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Glossario

Alloy Steel

A steel in which a deliberate addition of one or more alloying elements, e.g. Mn, Ni, Cr, Mo etc has been made during steelmaking to enhance the properties of the steel. The amounts of each element that must be present in steel before it is classified as an alloy steel are given in Table 1 in EN 10020: 2000. At low levels of addition the steels may be classified as low alloy. The same standard classifies steels which do not meet the minimum requirements as 'non-alloy' steels.

Alpha-Iron

The form of iron (also referred to as ferrite) which exists naturally below 910C in which the iron atoms are arranged in a body centred cubic (bcc) crystalline pattern, ie an iron atom at each corner of a cube and a single one right in the middle of the cube.

Anisotropy

Anisotropy is the word used to describe the fact materials in general, and steels in particular, are characterised by mechanical properties which differ depending upon the direction in which they are assessed. Particular use is made of this in cold reduced formable steels intended for deep drawing applications; the production process route is such as to enhance this particular property, which is given a numerical value by a parameter known as the 'r' value.

Annealing

A heat treatment that is used to soften steel and involves heating the steel to a pre-determined temperature, soaking the steel at that temperature for a pre-determined time and then cooling the steel down under controlled conditions. After being annealed a steel will be closer to its equilibrium state and will exhibit improved formability and machinability. The temperature used can depend upon the chemical composition and the initial state of the steel and on the outcome desired of the treatment. This requirement of the treatment gives rise to the terms: stress-relief annealing, re-crystallisation annealing, spheroidisation annealing, sub-critical annealing, inter-critical annealing, isothermal annealing, full annealing.

Arc Furnace

A melting unit in which the heat is generated by striking an arc between graphite electrodes and the metal charge, which is usually in the form of solid scrap.

Austenite

A solid solution of one or more elements in gamma iron. (q.v.)

Austenitic Steels

These are steels which contain sufficient austenite stabilising elements, such as Mn, Ni and N, so that the microstructure of the steel is austenitic at room temperature. Such steels cannot be quench or air hardened but will work harden rapidly; they are non-magnetic. Important examples of austenitic steels are 18/8 (18% Cr, 8% Ni) stainless steel and Hadfield's Manganese (14% Mn) steel.

Bainite

An acicular aggregate of ferrite and carbide particles formed when austenite is transformed on cooling at temperatures in the intermediate (200-450C) range, ie above the martensite and below the pearlite range.

Batching

The grouping together of parts to achieve an economic use of the process.

Bend Test

A form of mechanical testing used to assess the ductility of a piece of steel. In carrying out such a test it will often be necessary to follow a detailed procedure which may cover the form, selection and preparation of the test specimen and exactly how the specimen is to be bent and the result assessed and reported, see ASTM E290-97a:2004. The results are normally expressed as a minimum bend diameter in the form nT, where n is a number (sometimes a decimal fraction), and T is the thickness of the steel.

Blast Furnace

A tall, 60-70m high, refractory lined furnace of circular cross-section (diameter at the base - 12m) from the bottom of which liquid cast pig iron it tapped periodically. This is produced by feeding in a solid mixture of iron ore, limestone and coke at the top and by blowing in pre-heated air, and usually fuel, at the bottom.

Boron Steels

Steels that contain additions of boron, generally between 0.002-0.003%, which is added to increase the hardenability of the steel.

Bright Annealing

An annealing heat treatment carried out using either a specially controlled atmosphere or a vacuum, thus preventing oxidation and so keeping the surface of the steel being heat-treated bright and shiny.

Brinell Hardness Test

A test in which a hardened steel ball, usually 10mm in diameter, is pressed into the surface of the steel for a set time using a load of 3000kgf. The steel ball indenter is then removed and the diameter of the indentation is measured and used to determine the Brinell Hardness Number, HB, of the steel by reference to standard tables.

CF - Cremona Furnace (or Cremona Box) - patented by Arvedi

A typical gas-heated furnace with a mandrel to accumulate material from the casting line and feed it to the finishing mill. It is used as a decoupler between casting and finishing and it is a patented component inside ISP technology.

