Future Steel Buildings

8/12/2019 Future Steel Buildings

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Future Steel Buildings/Introduction

Introduction

What is steel?

Steel is an alloy that consists of iron and carbon. Carbon content added tosteel depends on the grade of steel and typically ranges from 0.2 to 2.1 %.Carbon is mostly used for alloying ith iron but a number of other alloyingelements ha!e also been used such as manganese" chromium" !anadium andtungsten.

Carbon and other elements function as hardening agents pre!entingdeformations of iron atom crystal lattice. #he in!ention of Bessemer processin the mid 1$th century impro!ed steel production methods. Furthermodifications ere made in the process to ma e it cost effecti!e and producesteel of better &uality.

'odern processes ma e steel ith different combinations of metal alloys toproduce steel ith different properties for !arious purposes" such as(

Carbon steel is composed of mainly carbon and iron. It ma es up $0 %of steel production.

)igh Strength lo alloy steel *)S+,- has small additions of otherelements such as manganese to increase steel strength.

+o ,lloy steel uses alloys of manganese" chromium" nic el ormolybdenum to impro!e the hardness of thic sections.

Stainless Steel uses 11 % chromium usually combined ith nic el toresist rust formation *corrosion-.

What are steel structures? Steel buildings are metal structures made of steel. #hese metal structures canbe used to build offices" hospitals" homes" schools" arehouse and

or shops. #hese steel buildings ha!e gained popularity orld ide. #he useof computer aided design technology has gi!en a ne dimension to buildingdesigns. #he future steel buildings can be assembled easily as most of thesteel components are pre engineered. uts and bolts can be fi ed in thespecified holes and the structure can be made in minimum time ith lesslabor. ersonali ed commercial and industrial buildings can also be made" assteel is no a!ailable in different colors and shapes.


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Steel has become the leading choice as construction material due to itsnumerous ad!antages o!er other building materials. #he steel functions as as eleton for the building. It performs all the functions a human s eleton does.Steel helps eep the building standing tall. It pro!ides strength to thestructure. In addition" steel pro!ides resistance against harsh climatic

conditions and gi!es a slee appearance to the structure. 'aintenance of thesteel structure is easier compared to if concrete is used for the same purpose.

Properties of Structural Steel

Follo ing properties of structural steel are considered before using them for aconstruction. #hese properties are useful for determining the &uality of steel.)igh &uality steel is used so that dependable and long lasting construction ispossible. #he most important components include the follo ing(

1. Density

3ensity of a material is defined as mass per unit !olume. Structuralsteel has density of 4.45 to 6.1 g/cm7.

2. Elastic Modulus

8lastic modulus or modulus of elasticity is the measurement oftendency of an ob9ect to be deformed hen force or stress is applied toit. #ypical !alues for structural steel range from 1$0 210 gigapascals.

3. Poisson's RatioIt is the ratio bet een contraction and elongation of the material. +o erthe !alue" lesser the ob9ect ill shrin in thic ness hen stretched.

,cceptable !alues for structural steel are 0.24 to 0.7.

4. Tensile Strength

#ensile strength of an ob9ect is the determination of limit up to hich anob9ect can be stretched ithout brea ing. Fracture point is the point at

hich an ob9ect brea s after application of stress. Structural steel has

high tensile strength so is preferred o!er other materials forconstruction.

. !ield Strength

:ield strength or yield point is the stress at hich an ob9ect deformspermanently. It cannot return to its original shape hen stress isremo!ed. Structural steel made of carbon has yield strengths of 164 to456 megapascals. Structural steel made of alloys has !alues from 7;;to 14$7 megapascals.

". Melting Point


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#here is no defined !alue for melting point due to the ide !ariations intypes of structural steel. 'elting point is the temperature at hichob9ect starts to melt hen heated.

#. S$eci%ic &eat

Specific heat or heat capacity is the amount of heat hich needs to beapplied to the ob9ect to raise its temperature by a gi!en amount. ,higher !alue of specific heat denotes greater insulation ability of theob9ect. ilogram >el!in. Structuralsteel made of carbon has !alues from ?50 to 2061 and that made fromalloys has !alues ranging from ?52 to 1?$$.

