7-Engineering Alloys

Austenite proeutectoid ferrite pearlite hypoeutectoid

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Unformatted text preview: oduces. Austenite Proeutectoid Ferrite + Pearlite HYPOEUTECTOID PLAIN CARBON STEELS Slow cooling from austenite phase produces Proeutectoid ferrite - nucleates and grows at austenite grain boundaries. As temperature decreases more proeutectoid ferrite forms. Austenite phase is enriched with carbon just below 723ºC. Remaining liquid transforms to pearlite. Austenite Proeutectoid Ferrite + Pearlite HYPEREUTECTOID PLAIN CARBON STEELS Slow cooling from austenite phase produces: HYPEREUTECTOID PLAIN CARBON STEELS Slow cooling from austenite phase produces Proeutectoid cementite - nucleates and grows at austenitic grain boundaries. As temperature decreases more proeutectoid cementite forms and austenite is depleted in carbon. Just below 723ºC remaining austenite transforms to pearlite by the eutectoid reaction. NON - EQUILIBRIUM STRUCTURES Transformations that occur without enough time for equilibrium. Athermal transformation Martensite Isothermal transformation Pearlite Bainite MARTENSITE Metastable phase of supersaturated interstitial carbon in BCC or BCT. Transformation is diffusionless and occurs by shear. Occurs only upon rapid cooling from austenite. MARTENSITE Metastable phase of supersaturated interstitial carbon in BCC or BCT. Transformation is diffusionless and occurs by shear. Athermal transformation in which temperature determines amount of phase formed. Ms temperature is the start of transformation Mf temperature is the end of transformation Occurs only upon rapid cooling from austenite. MARTENSITE Carbon lowers the Ms temperature. Carbon changes the microstructure of martensite. Low C - lath martensite High C - plate martensite MARTENSITE Carbon lowers the Ms temperature. Carbon changes the microstructure of martensite. Low C - lath martensite High C - plate martensite MARTENSITE Carbon lowers the Ms temperature. Carbon changes the microstructure of martensite. Low C - lath martensite High C - plate martensite ATOMIC SCALE STRUCTURE Diffusionless transformation takes place without a compositional change. Atoms r...
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