Calcium (Ca)

Aluminium - killed steel, while in the ladle prior to being cast, often has calcium, in the form of calcium silicide, injected into the liquid bath. The addition of calcium lowers the level of the remaining oxygen and sulphur contents of the steel and modifies the residual inclusion composition and shape. This has the effect of improving the cleanliness, castability, machinability and of reducing the anisotropy of toughness and ductility of the steel.

Carbides

Carbides are chemical compounds comprising carbon and either single metallic elements, or more complex combinations of more than one metallic element. The simplest example is iron carbide which is always present in steels. Provided carbides are present in the correct form, i.e. with regard to size and dispersion, they are beneficial. Carbides of iron, chromium, molybdenum are formed in quenched and tempered steels and help create the required combination of strength and toughness. Particular use is made of carbides, (or the more complex carbonitrides, which include nitrogen) in high strength low alloy (HSLA) micro alloyed steels. A proportion of the increased strength of these materials is due to the effects which e.g. niobium carbide precipitates have on the structure of the product. The composition, size and distribution of carbides has a significant effect on steel properties.

Carbon (C)

An essential alloying addition in steel. As the carbon content of steel increases so does the strength and hardness. To optimise the ductility and toughness for a given strength level the steel would be quenched and tempered. The majority of carbon would then be in the form of fine carbides. Carbon besides increasing the strength and hardness also increases hardenability (q.v.). In general, the higher the carbon content, the greater the care required in welding. (See Carbon Equivalent.)

Carbon Equivalent

A key parameter (CEV) in assessing the weldability of a steel. The higher the value, the greater the care needed, especially with regard to pre- and post- heat treatment. Cev = C + Mn + Cr + Mo + V + Ni + Cu 6 5 15

Carbon Steel

A non alloy steel generally with a carbon content greater than 0.25%, in which the amount of carbon present is the major factor in determining its mechanical properties.

Case-Hardening

A process in which the surface (case) of the steel is hardened and the interior (core) of the steel is left unchanged. A number of different techniques are available for achieving this objective.

CAST ROLLING PHASE

The direct connection of casting and rolling, a patented process phase of ISP/AST Technology.

Cementite

This is the name given to the compound of iron and carbon, Fe3C (iron carbide) which is a microstructural constituent found in many steels. It is very hard and brittle.

Charpy Test

A test used to determine the degree of toughness of a steel. A standard Charpy test specimen is 10mm square in cross-section, 55mm long and has a V-notch machined in it at mid-length. The specimen is supported in a machine in which it is fractured by a swinging pendulum. The energy absorbed in fracturing the specimen in Joules (J) is read from a scale on the instrument, and is a measure of the toughness of the steel being tested. (See EN 10045-1: 1990). Charpy tests are usually conducted over a range of temperatures in order to determine the ductile-brittle transition temperature of a steel.

Chromium (Cr)

Added to increase the hardenability of steel. A strong carbide former, so is present in quenched and tempered engineering steels, up to 3.5%, ball bearing steel, 1-1.5%, tool steels, (up to 12% in cold-working die steel) and in creep and heat resisting steels. When steels contain 11% or more of chromium they are termed stainless because of their corrosion resistance which is due to the thin passive chromium-rich oxide film which forms on the steel surface.

Clean Steel

A clean steel is one with a low and controlled content of non-metallic (oxide and sulphide) inclusions in order to maximise ductility, toughness, fatigue resistance, formability and isotropy of properties.

Cold Rolled

The term cold rolled is used to describe materials which have been rolled at a temperature below the recrystallisation temperature. As a result of cold rolling the product is extremely hard, and in the great majority of cases it is necessary to anneal it before it has any commercial value. The product so produced is characterised by a good surface and enhanced thickness tolerances. Such a product is also referred to as 'cold reduced'.

Coil

Steel strip wound into a roll.