. &ardness

)ardness is the resistance of an ob9ect to shape change hen force isapplied. #here are 7 types of hardness measurements. Scratch"indentation and rebound. Structural steel made by using alloys hashardness !alue bet een 1?$ ;24 >g. Structural steels made of carbonhas !alue of 6; to 766 >g.

Steel in Construction Industry

@sing steel as construction material is not only limited to industrial buildings ortemporary shelters. Steel has established itself as one of the most !ersatileconstruction materials a!ailable for use. It has become a popular choice dueto its durability" strength and resilience.

Steel is also called as a green product. Concrete and ood cannot be reused"steel can be recycled thus is more cost effecti!e.

Advantages of Using Steel

Steel buildings can be produced and engineered faster than con!entionalbuildings. re engineered steel has cut do n the cost and labor. Constructiondoes not re&uire long times. #he material can be shipped to the location and

9oined together to ma e a strong structure.

Steel buildings are able to ithstand the natural disasters. 8arth&ua es"cyclones" hurricanes" sudden climatic changes can stri e anytime. @se ofconcrete can cause a number of causalities. ,lso damages caused to theconcrete structure need a lot of money to be repaired. Steel is cost effecti!eand resilient.In addition#ermites" rodents and insects cannot house in steel.#his ill reduce the sufferings of many people ho spend loads of money onfumigations.


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Since steel is lighter but has more tensile strength" it can be used ith otherconstruction materials if needed. #hese steel structures ha!e more fle ibilityas compared to other building materials. Components can be shifted from oneplace to the other ithout difficulties. :ou can e!en add space by e tendingthe structure.

Grades of Steel Classification of steel in different grades is based on their chemicalcomposition and physical properties. It has been de!eloped by many standardorgani ations.

Society of ,utomoti!e 8ngineers *S,8- steel grades. British Standards. International Argani ation for Standardi ation *ISA- ,S#' International =apanese steel grades =IS standard ermany steel grades 3I standard China steel grades B standard

Structural Steel Structural steel is made from high strength lo alloy *)S+,- steel. )S+,

steels are different from other steels in the ay that they are made accordingto specific mechanical properties not chemical composition. #his type of steelis used to produce shapes" structural bars and plates hich are used forbuilding and bridge construction. Structural steel has high strength and isfle ible.

#ypical carbon content of )S+, steel is 0.05 0.25%. Carbon is included forsteel to retain its eld ability. Ather alloy elements include up to 2 %'anganese and small &uantities of copper" nic el" calcium" chromium"!anadium and titanium. #hese elements are added to strengthen steel andincrease resistance to corrosion. Structural steel is formed using heatanalysis.

Structural steel shape" composition" si e" strength and storage are regulatedin most industriali ed countries. Steels used for building construction in the@S are identified and specified by ,S#' International.

Before proceeding ith the building design" figure out the e act purpose ofconstruction. 'ost of the time greater attention is paid to the final loo of the

building" not the purpose for hich it has to be built. It is important to consider


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ho big and tall a structure needs to stand. #he time for hich building needsto be used is also an important factor.

If the building needs to be used for long periods" steel is a good choice. It ill

gi!e greater strength and durability. Steel does not bend" brea or t ist ithincreasing load. Changes can be made !ery easily to the steel structure.

re engineered steel used for construction these days has pre defined pointsat hich bolts need to be fi ed.

#he most impressi!e feature of steel is that it is recyclable and is !eryen!ironmentally friendly.

'ost steel buildings used for offices or e!en apartments are located on busystreets of the city. It becomes more important to consider the safety of theresidents and people a ing around these structures. Structural fla s need tobe a!oided at all costs.(uilding Design

#he design of a modern building in!ol!es a team of e perts from differentdisciplines. #he team needs to communicate clearly to a!oid any undesiredoutcome at the end of the procedure. #he concept of the final design of thebuilding starts ith a dra ing. )ere the architecture comes into action.3esigners *architects- start ma ing ne dra ings and s etches. , roughdesign is made initially. ,ny problems in the design need to be corrected inthe early stages. ith support from the structural engineer" the compleprocedure of dra ing a building structure can become easier.

