Transcript DERS14_ISILİŞLEMLER.ppt

Heat Treatment
Outline
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Annealing
Martensite Formation in Steel
– Time-Temperature-Transformation Curve
– Heat Treatment Process
– Hardenability
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Precipitation Hardening
Surface Hardening
Heat Treatment Methods
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Heat Treatment
Annealing
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Heat, Soak and Cool slowly to
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reduce hardness and brittleness
alter microstructure
reduce residual stresses
recrystallise (original grain structure) and
soften
Full annealing and Normalising of Ferrite
Metals creates course and fine pearlite
Recovey anneal is partial annealing
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Heat Treatment
Martensite Formation in Steel
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Equilibrium diagram assumes slow
cooling
Austenite -> Ferrite and Cementite (Fe3C)
Rapid cooling causes non-equilibrium
Austenite -> Martensite
Martensite formation described through:
– Time-Temperature-Transformation Curve
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Hardness is a function of Carbon content
– Martensite
– Pearlite
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Heat Treatment
TTT Curve
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Heat Treatment
Heat Treatment Process
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Austenitising
– Raise temp. into
Austenite region
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Quenching
– Rapid cooling in oil
or water
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Tempering
– Reduces brittleness
– Increases toughness
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Heat Treatment
Hardenability
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Capacity to transform to martensite over a certain
depth
Harness is function of carbon and alloys
– chromium, manganese, molybdenum and nickle
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TTT curve is moved to right
Jominy end-quench test
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Heat Treatment
Precipitation Hardening
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Fine particals block
movement of
dislocations
– Aluminium, Copper
– Magnesium, Nickel etc.
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Solvus line must be
present
Three step process
Aging dictates degree
of precipitation
(hardness)
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Heat Treatment