Continuous Casting

Process for producing slabs from molten steel. The steel is cast via a tundish into a cooled mould which determines the dimensions (width, thickness) of the slab. The cast strand emerges from the mould with a solidified skin and is guided by rolls through a cooling section before being cut by torches into required slab lengths

Controlled Atmosphere

A type of atmosphere, e.g. a mixture of nitrogen and hydrogen, which is used in a heat treatment furnace to prevent unwanted reactions such as oxidation or decarburisation occurring to the work piece.

Core

The centre, as opposed to the surface layers, of a piece of steel, e.g. a coil, bar or component.

Corrosion Fatigue

Fatigue accelerated by simultaneous attack from a corrosive environment.

Cut-to-length line

Used to cut sheets from strip and to shear slit strip (slit strip in cut lengths). In between are straightening and levelling units. The cut-to-length line is usually arranged parallel to the slitting line.

Critical Temperature

The temperature at which a phase change occurs in steel. The exact value of this temperature depends on the particular phase change occurring e.g. austenite to ferrite or cementite or the reverse, on the chemical composition of the steel, on whether the steel is being heated or cooled and on the rate of heating or cooling.

Crystalline Fracture

When this type of fracture occurs in a steel it will have a shiny appearance as the fracture path in each grain has followed a cleavage plane so producing in each grain a flat reflective surface.

Decarburisation

A loss of carbon from the surface layers of steel caused by the steel having been held at high temperatures in an oxidising atmosphere.

Decoiling and Cutting to Length

The uncoiling, flattening if necessary and cutting to required length of strip originally in coil form.

Deep Drawing Steel

A steel, produced usually in the form of sheet, in which the composition and microstructure have been carefully controlled such that it has excellent cold forming properties when shaped by drawing or by pressing. In the case of carbon steel sheet a deep drawing quality grade would contain <0.06%C, <0.25%Mn and would have limitation on the sulphur and phosphorous contents. It will be aluminium killed.

Delta Iron

The form of pure iron that exists between 1392C and its melting point in which the iron atoms are arranged in a body centred cubic (bcc) crystalline pattern.

Deoxidation

The practice of adding elements to liquid steel before it is cast to reduce and control the level of dissolved oxygen in the liquid and therefore to control the amount of carbon monoxide evolved during solidification. Elements added for this purpose are Mn, Si and Al. Modern casting practice requires the complete removal of gaseous oxygen before casting commences; this steel is 'fully killed'.

Descaling

A process in which oxide (scale), formed on steel when it is at high temperature in an oxidising environment, is removed from the steel surface. Primary scale is usually removed in the first stage of a hot working operation using high pressure water jets whereas secondary scale is usually removed by hot acid pickling or by shot blasting.

EBIT

Earnings before interest and taxes

EBITDA

Earnings before interest, taxes, depreciation and amortization

Elastic Limit

The maximum stress a metal can withstand without any permanent strain (deformation) remaining when the load is removed.

Elasticity

The property of a material which enables it to return to its original shape and dimensions when the stress on it causing these changes is removed.

Electric furnace steel

Steel produced in an electric arc or induction furnace. The operation of electric furnaces allows the production of chemically resistant steels, tool steels, high-speed steels, special engineering, aerospace and nuclear steels as well as magnet materials.

Elongation

A measure of the ductility of a metal assessed in a tensile test. It is determined by dividing the elongation of the gauge-length of the fractured test piece by the original gauge-length.

Endless Strip Production (ESP)

ESP a process technology directly derived from ISP (In-line Strip Production) - see separate entry - is a cast-rolling technology based on continuous thin slab casting and rolling. The first example in the world of this endless technology has been applied at the Acciaieria Arvedi steel works in Cremona.

Etching

The treating of a prepared polished metal surface with a chemical solution (typically acidic), or by other means, so that structural details of the metal surface are revealed. This may be a macro structure, or more commonly requires examination under an optical microscope.

Fatigue

The effect on a metal of repeated cycles of stress. If these changes in stress are of sufficient magnitude and number the metal can fracture at a stress level considerably below that of its tensile strength.

