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PHASE DIAGRAM, PYHSICAL METALLURGY, AUSTENITE, MARTENSITE, DUCTILITY -->…
PHASE DIAGRAM
- describe equilibrium microstructural development that is obtained at extremely slow cooling or heating conditions
- provides no information on time taken to form phase
PYHSICAL METALLURGY
TRANSFORMATION DIAGRAMS
TTT DIAGRAM
- for a given alloy composition, the percentage completion of a given phase transformation on temperature-time axes is described
CCT DIAGRAM
- most heat treatments for steels involve the contiuous cooling of a specimen to room temperature
- there exists a critical queching rate that represents the minimum rate of quenching that will produce a totally martensitic structure (for steel alloy)
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HEAT TREATMENT
ANNEALING
PURPOSE
- improve ductilty and toughness
- change grain size
- harden and strengthen metals
- cause relief of internal stresses developed
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AUSTENITE
FAST COOLING
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- composition changes require diffusion in solid (slow) and liquid phases
- upon heating grain boundaries will melt first. this can lead to premature mechanical failure.
SLOW COOLING
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- soliification in the solid + liquid phase occurs gradually upon cooling from the liquidus line
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