AMME1362 Chapter Notes - Chapter 10: Diffusionless Transformation, Heat Treating, Alloy Steel

• School: University of Sydney
• Department: Aeronautical Engineering (Mechanical)
• Course: AMME1362
• Professor: Xiaozhou Liao

Document Summary

Simple diffusion-dependent transformations (no change in either number or composition of phases- including solidification of pure metal, allotropic transforms and recrystallization and grain growth): 2. Diffusion-dependent transformation (some alteration in phase compositions and often number of phases present-final microstructure consists of two phases-eutectoid reactions): 3. Diffusionless, wherein a metastable phase is produced-martensitic transformation including steel alloys) 10. 3 the kinetics of phase transformations: normally at least one new phase is formed that has different physical/chemical characteristics or different structure than the parent phase, most phase t(cid:396)a(cid:374)sfo(cid:396)(cid:373)atio(cid:374)s do(cid:374)"t o(cid:272)(cid:272)u(cid:396) i(cid:374)sta(cid:374)ta(cid:374)eously. Rathe(cid:396), they begin by formation of numerous small particles of the new phase: progress of phase transformation broken down to two stages: nucleation and growth. Nucleation: two types: homogenous and heterogeneous, homogenous nucleation-nuclei of the new phase form uniformly throughout parent phase, heterogeneous nuclei form preferentially at structural inhomogeneities, such as container surface, insoluble impurities (e. g. container surfaces, grain boundaries, dislocations)