ENGN1215 Study Guide - Final Guide: Eutectic System, Martensite, Work Hardening
Austenise: heat to T above eutectoid T
Martensite:
• Too brittle
• Dislocations hindered at
Tempered martensite:
• Reduce internal stresses with increased ductility and toughness
• Deformation is hindered on particle level → lots of grain boundaries
• Improved material
Annealing: exposure material to high temperature for some time and slowly
cool
• Specific microstructure
• Increased softness
• Increased toughness
• Relieve stress
Process annealing:
• Used to negate the effects of cold work
• Effectively resetting stresses
• Soften and increase ductility of strain hardening material
• For low oxidation anneal at low T
Stress relief:
• No recrystallization unlike annealing
• Plastic deformation process
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• Non uniform cooling
• Phase transformation involving change in crystal structure
• Can cause warpage
• Heat to uniform temp → cool
Normalizing
• Annealing to refine grains
• Allows for consistency
Full Anneal
• Very slow annealing
• Soft and ductile
Spheroidizing
• Heat to just below eutectoid T for 15-25 hours
• Spheroids of Fe3C
• Softens medium/high carbon steels → machinable
Hardenability
• The ability of an alloy to be hardened by martensite formation
• Measured by Jominy End Quench Test (jet at lower end of cylinder) →
graphed → shallow curve high hardenability
Quenching medium
• Water, oil, air
Precipitation hardening
• Ideal: atoms are most stressed
• Theta: maximum strength minimum ductility
• Over aged: softer, weaker
• Some alloys age harden at ambient → natural ageing
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Document Summary
Tempered martensite: reduce internal stresses with increased ductility and toughness, deformation is hindered on particle level lots of grain boundaries. Annealing: exposure material to high temperature for some time and slowly cool: specific microstructure, relieve stress. Process annealing: used to negate the effects of cold work, effectively (cid:494)resetting(cid:495) stresses, soften and increase ductility of strain hardening material, for low oxidation anneal at low t. Stress relief: no recrystallization unlike annealing, plastic deformation process, non uniform cooling, phase transformation involving change in crystal structure, can cause warpage, heat to uniform temp cool. Normalizing: annealing to refine grains, allows for consistency. Full anneal: very slow annealing, soft and ductile. Spheroidizing: heat to just below eutectoid t for 15-25 hours, spheroids of fe3c, softens medium/high carbon steels machinable. Hardenability: the ability of an alloy to be hardened by martensite formation, measured by jominy end quench test (jet at lower end of cylinder) graphed shallow curve high hardenability.
