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Glossary - Hardness Testing Terms and Explanations

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  • A

    • Age-Hardening
      A process of aging that increases hardness and strength and usually decreases ductility.
    • Air-Hardening Steel
      Sometimes referred to as self-hardening steel. A steel that becomes fully hardened when cooled in air from above its critical point and does not require rapid quenching by oil or water. The risk of distortion is greatly reduced by air hardening. High Speed Steel was one of the earliest examples of this type of steel.
    • Allotropy
      The property possessed by certain elements to exist in two or more distinct forms that are chemically identical but have different physical properties. In the case of iron the crystal structure has one form at room temperature and another at high temperature. When heated above 910°C the atomic structure changes from body centered cubic to face centered cubic but reverts again when cooled. The allotropy of iron modifies the solubility of carbon, and it is because of this that steel can be hardened.
    • Alloy
      A material that has metallic properties and is composed of two or more chemical elements of which at least one is a metal (i.e. steel is an alloy of carbon in iron; stainless steel is an alloy of carbon, chromium and sometimes nickel in iron).
    • Alloy Steel
      A steel to which one or more alloying elements other than carbon have been deliberately added (e.g. chromium, nickel, molybdenum) to achieve a particular physical property.
    • Alloying Element
      Any metallic element added during the making of steel for the purpose of increasing corrosion resistance, hardness, or strength. The metals used most commonly as alloying elements in stainless steel include chromium, nickel, and molybdenum.
    • Annealing
      Heating steel to, and holding at a suitable temperature, followed by relatively slow cooling. The purpose of annealing may be to remove stresses, to soften the steel, to improve machinability, to improve cold working properties, to obtain a desired structure. The annealing process usually involves allowing the steel to cool slowly in the furnace.
    • Anodizing
      (Aluminum Adic Oxide Coating) A process of coating aluminum by anodic treatment resulting in a thin film of aluminum oxide of extreme hardness. A wide variety of dye-colored coatings are possible by impregnation in process.
    • Austempering
      Quenching from a temperature above the transformation range to a temperature above the upper limit of martensite formation, and holding at this temperature until the austenite is completely transformed to the desired intermediate structure, for the purpose of conferring certain mechanical properties.
    • Austenite
      The solid solution of carbon in gamma (face centered cubic) iron.
    • Austenitic Steels
      Steels containing high percentages of certain alloying elements such as manganese and nickel which are austenitic at room temperature and cannot be hardened by normal heat-treatment but do work harden. They are also non-magnetic. Typical examples of austenitic steels include the 18/8 stainless steels and 14% manganese steel.

  • B

    • Balanced Steel
      Steels in which the deoxidization is controlled to produce an intermediate structure between a rimmed and killed steel. Sometimes referred to as semi-killed steels, they possess uniform properties throughout the ingot and amongst their applications are boiler plate and structural sections.
    • Ball Indenter
      A spherical indenter used in the Brinell test and certain Rockwell tests. Ball indenters are made of hardened steel or tungsten carbide.
    • Base Metal
      A metal which oxidizes when heated in air, e.g. lead, copper, tin, zinc, as opposed to noble metals such as gold and platinum.
    • Basic Steel
      Steel produced in a furnace in which the hearth consists of a basic refractory such as dolomite or magnesite, as opposed to steel melted in a furnace with an acid lining. The basic process permits the removal of sulphur and phosphorous and in this respect is superior. Present day BOS and electric arc furnaces use basic linings.
    • Billet
      A section of steel used for rolling into bars, rods and sections. It can be a product of the ingot route, or increasingly today produced directly by continuous casting.
    • Blast Furnace
      A tall, cylindrical, refractory lined furnace for the production of pig iron or hot metal for direct conversion into steel.
    • Bloom
      A large square section of steel intermediate in the rolling process between an ingot and a billet. Blooms are now also being produced by the continuous casting process eliminating the necessity of first producing an ingot.
    • Boron Steels
      The addition of boron in the range 0.0005-0.005% to certain steels increases the hardenability. A range of boron steels is now listed in the current BS 970 and are widely used for the production of cold headed fastenings.
    • Brale®
      Brale is a registered trademark of Instron Corporation. Brale is a term often used generically to describe a diamond indenter.
    • Bright Annealing
      An annealing process that is carried out in a controlled atmosphere furnace or vacuum in order that oxidation is reduced to a minimum and the surface remains relatively bright.
    • Bright Drawing
      The process of drawing hot rolled steel through a die to impart close dimensional tolerances, a bright, scale free surface, and improved mechanical properties. The product is termed bright steel.
    • Brinell Hardness Test
      The Brinell hardness test for steel, involves impressing a ball 10 mm diameter, of hard steel or tungsten carbide, with a loading of 3000 kgf into the steel surface. The hardness of the steel is then determined by measurement of the indentation. For steels with a hardness over 500 BHN the Vickers test is more reliable.

