| N | Chemical symbol for Nitrogen. |
| Na | Chemical symbol for Sodium. |
| Natural Aging | Spontaneous aging of a supersaturated solid solution at room temperature. |
| Nb | Chemical symbol for Niobium. |
| Neutral Flame | 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. |
| Ni | Chemical symbol for Nickel. |
| Nickel | 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. |
| Niobium | 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. |
| Nitriding | 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. |
| Nitrocarburizing | 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. |
| Nitrogen | 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. |
| Noble Metals | Metals such as gold, silver and platinum which are resistant to corrosion by all but the most powerful acids. |
| Non Destructive Testing | 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. |
| Non Magnetic Steels | Austenitic steels such as the 14% manganese steels and the 303 type 18/8% chromium-nickel stainless steels. |
| 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. |
| Normalizing | 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. |
| Notched Bar Test | 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. |
