steel cleanliness and environmental metallurgy

Metall Res Technol 113 201 (2016)ccopy EDP Sciences 2016DOI 101051metal2015050wwwmetallurgical-researchorg

Metallurgical ResearchampTechnology

Review

Steel cleanliness and environmental metallurgy

Jean-Pierre Birat12

1 ESTEP Belgium2 IF Steelman France

e-mail jean-pierrebiratifsteelmaneu

Key wordsMetallurgy non-metallic inclusioncleanliness environmentcleanliness of air emissionsenvironmental metallurgy

Received 22 September 2015Accepted 7 December 2015

Abstract ndash Clean steels were ldquoinventedrdquo in the middle of the 20th century at a time whensteels started to be produced en masse and when it was understood that quality should alsobe addressed as a special and important issue both in terms of the strategy of the sectorand as a major research topic for the science and technology that accompanies the industryThe series of Clean Steel conferences launched in Hungary in 1970 and organized every4 years since then with Paul Tardy in the organizing committee or in the lead have beenproviding important time markers of this evolution Since then major progress was made bythe introduction in most steel shops of secondary or ladle metallurgy which was inventedin the process while steel cleanliness was defined precisely in standards and textbooksThe discoveries of pioneers have become state-of-the art and today a steady state situa-tion has been reached where research continues in using new tools and methods to refinethe topic while new comers mainly from the BRIC countries are contributing their under-standing of the topic to the international steel community The distinction between specialsteels and carbon steels got blurred in this historical process as similar secondary metal-lurgy tools were used for making both kinds of steels and in essence steel ceased to be asimple commodity and most steels became special to some extend Clean steels have thusnot become much more sophisticated recently but rather much more common and main-stream The expression ldquoclean steelrdquo stems from a vision of the purity of the metal in termsof minor elements which had been controlled until then only at the margin compared tothe major elements iron carbon silicon and manganese This is today a somewhat passeacuteedvision as metallurgy has become a much more holistic and systemic technology wherebysteels are defined in terms of global composition of distribution of phases including theminor phases that are known as non-metallic inclusions of microstructures and more of-ten than not in terms of applications and properties in service Moreover steels have timeextensions which are discussed as life cycle or value chain and are thus embedded in theanthroposphere and its intersection with the biosphere and the geosphere This emphasizesthe fact that steels are made from raw materials primary and secondary ndash thus includingscrap from recycling - that they are transformed into artifacts that participate to the life ofsociety and eventually are disposed of at end of life to feed back into the circular economyThis holistic vision is what we call ldquoenvironmental metallurgyrdquo It is linked to clean steelproduction and constitutes another dimension of the cleanliness of steelPlenary presentation to the 9th International Conference on Clean Steel 8ndash10 September2015 Budapest Hungary

S teel is a metal which combines arobust set of properties for mak-ing a wide variety of things with a

fairly ldquocheaprdquo price It has thus becomeubiquitous

Iron and steel emerged into History atthe end of the Neolithic when villagers firstlearned how to smelt iron from earths [1]Iron was used initially as a sign of wealthand power but it soon became the preferredmaterial to make weapons pots and pansand eventually ploughs [2] from a marker ofaristocracy which was a new social construct

of the settlers who had replaced the hunters-gatherers of the Mesolithic [3] it turned intoa structural material used to give shapestrength elasticity toughness and eventu-ally engineering audacity to the explodingnumber of small and large artifacts designedand produced by humankind around thetime of the industrial revolution What istruly remarkable is that this trend has beencontinuing across centuries and that produc-tion has been multiplied almost one hun-dred times since the beginning of the 20thcentury The robustness of steel to serve as

Article published by EDP Sciences

J-P Birat Metall Res Technol 113 201 (2016)

Acronyms

AOD Argon Oxygen DecarburizationAS Anthropospheric ServicesBES Biodiversity and Ecosystem ServicesBF Blast FurnaceBFG BF GasBOF Basic Oxygen FurnaceBOG BOF gasCAS-OB Composition Adjustment by Sealed

argon bubbling with Oxygen blowingCC Continuous CastingCCC Centrifugal Continuous CastingCCS Carbon Capture And StorageCFD Computer Fluids DynamicsCOG Coke Oven GasDH Dortmund-Horder processEC European CommissionEP European ParliamentEU European UnionLCAK Low-carbon aluminum killed steelLIBS Laser Induced Breakdown

SpectroscopyMIDAS Mannesmann Inclusion

Detection by Analysis SurfboardsNMI Non-Metallic InclusionPAH PolyAromatic HydrocarbonsPM Particulate MatterPOC Persistent Organic CompoundRH Ruhrstahl Heraeus processRH-OB RH with Oxygen BlowingSLM Secondaryladle metallurgySAM Society and MaterialsSEV Statistics of Extreme valuesSOVAMAT SOcial VAlue of MATerialsTEEB The Economics of Ecosystems

and BiodiversityTRL Technology Readiness LevelTSC Thin Slab CastingULCOS Ultra-Low CO2 SteelmakingULCOS-BF Ultra-Low CO2

Steelmaking Blast FurnaceUNFCC United Nations Framework

convention on Climate ChangeVOC Volatile Organic CompoundVOD Vacuum Oxygen Decarburization

a core structural material of society and akey part of its evolving technological epis-temes has been constantly at work in thesechanging times of demographic and eco-nomic explosion

Other materials like wood and concretedemonstrate similar features but only steelexhibits such universality

This role of steel is bound to continuein the future and the only questions openare the exact years when production level

passes the 2 billion ton threshold and thenthe 3 billion one [4]

Iron and steel went through manytransformations during this long historicalprocess and their properties as well as thetechnologies used for making them havetransformed congruently by several ordersof magnitude If steel is an invariant of thetechnological epistemes of society it is be-cause of its plasticity to adapt to changingtimes and changing needs This is what iscalled today in European Commission (EC)speech a Key Enabling Technology (KET) ndashadvanced materials are the relevant KETwhich introduces the idea that new materi-als are being invented continuously but alsothat existing ones are being refined refor-mulated and changed just as continuouslyA former expression used by the EC was thatof cumulative technologies thus emphasiz-ing that materials like steel demonstrate apawl and ratchet effect where features ac-cumulate and do not vanish as they wouldin a marketing product of limited life

In a holistic vision steel partakes of theanthroposphere1 and of the biogeosphereand it circulates between both it is thusnot simply part of the anthroposphere orof the technosphere In simpler economicterms the matter is the circular economy ofwhich the EC is fond nowadays Steel is usedto mark frontiers separations between arti-facts society and nature [5] (cf further ldquoSo-cietal challenges and steel anthroposphericservicesrdquo)

Steel originates from earths concentratedinto usable ores from energy resources andfrom reducing agents and other fluxes allfrom the geosphere and it enters the tech-nosphere to become metallic and alloyedwhile the ldquoganguerdquo is separated out of themajor element iron to become a by-productsolid (slag dust mill scale etc) gaseous(eg COG BOG BFG etc) sometimes liquid(pickling solution etc) or mixtures of these

1 The anthroposphere is the physical symbolicand cultural part of the planet where mankindlives and which it has transformed to create itshabitats through arts crafts and technology It isalso called society or technosphere The expres-sion originates from scientific ecology and geog-raphy Many disciplines like most of the socialsciences are interested in the anthroposphere andthus use different words to refer to it

201-page 2


(eg sludge oily scales) While steel movesfurther into becoming a material embeddedin artifacts which are used for short or longlives and then eventually get discarded thebyproducts are either used in other sectors inan industrial ecology synergy or landfilledAll may be dissipated to the environment toa small extent

Steel itself can be reused or recycledand indeed steel is the most recycled ma-terial [6] The complexity of this scheme isobvious but is compounded by the fact thatsteel is not simply iron but contains otherelements either originating from the initialraw materials or added as alloying and sim-ilar elements These have a different fate inthe recycling loop from ironrsquos some are alsorecycled often co-recycled with iron whileothers are simply lost

Steel is thus not simply identical to ele-ment iron even if carbon steel is one of thesimplest alloys in metallurgy Steel is a com-plex mixture of elements a complex alloyand a complex set of phases depending ontemperature and kinetics histories

Why have minority elements and tertiaryphases been ignored initially when metal-lurgy developed the power to explain howmetals function and were given ancillarynames like trace elements tramp elementsnon-metallic inclusions (NMI) and precipi-tates like an afterthought

On the one hand because steelrsquos mi-crostructure and properties could be ex-plained only in terms of the major chemicalelements in its composition ie iron car-bon and possibly silicon and manganese aswell even phosphorous and sulfur whichis a tribute to the synthetizing and unifyingstrength of scientific theories ndash a kind of ap-plication in a different realm of the Paretoprinciple and of the universality in simplephysics of the linearity between causes andeffects23

On the other hand the human mind hasa finite number of categories and models ac-cording to which to organize thought and

2 It also makes it possible to teach metallurgyin a simple way like physics or chemistry aretaught So much for the Professors

3 Non-linearities are often initially handled byperturbation theory as if the complexity of naturewas perturbing the simple beauty of the constructof basic theory

knowledge [7] and the concepts of purity andcleanliness (or cleanness) were powerful andavailable to acknowledge the gap betweenreality and the simple models that scienceproposes

Steel is mainly a binary alloy of iron andcarbon but many more elements are part ofits composition Some remain as a memoryof the raw materials and reactants used in theiron and steelmaking processes while somemore have been added voluntarily since itwas understood in the Neolithic that prop-erties could be changed greatly by addingsome small amounts of alloying elements4The detailed composition of a steel serves asa record of the history of the metal

