Air-Hardening Steel Often called "self-hardening" steel. It is a steel that achieves full hardness when air-cooled from above its critical point. It does not need rapid quenching by oil or water. Air hardening greatly reduces the risk of distortion. 

Alloy Steel Any steel to which alloying elements besides carbon have been intentionally added (e.g. nickel, molybdenum) for purposes of creating a desired property.

Annealing Heating steel to a certain temperature, holding it at that point, then cooling it slowly. The purposes of annealing vary (e.g. to improve machinability, cold working properties, to remove stresses, to soften, etc.). Annealing usually takes place in the furnace where it can cool slowly. 

Arc Furnace A melting furnace wherein heat is created by an arc working between two electrodes. Carbon and alloy steels are produced in this manner. Capacities for this type of furnace may exceed 200 tons. 

Austenite The solid carbon solution in gamma iron.

Austenitic Steels Steels with large amounts of alloying elements (e.g. manganese, nickel) which work harden, but otherwise contained be hardened by normal heat treatment. This type of steel is also non-magnetic. 

Bessemer Process A manner for creating steel using high-pressure air blown through molten iron, which removes the impurities of oxidation. 

Blast Furnace A cylinder-shaped furnace that produces pig iron or hot metal, which can be directly converted into steel.

Brinell Hardness Test A test involving a ball of some hard steel or carbide with a 10 mm diameter that is propelled into a steel's surface with great force (3000 kg). The test evaluates hardness by measuring the ball's indentation into the face of the steel. 

Calcium (Ca) Acts as a deoxidizer and degasifier when added to steel in the form of calcium silicide. Enhances tranverse ductility and toughness. May improve machinability and lengthen the steel's life. 

Carbon (C) Carbon is an essential element in steel, it is added in specific amounts to control the hardness and strength of the material. In general, increased carbon content reduces ductility but increases tensile strength and the ability of the steel to harden when cooled rapidly from elevated temperatures. With an increase in the amount of carbon, the hardness and tensile strength of the steel also increase (which slows as the level of carbon rises). An increase in carbon thusly causes a decrease in both ductility and weldability.

Carbon Steel A steel defined by the amount of carbon present. Other elements, such as manganese (up to 1.5%) and residual amounts of alloying elements such as nickel, chromium and molybdenum may also be present. It becomes an alloy steel when one or more alloying elements have been added in sufficient amounts.

Carburizing Occurs when carbon is introduced into the surface layer of a low carbon steel by heating either a solid, liquid or gaseous medium which contains carbon. Penetration into the surface of the steel increases with heightens temperatures and increased time in this process. Quench and tempering is necessary to harden the steel following carburization.

Case-Hardening The process of hardening the outer surface of the steel only. Requires only a low carbon content (usually less than 0.2%) to perform on alloy or carbon steel. Leaves the steel with a very hard and highly wear-resistant case. 

Cast Iron An alloy of carbon and iron wherein carbon is largely present, usually in the range of 1.8% to 4.5%. Silicon, manganese, sulphur and phosphorus may also be present in some amount. Other elements can be added to produce alloy cast irons, including nickel, molybdenum, vanadium, and chromium among others.

Charpy Test Measures how well a steel wears under impact. In this test a piece of steel, usually notched, is cracked by a pendulum. The measured result, i.e. how much energy is used in breaking the steel, is given in Joules. A brittle steel thereby will break more easily and have a lower impact strength.

Chromium (Cr) Increases the steel's hardenability, corrosion resistance, and provides wear and abrasion resistance in the presence of carbon. It is largely present in stainless steels, usually ranging from 12 to 20%. 

Coefficient of Expansion A change in length, area or volume given a degree change in temperature. 

Cobalt (Co) Most often used in tool, magnet and heat-resisting steels, Cobalt improves the red hardness of the alloy. n alloying element used in tool, magnet and heat resisting steels. Used to form high speed steels with molybdenum and tungsten. 

Cold Drawing The process of reducing the cross sectional area of wire, bar or tube by drawing the material through a die without any pre-heating. Cold drawing is used for the production of bright steel bar in round square, hexagonal and flat section. The process changes the mechanical properties of the steel and the finished product is accurate to size, free from scale with a bright surface finish.

