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An in-depth analysis of the various phases that appear on the Iron-Carbon equilibrium phase diagram, including Austenite, Ferrite, Pearlite, Cementite, and Martensite. It covers their definitions, structures, average properties, and transformation processes. The document also discusses the importance of the Iron-Carbon diagram in material science and engineering.
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Austenite Average properties are: Tensile strength = 150,000 psi; Elongation = 10 percent in 2 in.; Hardness = Rockwell C 40, approx; and toughness = high
Ferrite is known as α solid solution. It is an interstitial solid solution of a small amount of carbon dissolved in α (BCC) iron. stable form of iron below 912 deg.C. The maximum solubility is 0. 025 % C at 723 C and it dissolves only 0. 008 % C at room temperature. It is the softest structure that appears on the diagram.
Pearlite is the eutectoid mixture containing
Pearlite Average properties are: Tensile strength = 120 , 000 psi; Elongation = 20 % in 2 in.; Hardness = Rockwell C 20 , BHN- 300
Martensite - a super-saturated solid solution of carbon in ferrite. It is formed when steel is cooled so rapidly that the change from austenite to pearlite is suppressed. The interstitial carbon atoms distort the BCC ferrite into a BC-tetragonal structure (BCT).; responsible for the hardness of quenched steel
Ledeburite is the eutectic mixture of austenite and cementite. It contains 4. 3 percent C and is formed at 1130 °C.
Cooling curve for pure iron
Max. solubility of C in ferrite=0.022% Max. solubility of C in %austenite=2%
Peritectic, at 1490 deg.C, with low wt% C alloys (almost no engineering importance). Eutectic, at 1130 deg.C, with 4.3wt% C, alloys called cast irons. Eutectoid, at 723 deg.C with eutectoid composition of 0.8wt% C, two-phase mixture (ferrite & cementite). They are
Redistribution of carbon by diffusion Austenite – 0.76 wt% C Ferrite - 0.022 wt% C Cementite - 6.70 wt% C Pearlite y↔α + Fe 3 C