KeluliDaripada Wikipedia, ensiklopedia bebas.

Keluli jambatan

Kabel keluli yang digunakan di menara lombong batu arangKeluli, juga dikenali sebagaibesi bajaataubesi wajaadalah sejenisaloiyang bahan utamanya ialahbesi, dengan sedikit kandungankarbondi antara 0.02% dan 1.7 atau 2.04% mengikut berat (C:100010,8.67Fe), bergantung kepada gred. Karbon adalah bahan sebatian paling murah dan berkesan bagi besi, tetapi pelbagai unsur sebatian lain yang turut digunakan seperti manganese dan tungsten.[1]Karbon dan unsur lain bertindak sebagai agen pengeras, menghalang kerawang kristal (crystal lattice) dalam atom besi berpisah dengan tergelincir sesama sendiri. Jumlah unsur sebatian yang berbeza dan bentuk kehadirannya dalam keluli (unsur solute, fasa precipitated) mengawal kualiti seperti kekerasan, kelenturan, dan kekenyalan keluli yang terhasil. Besi dengan peningkatan kandungan karbon mampu menjadi lebih kukuh dan kuat berbanding besi , tetapi ia juga lebihrapuh. Maksima kelarutan karbon dalam besi (di kawasan austenite) adalah 2.14% menurut berat, berlaku pada 1149C; kandungan karbon yang lebih tinggi atau suhu yang lebih rendah akan menghasilkancementite. Sebatian besi dengan kandungan karbon lebih tinggi dari ini dikenali sebagaibesi tuangkerana kadar leburnya yang lebih rendah.[1]Keluli juga dibezakan daribesi tempa (wrought iron)dari segi kandungan yang mengandungi hanya sejumlah kecil unsur lain, tetapi mengandungi 13% slag menurut berat dalam bentuk partikel memanjang pada satu arah, memberikan ciri-ciri urat besi. Ia lebih tahan karat berbanding keluli dan lebih mudah dipetri. Tetapi pada masa kini istilah ini jarang digunakan dalam industri keluli. Ia merupakan perkara biasa pada masa kini bagi merujuk 'industri besi keluli' seolah-olah ia satu entiti, tetapi dalam sejarah ia merupakan keluaran yang berbeza.Sungguhpun besi telah dihasilkan melalui pelbagai kaedah tidak efisen lama sebelumRenaissance, kegunaannya lebih biasa selepas kaedah lebih efisen dicipta pada abad ke-17. Dengan ciptaan proses Bessemer pada pertengahan abad ke-19, besi menjadi barangan keluaran pukal yang murah dari segi perbandingan. Peningkatan lanjut dalam proses tersebut, seperti penghasilan besi asas oksijen, menurunkan lagi kos penghasilan sementara pada masa yang sama meningkatkan kualiti logam. Hari ini, keluli merupakan salah satu bahan yang biasa didapati di dunia dan merupakan komponen utama dalam pembinaan bangunan, perkakasan, kereta, dan peralatan utama. Keluli moden biasanya dikenali menurut gred keluli yang ditakrifkan oleh pelbagai organisasi piawaian.

