Question

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By using the Iron-Carbon (Fe-C) phase diagram provided herein, answer the following questions: (a) Sketch the microstructure of alloys A, B, and C in the following temperature ranges when they are cooled from 1000 °C very slowly (equilibrium cooling). Sketch and identify all phases in the microstructures. Comment on the mechanical properties of the resultant alloy as well its constituent phases. For alloy A: T-1000 °C, TA (slightly below), T=728 °C and T- 726 °C; for alloy B: T-728 °C, Ta 727 °C and T- 726 °C; and for alloy C: T=1000 °C, T-Tc (slightly below), T 728 C and T 726 °C. (b)Would you choose steel with a carbon content greater or smaller than 0.77 WI% C if you needed moderate strength and good ductility? Justify your answer by taking microstructural considerations into account, (c) Identify all phases marked on the phase diagram. What are the invariant reactions below 1200 C7 Write the reactions, including the temperature at which they occur and the % of carbon of each phase participating in the reaction. These reactions correspond to a certain type of phase transformations. What are the main characteristics of such transformations? Briefly describe and discuss; (d) What is the melting point of pure Fe? What is the melting temperature of Fe containing 4.3% carbon? What is the temperature at which &-Fe transforms to y-Fe? (e) Calculate the amount of proeutectoid Fe,C in Alloy B (1.15 wt%) at room temperature at 726.9oC. The Fe-C Phase Diagram 1600 P=1 atm 1539 °C L 1400--1394°C y+L Y 1200 L+Fe,C 1148 °C ABC 2.119 4.3% 1000 y+Fe,C Tc 800- 727 C 096רה 600 0.022 a+Fe,C 400 0 0.42 1 1.15 2 3 4 Fe 6 6.67 wt% C Fe,C T (C)

Answer 1

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