  • C

    • Carbide
      A compound of carbon with one or more metallic elements.
    • Carbon Steel
      A steel whose properties are determined primarily by the amount of carbon present. Apart from iron and carbon, manganese up to 1.5% may be present as well as residual amounts of alloying elements such as nickel, chromium, molybdenum, etc. It is when one or more alloying elements are added in sufficient amount that it is classed as an alloy steel.
    • Carbo-Nitriding
      A case-hardening process in which steel components are heated in an atmosphere containing both carbon and nitrogen.
    • Carburizing
      The introduction of carbon into the surface layer of a steel that has a low carbon content. The process is carried out by heating the components in a solid liquid, or gaseous carbon containing medium. The depth of penetration of carbon into the surface is controlled by the time and temperature of the treatment. After carburizing it is necessary to harden the components by heating to a suitable temperature and quenching.
    • Case-Hardening
      The process of hardening the surface of steel while leaving the interior unchanged. Both carbon and alloy steels are suitable for case-hardening providing their carbon content is low, usually up to a maximum of 0.2%. Components subject to this process, particularly in the case of alloy steels, have a hard, wear-resistant surface with a tough core.
    • Cast Iron
      A definition can be applied that Cast Iron is an alloy of iron and carbon in which the carbon is in excess of the amount that can be retained in solid solution in austenite at the eutectic temperature. Carbon is usually present in the range of 1.8% to 4.5%, in addition, silicon, manganese, sulphur and phosphorus are contained in varying amounts. Various types of cast iron are covered by an International Standard classification and include grey, malleable and white irons. Elements such as nickel, chromium, molybdenum, vanadium can be added to produce alloy cast irons.
    • Cast Steel
      A term originally applied to crucible steel and sometimes today used to describe tool steels. The term is misleading and is falling into misuse. It can also be applied to steel castings made by pouring molten steel into a mould but which are not subject to further forging or rolling.
    • Casting
      (1) An object at or near finished shape obtained by solidification of a substance in a mold. (2) Pouring molten metal into a mold to produce an object of desired shape.
    • Cementite
      An iron carbide (Fe3C) constituent of steel. It is hard, brittle and crystalline. Steel which has cooled slowly from a high temperature contains ferrite and pearlite in relative proportions varying with the chemical composition of the steel. Pearlite is a lamellar structure of ferrite and cementite.
    • Cermet
      A powder metallurgy product consisting of ceramic particles bonded with a metal.
    • Clad Metal
      A composite metal containing two or more layers that have been bonded together. The bonding may have been accomplished by co-rolling, co-extrusion, welding, diffusion bonding, casting, heavy chemical deposition, or heavy electroplating.
    • Coefficient of Expansion
      The ratio of change in length, area, or volume per degree to the corresponding value at a standard temperature.
    • Cogging
      An intermediate rolling process when a hot ingot is reduced to a bloom or slab in a cogging mill.
    • 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 Treatment
      Exposing steel to suitable subzero temperatures (-85 °C, or -120 °F) for the purpose of obtaining desired conditions or properties such as dimensional or microstructural stability. When the treatment involves the transformation of retained austenite, it is usually followed by tempering.
    • 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.
    • 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. The continuous casting process is also used in the production of cast iron, aluminum and copper alloys.
    • 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.
    • 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.
    • Cyanide Hardening
      A process of introducing carbon and nitrogen into the surface of steel by heating it to a suitable temperature in a molten bath of sodium cyanide, or a mixture of sodium and potassium cyanide, diluted with sodium carbonate and quenching in oil or water. This process is used where a thin case and high hardness are required.