Isi kandungan[sorokkan] 1Ciri-ciri bahan 1.1Early modern steel 1.1.1Blister steel 1.1.2Crucible steel 1.2Modern steelmaking 2Steel industry 3Recycling 4Contemporary steel 5Modern production methods 6Uses of steel 6.1Historically 6.2Since 1850 6.2.1Long steel 6.2.2Flat carbon steel 6.2.3Stainless steel 7Rujukan 8Bacaan lanjut 9Pautan luarCiri-ciri bahan[sunting|sunting sumber]Templat:SteelsBesi, sebagaimana kebanyakan logam, biasanya tidak dijumpai dalam kerakBumidalam bentuk unsur.[2]Besi hanya boleh didapati dalam kerak Bumi dalam bentuk sebatian denganoksigendanbelerang. Biasanya galian mengandungi besi termasuk Fe2O3bentukiron oxidayang terdapat dalam galianhematite, dan FeS2pyrite(emas dungu).[3]Besi dikeluarkan dari bijih dengan menyingkir oksigen dengan mengabungkannya dengan pasangan kimia yang lebih digemari seperti karbon. Proses ini yang dikenali sebagai peleburan, pada awalnya digunakan dengan logam yang mempunyai tahap lebur rendah.Tembagacair pada suhu lebih sedikit pada 1000C, sementaratimahcair sekitar 250C. Besi tuang besi sebatian dengan lebih dari 1.7% karboncair sekitar 1370C. Kesemua suhu ini mampu dicapai dengan kesemua kaedah kuno yang telah digunakan sekurang-kurangnya lebih 6,000 tahun (semenjakZaman Gangsa). Disebabkan kadar pengoksidaan itu sendiri meningkat pada suhu melebihi 800C, ia penting bahawa peleburan dilakukan dikawasan rendah oksigen. Tidak seperti tembaga dan timah, besi cair menyerap karbon dengan mudah, oleh itu hasir peleburan menghasilkan sebatian yang mengandungi terlalu banyak karbon untuk dipanggi keluli.[4]Walaupun dalam julat kepekatan sempit yang menghasilkan keluli, campuran karbon dan besi boleh membentuk beberapa struktur berlainan, dengan ciri-ciri yang amat berbeza; memahami ini amat penting bagi menghasilkan keluli berkualiti. Pada suhu bilik, bentuk besi paling stabil adalah kubik pusat badan - (body-centered cubic - BCC) struktur besi ferrite atau besi-, bahan logam yang agak lembut yang hanya mampu melarutkan sedikit kepekatan karbon (tidak melebihi 0.021wt% pada 910C). Melebihi 910C ferrite melalui fasa perantaraan dari kubik pusat badan kepada struktur kubik pusat muka - (face-centered cubic - FCC), dikenali sebagaiausteniteatau besi-, yang sama logam dan lembut tetapi mampu melatutkan lebih banyak karbon (sehingga 2.03 wt% karbon pada 1154C).[5]Ketika austenite yang kaya dengan karbon menyejuk, campuran itu cuba kembali kepada fasa ferrite, menyebabkan lebihan karbon. Satu cara bagi karbon meninggalkan austenite adalah bagicementiteuntuk terpelowap (precipitate) keluar dari campuran, meninggalkan besi yang cukup tulin bagi membentuk ferrite, menghasilkan campuran cementite-ferrite. Cementite adalah fasastoichiometridengan formula kimia Fe3C. Cementite terbentuk dalam kawasan kaya kandungan karbon sementara kawasan lain kembali kepada ferrite sekitarnya. Pola pengukuhan dir seringkali muncul dalam proses ini, mendorong kepada lapisan pola yang dikenali sebagaipearlite(Fe3C:6.33Fe) disebabkan rupanya sepertimutiara, ataubainiteyang serupa tetapi kurang cantik.Fail:Phase diag iron carbon-color temp.pngDiagram fasa besi-karbon, menunjukkan keadaan yang diperlukan bagi membentuk fasa berlainan.Kemungkinan allotrope yang paling penting adalahmartensite, bahan yang metastabil secara kimia dengan empat hingga lima kali kekuatan ferrite. Kandungan minima Karbon 0.4wt% (C:50Fe) diperlukan bagi membentuk martensite. Apabila austenite disejukkan bagi membentuk martensite, karbon di "kakukan" apabila struktur sel bertukar dari FCC kepada BCC. Atom karbon adalah terlalu besar untuk muat kedalam kekosongan interstitial dan dengan itu mengherotkan struktur sel menmbentuk struktur tetragonal pusat badan (BCT). Martensite dan austenite mempunyai komposisi kimia yang serupa. Dengan itu, ia memerlukan amat sedikit tenaga pengaktif haba bagi terbentuk.Proses rawatan haba bagi kebanyakan keluli membabitkan memanaskan sebatian sehingga austenite terbentuk, kemudian merendam logam merah membara kedalamairatau minyak, menyejukkannya dengan pantas sehinggakan penukaran kepada ferrite atau pearlite tidak mempunyai masa yang mencukupi untuk berlaku. Penukaran kepada martensite, sebaliknya berlaku hampir serta merta, disebabkan tenaga pengaktif yang lebih rendah.Martensite adalah kurang tumpat berbanding austenite, dengan itu penukaran antara mereka menyebabkan isipadu merosot. Dalam kes ini, pengembangan berlaku. Tekanan dalaman dari pengembangan ini mengambil bentuk pemampatan fizikal pada kristal martensite dan ketegangan pada baki ferrite, dengan sejumlah besar pengasingan (shear) pada kedua konstituent. Sekiranya rendaman tidak dilakukan dengan betul, ketegangan dalaman ini mampu menyebabkan ia berkecai ketika menyejuk; sekurang-kurangnya, ia menyebabkan pengerasan kerja (work hardening) dalaman dan kecacatan mikroskopik yang lain. Adalah perkara biasa bagi retakan rendaman berlaku apabila air digunakan, sungguhpun ia tidak selalunya kelihatan.[6]

