Q1: Q1 Section A Complete both questions in this section in the BLUE answer booklet You are using an ...

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Q1: Q1 Section A Complete both questions in this section in the BLUE answer booklet You are using an AISI 4340 (Fe-0.4wt% C+ alloying additions) steel to produce forged/machined ground anchors for a large mobile phone mast. (a) The steel is supplied in the normalised condition. What fraction of the steel do you expect to be austenite, martensite and pearlite? Justify each answer. (5 marks) (b) Upon examination you find the steel is mostly bainite and martensite with a small amount of proeutectoid ferrite. Determine the range of possible cooling rates this material might have experienced? Would the presence of these microconstituents cause you any concern considering the steel will be hot-forged? (5 marks) (c) The steel needs to be processed in the following manner: (i) Hot forge to the basic shape. (ii) Substantial machining to create threads. (iii) Heat treatment and cooling to create a 100% martensite microstructure. (iv) Tempering to modify the toughness. Sketch a time-temperature history that you would use for this process. Focus on specify- ing the temperatures and the required cooling rates for each stage. Clearly indicate where you have had to use your judgement to estimate a value. (5 marks) (d) You decide that the forging should be a dual-phase steel consisting of 50% ferrite and 50% martensite in order to improve the damage resistance of the anchor. What single change could be made to the above process to produce this desired microstructure? Fully explain your reasoning. (5 marks)/n8-iron (BCC) Temperature, T (°C) Ferrite a (BCC) 1600 1400 1200 1000 800 600 400 200 0 Melting point /of pure Fe 1534°C L+8 Peritectic point 0 Fe Austenite Y (FCC) 910°C 0.8 ?+Y 0.035 1 L+Y Liquid, L 2.1 Eutectoid point 2 Eutectic point 3 Ferrite, & + Fe,C Austenite. Y + Fe?C 723°C 4.3 wt% C 4 1147°C Compound, Cementite Fe?C 5 6 7/nTemperature (C) 900 800 700 600 500 400 300 200 100 0 10? M? M? B. Rate (C/s) 20 8 10¹ 10² 10³ time (s) Figure Q1 4 AISI 4340 0.33 0.08 0.023 0.006 104 105/nFORMULAS Emax = VjEj + (1 - V?) Em 1 [r+rs(f ? 2)]¹/2 - agelSee Answer