Fatigue Limit

The maximum value of the applied alternating stress that the material can withstand without failure ever occurring.

Ferrite

A solid solution of one or more elements in alpha or delta iron.

Ferro Alloys

An alloy of iron containing sufficient of one or more other elements such as Si, Mn, Cr, Ti, V etc, making them of use as additions to molten steel, or cast iron, to meet an ordered specification.

FINISHING MILL

Complex of stands normally used continuously which carry out finishing rolling, understood as the phase subsequent to the roughing rolling carried out in the roughing mill (in Arvedi technology defined as the HRM)

Forming

The process of changing the shape of sheet metal by the application of load, ie in presswork or metal spinning.

Galvanising

Galvanising is the process in which corrosion protection is provided to a steel product by coating it in zinc. This can be achieved either through a hot dip process, or electrolytically. In the former, the steel, typically a cold reduced strip passes through a series of heat treatments in which it is annealed and the surface is cleaned prior to the strip being passed continuously into a bath of molten zinc at about 440C. The coating mass is controlled as a result of the strip then passed through a set of air (or nitrogen) knives which force surplus zinc back into the bath. The action of these knives is controlled by a meter which is set according to the coating mass actually required. The alternative method of coating is to do it electrolytically; in this case the feedstock is an annealed and temper rolled cold reduced product. Generally speaking, the coating masses so applied are much lighter than by hot dipping. Other steel products such as wire and sections may also be hot dip galvanised, often at a later stage in the production route. It should be remembered that hot dip galvanising alters the properties of the steel and therefore if steels are to be post-galvanised as part of the manufacturing process this should be stated at the time of ordering.

Gamma Iron

The form of iron (also called austenite) which exists between 910C and 1392C in which the iron atoms are arranged in a face centred cubic (fcc) crystalline pattern, ie an atom at each corner of a cube, and a further atom in the centre of each face. See also austenite.

Grain Size Control

A term used to describe methods for controlling the grain size of steel during its manufacture.

Grain Size Measurement

The measurement of the grain size of a metal by observation of a metallographically prepared sample under a microscope. There are several methods available for quantifying the observations.

Hardenability

A term applied to steels to describe the relative ease with which martensite can be formed in the steel. The lower the cooling rate at which a fully martensitic microstructure can be formed in the steel when it is cooled from austenitic condition the higher is the hardenability. Hardenability is commonly assessed by the Jominy end quench test.

Hardness

A measure of the resistance of a metal to indentation by a loaded indenter. The common tests used to determine hardness are the Vickers, Brinell or Rockwell tests.

Heat

In steel making this is often used to describe the steel produced from a single melting operation.

Heat Treatment

Heating and cooling a solid metal or alloy in such a way as to obtain desired microstructure and properties. Heating for the purpose of hot-working is excluded from this definition.

High Yield Strength Steel

Other terms used to describe this type of steel are High Strength Low Alloy (HSLA) steel or Microalloyed steel. It is a steel that with a combination of small amounts of niobium (Nb), vanadium (V) or titanium (Ti), or a controlled combination, and a controlled hot rolling practice has a yield strength greater than that obtainable in a mild steel, (ie greater than ~250 MPa).

Hooke's Law

A law which states that when a material is behaving elastically, the strain in the material is directly proportional to the stress producing it.

Hot strip

Hot rolled product with a rectangular cross section and a width of at least 600 mm which is wound into accurate coils directly after rolling. Produced on (wide) hot strip mills, mainly continuously in thicknesses from 1.5 to 25.0 mm and widths up to 2,000 mm. Hot strip is used as a starting material for sheet, plate and cold rolled strip.

Hot strip mill

Facility for the production of wide hot strip. Fully continuous lines consist of one or more roughing stands and a finishing train with seven finishing stands.

Hot-rolled wide strip

Hot-rolled steel strip with a width of >600 mm that is rolled directly from slabs in a semi- or completely continuous hot strip mill or - in the case of pure stainless products - in separate Steckel mills. Hot-rolled strips can be used for specific applications and especially as starting material for the cold-rolling process.

