baja paduan dan super alloy

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Department of Metallurgy and MaterialsUniversity of Indonesia2008

BAJA PADUAN DAN SUPER ALLOY

Dr.-Ing. Bambang SuharnoDr. Ir. Sri Harjanto

1. ALASAN PENGGUNAAN2. KLASIFIKASI3. PENGGUNAAN

University of Indonesia

Department of Metallurgy and Materials University of Indonesia

Silabus

Tujuan : Memahami berbagai jenis material baja paduan dan super Alloy sertapenggunaannya dalam bidang rekayasaEvaluasi:

UTS = 35 %UAS = 45 %Tugas = 20 %Lain-lain = 5 %

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Silabus

Penggunaan Baja Paduan dan Super AlloyPengaruh Unsur PaduanStainless Steel (Baja Tahan Karat)Heat Resistant SteelWear/ Abrassion Resistant SteelTool SteelSuper Alloy

Ni based, Co based



BAJA KARBON

Low-carbon < 0.30% C.Flat-rolled products (sheet or strip), usually in the cold-rolled and annealed condition. The carbon content for these high-formability steels is very low, less than 0.10% C Typical uses are in automobile body panels, tin plate, and wire products. For rolled steel structural plates and sections, the carbon content may be increased to approximately 0.30%, with higher manganese content up to 1.5%. These materials may be used for stampings, forgings, seamless tubes, and boiler plate.

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Steel Making Flowlines



Steel Making Flowlines

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BAJA KARBON

Medium-carbon steels carbon ranges from 0.30 to 0.60% and the manganese from 0.60 to 1.65%. Medium carbon steels to be used in the quenched and tempered condition. The uses of medium carbon-manganese steels include shafts, axles, gears, crankshafts, couplings and forgings. Steels in the 0.40 to 0.60% C range are also used for rails, railway wheels and rail axles.

High-carbon steels0.60 to 1.00% C with manganese from 0.30 to 0.90%. used for spring materials and high-strength wires.



PengaruhKarbonPada Baja

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Fe-Fe3C

0.5% C ferrite + pearlite

1.5% C ferrite + cementite0.5%C 0.8%C 1.5%C



WHY WE NEED ALLOYS?

Keterbatasan Baja Karbon:a) A high critical cooling rate which leads to cracking when

quenching hardening.b) Poor Hardenability.c) Ultimate Tensile Strength rendah

Jika di Heat Treatment → Elongasi RendahToughness Rendah

d) Ketahahan Korosi (Corrosion Resistant) RendahKetahanan Aus (Wear Resistant) RendahKetahanan Panas (Heat Resistant) Rendah

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KLASIFIKASI BAJA

Definisi Baja : Material berbahan dasar Fe, dengan C maks : 2%Kadar C boleh ≥ 2% → Tetapi harus ada unsur lain (paduan) Serta mengandung

unsur pengikut seperti Si, P, S, Mndan unsur paduan seperti Cr,Ni, Mo, V, W dll.



KLASIFIKASI BAJA

Klasifikasi Baja dapat berdasarkan:

The composition, such as carbon, low-alloy or stainless steel. The manufacturing methods, such as open hearth, basic oxygen process, or electric furnace methods. The finishing method, such as hot rolling or cold rolling The product form, such as bar plate, sheet, strip, tubing or structural shape The deoxidation practice, such as killed, semi-killed, capped or rimmed steel The microstructure, such as ferritic, pearlitic and martensiticThe required strength level, as specified in ASTM standards The heat treatment, such as annealing, quenching and tempering, and thermomechanical processing Quality descriptors, such as forging quality and commercial quality.

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Penggunaan Baja Paduan

Industry Minyak, Gas dan Petrokimia : Corrosion Resistant and Heat Resistant SteelSS 304, 316, 309, 310Industri Semen dan Pertambangan: Wear Resistant Steel (Keras dan Tangguh)Ni Hard, High C-Chrom Steel, Baja MnIndustri Manufacture Tool Steel (H13 = SKD61, P20)

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Super Alloys

Adalah paduan yang dikembangkan untukpenggunaan material pada temperatur tinggi, tahan hot corrosion and errosionSemula dikembangkan untuk aircraft turbine engineUmumnya mengandung Fe, Ni, Co, Cr dansejumlah W, Mo, Ta,Nb, Ti dan Al. Contoh Hastealloy, Inconel



Elemen Paduan

Terdiri atas :Carbide Former.Austenite Stabilizer.Ferrite Stabilizer.Graphitizer.

Secara Umum1. Penstabil γ →

memperlebar daerah γ2. Penstabil α →

memperlebar daerah α

Seluruh paduan, kecuali Co :1. Menurunkan Ms dan Mf

2. Mendorong kurva TTT kekanan → memperlambatpembentukan Perlit / Bainit

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Pengaruh Elemen Paduan TerhadapDiagram Time Temp Transformation



Carbide Former (Pembentuk Karbida)

Beberapa elemen paduan membentuk karbida stabilyang lebih keras dari iron carbides (Fe3C)

Dapat meningkatkan kekerasan (hardness) → cocokuntuk keperluan tool (perkakas), tahan panas

Cr, Mn, Nb, Mo, Ti, W, V.

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Austenite Stabilisers

C, Co, Cu, Ni, Mn, N meningkatkan A4 Temp (austenine-delta)menurunkan A3 Temp

Jika elemen tersebut ditambahkanpada C-Steel akan menstabilkan fasaγ.Elemen paduan ini tidak membentukcarbida, C tetap tinggal dalam “solid solution” dalam γ.Bahkan jika paduan jumlahnyabanyak pada temperatur kamar tetapberfasa γ (non magnetis)

misal : Austenitik Stainless Steel



Mn Sebagai Austenite Stabilizer

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Fe-C Diagram



Ferrite StabilisersAl, Cr, Si, Mo, Nb, Ta, Ti, W, V, ZrJika ditambahkandalam bajamenstabilkan fasaFerit (alpha)Pada Temperaturkamar, berfasa FeritStruktur kristasl BCC (Body Centered Cubic)Contoh: FerriticStainless Steel

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Cr Sebagai Ferrite Stabilizer



Mo Sebagai Ferrite Stabilizer

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Graphitisers

Tak semua elemen paduan berkombinasi dengan C (Ni, Al, Si), sehingga C cenderung sebagai “free graphite”.Jika unsur tersebut harus ada, maka:Perlu adanya elemen paduan pembentuk karbida, ataukandungan C dibuat “very low”.Karenanya tak mungkin membuat high C-high Ni alloy steel.

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baja paduan dan super alloy