Another conceptual dimension is re-lated to how useful or perturbing theminor components are the minor ele-mentscomponents that bring positive valueor usefulness to steel have been givenspecially positive names like alloying ele-ments additions precipitates or more re-cently nano-features Those that bring neg-ative value are given negative names liketramp elements inclusions and non-metallicinclusions5 impurities third phases slagparticles etc

Note further that the value is relative tothe steel itself its properties and applica-tions The more holistic dimension of steelin terms of temporality and of context is ig-nored at that stage which corresponds to thestate of knowledge of the middle of the 20thcentury The impact on resources air waterand soil quality health of workers and popu-lation or its general societal role are ignoredin this narrow one-dimensional definition ofsteel

Purity in metallurgy relates to chemi-cal composition and on to how close thatcomposition is from that of a model metalwhich would contain only the core basicand ldquousefulrdquo elements Cleanliness relates tophases with an ideal of no ternary phases atall One concept does not necessarily leadto the other in this case cleanliness to pu-rity like it does in the philosophy of the

4 Even if this does not contradict the linearityldquoprinciplerdquo the amount of effect of a small addi-tion can be very large

5 As if referring to a mineral ie a non-metalwas being even more derogatory

201-page 3


Ancient Greeks of Nietzsche or in the ma-jor religions although purity and cleanli-ness in metallurgy separate reality from thebeauty of the model metal taught in uni-versity classes and born of theory thus ofthe human mind Thus the three words ofNietzschersquos quote cleanliness purity andbeauty are relevant in this area as well

Note also that this dichotomic view ofmetals does not help understand why someelements like chromium nickel or cobaltare sometimes called tramp elements whilein other cases there are termed additions oralloying elements It does not help under-stand either how inclusions and precipitatesmay cooperate or why the distinction be-tween them gets blurred like in oxide met-allurgy [8 9]

A more holistic view is necessary todayto reach beyond the distinction between ma-jority and minority phenomena between in-side and outside of steel6 It is probablynecessary to implement a paradigm shiftthat would acknowledge the complexity ofthe connection between anthroposphere andbio-geosphere and to address it directly

Cleanliness the subject matter of thispaper and of this conference cleanlinessshould therefore be seen as a remnant of thehistory of science and technology rather thana proper up-to-date account of a metallur-gical issue The deconstruction of conceptslong taken for granted in the past is commonnowadays in many areas of social sciencesfor example in history anthropology arche-ology and prehistory [2] metallurgy shouldnow follow suit

1 Historical constructionof the concept of clean steels

Reviewing the construction of the conceptof clean steels sheds light on the concept ofmodern materials

6 The papers published in this conference thatoriginate from emerging economies where theculture is based on non-European paradigmsmay eventually help implement this shift As theyare the most numerous this may happen fast

11 Historical narrative

When iron and steel emerged in history7 themetal was reduced in the solid phase in abloomery thus the iron bloom was a mix-ture of reduced iron8 and of the gangue of theore a true composite material The ganguewas removed by forging the bloom to expelthe mineral elements out of the metal Theoutcome was an iron very different from to-dayrsquos steel for example the amount of min-erals in samples from the late Iron Age (LaTegravene final) was between 10 and 2 in vol-ume the latter being considered as a cleanpiece of material [10] in terms of total oxy-gen content the spread was thus roughly be-tween 14 000 and 200 ppm Nobody talkedexplicitly about cleanliness then althoughthe quality issues that were raised (earlyfracture) were probably understood by thesmiths of that time

The evolution towards modern steel-making ie to an all-through liquid pro-duction from hot metal to liquid steel(Bessemer and Martin-Siemens processes)has changed the picture in terms of cleanli-ness very significantly The production of liq-uid hot metal in the early blast furnaces elim-inated gangue inclusions the liquid ganguebeing separated by density however newinclusions of a different kind due to oxi-dation were introduced during subsequentforging a completely new genesis of theseternary phases Most of these were elimi-nated when liquid steel was produced ascrucible steel or puddled iron but new kindsof inclusions were created due to reoxida-tion of liquid steel along with contamina-tion by refractory and liquid mineral phases

7 The first reduction of iron ore into iron metalis attributed to the Hittites in Asia Minor at theend of the 3rd millennium ie before the onsetof the Bronze Age (1600) Then the metal moveswest to Europe and the first artifact made of ironare from the 17th century Then in the 8th cen-tury it became fairly widespread from Greece toScotland as a series of prestige artifacts includ-ing swords (the famous Halstatt words) ownedby the aristocracy of the chiefdoms Their func-tions as weapons may have been secondary totheir role as a marker of power Only by the 3rdcentury was it incorporated into peasantsrsquo toolsand was widely used by society at large [2]

8 Plus some steel and possibly some pig iron aswell

201-page 4


(slags) Studies picturing this historical evo-lution in a quantitative way ie a time-evolution of cleanliness measured for ex-ample by total oxygen content are lacking

The concept of cleanliness was born ini-tially from the observation under the opticalmicroscope of non-metallic inclusions by thenewborn discipline of metallography

Cleanliness was rated against standardimages of microscopic fields where geom-etry (shape and size) and distribution ofnon-metallic inclusions was distinguishedagainst various image types [11] The trainedobserver had established that some shapeswere acceptable in some steel grades andthat smaller inclusions generally were moreacceptable than larger ones Although thecomposition of inclusions was not availableby then the observer had established a cor-respondence between grades and inclusioncomposition by families (sulfides silicatesaluminates alumina composite inclusions)based on the sulfur content and deoxidationhistory of the steel These methods devel-oped in the 20th century and standardizedafter the 2nd World War preempted the gen-eral use of continuous casting and of ladlemetallurgy and therefore were invented ina process technology context fairly differentfrom todayrsquos

The further development of the conceptof cleanliness went on by exploring variousissues in parallel based on laboratory workbasic research into the physical chemistryof steelmaking steelshop experimentationdevelopment of new process reactors andnew innovative solutions to control inclu-sions composition shape size and distribu-tion to be eventually introduced in the rou-tines of steelmaking practice

12 A modern vision of cleanliness

A modern vision of cleanliness has emergedfrom this 30ndash40 year concept-building ef-fort [8 12]

Inclusions constitute a cloud of phasesdispersed in the metal matrix and definedby a multi-dimensional set of parametersincluding composition shape size and dis-tribution This full description is not read-ily available and one of the main issues re-lated to assessing cleanliness is to observe

representative samples to estimate these pa-rameters with a reasonable accuracy andrepresentativity one difficulty is related tolarge inclusions (eg 100μm or more) whichare extremely rare and therefore difficultto see unless very large-size samples areanalyzed

Another issue is due to the fact that theNMI population depends on time (in theprocess timeline of the steel shop) and ontemperature Thus a ladle sample collectedand analyzed with care and finesse maygive a reasonably good estimate of the clean-liness there and then but it may bear almostno connection whatsoever with the clean-liness of solid steel There is thus a hugeamount of literature devoted to discussingwhen a representative sample of liquid steelought to be taken in order to assess both steelcomposition and NMI cleanliness [13]

13 Elements purity andthermodynamic equilibriums

The chemical elements initially involved incleanliness are mostly the non-metals ofthe Mendeleev table because they exhibithigher solubility in liquid steel than in thesolid thus carbon nitrogen oxygen phos-phorous sulfur selenium and hydrogen Tothis list one can add metalloid neighbors inthe table like boron arsenic antimony andtellurium Some of these elements originatefrom primary raw materials (P S As Sb) orfrom ironmaking (C) while most of the oth-ers are due either to contamination by theatmosphere (O N H) to the general oxidiz-ing practice (O) used in steelmaking to theelectric arc in the EAF (N) or are voluntarilyadded (C Se Te B) Recycling and circulareconomy practices in place or to come (will)bring in some of these elements in differentways (eg Sb from red mud if it were usedas an iron ore substitute) Pollution by trampelements (metals like copper tin chromiumetc) related to the use of scrap is usuallynot considered as a cleanliness issue

Phosphorous and sulfur levels are usu-ally handled prior to the steel shop first byselecting the raw materials and then by con-trolling P and S levels in hot metal (desul-furization more rarely dephosphorizationof hot metal) or during oxygen steelmaking

201-page 5


(dephosphorization in the converter) Fur-ther control on steel is always possible butonly necessary for some high-end specificgrades (eg slag desulfurization in ladle met-allurgy whenever S lt 10 ppm) [14]

At the end of steelmaking in the BOFor the EAF oxygen is at equilibrium withcarbon which means very high levels forlow carbon grades (1250 ppm oxygen for002 carbon) If steel would simply so-lidify as such eutectics of iron sulfur andoxygen would precipitate in the interden-dritics while a strong carbon deoxidationwould take place in the initial stages of so-lidification thus producing rimming steelsfull of blowholes near the surface The re-sulting metal in addition to being porouswould be brittle during hot forging andsubsequent use at room temperature (rou-verain iron) To avoid precipitating oxygenand sulfur iron eutectics deoxidation agents(carbon especially under reduced pressuremanganese silicon aluminum calcium tita-nium etc) and desulfurizing agents (man-ganese calcium) are introduced into thesystem in order to promote new equilibri-ums whereby third phases precipitate andrimming is avoided altogether9 The thirdphases constitute the endogenous NMIs (ox-ides nitrides carbides sulfides phospho-rides etc) that are initially created in liquidsteel usually in the ladle [15]

These equilibriums can be implementedby adding deoxidants into liquid steel bybulk additions or wire injection or by en-suring that the liquid metal is in equilib-rium with an active metallurgical slag of theproper composition

