a glossry of steel terminology

8/10/2019 A Glossry of Steel Terminology

1/4

neelI, SCENARIO ection teel Terminology

A Glossary of Steel Terminology

Equiaxed crystals Grains (crystals) thathave approximately ((qual dimensions ineach of three orthogonal directions. (i.e.

at right angles to one another).Equilibrium diagram A plot oftemperature against alloy compositionshowing the limits of composition andtemperature ranges within which thevenous constituent phases of the alloyexist under equilibrium conditions.Etching The treating of a preparedpolished metal surface with a chemicalsolution, or by other means, so thatstructural details of the metal surface arerevealed. This may be a macro structure,or more commonly requires examination

under an optical microscope.Extrusion The production of a length ofuniform cross-section of metal frombillet or ingot stock by forcing the metalto flow through a die, in direct extrusion,or to flow through or around the ram (die)in backward extrusion. In both cases, thefinished section will have a smaller cross-sectional area than the starting materialand therefore will be longer.Fatigue The effect on a metal of repeatedcycles of stress. Ifthese changes in stressare of sufficient magnitude and numberthe metal can fracture at a stress levelconsiderably below that of its tensilestrength.Fatigue limit The maximum value of theapplied alternating stress that thematerial can withstand without failureever occurnng.Fatigue testing A mechanical testmethod for determining the range ofalternating (fluctuating) stresses and thenumber of cycles a material canwithstand before failure. The stresses canbe tensional, compression or torsional, ora combination.Ferrite A solid solution of one or moreelements in alpha or delta iron.Ferro alloys An alloy of iron containingsufficient of one or more other elementssuch as Si, Mn, Cr, Ti, V etc, making themof use as additions to molten steel, or castiron, to meet an ordered specification.Flame hardeni~g A process in which ahigh temperature flame is applied to thesurface of a hardenable steel to convert itto austenite. The surface is then quenched

to harden it.

Forming The p rocess of changing theshape of sheet metal by the application of

load, i.e. in presswork or metal spinning.Fracture face The irregular surfaceproduced when a piece of metal isbroken. Freecutting steels Steels inwhich specific additions, the mostcommon being Sand Pb, have been madein order to improve their machinability.Galvanic action CorrosIon induced bythe action of an electric current caused toflow when two m~tals of dissimilarcomposition are connected electricallyby an electrolyte. The metal higher in thegalvanic series will act as cathodt:, whilethe other will act as anode and willthereforecorrode. Galvanising Galvanising is the processin which corrosion protection is providedto a steel product by coating it in zinc.This can be achieved either through a hotdip process, or electrolytically. In theformer, a cold reduced product passesthrough a series of heat treatments inwhich it is annealed and the surface iscleaned prior to the strip being passedcontinuously into a bath of molten zinc atc 44 C The coating mass is controlled

as a result ofthe strip then passed througha set of air (or nitrogen) knives whichforcesurplus zinc back into the bath. Theaction of these knives is controlled by ameter that is set according to the coatingmass actually required. The alternativemethod of coating is to do itelectrolytically; in this case the feedstockis an annealed and temper rolled coldreduced product.Generally speaking, the coating massesso applied are much lighter than by hot

dipping. It should be remembered that inaddition to the continuous processesdescribed above, for some applicationspost galvanising, i.e. hot dip galvanisingalter forming or fabrication, isappropriate. If steels are to be post-galvanised as part of the manufacturingprocess this should be stated atthe time ofordering.Galvanneal A variation of thecontinuous hot dip galvanising process.Following the solidification of the strip

22

on exit form the galvanising bathpassed through another furnace in wthe iron and zinc are caused to alloy12 iron) mOre strongly than canachieved purely by dipping. This prois used in the automotive industry wgood corrosion resistance is combwith much improved weldabilcompared with a pure zinc coating.Gamma iron The form of iron that ebetween 910C and 1392C, in whichiron atoms are arranged in a face cencubic (fcc) crystalline pattern, i.eatom at each comer of a cube, afurther atom inthe centre ofeach faceGas carburising A method ofhardening a steel in which carbon, fr

