Knife Steel - A Brief History + Modern Understanding

S30VN, AUS-10A, MagnaCut. Knife steel is one of the most important parts of your knife – it directly affects how well your blade can perform. This week we’ll look into knife steel and the nitty gritty of what makes a steel “good”.

Steel is an alloy between iron and carbon, and the earliest steel artifacts date back to 1800 BC. Iron ore was heated with carbon (wood, coal, and charcoal) producing the earliest types of steel. As early as 600 BC, crucibles were used to create the famous Wootz steel (true Damascus). Iron was heated with charcoal in crucibles to allow the carbon to diffuse into the iron. Pig iron is iron with a high carbon content created in a blast furnace and is the basis of modern steel production. This allowed for large quantities of steel to be produced and then melted with normal cast iron to reduce the carbon levels. Today, modern steel production employs BOS, Basic Oxygen Steelmaking. Large amounts of pure oxygen are pumped into a blast furnace, which helps reduce impurities.

Steel goes through a hardening and tempering process to make it stronger. Steel is repeatedly heated to a high temperature, held at said temperature, and then quenched (cooled). Quenching can be done through water, oil, or air, depending on the steels composition. Quenching by water is extremely fast, but can crack the steel. Quenching by air can help certain steels retain the properties needed to withstand extreme environments. 

Modern premium steel often employs Powder Metallurgy (PM). Forged steel often is cooled in bars (ingots) or slabs. These large structures will often have segregation within the alloys, leading to a non-uniform structure. Most notably, there are large irregular carbide forms which decrease the strength of the steel. With PM – the molten steel mixture is poured out in a small stream and then sprayed with air – allowing for tiny spheres to rapidly cool and retain a uniform structure. These tiny ingots are then combined in an isolated environment retaining a small uniform carbide structure.

Steel is an extremely strong and versatile material. It’s durable, easy to machine and weld, and recyclable. It has low electrical and thermal conductivity, and depending on its composition can be extremely corrosion resistant. Mild steel consists of iron and less than 2% of carbon, but by adding other elements in both trace and large amounts, steel can take on a whole gamut of properties. For example, stainless steel has over 10.5% chromium, and the addition of nickel or molybdenum can increase corrosion resistance. However, it’s important to note that the increase of carbon content (carbides) results in a harder steel that’s more prone to fracturing/shattering. Often, when a standout steel formula is developed, it's studied and then duplicated by other manufacturers.

Most modern-day folders are a type of stainless steel, such as S35VN, MagnaCut, and 20CV. You’ve probably noticed on some household appliances, that just because something is marketed as stainless steel doesn’t mean it won’t rust at all. Some stainless steels have alloy content greater than 50% to help increase rust resistance. It’s important to have a corrosion resistant knife as over time the corrosion can compromise the knife and it’s cutting edge. The most stainless steels are in the 300 or 400 series - differentiated by their main alloys components. 300 series steels have carbon, chromium, nickel, and molybdenum, and the 400 series contains carbon, chromium, and manganese. The 400 series is magnetic and can be hardened. Knife makers have begin developing steels specifically for knives and not just general use.

A good steel is dependent on the use case. Some steels benefit from an extremely high corrosion resistance – for example the Spyderco Salt Line uses H-1, H-2, CPM MagnaCut, and LC200N – all highly corrosion resistant steel meant to be used in ocean environments with no or minimal rusting. When it comes to toughness and edge retention, it’s hard to increase the properties of one without decreasing another. Toughness measures how resistant a knife is to breaking or chipping, and edge retention measures how long an edge can remain cutting. In general, the best edge retention is found in knives with high hardness and high carbide counts. However, high carbide counts are usually the hallmark of a knife with low toughness.

Damascus steel is another commonly known consumer steel. Two steels of differing carbon levels are pattern welded at high temperatures to create intricate designs. When two steels of highly differing carbon levels are welded together, the carbon diffuses across the steel in an evenly distributed manner - leading to a consistent toughness. In order to get a true Damascus sawing effect (ie micro serrations) steel must be combined with a non-steel - i.e. pure nickel. The steel provides the strength and toughness whereas the nickel wears out faster. Damascus steel in general is not stronger or better than normal steel, some chef knives remedy this fact by wedging a strong core of solid steel between two layers of Damascus. This allows the knife to look good while having a strong spine.