CIVE265 Chapter Notes - Chapter 9: Ferrous, Phase Boundary, Phase Rule
15 Nov 2016
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9. 1 introduction: component: pure metals/ compounds of which an alloy is composed. 9. 3 phases: homogeneous portion of a system that has a uniform physical and chemical characteristics. Free energy: function of the internal energy of a system & also the randomness/disorder of the atoms/molecules (entropy) Solvus line: the solid solubility limit line separating the and + phase region. Solidus line: boundary ab between and + l field. Liquidus line: temperature at which alloys become totally liquid. 9. 18 the iron-iron carbide (fe-fe3c) phase diagram: upon heating, pure iron experiences two changes in crystal structure before it melts. In practice, steel alloys rarely exceed 1. 0 wt% c: cast irons: 2. 14-6. 70 wt%c; commercially contain < 4. 5 wt% c. Redistribution of carbon diffusion; carbon diffuses away from 0. 022wt% ferrite regions to. 6. 70wt% cementite; as pearlite extends from the grain boundary to unreacted austenite grain; layered pearlite forms b/c carbon atoms diffuse only minimal distances: properties intermediate between soft, ductile ferrite & hard, brittle cementite.
