STEEL TERMS GLOSSARY: I - N

INCLUSIONS - Particles of impurities (usually oxides, sulfides. silicates, etc.) that are held mechanically or are formed during the solidifica­tion or by subsequent reaction within the solid metal.

INCLUSION SHAPE CONTROL - Processing of molten metal to produce a product with reduced levels of linear ('Stringer') type inclusions resulting in improved formability and impact strength in the final product. Desulfurization, calcium-silicon treatment and addition of other strong deoxidizers, such as zirconium, are methods generally employed.

INDENTATION HARDNESS - The resistance of a material to indentation. This is the usual type of hardness test, in which a pointed or round­ed indenture is pressed into a surface under a substantially static load.

INDUCTION HARDENING - A surface hardening process in which only the surface layer of suitable ferrous workpiece is heated by electrical induction to above the upper transformation temperature and immediately quenched.

INDUCTION HEATING - Heating by electrical induction.

INGOT - A casting for subsequent rolling or forging.

INHIBITOR - A substance which retards some specific chemical reaction. Pickling inhibitors retard the dissolution of metal without hinder­ing the removal of scale from steel.

INTERLEAVING - The placing of a sheet of paper between two adjacent layers of metal to facilitate handling and shearing of rectangular sheets, or to prevent sticking or scratching.

INTERMEDIATE ANNEALING - An annealing treatment given to wrought metals following cold work hardening for the purpose of softening prior to further cold working. (See PROCESS ANNEALING.)

INTERRUPTED QUENCHING - A quenching procedure in which the workpiece is removed from the first quench at a temperature substantially higher than that of the quenchant and is then subjected to a second quenching system having a different cooling rate than the first.

INTERSTITIAL FREE (I.F.) STEEL - Ultra low carbon, aluminum killed, titanium, and/or columbium stabilized cold rolled steel. A nonaging, superior deep drawing grade that exhibits no yield point elongation. Not recommended for parts that are drawn without hold down or flanges in the drawing dies.

IRON - (Chemical Symbol Fe) - A magnetic silver - white metal of high tensile strength and ductility. Principal commercial forms are steel, cast iron, and wrought iron.

IRONING - Thinning the walls of deep drawn parts by reducing clearance between punch and die.

ISOTHERMAL ANNEALING - Austenitizing a ferrous alloy and then cooling to and holding at a temperature at which austenite transforms to a relatively soft ferrite-carbide aggregate.

ISOTHERMAL TRANSFORMATION - A change in phase at constant temperature.

JOMINY HARDENABILITY TEST - A test to determine the heat treat response of steel. A standard sample bar (preferably forged) is heated to a suitable temperature, placed in a fixture, and quenched by spraying water on one end only. Since the cooling rate decreases as distance from the quenched end increases, hardness values taken at intervals from the quenched end may be plotted to determine the depth of hardness that may be obtained with a given quench rate.

KILLED - The term 'killed' indicates that the steel has been sufficiently deoxidized to suppress gas evolution from the molten metal as it solidifies. The general practice is to use aluminum, ferrosilicon or manganese as deoxidizing agents. A properly killed steel is more uniform as to analysis and is comparatively free from aging. However, for the same carbon and manganese content killed steel is harder than rim­med steel. In general, all steels above 0.25% carbon are killed; also all forging grades, structural steels from 0.15% to 0.25% carbon and all continuously cast steels.

LADLE ANALYSIS - A term applied to the chemical analysis representative of a heat of steel as reported by the producer. It is determined by analyzing a rapidly cooled (to minimize chemical segregation) test sample obtained during the pouring of the steel.

LAMINATIONS - A defect that appears in flat rolled steel as layers or as segregation, LAMINATIONS can occur at the surface (SCABS, SLIVERS) or in the interior of the steel cross section (PRIMARY PIPE).

LAMINATIONS, MOTOR - A specialized steel application requiring specific electrical properties and/or hardness and punchability characteristics. Motor Lamination steels are often specified to detailed public (ex:ASTM A726) and/or proprietary specifications.

LAP - A surface defect appearing as a seam, caused by folding over hot metal, fins or sharp corners and then rolling or forging them into the surface, but not welding them.

LATTICE - Space lattice. Lattice lines and lattice planes are lines and planes chosen so as to pass through collinear lattice points, and non-collinear lattice points, respectively.

L.D.H. TEST (LIMITING DOME HEIGHT) - A test for evaluating sheet metal formability in which a series of specimens of varying widths are stretched by a 100mm spherical punch until fractures occur. The height of the dome at fracture of the narrowest width specimen that may be drawn without a decrease in specimen width is the limiting dome height. The test may be tailored to predict a steel's press performance when stretch-drawing is the primary forming mode.

LECO CHEMICAL ANALYSIS - See COMBUSTION CHEMICAL ANALYSIS.

LEVELING - Flattening rolled metal sheet or strip (See ROLLER and STRETCHER LEVELING).

