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Heat Treatment Requirements
Natural
Aging
Spontaneous aging of a supersaturated solid solution at room temperature.
Natural Aging
Spontaneous aging of a supersaturated solid solution at room temperature.
Necking
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.
Neumann Band
A mechanical (deformation) twin in ferrite.
Nickel
(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. 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
(Chemical symbol Nb) Element No. 41 of the periodic system. See Columbium
Nitriding
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.
Nitriding
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.
Non-Ferrous Metals
Metals or alloys that are free of iron or comparatively so.
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.
Normalizing
Heating a ferrous alloy to a suitable temperature above A3 or Acm and then
cooling in still air to a temperature substantially below A1. The cooling rate
usually is in the range 900 to1800 F/h (500 to 1000C/h).
Normalizing
Heating a ferrous alloy to a suitable temperature above the transformation range
and then cooling in air to a temperature substantially below the transformation
range.
Normalizing
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 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.
Number as Pertaining to Hardness
In copper base alloys inductry; 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 gloor where by 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.