Lecture12-13.heat Treatment Of Steel

METALLURGY I (RM-1420)

LECTURE XII-XIII Pendahuluan Heat Treatment Hardenability Tempering Age Hardening Dosen: Fahmi Mubarok, ST., MSc. Metallurgy Laboratory Mechanical Engineering ITS- Surabaya 2008

http://www.its.ac.id/personal/material.php?id=fahmi

Pendahuluan

Fahmi Mubarok

 Sifat mekanik tidak hanya tergantung pada komposisi kimia suatu paduan, tetapi juga teragntung pada strukturmikronya.  Suatu paduan dengan komposisi kimia yang sama dapat memiliki strukturmikro yang berbeda, dan sifat mekaniknya akan berbeda.  Strukturmikro tergantung pada proses pengerjaan yang dialami, terutama proses laku-panas yang diterima selama proses pengerjaan.  Proses laku-panas adalah kombinasi dari operasi pemanasan dan pendinginan dengan kecepatan tertentu yang dilakukan terhadap logam/paduan dalam keadaan padat, sebagai suatu upaya untuk memperoleh sifat-sifat tertentu.  Proses laku-panas pada dasarnya terdiri dari beberapa tahapan, dimulai dengan pemanasan sampai ke temperatur tertentu, lalu diikuti dengan penahanan selama beberapa saat, baru kemudian dilakukan pendinginan dengan kecepatan tertentu. Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Heat Treatment

Fahmi Mubarok

Heat treatment Dekat Keseimbangan Near-equilibrium

Tidak seimbang Non-equilibrium

Tujuan Umum • Melunakkan • Menghaluskan butir • Menghilangkan tegangan dalam • Memperbaiki machine ability

Tujuan Umum Mendapatkan kekerasan dan kekuatan yang lebih tinggi

Macam Proses: Full Annealing (annealing) Stress relief Annealing Process annealing Spheroidizing Normalizing Homogenizing Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Macam proces: Hardening Martempering Austempering Surface hardening • Carburizing • Nitriding • Cyaniding • Flame hardening • Induction hardening xi 3

Heat Treatment

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Heat Treatment •

•

•

Fahmi Mubarok

Full annealing (annealing) – Proses perlakuan panas untuk menghasilkan perlite yang kasar (coarse pearlite), tetapi lunak dengan pemanasan sampai temperature austenitisasi dan didinginkan dengan dapur. – Tujuan  memperbaiki ukuran butir, melunakkan material sehingga keuletannya naik. – Diterapkan pada baja yang mengalami deformasi plastis atau proces maching/forming Normalizing – Process perlakuan panas yang menghasilkan perlite halus, pendinginan dengan udara, lebih keras dan kuat dari hasil anneal. Spheroidizing – Process perlakuan panas untuk menghasilkan struktur carbida berbentuk bulat (spheroid) pada matriks ferrite – Akan memeperbaiki kemampuan di machining pada baja paduan %C tinggi – Methods: • 24 hours below A1 line • Heating and cooling alternately between A1 line • Heating above A1 line

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Heat Treatment

Fahmi Mubarok

• Process Annealing – Proses perlakuan panas untuk melunakkan dan menaikkan kembali keuletan benda kerja agar dapat dideformasi lebih lanjut. – Low %C steel 1 hr @ 600-650°C (no austenizing) – Recrystallizes cold worked ferrite – Y.S and UTS drastically reduced • Stress relief Annealing – Process perlakuan panas untuk menghilangkan tegangan sisa atau tegangan dalam akibat proses sebelumnya. – Low %C Structural

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Normalizing and Full Annealing

Fahmi Mubarok

Full annealed - ~1oC/min

Reason for full annealing

Struktur mikro • Full annealed (1oC/min)

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

• Normalized (10 oC/min)

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Spherodizing

Fahmi Mubarok

• 24 hrs @ temp just under A1 - Carbides will spherodize if held for long time <723oC - Softens and puts steel in free machining condition • Sometimes buy steel in spherodized condition for good dimensioning on machining and then heat treat later to increase its strength

Spheroidizing microstructure Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Process Anneal • • • • •

Fahmi Mubarok

1 hr @ 600-650oC Recrystallizes cold worked ferrite Yield Strength and UTS drastically reduced Sometimes used to selectively treat localized cold worked areas Used in production of steel wire, nails etc.

