After forging, many knives are hardened and tempered. Hardening is accomplished by heating the blade to a high temperature and then quenching it in a cold liquid, usually oil. This process makes the steel of the blade extremely hard, but also brittle. In tempering, the hardened blade is reheated to a moderate temperature, the edge is quenched, and the whole blade is allowed to cool to a temperature of between 400° and 600° F. before being quenched again. Tempering makes the blade less brittle and still very strong. The knife blade is ground smooth and its cutting edge is formed by rotating grinding wheels. Finally the blade is whetted to a fine sharpness.
A knife blade is often thicker near the junction with the handle. The thickening is called the shoulder of the knife. Beyond the shoulder is the tang, which extends into the knife handle. On many knives the tang is relatively short and is held in the handle by friction. Other knives may have a half tang or a full tang. The half tang extends part way into the handle and is held by two or more rivets through the handle. The full tang extends the full length of the handle and is held in place by three or more rivets. The rivets can usually be seen in knives that have wood handles.
Folding knives have a rivet through the tang that acts as a hinge. A spring in the knife acts on a projecting piece of the tang in order to prevent the knife from opening or closing inadvertently.
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