Navy Seal Knives

Steel is the heart of any knife, and the choice of steel determines every aspect of the blade. There are many types of steel. Each one offers benefits and compromises between hardness, brittleness, ease of sharpening, edge retention and other qualities. One very popular steel is 440A (sometimes referred to as AUS 6) stainless steel, a high carbon, low chromium stainless steel that is a very good compromise between toughness, strength, edge holding and resistance to corrosion. These qualities make it the steel of choice for the SOG SEAL 2000 and the SOG SEAL Pup. Both are knives used by U.S. Navy SEALs.

There are two features necessary for a sharp edge. The first is the ability to make it and the second is the ability to maintain it. It is very difficult to produce a sharp edge on soft metal because of its tendency to deform and round off. Of course high hardness means it will hold an edge fairly well, but it is more difficult to get an edge on it in the first place. The primary goal of 440A steel is stain and wear resistance rather than holding a high performance edge, but that doesn’t mean it can’t be used for a quality knife blade. Proper heat treating of 440A can result in the high hardness necessary for a blade.

There are several main “ingredients” in stainless steel (in fact in all steels.) Each one gives the metal certain properties.

Carbon
Steel is an alloy of iron and carbon. The amount of carbon in a steel determines its hardness. 440A is between 0.6 and 0.75% carbon. Compare this to the 0.3 to 0.25% carbon in steel in the 300 series. The high carbon content is instrumental in giving 440A steel its hardness.

Chromium
The presence of chromium is what distinguishes stainless steels from other corrosion-resistant materials. Due to its strength and its high resistance to corrosion, chromium is often used in plating and metal finishing. In stainless steel the chromium forms a protective layer called a passive layer or passive film which reduces the corrosion rate.

Nickel
Nickel promotes the resistance to corrosion, especially pitting corrosion. Pitting corrosion can occur when stainless steel is subjected to high concentration of chloride ions (for example, sea water) and moderately high temperatures. Nickel is also a mild strengthener. Stainless steel contains less than 2% nickel.

Molybdenum
Molybdenum is important for giving strength to steel at high temperatures. It is also resistant to corrosion. 440A stainless steel contains a maximum of 0.75% molybdenum, but even that small amount has significant effects on corrosion resistance.

Other elements in 440A stainless steel are manganese (1% maximum), phosphorus (0.04% maximum), silicon (1% maximum), and sulphur (0.03% maximum.)

Although there are higher quality steels, the compromise between price and performance make 440A stainless steel a popular choice for knife blades. It’s resistance to salt water and other corrosion makes it a good choice for the SEALs and other special forces.