Question

Question 3 (1) Sketch the microstructures (at temperature just below eutectold temperature) of slow-cooled pure Iron (Owt%C) and steels with 0.3wt%C, and 0.76wt%C, and explain how the structures develop on cooling from 1100°C to room temperature (Figure 3.1 for Fe-Fe,c phase diagram, see below). (18marks] 1600 Composition Cat C) 10 is 20 25 1538"C 149346 1400 1394°C 2500 72 1200 1147°C > Austenite 2.14 4.30 Temperature) 2000 1000 Temperature (°F) 912°C y + Fe3c 800 1500 0.76 727°C 600 0.022 a Ferrite Feyc Cementite (FeyC) 1000 1000 (Fe) 4 Composition (wt% C) 5 6 6.70 Figure 3.1 2) A hypo-eutectoid plain-carbon steel which was slow-cooled from the austenitic region to room temperature contains 9.3wt% eutectoid ferrite. Assume there is no change in structure on cooling from just below the eutectoid temperature to room temperature. What is the carbon content of the steel? [7marks) [25 marks in total]

Answer 1

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() Steel with 0.3%, C. Called rutectoid steel. from diagrame shown about when steel is coold abcal co-o sin dype -- kereketsid teet): - at (a) Only 8-p , hare exist -> at (b) as cooled olew w phase reaches into ixty sety relgian and pro Senesteettid Fersite mixture appt as Pro-Eutectoid. Carbon atou more and more looks like: at (c) At feather cooling sleffuses to grain in boundary and phase Poco V at (d). At further cooling & desappers 87 } - Peutectoid composition place. art foc appears. ee Boa rec

When 0.76% c steel is cooled, - § comilated into A Pearlite. ee rece Pearlite fez c ta 2 A AN 0.76. Dotyc 9.3 AB 2 AB 6.9-002 X ICON AB - - 6 2 124 6.68 x 9.3 100 - o.Garry 6.05876 %. Wypoeusteederik Composite if - 93% 932 6.78 64-002 U 0-5155 % w.ting = 93637 typeut toid a be may