6 Important Knife Blade Properties

STRESS AND STRAIN

All materials have a stress and strain relationship. Stress is the force applied to a member and strain is the distance that the member moves (deformation) under the applied force. Imagine a rubber band stretched between your two hands. The force applied to move your hands apart shows up as a resistance force (stress) in the rubber band. The distance the band moves under the force is the strain. If the stress and strain for the band are plotted on a graph a line is drawn representing the behavior of the band from the initial load to the time it finally breaks. This is called a stress/strain curve. This curve is unique for all materials and gives a vast amount of information on how the material acts under applied force.

TOUGHNESS/ DUCTILITY

When a material can absorb forces from many different load types with out breaking then it is very tough or ductile. Steel company data sheets refer to toughness in terms of "Charpy C Notch" values. This is a measure of the ability of a notched test piece to resist breaking under an impact load.

STRENGTH

The ability of a steel part to withstand force trying to pull it apart is called tensile strength. The ability of the part to withstand force trying to push it together or compress it is called compressive strength. Strength is a very important consideration for a knife blade because we like to make the cutting edge as thin as possible for cutting efficiency.

HARDNESS

The tensile strength of steel is proportional to its hardness. The harder it is the more is resists deformation forces. In other words the edge will resist bending or breaking while cutting some very hard materials. Hardness is the most critical property for a knife blade because it is an indication all the other properties. The normal range for knife blades is HRC 50-63.

WEAR RESISTANCE

Abrasive wear resistance (most important type for a knife blade) is a measure of the tool to resist being worn away by contact with other materials. Wear resistance correlates with hardness of the material in general. Even mild steel in contact with an abrasive surface will wear much longer than brass for example. In that case mild steel will make a better knife blade than brass.

CORROSION RESISTANCE

Plain carbon steel has very little corrosion resistance. Alloys are added to the carbon steel to reduce corrosion.