HRM - High Reduction Mill

The roughing mill that works directly connected with the casting line - typical of ISP/AST Technology.

Hydroforming

Innovative forming method in which pressurized fluid is used to form metal in a closed die. It allows the production of extremely complex shapes from different starting materials, including tubes.

Hydrogen (H)

A gas which, when present in steel, can cause embrittlement, hair-line cracking, or even complete fracture, especially of high strength steels. Is an option as a controlled atmosphere medium for annealing, eg Ebher annealing, and also in high temperature annealing of grain oriented electrical steels.

Impact Test

A test using, for example, an Izod or a Charpy notched specimen to determine the toughness of the metal by measuring the energy absorbed when the test specimen is fractured by a weighted pendulum.

Inclusion Count

A quantitative assessment of the inclusion population of a metallic alloy. It is carried out microscopically on a prepared sample of the alloy and may include one or more of the following assessments: the number of inclusion particles present, their size, their shape, their type and their distribution.

Inclusions

Particles which are usually compounds, such as oxides or sulphides, but that could also be of any substance that is essentially insoluble in the steel matrix, eg particles of lead. Inclusions may occur from several sources. They may be the result deliberate additions, e.g. deoxidation (indigenous) or undesirable, e.g. entrapped slag of refractories (exogenous).

In-line Strip Production ISP - patented

A process technology which consist of casting thin slabs of steel, the stock thickness being reduced while passing through the curved roll girder behind the mould and an in-line rolling mill, having said strip approximately 800 to 1700 mm in width, followed by inductive heating odf the strip and rolling temperature homogenization of the coiled strip through a gas fired coiler furnace (the strip at this stage having a thickness of approximately 10 to 20 mm) and then hot rolling of the strip in a finishing train to a finale thickness. The continuously cast thin slab is cut to bars of a certain length before the inductive heating.
The finishing train is therefore operating in a batch rolling mode.

Intercrystalline Corrosion

Corrosive attack occurring preferentially in the grain boundary regions of an alloy. It is also known as intergranular corrosion.

Iron

When used in the scientific or chemical sense this word refers to the chemical element Fe or to pure iron. It is the principal element present in steels and cast irons.

Izod Impact Test

An Izod impact test is similar to a Charpy test in that the notched specimen is of the same dimensions as a Charpy test piece and the energy absorbed when the specimen is fractured by a falling pendulum is used to assess the toughness of the steel sample. In the Izod test the specimen is struck by the pendulum when it is held vertically in a vice, whereas in the Charpy test the specimen is struck when in a horizontal position.

Killed steel

Made by complete deoxidation of the molten steel before it is cast so that no gas evolution occurs during solidification. Normally this is achieved through additions of aluminium and/or silicon.

Laser Cutting and Welding

Laser cutting is a process in which a laser beam is used to cut e.g. blanks from a sheet of metal. Because of the intense and highly localised nature of a laser beam, a high degree of precision can be achieved. Provided the material being cut is of adequate quality, the risk of distortion is greatly reduced. The cut is much cleaner than one produced by any other means. Laser welding is the reverse of cutting; in this case the intense heat of a laser beam is being used to execute a precision weld of high quality.

Limit of Proportionality

The maximum level of stress which a metal can withstand and still obey Hooke's Law, i.e. it is the point on the stress-strain which any increase in stress will cause a deviation from linearity. In practice, this means a permanent set.

Machinability

A term used to describe the ease with which a metal can be machined.

Macrostructure

The structure of metals as seen when viewed with the naked eye or at low magnification.

Manganese (Mn)

A most useful additive to steels. Mild deoxidiser. Combines with sulphur and so decreases the chance of the steel suffering from hot shortness. Improves the toughness of ferrite-pearlite steels. Improves hardenability. Hadfield's manganese steel, which is characterised by its great resistance to wear, contains around 13% Mn. It is used in some grades of austenitic stainless steel to replace the more expensive nickel as it is an austenite stabiliser.