The NMI population changes all the timebecause existing inclusions coalesce floatout and get finally adsorbed in a slag ora simple covering powder or flux by ag-gregation against refractory in the ladlethe tundish or inside nozzles that some ofthem (solid NMI like alumina or spinels)tend to clog Steel and slag change as welland inclusions entertain complex connectionwith them at equilibrium if time allows orout of it More inclusions appear because

9 Gas evolution at the solidification front canstill take place if nitrogen and hydrogen are notproperly controlled

temperature drops10 which usually meansmore precipitation or solidification startsor oxygen penetrates the system (reoxida-tion) from the slag the refractories from theatmosphere at refractory junctions (slidinggates submerged nozzle mounting acrossthe refractories etc)11 or because the slagor the refractories generate new inclusionsor release inclusions previously capturedThe latter fall under the name of exoge-nous NMIs Of course the trend is usuallytowards improved cleanliness and researchhas been looking deeply at all these mecha-nisms at modeling them by simulation withmore and more sophisticated mathematicalmodeling (CFD) and at proposing counter-measures based on this insight

A comparison of the various mechanismsof inclusion elimination taking place in theladle is shown in Figure 1 which was pro-duced by computer CFD simulations [16]

An important point regarding reoxida-tion is that the phenomenon does not takeplace at thermodynamic equilibrium butrather generates oxides of whichever ele-ment happens to meet the incoming oxygenmost often generating iron oxides Out ofequilibrium in deoxidized liquid steel theywill later reverse back to equilibrium NMIif time allows

The distinction between endo- and ex-ogenous NMI is however somewhat ad hocas deoxidation or reoxidation are actually anintegral parts of the total system of steelmak-ing and both result from the technology putin place to produce steel for example deoxi-dation does not take place inside liquid steelbut at the interface of the deoxidant injectedfor example as a wire into the ladle and thusthe resulting NMIs do not quite deserve tobe called endogenous

NMI inclusions are large enough to inter-act with the metal matrix as mechanical dis-continuities basically like holes There areother third phases in steel of much smallerdimensions called precipitates which

10 A drop in temperature of 100 C cuts dis-solved oxygen level by half

11 Direct contact with the atmosphere is usu-ally completely avoided nowadays except in thecase of billet open stream casting of centrifugalcontinuous casting and of ingot casting becauseof surface fluxes and powders and of refractorynozzles mostly submerged

201-page 6


Fig 1 Simulation of the mechanisms of elimination of NMI in a ladle furnace The initial distri-bution is a log-normal one with 0176 kgm of calcium aluminates corresponding to 79 ppm oftotal oxygen [16]

interact with the matrix as the scale ofdislocations or even at atomic scale (GPzones12 [17]) Precipitates usually carbidesor nitrides constitute the key features ofmicro-alloying as in HSLA steels (driven byniobium titanium vanadium aluminumbut also copper) or of more substantialalloying like in tool steels or in sophisticatedstainless steels They provide precipita-tion hardening They are not within thescope of the present paper Structureslike GP zones or perlite are some of thefirst nano-structures identified in materialscience

The many phases that can impersonateiron (ferrite perlite bainite residual austen-ite martensite and their infinite variants) arenot part of the present discussion of cleanli-ness either as they lie at the very core of steelmetallurgy ie of the physics of ldquopure steelrdquoThey are controlled by static or thermo-mechanical heat treatment Grain bound-aries which are not phases by themselvesare also part of this metallurgy universe

There is a porous interface between NMIand precipitates of which oxide metallurgygives a good example The concept is to use

12 ldquoa first example of a structure which is foundin many oversaturated solid solutions in thecourse of their returning to stable equilibriumrdquoA Guinier Personal reminiscence

inclusions to promote ferrite nucleation incarbon steels at the α rarr γ transformationinterface to foster fine grain size [8] Forexample titanium oxides coated by man-ganese sulfides have been used for that pur-pose in weldable plate grades This exhibits asynergy between NMIs and precipitates anddemonstrates that a continuum connects thetwo categories of third phases

The focus here has been on oxygen elim-ination or on avoiding oxygen contamina-tion A similar discussion should addressnitrogen and hydrogen as well but it willnot be exposed here (see for example [18])The same comment is valid for sulfur (eg acommon rule is for manganese to be presentin excess of sulfur in order to favor precipi-tation of MnS inclusions Mn gt 40 S)

14 Process tools for cleanlinesscontrol

The construction of the concept of cleanli-ness took place in parallel with the devel-opment of new specific tools in the steelshop thus new process reactors and tech-nologies which are widely used today tocontrol cleanliness and have redefined thefield

This transformation has been progres-sive

201-page 7


Fig 2 ladle furnace with argon bubbling cored-wire injection with argon bubbling tank degasingRH

It started from the production of engi-neering steels for the automotive power andaircraft sectors with the purpose of increas-ing the reliability and life of the mechanicalparts of vehicles or nuclear reactors The ma-jor need hic et nunc was to control the hydro-gen level in liquid steel (to less than 1 ppmin a carbon steel) in order to avoid its de-parture at solidification and its entrapmentin the solid which leads to serious integritydefects during the use of the metal part Theuse of vacuum which removes hydrogenstraightforwardly was proposed and gen-eralized in these steel shops using varioustechnologies like tank degasing stream de-gasing DH or RH It was also understoodthat vacuum treatment allowed for otherbenefits like carbon deoxidation which hasthe major advantage of producing gaseousdeoxidation products and not NMIs intensestirring with its various advantages and al-lows for time management in the logistics ofladle flow therefore on the quality of tem-perature control of liquid steel ndash includingreheating by aluminum and oxygen injec-tions (RH-OB CAS-OB) cf Figure 2

Continuous casting (CC) was also at thetime overwhelmingly taking over the solid-ification function in the steel shop [19] be-cause it increased metal yield cut cost andmake it possible to improve steel quality atthe same time CC imposed a new sophis-tication on the control of steel temperaturein the ladle ie on superheat in the tundishand this was made easier to manage by ded-icating a specific area of the steel shop to

secondary or ladle metallurgy (SLM) Ad-ditions for deoxidation and alloying werecarried out there and several other func-tions were added a mixing function (bygas stirring or purging or by electromag-netic stirring) and agrave la carte vacuum de-gasing and heating with an electric arc orless frequently plasma torches inductionheating or aluminum oxidation in the meltThe outcome of this evolution was that sec-ondary metallurgy became a permanent fea-ture of the steel shop it often included vac-uum and preheating devices in steel shopsboth for long and flat carbon steels Stainlesssteelshops had their own specialized reac-tors usually VOD or AOD to cater to thespecial needs of chromium metallurgy

SLM became a marvelous tool to man-age steel cleanliness addition under con-trolled conditions became possible butalso careful slag-metal stirring slag re-duction temperature trimming inclusioncoalescence elimination by flotation andentrapment in the slag and composition con-trol vacuum degasing and sometimes car-bon deoxidation etc The functions availablefor engineering steels thus became availableto all steel producers and a subset of themwere used for all grades of steel the distinc-tion between commodity and specialty steelsthus became blurred

One important feature of SLM and CCis that the metallurgical functions are spreadout in space along the equipment line de-ployed as along a time scale and thereforethey can become standardized sometimes

201-page 8


Fig 3 Schematics of phenomena taking place in the continuous casting tundish in connection withsteel cleanliness

automated and better controlled On theother hand sources of contamination havemultiplied but can also be better controlledladle to tundish (ladle nozzle sliding gateladle stream gas protection) tundish (pow-der weirs dams and baffles bubbling ele-ments etc) tundish to mold (nozzle slid-ing gate or stopper rod submerged nozzleand gas bubbling etc) mold (mold pow-der mold level control submerged nozzlegeometry etc) CC itself (straight curvedmold straight mold and curved electro-magnetic stirring electromagnetic braketransversally-shaped molds of thin slab cast-ers etc) all have become part of the processchain and turn into true metallurgical reac-tors The expression ldquotundish metallurgyrdquohas become common lore (for example cfFig 3)

The continuous caster especially itsmold also act as a metallurgical reactorwhere the fate of NMI continues to be de-cided (cf Fig 4) [20 21]

Much of research and development workfocuses on the various devices that can beimagined to mitigate NMIs

Note that completely new issues interms of cleanliness were raised by the

introduction of continuous casting aftersearching for the martingale to cast rimmingsteels on CCs for many years with limitedsuccess steelmakers understood the advan-tages of aluminum grain-controlled steelswhich triggered the overwhelming move toaluminum deoxidation away from rimmingsteel or semi-killed grades

However alumina was collected by noz-zles This reduced the number of heats dur-ing sequence casting13 and resulted in catas-trophic events when the inclusion plug gotaccidentally discharged and trapped in thebloom or the slab This issue was particularlyacute in the case of thin slab casting (TSC)

A technique to prevent clogging wasreinvented consisting in changing the na-ture of inclusions by a treatment in the ladlewith calcium as the inclusion modifier sim-ply put calcium aluminates with a compo-sition close to the eutectic in the Al2O3-CaOphase diagram are liquid at the tempera-ture of operation and thus will not depositin the nozzle (cf Fig 5) This technology hasbeen used systematically in the case of TSC

13 3 ppm of oxygen contamination generate 1 kgof inclusions in a 100 t heat

201-page 9


Fig 4 Schematics of phenomena taking place in the continuous casting mold in connection withsteel cleanliness14

Fig 5 Modification of the nature and morphology of inclu-sions by calcium treatment (sans traitement no treatmentapregraves traitement au calcium with Ca treatment) sulfuressulfides alumine alumina inclusion globulaire calciqueglobular calcium inclusion)

while other solutions were preferred in thecase of slab casting based on argon injection

in the submerged nozzle and on curved cast-ers with a vertical mold

While CC and SLM were becomingmainstream process technology the produc-tion of high-end engineering steels contin-ued to explore more advanced cleanlinessand developed original production routesbased on remelting especially under vac-uum (VAR) [22] For slightly less demand-ing applications (bearing steels for races tirecord piano wires) vertical continuous cast-ing of large sections was developed and afew examples of such casters exist across theworld for these niches