Cold Working Altering the shape or size of a metal by plastic deformation. Processes include rolling, drawing, pressing, spinning, extruding and heading, it is carried out below the recrystallization point usually at room temperature. Hardness and tensile strength are increased with the degree of cold work whilst ductility and impact values are lowered. The cold rolling and cold drawing of steel significantly improves surface finish.

Controlled Atmosphere A gas or mixture of gases in which steel is heated to produce or maintain a specific surface condition. Controlled atmosphere furnaces are widely used in the heat treatment of steel as scaling and decarburization of components is minimized by this process.

Copper (Cu) The sole purpose of copper is to increase resistance to atmospheric corrosion. It does not significantly affect mechanical properties, but causes brittleness in the steel at high temperatures, thereby negatively affecting surface quality.

Core In the case of steel this refers to a component that has been case-hardened where the center is softer than the hard surface layer or case. It can also be applied to the central part of a rolled rimming steel.

Corrosion Fatigue Fatigue that arises when alternating or repeated stress combines with corrosion. The severity of the action depends on the range and frequency of the stress, the nature of the corroding condition and the time under stress.

Creep The form of plastic deformation that takes place in steel held for long periods at high temperature. Methods of creep testing involve the determination of strain/time curves under constant tensile load and at constant temperature.

Critical Cooling Rate The slowest rate of cooling from the hardening temperature which will produce the fully hardened martensitic condition.

Critical Point This generally refers to a temperature at which some chemical or physical change takes place. These transformations cause evolution of heat on cooling or absorption of heat on heating and appear as discontinuities or arrest points in the heating and cooling curves. The temperatures vary with the carbon content of the steel and the rate of cooling.

Critical Temperature The temperature at which some phase change occurs in a metal during heating or cooling, i.e. the temperature at which an arrest or critical point is shown on heating or cooling curves.

Crystalline Fracture A type of fracture that appears bright and glittering, it having formed along the cleavage planes of the individual crystals. Normally an indication that brittle fracture has occurred.

Decarburization The loss of carbon from the surface of steel as a result of heating in a carbon weak atmosphere. During the rolling of steel hot surfaces are exposed to the decarburizing effects of oxygen in the atmosphere and as a result the surface is depleted of carbon. In steels where the components are to be subsequently heat treated it is necessary to remove the decarburized surface by machining.

Deoxidation Elements such as silicon and aluminum when added to molten steel react to form stable oxides and reduce the amount of dissolved oxygen. The solubility of oxygen in steel is reduced as temperature is lowered during solidification and the excess oxygen combines to form carbon monoxide. If the molten metal is not deoxidized the effervescence produced by the evolution of carbon monoxide during solidification would result in blow holes and porosity. Steel treated in this way is termed, "Killed Steel".

Diamond Pyramid Hardness Test This test, more commonly known as the Vickers test, finds greater use in the laboratory than the workshop. It employs a pyramid shaped diamond with an included angle of 136o which is impressed into the specimen using loads of 5 to 120 kg making a small square impression. This test is used for finished or polished components because the impression can be very small. The diamond pyramid hardness number is obtained from a calculation based on measuring the diagonals of the impressions in the steel.

Die The term die is most commonly used in tooling, i.e. press tools "punch and die" but there are many other types of die, e.g. thread cutting dies, forming dies, forging dies, die-casting dies, etc. The term when applied to steel often refers to drawing dies through which hot rolled wire and bar are drawn to produce the finish and dimensional accuracy that is required for bright steel.

Drawing The process of pulling metal wire, rods, or bars through a die with the effect of altering the size, finish and mechanical properties. In the USA, it is a term used for tempering.

Drop Forging An operation in which a metal shape is formed by forcing hot metal into impressions formed in solid blocks of hardened alloy steel, the forging dies. The dies are made in halves, one attached to the rising and falling block of the drop forge and the other to the stationary anvil. Drop forgings are widely used in the automotive industry for crankshafts, stub-axles, gears, etc.

Ductility The property of metal which permits it to be reduced in cross sectional area without fracture. In a tensile test, ductile metals show considerable elongation eventually failing by necking, with consequent rapid increase in local stresses.

Elastic Limit The maximum stress that can be applied to a metal without producing permanent deformation. When external forces act upon a material they tend to form internal stresses within it which cause deformation. If the stresses are not too great the material will return to its original shape and dimension when the external stress is removed.

Elasticity The property which enables a material to return to its original shape and dimension.

