FREE Learning - The Great Steel Debate
Carbon Steel vs Stainless Steel For Knives?
Which Is Right For You?
Carbon or Stainless steel for your Custom Knife? Why is one better or worse than the other for my knife design? Why do some people have a preference? The great steel debate has raged for decades about which is better, carbon steel or stainless steel for custom knifemaking. I don't know your answer, so I make stainless and Carbon steel knives! Let's explore some facts here. We'll discuss these questions and rather than try to defend one side or the other, try to explain the facts and fallacies that both sides stand on in this argument.
Simple Carbon Steels--
The conversation about Carbon Steel vs. Stainless Steel begins with the simplest form of steel. The definition of steel is "iron with carbon added." The carbon helps refine the iron ore and make it hardenable, along with trace elements like manganese and silicon. When steelmakers provide a chemical analysis of a given steel, they list all alloys by the percentage of the weight. Simple Carbon steel for knives must contain no less than about .6% carbon to provide the hardness necessary to make a good knife.
They take an excellent, keen edge, but don't hold it very long(remember Edge Retention), yet are easily resharpened. Simple carbon blades rust quite easily and require special care to avoid corrosion. This class includes steels in the "10xx" category, like 1060, 1075, and 1095, where the last two numbers indicate the carbon content in fractions of one percent. So 1060 is .6%, and 1095 is .95 % nominally. Several steels from Japan and Europe are of this type, the Japanese being the most renowned. All these steels are called "water quenched" and need a fast quench like water, brine, or a fast-engineered quench oil to harden fully. Some of these are quite forgiving in heat treat, are fairly easy to forge, and a barely serviceable knife can be made with a homemade forge or even a torch.
When the carbon content of simple steels gets over 1%, the hardening process can result in an extremely hard blade, around 65-66 HRC, or even harder. In Japan, due to low alloying and careful heat treatment, these steels' carbide and grain structures are extremely fine. This is the trademark of carbon steel Japanese knives. Exceptionally high working hardness and thin, acutely ground, KEENLY sharpened edges make these knives feel and cut like lasers! This combination of geometry, hardness, thinness, and acute edges is the epitome of cutting, and many makers in the west are just catching up!
Alloy Steels--
Another subclass of steel is referred to as Alloy Steel. The alloying elements are a bit higher in these steels, including molybdenum, manganese, nickel, vanadium, cobalt, and chromium, among other elements. These alloys help to make a stronger steel that will harden without the shock of a water quench, and with better edge retention. They still need special care to prevent corrosion. These steels include 5160, 15N20, and 52100, among many others. 52100 is among this group, at 1% carbon and 1.5% chromium, and is one of the toughest, finest-grained alloy steels available.
Tool Steels --
The next category is Tool Steels. These steels have an even higher content of alloying elements, including those listed above and tungsten, niobium, nitrogen, and cobalt, although some are essentially simple carbon steels. Most of these still need care to prevent corrosion, as they are not stainless steel. This class includes A2, D2, W2, O1, M2, M4 and many newer additions. The more complex of these are called "High-Speed Steels" for their ability to withstand higher temperatures in cutting applications without losing temper or seeing failed edges. With some of these tool steels, adding certain alloying elements slows the quench time into the realm of "air hardening," meaning the steel can be quenched from heat in still air and achieve full hardness. Most of these steels sacrifice some toughness for increased hardness, abrasion resistance, and edge retention.
Stainless Steels For Knives --
Then there are Stainless steels. Stainless steel for knives must contain enough "free" Chromium(Cr) to form a Chromium oxide film on the surface of the steel, which then helps prevent corrosion. They must also have enough carbon to properly harden for knife use. Generally speaking, the Cr content must be around 13% or above for a steel to be considered stainless, though Cr must be balanced with carbon content.
Chromium also combines with carbon to create chromium carbides. These particles interspersed in the steel increase edge retention and wear resistance, sometimes at the expense of toughness. The earlier stainlesses had big clumpy carbides, microscopically speaking. Due to the processing of the molten alloy at the foundry, these alloys would experience "carbide segregation," where clumps of one element or another would segregate into relatively large clusters of nonhomogenous material. These large carbides adversely affected toughness by creating crack initiation points.
Additionally, early on, many stainless cutlery steels did not achieve higher working hardnesses and gained a bad reputation for being too soft to hold an edge. These conditions initially started the Great Steel Debate. I hold many European and American mass producers responsible for the bad reputation of stainless steel. In the early days of stainless cutlery, these producers sold inferior products with inferior heat treatments to be in the "stainless game." To a lesser degree, that continues today. With new alloys in the stainless category, that doesn't HAVE to be the case. I doubt any custom knifemaker would spend time making custom kitchen knives from those old steels chosen for all the wrong properties.
Carbides, Toughness, and Edge Retention--
To this day, I read articles stating that "xyz" carbon steel is "harder, tougher, better edge retention, holds an edge forever"; you get the drift. Look at the chart above showing carbide types and their hardness. The top one is iron carbide. This is the carbide formed by iron and carbon(steel). When no other alloying elements are present, this will be the only carbide in the steel matrix. Being the softest carbide, it seems impossible that iron carbide (cementite) can possess all those magical properties. The facts show that this is a fallacy; Carbon steel does not outperform stainless in any category except toughness, and there are a few stainless steels that are tougher than your favorite carbon steel.
These days many stainless steels offer high hardness, excellent toughness, better edge retention than carbon steels, very fine carbide and grain size, and excellent stain resistance. These alloys are easily sharpened with conventional abrasives and offer a less intense maintenance regime than their carbon steel counterparts. Possibilities exist for those who want performance steel without a demanding maintenance schedule!
Summary--
It's important to note that every knife steel contains iron and therefore is not genuinely STAINLESS or rust PROOF. The chromium delays corrosion but cannot entirely prevent it from happening. For example, if you wash your stainless knife, don't dry it, and leave it in the drainer, you will likely see a clean knife in the morning. If you leave your stainless knife soaking in the sink for a couple of days, don't be surprised to see the beginning of some corrosion.
Stainless alloys can also provide improved edge retention over simple carbon steels. If your application doesn't require exceptional toughness (think kitchen knives), you have a perfectly viable stainless option without sacrificing performance. However, if you need a hard-use camping or hunting blade, carbon steel could still be the right choice! So while the Great Steel Debate still rages, the sides are getting closer to the center!
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Thanks for reading,
Keith
Keith Nix Knives