. gaseous atmosphere, is diffused intosurface of the steel while it is attemperature in the austenitic conditioGauge length A length on the parasided central portion of a tensilespecimen that is used as the basidetermining the strain andelongation of the specimen.Gauge plate In the trade this isknown as ground flat stock . It is a tosteel usually containing 0.9 C, 1Mn, 0.5 Cr. It is supplied, inannealed condition, in short lengthrectangular cross-section strip with fground flat to close tolerances. It isin the manufacture of gauges,templates etc.Grain size control A term usedescribe methods for controllinggrain size of steel duringits manufactGrain size measurementThe measurement of the grain sizemetal observationmetallographically prepared saunder a microscope. There are semethods available for quantifyingobservations.Graphitising The partial, or com

conversion of the combined carbon thin the form of iron carbide,(cementite) uncombined carbon (grapand ferrite. This reaction can take plasteel or in cast iron. In the latter itoccurs at solidification rather, thanthe cast ironis in solidform.Grey iron A common form of castso-called because the fracture surfathe iron has a grey appearance due tgraphite flakes present inmicrostructure.

VOLUME 22 . Mll . MAY


2/4

on .:Steel Terminology Ineel. SCENARIO

ng The removal of material from aece surface using a grindingr abrasive belt.

g cracks The formation ofsurface cracks on a ground work~

Normally caused by the generationessive heat when an incorrectg procedure has been used. Mostnly seen on hardened steel.

angular steel abrasive used in theeaning process.metal facing The coating of asurface with hard metal alloys in order to increase the wearce ofthe surface.ability A term applied to steels toe the relative ease with whichsite can be formed inthe steel. Thehe cooling rate at which a fully

sitic microstructure can be formedsteel when it is cooled fromitic condition the higher is theability. Hardenability isnly assessed by the Jominy endtest.ing Increasing the hardness of

by mechanical, thermo-ical, thermal or thermo-chemicalnts.ss A measure of the resistance ofl to indentation by a loadedr. The common tests used tone hardness are the Vickers,or Rockwell tests.

n steel making this is often used toe the steel prod~ced from a singleoperation.

resisting steel These are steelsd to operate at very highatures and therefore they may

one or more of the followingteristics: creep resistance,nce to oxidation, or other forms ofs attack, and freedom from

tructural changes that would leadr embrittlement.Because serviceons can vary greatly a wide rangel compositions came under they of heat resisting with C-Mn, oroy steels of the CR Mo- V type

used to 500 525C and austeniticss grades, containing for example

20 Ni, being used at higheratures.reatment Heating and cooling a

metal or alloy in such a way as to

ME 22 . Mll . MAY 2013 I

obtain desired properties. Heating for thepurpose of hot working is excluded fromthis definition.

High speed tool steel Steel which isalloyed inn such a way that it can be useda s a cutting tool material to machineother metals at high speeds, and stillretain its cutting ability, even though thetool tip is at a low red heat. The variousgrades of this steel all contain 0.6 ormore of carbon, a combined content of7 , or more, of the elements tungsten,molybdenum and vanadium, 3-6 ofchromium and in those required tooperate at the .highest temperaturesadditions of 4-13 of cobalt.

High yield strength steelOther terms used to describe this type ofsteel are High Strength Low Alloy

(HSLA) steel or Microalloyed steel. It is asteel that with a combination of smallamounts of niobium (Nb), vanadium (V)or titanium (Ti), or a controlledcombination, and a controlled hot rollingpractice has yield strength greater thanthat obtainable in a mild steel, (i.e.greater than ~ 275Mpa).Hooke s law A law that states that when amaterial is behaving elastically, the strainin the material is directly proportional tothe stress producing it. ,Hot quenching An imprecise term fordescribing the cooling of a material byquenching it into a medium, thetemperature of which is above that ofambient.