#here are t o basic parts of a building design. First is the aesthetic andsecond is practical. #he physical and !isual appearance of the building needsto be attracti!e. It ill influence the perception people ha!e of the building.#he practical aspect of the building design is mainly concerned ith the spaceallotment for different acti!ities. It includes entry and e it of people" lighting"acoustics" legal matters and building codes.

Computer ,ided 3esign *C,3- is idely used computer soft are to createtechnical dra ings. #here is no need to ma e the dra ing on paper. , 73model of the building can be made using C,3.


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Steel Frame

, steel frame refers to the building techni&ue ith a steel s eleton.


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adaptability and insensiti!ity to faulty manipulation possessed by mild steel.#hese steels may be used in the hot rolled condition.Four characteristics are important(*1- yield strength for design

*2- notch ductility to a!oid brittle fracture*7- eldability*?- cost.From the point of !ie of cost" therefore" &uench and tempering processes onthic plates and sections are usually ruled out. )o e!er" the installation ofspecial e&uipment" such as roller &uench presses" may ma e the techni&uean alternati!e to e pensi!e alloy additions.Further" although illed steels are established in 8uropean technology"balanced steels remain in fa!or in @> because hot top practice is not idelyused and a greater yield is obtained in balanced steels. Increased use ofcontinuous casting may affect this in the future.#he most popular types are those ith manganese raised to 1.7 1.4% ithcarbon 0"2 0"?%" but for elding the carbon is ept lo . #he ,mericanECorten ,E Steel has a composition of C" 0.12 Si" 0.5 Cu" 0.5 Cr" 0.6 " 0.1and 'n" 0.5%. ,lthough the tensile strength is less than ?$? ' a the yield isin the region of 741 ' a.#he combination of copper and phosphorus also increases the resistance toatmospheric corrosion hich is important hen thinner plates are used. #heoriginal steel E,E suffers a decrease in yield strength and notch ductility inthic ness o!er 25 mm" to o!ercome hich ECorten BE as de!eloped C 0.1?

0.0? 'n 1.1 Cr 0.5 Cu 0.? < 0.1 Bol ,l 0.02.#he addition of 0.5 nic el and 0"25 % molybdenum to a manganese steelgi!es a good general purpose steel *465 ' 1$-. Forti eld steel containing 'o"0.5 B" 0.007 C" 0.11%. has a #S of ;16 ' a and is readily elded since ittransforms in the bainitic region.Pearlite Reduced Steel. earlite increases the tensile strength but not theyield stress" and since it raises the brittle ductility transition temperature" thereis a good case for reducing the carbon content. +o carbon steels *G 0.15%-strengthened ith 'n H b and control rolled ha!e good eldability andtoughness and are called earlite educed Steel * S-.

Grain refinement% 3ecreasing the ferrite grain si e significantly increases both yield strengthand notch ductility ithout increasing the carbon e&ui!alent" hich affects

eldability. #he relation of yield strength y to structure is gi!en by the etche&uation( y J i H > y d 1/2

Fine grained steels using ,l ha!e to be produced as illed steel ith lo*production- yield *BS 503-. iobium and !anadium ha!e a lo er affinity foro ygen than aluminium and can be used in semi illed steels" an economicad!antage. Since 1$;0 about 0.70 0.1% b forming b7C? has beenincreasingly used as a grain refiner and precipitation hardening element and


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is the basis of se!eral eldable steels in BS ?7;0" replacing $;6 44;2 740;"and includes ? tensile ranged *?0" ?7" 50" 55 h bar- ith se!eral sub grades

hich are distinguished by increased stringency of yield stress and notchductility re&uirements. Both ladle and product analyses and carbone&ui!alents are included .

Precipitation &ardening%In iobium steels b?C7 dissol!es abo!e 1250KC" large grains and

subse&uent precipitation hardening is pronounced" but brittle transitiontemperature is high. ormalising at $00 $50KC forms a precipitate" resulting ina grain refined steel" slight precipitation hardening" but lo impact transitiontemperature.

