A portion of the iron-carbon phase diagram is presented in Fig.1. Please use Fig.1 and answer the following: (a) Give all invariant reactions (specify the phases involved and the approximate temperature and composition). You need write down the name of invariant reactions in English. (5 points) (b) Considering 1 kg of steel containing 99wt% Fe-lwt%C alloy, make schematic sketches of the microstructure that would be observed for conditions of very slow cooling to 726C. Then, how many kilograms of pearlite, proeutectoid cementite, and total ferrite form on steel at 726C. (10 points) Composition (at) 5 10 15 20 26 1600 1538C 1493C 1400 & L 2500 1394C 7+Z 1200 1147C 2.14 4.30 7. Austenite 2000 Temperature (C) 1000 Temperature (F) 912C & + Fec 800 1500 + 727 C 7 0.76 600 0.022 a, Ferrite + Fec Cementite (FeyC) 1000 400 0 (Fe) 6 6.70 4 Composition (wt% C) Fig. 1