Hot work The ptastic deformation of ametal by processes such as rolling,forging, or extrusion, carried out at atemperature and strain rate such thatsubstantial strain hardening does notoccur but instead the metal continues toyield relatively easily because the metalis recrystallising continuously.

Hydrogen (H) A gas which, whenpresent in steel, can cause embrittlement,hair-line cracking, or even completefracture, especially of high strengthsteels. Is an option as a controlledatmosphere medium for annealing, e.g.Ebher annealing, and also in hightemperature annealing of grain orientedelectrical steels.

Impact test A test using, for example, anIzod or a Charpy notched specimen todetermine the relative toughness of the

metal by measuring the energy absorbedwhen the test specimen is fractured by aweighted pendulum.Inclusions Particles, usually compounds,such as oxides, sulphides or silicates, butthat could also be of any substance that isforeign to and essentially insoluble in thesteel matrix, e.g. particles oflead.Inclusion count A quantitativeassessment of the inclusion population ofa metallic alloy. It is carried outmicroscopically on a prepared sample ofthe alloy and may include one or more ofthe following assessments: the number ofinclusion particles present, their size,their shape, their type and theirdistribution.

Induction hardening A process forsurface hardening steel in which the

surface of the steel is heated to anaustenitic condition, by eddy currentsfrom an inductor coil carrying a high-frequency alternating current, and thenquenched immediately to formmartensite. Changing the frequency oftheinductor coil current can modify the depthof hardening achieved.Toobtain sufficienthardness the steels hardened in thismanner usua11ycontain at least0.3 C.Ingot A term used to describe a block ofsolid steel resulting from the batchcasting of liquid steel into a stationarymould made usually of cast iron.Ingot mould The container into whichmolten steel is poured to produce aningot. Usually it would be made of castiron but for the production of very largeforging ingots itwould be made of sand.Intercrystalline corrosionCorrosive attack occurring preferentiallyinthe grain boundary regions of analloy.Itis also known as intergranular corrosion.Interrupted quenching A term used todescribe a quenching procedure in which

steel, instead of being quenched into aliquid at ambient temperature, isquenched into a liquid, usually moltensalt, at some elevated temperature. Whenthe steel has been held for sufficient timeat this temperature to achievetemperature uniformity, and/or hasachieved the required microstructuraltransformation, it is further quenched toroom temperature.Iron When used, in the scientific orchemical sense this word refers to the

3


3/4


4/4

Section: Steel Terminology Ineel SCENARIO

Martempering A heat transformationprocedure in which an austenitised steels quenched to a temperature just above

MS, the martensite start temperature, ata rate fast enough to avoid the formationofferrite, pearlite or bainite. The steel is

hen held at this temperature for longenough to achieve temperatureuniformity without transformation andthen cooled to room temperature. Theprocess is employed to minimise thechance of quench cracking or distortionoccurnng.Martensite A microstructural formfound in steel when it has been cooledfrom its austenitic state to roomtemperature at a greater than the criticalcooling rate of the steel. It is ametastable solid solution with a body-

centred tetragonal structure and itshardness depends primarily upon thecarbon content ofthe steel.

Mass effect A term used to emphasisethe effect of section size on the rate atwhich a steel can be cooled through itsaustenitic transformation, and hence theeffect of section size on themicrostructure and mechanicalproperties that can be produced in a steelof a particular chemistry when cooled inthis manner.Maximum stress When used in relation

to the tensile testing of a metal the valueof the maximum stress is obtained bydividing the maximum load to which thetest piece is subject to by the originalcross-sectional area of the specimensgauge length.Melting point The temperature at whicha solid begins to melt.Micron A unit of length. It is 1 X 1006(O.OOlmm).Microstructure The internal structureof a material revealed when a sample ispolished, etched and viewed under a

mIcroscope.Mild steels A description generally takento mean non-alloy steel with a maximumcarbon content of about 0.25 .Mill margin Material allowed betweenmill supplied size final cut size toallow cutting operations.Modulus of elasticity The ratio of theapplied stress to the resultant strain,produced by the stress, occurring whenthe metal is behaving in an elastic

VOLUME 22

MAY ~O13I

. Mll .

manner. f the stress occurs from tensileloading conditions the ratio, themodulus elasticity, is known as Young'smodulus (E) and it is a measure of thestiffness of the metal.

