Natural Aging

Spontaneous aging of a supersaturated solid solution at room temperature.

Necking

Local reduction of the cross-sectional area of metal by stretching.

Nick

A surface or edge discontinuity in the form of a slight cut, indentation, or notch. Also referred to as "Scratch" and "Gouge".

Non-Ferrous Metals

Metals or alloys that are free of iron or comparatively so.

Non Heat-Treatable Alloy

The correct and possibly the most definitive term for the 1XXX, the 3XXX, the 5XXX and some 8XXX alloy classes. These alloys gain strength through cold working and lose strength through thermal treatments. They are also called the soft or common alloys.

Non-Metallic Inclusions

Impurities (commonly oxides), sulphides, silicates or similar substances held in metals mechanically during solidification or formed by reactions in the solid state.

Notch, Double Shear

An abrupt deviation from straight on a sheared edge. This offset may occur if the flat sheet or plate product is longer than the blade for the final shearing operation.

Notch Sensitivity

A measure of the reduction in strength of a metal caused by the presence of stress concentration. Values can be obtained from static, impact or fatigue tests.

Nucleation

Initiation of a phase transformation at discrete sites, the new phase growing from nuclei.

Nucleus

(1) The first structurally stable particle capable of initiating recrystallization of a phase or the growth of a new phase, and separated form the matrix by an interface. (2) The heavy central core of an atom, in which most of the mass and the total positive electrical charge are concentrated.