Question

Question-5. (30 points): In the Fe-Fe3C phase diagram, answer the following questions: (i) explain the detailed cooling process of a molten Fe-C alloy (5wt% C) from 1600 °C to room temperature, including phase transitions (write the transition equation) and phase composition changes. (ii) A piece of carbon steel contains 50% pearlite and 50% ferrite under the equilibrium conditions, what is the carbon concentration in the alloy? What is the phase composition at 730 °C? What is the phase composition at 850 °C?

Answer 1

Bethez C with decreasing af Solubility is decreasing 5wt% Solidification proces i C5wty.c) l+ proeutectic Fezc | 5 wt%C 12075 l + Fenc 6.7 wtro Leduburite & Proeutectic Fez C. 1 11434 8 + FzC [8+ Bezc] 2.1 wilc 6.7wtyc brith decreasing Temprature solubility limit of c A in f-phase decreases. I - Below eutectoid Temprature (<723 ) Leduburite dissociates into pearlite. peaklite + proeutectic Teze] final microstrure) at Room TG:- .pearlite a Proeutectic Tezc = 0.008 wt% 6.7 wt%C d + Fezc FzC = 6.7 wt%.

- at room Temprature. 50 50 I Ferrite & pearlite | 0.008 2 0.76 6.7 21 -0.008 Ho = O 76 -0.000X100 2676-0.008 x = ( 50 )(0.76-0.008) +0.008 2 = 0.384 wt sich at Just below eutectoid (720) 20 -0.022 x100 50 = 976 -0.092 a = {(0.76-00022}\x 0.022 x = 0.391 wt%C]

at 730 c I phase Composition i d + 0-022 wtric V 0.76wt%C at 8500 phase composition - 8-phase [ 0.391 wtC
Note :- I have calculated composition with fraction of phases at different temperature s. But in reality phase fraction s will change with respect to Temperature.