Molybdenum (Mo) A strong carbideforming element in steel. Produces apronounced secondary hardening effectand so is present in hot working toolsteels and is used as a partialreplacement for tungsten in certaingrades of highspeed steel. Greatlyimproves hardenability (of the elementscommonly added for this purpose onlyvanadium has a stronger effect), andreduces temper embrittlement, so isoften used in quenched and temperedengineering steels. Used in conjunctionwith Cr and V in creep resistant steels.

Up to 5 can be present in maragingsteels. Added to stainless steels topromote resistance to pitting andcrevice corrosion attack.

Nesting Where parts are groupedtogether on a plate to achieve best fit andhence minimise yield loss.Nickel (Ni) Widely used as an alloyingelement in steels. Up to 5.0 can bepresent in general engineering and incase hardening steels. Improvesstrength and toughness and increaseshardenability. Larger amounts are

present in austenitic stainless and in heatresisting steels. Also used in Invar, acontrolled thermal expansion alloy, andin permanent magnet alloys.Niobium (Nb) Known as columbium inthe USA. A strong carbide formingelement in steel. Present in amounts upto 0.1 in high strength low alloy(micro alloyed) structural steel and usedin stabilised grades of austeniticstainless steel. Can also be used as astabilising element in ultra low carbon(ULC) steels.Nitriding A thermochemical treatmentin which nitrogen is diffused into thesteel.

The treatment is usually carried out at atemperature around 500C, in either agas or salt bath atmosphere, or with theuse of a plasma.

Non-Destructive Testing (NDT)Also known as non-destructiveinspection. Any technique that usesradiography, ultra-sonics, dye-

penetrant, magnetic particles, eddycurrents etc. to determine the quality ofa material without permanently alteringthe completeness or properties of thematerial being tested.Non-Magnetic steels Steels that have astable, fully austenitic microstructure.Normalising Heating up a steel to justabove its upper critical temperature inorder to transform it to austenite,followed by cooling to roomtemperature at such a rate that a refinedequilibrium microstructure is produced.Often this means cooling in still air.Notched bar test A test in which the testspecimen has a notch of a standardgeometry machined in it in order toproduce a local stress concentration at thenotch root when the specimen is tested.

(See Charpy and Izod Impact tests)Notching The cutting out of any of avariety of possible shapes from the edgeof a section, plate, blank or part.Oil hardening steel A steel for whichthe liquid used for quenching is oilrather than any other medium.Oiling The coating of steel with oil as atemporary rust preventative.Open hearth furnace A meltingfurnace with a shallow hearth, on whichthe charge is placed beneath a low roof.Heating of the charge is both by direct

flame and by radiation from the furnaceroof and sidewalls. This type of furnaceis no longer used in Western Europe as asteel making unit as the Basic Oxygenand the Electric Arc Furnace Steelmaking processes have now replaced it,for economic and quality reasons.Orange peel effect The name given tothe appearance of the surface rougheningthat can occur when a metal with anunusually coarse grain size is plasticallydeformed.Ore A naturally occurring mineral thatcan be mined and treated for theextraction of any of its components,metallic or otherwise, on a commercialbasis.

Over heating Heating a metal to such ahigh temperature, or for such a long timethat its properties are degraded. When theoriginal properties of the metal cannot berestored by thermal, mechanical orthermo-mechanical treatment theoverheating is often termed 'burning'.

o be continued in next issue

a glossry of steel terminology

Documents