Nailing
Slow heating to visible redness of refractory crucibles prior to use of crucibles for the melting of steel.

Natural Gas
Derived from the remains of marine animal and plant life (same as petroleum), natural gas is made up predominantly of hydrocarbons. Petroleum rarely is free of natural gas and the same fields usually produce both fuels. Gas found in a field is usually under pressure which diminishes with extended use or from the presence of too many other wells.

Necking
Strip condition caused by the application of too much tension which causes the strip to become narrower (or stretched) before fracture.

Neutral Refractory
A refractory having neither strongly acidic nor basic properties, for example, chromite.

NDT
Non-destructive testing, mainly used in pipe mills.

Nickel (Ni)
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.

Nitriding
The nitrogen case-hardening process which consists of subjecting machined and heat-treated parts to the action of a nitrogenous medium, commonly ammonia gas, at temperatures of about 510o to 538o. The outer layer of a conventionally nitrided case contains a shallow (0.05mm) but very brittle ‘white layer’ consisting or iron and other nitrides. Quenching is not required to produce a hard case.

Nitrocarburizing
Any of several case-hardening processes in which 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. Compare with carbonitriding.

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-Aging
Little to no change in mechanical and physical properties over time; Yield point elongation is zero. See Aging.

Normalizing
Heating to a temperature about 100o F above the critical range, as indicated by the iron carbon diagram, and cooling in still air. Normalizing is used to restore the steel to its normal condition after hot working, cold working, non-uniform cooling or overheating, or to eliminate the effects of previous heat treatment. Other common objects of normalizing include the development of uniformity in grain, structure and physical properties, a slight hardening of medium carbon steels to improve machinability and the removal of stresses, strains, or course grain prior to hardening. The usual normalizing temperatures range from about 1500o degrees to 1800o F depending on the steel involved.

Non-Temper Passed Bands
Hot bands.

Nozzle
The refractory lined outlet tube, generally between 25 to 50 mm in diameter, through which molten steel is released from the ladle to fill up moulds.