By controlled hot rolling from 1250KC to a lo finishing temperature *$00KC- ith a substantial amountof deformation in range $50 650KC" a fine ferrite grain si e is obtained insections up to 25 mm" ith a minimum yield of ?;7 ' a due to dispersionhardening occurring in the ferrite during cooling.#hic plates present difficulties in getting the re&uired drop in rollingtemperature. )olding at an intermediate temperature produced a partiallyrecrystallised structure of large grains surrounded by small ones. #he finalstructure is of !ery mi ed si e ith poorer mechanical properties.It is possible to &uench similar steels from 1050KC to form a lo carbonmartensite or ith lo er carbon content" acicular ferrite follo ed by temperingto gi!e higher properties. icuage steel" C" 0.0;" i" 1" Cu" 1.1" b" 0.02" 'n"0.5 rolled and aged at 500 540KC has a yield of ;00 ' a and a tensilestrength of 400 ' a" elongation 27% and 7? 62 =oules charpy < notch impactat 20KC coupled ith good eldability and corrosion resistance.

Steels Above 680 MPa Tensile

elati!e to the steels 9ust discussed" those in this group are designed solelyfor their mechanical properties" hich depend on accurately controlled heat

treatment.In 1$?1 BS $40 co!ering bars" billets and forging in this strength rangerationali ed steel specifications to conser!e essential alloys. #he basicprinciple as the specifying of mechanical properties related to si e of bar

hen heat treated rather than chemical composition. #he cheapest steel illde!elop the re&uisite properties in the limited ruling section of the componentused although other factors may modify the choice such as forgingcharacteristics and die ear" machinability and ease of heat treatment.Suitable compositions ithin the range ha!e to be chosen in relation to mass.#hus nic el alone has a lo efficiency in spite of its pre ar popularity. ,conception ne to many engineers is that the actual steel used for a gi!entensile strength depends on the size of the article at the time it is heat-treated .


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In 1$40" BS $40 as re!ised and the 8n designation as replaced by a sidigit system. #he first three digits refer to alloy type" the fifth and si th digitsrepresent 100 times the mean carbon content. ,t the fourth digit letters" ," 'and ) indicate if the steel is supplied to analysis" mechanical property orhardenability re&uirements" hich are the ne alternati!e methods.

Ultra'high (ensile Structural SteelsInterest in *15?? 21;0 ' a- tensile steels for use in the aircraft industry isleading to the de!elopment of modified steels hich can be used up to ?00KCin supersonic aircraft and hich possess ade&uate ductility and notch impactstrength.


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$araging Steels#hese use the martensitic reaction hich end high hysteresis occurs in Fe ialloys. #hey are iron based alloys containing 16 i 6 Co 5 'o ith smallamounts of ,l and #i and less than 0"07% C" hich ma es such a differenceto fracture toughness and ease of elding. #he strength is maintained ithincrease in section thic ness and also up to 750KC. ,lloy cost is balanced bylo er production cost" !irtually no ris of decarburisation" distortion orcrac ing. #hese steels are used for air frame and engine components"in9ection moulds and dies.An cooling from the austenitic condition the alloy transforms to a fine lath typemartensite" and precipitation hardening is induced by EmaragingE at ?60KC.'any types of precipitates ha!e been reported *e.g. i7#i,l- but the mainhardener is probably orthorhombic i" 'o" the solubility of hich is probablyreduced by Cobalt. #he steels ha!e high fracture toughness" >Ic due to acombination of fine grain si e of the martensite and the high dislocation

density" leading to fine precipitation. #he steels can be nitrided. #he corrosionresistance is only slightly impro!ed but the 12% Cr !ariety has beende!eloped for corrosion resistance.