  • D

    • Dead Soft Temper
      Condition of maximum softness commercially attainable in wire, strip, or sheet metal in the annealed state.
    • Decalescence
      A term used in reference to the absorption of heat without a corresponding increase in temperature, when steel is heated through the critical points (phase changes).
    • 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 136° 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.
    • 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 United States, 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.
    • Durability
      The ability to accept permanent deformation.
    • Durometer
      An instrument used to determine the hardness of elastic materials such as rubber and plastic. The ASTM test method for durometer hardness is D 2240. Other test methods are ISO 7619 and ISO 868; DIN 53505; and JIS K 6253.
    • Dwell Time
      An intentional time delay during with an indenter is held against a material under load during a hardness test. Dwell time is used to ensure accurate hardness ratings.

  • E

    • 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.
    • Elastic Recovery
      A period of slight rebound in a material after a load has been removed.
    • Elasticity
      The property, which enables a material to return to its original shape and dimension.
    • Electroslag Refining
      A specialized steel making process in which a rolled or a cast ingot in the form of an electrode is remelted in a water cooled copper mould. The melting is activated by resistive heat generated in a conductive slag. The resulting product has a similar basic chemical composition to the original ingot, but is characterized by high purity and low inclusion content. Typical applications include high integrity components for the aerospace industry.
    • Elevated Temperature Drawing
      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.
    • 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.
    • 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.

  • F

    • 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.
    • Fatigue Limit
      The maximum value of the applied alternating stress, which a test piece can stand indefinitely.
    • Fatigue Testing
      Fatigue tests are made with the object of determining the relationship between the stress range and the number of times it can be applied before causing failure. Testing machines are used for applying cyclically varying stresses and cover tension, compression, torsion and bending or a combination of these stresses.
    • Ferrite
      The solid solution of carbon in body-centered cubic iron, a constituent of carbon steels.
    • Ferritic Steel
      A term usually applied to a group of stainless steels with a chromium content in the range of 12-18% and whose structure consists largely of ferrite. Such steels possess good ductility and are easily worked but do not respond to any hardening or tempering processes. Types of applications include automotive trim and architectural cladding.
    • Ferro Alloys
      Alloys of iron with chromium, manganese, silicon, tungsten, molybdenum or vanadium. Used in steelmaking as a means of introducing these alloying elements into the cast or as deoxidizers.
    • Finished Steel
      Steel that is ready for the market and has been processed beyond the stages of billets, blooms, sheet bars, slabs, and wire rods.
    • 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%.
    • Flow Stress
      The shear stress required to cause plastic deformation of solid metals.
    • Foil
      Metal in any form less than 0.006 in. in thickness.
    • 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.
    • Freecutting Steels
      Freecutting steels have had additions made to improve machinability. The most common additives are sulphur and lead; other elements used include tellurium, selenium and bismuth.

