Steel Composition and How it affects your Cutting Tools
This article series explores a range of cutting solutions, focussing on the key elements in blade design and how they affect the performance of your knives, and zooming in each episode on a focussed product.
When it comes to industrial cutting solutions, blade performance starts long before a knife reaches the machine. The composition of the steel itself plays a major role in determining how a blade performs, how long it lasts, and how well it handles the demands of its application.
In this article, we take a closer look at blade steels, alloying elements, and some of the key metallurgical terms that influence knife performance.
What Is Steel?
To understand blade steels, it helps to start with the basics.
A metal is defined as any element of the periodic table with a positive electrical charge. Metals are typically shiny and are good conductors of heat. There are approximately ninety metals, including examples such as aluminium, gold, mercury, and iron.
Steel is an alloy, or mixture, of iron, carbon, and other elements.
The carbon content in steel can contribute up to 2.2% of the alloy’s weight. By varying the amount of carbon and adding specific alloying elements, manufacturers can control and enhance the characteristics of the finished steel.
These characteristics include hardness, strength, corrosion resistance, wear resistance, and response to heat treatment.
Without alloying elements, these performance enhancements would not be possible.
The carbon content of steel generally ranges between 0.002% and 2.2% by weight for iron-carbon alloys. The exact composition depends on the alloying elements added, such as manganese, chromium, nickel, tungsten, and others.
Understanding Common Metallurgical Terms
When discussing industrial blade steels, a few technical terms appear regularly. Understanding the difference between them is important because they each describe different material behaviours.
Hardness
Hardness measures a material’s resistance to scratching and indentation.
A harder blade generally offers improved wear resistance, but hardness alone does not determine overall blade performance.
Toughness
Toughness measures a material’s ability to withstand bending, stretching, or other deforming forces without cracking.
A blade can be extremely hard, but if it lacks toughness, it may chip or fracture under impact or shock loading.
Strength
Strength refers to a material’s ability to resist deformation.
This affects how well a blade maintains its shape under operating loads and cutting pressures.
Critical Temperature
Critical temperature is the temperature at which the alloying elements in steel combine to form the hard structure known as martensite during heat treatment.
This transformation plays a major role in achieving the final hardness and performance characteristics of industrial knife steels.
Hardness vs Toughness: Why the Difference Matters
One of the most misunderstood aspects of blade materials is the relationship between hardness and toughness.
The two are not the same thing.
A simple example is glass and rubber. Glass is harder than rubber, but when force is applied, glass will shatter while rubber will deform without breaking. In this case, rubber is tougher than glass.
Another example is comparing a strip of wood with a similarly sized piece of rubber. The rubber bends more easily because the wood is stronger. However, if bent too far, the wood will break while the rubber continues to flex. Again, the rubber is tougher.
These examples highlight why industrial blade design is always a balance between properties rather than a pursuit of maximum hardness alone.
Common Alloying Elements in Blade Steels
Industrial knife steels rely on a combination of alloying elements to achieve the required mix of strength, toughness, wear resistance, corrosion resistance, and heat resistance.
Each element contributes different characteristics to the steel.
Chromium
Chromium is a key component of stainless steels. At levels above 11%, it significantly improves corrosion resistance.
It also improves hardenability, strength, wear resistance, and response to heat treatment.
Cobalt
Cobalt improves strength at high temperatures.
Manganese
Manganese increases strength at elevated temperatures while also improving hardenability and wear resistance.
Molybdenum
Found in small quantities in stainless steels, molybdenum improves hardenability and increases strength, particularly at high temperatures.
Nickel
Nickel increases strength while improving resistance to oxidation and corrosion.
When added in small quantities, it also improves toughness at low temperatures. This makes nickel an important element in steels used in sub-zero environments because it improves resistance to cracking at low temperatures.
Tungsten
Tungsten forms stable carbides which increase hardness, especially at high temperatures.
Vanadium
Vanadium forms stable carbides that improve high-temperature strength.
It also promotes a fine grain structure, helping retain the ductility, or “stretchiness”, of the steel.
The Balance Behind Blade Performance
Standard knife steels combine these alloying elements in different ways to achieve the ideal balance of strength, wear resistance, toughness, corrosion resistance, and cost.
And cost certainly matters because these alloying elements are not inexpensive.
Choosing the correct blade steel is therefore not simply about selecting the hardest material available. The operating environment, cutting application, temperatures, machine condition, and expected blade life all influence which material composition is best suited to the job.
Understanding blade steel composition is the first step in understanding why some blades perform better in certain applications than others.
In the next part of our blade steel series, we will look at the hardening process and how heat treatment directly affects blade performance.
