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NC State UniversityDepartment of Materials Science and Engineering 1
MSE 360: Phase Transformation and Diffusion
Instructor: Yuntian ZhuOffice: 308 RBIIPh: 513-0559
Lecture 19
NC State University
Martensitic formation
Department of Materials Science and Engineering 2
http://.blogspot.com//martensite-formation_08.hmetallu2010/04rgyfordummiestml
NC State University
Diffusionless Transformation (Martensitic transformation)
Department of Materials Science and Engineering 3
High c% Medium c% Low c%Plate Martensite Lathe martensiteTwin Dislocation
Morphology of Martensites
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NC State University
Plate (Lenticular) Martensite
Department of Materials Science and Engineering 4
NC State University
Lathe Martensite
Department of Materials Science and Engineering 5
NC State University
Characteristics of martensite
Department of Materials Science and Engineering 6
• Surface tilting• Surface continuous• Coherent with the matrix• Grow very fast (near the
speed of sound)• Military transformation• Accompanied by a volume
expansion• Supersaturated solution• Metastable
Habit plane is the interface plane of the α’/γHabit plane is not distorted
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Thermodynamics and kinetics of martensitic transforamtion
Department of Materials Science and Engineering 7
ΔGγ→ #α = ΔH γ→ #α T0 −MS
T0
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NC State University
Effect of alloy elements
• Increased hardenability• Mechanisms
• Austenite stabilizer– Ni, Mn, Cu
• Ferrite stabilizer– Cr, Mo, Si
Department of Materials Science and Engineering 8
NC State University
Home Work
• Reading assignment (to be quizzed at the next lecture): Ch. 6.2, 6.3
• HW: none
Department of Materials Science and Engineering 9