Mettalurgical terms

Steelstrip Metallurgical Terms

Most common metallurgical terms can be found in this section. Where appropriate we have added external links to technical information located elsewhere on the internet.
Arc Furnace	A steel melting furnace in to which heat is generated by an arc between graphite electrodes and the metal. Both carbon and alloy steels are produced in electric arc furnaces, and scrap rather than molten metal is used as the base material.
Annealing	The cold rolling of steel strip hardens the material. Although it can be used in this condition (Known as hard bright), most strip requires annealing in order to soften it for further processes such as forming. The softening process or annealing, takes place in a furnace where the temperatures and the rates of heating and cooling are carefully controlled. To avoid scaling it is necessary to exclude oxygen from the furnace which is replaced with an atmosphere containing nitrogen or hydrogen as the predominant gas.
Austempering	A trade name for a patented heat treating process that consists of quenching a ferrous alloy from temperature above the transformation ranges, in a medium having a rate of heat abstraction sufficiently high to prevent the formation of high-temperature transformation products and in maintaining the alloy, until transformation is complete, at a temperature below that of pearlite formations and above that of martensite formation.
Austenitic Steels	Steels containing high percentages of certain alloying elements such as manganese and nickel. These cannot be hardened by normal heat treatment, but do respond to work hardening.
Automatic Gauge control	Using hydraulic roll force systems, steelmakers have the ability to control precisely their steel sheet's gauge (thickness) while it is travelling at more than 50 miles per hour through the cold mill. Using feedback or feed-forward systems, a computer's gap sensor adjusts the distance between the reduction rolls of the mill 50-60 times per second. These adjustments prevent the processing of any off-gauge steel sheet.
Bend Radius	The inside radius of a formed feature. The bend radius should be equal to, or greater than, the material thickness. A small bend radius can create fracturing at the bend due to the natural thinning that does occur at the bend radius. Also called inside radius.
Bend Test	These are carried out to ensure ductility is sufficient to withstand the deformation during pressing and forming. A standard size test piece is bent through a specific arc without fracturing.
Blast Furnace	A tall cylindrical refractory lined furnace for the production of pig iron or hot metal for direct conversion into steel.
Bluing	(1) Sheets - A method of coating sheets with a thin, even film of bluish-black oxide, obtained by exposure to an atmosphere of dry steam or air, at a temperature of about 1000 0øF., generally this is done during box-annealing. (2) Bluing of tempered spring steel strip; an oxide film blue in color produced by low temperature heating.
Boron	(Chemical Symbol B)- Element No. 5 of the periodic system. Atomic weight 10.82. It is gray in color, ignites at about 1112°F. and burns with a brilliant green flame, but its melting point in a non-oxidizing atmosphere is about 4000°F. Boron is used in steel in minute quantities for one purpose only - to increase the hardenability as in case hardening and to increase strength and hardness penetration.
Boron Steels	Medium carbon steels (0.20-0.30% Carbon) to which the element Boron has been added in the range 0.0005% to 0.005% to increase hardenability.
Brinell hardness	This involves impressing a hard metal ball (often tungsten carbide) of a given diameter with a given load into the steel surface. The hardness of the steel is calculated from the depth of the indentation.
Carbon	An essential element of steel. Low carbon enhances ductility, whilst higher carbon lowers ductility, increases tensile strength, and the ability to further increase hardness as a result of heat treatment.
Carbo-nitriding	A case hardening process in which steel components are heated in an atmosphere containing hydrogen and carbon.
Case Hardening	The process of hardening the surface of steel to improve wear resistance whilst leaving the core relatively soft. More information at the excellent Wikipedia.
Cluster Mill	A rolling mill where each of the two working rolls of small diameter is supported by two or more back-up rolls.
Coil Breaks	Creases or Ridges appearing in sheets as parallel lines transverse to the direction of rolling and generally extending across the width of the sheet.
Coining	A process of impressing images or characters of the die and punch onto a plane metal surface.