Stress relief • •

Up to 678oC with times up to 24 hrs; (use thermal blankets) Done to relieve residual or internal stresses – @ high temperature dislocations rearrange to relieve stresses (easier mobility @high Temp -> lower Y.S) – After cooling residual stress is reduced

• •

Less chance of fatigue, stress corrosion, etc. Digestors and other pressure vessels have to be stress relieved to remove residual stresses associated with welds

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Full Annealing, Normalizing , Process Anneal and Spheroidize

Fahmi Mubarok

©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Hardening

Fahmi Mubarok

Hardening/ Pengerasan • Proses pelakuan panas untuk meningkatkan kekerasan, ketahanan aus atau ketangguhan dengan kombinasi kekerasan • Kekerasan sangat tergantung dari: – Temperatur pemanasan (Austenitizing Temperature) – Lama pada temperatur tersebut (Holding Time) – Laju pendinginan (Cooling Rate) – Komposisi kimia (%C and Alloying) – Kondisi Permukaan (Surface Condition) – Ukuran dan berat benda kerja (Size and Mass) • Kekerasan maksimum didapatkan dari pembentukan fase martensite atau atau fase karbida pada struktur mikro baja

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Austenitizing Temperature

Fahmi Mubarok

• Pemanasan pada temperatur austenitisasi: – 25-50 oC diatas temperatur A3 untuk baja hypoeutectoid – 25-50 oC diatas temperatur A1 untuk baja hypereutectoid • Homogenity austenite, dilakukan dengan memberikan holding time pada temperature austenitisasi • Laju pendinginan – Brine (air + 10 % garam dapur) – Air – Salt bath – Larutan minyak dalam air – Udara • Komposisi Kimia • Kondisi permukaan • Ukuran dan berat benda kerja

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Cooling Rate

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Cooling Rate

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Size and Mass

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Size and Mass

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Hardenability

Fahmi Mubarok

• Kekerasan baja sangat ditentukan oleh jumlah relatif martersite didalam strukturmikro dan juga ditentukan oleh kekerasan martensite • Hardenability adalah kemampuan baja untuk dikeraskan dengan membentuk martensite dengan proses heat-treatment • Metode Pengujian hardenability – Jominy End Quench Test – Grossman

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Parameter yang berpengaruh terhadap hardenability

Fahmi Mubarok

1. The chemical composition (carbon + other elements) - increasing wt.%C increases hardenability - of the common alloying elements, only Co is known to decrease hardenability 2. The austenite grain size at the instant of quenching - the larger the grain, the better (due to reduction in pearlite nucleation sites).  depend on heating rate, holding time and cooling rate But, beware of growing the austenite grain! 3. The shape, size (thickness) and geometry of the part being quenched; 4. The quenchant used

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Procedure of Jominy Test 1. 2. 3. 4. 5.

6. 7. 8. 9.

Fahmi Mubarok

Prepare specimen with 1 inch round and 4 inch long Pre-heat the furnace to about 925 °C. Place the Jominy specimen in the furnace and soak for one hour. Turn the water on at the Jominy sink. Adjust the free water column to about ½ inch. Remove the Jominy specimen from the furnace and place it in the fixture. Swivel the baffle out of position so that the water impinges on the bottom of the specimen without wetting the sides of the specimen. Leave water to run for about 15 minutes. Remove the Jominy specimen from the fixture and grind a smooth flat on the side of the specimen. Mark points on the ground surface at an interval of 1/16 in. up to 2 in. distance from the quenched end. Take readings at an interval of 1/16 in. by measuring the Rockwell C hardness at each point marked in the previous step. Plot the data for Rockwell Hardness versus Distance from quenched end as shown in Page 21

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Jominy Test

Fahmi Mubarok

A standard simple test adopted by the ASTM and the SAE - ASTM Method A255 - SAE Standard J406