LONG TERNE - A term applying to steel sheets that have been teme coated (LEAD AND TIN) by immersion in a bath of Terne Metal (See TERNE PLATE).

LOOSE METAL - Refers to an area of a panel that is not stiff enough to hold its shape.

LOW CARBON STEEL - Contains approximately .30 max carbon and .60 max manganese.

LUDERS LINES - Long crosshatch marks appearing on the surface of certain metals, in the direction of the maximum shear stress, when the metal is subjected to deformation beyond the yield point. Also called STRETCHER STRAINS.

LUSTER FINISH - A finish produced on ground rolls suitable for decorative painting and plating with additional surface preparation after forming.

MATTE FINISH - The texture produced on sheets by rolls which have been blasted to various degrees of roughness depending upon the end use.

MACRO ETCH TEST - Consists of immersing a carefully prepared section in hot acid and then examining the etched surface to evaluate the soundness' and homogeneity of the product being tested.

MACROGRAPH - A photographic reproduction of any object that has not been magnified more than ten times.

MACROSCOPIC - Visible either with the naked eye or under low magnification (as great as about ten diameters).

MACROSTRUCTURE - The structure of metal as revealed by macroscopic examination.

MALLEABILITY - The property that determines the ease of deforming a metal when the metal is subjected to rolling or hammering. The more malleable metals can be hammered or rolled into thin sheet more easily than others.

MANGANESE - (Chemical Symbol Mn) - A lustrous, reddish-white hard, brittle metal whose principal function is as an alloy in steelmaking. It inhibits embrittlement caused by sulfur, acts as a ferrite strengthener and carbide former and tends to increase hardenability.

MARTEMPERING - (1) A hardening procedure in which an austenitized ferrous workpiece is quenched into an appropriate medium whose temperature is maintained substantially at the Ms of the workpiece, held in the medium until its temperature is uniform throughout but not long enough to permit bainite to form and then cooled in air. The treatment is frequently followed by tempering. (2) When the process is applied to carburized material, the controlling Ms temperature is that of the case. This variation of process is frequently called marquenching.

MARTENSITE RANGE - The temperature interval between Ms and MI. MI- Defined under TRANSFORMATION TEMPERATURE.  Ms - Defined under TRANSFORMATION TEMPERATURE.

MARTENSITE - A distinctive, needlelike microstructure produced by rapid cooling of austenite at a rate sufficient to prevent pearlite formation. Martensite is a very hard and brittle phase that is almost always tempered to impart some limited amount of impact strength.

MECHANICAL PROPERTIES - The properties of a material that reveal its elastic and plastic behavior when force is applied, for example, yield strength, ultimate tensile strength, elongation, hardness, etc.

MECHANICAL WORKING - Plastic deformation or other physical change to which metal is subjected, by rolling, hammering, drawing, etc. to change its shape, properties or structure.

METALLOGRAPHY - The science concerning the constituents and structure of metals and alloys as revealed by microscope.

MOLYBDENUM - (Chemical symbol Mo) - A hard. tough metal of grayish-white color, becoming very ductile and malleable when properly treated at high temperatures. Its principal function is as an alloy in steel making: (1) Raises grain-coarsening temperature of austenite. (2) Deepens hardening. (3) Counteracts tendency toward temper brittleness. (4) Raises hot creep strength, red hardness.

MICROSTRUCTURE - The structure of polished and etched metal and alloy specimens as revealed by microscope.

MILL EDGE - The normal edge produced in hot rolling. This edge is customarily removed when hot rolled sheets are further processed.

MINIMIZED SPANGLE - Minimized spangle galvanized sheet has very small spangles which are obtained by' treating the galvanized sheet during the solidification of the zinc to restrict the normal zinc spangle formation.

NATURAL AGING - Spontaneous aging of a supersaturated solid solution at room temperature.

NECKING - Reducing the thickness of a sheet in a localized area by stretching.

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.

NICKEL - (Chemical symbol Ni) - Silvery white, slightly magnetic metal, of medium hardness and high degree of ductility and malleability and resistance to chemical and atmospheric corrosion. 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.

NIOBIUM - (Chemical Symbol Nb) - A steel gray, lustrous metal that is frequently used as a grain refining strengthener in high strength low alloy steel. It is sometimes called COLUMBIUM.

NITRIDING - Process of surface hardening certain types of steel by heating in ammonia gas at about 935 - 1OOO°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.

NON-METALLIC INCLUSIONS - Impurities (commonly oxides). sulfides, silicates or similar substances held in metals mechanically during solidification or formed by reactions in the solid state.

NONSCALLOPING - (Non-Earing) Absence of the tendency for steel to form scallops or ears (marked unevenness) around the top edge of a drawn cup; caused by differences in directional properties of the metal.

NORMALIZING - Heating steel to a suitable temperature in the austenite range and then cooling in air to a temperature substantially below the transformation range.