For making seamless tubes a special pro-cess was developed in which round billetswere cast and the mold and billet rotated sothat the meniscus developed as a vortex andNMIs accumulated at its center thus ensur-ing that the outer skin was clean of themThis Centrifugal Continuous Casting (CCC)technology developed by Vallourec has nowmostly been replaced by standard CC15

14 The cartoon from the right-hand side of thepicture is part of a series developed by Ecole desBeaux Arts of Metz in the 1980s to illustrate con-tinuous casting technology for didactic purposesThe blue ldquoangelsrdquo are working in favor of thequality of the slab while the black ldquodevilsrdquo try todestroy it

15 Developed in the 1960s this technologyaimed at a particular niche by solving a specific

201-page 10


Fig 6 Alumina inclusion size distribution in the ladle and the tundish [26]

15 Cleanliness estimationand measurement

The ideal estimation of cleanliness woulddescribe each NMI in an exhaustive waythus by its composition size shape and lo-cation at the scale of the total system (eg thesteel ladle or the cast heat) This is impossibleto accomplish ndash although X-ray tomography(CT Computerized Tomography) makinguse of a synchrotron source is progress-ing rapidly [23 24] ndash except if some specificdefect is targeted and controlled in an ex-haustive way eg cold rolled coated sheetschecked for surface defects by operators orautomatic devices bars or plates controlledby ultrasonic or eddy-current devices16 etc

Therefore statistical estimates have to beused

issue in an original way Steels were silicon-killed and liquid steel was injected in the moldtangentially by a special refractory device andwith an open stream Since then the idea of astandard ldquoone size fits allrdquo CC technology wasadopted Technology variants got relegated tofootnotes and historical papers except for ThinSlab Casting the last major breakthrough inno-vation related to CC

16 These methods are used to monitor all kindsof defects and are not focused directly on inclu-sions which in some cases may be below theirthreshold of sensitivity

ldquoOne kilogram of typical LCAK steelcontains 107ndash109 inclusions [3] includingonly four hundred 80μmndash130μm inclusionsten 130ndash200 μm inclusions and less than one200ndash270 μm sized inclusionsrdquo according toa classical paper by Kiessling published in1980 [25]

Cleanliness can be estimated at varioustimes in the steel production process chainor on the solid product cf Figure 6 The for-mer estimates are made in order to monitorsteelmaking casting or rolling practices andsubsequently to rate the quality of a particu-lar heat and thus to accept or to reject it (qual-ity management) or to modify the practiceand improve it in a process of quality im-provement including research analyses andintroduction of new technologies

To monitor the cleanliness of steel acrossthe process route or to compare historicalevolutions total oxygen Ot still gives usefulglobal estimates of trends A simple deriva-tion of the connection between Ot and inclu-sion size distribution is shown in Figure 7

Estimating inclusion size distributionespecially when the larger sizes are the realconcern is more complex and always endsup in a compromise To obtain statisticallysignificant information two directions havebeen explored either observation of largesurfaces or volumes (eg automatic imageanalysis sometimes on samples produced

201-page 11


Fig 7 Number of inclusions in 1 cm3 as a function of Ot and inclusion size

automatically) or some kind of three dimen-sional monitoring (eg electrolytic dissolu-tion of a sample and granulometric analysisof the resulting sludge (slime method) MI-DAS method (forging of a tundish samplein order to weld porosities and to elongateinclusions then US testing of the deformedsample) LIBS analysis of liquid steel sam-ples (eg LUS lollipop)) etc Steelmaking isstill looking for the Grail in this area al-though existing methods already providemuch useful information

One trick to guess at the dimension andnumber of large-size inclusions that cannotbe observed ndash except by chance ndash is to exe-cute a statistical sleigh of hand whereby thedistribution of inclusions measured at smallor intermediate dimensions is extrapolatedto the larger sizes (Statistics of extreme val-ues (SEV) method) [27 28] Practically thereare several inclusion populations in solidsteel due for example to deoxidation reox-idation various other contamination mech-anisms and process mishaps and thereforethe case for all of them to align along a sin-gle distribution curve is fairly weak The ex-treme values estimated in this manner arefuzzy at best

Note that there are biases when samplingliquid steel to obtain cleanliness informa-tion as the sampling operation unless car-ried out under special conditions with argoninjection for example can lead to an oxygenpick up of as much as 35 ppm moreover in-

clusions float up in the sample like in anyliquid metal vessel etc

Finally there are many transient phe-nomena (first heat in a sequence end of la-dle change of ladle change of ladle tubespeed changes on the continuous casterchange of submerged nozzle in the castermold change of tundish etc) which causetime variations during a casting sequenceand may lead to the deterioration of cleanli-ness which is best handled by downgradingpart of the production

16 Cleanliness steel propertiesduring processing and in usesteel quality

The limiting case of rouverain iron whichbreaks up under the blacksmithrsquos hammermakes the point that foreign phases in steelcan affect steel processing ndash if they arepresent in large quantities and large enoughsizes ndash and also steel properties either theirbulk level or their spread

This is the basic reason of course whyso much interest has been devoted to NMIsand to cleanliness

NMIs carried over into the CC mold cancause various kinds of defects during contin-uous casting including breakouts or majorsurface defects

Many NMIs are trapped in the metal atsolidification Then another of their prop-erties becomes paramount their plasticity

201-page 12


Fig 8 Fate of non-metallic inclusions depending on their plasticity during hot deformation [29]

compared to that of the metal matrix in-deed NMIs will deform during hot form-ing either congruently or differently ndash tothe point of breaking up ndash align with thedeformation and create ldquoweaknessesrdquo likeseparations and internal cracks (eg lamel-lar tearing) or traps for hydrogen plus ananisotropy between longitudinal and trans-verse directions (cf Fig 8) Inclusions canalso emerge at the surface and create super-ficial defects which can be unaesthetic orinitiate cracks or corrosion In tough highstrength steels some inclusions can behaveas internal cracks even if there is continu-ity with the matrix and thus influence fa-tigue properties in a detrimental way in ef-fect significantly decreasing the fatigue limitof steel [30]

This has also been a rich domain for RampDAll of these phenomena are mainly re-

lated to the larger inclusions but the generallevel of cleanliness remains a factor in as faras large inclusions are less frequent in cleansteels This is the reason why the very high-end applications resort to remelting under

vacuum after a step of very clean produc-tion of the remelting electrode

The complexity of the phenomena thatcontrol cleanliness their transient naturethe occurrence of operating mishaps or ac-cidents as well as the imperfection of themethods available to monitor cleanliness ina satisfactory quantitative way make it suchthat high-level performance requires contin-uous tension and that crisis of defects cannotbe avoided the cause of which is always longand painful to identify and to correct

The connection with steel propertiesduring processing and in use is also com-plex and not fully understood in the real timemonitoring of steel production and of steelquality Steel producers have been devel-oping methods to improve performance inthis domain like the Global Product QualitySystem (GPQS) of ArcelorMittal [31] whichmonitors carbon steel coil quality ndash in a gen-eral way and without a particular focus oncleanliness moreover the technologies arenot widely reported in the literature as theyare in part proprietary

201-page 13


The steel sector is quite different frommanufacturing sectors which deal with sim-pler physics and thus with more repro-ducible phenomena Steel indeed has notreached the same level of reliability and pre-dictability and it may never do so This isdue to the complexity of steel processes thatextend from physical chemistry to technol-ogy in connection with the very high pro-duction volumes involved

Some level of complexity should prob-ably be accepted as a limit to some over-rational practices and considered as astrength rather than a problem A steel millis not a car manufacturing plant and there-fore it will probably never be run as oneThis is an important caveat to keep in mindwhen narratives like integrated intelligentmanufacturing (IIM) [32] and Industry 20are marketed across the media

17 Provisory conclusions

A first conclusion is that the cleanliness ofsteel is a story that has been told since the1980s and 1990s Thus research in the fielddoes not necessarily connect with innova-tion any more at least radical innovationThis is due to the fact that the innovationdrivers in the steel sector have matured andsaturated 20 or 30 years ago (mass produc-tion quality management cost control andproduct engineering) [33] This is unlikely tochange until a new driver takes over whichmost likely will be related to sustainabilityand to environmental issues

This connects wit the next section of thispaper

Research has not stopped however evenif it has slowed down significantly It is nowdirected at maintaining the state of the art ofprocess technologies in terms of modelinginstrumentation and control and of adapt-ing technologies which have become stan-dard and have proven their robustness tonew product challenges and generally newcontexts and maybe eventually new innova-tion drivers

On the other hand emerging economieshave adopted steelmaking technologies asthey were marketed by sophisticated andpowerful engineering companies and are

demonstrating an acute ability to push themquickly to their limits and beyond

Large global companies use their re-search teams not to innovate in the processsector any longer but to make sure that thepractices of their best mills usually locatedin Europe are transferred seamlessly to theirmills in the rest of the world As a matterof fact the large European companies arealmost invisible in the present Clean Steelconference

2 Clean steelmaking

The very basic reason why clean steels canno longer be considered as a self-centeredissue looking at steels from the inside isthat making steel is about sorting out non-ferrous elements and discarding them whenthey work against the purity of the metal themain profit-making product on one side andby-products or waste on the other side Thisthen leads to two questions

ndash how are these discarded substances han-dled in term of environmental issuesand of sustainability Is a clean sustain-able steelmaking meant in a holistic sensepossible

ndash Is not there a different way to approachthings using raw material without trans-forming them as much as is done in to-dayrsquos technological paradigm Like mu-tatis mutandis bio-based materials (woodnatural textiles) do