Electrical Steels Steels which are characterized by their magnetic properties and are intended for the manufacture of electrical circuits. They are supplied in the form of cold rolled sheet or strip, generally less than 2mm thick and up to 1500mm wide. Grain orientated steels have preferential magnetic properties in the direction of rolling and non- grain orientated steels have similar magnetic properties both transversely and in the direction of rolling.

Elevated Temperature Drawing A process of drawing steel bars at elevated temperatures (normally 250-300oC) which under optimum conditions produce steels that have higher tensile and yield strengths than those cold drawn with the same degree of reduction. The process is little used in the United Kingdom.

Elongation A test to measure the ductility of steel. When a material is tested for tensile strength it elongates a certain amount before fracture takes place. The two pieces are placed together and the amount of extension is measured against marks made before starting the test and is expressed as a percentage of the original gauge length.

End Quench Test More commonly referred to as Jominy Test it is used to determine the hardening ability of steel.

Equilibrium A diagram constructed from thermal and other data showing the limits of composition and temperature within which the various constituents or phases of alloys are stable.

Etching Treatment of a prepared metal surface with acid or other chemical reagent which, by differential attack, reveals the structure.

Extrusion The production of a section by forcing a billet to flow through a die. Often used for producing complex sections, the process is used with both hot and cold metal. Seamless tubes are produced by forcing a hot billet to flow through a die over a mandrel positioned centrally in the die.

Fatigue The effect on metal of repeated cycles of stress. The insidious feature of fatigue failure is that there is no obvious warning, a crack forms without appreciable deformation of structure making it difficult to detect the presence of growing cracks. Fractures usually start from small nicks or scratches or fillets which cause a localized concentration of stress. Failure can be influenced by a number of factors including size, shape and design of the component, condition of the surface or operating environment.

Flame Hardening A surface hardening process in which heat is applied by a high temperature flame followed by quenching jets of water. It is usually applied to medium to large size components such as large gears, sprockets, slide ways of machine tools, bearing surfaces of shafts and axles, etc. Steels most suited have a carbon content within the range 0.40-0.55%.

Forging A process of working metal to a finished shape by hammering or pressing and is primarily a "hot" operation. It is applied to the production of shapes either impossible or too costly to make by other methods or needing properties not obtainable by casting. Categories of forgings include Hammer, Press, Drop or Stamping.

Fracture Fractures are often described by the appearance of the surface of the break in a piece of steel. Crystalline is bright and glittering, failure having developed along the cleavage planes of individual crystals and can be typical of brittle material. A silky fracture has a smooth dull grain indicative of ductile material such as a mild steel. In tensile testing fractures are described by shape, e.g. cup and cone.

Grain Size Control When a steel is austenitized by heating to above the critical range, time is required for the production of a homogeneous structure during which there is a tendency towards grain growth. Although subsequent hot and cold working affect the grain size, it is originally controlled at the steel making stage by the addition of aluminum.

Grain Size 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 better combination of strength and toughness, whereas coarse grained steels have better machinability.

Grinding A machining process:- (a) to shape components that are too hard to be machined by conventional methods such as hardened tool steels and case or induction hardened components. (b) to obtain a high degree of dimensional accuracy and surface finish on a component.

Hard Metal Facing A method of increasing the wear resistance of a metal by the deposition of a hard protective coating. Alloys such as Stellite or a metallic carbide are most often used for the coating.

Hard Metals A group of materials more commonly known as cemented carbides. They consist of mixtures of one or more of the finely divided carbides of tungsten, titanium, tantalum and vanadium embedded in a matrix of cobalt or nickel by sintering. Widely used for cutting tools where for many applications they have replaced conventional high speed steels.

Hardenability The property that determines the depth and distribution of hardness when steel is heated to a given temperature and then quenched (more precisely it may be defined as an inverse measure of the severity of cooling conditions necessary to produce on continuous cooling a martensitic structure in a previously austenitized steel i.e. to avoid transformations in the pearlitic and bainitic ranges). The lower the cooling rate to avoid these transformations, the greater the hardenability. The critical cooling rate is largely a function of the composition of the steel. In general the higher the carbon content, the greater the hardenability, whilst alloying elements such as nickel, chromium, manganese and molybdenum increase the depth of hardening for a given ruling section.

Hardening Increasing the hardness of steel by heat treatment. This normally implies heating the steel to a required temperature and quenching in a suitable medium, e.g. oil or water.