Continuous Casting	A method of producing blooms, billets and slabs in long lengths using water cooled moulds. The castings are continuously withdrawn through the bottom of the caster whilst the teeming of the metal is proceeding. The need for primary and intermediate mills and the storage and use of large numbers of ingot moulds is eliminated.
Decarburisation	Removal of carbon from the outer surface of iron or steel, usually by heating in an oxidizing or reducing atmosphere. Water vapor, oxygen and carbon dioxide are strong decarburizers. Reheating with adhering scale is also strongly decarburizing in action.
Deep Drawing	The process of cold working or drawing sheet or strip metal blanks by means of dies on a press into shames which are usually more or less cup-like in character involving considerable plastic deformation of the metal. Deep-drawing quality sheet or strip steel, ordered or sold on the basis of suitability for deep-drawing.
Descaling	The removing of the scale which is a inherent feature of hot rolled strip. Most commonly done by Pickling (removal with acid) or occasionally by blasting.
Ductility	The property of metals that enables them to be mechanically deformed when cold, without fracture. In steel, ductility is usually measured by elongation and reduction of area as determined in a tensile test.
Earing	Wavy projections formed at the opera end of a cup or shell in the course of deep drawing because of differences in directional properties
Elasticity	The property which enables material to return to its original shape and dimension
Electrical Steels	Also known as silicon steels, this is a very low carbon steel (0.005% or lower), with silicon between 0.05 and 3.5%. Addition of silicon increases the alloy's electrical resistance, which inhibits the eddy currents and narrows the hysteresis loop of the material, thus lowers the core losses. Silicon steel can be manufactured either as grain oriented (GO), or grain non-oriented (GNO). more information
Electro- Galvanising	Zinc plating process whereby the molecules on the positively charged zinc anode attach to the negatively charged sheet steel. The thickness of the zinc coating is readily controlled. By increasing the electric charge or slowing the speed of the steel through the plating area, the coating will thicken.
Elongation	A measure of ductility related to the measurement of tensile strength and the percentage of elongation that strip will withstand before fracturing.
Galvannealing	Produced to enhance machinability by the addition of elements such as sulphur or lead. Galvanneal is a hot-dip zinc coating applied to steel. It is similar to hot-dip galvanizing but is specifically designed for steel that will subsequently be painted, such as the rocker panels and other corrosion sensitive areas on cars.
Galvanising	Coating steel with zinc and tin (principally zinc) for rustproofing purposes. Formerly for the purpose of galvanizing, cut length steel sheets were passed singly through a bath of the molten metal. Today’s galvanizing processing method consists of uncoiling and passing the continuous length of successive coils either through a molten bath of the metal termed Hot Dipped Galvanizing or by continuously zinc coating the uncoiled sheet electrolytically - termed Electro-Galvanizing.
Grain Size	Average diameter of grains in the metal under consideration, or alternatively, the number of grains per unit area. Since increase in grain size is paralleled by lower ductility and impact resistance, the question of general grain size is of great significance. The addition of certain metals affects grain size, for example vanadium and aluminum tend to give steel a fine grain. The ASTM has set up a grain size standard for steels, and the McQuaid-Ehn Test has been developed as a method of measurement. Grain size is normally quantified by a numbering system. Coarse 1-5 and fine 5-8. The number is derived from the formula N=2n-1 where n is the number of grains per square inch at a magnification of 100 diameters. Grain size has an important effect on physical properties. For service at ordinary temperatures it is generally considered that fine grained steels give a bettercombination of strength and toughness, whereas coarse grained steels have better machinability.
Ground flat stock	Annealed and preground (to close tolerances) tool steel flats in standard sizes ready for tool room use. These are three common grades; water hardening, oil hardening and air hardening quality.
HSLA	Abbreviation for high strength low alloy. These types of steel give improved tensile and yield strengths over traditional grades whilst restricting the carbon content to enhance formability and weldability. The production relies on close control of structure by tightly controlled coiling temperatures and grain refining elements (commonly, Niobium and Titanium) added during steelmaking.
Hardenability	The property that determines the depth and distribution of hardness after heating and quenching.
