Chapter 9_Part_10

Chapter 9_Part_10 - In the micrograph, dark areas are Fe 3...

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46 MSE 2090: Introduction to Materials Science Chapter 9, Phase Diagrams Development of Microstructure in Iron - Carbon alloys Microstructure depends on composition (carbon content) and heat treatment. In the discussion below we consider slow cooling in which equilibrium is maintained. Microstructure of eutectoid steel (I)
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47 MSE 2090: Introduction to Materials Science Chapter 9, Phase Diagrams When alloy of eutectoid composition (0.76 wt % C) is cooled slowly it forms perlite , a lamellar or layered structure of two phases: α -ferrite and cementite (Fe 3 C) The layers of alternating phases in pearlite are formed for the same reason as layered structure of eutectic structures: redistribution C atoms between ferrite (0.022 wt%) and cementite (6.7 wt%) by atomic diffusion. Mechanically, pearlite has properties intermediate to soft, ductile ferrite and hard, brittle cementite. Microstructure of eutectoid steel (II)
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Unformatted text preview: In the micrograph, dark areas are Fe 3 C layers, light phase is -ferrite 48 MSE 2090: Introduction to Materials Science Chapter 9, Phase Diagrams Compositions to the left of eutectoid (0.022 - 0.76 wt % C) hypoeutectoid ( less than eutectoid -Greek) alloys. + + Fe 3 C Microstructure of hypoeutectoid steel (I) 49 MSE 2090: Introduction to Materials Science Chapter 9, Phase Diagrams Hypoeutectoid alloys contain proeutectoid ferrite (formed above the eutectoid temperature) plus the eutectoid perlite that contain eutectoid ferrite and cementite. Microstructure of hypoeutectoid steel (II) 50 MSE 2090: Introduction to Materials Science Chapter 9, Phase Diagrams Compositions to the right of eutectoid (0.76 - 2.14 wt % C) hypereutectoid ( more than eutectoid -Greek) alloys. + Fe 3 C + Fe 3 C Microstructure of hypereutectoid steel (I)...
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This note was uploaded on 02/14/2012 for the course MSE 2090 taught by Professor Leoindzhiglei during the Fall '10 term at UVA.

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Chapter 9_Part_10 - In the micrograph, dark areas are Fe 3...

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