Transcript Lecture-14 - LearnEASY.info

ENMAT101A Engineering Materials and Processes
Associate Degree of Applied Engineering
(Renewable Energy Technologies)
Lecture 14 – The surface hardening of steels
Flame Hardening
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The surface hardening of steels
Reference Text
Section
Higgins RA & Bolton, 2010. Materials for Engineers and Technicians,
5th ed, Butterworth Heinemann
Ch 14
Additional Readings
Section
EMMAT101A Engineering Materials and Processes
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The surface hardening of steels
Note: This lecture closely follows text (Higgins Ch14)
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Principles of hardening (Higgins 14.1)
READ HIGGINS 14.1
Many metal components require a hard outer skin and tougher inner
core. E.g. Machine elements like shafts, bearings, gears, cams etc.
There are two ways to achieve this;
1. Use low-carbon steel (tough) and add carbon to the outer skin.
2. Use carbon steel and heat only the surface before quenching.
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Case-hardening (Higgins 14.2)
1. Use low-carbon steel (tough) and add carbon to the outer skin.
Higgins
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Case-hardening (Higgins 14.2)
READ HIGGINS 14.2
14.2.1 Carburising
in solid media:
(pack carburising)
Higgins
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Case-hardening (Higgins 14.2)
READ HIGGINS 14.2
14.2.2 Carburising in liquid media (cyanide)
Higgins
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Case-hardening (Higgins 14.2)
READ HIGGINS 14.2
14.2.3 Carburising by
gaseous media
Higgins
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Heat-treatment after carburising (Higgins 14.3)
READ HIGGINS 14.3
Refining the core
Refining the case
Higgins
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Case-hardening steels (Higgins 14.4)
READ HIGGINS 14.4
Higgins
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VIDEO: Crystals and Grain Structure
BBC (1973)
Part 3: Heat Treatment
1. What is a grain?
2. Recrystallisation
• Steel grains are too small to be visible - need a microscope approx 250 times
magnification.
• Ferrite: Light coloured. Made of iron. Gives ductility to the steel
• Pearlite: darker coloured. Layers of Iron + Iron Carbide. Hardness and strength to
the steel.
• 100% Pearlite: 0.83%C. Recrystallisation temperature 723C. Eutectic alloy.
• Normalising - cooled in air, grain size reduced and more uniform shape, toughness
increased due to smaller grains
• Quenching - increases hardness. Not enough time for pearlite to form, so a needle
like structure forms - martensite. Very hard and brittle.
• Tempering - (after quenching) restores toughness. Modifies the martensite needles
with small flakes of carbon. This gives keeps most hardness, adds toughness.
• 0.1%C steel (Mild Steel). Recrystallisation 900C. Not enough carbon to produce
martensite.
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Nitriding (Higgins 14.5)
READ HIGGINS 14.5
• Requires Steel with
alloys that form carbides
with N
• Lower temperature for
diffusion (500oC for 40 to
100 hours)
Higgins
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Nitriding (Higgins 14.5)
READ HIGGINS 14.5
Higgins
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Nitriding (Higgins 14.5)
READ HIGGINS 14.5
14.5.1 Heat treatment
14.5.2 Advantages and disadvantages of nitriding
14.5.3 Carbonitriding
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Ion Nitriding (Higgins 14.6)
READ HIGGINS 14.6
Plasma nitriding and ion implantation.
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Flame-hardening (Higgins 14.7)
READ HIGGINS 14.7
Localised heating/quenching
Higgins
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Induction-hardening (Higgins 14.8)
READ HIGGINS 14.8
Powerful, high frequency current induces eddy currents in the surface of the
component, heating it locally.
Higher frequencies heat to a shallower depth (skin effect).
Induction Heating
http://www.automotive-business-review.com
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Summary (Higgins 14.9)
Higgins
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Video:
Heat Treatment:
BBC: 1981
Heat treatment [videorecording] / producer Brian Davies.
Video: Discusses the use of heat which changes the properties of
metals. Outlines different techniques including hardening,
tempering, annealing, normalising as well as a non-heat process,
cold-working.
Recommended viewing: All
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Online Resources.
Teach yourself phase diagrams
Handout
http://www-g.eng.cam.ac.uk/mmg/teaching/phasediagrams/i2a.html
Heat Treatment: BBC: Heat treatment [videorecording] / producer Brian Davies.
[B.B.C.], 1981.
Video: Discusses the use of heat which changes the properties of metals. Outlines different
techniques including hardening, tempering, annealing, normalising as well as a non-heat
process, cold-working.
Wikipedia:
EMMAT101A Engineering Materials and Processes
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GLOSSARY
Carburising
Plasma Ion
Nitriding
Pack carburising
Cyanide hardening
Gas-carburising
Flame hardening
Induction hardening
Carbonitriding
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QUESTIONS
Moodle XML: Some questions in 10105 Steel
1. Define all the glossary terms.
2. Describe why a part would need a hard skin and a soft core.
3. Use a table to summarise the advantages and disadvantages of the three
carburising methods as shown in the video: Pack carburising, cyanide and
plasma.
4. List advantages and disadvantages of nitriding
EMMAT101A Engineering Materials and Processes
TAFE NSW -Technical and Further Education Commission