Note that the approach used to make steel to-day is quite general in designing and mak-ing any material including more emphati-cally the new ones select the best possibleset of elements from which to make a mate-rial in order to fulfill the targeted property atthe highest level possible and then deal withsustainability issues as a corrective measuresome would say as an afterthought

Much of the present problems related tothe scarcity and geopolitical status of rawmaterials are due to this attitude of prod-uct and material designers which aim at thehighest level of performance without muchregard to resource efficiency and thus toeco-design

201-page 14


21 Raw material utilizationand the circular economy

Raw materials for steel production ndash ironore and coal mostly ndash are neither rare norscarce except for a very few alloying and re-actant elements for the fundamental reasonthat iron is the most abundant element in theEarth and a fairly common one as well in theEarth crust [1] This does not mean howeverthat they will be used indiscriminately inthe future because steel is presently alreadyrecycled to a high level (83 and 36 yearsof average life) [34] and when peak steelproduction is reached probably towards theend of this century a full circular economywill take over except possibly at the marginfor a small number of niche applications

When steel is recycled the alloying el-ements and ternary phases that it containsare recycled as well while some will be ox-idized out of the steel at steelmaking andincorporated into EAF slag (silicon half ofthe manganese part of the chromium mostof sulfur and phosphorous molybdenumrare earths aluminum and other deoxidiz-ing agents all of the ternary phases) orvaporized (zinc from coatings some sul-fur emitted as COS) others will be dilutedinto the steel matrix and thus either dissi-pated (tin) or co-recycled (part of the man-ganese most of the chromium nickel) Onlythe non-recycled steel will be dissipated orabsorbed in the ldquourban or anthropologicalminesrdquo (ships sunk at sea legally or illegallylandfilled material hidden scrap piles deepfoundations of buildings etc)

A quantitative and exhaustive mass bal-ance of all items involved in the steel valuechain is not readily available although themain orders of magnitude are not in doubt

The iron ore used today has skimmedthe best deposits of high-grade ore that canbe shipped directly to the steel industry ei-ther as natural ore or after beneficiationEven with such a favorable scheme the min-ing industry discards between half and twothirds of the material removed from themine17 usually as tailings in addition to theoverburden of rocks inside which the iron-rich deposit is geologically enclosed Tail-

17 Except for exceptional mines like LKABrsquos inKiruna where virtually pure magnetite is mined

ings constitute a slurry which is difficult todry and therefore is stored in natural val-leys behind dams The tailings also con-centrate heavy metals in the slime and indischarged water which has to be treatedaccordingly Tailings and the conditions un-der which they are stored constitute one ofthe major environmental burdens carried bythe steel value chain The issue will dis-appear when the recycling economy fullytakes over towards the end of the centuryAn opportunity to use some of these tailingswould be to use them as raw materials forthe ULCOWIN process which needs low-granulometry ores dispersed in an aqueoussolution (see further in the text)

In the future and during the 80 years orso when ore will continue to be used in highvolumes less pure ores will be called uponand therefore the energy needs for steel pro-duction will increase while its purity willdecrease [35] The same will eventually betrue for the secondary raw material route(scrap) which will become enriched in non-ferrous elements18

22 Energy needs and energytransition

The steel industry because of its nature (re-duction of an iron oxide by carbon whichinvolves breaking a strong Fe-O bond) andof its size (16 billion tons in 2014) is knownas an energy-intensive industry along withother material producing sectors and withchemistry This is often taken as a valuejudgment even though it is only a scientificfact that should be judged in a cost-benefitanalysis of the proper ambition ldquono painno gainrdquo as Benjamin Franklin put it or inphysics language there is no work withoutexergy

Steel is not particularly energy-intensiveas compared to other materials [36] indeedmaterials are in essence all energy intensivewhich is the price to pay for the functions

18 This is not a problem today because the el-ements that are not recycled are diluted by theinput of purer primary raw materials Technol-ogy is available for recycling some of these ele-ments but it is mostly not used today for lack ofeconomic and ecological incentives

201-page 15


they provide to society Moreover the en-ergy involved is mainly exergy not simplyheat dissipated as is the case for combustionprocesses

In a practical way the steel sector hasachieved a high level of energy efficiencypulled by the driver of cost cutting19 andtherefore the leeway left open for improv-ing it further is small of the order of 10 to15 [37] Higher levels could be achievedif radical changes in the steel productionprocesses were introduced (thus reaching 15to 25 of energy efficiency increase) [38]However the business model for introducingthese changes is still elusive which meansthat the cost of introducing more energy sav-ings is far higher than the value of the energysaved

The energy transition which is takingplace now and especially in Europe with dif-ferent flavors in each country is also a chal-lenge for the steel sector Steel has been orga-nized around the use of the cheapest energysources and therefore renewables can onlybe introduced through the electric grid hicet nunc

However the ULCOWIN process pro-posed as part of ULCOSrsquo solutions can playan important role in a grid fed by a largeproportion of renewables indeed large steelmills based on electrolysis could contributesignificantly to the grid management in theface of the intermittency of green electricityby introducing a strong and significant op-tion for demand-side load management [39]This is a long shot but the energy transitionis also a long-term endeavor

More options to integrate renewables inthe steel sector will probably emerge in thefuture

23 GHG emissions of steelproduction and transitionto a low carbon economy

Regarding GHG emissions the ambition ofthe UNFCC is to cut emissions by 80 by2050 in order to avoid a surface tempera-ture increase of more than 2C This cannotbe achieved in the Steel sector by imple-menting energy efficiency solutions which

19 Energy costs account for roughly 20 of op-erating costs in an integrated steel mill

fall short of the target by a factor 6 Newbreakthrough processes are needed and apath for achieving this has been outlined inthe ULCOS programs [40] proposing a se-ries of ldquoULCOS solutionsrdquo based either onsmelting reduction and CCS in a modifiedblast furnace or a liquid metal smelting ves-sel (ULCOS BF and HIsarna) or a stream-lined direct reduction furnace implementingCCS as well (ULCORED) or two electrolysisoptions based on the use of carbon-lean elec-tricity (ULCOWIN amp ULCOLYSIS) Thesesolutions have matured to different levels ofTRL the most advanced one ULCOS-BF hasbeen engaged to level 7 These are long-termendeavors maybe still 10 years or more inthe future requiring very large RampD bud-gets especially when demonstrators are tobe built

Engaging in these major changes formaking steel with greatly reduced CO2 emis-sions is similar to engaging in the energytransition The change will only happenwhen RampD is finished and confirmed at TRL9 and when a ldquobusiness modelrdquo is developedin connection with the world governanceof climate change policies ndash as any climate-related transformation is today still an ex-ternality in the market economy Moreovera world level playing field to avoid carbonleakage will also be necessary and COP21might bring the necessary framework forachieving this There will be a progressiv-ity of introduction of the new technologiesif and when these conditions are met butits kinetics will not run in parallel with theevolution announced by the Commission inJuly 2015 20 [41 42]

Beyond the discussions around free al-lowances to avoid carbon leakage and thecontinuous bickering regarding how to ad-just these a radical solution would consistin moving the steel sector out of the ETS

20 22 linear reduction factor of the annualemission cap compared to currently 174 (2013ndash2020) 1 annual reduction of benchmark val-ues ie at least 15 below the current level ofmost efficient installations However free allo-cations based on carbon leakage assessment aremaintained under certain conditions and newschemes for funding the development of break-through technologies are proposed (NER 400plus an innovation fund for demonstration ofbreakthrough technologies)

201-page 16


Fig 9 Air pollution is not easy to photograph coming out of a smokestcak and therefore the mediatend to show plumes of steam which have absolutely no environmental impact

until breakthrough solutions are availablewhile putting in place mechanisms to en-sure that these technologies will actually bedeveloped [43]

One should also acknowledge that thesteel sector worldwide is seriously andunambiguously involved in the circulareconomy with world-record recycling ratesachieved on a regular basis and thereforethat the long-term future of the blast fur-nace route is already compromised and willdwindle to a niche production eventuallyThe point then is to decide whether trans-forming the sector for the coming 50 years orso is worth it in terms of cost of investmentin particular in light of the CO2 emissionsthat would be avoided

24 Air emissions

Air pollution has been traditionally associ-ated with steel mills long after most prob-lems had found solutions (Fig 9)

Some of the elements separated from ironleave the ironmaking or the steelmaking re-actors as dust or volatiles

Dust otherwise known as particulatematter (PM) originates from ore piles sin-ter plants (the most profligate emitters) coke

ovens blast furnaces steel shops roughly 10to 20 kg per major reactor more dust comesfrom downstream at every smokestack butless in volume Most of the dust is collectedand either recycled (in the integrated millat the sinter plant or externally for exam-ple in a Waelz kiln to recover zinc from EAFdust) or marginally landfilled Air pollutionissues related to dust were handled in thesecond half of the 20th century especiallysince many steel mills were quickly enclosedin cities subject to urbanization growth

Volatiles emissions are related to heavymetals (cadmium mercury nickel copperzinc lead etc) inorganic compounds (H2SCO SOx NOx O3) and organic compounds(PAHs dioxins and furans VOCs POCsetc)

Air pollution has been brought undercontrol at the best-run steel mills of theworld following very active research andabatement technology development More-over lists of technologies to guarantee con-formity to present standards have beencompiled for example by the EuropeanCommission [44]