&air-line *rac s'any alloy steel ingots and large forging are susceptible to the formation ofsmall sil!ery crac s or fla es in their interior. #hese crac s often form at roomtemperature after an incubation period and the cause of them is notcompletely no n but is related to the crac ing of elded hightensile steels inthat hydrogen has a large influence in promoting embattlement hich

increases ith the tensile strength of the steel. +ess trouble is e periencedith acid open hearth steel *usually containing ? cc per 100 gm- than ith

basic electric steel containing about ; 6 cc per 100 gm of hydrogen in theladle. Slo cooling and also isothermal transformation at about ;00KC tendsto reduce the incidence of hair line crac s and this is materially assisted bythe !acuum melting. #o reduce the abo!e hydrogen concentrations to about 1cc per 1 00 gm re&uires beat treatments of the follo ing magnitude at ;50KC(

Dia bar (metre 0.0 ! 0. ! 0.! "

Hours " "00 #00 "$00#he problem is therefore more acute ith large ingots.

Alloy spring steels of the chromium !anadium *Cr" 1


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been formed" the springs" *a" b" c- are only gi!en a lo temperature temper*140 700KC- to relie!e forming stresses.d- ,nnealed steel. ,fter ha!ing been formed" the spring is then &uenched andtempered. ,ll hea!y springs are formed hot and fre&uently hardenedimmediately after forming. ,ero engine !al!e spring steel must be free from

any ind of surface defect. Springs for atches and aircraft instruments"Bourden tubes" diaphragms etc. are often made from i span containing ?2

i" 5 Cr" 2"7 #i" 0"02 C" 0"55 ,l hich has lo mechanical hysteresis and canbe heated to reduce the effect of changes in ser!ice temperatures.Faults in springs are due to(1- 3ecarburisation due to annealing" etc." affecting the fatigue properties.2- Segregations forming lines of ea ness in the material hich may open upinto splits in ser!ice.7- Internal cup and cone fractures due to o!erdra ing.?- 'echanical damage" such as rolling laps" deep groo!es" scratches due to

ire dra ing" !ice mar s and scoring due to inding.5- Incorrect tempering" especially in chromium !anadium steels.

&igh and )o (hermal *+pansion Steels#here are cases in engine construction here steel has to or in con9unction

ith light alloys" such as cylinder head bolts" !al!e seating" or cylinder linersin aero engines. #he comparati!ely high thermal e pansi!ity of aluminiumleads to looseness unless the steel has a similar coefficient of e pansion. #heaustenitic steel of the follo ing compositionC" 0"5$ i" 12 'n" 5"1 Cr" 7"?has a thermal e pansion of 0"000021 per degree C up to ?00KC" hich is onlyslightly lo er than that of aluminium" and it combines good mechanicalproperties ith resistance to abrasion.Cold rolled austenitic stainless steel is another alternati!e. here anabnormally lo coefficient of e pansion is re&uired" In!er" containing 7;% i"is used.

(all-race steel . , typical composition is C" 1"0 'n" 0"5 Cr" 1"7;%. ,fter&uenching in oil from 610KC the steel is usually tempered at 100 200KC toa- reduce hardening stresses"b- reduce crac s in grinding.#empering at 100KC also increases the hardness slightly" e.g.(#empering temperature nil 100 200 250 < 600 64; 450 47;

Creep'resisting Steels for Use at Steam (emperatures#he use of higher temperatures and pressures in modern po er stations hasnecessitated the use of special steels for the pipe lines and other parts. #heessential characteristic of these steels is higher resistance to creep attemperatures !arying from ?00K to 5;5KC. , common steel used for this

purpose is one containing appro imately 0"55% molybdenum ith a carboncontent of appro imately 0"15 0"2%.


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Failures of pipes ha!e occurred in ,merica" hich ha!e been traced to theformation of a net or of graphite in the heat affected one of the pipead9acent to the eld. )eating the steel to appro imately 450KC appears toaccelerate the formation of this graphite" hich is also largely affected by theprocess of ma ing a steel" particularly as regards the use of aluminium as a

deo idi es" hich is more commonly used in ,merica than reat Britain. Ithas been found that a small addition of a carbide stabili er" such as 1"0%chromium" is beneficial in minimi ing this trouble.#he addition of 25% < raises the creep resistance still further. #he 1% Cr 'o< steels currently in use are chiefly of t o types" those for steamchestcastings here due to elding considerations the carbon le!el is limited to0"5% and those used in ) /I rotors in hich the need for impro!edhardenability ith large rotors has necessitated carbon le!els of 0"25 0"70%.Creep seems to be related to the uniformity of the


