San Mai III Steel
It’s hard to find the perfect knife. Many blades sacrifice quality for durability, or vice versa. However, it is possible to find one that doesn’t compromise on either of these features. Laminated knives such as those made from San Mai III steel are able to pack multiple qualities into one blade.
What is San Mai steel?
“San Mai” is a Japanese term meaning “three layers”. It refers to lamination, a technique in which multiple layers consisting of different types of material are fused with each other. In this case, three steel sheets are welded together, as opposed to the entire blade being composed of one kind of steel.
Hundreds of years ago, Japanese bladesmiths employed this technique to forge their katana, or samurai swords. They used a hard steel in the centers of their swords and a softer steel on the outer edges. This combination of steels made the blades both supple and incredibly sharp.
The very properties that made good samurai swords also make good modern-day knives. A knife forged in the San Mai tradition has that same hard edge and flexible blade as its ancient counterpart. Specifically, a high-carbon core is encased between two layers containing lower amounts of carbon. This carbon content is important because it is what determines the characteristics of the metal.
High-carbon steel vs. low-carbon steel
Steel is a mix of iron and carbon. Alone, iron is soft and weak, but it becomes much harder through the addition of carbon. By varying the carbon content, the properties of the resulting steel can be changed.
There are two properties in particular that impact the performance of a steel blade. These properties are hardness and toughness.
Hardness is just what it sounds like: the ability to withstand shape change under force. In terms of knives, this property is what determines how well a blade can hold its edge.
Toughness is the ability of a metal to bend without breaking. Knives that are tough are more pliable and less likely to break under impact.
Unfortunately, these two properties tend to have an inverse relationship. Remember how we mentioned the carbon content of steel as an important determinant of a blade’s performance? Well, high amounts of carbon make steel hard but brittle while low amounts of carbon make steel flexible but soft.
Because of this carbon-based tug of war between hardness and toughness, most steel blades have to compromise on both properties. The result is often a knife that isn’t much good in either respect. Remember, a knife that’s too hard can shatter while one that’s too soft is ineffective in terms of its ability to cut.
A laminated blade, however, does not need to make this trade-off. By sandwiching a high-carbon core between two low-carbon layers, this type of knife is able to capitalize on the strengths of both grades of steel. The result is a blade that can chop while still being flexible.
So far, we have only discussed a knife’s in-the-moment performance. What about its durability?
High-carbon steel vs. stainless steel
Durability is how well a knife lasts over time. In the short-term, this can be measured by how well a blade retains its edge before it needs to be sharpened. A knife’s ability to withstand the elements is a long-term indicator of durability.
It’s no secret that iron is prone to rust, an orange, flaky coating that forms when iron combines with oxygen. As surface rust flakes away, more rust develops on the newly exposed metal. Rust can eat iron away completely, given enough time. Because steel contains large amounts of iron, it too is vulnerable to this corrosive process.
A common way to protect steel from rust is to add chromium to the alloy as it is being smelted. The chromium in the resulting steel rusts before the iron does. Unlike iron, however, chromium doesn’t turn into flakes when it rusts. Instead, it forms a continuous barrier within the steel that protects the rest of the metal from oxidation. This mix of iron, carbon, and chromium is commonly known as stainless steel.
Stainless steel has a bad rep among knife aficionados. Adding chromium to steel means reducing the amount of carbon that it contains. Remember, decreasing carbon content decreases steel’s hardness. Stainless steel blades are known for being dull and difficult to sharpen. So how to make a stainless blade that still retains a sharp edge?
Again, a laminated blade provides an effective solution. To make it weather-proof, the outer layers of the knife can be made of steel containing greater amounts of chromium. The high-carbon steel can then be reserved for the interior of the knife. There, it is protected from the elements but will still give the knife a good edge.