Hardness The hardness of steel is generally determined by testing its resistance to deformation. A number of methods are employed including Brinell, Vickers and Rockwell. The steel to be tested is indented by a hardened steel ball or diamond under a given load and the size of the impression is then measured. For steel there is an empirical relationship between hardness and tensile strength and the hardness number is often used as a guide to the tensile strength, e.g. 229 Brinell = 772N/mm2 (50 tons/sq.in).

Heat In steel making terms this is often used to define the batch or cast produced from a single melting operation.

Heat Treatment A process where solid steel or components manufactured from steel are subject to treatment by heating to obtain required properties, e.g. softening, normalizing, stress relieving, hardening. Heating for the purpose of hot-working as in the case of rolling or forging is excluded from this definition.

High Speed Steel The term `high speed steel' was derived from the fact that it is capable of cutting metal at a much higher rate than carbon tool steel and continues to cut and retain its hardness even when the point of the tool is heated to a low red temperature. Tungsten is the major alloying element but it is also combined with molybdenum, vanadium and cobalt in varying amounts. Although replaced by cemented carbides for many applications it is still widely used for the manufacture of taps, dies, twist drills, reamers, saw blades and other cutting tools.

Hot Quenching Cooling in a medium, the temperature of which is substantially higher than room temperature.

Hot Work The rolling, forging or extruding of a metal at a temperature above its recrystallization point.

Hydrogen (H) An undesirable impurity if present in steel and a cause of fine hairline cracks especially in alloy steels. Modern vacuum treatment eliminates this problem

Impact Test A test designed to give information on how a specimen of a known material will respond to a suddenly applied stress, e.g. shock. The test ascertains whether the material is tough or brittle. A notched test piece is normally employed and the two methods in general use are either the Izod or Charpy test. The result is usually reported as the energy in ft.lbs. or KJ. required to fracture the test piece.

Inclusions Usually non-metallic particles contained in metal. In steel they may consist of simple or complex oxides, sulphides, silicates and sometimes nitrides of iron, manganese, silicon, aluminum and other elements. In general they are detrimental to mechanical properties but much depends on the number, their size, shape and distribution.

Inclusion Count A method of assessing the number and size of non-metallic inclusions present in metal.

Induction Hardening A widely used process for the surface hardening of steel. The components are heated by means of an alternating magnetic field to a temperature within or above the transformation range followed by immediate quenching. The core of the component remains unaffected by the treatment and its physical properties are those of the bar from which it was machined, whilst the hardness of the case can be within the range 37/58 Rc. Carbon and alloy steels with a carbon content in the range 0.40/0.45% are most suitable for this process.

Iron (Fe) The term iron, as used in the chemical or scientific sense of the word, refers to the chemical element iron or pure iron and is the chief constituent of all commercial iron and steel.

Jominy Test A method for determining the hardenability of steel. The Jominy test is covered by BS 4437:1987. A standard test piece 25mm x 100mm is heated to a pre- determined temperature and quenched by a jet of water sprayed onto one end. When the specimen is cold, hardness measurements are made at intervals along the test piece from the quenched end and the results are plotted on a standard chart from which is derived the hardenability curve. BS 970 contains hardenability curves for many of the steels in the Standard. Properly carried out, this test will illustrate the effect of mass upon a chosen steel when heat treated and indicate if the steel is of a shallow, medium or deep hardening type.

Joule A unit of energy. One joule is equal to the energy expended in one second by one ampere against the resistance of one ohm. In the mechanical testing of steel it is the unit used in the Charpy V notch impact test.

Killed Steel The term indicates that the steel has been completely deoxidized by the addition of an agent such as silicon or aluminum, before casting, so that there is practically no evolution of gas during solidification. Killed steels are characterized by a high degree of chemical homogeneity and freedom from porosity.

Leaded Steels When added to steel, lead does not go into solution but exists in a very finely divided state along the grain boundaries. It greatly assists machinability as it acts as a lubricant between the steel and the tool face. Lead is normally added in amounts between 0.15-0.35% and when combined with similar amounts of sulphur, optimum machinability is attained as in such steel as BS 970 230M07 Pb.

Machinability Simply defined as a measure of the ease with which a metal can be machined satisfactorily.