Besides these ldquoeliterdquo mills howeverthere are still air pollution issues in partsof the world [45] Moreover the standardsare very likely to be raised to much tougher

201-page 17


limits by the middle of the century [46] dueto increased urbanization to the fact that lo-cating production plants away from citieswill no longer be an option and to severalair pollution issues stepping up from localto global scale (cf Fig 10)

The discussion should now addressemissions to water and emissions to soilbut it will be kept very short These issueshave also been scrutinized at the end of the20th century regulated and carefully moni-tored for example in Europe so that prob-lems have dwindled Some European steelproducers like to state that the water theydischarge is cleaner than the water they takein and anyway recycling water internally inthe steel mill has become the norm [47] andin the EU the specific consumption of waterof the steel industry is negligible comparedto some other parts of the world

Soil pollution is mostly a legacy of thepast an archeological signature of steel millslong shut down As a matter of fact soil andwater table pollution went hand in hand atthat time but this has been long past

25 Biodiversity and more holisticissues

Biodiversity is a global threat to the eco-sphere and trends seem to announce the6th largest biodiversity extinction in the his-tory of the planet [48] The United Nationshave pointed this danger out as early as theEarth Summit in Rio in 1988 when the Con-vention on Biodiversity was launched [49]at exactly the same time as the UNFCC Asharp reduction in biodiversity endangersthe ecosystem of the planet as a whole orat the very least announces major evolu-tionary changes at a scale that was neverobserved in human history

Steel as an economic sector or a mate-rial cannot be considered as causally con-nected to or partly responsible for this bio-diversity or its loss ndash except at the localscale of steel mills and mines where regula-tions and legislation has provided a frame-work that steel and mining companies fol-low However globally the industry itselfis threatened as an element of society andfurthermore it holds part of the solutionsto alleviate the risk The loss in biodiversity

being related to climate change and to theincrease in the urban footprint industry canact globally by reducing its GHG emissionsand by abating the impact of cities for exam-ple in providing biodiversity or ecologicalcorridors a new kind of large scale infras-tructures which will need a strong materialbackbone based in part on steel This is an-other example of the slogan ldquosteel is part ofthe solutionrdquo which should probably read asa scientifically optimistic statement regard-ing how the present technological epistemeis flexible and plastic enough to address rad-ically new challenges and new problems

26 Societal challenges and steelanthropospheric services

Materials and steel are deeply woven intothe present technological episteme and havebeen playing such a role across many morepast ones Materials have been used to cre-ate barriers between the ecosphere and theanthroposphere because from a physicalstandpoint they can sustain large gradientsof temperature stresses or chemical poten-tial Inside the anthroposphere they sepa-rate the space where people live and workfrom the reactors of the technosphere whereconditions are decided by engineers andnot friendly to life like a blast furnace adistillation tower or a nuclear reactor [50]The energy system from energy harvestingelectricity generation to energy distributionthrough power or pipe lines relies heavilyon steel which constitutes its backbone andits structure inside which more specializedfunctional materials like copper silicon orfiber-reinforced composites assume specificmissions [51]

Steel producers sell steel to make powerplants or power poles but not to assume thefunction of holding and tying the energy sys-tem together This constitutes a service that ismostly taken for granted and thus not mon-etized The concept is similar to the ecosys-tem services that biodiversity delivers to thebiosphere and the anthroposphere We havecalled them anthropospheric services (AS) Itwould probably be possible to estimate theirmonetary value following the methodologyfollowed for climate change or BES [52 53]but the work remains to be done

201-page 18


Substances 2000 2010 2020 2030 2040 2050GHG 0 10 20 30 40 50VOC 0 24 49 60 70 81SOx 0 20 75 77 80 82NH3 0 0 27 44 62 79PM 0 0 50 50 50 50NOx 0 26 53 64 74 85

Others 0 10 20 30 40 50

Fig 10 Evolution of emission targets for various indicators and output streams as projected from2010 to 2050

Contrary to the issues discussed in theprevious sub-sections and related to the neg-ative effects of industrial activities on theecosphere or the anthroposphere AS are apositive contribution of steel to society andto the resolution of the societal challengeswhich the European Commission stressesfor example in its Europe 2020 agenda [54]This approach does not fully cover the scopeof the assets that steel materials or industryin general provide For example industryis widely expected to provide jobs and thusto contribute to monetary flow and to eco-nomic growth but also to participate in thecreation of well-being as steel like manycommodities in the economy has been di-rectly connected to GDP per capita [4] Allthese issues cover what we have called thesocial value of steel

The liabilities of industry have beencovered more extensively in publicationsapproaches (LCA) and narratives than itsassets this remark was indeed one of thestarting points of the SOVAMAT initia-tive [55] and of the series of Society andMaterials seminars (SAM) [56]


The section on clean steelmaking has beenpresented in a classical way thus startingfrom environmental issues enlarging theviewpoint to sustainability and then to thesocial value of steel a common attempt atreaching some level of holism

The approach differs from that of thefirst section because the figures involved arecompletely different in nature larger (up toone order of magnitude higher than ironrsquosand not ppm) less precise or well known(the amount of published work is much less

abundant) less specific (there are elite millsand others)

Moreover the discussion on clean steel-making describes the interaction of the steelvalue chain with the ecosphere (harvest-ing of natural resources role of secondaryraw materials creation of ancillary mate-rial flows [waste co-products by-productsresidues] emissions to air water and soilsometimes pollution contribution to an-thropogenic emissions of greenhouse gasesinteraction with biodiversity and BES) orwith the anthroposphere (emissions becom-ing pollution work health and safety is-sues public health issues positive value ofsteel anthropogenic services rendered bysteel to society etc) These descriptions areless finely analyzed and quantified than thefirst part on steel cleanliness and they tellstories narratives rather than state scientificfacts [57] The objective is conformity withan ideal which would preserve the environ-ment save it for future generations this hasbeen turned into targets and standards byhoards of legislation at country and supra-regional levels like the EU in Western-stylecountries where this approach has beenstrong one can consider that the contracthas been met until more issues are raisedand the severity of regulations increases ac-cordingly in the future

However this is the other face of the coinif one ambitions to speak about clean steelsin a holistic way Indeed steel is a major ma-terial produced by industry to provide so-ciety with anthropospheric services To doso the present technological episteme pro-vides solutions to collect the element ironfrom primary or secondary resources andin doing this mines much larger resourceswhich are then sorted out and transformed

201-page 19


into primary (iron and steel) and secondary-ancillary (waste emissions) flows The sec-ondary flows are different from natural re-sources which were in equilibrium with theenvironment being displaced spatially andmore concentrated sometimes to the pointthat they need to be treated to cope with anew toxicity to the ecosphere or to the an-throposphere Thus clean in the sense ofsteel production does not mean purity butrather returning the secondary flows to theirinitial complexity and state of mixing di-luting them to regain their primal naturalessence (purity)21 therefore quite the con-trary to what was targeted in clean steels

As was pointed out in several sub-sections some of the underlying issues arestill open and will require much more workincluding research and development in thefuture This is the case of low-carbon steelproduction which needs to demonstratepromising technologies like ULCOS solu-tions at a larger scale but also of biodiver-sity issues where more thought is needed toidentify how the steel sector can contributeto solving this huge societal challenge More-over as emissions targets will become moresevere in the future more technology willhave to be invented and deployed

Last there is a vacuum in methodolo-gies to deal with these matters One can con-sider that LCA and MFA are a first step inthe proper direction but the former focuseson the value-chain of a specific consumer(sub-)items while the latter focuses on mon-itoring the flow of specific substances or ele-ments in the economy mainly as a functionof time What is still missing is a mass flowdescription of the shower of primary andsecondary materialsresidues generated bya value chain (like steelrsquos) and of their fatethus the grafting of an MFA approach on anLCA framework

There is thus much more work left to doin the area of clean steelmaking than in thatof clean steels

21 Diluting has been considered as a ldquono-nordquo inecological thinking because it did not deal withissues close enough to their causes The idea putforward here is of a different nature as it talksin favor of dilution as a restoration of naturalequilibriums

3 Conclusions

The concept of cleanliness in connectionwith steel has been discussed extensively inthis paper in line with the objectives of thelong series of Clean Steels conferences

On the one hand steel cleanliness is aconcept which has been worked out exten-sively and probably exhaustively on the ba-sis of the needs of the present technologicalepisteme The construction of the conceptof cleanliness has been contemporary andparallel to the construction of the conceptof the modern steel shop with its system-atic use of ladle-secondary metallurgy andof continuous casting

Clean steels aim at minimizing theamount of ternary non-metallic phases thatprecipitate by physical-chemical equilibri-ums when liquid metal cools down and so-lidifies and those that originate from con-tamination by atmospheric oxygen slagpowders and refractories Thus cleanlinessgoes along with purity and part of the prob-lem is solved prior to the final trimmingof steels in the ladle by cutting sulfur andphosphorous levels on hot metal or duringconversion and by the generalization of de-oxidation by wire injection rather than ladleadditions ndash thus renouncing once and for allto rimming or semi-killed steel grades

A clean steel in the ladle is a prerequi-site to a clean steel on the CC product al-though most of the inclusions created duringsecondary metallurgy will have been elimi-nated by then either by flotation driven byladle stirring coalescence or chemical modi-fication Curtailing furnace slag entrainmentin the ladle mainly at end of tap and re-ducing whatever amount is collected there isalso a prerequisite Obtaining the final cleansteel sold to the user makes it necessary tokeep all the contaminations under carefulcontrol and to allow more NMI eliminationin tundish and mold A complex series ofdetailed technologies is available to do sosome simple add-on features (eg argon in-jection in the sliding gate or the submergednozzle) and other hardwired features likea vertical straight-mold and curved CC formaking low-carbon high-end slabs