Hot dip galvanizing	The process of applying a zinc coating to fabricated iron or steel material by immersing the material in a bath consisting primarily of molten zinc. The simplicity of the galvanizing process is a distinct advantage over other methods of providing corrosion protection. The automotive industry depends heavily on this process for the production of many components used in car manufacturing
Impact test	Test designed to determine, the resistance of metal to breakage by impact, usually by concentrating the applied stress to a notched specimen.
interstitial-free	With modern steelmaking and continuous annealing it is now possible to produce interstitial-free (IF) cold rolled steels. These have a low strength and excellent ductility and formability. If titanium is used alone as the stabilizing agent then the aim Ti content is calculated from the formula: Ti = 4×%C + 3.42×%N + 1.5×%S + 0.02. If niobium is also used then the aim Ti = 3.42×%N + 1.5×%S and Nb = 7.75×%C A typical IF steel composition is 0.002%C, 0.01%Si, 0.15%Mn, 0.01%P, 0.01%S, 0.0025%N, 0.04%Al, 0.016%Nb, 0.025%Ti.
Inclusion	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.
Induction hardening	A process of hardening a ferrous alloy by heating it above the transformation range by means of electrical induction, and then cooling as required.
Killed Steel	The term "killed" indicates that the steel has been sufficiently deoxidized to quiet the molten metal when poured into the ingot mold. 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 some special steels
Laminations	A defect appearing in sheets or strips as a segregation or in layers. To become divided, caused by gas pockets in the ingot.
Manganese	An important element within steel which increases tensile strength and hardenability.
Modulus of Elasticity	Young's modulus (also known as the modulus of elasticity or elastic modulus) is a measure of the stiffness of a given material, further information
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.
Normalising	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.
Oil hardening	A process of hardening a ferrous alloy of suitable composition by heating within or above the transformation range and quenching in oil.
Orange Peel	(Effect) - A surface roughening (defect) encountered in forming products from metal stock that has a coarse grain size. It is due to uneven flow or to the appearance of the overly large grains usually the result of annealing at too high a temperature.
Pickling	The commonest method of descaling hot rolled steel strip. It is a chemical process involving the passing of strip through dilute acid. The acid is subsequently washed from the surface to neutralise further reaction. Often the strip is then coated with oil to protect the surface from oxidation.
Pinch Passing	A light rolling operation to eliminate the condition known as coil break which can be apparent in annealed strip, or to produce the desired temper or surface finish. Usually the reduction is between 1½ to 3%. More recently pinch passing is used to achieve tighter gauge tolerances on hot rolled strip, in this instance the percentage reduction may be greater.
Phosphorus	(Chemical symbol P) - Element No. 15 of the periodic system; atomic weight 30.98. Non-metallic element occurring in at least three allotropic forms; melting point 111°F.; boiling point 536°F.; specific gravity 1.82. In steels it is usually undesirable with limits set in most specifications. However, it is specified as an alloy in steel to prevent the sticking of light-gage sheets; to a degree it strengthens low carbon steel; increases resistance to corrosion, and improves machinability in free-cutting steels. In the manufacture of Phosphor Bronze it is used as a deoxidizing agent.
Residual Stress	Macroscopic stresses that are set up within a metal as the result of nonuniform plastic deformation. This deformation may be caused by cold working or by drastic gradients of temperature from quenching or welding.
Rimmed Steel	Low-carbon steel in which incomplete deoxidation permits the metal to remain liquid at the top of the ingot, resulting in the formation of a bottom and side rim of considerable thickness. The rim is of somewhat purer composition than the original metal poured. If the rimming action is stopped shortly after pouring of the ingot is completed, the metal is known as capped steel. Most steels below 0.15% carbon are rimmed steels. For the same carbon and manganese content rimmed steel is softer than killed steel.