Macrostructure The general crystalline structure of a metal and the distribution of impurities seen on a polished or etched surface by either the naked eye or under low magnification of less than x10.caleb

Malleability It can be defined as the property of a metal to be deformed by compression without cracking or rupturing. The load may be applied slowly or suddenly and will determine whether the material will be suitable for forging or rolling into thin sheet.

Manganese (Mn) One of the most important constituents of steel in which it fulfils a number of functions. It acts as a mild de-oxidizing agent. It combines with the sulphur present to form globular inclusions of Manganese Sulphide which are beneficial to machining. It increases tensile strength and the hardenability of steel. Will also increase hardness as levels increase, but not to the same degree as carbon. Ductility and weldability are decreased but, again, to a lesser degree than caused by carbon.

Martempering A heat treatment involving austenitization followed by step quenching, at a rate fast enough to avoid the formation of ferrite, pearlite or bainite to a temperature slightly above the Ms point. Soaking must be long enough to avoid the formation of bainite. The advantage of martempering is the reduction of thermal stresses compared to normal quenching. This prevents cracking and minimizes distortion.

Martensite The hard constituent produced when steel is cooled from the hardening temperature at a speed greater than its critical cooling rate. Martensite is an acicular phase when seen in the microstructure of steel.

Maximum Stress In the testing of the strength of steel a sample is machined into a standard test piece and is stretched in a tensile testing machine until it breaks. The results are expressed in N/mm2 and is the value of the maximum load reached in the test divided by the original cross sectional area of the specimen.

Melting Point The temperature at which a solid begins to liquefy.

Micron A unit of length equal to one millionth of a meter (0.001mm).

Microstructure The structure that is observed when a polished and etched specimen of metal is viewed in an optical microscope at magnifications in range of approximately x25 to x1500.

Modulus of Elasticity When a material is subjected to an external load it becomes distorted or strained. With metals, provided the loading is not too great, they return to their original dimensions when the load is removed, i.e. they are elastic. Within the limits of elasticity, the ratio of the linear stress to the linear strain is termed the modulus of elasticity or more commonly known as Young's Modulus.

Molybdenum (Mo) Its use as an alloying element in steel increases hardenability and in low alloy steels reduces the risk of temper brittleness. When added to stainless steels it increases their resistance to corrosion. It is also used in high speed steels.

Nickel (Ni) One of the most widely used alloying elements in steel. In amounts 0.50% to 5.00% its use in alloy steels increases the toughness and tensile strength without detrimental effect on the ductility. Nickel also increases the hardenability, thus permitting the steel to be oil- hardened instead of water quenched. In larger quantities, 8.00% and upwards, nickel is the constituent, together with chromium, of many corrosion resistant and stainless austenitic steels.

Nitriding A case hardening process that depends on the absorption of nitrogen into the steel. 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. 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.

Nitrogen (N) 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.

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 800-900oC 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.

Oil Hardening Steel Used to describe tool or alloy steels where oil is used as the quenching medium in the hardening process.

Open Hearth Furnace Developed in the middle of the last century, the open hearth or Siemens-Martins process, as it is known, accounted for a major proportion of UK steel production until the early 1970's. For economic and quality reasons it has been replaced by the Electric Arc Furnace and the Basic Oxygen Steelmaking process. There are no open hearth furnaces in use in Britain today but they are still in use in Russia and Eastern Europe.

Ore An ore is a material that contains a metal in such quantities that it can be mined and worked commercially to extract that metal. The metal is usually contained in chemical combination with some other element in addition to various impurities.

Overheating Failure of tools and components in heat treatment can arise through overheating. This may be caused due to quenching from a temperature too high for the type of steel involved. Overheating is evidenced by cracking, grain-coarseness, erratic surface hardness and pitting.

Oxidation A common form of chemical reaction which is the combining of oxygen with various elements and compounds. The corrosion of metals is a form of oxidation, rust on iron for example is iron oxide.

Oxy-Acetylene Welding A process for joining two pieces of metal in which the required high temperature is obtained by the combustion of acetylene gas and oxygen. The gases are thoroughly mixed in the nozzle or tip of the welding torch to ensure perfect combustion. The weld may be formed directly between two adjoining surfaces, but usually metal from a welding rod is fused in between the surfaces of the joint.

