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N
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Chemical symbol for Nitrogen. |
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Na
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Chemical symbol for Sodium. |
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Natural Aging
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Spontaneous aging of a supersaturated solid solution at room
temperature. |
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Nb
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Chemical symbol for Niobium. |
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Neutral Flame
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A gas flame in which there is no excess of either fuel or oxygen in
the inner flame. Oxygen from ambient air is used to complete the
combustion of CO2 and H2 produced in the inner flame. |
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Ni
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Chemical symbol for Nickel. |
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Nickel
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A
metallic element used in some steels. A silvery-white metal of
medium hardness, highly ductile and resistant to chemical and
atmospheric corrosion. Widely used as an alloying agent in
iron and copper base alloys. As an alloying element in steel,
it imparts a finer and more homogeneous structure. The most
suitable composition for cold working is said to be 0.2 to 0.5
percent carbon and 2 to 3.5 percent nickel. Also used for
plating and coating (see nickel coating). Nickel increases
hardenability, thus permitting steel to be oil-hardened instead of
water-quenched. In larger quantities, 8.00 percent and
upwards, nickel is the constituent, together with chromium, of many
corrosion resistant and stainless austenitic steels. |
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Niobium
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Also known as columbium. Niobium is a strong carbide forming element
which is added to certain 18/8% chromium-nickel stainless steels as
a stabilizer to prevent inter-granular corrosion arising from
welding. |
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Nitriding
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A
case-hardening process in which nitrogen is introduced into the
surface of a ferrous alloy, usually of special composition.
All machining, stress relieving, as well as hardening and tempering
are normally carried out before nitriding. The parts are
heated in a special container through which ammonia gas is allowed
to pass. The ammonia splits into hydrogen and nitrogen and the
nitrogen reacts with the steel penetrating the surface to form
nitrides. This takes place in an ammonia atmosphere of about
500°
to 540°C
(932°
to 1004°F)
or in contact with nitrogenous material to produce surface hardening
by the absorption of nitrogen, without quenching. Nitriding steels
offer many advantages: a much higher surface hardness is obtainable
when compared with case-hardening steels; they are extremely
resistant to abrasion and have a high fatigue strength. |
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Nitrocarburizing
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Any of several processes in which both nitrogen and carbon are
absorbed into the surface layers of a ferrous material at
temperatures below the lower critical temperature and, by diffusion,
create a concentration gradient. Nitrocarburizing is done mainly to
provide an antiscuffing surface layer and to improve fatigue
resistance. Compare with carbonitriding. |
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Nitrogen
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Nitrogen is a gas that forms approximately 79% by volume or 77% by
weight of the atmosphere. It can combine with many metals to form
nitrides and is thus applied to the case-hardening of steel, the
usual source for this purpose being ammonia. |
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Noble Metals
|
Metals such as gold, silver and platinum which are resistant to
corrosion by all but the most powerful acids. |
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Non Destructive Testing
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Those forms of testing that do not result in permanent damage or
deformation to the part being tested. Typical examples are magnetic
crack detection, ultrasonic inspection, X-Ray inspection and gamma
radiography. |
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Non-Expendable Thermocouples
|
Those thermocouples that are not covered with fabric or plastic
insulation. One type consists of ceramic insulators over bare
thermocouple wire, sometimes inserted in a tube for stability and
protection. A second type consists of a combination of thermocouple
wires, mineral insulation, and a protecting metal sheath compacted
into a small diameter. |
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Non Magnetic Steels
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Austenitic steels such as the 14% manganese steels and the 303 type
18/8% chromium-nickel stainless steels. |
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Normalizing
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A heat treatment process that has the object of relieving internal
stresses, refining the grain size and improving the mechanical
properties. The steel is heated to 800-900°C according to analysis,
held at temperature to allow a full soak and cooled in still air. |
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Notched Bar Test
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A test to determine the resistance of a material to a suddenly
applied stress, i.e. shock. A notched test piece is employed in an
Izod or Charpy machine and the results are recorded in ft.lbs. or
Joules. |