Rockwell hardness	A standard method for measuring the hardness of metals. The hardness is expressed as a number related to the depth of residual penetration of a steel ball or diamond cone ("brale") after a minor load of 10 kilograms has been applied to hold the penetrator in position. This residual penetration is automatically registered on a dial when the major load is removed from the penetrator. Various dial readings combined with different major loads, give "scales" designated by letters varying from "A" to "H"; the "B" and "C" scales are most commonly in use.
Rolled edges	Finished edges, the final contours of which are produced by side or edging rolls. The edge contours most commonly used are square corners, rounded corners and rounded edge. Alternatively from hot rolled narrow strip, with natural edges.
Rolled in scale	A surface defect consisting of scale partially rolled into the surface of the sheet.
Roller levelling	Passing sheet or strip metal through a series of staggered small rolls so as to flatten the metal. This method is relatively ineffective in removing defects such as buckles, wavy edges, corrugations, twists, etc., or from steel in the higher hardness ranges.
Rotary shear	(Slitting Machine) - A cutting machine with sharpened circular blades or disc-like cutters used for trimming edges and slitting sheet and foil. NOTE: Cutter discs are also employed in producing circles from flat sheets but with differently designed machines.
Segregation	In an alloy, concentration of carbon or alloying elements at specific regions, usually as a result of the primary crystallization of one phase with the subsequent concentration of other elements in the remaining liquid.
Scale	The oxidised surface of strip produced during the hot rolling
Silicon	(Chemical Symbol Si) - Element No. 14 of the periodic system; atomic weight 28.06. Extremely common element, the major component of all rocks and sands; its chemical reactions, however, are those of a metalloid. Used in metallurgy as a deoxidizing scavenger. Silicon is present, to some extent, is all steels, and is deliberately added to the extent of approximately 4% for electric sheets, extensively used in alternating current magnetic circuits. Silicon cannot be electrodeposited.
Silicon Steel	Also known as Electrical Steel. See above.
Skin Passing	See Pinch passing
Sorbite	Structure of steel, resulting from the tempering of martensite. In a truly sorbitic structure, the cementite is completely dispersed in the matrix. The trend is to call this structure tempered martensite.
Spheroidizing	An annealing process that generally involves the heating and more prolonged soaking of strip at a temperature around or just below the transformation point to globularise the carbides. This increases ductility in high carbon steels.
Spring Steel	The generic term for steels used for spring making. Typically they range from 0.50% carbon through to 1.00% and include alloy grades containing chromium, Nickle and Molybdenum.
Spheroidising	Any process of prolonged heating and slow cooling of steel which will convert the carbide content into rounded or spheroid form.
Stress Relieving	An annealing process where the temperature, soak time and cooling are designed to reduce the internal stresses without substantially modifying the structure of the steel
Sulphur	Generally considered an impurity in steel due to its detrimental effects upon ductility and weldability. It has beneficial effects upon machinability however.
Temper Rolling	A light rolling operation to give a restricted hardness in finished cold rolled strip
Tempering	A process applied to steel after hardening. It involves heating to a temperature below the transformation range for a given time to decrease hardness and increase toughness to the desired combination.
Tensile Strength	The maximum load applied to break a tensile test piece divided by the original cross section of the test piece. It is normally today measured as N/mm². Also referred to as Ultimate Tensile Strength.
Ultimate Tensile Strength	See above
Vanadium	(Chemical Symbol V) - Element No. 23 of the periodic system; atomic weight 50.95. Gray-white, hard metal, unaffected by atmospheric influences or alkalies but soluble in most strong acids; melting point 31190°F.; boiling point about 61500°F.; specific gravity 5.87. It cannot be electrodeposited. Its principal functions as an alloy in the making of tool steels. (1) Elevates coarsening temperature of austenite ( promotes fine grain). (2) Increases hardenability (when dissolved). (3) Resists tempering and causes marked secondary hardening
Water hardening	Process of hardening high carbon steels by quenching in water or brine after heating
Work hardening	Increase in resistant to deformation (i.e. in hardness) produced by cold working.
Yield Point	The load per unit of original cross section at which, in soft steel, a marked increase in deformation occurs without increase in load.
Yield Strength	The stress at which general plastic elongation of the test piece takes place.