Peletbijih besibagi penghasilan keluli.Pada titik ini, sekiranya kandungan karbon cukup tinggi untuk menghasilkan ketumpatan martensite yang banyak, ia menghasilkan bahan yang amat keras tetapi rapuh. Seringkali keluli melalui rawatan haba berikut pada suhu lebih rendah untuk memusnahkan sebahagian dari martensite (dengan membenarkan cukup masa bagi pembentukan cementite.) dan membantu mengimbangi ketegangan dalaman dan menghapuskan kecacatan. Proses ini melembutkan keluli, menghasilkan logam yang lebih kenyal (ductile) dan tidak mudah patah. Disebabkan masa amat penting kepada hasil akhir, proses ini dikenali sebagai baja (tempering), yang membentuk keluli baja.[7]Bahan lain sering kali ditambah kepada campuran karbon-besi bagi mengawal ciri-ciri akhir.Nickeldanmanganumdalam keluli menambah ketahanan kelenturan (tensile strength) dan menjadikan austenite lebih stabil dari segi kimia,chromiummeningkatkan kekerasan dan tahap lebur, danvanadiumturut meningkatkan kekerasan disamping mengurangkan kesankelesuan logam.

Steel was known in antiquity, and may have been produced by managing thebloomeryso that the bloom contained carbon.[8]Some of the first steel comes from East Africa, dating back to 1400BCE.[9]In the 4th centuryBCEsteel weapons like theFalcatawere produced in the Iberian peninsula. TheChineseof theHan Dynasty(202BCE 220CE) created steel by melting togetherwrought ironwithcast iron, gaining ultimate product of a carbon intermediatesteelby the 1st centuryCE.[10][11]Along with their original methods of forging steel, the Chinese had also adopted the production methods of creatingWootz steel, an idea imported fromIndiato China by the 5th centuryCE.[12]Wootz steel was produced in India andSri Lankafrom around 300BCE. This early steel-making method employed the use of a wind furnace, blown by the monsoon winds.[13]Also known asDamascus steel, wootz is famous for its durability and ability to hold an edge. It was originally created from a number of different materials including varioustrace elements. It was essentially a complicated alloy with iron as its main component. Recent studies have suggested thatcarbon nanotubeswere included in its structure, which might explain some of its legendary qualities, though given the technology available at that time, they were probably produced more by chance than by design.[14]Crucible steelwas produced inMervby9thto10th centuryCE.In the 11th century, there is evidence of the production of steel inSong Chinausing two techniques: a "berganesque" method that produced inferior, inhomogeneous steel and a precursor to the modern Bessemer process that utilized partial decarbonization via repeated forging under a cold blast.[15]Early modern steel[sunting|sunting sumber]