Martensite

A microstructural form found in steel when it has been cooled from its austenitic state to room temperature at a greater than the critical cooling rate of the steel. It is a metastable solid solution with a body-centred tetragonal structure and its hardness depends primarily upon the carbon content of the steel.

Mass Effect

A term used to emphasise the effect of section size on the rate at which a steel can be cooled through its austenitic transformation, and hence the effect of section size on the microstructure and mechanical properties that can be produced in a steel of a particular chemistry when cooled in this manner.

Melting Point

The temperature at which a solid begins to melt.

Microstructure

The internal structure of a material revealed when a sample is polished, etched and viewed under a microscope.

Mild Steels

A description generally taken to mean a non-alloy steel with a maximum carbon content of about 0.25%.

Modulus of Elasticity

The ratio of the stress applied to the metal to the strain which the stress produces, when the metal is behaving in an elastic manner. If the stress occurs from tensile loading conditions the ratio, the modulus elasticity, is known as Young's modulus (E). It is a measure of the stiffness of the metal.

Molybdenum (Mo)

A strong carbide forming alloying element in steel. Produces a pronounced secondary hardening effect and so is present in hot working tool steels and is used as a partial replacement for tungsten in certain grades of high speed steel. Greatly improves hardenability (of the elements commonly added for this purpose only vanadium has a stronger effect), and reduces temper embrittlement, so is often used in quenched and tempered engineering steels. Used in conjunction with Cr and V in creep resistant steels. Up to 5% can be present in maraging steels. Added to stainless steels to promote resistance to pitting and crevice corrosion attack.

MOULD SYSTEM (patented by Arvedi)

The patented complex of nozzle, mould and oscillator used within ISP/AST Technology

Nickel (Ni)

Widely used as an alloying element in steels. Up to 5.0% can be present in general engineering and in case-hardening steels. Improves strength and toughness and increases hardenability. Larger amounts are present in austenitic stainless and in heat resisting steels. Also used in Invar, a controlled thermal expansion alloy, and in permanent magnet alloys.

Niobium (Nb)

Known as columbium in the USA. A strong carbide forming alloying element in steel. Present in amounts up to 0.1% in high strength low alloy (microalloyed) structural steel and used in stabilised grades of austenitic stainless steel. Can also be used as a stabilising element in ultra low carbon (ULC) steels.

Non-Destructive Testing (NDT)

Also known as non-destructive inspection. Any technique that uses radiography, ultra-sonics, dye-penetrant, magnetic particles, eddy currents etc. to determine the quality of a material without permanently altering the completeness or properties of the material being tested.

Non-Magnetic Steels

Steels that have a stable, fully austenitic microstructure.

Normalising

Heating up a steel to just above its upper critical temperature in order to transform it to austenite, followed by cooling to room temperature at such a rate that a refined equilibrium microstructure is produced. Often this means cooling in still air.

Notched Bar Test

A test in which the test specimen has a notch of a standard geometry machined in it in order to produce a local stress concentration at the notch root when the specimen is tested. (See Charpy and Izod Impact tests)

Oxidation

A chemical reaction in which oxygen combines with the metal to convert it to its oxide form.

Oxygen (O)

Used in the Basic Oxygen Steelmaking process. When present in the form of oxide, inclusions in steel will reduce all mechanical properties, including ductility, and decrease machinability.

Pearlite

A microstructural constituent of steel. It is a mixture of ferrite and cementite which normally exists in lamellar form and results from the eutectoidal transformation of cooling of austenite.

Pickling

The removal of surface oxides from metals by chemical or electrochemical reaction.

Pig Iron

The high carbon iron produced from the blast furnace and cast into 'pig'.

Precision strip

Cold-rolled strip with an ideal thickness of between 0.01 and 0.4 mm and a maximum width of 650 mm and/or which fulfill special demands in terms of strength or edge quality, as well as displaying a high degree of dimensional accuracy.

Quenching

The rapid cooling from high temperature, generally by immersion in water, oil or polymer solutions.