Oxygen (O) Oxygen is one of the chief constituents of the atmosphere of which it forms approximately one fifth. It is odorless and invisible. Although oxygen itself does not burn it is extremely efficient in supporting combustion, nearly all other chemical elements combine with it under evolution of heat. It has many uses in industry and is essential to the BOS (Basic Oxygen Steelmaking Process).

pH Value A method of expressing differences in the acidity or alkalinity of a solution. A figure of 7 is regarded as neutral, figures below this indicate the decree of acidity and above alkalinity.

Phosphorus (P) An element that forms 0.12% of the earth's crust, chiefly in the form of phosphates. Its presence in steel is usually regarded as an undesirable impurity due to its embrittling effect, for this reason its content in most steels is limited to a maximum of 0.050%. Benefits machinability and resistance to atmospheric corrosion. It increases strength and hardness, much akin to carbon, but it decreases ductility and impact strength (toughness). Phosphorus is often considered an impurity except in specific situations.

Pipe A defect that arises during the solidification of steel in the ingot mould. As steel contracts on solidification a central cavity forms in the upper portion of the ingot, if this is not completely removed before rolling into bars a central defect known as "pipe" results. The risk of piping is considerably reduced on continuously cast steel due to molten steel being available to fill any shrinkage cavity.

Pre-Heating Used in the hardening process. Tools are pre- heated before heating to the final temperature, this is particularly important in tools of complex shape to prevent distortion or cracking. Pre-heating reduces the time of exposure to the hardening temperature and helps to minimize scaling and decarburization.

Quenching Rapid cooling from a high temperature by immersion in a liquid bath of oil or water. Molten salts may also be used.

Quenching Crack A fracture, often termed a hardening crack, which arises from thermal stresses induced during rapid cooling.

Red Hardness A term sometimes associated with high speed steel because it has the property of retaining sufficient hardness for cutting metals even when heated to a temperature high enough to cause a dull redness. The tungsten content has a significant influence on this property.

Reduction of area The percentage decrease in the cross- sectional area of a tensile test piece caused by wasting or necking of the specimen. It is expressed as a percentage of the original area of the test piece and is a measure of ductility.

Refining (a) The removal of impurities and metallic oxides from the molten bath by the reaction of the slag and other additions. (b) A heat treatment process with the object of refining or making the grain size of the steel uniform.

Residual Stress The stress which exists in an elastic solid body in the absence of, or in addition to, the stresses caused by an external load. Such stresses can arise from deformation during cold working such as cold drawing or stamping, in welding from weld metal shrinkage, and in changes in volume due to thermal expansion.

Rockwell Hardness Testing A method for testing the hardness of metals by determining the depth of penetration of a steel ball or a diamond sphero-conical indenter. The value is read from a dial and is an arbitrary number related to the depth of penetration. For testing hard steels, a sphero-conical diamond is used with a 150 kg load, the result is read from the black scale on the dial and is prefixed with the letter C. A hardened tool steel would typically give a reading of 62Rc. For softer metals Scale B is used with a 1/16" diameter steel ball and a standard load of 100 kgs.

Rolling The process of shaping metal by passing it between rolls revolving at the same peripheral speed and in opposite directions. In steel there are a number of different types of rolling mill for processing the ingot to its finished shape. These are variously known as Cogging mills, Slabbing mills, Billet mills, Bar mills and Strip mills, which produce plate, sections, bars, sheet and strip. Cold rolling of previously hot rolled strip is carried out to produce strip that is accurate to size and with a smooth bright polished surface.

Scale The oxidized surface of steel produced during hot working, as in rolling, and by exposure to air or steam at elevated temperature.

Scrap It forms the basic raw material for making steel by the electric arc process. Steel offers ecological advantages as it can be recycled enabling the discarded car of today to appear as part of a new model tomorrow. Scrap is sorted and graded before use and the necessary elements are added during the steel making process to achieve the desired specifications.

Seams A surface defect caused during the steel making process. Seams are generally formed from blow holes in the ingot, non metallic inclusions, or stresses arising during the solidification stage. They appear as longitudinal discontinuities in the bar.

Secondary Hardness An increase in hardness which sometimes occurs when hardened steel is re-heated. It can be caused by the transformation of retained austenite to martensite or by the precipitation of alloy carbides.

Segregation A term applied to the concentration and partial separation of one or more elements from solution during solidification of liquid steel in an ingot mould. Sulphur and phosphorus tend to segregate to a greater extent than other elements which can have a particular adverse effect on machinability in high sulphur free- cutting steels. Modern steel making and continuous casting have largely overcome this problem.

