lecture12-13.heat treatment of steel

METALLURGY I(RM-1420)

Dosen:

Fahmi Mubarok, ST., MSc.

Metallurgy Laboratory

Mechanical Engineering

ITS- Surabaya

2008

Pendahuluan

Heat Treatment

Hardenability

Tempering

Age Hardening

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

LECTURE XII-XIIILECTURE XII-XIII

Fahmi Mubarok

xi 2Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Pendahuluan

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.

Fahmi Mubarok

xi 3Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Heat Treatment

Heat treatment

Dekat Keseimbangan Near-equilibrium

Tidak seimbang Non-equilibrium

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

Macam Proses:Full Annealing (annealing)Stress relief Annealing Process annealingSpheroidizing NormalizingHomogenizing

Tujuan Umum

Mendapatkan kekerasan dan kekuatan yang lebih tinggi

Macam proces: Hardening MartemperingAustempering

Surface hardening• Carburizing • Nitriding • Cyaniding • Flame hardening• Induction hardening

Fahmi Mubarok

xi 4Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Heat Treatment

Fahmi Mubarok

xi 5Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Heat Treatment

• 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

Fahmi Mubarok

xi 6Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Heat Treatment

• 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

Fahmi Mubarok

xi 7Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Normalizing and Full Annealing

Struktur mikro

Reason for full annealing

• Full annealed (1oC/min) • Normalized (10 oC/min)

Full annealed - ~1oC/min

Fahmi Mubarok

xi 8Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Spherodizing

Spheroidizing microstructure

• 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

Fahmi Mubarok

xi 9Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Process Anneal

• 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.

• 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

Stress relief

Fahmi Mubarok

xi 10Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Full Annealing, Normalizing , Process Anneal and Spheroidize

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

Fahmi Mubarok

xi 11Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Hardening

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

Fahmi Mubarok

xi 12Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Austenitizing Temperature

• 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

Fahmi Mubarok

xi 13Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Cooling Rate

Fahmi Mubarok

xi 14Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Cooling Rate

Fahmi Mubarok

xi 15Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Size and Mass

Fahmi Mubarok

xi 16Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Size and Mass

Fahmi Mubarok

xi 17Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Hardenability

• 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

Fahmi Mubarok

xi 18Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Parameter yang berpengaruh terhadap hardenability

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

Fahmi Mubarok

xi 19Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Procedure of Jominy Test

1. Prepare specimen with 1 inch round and 4 inch long2. Pre-heat the furnace to about 925 C.3. Place the Jominy specimen in the furnace and soak for one hour.4. Turn the water on at the Jominy sink. Adjust the free water column to about ½ inch.5. 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.

6. Remove the Jominy specimen from the fixture and grind a smooth flat on the side of the specimen.

7. Mark points on the ground surface at an interval of 1/16 in. up to 2 in. distance from the quenched end.

8. Take readings at an interval of 1/16 in. by measuring the Rockwell C hardness at each point marked in the previous step.

9. Plot the data for Rockwell Hardness versus Distance from quenched end as shown in Page 21

Fahmi Mubarok

xi 20Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Jominy Test

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

Fahmi Mubarok

xi 21Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Jominy Test

Fahmi Mubarok

xi 22Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Jominy Test

Fahmi Mubarok

xi 23Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Jominy Test

Fahmi Mubarok

xi 24Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Jominy TestJominy Test

Fahmi Mubarok

xi 25Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Grossman Test

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)

Fahmi Mubarok

xi 26Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Grossman Test

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)

Fahmi Mubarok

xi 27Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Grossman Test

Harga Di dapat di bandingkan antara satu baja dengan baja yang lainnya, harga ini menyatakan hardenability suatu baja dengan komposisi kimia tertentu

Fahmi Mubarok

xi 28Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Grossman Test

(a) Radial hardness for two alloys quenched in agitated water.

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

Fahmi Mubarok

xi 29Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Tempering: Austempering and Martempering

• 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 temperature2. 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 steel4. 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

Fahmi Mubarok

xi 30Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Martempering

Procedure Microstructure Result

Fahmi Mubarok

xi 31Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Temper Martensite

Microstrukture Transformation

Perubahan sifat mekanik

Fahmi Mubarok

xi 32Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Microstructure Temper Martensite

Pengaruh kadar karbon pada kekerasan martensit

Fahmi Mubarok

xi 33Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Austempering• An isothermal heat treatment designed to produce

bainite in plain-carbon steels• Purposes:

o improves strength and toughnesso decreases cracking and distortiono but takes a long time to complete

• Steps: 1. Austenitize the steel at the appropriate

temperature2. Quench to a temperature just above the Ms3. 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

Fahmi Mubarok

xi 34Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Austempering

Fahmi Mubarok

xi 35Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Age Hardening

Fahmi Mubarok

xi 36Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Age Hardening

Fahmi Mubarok

xi 37Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Age Hardening

Fahmi Mubarok

xi 38Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Age Hardening

Fahmi Mubarok

xi 39Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Age Hardening

Fahmi Mubarok

xi 40Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Age Hardening

Fahmi Mubarok

xi 41Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Age Hardening

Fahmi Mubarok

xi 42Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Surface Hardening

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 -Shafts-Bearing races -Cams -Hand tools-Rolls -Machine tools -Sprockets

Fahmi Mubarok

xi 43Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya

Surface Hardening

Induction Hardening

METALLURGY I(RM-1420)

Dosen:

Fahmi Mubarok, ST., MSc.

Metallurgy Laboratory

Mechanical Engineering

ITS- Surabaya

2008

LECTURE XIV

Surface Hardening-Methods

-Applications