Recrystallisation

The formation of new strain-free grains in a metal brought about either by heating a cold-worked metal, or by hot working a metal, or by heating a metal through an allotropic change.

Rolling

The reduction of the cross-sectional area of metal stock by its passage between rotating rolls.

Scale

The thick oxide skin that forms on a steel when it is exposed to an oxidising environment for any length of time at high temperature.

Scarfing

The cutting out of surface defects on steel with the use.

Scrap

Discarded metallic material, arising from processing, from use or at the end of life. It is usually reclaimed by remelting and refining to produce new material. Steel is the most recycled material on earth.

Sheets

Flat rolled steel product with a width of 600mm and a thickness of up to 3mm.

Silicon (Si)

Used as a deoxidiser in steelmaking, and also as a strengthening agent. An alloy addition in spring steels (~1.5%), in heat resisting steel (1.5 - 3.5%) and in steel sheet for transformer cores (>3%). It is important to be aware silicon can influence the control of post-galvanising, especially in combination with phosphorous.

Slab

Compact block of crude steel, product of the casting process in the melt shop, used as a starting material in the rolling mills to produce hot strip or quarto plate

Slit strip

Hot or cold rolled wide strip (wider than 600 mm), cut lengthways into widths of less than 600 mm on slitting lines. Delivered in coils or cut lengths. Slitting is also used for coated wide strip.

Slitting

The cutting of wide strip into narrower strip usually carried out using rotary cutters. The strip is normally decoiled before it is slit.

Stabilisation

A term used in a number of different contexts: (i) A thermal treatment to stabilise the microstructure, mechanical properties or dimensions of a metal. (ii) The addition of the elements Ti or Nb in certain grades of austenitic stainless steel, to prevent intragranular corrosion. (iii) The effect of the addition of Al to deep drawing sheet steel to prevent it from ageing. (iv) The addition of Ti and/or Nb to interstitial free steels to prevent ageing, by combining the C and N.

Stainless Steel

An iron-based alloy containing 10.5%, or more, of chromium. By the addition of other alloying elements to this basic ferritic alloy, such as Ni, C, N and Mo, a variety of different grades of stainless steel, namely austenitic, martensitic duplex and precipitation-hardened can be produced.

Steel

An iron-based alloy in which the carbon content is less than its solubility limit in austenite. This limit is approximately 2.0% in a non-alloy steel but may be higher in certain alloy steels.

Steel service centers

Steel service centers are modern efficient processing operations offering a wide range of products and service capabilities including hot and cold rolled, coated slit strip, sheet and blanks in carbon and stainless steel. Steel service centers are an important link between rollers and steel fabricators.

Strain Hardening

The increase in strength and hardness that occurs when a metal is plastically deformed under such conditions that softening does not take place i.e. below the recrystalisation temperature. Also known as work hardening.

Stress Relieving

Although a degree of stress relaxation (stress relief) may occur at room temperature, this term normally implies a heat treatment in which the material is heated up and soaked at a suitable temperature before being control cooled back to room temperature. Stress relief occurs by creep, so the degree of relief achieved is both time and temperature dependent.

Stress-Strain Curve

A graphical plot of data obtained from a tensile test, in which the stress on the metal being tested (the force causing the specimen to deform divided by the original cross-sectional area of the gauge length) is plotted against the resulting strain (the extension of the gauge length divided by its original length).

Sulphur (S)

Normally kept as low as possible in steels as it has a detrimental effect on hot and cold formability, ductility, fatigue properties and on weldability. It is beneficial, through the form of manganese sulphide particles, on the machinability of steel and up to ~0.35% can be present in free-cutting steels.

Temper Rolling

This is a finishing light cold rolling reduction applied to cold-reduced and annealed low-carbon steel sheet to achieve one or more of the following: suppression of the yield point, increase in strength and hardness, improvement in flatness, attainment of a specific finish. In the case of metallic-coated steel sheet it may also be for the elimination and correction of flaws in the coating.