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,evelopments in the Processing of Alloy andStainless Steels for (ur-ine Blading andBolting Applications

A-stract

#he ma9ority of special steels for turbine applications are made by the electricarc furnace route. Careful selection of ra material is necessary to ensureundesirable residual elements are ept to a minimum. Secondary refiningtechni&ues such as !acuum arc degassing and ladle furnace technology"coupled ith impro!ed casting methods" ha!e gi!en significant &ualityimpro!ements so that it is no possible to use air melted steels to replace

remelted steels in many applications ith resultant cost sa!ings. Closecompositional control and uniform heat treatment ha!e impro!ed theconsistency of the finished product.

Introduction

Steel played a significant role in the early stages of turbine and 9et enginede!elopment and retains its dominant role as the first choice material forblading and bolting in steam turbines and the compressor section of landbased gas turbines. Steel still has its part to play in current 9et engineconstruction in the form of shafts" gears" bearings and rings but has no beenreplaced as a turbine blade material in ne designs. #he ma9ority of installedsteam turbine e&uipment po ered by fossil fuel boilers operates ith ama imum steam temperature in the range 570 5;5KC" nuclear boiler steamtemperatures are in the range 750 550KC. #hus steel must be adaptable andoperate o!er a ide range of temperatures from 5;5KC do n to near ambienttemperatures.

#he increasing si e of turbines has placed greater demands on the integrity ofthe steel used as components become larger" rotational speeds increase andcontainment forces rise. 3e!elopments in steel production and inspectiontechni&ues o!er the past 20 years ha!e gi!en significant impro!ements inconsistency and integrity to satisfy the increasing e pectations of the turbineindustry. #he ma9ority of steels used in turbines ha!e been specifically


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de!eloped to cater for the !ariety of ser!ice temperatures" stresses" pressuresand corrosi!e conditions that e ist in the turbineDs en!ironment anddemonstrate the adaptability of steel as a material. )o e!er" the ide rangeof steels in a turbine often means that each type is anted in a !ariety ofsections and product forms" conse&uently order &uantities per grade and si e

are small and production is predominantly !ia the fle ible electric arcsteelma ing and ingot cast route follo ed by rolling to the desired profile.

*lectric Arc $elting

#he si e and po er rating of electric arc furnaces has continued to increasesuch that many units are no in the $0 to 160 tonne range ith po er ratingsup to 120 '


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During slag free tapping from the arc furnace into the ladle a cleansynthetic slag is added to maintain low oxygen levels which is necessary ifinclusion levels are to be minimised and a consistent yield from ferro alloysadditions is to be achieved. The composition of the slag is controlled toachieve the desired sulphur level. Heating is provided by three electrodes,see fig. 4, and enables precise temperature control. Inert gas bubbling isused to stir the molten steel and promote better mixing of the steel andalloying additions and to homogenise temperature. Turbine steels oftenhave a complex, carefully balanced composition to optimise properties.Close analytical control is therefore important to ensure that every castmeets tight composition ranges and to ensure that cast to cast variability isminimised hence giving consistency in downstream processing

characteristics and service performance. The ma ority of ladle furnaces aree!uipped with computer controlled, conveyor fed, metered alloyingsystems which give precise alloy additions. Coupled with the fact that theuse of a synthetic slag gives a predictable alloy yield in the molten steel thisgives much more accuratecompositional control. "t the end of secondary steelma#ing very gentlestirring promotes the flotation ofinclusions leading to a clean product. $adle furnaces may also have a

vacuum facility and thistype of unit is generally known as a %acuum arc degassing (&'D unit.


