Natural Aging
Spontaneous aging of a supersaturated solid solution at room temperature.

Non-destructive testing.

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

Needle Cutter Steel
Usually supplied quarter hard rolled, extra precision rolled with sheared edges. Carbon content 1.25 - Chromium .15. Usually supplied in a 2 width from .002 to .035. Used for cutting the eyes of needle and milling the latch in a latch needle.

Network Structure
A structure in which the crystals of one constituent are surrounded by envelopes of another constituent which gives a network appearance to an etched test specimen.

Nick-break test
A fracture test in which a specimen is broken from a notch cut at a predetermined position where the interior of the weld is to be examined.

Nickel (Ni)
(Chemical symbol Ni) Element No. 28 of the periodic system; atomic weight 58.69. Silvery white, slightly magnetic metal, of medium hardness and high degree of ductility and malleability and resistance to chemical and atmospheric corrosion; melting point 2651 (degrees) F.; boiling point about 5250 (degrees) F., specific gravity 8.90.
An alloying element used as a raw material for certain classes of stainless steel. Nickel provides high degrees of ductility (ability to change shape without fracture) as well as resistance to corrosion. Approximately 65% of all nickel is used in the making of stainless steel.
Also used for electroplating. Used as an alloying agent, it is of great importance in iron-base alloys in stainless steels and in copper-base alloys such as Cupro-Nickel, as well as in nickel-base alloys such as Monel Metal. Its principal functions as an alloy in steel making: (1) Strengthens unquenched or annealed steels.
(2) Toughens pearlitic-ferritic steels (especially at low temperature).
(3) Renders high-chromium iron alloys austenitic.

Nickel Silver
Copper base alloys that contain 10-45% Zn. and 5-30% Ni.

Nickel Steel
Steel containing nickel as an alloying element. Varying amounts are added to increase the strength in the normalized condition to enable hardening to be performed in oil or air instead of water.

Niobium (Nb)
(Chemical symbol Nb) Element No. 41 of the periodic system.

Introducing nitrogen into a solid ferrous alloy by holding at a suitable temperature (below Ac1 for ferritic steels) in contact with a nitrogenous material, usually ammonia of molten cyanide of appropriate composition. Quenching is not required to produce a hard case.
Process of surface hardening certain types of steel by heating in ammonia gas at about 935-1000 (degrees) F., the increase in hardness being the result of surface nitride formation. Certain alloying constituents, principal among them being aluminum, greatly facilitate the hardening reaction. In general, the depth of the case is less than with carburizing.

Nitriding Steel
Steel which is particularly suited for the nitriding process, that is, it will form a very hard and adherent surface upon proper nitriding (heating in a partially dissociated atmosphere of ammonia gas). Composition usually .20-.40 carbon, .90-1.50 chromium, .15-1.00 molybdenum, and .85-1.20% aluminum.

Nodular Pearlite
Pearlite that has grown as a colony with an approximately spherical morphology.

No. 1 Heavy Melt
Obsolete steel scrap grade, at least one-quarter inch in thickness and in sections no larger than five feet by two feet. Much of the metal comes from demolished buildings, truck frames and heavy duty springs. Mini-mills are primary consumers of No. 1 heavy scrap.

Non-Ferrous Metals
Metals or alloys that are free of iron or comparatively

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.

Non-Refractory Alloy
A term opposed to refractory alloy. A non-refractory alloy has malleability, that is, ease of flattening when subjected to rolling or hammering.

Non-Scalloping Quality Strip Steel
Strip steel ordered or sold on the basis of absence of unevenness, or ears, on the edges of the steel, when subjected to deep drawing.

A heat treatment applied to steel, Involves heating above the critical range followed by cooling in still air. Is performed to refine the crystal structure and eliminate internal stress.

Notch Brittleness
A measure of the susceptibility of a material to brittle fracture at locations of stress concentration. For example, in a notch tensile test a material is said to be notch brittle if its notch strength is less than its tensile strength; otherwise, it is said to be notch ductile.

Notch (Impact) toughness
An indication of a steel's capacity to absorb energy when a stress concentrator or notch is present. examples are Charpy V-Notch,  dynamic tear, drop-weight and drop-weight tear tests.

Number as Pertaining to Edge
(See Edges)

Number as Pertaining to Hardness
In copper base alloys industry; temper is referred to as so many numbers hard, i.e.; Yellow Brass Half Hard is termed 2 numbers hard. This term is derived from terminology used on the mill floor whereby temper or hardness is imparted by cold working and classified as to hardness by the number of Brown & Sharpe gages away from the soft or as-annealed state.

Number as Pertaining to Temper
(See Temper)