Shearing Test The test applied to metal to determine the stress required to fracture it across its section.

Shore Scleroscope An instrument that measures the hardness of a sample in arbitrary terms of elasticity. A diamond tipped hammer is allowed to fall freely down a graduated glass tube on to the sample under test. The hardness is measured by the height of the rebound. In another form the rebounding hammer actuates the pointer of a scale so that the height of the rebound is recorded.

Silicon Silicon serves as a principal deoxidizer in steel. Its content in the steel is dependent upon the steel type. Killed steel has the highest percentage of silicon, upwards of 0.60 percent.

Spinning The formation of sheet metal blanks into hollow circular shapes. This is carried out on a lathe with forming tools which service to press and shape the metal. Annealing may be needed during and/or after the operation to remove the effects of work hardening.

Spot Welding A process for joining steel sheets. The two parts are held between electrodes and the heat generated at the interface between the sheets causes local welding when pressure is applied.

Stabilization A term applied to a number of processes: a) A type of heat treatment to relieve internal stresses: b) The retarding or prevention of a particular reaction by the addition of a stabilizing element; c) A thermal and/or mechanical treatment given to magnetic material in order to increase the permanency of its magnetic properties or condition.

Stainless Steel Can be defined as a group of corrosion resisting steels containing a minimum 10% chromium and in which varying amounts of nickel, molybdenum, titanium, niobium as well as other elements may be present. An Englishman, Harry Brearley, is generally acknowledged to be the pioneer who developed stainless steels for commercial use.

Steel Generally defined as a metallic product whose principal element is iron and where the carbon content is not more than 2%. (The presence of large quantities of carbide forming elements may modify the upper limit of the carbon content.)

Stress Relieving A heat treatment including heating and soaking at a suitable temperature (e.g. 600-650oC) followed by cooling at an appropriate rate in order to reduce internal stresses without substantially modifying the steel's structure. This treatment may be used to relieve stresses induced by machining, quenching, welding or cold working.

Sulphur (S) Generally regarded as an impurity in steel as it can have detrimental effects on strength, ductility and weldability as well as producing hot and cold shortness. Its content in most steels is limited to a maximum of 0.050%. Sulphur is beneficial to machining and is added to freecutting steels in amounts up to 0.35% with the manganese content increased to overcome any detrimental effects. Like phosphorus, sulphur is generally undesired, except where machinability is an important goal for the steel. Ductility, impact strength or toughness, weldability, and surface quality are all adversely affected by sulphur content.

Surface Hardening A method of hardening the surface of steel to increase its wear resistance. Depending on the analysis of the steel, the following treatments can be employed: Case-hardening, Nitriding, induction hardening, Flame hardening.

Temper A term to which a number of definitions can be applied. These include: a) The operation of tempering; b) The degree of hardness left in a steel bar after quenching and tempering; c) The grading of the hardness of low carbon cold rolled strip, e.g. Hard, Half Hard, Quarter Hard, Skin Passed, Soft; d) An indication of the amount of carbon present in a tool steel, e.g. razor temper, file temper, die temper, etc.

Temper Brittleness The loss in impact resistance that is present in some low and medium carbon alloy steels when tempered in the range of 350oC - 600oC. It is revealed by the notched bar impact test but not the tensile test.

Tempering A heat treatment applied to ferrous products after hardening. It consists of heating the steel to some temperature below the transformation range and holding for a suitable time at the temperature, followed by cooling at a suitable rate. The object of tempering is to decrease hardness and increase toughness to produce the desired combination of mechanical properties.

Tensile Strength The maximum load applied in breaking a tensile test piece divided by the original cross-sectional area of the test piece. Originally quoted as tons/sq.in. it is now measured as Newtons/sq.mm. Also termed Maximum Stress and Ultimate Tensile Stress.

Tensile Test A standard test piece is gripped at either end by suitable apparatus in a testing machine which slowly exerts an axial pull so that the steel is stretched until it breaks. The test provides information on proof stress, yield point, tensile strength, elongation and reduction of area.

Tin (Sn) When present in steel it is an undesirable impurity which gives rise to temper brittleness. When used as a coating on steel, it has a good resistance to corrosion for many applications.

