Folding Pocket Knife Steel: Hardness, Toughness, and Corrosion-Resistance

Whether you’re getting your first folding pocket knife or your fiftieth, now is a good time to learn a little bit more about steel.

The truth is, the steel used in the creation of a folding pocket knife is the number one determinant of its quality.

A knife with excellent fit and finish, great ergonomics, and quality construction, which is made from low-grade steel, is, well, low grade. It’s like a wall-hanger. It can look nice, but it can’t perform the job for which it was intended.

There are three main (high-level) criteria used to evaluate the quality of a knife steel. These are hardness (which corresponds to edge retention), toughness, and corrosion resistance, or how well the knife resists rust.

Old-timers will tell you that you can get at most two of these traits in a steel. Modern metallurgical advances have created super steels that offer all three – hardness, strength, and resistance to corrosion.

Here’s what you need to know.

Hardness (Edge Retention)
Carbon is the chief element that determines how hard a steel can be. The more carbon, and the more precise the heat treatment, the harder the steel will be.

Hard steels hold an edge for longer, but they’re also more brittle and at a higher risk of chipping, cracking, or breaking.

Toughness
Toughness refers to how strong a steel is, in terms of tensile and compressive strength. Toughness also refers to resistance to torsion and shear stresses, as well as to impulse.

Folding pocket knives made with tough steel are unlikely to snap, crack or chip. There are several elemental additives that improve the toughness of steel.

Corrosion-Resistance
A steel that is corrosion resistant is less likely to rust. Primarily, metallurgists add chromium to steel to improve corrosion resistance, although some modern steels use nitrogen.

Knives marketed as having stainless steel blades offer high resistance to corrosion.

Iron
Iron is the principal element in steel, responsible for the bulk of strength and integrity. Native iron is strong and tough, but not as strong or as hard as steel, and extremely prone to oxidation (corrosion).

Carbon
Carbon is a nonmetal added to iron that makes it become steel. The addition of carbon allows iron to form a unique, more rigid matrix that is much harder and stronger, which is known as steel.

However, the more carbon in the alloy, the more brittle the steel tends to be.

Chromium
The addition of chromium in a steel improves its corrosion resistance. Therefore, the vast majority of steel alloys contain some measure of chromium. However, the higher the chromium content, the softer the steel.

Nitrogen
Nitrogen is added to steel because it can form nitrides which improve the strength and wear resistance of the alloy. Nitrogen also can improve corrosion resistance.

Vanadium
The inclusion of vanadium in steel improves the grain structure of the steel, which in turn improves toughness and wear resistance. Vanadium also combines with carbon to form vanadium carbide, which increases the hardness of the alloy.

Manganese
Manganese is included in steel because it also helps improve the hardness, and therefore the edge retention, of the steel.

Molybdenum
Molybdenum is frequently included in steel alloys because it offers a number of significant benefits. This element improves not only hardness and toughness but also corrosion resistance since molybdenum does not readily oxidize at low temperatures.

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