All of these steps and measures imply asmuch automatic devices and computer con-trol as possible along with talented and very

201-page 20


experienced operators following strict pro-cedures Mishaps and incidents which areinevitable should be chased relentlessly butthis will always mean that some slabs are di-verted to less demanding applications andthat the whole process is unlikely to everbecome fully automated like an automo-tive production plant can be A continuoustracking of quality from the steel shop to theshipping of commercial steel product rest-ing on the collection of sensor data real-timeon-line modeling has been developed andused in the most elitist steel mills ndash a sort ofprequel to ldquoBig Datardquo

This draws a picture of a mature fieldwhere the technology has been solidly devel-oped and frozen into equipment and prac-tices which has guaranteed systematic ro-bust and stable quality and cleanliness sincethe 1990s Research carries on not so muchto exhibit radically new concepts but to en-sure that the level of competencies and ex-cellence in controlling quality is maintainedat the highest level This means a contin-uous stream of research updating the de-scription of the state of art as it changesincrementally refining the physical under-standing of physical chemical phenomenathrough more and more sophisticated mod-eling and simulations adding more complexsensors along the production lines and inte-grating them into a holistic systemic qualitymanagement system possibly based on ldquoBigDatardquo approaches

On the other hand clean means alsoclean steelmaking ie making sure that theprice to pay for very clean steels is not a dirtyenvironment

Apart from being a different disciplinerun mostly by teams of environmental andprocess engineers clean steelmaking ex-tends across the whole value chain thusfrom the mines to the industrial manu-facturing of goods and eventually to theirend of life their reuse and their recyclingClean steelmaking is addressing a broadrange of complex issues from airwatersoilemissions to raw material and energy sav-ings and more generally societal challengeslike pollution climate change or biodiver-sity conservation and social challenges likeproviding the eco- and techno-spheres with

anthropospheric services and participatingto the enforcement of peoplersquos well-being

Clean steelmaking is handled by tech-nologies which adjust to objectives set byscientists and to quantitative targets set byregulations Note incidentally that the levelof control necessary to make clean steelshelps control steelmaking in general andthus participates in keeping it clean

The general trend is met by compliancerather than by the manic detailed controlthat clean steels necessitate Thus the num-bers describing clean steelmaking are of adifferent nature from those describing cleansteels

The field of clean steelmaking is proba-bly still under construction as the ecologi-cal transition under way to meet the threatsof climate change (low-carbon production)and the need to use resources more spar-ingly makes it necessary to look for solu-tions which are still to be scaled up to TRL9for some and invented from scratch for oth-ers There are also unsolved issues withmine tailings This is a major difference withmaking clean steels

Note also that because technology usesmaterials that are extracted at great energyand logistical costs from natural resourcesindustry creates a stream of secondary ma-terials which needs to be handled with careand differently from the primary stream thatincludes steel Very schematically the pointis to make sure that the concentration ofeco- or human-toxic components in the sec-ondary stream are diluted back into the envi-ronment to the level where the miners foundthem andor treated to alleviate pollution is-sues thus to revert them to a purity definedby the ldquonaturalrdquo state in which they werefound rather than the purity as defined fora clean steel

The holistic nature of the industrial pro-cess thus raises a diverse and complex setof issues an explanandum22 that ought tobe addressed in the future including bydefining it better The storyline of a contin-uous progress does not hold any longer So-cial sciences such as anthropology ethnol-ogy archeology and history will probably

22 An explanandum is a set of basic theoreticalissues that a discipline should strive to tackle andeventually to explain

201-page 21


provide intellectual guidance to move in thisdirection This connects with the endeavor ofthe SOVAMAT initiative [55]

The concept of purity should probablyalso be questioned Steel and materials ingeneral have seemed content in providingpurity and cleanliness to manufacturing in-dustries which strive on complexity andon mixing of very many components intosophisticated but very ldquodirtyrdquo artifacts Onesolution is eco-design a lively active andcreative field

As far as steel is concerned purity maynot be sustainable in the long term becauseraw materials primary but also secondarywill become less and less pure because thecost of purity is more energy and because thepurity may not be necessary for examplecopper which is a poison in steel because ofsurface cracking during continuous castingis no longer a problem (up to 10 [58]) ifsolidification takes place at higher kineticson a strip caster Similarly phosphorous isnow added to new high-end steel for the au-tomotive sector for hot forming and quench-ing (eg ArcelorMittalrsquos USIBOR [59]) Muchmore options are potentially feasible due tothe almost infinite possibilities offered bymetallurgy

This paper is part of a continuing effortto think the activities related to steel and ma-terials in a broader context than that of en-gineering sciences It is a contribution to theSOVAMAT initiative [55] and to the work ofits community presented at the Society andMaterials Conferences It is also part of theeffort to propose a sustainability dimensionto metallurgy and to material science [46]

Acknowledgements

Special thanks to Michel Faral who shared hisdeep understanding of clean steels with me

References

[1] J-P Birat Alternative ways of making steelretrospective and prospective Centenairede la Revue de Meacutetallurgie Paris 9 deacutecem-bre 2004 La Revue de Meacutetallurgie-CITNovembre 2004 pp 937-955

[2] P Brun P Ruby Lrsquoacircge du fer en Francepremiegraveres villes premiers eacutetats celtiques LaDeacutecouverte 2008 p 177

[3] A Testard Avant lrsquohistoire lrsquoeacutevolution dessocieacuteteacutes de Lascaux agrave Carnac nrf eacuteditionsGallimard 2012 p 549

[4] E Bellevrat P Menanteau Introducingcarbon constraints in the Steel sectorULCOS scenario and economic modelingLa Revue de Meacutetallurgie-CIT September2009 pp 318-324

[5] J-P Birat Mateacuteriaux amp Techniques 103 (2015)501

[6] J-P Birat Metall Res Technol 112 (2015) 206[7] J Friedel personal communication 1975[8] J-P Birat Ironmak Steelmak 28 (2001) 152-

158[9] S Ogibayashi Advances in Technology of

oxide metallurgy Nippon Steel TechnicalReport No 61 April 1994 pp 70-76

[10] S Beauvais P Fluzin Archeo Sci 30 (2006)25-43

[11] httpwwwastmSOghibayashiorgStandardsE45htm

[12] YD Yang A McLean Some metallurgi-cal considerations pertaining to the de-velopment of steel quality in Treatise onprocess metallurgy edited by SeshadriSeetharaman Elsevier 2014 pp 251-282

[13] F Ruby-Meyer A Carreacute E HeacutenaultOptimisation of sampling at liquid steelstate and correlative inclusion assessmentof liquid steel for the improvement of highperformance steel grades production pro-cess (SOpliqS) Contract No RFSR-CT-2007-00005 1 July 2007 to 30 June 2010 Final report

[14] AD Wilson Clean Steel technology ndash fun-damental to the development of high per-formance steels Advances in the produc-tion and use of steel with improved internalcleanliness ASTM STP 1361 1999

[15] J Pokorny A Pokorny Inclusions nonmeacutetalliques dans lrsquoacier Techniques delrsquoingeacutenieur Reacutefeacuterence M220 10 juin 1998

[16] JP Bellot Maicirctrise du comportement desinclusions dans les poches drsquoacier liquidendash CIREM ANR 18102013 httpwwwagence-nationale-recherchefrfileadmindocuments2013matetpro2013pres14_CIREM_Bellotpdf

[17] A Guinier Personal reminiscence in Fiftyyears of X-Ray diffraction PP Ewald edi-tor International Union Of CrystallographyJuly 1962 574-578 httpwwwiucrorg_dataassetspdf_file0004769guinierpdf

[18] L Zhang BG Thomas Inclusions in con-tinuous casting of steel XXIV NationalSteelmaking Symposium Morelia Mexico26-28 November 2003 pp 138-183

[19] J-P Birat Continuous casting ndash history ac-tual situation and future prospects ECCC2005 5th European Continuous CastingConference Nice 20-23 June 2005

201-page 22


[20] J-P Birat JY Lamant M Larrecq JPeacuteteacutegnief The continuous casting mold abasic tool for surface quality and strand pro-ductivity Steelmaking Proceedings 1991

[21] J-P Birat C Marchionni ContinuousCasting Past Present And Future ECCC2005 5th European Continuous CastingConference Nice 20-23 June 2005

[22] J Saleil J Le Coze La propreteacute des aciersune longue conquecircte scientifique et tech-nologique de la sideacuterurgie Mateacuteriaux ampTechniques 103 (2015) 506 507 508

[23] X-ray tomography in material scienceedited by J Baruchel JY Buffiere E Maire2000 208 p Hermes science publicationsParis France 2000 208 p

[24] C Gusenba M Reiter J Kastner G KloeschDetection of Non-Metallic Inclusions in Steelby X-ray Computed Tomography and AfterFatigue Testing 11th European Conferenceon Non-Destructive Testing (ECNDT 2014)Prague Czech Republic October 6-10 2014

[25] R Kiessling Met Sci 15 (1980) 161-172[26] L Zhang BG Thomas Alumina inclu-

sion behavior during steel deoxidation 7thEuropean Electric Steelmaking ConferenceVenice Italy Associazione Italiana diMetallurgia Milano Italy May 26-29 2002pp 277-286

[27] T Toriyama Y Murakami T Yamashita KTsubota K Furumura J Iron Steel Instit Jpn81 (1995) 77-82