Titanium (Ti) Small amounts added to steel contribute to its soundness and give a finer grain size. In austenitic stainless steels it acts as a carbide stabilizer and is used to prevent intercrystalline corrosion, commonly termed "weld decay". Titanium carbide is also used with tungsten carbide in the manufacture of hard metal tools.

Tolerances The amount of variation permitted on dimensions or surfaces. The tolerance is equal to the difference between the maximum and minimum limits of any specified dimension.

Tool Steel A generic term applied to a wide range of steels, both plain carbon and alloy. It includes steels suitable for various types of cutting tools, press tools, hot and cold heading dies, moulds for plastics and die- casting, extrusion tools, hand tools, etc.

Torsional Strength The resistance of a bar to twisting. Closely related to its shear strength.

Toughness The ability of a metal to rapidly distribute within itself both the stress and strain caused by a suddenly applied load, or more simply expressed, the ability of a material to withstand shock loading. It is the exact opposite of "brittleness" which carries the implication of sudden failure. A brittle material has little resistance to failure once the elastic limit has been reached.

Transformation Range The temperature range within which austenite forms and ferrite or carbide progressively dissolves while ferrous alloys are being heated. Also the temperature range within which austenite decomposes to form ferrite and carbide on cooling.

Transformation Temperature The temperature at which a change in phase occurs or the limiting temperature of a transformation range. These critical points are denoted by symbols, e.g. Ac1; the temperature at which austenite begins to form on heating. There are 12 principal temperatures to which symbols are applied.

Transition Temperature The temperature at which a transition from ductile to brittle fracture takes place in steel. It is usually determined by making a series of Charpy impact tests at various temperatures, the transition temperature is usually taken as the point where 50% of the fracture is brittle.

Transverse Strength A measurement of strength when the load is applied across the longitudinal flow of the grain of a metal. Certain impurities such as sulphur have a detrimental effect on the transverse strength. This can be minimized by the inclusion modification process.

Transverse Test A test taken at right angles to the principal direction of rolling or forging.

Tungsten (W) When used as an alloying element it increases the strength of steel at normal and elevated temperatures. Its "red hardness" value makes it suitable for cutting tools as it enables the tool edge to be maintained at high temperatures. In conjunction with other alloying elements it finds applications in heat resisting and other severe service conditions.

Ultimate Tensile Strength The highest load applied in breaking a tensile test piece divided by the original cross- sectional area of the test piece.

Unkilled Steel Steel which has been insufficiently deoxidized and evolves gas during solidification with the formation of blow-holes.

Vacuum Arc Remelting A process used for producing advanced steels to the most demanding and critical specifications, particularly in such areas as aerospace applications. The steel is first produced to a very close analysis and the resulting ingot is slowly remelted in a Vacuum Arc Remelting furnace for up to 14 hours. Such steels are, by necessity, expensive to manufacture.

Vacuum Degassing A ladle of molten metal is placed within a chamber which is then evacuated. This reduces the gas content, particularly hydrogen, as well as reducing non- metallic inclusions. Modern secondary steel making processes using Vacuum Arc Degassing units that include automated stirring and control of temperature and chemical analysis, ensure a consistent and high quality product.

Vanadium (V) - Steels containing vanadium have a much finer grain structure than steels of similar composition without vanadium. It raises the temperature at which grain coarsening sets in and increases hardenability where it is in solution in the austenite prior to quenching. It also lessens softening on tempering and confers secondary hardness on high speed steels. Vanadium is used in nitriding, heat resisting, tool and spring steels in conjunction with other alloying elements.

Welding The process of joining together two pieces of metal so that bonding accompanied by appreciable interatomic penetration takes place at their original boundary surfaces. The boundaries more or less disappear at the weld, and integrating crystals develop across them. Welding is carried out by the use of heat or pressure or both and with or without added metal. There are many types of welding including Metal Arc, Atomic Hydrogen, Submerged Arc, Resistance Butt, Flash, Spot, Stitch, Stud and Projection.

Work Hardening The increase in hardness and strength produced by cold plastic deformation or mechanical working.

Yield Strength The stress at which general plastic elongation of the test piece takes place. This point is well defined in hardened and tempered or annealed structures but can be ill defined in "as drawn" structures.

Zinc (Zn) - Zinc is a metallic chemical element, it has a white color with a bluish tinge. It has a high resistance to atmospheric corrosion and a major use is as a protective coating for iron and steel sheet and wire. Galvanized sheets are a prime example. The melting point of zinc is 419oC.