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Future developments and applications ofnitrogen-bearing steels and stainless steels

1. Introduction

%&erba volant, scripta manent', so thought the (omans for whom the fateof speech was to y away and to disappear in the general noise, in

contrast to that of writing that was li#ely to stay. )ecause this $atin
http://www.google.co.in/url?sa=i&rct=j&q=ladle+furnace&source=images&cd=&cad=rja&docid=dEebezoGbEm4cM&tbnid=VSvl2aGpG3YLLM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.substech.com%2Fdokuwiki%2Fdoku.php%3Fid%3Dladle_refining&ei=OU4nUdrqBK3MmgXWroHAAQ&bvm=bv.42768644,d.bmk&psig=AFQjCNGvcCX4UfZ6W-rcpcqD3kxKPQByag&ust=1361616770380453


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sentence was %written' much before *utenberg and the Internet, theerosion of %scripta' was not so well+established, although even now somepeople believe that what is simply written is in fact engraved inunperishable marble. Doubts about thiseternity can be expressed and therefore it is worth ta#ing the ris# todocument the future of high+nitrogen steels H- /. This exercise demandsat the same time several contradictory !ualities0 prudence andimprudence, modesty and pride. This precautionary paragraph offers theright if not the duty to abandon a cautious attitude in order to explore stillundiscovered elds. " strict, rigorous and scienti c process is to be

replaced by a %soft' philosophical andimaginative approach. 1eanwhile, this approach needs to be supported by

more arguments and observations 2 the basic principles of physicalmetallurgy and materials sciences 2 some of the results and interpretationshave already been published. Trends in steel ma#ingand technology as well as the attitude of the global society are to someextent more ris#y to decipher and base predictions on. "fter a reasonableattempt to deduce generic trends, some special domains where nitrogenalloying could be promising are listed and commented upon in this paper.

2. Deciphering of global trends likely to inuence futuredevelopments of !S

ociological, political, economical studies brought out many aspects aboutthe present evolution of society0 globalisation, ef ciency, exibility and

contradiction. " rather important ignorance about these domains has tobe admitted by the author, who proposes a caricatural resume of theattitude of society in many parts of the world, as depicted by a cartoonwhich shows a top tribune triumphalanty announcing %-ow you goteverything', and to whom the crowd answers, %3e demand everythingelse'. This anecdote is rather consistent with the very common feelingaccording to which society simultaneously desires one thing and itsconverse0 ris# and security, !uality and cheapness, e!uality and privilege.Despite the dif culty in evaluating the impact of these human factors on

the future of H- many demands ofsociety may in uence positively the development of H- .

afety in the eld of transportation cables for telphers, blades of

reactors, landing partsof aircraft, wheels for trains, bodies for cars, double shells for fuel tan#ers.


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5nvironment+friendly technologies safety in oil pipelines, oilexploration.

afety and reliability of industrial plants and e!uipment mechanicalindustry, car industry, nuclear reactors, control devices, cutting machine,paper industry.

(eliability and new possibilities in civil engineering and structures. $eisure and sport industry high demand for extreme mechanical

resistance and lightness/. Defence and space industry.

"ll the possible niches afforded to H- by above domains correspond tohigh mechanicalresistance yield stress, ultimate tensile stress, ductile2brittle temperature

transition, fatigue life, critical stress intensity factor, ductility/ andincreased corrosion resistance pitting corrosion, crevice corrosion, stresscorrosion, corrosion fatigue/, i.e. all properties for which the addition ofnitrogen is found to be bene cial. The industrial society also imposes some constraints to the development of H- and even poses some obstacles.Constraints are related to price, availability of materials need for differentsuppliers/, well+established !uali cation and norms, data ban# of

properties.

These constraints suggest that there exists some sort of threshold that hasto be overcome for spreading the applications of H- over a wider range.Time scales of economics and research do not always coincide. Time scalein industrial management results from the actualisation of assets, expensesand revenue. ince the re!uired time to nalise new H- grades, protocol

of use and implementation is decreasing with new techni!ues ofmodelling and simulation, and because some clear and appreciableadvantages from the usage of H- are established, matching the two apriori different time constraints is far from being insurmountable.6bstacles are also related to inertia and intellectual la7iness which havesome conse!uences on education and research. The probable and implicitreasoning which leads to this attitudeis based on a biased interpretation of the #inetics of evolution of anydomain according to which an +shaped curve would be followed see

gure 8/. If axes are considered in arbitrary units, any domain is e!uivalent

to the other. If in contrast with this view relevant units such as gross globalproduct .9 : vs:time .t: is considered, domains for which the derivative d9;dt


