So, in our blogs about paring knives and kitchen knife set, we talk a lot about steel ratings, knife strength, flexibility, and toughness. We never really go into the science or history behind those terms. Before discussing a knife steel chart, we first need to consider the Rockwell rating, high-carbon steel, and stainless steel.
And, to understand why some steel is stronger than other steel, we have to dial back the clock to the turn of the Century. When Swedish inventors created the Brinnel test. The test was, mainly, a math equation. It is applied to the depth of an indentation that resulted from a material struck by a hard edge. It yielded an effective enough understanding of hardness. The test cumbersome and time-consuming and usually destroyed the test material.
It wasn’t until Hugh M. Rockwell and his colleague co-invented and patented the “Rockwell Hardness Tester” in 1919, that the world of metallurgy would have access to a practical and easy-to-operate “hardness” testing machine. The Rockwell Hardness Tester was capable of testing on different scales – HRA, HRB, HRC, etc. – for different types of materials, and the way the application can be explained in three basic steps, although this video may best illustrate the process:
3 Basic Steps in Testing Metal Hardness
The difference between the measurements of steps two and three calculates to equal the total Rockwell Hardness. It measures in HRC’s (in this case). Machines like the Hardwell Hardness Tester are “differential-depth machines”. They measure hardness and the process remains a standard for testing metal even today. (although the process is entirely automated and takes only seconds).
An initial test compression (of 10kp or kilopond) apply to the material.
Then an additional 14kp adds to the initial amount of the test compression (for a total of 150kp sustained force against the material).
And, finally, step two is reverse, leaving only the pressure of the initial test compression.
Knife Steel Chart Terms and Materials
So, with hardness covered, let us, then, turn to comparing materials used for the making of knife steel so that we may understand how the iron gains this hardness.
There is a handy chart that you can find floating around the internet on various sites the lend visual representation to this text, and one knife steel chart we like a lot because it lists common knife metal alongside tool metals, and other metals in one list.
Be Familiar with Elements and Concepts
You do not, of course, need to memorize an entire knife steel chart to buy a knife or knife set, but it is good to get familiar with the elements and concepts on one so that you can make informed choices over time.
Let’s start with carbon steel since it has been around the longest and, now, many knife-makers seem to giddily boast about their new and improved high-carbon steel and rock-hard knives.
Generally speaking, all steel has carbon in it, and this is a four-digit number, such as 1048, which refers to an iron that has 0.84 percent of carbon added, 1095 equals 0.95, and so on.
Any carbon steel in the range of 0.55 – 0.95 percent is to be of high carbon. Note that carbon is a steel hardener, and mid-grade to high-end high-carbon knives will usually rate between 56-62 HRC on the Rockwell Hardness Scale. The higher the HRC number, the longer your knife will stand up the wears and tears of your kitchen and keep its sharp edge. When you compare the numbers in high-carbon steel to those commonly found in stainless steel, we’ll see that the base stainless product is softer than carbon steel. That is because both carbon and chromium tend to produce carbides. Knife manufacturers have found ways around the side effect of these additives. However, they can now create stainless steel with up to three percent carbon and an HRC rating of between 64 and 66. For comparison, high-end tool regularly uses steel has an HRC of between 67-70.
Knife Steel Wrap-up
The bottom line with all of this is not that you know everything there is to know about steel by heart. You just should know a good quality knife steel from an inferior one. For hardness, unless you are in the market for a, you can probably find perfectly acceptable cutlery for between 55-60 HRC without worrying about all of that high-carbon mumbo-jumbo. Unless you are in the market for a Kramer by Zwilling JA Henckels, you can probably find perfectly acceptable cutlery for between 55-60 HRC without worrying about all of that high-carbon mumbo-jumbo. Plus, high-carbon and stainless steel products are easily found on the market. You don’t have to choose between a harder knife and one that deters rusts and stains.