[28] HV Atkinson G Shi Progress Mater Sci 48(2003) 457-520

[29] DC Hilty DAR Kay Electric FurnaceSteelmak Conference Proc 1985 Vol 43p 237

[30] Y Murakami S Kodama S Konuma Int JFatigue 11 (1989) 291-298

[31] D Quantin Aciers juste de la matiegraveregrise SF2M 1945-2015 70 ans de Meacutetallurgieet de Mateacuteriaux maison de la chimie Paris20 mars 2015

[32] ESTEP web site Ensuring profit and inno-vation httpcordiseuropaeuestepwg1-profit-innovation_enhtml accessed on 27July 2015

[33] J-P Birat Steel Products developmentEuroSteel Master 2015 VII edition 11-15May 2015 Terni Mateacuteriaux amp Techniques tobe published

[34] J-P Birat P Destatte Prospective in-dustrielle et eacuteconomie circulaire concepteacuteleacutegant et reacutealiteacute complexe cours-confeacuterenceau Collegravege Belgique mardi 5 mai 2015 de17 agrave 19 heures Palais provincial deNamur httplacademietvconferencesprospective-industrielle-et-economie-circulaire

[35] Raw Materials Improvement Report 2 April2014 World Steel Association ISBN 978-2-930069-72-2

[36] J-P Birat M Chiappini C Ryman JRiesbeck Revue de Meacutetallurgie 110 (2013) 97-131

[37] B de Lamberterie et al ESTEP-EUROFERSteel production - energy efficiency work-ing group Final report January 2014 ftpftpcordiseuropaeupubestepdocswg7-final-reportpdf

[38] J-P Birat Steel sectoral report Contributionto the UNIDO roadmap on CCS GlobalTechnology Roadmap for CCS in Industrysectoral workshop Abu Dhabi 30 June-1July 2010 httpwwwunidoorgfileadminuser_mediaServicesEnergy_and_Climate_ChangeEnergy_EfficiencyCCSStee_sectoral_20reportpdf

[39] J-P Birat H Lavelaine Steel production ampsmart electricity grids 2014 httpcordiseuropaeuestepdocssteel-production-and-smart-electricity-grids-website2pdf

[40] J-P Birat J Borleacutee H Lavelaine P NeacutegroK Meijer J van der Stel P SikstromULCOS PROGRAM AN UPDATE IN 2012Scanmet IV 10-13 June 2012 Lulearing Swedenvol 1 pp 35-44

[41] Directive of the European parliamentand of the council amending Directive200387EC to enhance cost-effective emis-sion reductions and low-carbon invest-ments European Commission 15 July2015 httpeceuropaeuclimapoliciesetsrevisiondocscom_2015_337_enpdf

[42] httpeceuropaeuclimapoliciesetsrevisionindex_enhtm

[43] J-P Birat Unconventional ways on whichto base the value of CO2 CO2 Economicsseminar ESTEP Brussels 17 September2013 ftpftpcordiseuropaeupubestepdocsco2-economic-seminar-final_enpdf

[44] Best Available Techniques (BAT) ReferenceDocument for Iron and Steel Productionindustrial Emissions Directive 201075EU(Integrated Pollution Prevention andControl) 2013 httpeippcbjrceceuropaeureferenceBREFIS_Adopted_03_2012pdf

[45] L Liu L M Kauri M Mahmud SWeichenthal S Cakmak R Shutt H YouE Thomson R Vincent P KumarathasanG Broad R Dales Int J Hygiene EnvironHealth 217 (2014) 279-286

[46] J-P Birat Sci Technol Steelmak 85 (2014)1240-1256

[47] Water and Steel Research and Technologydevelopment needs ESTEP and WssTPJune 2013 edited by JP Birat 52 p ftpftpcordiseuropaeupubestepdocswater-steel-report_enpdf

201-page 23


[48] J-P Birat C Alzamora S Carler A-CMoonen E Malfa Biodiversity businessand the steel sector ESTEP working docu-ment February 2014 23 p

[49] Convention on Biological Diversity UnitedNations 1992 httpswwwcbdintdoclegalcbd-enpdf

[50] J-P Birat Metallurgy in Society andScientific excellence Invited keynote SFIMetal Production NTNU Trondheim 23June 2015

[51] H Lavelaine JP Birat Eco-design of steelproduction and induced social services8th International Conference on Society ampMaterials SAM-8 Liegravege 20-21 May 2014

[52] N Stern The Stern review the eco-nomics of climate change 576 pages2006 httpsiteresourcesworldbankorgINTINDONESIAResources226271-11709110563143428109-1174614780539SternReviewEngpdf Archived from theoriginal on 31 January 2010 Retrieved 4August 2015

[53] The Economics of Ecosystems andBiodiversity (TEEB) An Interim ReportEuropean Communities 2008 70 p and sub-sequent publications httpwwwteebweborgour-publicationsall-publications

[54] Europe 2020 strategy httpeceuropaeueurope2020index_enhtm and Horizon2020rsquos societal challenges httpeceuropaeuprogrammeshorizon2020enh2020-sectionsocietal-challenges

[55] presentation of the SOVAMAT Initiativewwwsovamatorg

[56] J-P Birat A Declich S Belboom G FickJ-S Thomas M Chiappini Metall ResTechnol 112 (2015) 501

[57] J-P Birat Mateacuteriaux et Techniques 103 (2015)N5

[58] J-P Birat Couleacutee continue de bandesdrsquoacier Techniques de lrsquoIngeacutenieur M78162000 pp 1-20

[59] httpautomotivearcelormittalcomeuropeproductsFR

201-page 24

Steel cleanliness and environmental metallurgy-15mm

Acronyms

Historical construction of the concept of clean steels

Historical narrative

A modern vision of cleanliness

Elements purity and thermodynamic equilibriums

Process tools for cleanliness control

Cleanliness estimation and measurement

Cleanliness steel properties during processing and in use steel quality

Provisory conclusions

Clean steelmaking

Raw material utilization and the circular economy

Energy needs and energy transition

GHG emissions of steel production and transition to a low carbon economy

Air emissions

Biodiversity and more holistic issues

Societal challenges and steel anthropospheric services


Conclusions

Acknowledgements

References


Acronyms

AOD Argon Oxygen DecarburizationAS Anthropospheric ServicesBES Biodiversity and Ecosystem ServicesBF Blast FurnaceBFG BF GasBOF Basic Oxygen FurnaceBOG BOF gasCAS-OB Composition Adjustment by Sealed

argon bubbling with Oxygen blowingCC Continuous CastingCCC Centrifugal Continuous CastingCCS Carbon Capture And StorageCFD Computer Fluids DynamicsCOG Coke Oven GasDH Dortmund-Horder processEC European CommissionEP European ParliamentEU European UnionLCAK Low-carbon aluminum killed steelLIBS Laser Induced Breakdown

SpectroscopyMIDAS Mannesmann Inclusion

Detection by Analysis SurfboardsNMI Non-Metallic InclusionPAH PolyAromatic HydrocarbonsPM Particulate MatterPOC Persistent Organic CompoundRH Ruhrstahl Heraeus processRH-OB RH with Oxygen BlowingSLM Secondaryladle metallurgySAM Society and MaterialsSEV Statistics of Extreme valuesSOVAMAT SOcial VAlue of MATerialsTEEB The Economics of Ecosystems

and BiodiversityTRL Technology Readiness LevelTSC Thin Slab CastingULCOS Ultra-Low CO2 SteelmakingULCOS-BF Ultra-Low CO2

Steelmaking Blast FurnaceUNFCC United Nations Framework

convention on Climate ChangeVOC Volatile Organic CompoundVOD Vacuum Oxygen Decarburization

a core structural material of society and akey part of its evolving technological epis-temes has been constantly at work in thesechanging times of demographic and eco-nomic explosion

Other materials like wood and concretedemonstrate similar features but only steelexhibits such universality

This role of steel is bound to continuein the future and the only questions openare the exact years when production level

passes the 2 billion ton threshold and thenthe 3 billion one [4]

Iron and steel went through manytransformations during this long historicalprocess and their properties as well as thetechnologies used for making them havetransformed congruently by several ordersof magnitude If steel is an invariant of thetechnological epistemes of society it is be-cause of its plasticity to adapt to changingtimes and changing needs This is what iscalled today in European Commission (EC)speech a Key Enabling Technology (KET) ndashadvanced materials are the relevant KETwhich introduces the idea that new materi-als are being invented continuously but alsothat existing ones are being refined refor-mulated and changed just as continuouslyA former expression used by the EC was thatof cumulative technologies thus emphasiz-ing that materials like steel demonstrate apawl and ratchet effect where features ac-cumulate and do not vanish as they wouldin a marketing product of limited life

In a holistic vision steel partakes of theanthroposphere1 and of the biogeosphereand it circulates between both it is thusnot simply part of the anthroposphere orof the technosphere In simpler economicterms the matter is the circular economy ofwhich the EC is fond nowadays Steel is usedto mark frontiers separations between arti-facts society and nature [5] (cf further ldquoSo-cietal challenges and steel anthroposphericservicesrdquo)

Steel originates from earths concentratedinto usable ores from energy resources andfrom reducing agents and other fluxes allfrom the geosphere and it enters the tech-nosphere to become metallic and alloyedwhile the ldquoganguerdquo is separated out of themajor element iron to become a by-productsolid (slag dust mill scale etc) gaseous(eg COG BOG BFG etc) sometimes liquid(pickling solution etc) or mixtures of these

1 The anthroposphere is the physical symbolicand cultural part of the planet where mankindlives and which it has transformed to create itshabitats through arts crafts and technology It isalso called society or technosphere The expres-sion originates from scientific ecology and geog-raphy Many disciplines like most of the socialsciences are interested in the anthroposphere andthus use different words to refer to it

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steel cleanliness and environmental metallurgy

Documents