A Bessemer converter in Sheffield, England.Blister steel[sunting|sunting sumber]Rencana utama:Cementation processBlister steel, produced by thecementation processwas first made in Italy in the early17th centuryCEand soon after introduced to England. It was probably produced by SirBasil BrookeatCoalbrookdaleduring the1610s. The raw material for this was bars ofwrought iron. During the 17th century it was realised that the best steel came fromoregrounds ironfrom a region ofSweden, north ofStockholm. This was still the usual raw material in the19th century, almost as long as the process was used.[16][17]Crucible steel[sunting|sunting sumber]Rencana utama:Crucible steelCrucible steel is steel that has been melted in acruciblerather than beingforged, with the result that it is more homogeneous. Most previous furnaces could not reach high enough temperatures to melt the steel. The early modern crucible steel industry resulted from the invention ofBenjamin Huntsmanin the1740s. Blister steel (made as above) was melted in a crucible in a furnace, and cast (usually) into ingots.[17]Rencana utama: Penyimenan berjalan Keluli lecur, dikeluarkan oleh penyimenan berjalan adalah pertama dibuat di Itali dalam abad ke-17 dan awal CE dan tidak lama lagi sehabis diperkenalkan ke England. Ia adalah mungkin dihasilkan Sir Basil Brooke yang dekat di Coalbrookdale sepanjang 1610s. Bahan mentah untuk ini adalah batang-batang besi tempaan. Sepanjang ia abad ke-17 adalah sedar yang waja yang terbaik datang daripada oregrounds kuat daripada sebuah rantau Sweden, utara Stockholm. Ini adalah masih bahan mentah biasa dalam abad ke-19, hampir sebagai proses yang lama seperti telah digunakanModern steelmaking[sunting|sunting sumber]

Oven keluli Siemens-Martin di Muzium IndustriBrandenburg.See alsoHistory of the modern steel industry.Era moden dalam penghasilan besi bermula dengan pengenalan proses Bessemer olehHenry Bessemerpada akhir 1850-an. Ini membolehkan keluli dihasilkan dalam jumlah yang besar dengan murah, dengan itu besi serdahana kini digunakan bagi kebanyakaan tujuan yang sebelum ini besi tempa digunakan.[18]Ini hanyalah yang pertama dalam kaedah penghasilan besi. Proses Gilchrist-Thomas (atau asas proses Bessemer) merupakan peningkatan kepada proses Bessemer, melapik penukar dengan bahan asas bagi menyingkir phosphorus. Satu lagi adalah proses Siemens-Martin kaedah penghasilan besi relau terbuka, di mana proses Gilchrist-Thomas seiring dan bukan menggantikannya, proses asal Bessemer.[17]Ini dijadikan lapuk oleh proses Linz-Donawitz penghasilan besi oksijen asas, dibangunkan pada tahun1950-an, dan proses penghasilan besi oksijen yang lain.[19]Steel industry[sunting|sunting sumber]

