Baja Karbon(Steel)

Pertanyaan ttg Baja –> what, where, when, why? Apa itu baja? Berapa ton/tahun baja dibuat di dunia? Berapa ton/tahun di Amerika? Berapa ton/tahun digunakan/konsumsi di Amerika? Pengguna utama siapa? Jenis Baja?

Steel – what, where, when, why? Apa itu baja? Fe + C + (Mo, Mn, Cr, Ni, Si, etc.) Berapa ton/tahun baja dibuat di dunia? 100,000,000 Berapa ton/tahun di Amerika? 13,000,000 Berapa ton/tahun digunakan/konsumsi di Amerika? 31,000,000 Pengguna utama siapa? automotive, construction, oil & gas, appliances, containers, Jenis Baja? low C, high C, alloy, stainless, martensitic, etc.

AVERAGE IMPORT CUSTOMS VALUE PER NET TON* Produk2 baja dan harga: AVERAGE IMPORT CUSTOMS VALUE PER NET TON* Product August 2003 21 Year Ave % Change Wire Rods $302 $349 -13.60% Bars - Hot Rolled $429 $455 -5.90% Bars - Cold Finished $903 $927 -2.60% Standard Pipe $462 $468 -1.10% Oil Country Goods $598 $685 -12.70% Mechanical Tubing $677 $775 -12.60% Structural Pipe & Tubing $446 $452 -1.30% Wire-Drawn and/or Rolled $767 $811 -5.40% Tin Plate $557 $574 -3.00% Sheet & Strip Galv. (Electrolytic) $479 $555 -13.80% Electrical Sheet & Strip $715 $923 -22.50% Strip - Hot Rolled $379 $445 14.90% Note: record import surge began in the first quarter of 1998. * Includes Carbon, Alloy and Stainless Source: U. S. Dept. of Commerce, Bureau of the Census

Negara importir baja ke US? U.S. IMPORTS OF FINISHED STEEL MILL PRODUCTS BY COUNTRY OF ORIGIN (thousands of net tons) Prelim 8 Mos 2003 8 Mos 2002 2003 Annualized Prelim Annual Average 1994-1997* % change 2002 Annualized vs 94-97 Avg.* Canada 3,315 3,847 4,973 - European Union 2,256 2,954 3,384 6,111 -44.60% Mexico 988 1,136 1,482 Korea 812 1,148 1,218 1,432 -14.90% Turkey 685 694 1,028 460 123.50% Japan 650 1,184 975 2,200 -55.70% China 435 313 653 362 80.40% Brazil 350 344 525 850 -38.20% India 318 299 477 138 245.70% Australia 254 217 381 56 580.40% Argentina 189 150 154.00% Egypt 247 204 371 51 627.50% South Africa 218 180 327 321 1.90% Romania 190 140 285 92 209.80% Others 1,411 1,993 2,117 4,375 -51.60% Total 12,383 14,842 18,575 22,192 -16.30%

Kandungan karbon C pada baja : Type baja: Fe + ... Aplikasi: Low-C .04-.3% C Kontruksi umum, low  applications. Medium-C .3-.7% C machinery parts, nuts, bolts, shafts, gears, medium  High-C .7-1.7% C springs, cutting tools, dies, high uses. Cast Iron 1.8 - 4% C engine blocks, drain pipes, machine cabinets

Diagram Fasa : T  L A B b +b +L b+L

Diagram besi-karbon Fe-Fe3C Phase Diagram, Materials Science and Metallurgy, 4th ed., Pollack, Prentice-Hall, 1988 http://www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/examples/kimcon.html

Iron - carbon phases

Iron - carbon transformations http://www-g.eng.cam.ac.uk/mmg/teaching/typd/addenda/microstructures1.html

Fe murni berubah fasa :

Reaksi Eutectoid :

Lever rule :  %  is d c + d %  is c x c d T  A x1 x x2 B

Baja Hypoeuctictoid :

Baja Hypereutectoid :

Transformations : Equilibrium transformations (slow cooling)  ->  “ferrite”  -> Fe3C “iron carbide”  ->  + Fe3C “pearlite” Nonequlibrium (fast cooling / quenching)  -> ’ “martensite”

Pearlite : Two phases ( + Fe3C)

Martensite : Quenched in distortions : + C C Fe

Martensite mechanical prop. : Keras/very hard dan Getas/very brittle (too brittle !!!)

Transformations : Equilibrium transformations (slow cooling)  ->  “ferrite”  -> Fe3C “iron carbide”  ->  + Fe3C “pearlite” Nonequlibrium (fast cooling / quenching)  -> ’ “martensite”

Pearlite : Two phases ( + Fe3C)

Normalized (slow cooled) steels; mechanical properties : 2,500 50 Strength (MPa) Ductility (%) f UTS 500 YS 0 1% w/o Carbon

Martensite : Quenched in distortions : + C C Fe

Quench and Temper : Temper : heat treat at intermediate T (300-600 C) Mechanical properties: Toughness meningkat (critical) namun kekerasan sedikit turun Strukturmikro : C membentuk presipitates Fe3C, dan penurunan distorsi dengan turunnya kandungan C yang terlarut. Hilangnya distorsi membentuk struktur bcc yang ductility. Fe3C precipitates - precipitation strengthen the .

Quenched and tempered : 2,500 50 normalized UTS f YS Strength (MPa) Ductility (%) f UTS tempered 500 YS 0 1% w/o Carbon

Heat treatments and cooling : Normalizing (heating to form ) T ~ 1,000 C much easier to roll / forge / form at this temperature Quench - or - Slow cooling martensite • pearlite Tempering (heating to “soften” martensite) carbides form, distortions relax

Quench rates : To form martensite in pure Fe Critical Cooling Rate (CCR) ~ 100,000 C/sec To form martensite in mild steel : Fe - 0.8% C CCR ~ 200 C/sec To form martensite in alloy steels : Fe - 0.2-.6%C + 2-7% (Mo, Mn, Cr, Ni) CCR < 1 C/sec

Alloying elements are added to : improve hardenability of the steel aides nucleation of martensite solution strengthen and precipitation hardening MxCy carbides form give corrosion resistance especially Cr which forms Cr203 stabilize FCC austenite at RT especially Ni tougher, more ductile and easier to form non-magnetic and creep resistant (diffusion is slower in FCC)

Alloying of steels : Type of steel: Fe + ... Typical uses: Low-alloy .2%C + pressure vessels, aircraft .8Mn,1Cr,2Ni parts, high  applications. High-alloy .1% C High T and anti-corrosion, Stainless-steels .5Mn,18Cr,8Ni silverware, medical, etc.

Steel terminology (SAE-AISI) : Plain carbon 10xx Manganese steels 13xx Nickel steels 23xx Ni-Cr-Mo steels 43xx HSLA 9xx Note: xx indicates carbon content in hundredths of a percent

Other steel standards : SAE-AISI Society of Automotive Engineers ; American Iron and Steel Institute ASTM American Standards for Testing and Materials AMS Aerospace Materials Specifications DIN Deutsches Institut fur Normung JIS Japanese Industrial Standards Committee UNS Unified Numbering System