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Jominy Test

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Jominy Test

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Jominy Test

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Jominy Test

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Grossman Test

Fahmi Mubarok

Hardenability suatu baja diukur oleh diamater suatu baja yang strukturmikro tepat di intinya adalah 50 % martensite setelah dilakukan proses hardening dengan pendinginan tertentu. Baja berbentuk silinder (panjang min 5xD) dengan variasi diameter dilakukan pengerasan dengan media pendingin tertentu. Hasil pengersan diuji metallography dan kekerasan, diameter baja tersebut yang intinya tepat 50 % martensite dianyatakan sebagai diameter kritis (D0), pada suatu laju pendinginan tertentu Laju pendinginan dinyatakan dengan koefisien of severity (H)

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Grossman Test

Fahmi Mubarok

Karena harga Do masih tergantung dengan laju pendinginan tertentu maka dirumuskan Harga diameter baja tersebut (50% martensite) dengan pendinginan Ideal (H=tak Hingga) yang disebut sebagai diameter ideal (Di)

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Grossman Test

Fahmi Mubarok

Harga Di dapat di bandingkan antara satu baja dengan baja yang lainnya, harga ini menyatakan hardenability suatu baja dengan komposisi kimia tertentu Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Grossman Test

Fahmi Mubarok

(a) Radial hardness for two alloys quenched in agitated water. (b) Radial hardness for different diameters of SAE4140 steel quenched in agitated water.

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Tempering: Austempering and Martempering

Fahmi Mubarok

• Hasil quench hardening -> menghasilkan produk yang keras tetapi getas • Menghasilkan tegangan sisa • Keuletan dan ketangguhan turun Martempering (Marquenching) 1. Austenitize the steel at the appropriate temperature 2. Quench to a temperature just above the Ms (usually, into an oil or molten salt bath) 3. Hold in the quenchant to obtain uniform temperature throughout the steel 4. Cool at a moderate rate through the martensite transformation region. Mechanical properties of 1095 steel heat-treated by martempering and conventional quenching Heat Treatment

Hardness (HRC)

Impact (ft-lb)

Elongation in 1in (%)

Water quench and temper

53.0

12

0

Martemper and temper

53.0

28

0

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Martempering Procedure

Fahmi Mubarok

Microstructure Result

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Temper Martensite

Fahmi Mubarok

Perubahan sifat mekanik

Microstrukture Transformation

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Microstructure Temper Martensite

Fahmi Mubarok

Pengaruh kadar karbon pada kekerasan martensit

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Austempering

Fahmi Mubarok

• An isothermal heat treatment designed to produce bainite in plain-carbon steels • Purposes: o improves strength and toughness o decreases cracking and distortion o but takes a long time to complete • Steps: 1. Austenitize the steel at the appropriate temperature 2. Quench to a temperature just above the Ms 3. Hold isothermally in the quenching media until graphite → bainite transformation is complete 4. Cool to room temperature in air Mechanical properties of 1095 steel heat-treated by austempering and conventional quenching. Heat Treatment

Hardness (HRC)

Impact (ft-lb)

Elongation in 1in (%)

Austemper

52.0

45

11

Water quench and temper

53.0

12

0

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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Austempering

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Age Hardening

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Age Hardening

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Age Hardening

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Age Hardening

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Age Hardening

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Age Hardening

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Age Hardening

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Fahmi Mubarok

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Surface Hardening

Fahmi Mubarok

Harden surface layers (0.1mm – 5mm) - To improve wear resistance - To improve resistance to high contact stresses - To improve fracture toughness - To improve fatigue resistance Heat: • Induction • Flame • Laser • Light

Case Hardening: • Carburizing • Cyaniding • Carbonitriding • Nitriding

Components usually surface-hardened -Gears bearings -Valves -Bearing races -Cams -Rolls -Machine tools Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

-Shafts -Hand tools -Sprockets xi 42

Surface Hardening

Fahmi Mubarok

Induction Hardening

Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

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METALLURGY I (RM-1420)

LECTURE XIV Surface Hardening -Methods -Applications

Dosen: Fahmi Mubarok, ST., MSc. Metallurgy Laboratory Mechanical Engineering ITS- Surabaya 2008