  • G

    • Galvanic Action
      When iron and steel are subject to conditions of aqueous corrosion the incidence and rate at which the corrosion takes place will alter if the steel is coupled with other metals or alloys that are also exposed to the electrolyte. Copper, brass, bronze, lead and nickel are more "noble" and act as auxiliary cathodes to the steel and accelerate its anodic dissolution, that is, its corrosion. Magnesium, zinc and zinc-base alloy are nearly always less noble and tend to divert the attack from the steel to themselves. The galvanic relationship of various metals is an important factor affecting corrosion.
    • Galvanized Steel
      Steel coated with a thin layer of zinc to provide corrosion resistance in underbody auto parts, garbage cans, storage tanks, or fencing wire. Sheet steel normally must be cold-rolled prior to the galvanizing stage.
    • Galvannealed
      An extra tight coat of galvanizing metal (zinc) applied to a soft steel sheet, after which the sheet is passed through an oven at about 1200°F. The resulting coat is dull gray without spangle especially suited for subsequent painting.
    • Gas Carburizing
      A heat treatment method used in the case- hardening of steel. Carbon is absorbed into the outer layers of the components by heating in a current of gas, rich in carbon compounds. The process is more versatile than some other methods as the depth of the case and the limiting carbon content of the case can be controlled by the composition of the atmosphere, the dew point and the temperature.
    • Gauge
      The thickness of sheet steel. Better-quality steel has a consistent gauge to prevent weak spots or deformation.
    • Gauge Length
      Used in the mechanical testing of steel, it is the length marked on the parallel portion of a tensile test piece from which the elongation is measured.
    • Gauge Plate
      An alloy tool steel supplied in flat and square section with the surfaces ground to close limits. It is also known as Ground Flat Stock and is used for the manufacturing of gauges, punches, dies, jigs, templates etc.
    • Grain Boundary
      Bounding surface between crystals. When alloys yield new phases (as in cooling), grain boundaries are the preferred location for the appearance of the new phase. Certain deterioration, such as season cracking and caustic embrittlement, occur almost exclusively at grain boundaries.
    • Grain Growth
      The enlarging or coarsening of the individual grains within the metal or alloy during heating at a temperature above the recrystalization temperature. Excessive grain growth can cause Orange Peel during drawing.
    • 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 machineability.
    • Graphitizing
      An annealing process applied to cast iron and steels with a high carbon and high silicon content by which the combined carbon is wholly or in part transformed to graphitic or free carbon.
    • Gray Iron
      A cast iron characterized by a gray fracture surface due to the presence of flake graphite.
    • Grinding Cracks
      Cracks can arise from incorrect grinding and appear in the form of a network. They are caused by the generation of high heat and rapid cooling in the area of contact and they mostly occur when grinding fully hardened material such as tool steel.

  • H

    • 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/in2).
    • Hardness Value
      A number from a hardness testing scale that indicates the ability of a material to resist penetration or scratching.
    • 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.
    • High-Strength Low-Alloy Steel
      High-strength low-alloy (HSLA) steel is a type of alloy steel that provides better mechanical properties or greater resistance to corrosion than carbon steel. HSLA steels vary from other steels in that they aren't made to meet a specific chemical composition, but rather to specific mechanical properties.
    • Hooke’s Law
      Hooke's Law states that "within the limits of elasticity the strain produced by a stress of any one kind is proportional to the stress". The stress at which a material ceases to obey Hooke's Law is known as the limit of proportionality.
    • 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.

  • I

    • Indentation Test
      A type of hardness test in which a hardened indenter is forced against a material under a fixed load and often for a fixed period of time (dwell time). The size of the indentation, measured as a depth or as a cross-sectional diameter, is associated with a hardness value for a particular hardness scale.
    • Indenter
      A device used in hardness testing that is pressed into the test specimen in order to create an impression.
    • 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.
    • Ingot
      The mass of metal that results from casting molten steel into a mould. An ingot is usually rectangular in shape and is subsequently rolled into blooms and billets for rods, bars and sections and slabs for plates, sheet and strip. With the increasing use of the continuous casting process the ingot route is less used as the molten steel is now directly cast into a bloom or billet.
    • Intermediate Annealing
      An annealing treatment given to wrought metals following cold work hardening for the purpose of softening prior to further cold-working.
    • International Rubber Hardness Degrees (IRHD) Test
      A hardness test that uses a minor and major load to measure the elastic modulus of rubber test material.
    • Interrupted Aging
      The aging of an alloy at two or more temperatures by steps, and cooling to room temperature after each step. Compare with progressive aging.
    • Interrupted Quenching
      Rapid cooling to a selected temperature by quenching in a suitable medium, usually molten salt, holding at the temperature for an appropriate time and then cooling to room temperature. This process is used to minimize the risk of distortion.
    • Isothermal Annealing
      Heating to and holding at a temperature above the transformation range, then cooling to and holding at a suitable temperature until the austenite to pearlite change is complete.

  • J

    • 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.

  • K

    • 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.
    • Knoop Hardness Test
      A micro hardness test in which an elongated pyramidical diamond is pressed into the surface.

  • L

    • Leeb Test
      A portable hardness test that measures the rebound effect caused by a hammer mechanism. Unlike a scleroscope, the Leeb test can be administered from any angle regardless of gravity.
    • Low-Carbon Steel
      Steel with less than 0.005% carbon is more ductile (malleable): It is capable of being drawn out or rolled thin for use in automotive body applications. Carbon is removed from the steel bath through vacuum degassing.