Tata Steelplant in theUnited Kingdom.Fail:Steel (crude)1.PNGSteel output in 2005Because of the critical role played by steel in infrastructural and overall economic development, the steel industry is often considered to be an indicative for economic prowess.The economic boom inChinaandIndiahas caused a massive increase in the demand for steel in recent years. Between 2000 and 2005, world steel demand increased by 6%.[20]Since 2000, several Indian[21]and Chinese steel firms have rose to prominence likeTata Steel(which bought Corus Group in 2007),Shanghai Baosteel Group CorporationandShagang Group.Arcelor-Mittalis however the world'slargest steel producer.[20]TheBritish Geological Surveyreports that in 2005, China was the top producer of steel with about one-third world share followed by Japan, Russia and the USA.Lihat juga:List of steel producersdanGlobal steel industry trendsRecycling[sunting|sunting sumber]Steel is the most widely recycled material inNorth America. The steel industry has been activelyrecyclingfor more than 150 years, in large part because it is economically advantageous to do so. It is cheaper to recycle steel than to mineiron oreand manipulate it through the production process to form 'new' steel. Steel does not lose any of its inherent physical properties during the recycling process, and has drastically reduced energy and material requirements than refinement from iron ore. The energy saved by recycling reduces the annual energy consumption of the industry by about 75%, which is enough to power eighteen million homes for one year.[22]Recycling one ton of steel saves 1,100kilograms ofiron ore, 630kilograms ofcoal, and 55kilograms oflimestone.[23]76 million tons of steel were recycled in 2005.[22]Fail:Steel scrap.jpgA pile of steel scrap in Brussels, waiting to be recycled.In recent years, about three quarters of the steel produced annually has been recycled. However, the numbers are much higher for certain types of products. For example, in both 2004 and 2005, 97.5% of structural steel beams and plates were recycled.[24]Other steel construction elements such as reinforcement bars are recycled at a rate of about 65%. Indeed, structural steel typically contains around 95% recycled steel content, whereas lighter gauge, flat rolled steel contains about 30% reused material.Because steel beams are manufactured to standardized dimensions, there is often very little waste produced duringconstruction, and any waste that is produced may be recycled. For a typical 2000-square-foot two-story house, a steel frame is equivalent to about six recycled cars, while a comparable wooden frame house may require as many as 4050trees.[22]Global demand for steel continues to grow, and though there are large amounts of steel existing, much of it is actively in use. As such, recycled steel must be augmented by some first-use metal, derived from raw materials. Commonly recycled steel products include cans,automobiles,appliances, anddebrisfrom demolished buildings. A typical appliance is about 65% steel by weight andautomobilesare about 66% steel and iron.While some recycling takes place through the integratedsteel millsand thebasic oxygen process, most of the recycled steel is melted electrically, either using anelectric arc furnace(for production of low-carbon steel) or aninduction furnace(for production of some highly-alloyed ferrous products).Contemporary steel[sunting|sunting sumber]Modern steels are made with varying combinations of alloy metals to fulfill many purposes.[25]Carbon steel, composed simply of iron and carbon, accounts for 90% of steel production.[1]High strength low alloy steelhas small additions (usually < 2% by weight) of other elements, typically 1.5%manganese, to provide additional strength for a modest price increase.[26]Low alloy steelis alloyed with other elements, usually molybdenum, manganese, chromium, or nickel, in amounts of up to 10% by weight to improve the hardenability of thick sections.[1]Stainless steelsandsurgical stainless steelscontain a minimum of 10%chromium, often combined withnickel, to resistcorrosion(rust). Some stainless steels aremagnetic, while others arenonmagnetic.[27]Some more modern steels includetool steels, which are alloyed with large amounts of tungsten and cobalt or other elements to maximizesolution hardening. This also allows the use ofprecipitation hardeningand improves the alloy's temperature resistance.[1]Tool steel is generally used in axes, drills, and other devices that need a sharp, long-lasting cutting edge. Other special-purpose alloys includeweathering steelssuch as Cor-ten, which weather by acquiring a stable, rusted surface, and so can be used un-painted.[28]Many other high-strength alloys exist, such asdual-phase steel, which is heat treated to contain both a ferrite and martensic microstructure for extra strength.[29]Transformation Induced Plasticity (TRIP) steel involves special alloying and heat treatments to stabilize amounts of austentite at room temperature in normally austentite-free low-alloy ferritic steels. By applying strain to the metal, the austentite undergoes a phase transition to martensite without the addition of heat.[30]Maraging steelis alloyed with nickel and other elements, but unlike most steel contains almost no carbon at all. This creates a very strong but still malleable metal.[31]Twinning Induced Plasticity (TWIP) steel uses a specific type of strain to increase the effectiveness of work hardening on the alloy.[32]Eglin Steeluses a combination of over a dozen different elements in varying amounts to create a relatively low-cost metal for use inbunker busterweapons. Hadfield steel (after SirRobert Hadfield) ormanganesesteel contains 1214% manganese which when abraded forms an incredibly hard skin which resists wearing. Examples includetanktracks,bulldozerblade edges and cutting blades on thejaws of life.[33]A special class of high-strength alloy, thesuperalloys, retain their mechanical properties at extreme temperatures while minimizingcreep. These are commonly used in applications such asjet engineblades where temperatures can reach levels at which most other alloys would become weak.[34]Most of the more commonly used steel alloys are categorized into various grades by standards organizations. For example, theAmerican Iron and Steel Institutehas a series ofgradesdefining many types of steel ranging from standard carbon steel to HSLA and stainless steel.[35]TheAmerican Society for Testing and Materialshas a separate set of standards, which define alloys such asA36 steel, the most commonly used structural steel in the United States.[36]Though not an alloy,galvanizedsteel is a commonly used variety of steel which has been hot-dipped or electroplated inzincfor protection against rust.[37]Modern production methods[sunting|sunting sumber]