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decreases may be much more promising than other domains with largerderivatives, and this because the residual potential of growth of a domainsuch as steel considered classical, may still be large. 3hat is observed ineconomics is also shown by research, it would appear more fruitful toexplore a new promising domain rather than a more classical one and thisbecause the return publication, advertisement/ is fast. 1eanwhile othervery speci c demands for already existing grades of H- or new grades

li#ely to be developed in the future also exist in the following disciplines. )iomaterials necessary for new prostheses arti cial heart, arti cial oints

and bones/ Complex devices such as activators for which a functional propertymagnetic, shape memory effect, chemical property, electrical

property 0 0 0/ is coupled with the mechanical and corrosion resistance of anitrogen+containing alloy H-"/.

-anotechnology development also needs new high performancematerials such as nanostructured H- and nitrocermet nitride ceramic2metal composite/.". Scienti#c foundations of !S

In contrast with most other alloying elements which under %normal'

conditions are in solid or li!uid state, nitrogen is gaseous. This results fromthe stability of the -< molecule which is also consistent with the fact thatno natural nitride appears to exist. In order to achieve nitrogen alloying it istherefore necessary to utilise a nitrogen source in which the chemicalpotential of nitrogen source- is higher than that of the alloy alloy - .)ecause the gas phase is nearly always present in an elaboration process,gas - has to be at least e!ual to that of the source "-

? * D gas? D source?" D alloy0


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1eans to control*-?

- and"- are0 pressure of gas phase, temperature, decomposition ofnitrogen+containing molecule .-H@? 0 0 0/ plasma, composition of theslag 0 0 0 composition of the base metal 0 0 0 see gure


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Ee-, 1n-/ nitrides is li#ely to provide a very elegant and ef cient means to obtain near net+shape parts of hard H- . "nother method which can stillbe considered to be reliable is mechanical alloying which has been provento be ef cient in the preparation of different grades of H- . 1echanical

alloying can also be used very effectively in the preparation of nitrides withhigh melting temperatures


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micromechanisms it is observed that the =28A - composition range whichis considered to be relevant for steel ma#ing, a considerable number ofdifferent steel grades with very different properties are worth thin#ingabout. It was shown


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of nitrogen on basic mechanisms involved in the alteration of mechanicaland corrosion properties is considerable and varying. Therefore a widerange of compositions and microstructures of H- would be necessary tocharacteri7e the properties. Eor effective utili7ation of H- grades, adataban# concerning thermaland thermomechanical treatments, microstructures, properties arenecessary. imulation and automatisation of experiments dramaticallyreduce the time necessary to achieve a programme of certi cation.

-umerical simulation performed for different time scales and length scalesJit means at the atomic scale ab+initio, molecular dynamics, 1onte Carlo/,the mesoscopic scale phase eld, 1onte Carlo, 0 0 0 /, macroscopic scale

nite elements, thermodynamics codes, 0 0 0 /K and the coupling of these

codes now allows us to achieve virtual experiments @F Eoct whichreplace real ones completely. Therefore the re!uired time which separatesthe idea from the mar#eting of the new steel, as well as other newmaterials is vanishing dramatically.

$. %ctual& future and possible applications

Industrial applications of existing austenitic, martensitic and duplex H-

have been described by peidel in his boo#. H- nd applications in

chemical industry, transportation, ship yard biomaterials, sportinge!uipment, environment+friendly technology. Hard and wearresistant H-are li#ely to be used for cutting tools or for erosion+wear resistant parts.1any applications for H- are li#ely to emerge such as, high temperature+resistant alloys in casethe Ti Gr, &, -b, Cr, 1o content is high/, nanostructured H- , compositenitricermet, parts of actuators, some shape+memory alloys, nitrides withvery high saturation magnetisation. Ee8F-


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applications of H- and H-" high nitrogen alloys/ to ta#e advantage of aspeci c property improvement resulting from nitrogen addition.

'. (onclusion

"lthough ceramics and metallic materials are different, similarbrea#throughs resulted from nitrogen alloying0 in the rst case

%hybridation' of oxides "l

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