Tempering

A heat treatment in which steel hardened by transformation to martensite, is heated to a temperature below the lower critical temperature in order to decrease hardness and improve toughness.

Tensile Strength

This value is normally obtained from a tensile test and is then the maximum load applied to the tensile test specimen before it fractures, divided by the original cross-sectional area of the gauge length. It is also known as the maximum stress or ultimate tensile strength.

Tensile Test

A test in which a specimen of a standardised geometry is gripped at both ends and stretched at a slow controlled rate by axial loading until rupture occurs. The test provides information on the strength and ductility of the material tested. (See EN 10002-1: 2001).

Thermo-mechanically Controlled Rolling (TMCR)

Thermo-mechanically rolling: This is the conventional hot rolling process as a result of which, in combination with the chemical composition of the material, the prescribed mechanical properties are obtained in the as-rolled condition. Controlled Rolling involves a lower than normal finish rolling temperature and creates a fine grain size and an excellent combination of strength and toughness, without the need for subsequent heat treatment. Normalised rolling: By carefully selected chemical composition and finishing and coiling temperature a set of prescribed mechanical properties is obtained which will still be achievable after the product has itself been normalised, i.e. at >900C.

Tolerances

The permissible deviation in specified nominal dimensions, or in other characteristics, of a piece of material or a part.

Toughness

A measure of the ability of a material to absorb energy and deform plastically before it fractures. It is proportional to the total area under the stress-strain curve, plotted from zero stress to fracture for the material. It is nominally determined for a metal from the energy absorbed in an impact test. More sophisticated fracture toughness tests are also available to determine the susceptibily of a steel to a crack or defect and to determine critical crack size.

Transformation Temperature

The temperature at which a change in phase occurs.

Transition Temperature

An arbitrarily defined temperature lying within the temperature range in which the fracture of notched steel impact.

TTT Curve

An abbreviation for the Time-Temperature-Transformation curve. This is determined by dilatometer studies and are used to identify the phases that will be present after specific thermal treatments

Ultimate Tensile Strength

The maximum load that a material withstands in a tensile test before it fractures, divided by the original cross-sectional area of the gauge length of the specimen. A more correct term to apply to this parameter of a material is Tensile Strength.

Ultrasonic Inspection

An inspection technique in which high frequency sound waves are introduced into material in order to detect any surface or subsurface flaws that may be present.

Vacuum Degassing

A secondary refining process for liquid steel in which it is exposed to a low pressure environment with the aim of achieving one or more of the following: reduction of dissolved gases - improved cleanliness - greater uniformity control of chemical composition.

Vanadium (V)

Used in small amounts, up to 0.15% for grain refining and strengthening of microalloyed high strength structural steels and up to 0.2% in certain hot forging steels for improving hardenability. A strong carbide former, giving rise to secondary hardening, so is used in tool steels for use at elevated temperatures and in creep resistant steels.

Vickers Hardness Test

Also known as the diamond pyramid test, as the indenter used in the test is a pyramid shaped diamond. This is forced under a given load into the metal specimen for a fixed time. On removal of the load the diagonals of the diamond-shaped indentation are measured under a low-power optical microscope. The average value of the two readings together with the applied load is then used to determine from standard tables, a hardness number for the metal. The load used is varied according to the softness or hardness of the metal being tested, and also its thickness.

Welding

Joining two or more pieces of material together by the application of heat or pressure, or both, with or without the use of the filler material. The joint is formed either by inter-diffusion across the interface or by localised melting and re-solidification.

Yield

Resistance of material to bending.

Yield Point

The point on the stress-stain curve of a metal at which it finishes deforming solely in an elastic manner and begins to deform plastically.

Yield Strength

The stress at which a metal begins to deform plastically, i.e. the stress at which the stress-strain curve first begins to deviate from linearity. When this is difficult to distinguish, the yield strength is defined in terms of a 0.1% or a 0.2% strain has been obtained.

Zinc (Zn)

Applied to steels by hot dipping or by electroplating (galvanising) as a corrosion preventative coating.