White-hot steel pouring out of an electric arc furnace.Blast furnaceshave been used for two millennia to producepig iron, a crucial step in the steel production process, from iron ore by combining fuel, charcoal, and air. Modern methods usecokeinstead of charcoal, which has proven to be a great deal more efficient and is credited with contributing to the BritishIndustrial Revolution.[38]Once the iron is refined, converters are used to create steel from the iron. During the late 19th and early20th centurythere were many widely used methods such as the Bessemer process and the Siemens-Martin process. However,basic oxygen steelmaking, in which pure oxygen is fed to the furnace to limit impurities, has generally replaced these older systems.Electric arc furnacesare a common method of reprocessing scrap metal to create new steel. They can also be used for converting pig iron to steel, but they use a great deal of electricity (about 440kWh per metric ton), and are thus generally only economical when there is a plentiful supply of cheap electricity.[39]Uses of steel[sunting|sunting sumber]Iron and steel are used widely in the construction of roads, railways, infrastructure and buildings. Most large modern structures, such asstadiumsandskyscrapers, are supported by a steel skeleton. Even those with a concrete structure will employ steel for reinforcing. In addition to widespread use, in electrical appliances and motor vehicles (despite growth in usage of aluminium, it is still the main material for car bodies), steel is used in a variety of other construction-related applications, such as bolts,nails, andscrews.[40]Other common applications include shipbuilding, oil and gas pipelines, mining, aerospace, office furniture,steel wool,tools, andarmourin the form of personal vests orvehicle armour(better known asrolled homogeneous armourin this role).

A piece of steel woolHistorically[sunting|sunting sumber]Before the introduction of the Bessemer process and other modern production techniques, steel was expensive and was only used where no cheaper alternative existed, particularly for the cutting edge of knives, razors, swords, and other items where a hard, sharp edge was needed. It was also used forsprings, including those used in clocks and watches.[17]

A carbon steelknifeSince 1850[sunting|sunting sumber]With the advent of faster and more efficient steel production methods, steel has been easier to obtain and much cheaper. It has replaced wrought iron for a multitude of purposes. However, the availability ofplasticsduring the later20th centuryallowed these materials to replace steel in many products due to their lower cost and weight.[41]Long steel[sunting|sunting sumber]

A stainless steelsauce boat. As supports inreinforced concrete Wires railroad tracks Structural steelin modernbuildingsandbridgesFlat carbon steel[sunting|sunting sumber]

A steel pylon suspendingoverhead powerlines. The inside and outside body ofautomobiles,trains, andships. Major appliances Magnetic coresStainless steel[sunting|sunting sumber]

A steelroller coaster.Rencana utama:Stainless steel Cutlery Rulers Wrist watches Surgicalequipment

>Rujukan[sunting|sunting sumber]