They created this system to test metal and its ability to resist or react positively to force applied directly to it.
The original system features an indenter, a gauge for measuring the pressure applied to the metal, and two load systems, one major and one minor, that will test the resistance and force on two different levels.
First, you apply the major load, and once that is released, it automatically goes into the minor load. This force will create a depth of pressure caused by the blade that will then equal a certain strength, or hardness, on the Rockwell hardness testing.
These numbers are an inverse of each other in that the deeper the blade’s penetration, the lower the score or softer the metal is. A shallow indentation will result in stronger, harder metals.
The machine can be put together in a few different ways. For example, a diamond indenter or ball indenter can be swapped for each other. However, the components listed here are necessary to create a reputable machine and legitimate test.
These components work together to determine how strong the metal is and thus define the strength and overall toughness of the steel you keep in your kitchen.
Who Uses the Rockwell Hardness Scale?
The Rockwell hardness scale is actually used across a few metal-centered platforms. While professional and home chefs will want to refer to the scale when deciding on a reputable brand to consider buying knives from, the scale is actually crucial to those in the steel manufacturing industry.
No one wants to create a weak product. Any good steel manufacturer will want to consider the Rockwell scale and ensure that the steel created at their company is up to snuff.
Remember those childhood recess games? You knew if you were the last one chosen for games like red rover, you weren’t making it past the first round. The same goes for knives. Get a low score and you might as well retire now.
What Are the Basics of the Rockwell Hardness Scale?
There are 30 different types of Rockwell hardness scales that are used to test and measure metals, but the hardness scale that’s important to the production of kitchen knives is the Rockwell C scale, also known as the HRC scale.
Let’s examine the different levels of the HRC scale next.
Anything Below a 52 HRC Rating Is Too Soft
Knives made of softer steel or other malleable alloys will dull quickly. A rating of 52 or below from a testing machine is generally reserved for throwing knives or axes, not knives made of harder steel. These knife blades stick to the boards, but they aren’t going to cut through tomatoes with ease.
These soft materials are manipulated quickly by the test force applied as well as the food being sliced and diced. That’s not the performance you want in a knife.
The silver lining to how quickly they dull is their soft texture, which makes it easy to get a sharp edge — it’s relatively easy to sharpen these thin materials, so it keeps the process cheap. However, this does mean that you can expect to spend a considerable amount of time keeping your knives worthy of their place in your kitchen.
These aspects and qualities of softer alloys make them less than ideal when considering what type of chef’s knife to purchase.
Anything Between 52 and 54 Is Average
Standard, every day home chef kitchen knives fall between 52 and 54 on the HRC. These knives will be good enough to use daily yet keep a decent sharpness. They don’t require constant fine-tuning.
You will need to keep a regular schedule for sharpening, as the blade’s edge will dull faster with use than a harder blade, but it will still hold up.
These knives are fine, but that’s about it. They’re just fine. They aren’t the strongest or the most durable; they’re meh.
Anything Above 55 Is Considered Professional-Grade
For quality that the pros trust, you’ll need to find knives with a 55-rating on the hardness scale. These knives are going to require a maintenance routine that will require annual sharpening and monthly honing.
This category on the hardness scale includes carbides, some of the hardest metals on the planet.
However, this process gets more expensive with the strength of the knives. While you have the advantage of not needing many sharpenings a year, these sharpenings will require more expertise than the average Joe knife.
It might sound like a hassle, but considering the quality and price of the knife itself, you wouldn’t want to take the chance of ruining your blade with a low-quality sharpening system.
So the strength of the knife comes with the trade-off of needing a professional knife sharpening routine. But, considering the durability of the blade, you can go months between sharpening appointments without noticing any dulling of your blade.
HexClad’s HRC Rating Is a Whopping 60
Listen, if chefs require a blade with at least a 55 hardness, then consider yourself one step ahead when you choose HexClad. Our knives rate as a 60 on the hardness scale, making us the superior choice on the market.
These knives are strong, durable, and the most resistant to dulling. When your knife needs a little sharpening, there is the added necessity of needing to employ a professional service to sharpen your knives, but this is an annual thing (and not a monthly situation with the weaker knives in the bunch).
We also feature that gorgeous Damascus steel, which gives us an additional strength factor that our competitors are missing in their designs. Even if you consider it a hassle to get your knives sharpened yearly by the pros, considering the quality and expertise in the knife, would you really want to trust just anybody with this baby? We didn’t think so.
There are so many features to our knives that we love that it’s hard to pinpoint what one thing puts us ahead of the competition. It could be the fact that our knives are stronger than the standard and professional grade competition.
Maybe it’s the versatility and variability in our knives, giving you an option for every technique you want to master.
Even still, it could be the fact that the handle is ergonomic, providing your hand and wrist with precision comfort while you cut your way through all the prep work your meal requires. Better yet, it might be the gorgeous wood design on said handle.
Okay, it’s probably all of these reasons. We created the most superior knives on the market, and we aren’t afraid to brag.
Can You Do Rockwell Hardness Testing at Home?
The short answer is yes, there are ways to complete a Rockwell Hardness test at home, but it will require some tools and a little bit of tech.
The first way is an actual Rockwell Hardness Test. You can get one of these machines to use at home, but they are incredibly expensive. You might want to test the scale and hardness of your knives one time, but really, how many times will this machine come in handy after that?
You can employ some of the other options that were mentioned earlier; tests like the Knoop method or the Vickers hardness test are more basic tests that can be done with less expensive tools and a more straightforward at-home process.
However, much like the consistency of the Rockwell test, at-home tests can vary depending on the skill level and interpretation of the conductor. Which means that if you aren’t good at taking tests, chances are you won’t be any good at determining the strength of the metals you’re testing.
Why It’s Best To Leave the Testing to the Pros
Because of these reasons, it really is best to leave the testing to the pros. Metal experts and manufacturers train tirelessly to become skilled at their craft.
In addition to understanding metal on a level that the average person doesn’t, they use these testing materials habitually, making them skilled at conducting the tests and reading the results.
Instead of misinterpreting results or risking injury with machines you’re not sure how to use, leave that job to the pros.
The Only Knives You’ll Ever Need
Knowing that HexClad Japanese Damascus Steel Knives are the toughest and most durable knives on the market, there’s no real need to perform the Rockwell tests on other knives.
Sure, your other knives may get jealous, and maybe you’re feeling sorry for them, but who cares about those weaklings? It’s time to step out of the mundane and use the most badass knives on the market.
HexClad knives are strong enough to stand up to daily use and keep going, no matter how much prep work the future holds. Since you’ve got the best, go ahead and ditch the rest.
Rockwell Hardness: an Overview | ScienceDirect Topics
The Lost Art of True Damascus Steel | HowStuffWorks
How to Check the Hardness of Metal: A Complete Guide | MakeItFromMetal