Question

Using the isothermal transformation diagram for an alloy steel (type 4340) specify the nature of the final microstructure (in terms of micro-constituents present and approximate percentages) of a small specimen that has been subjected to the following time-temperature treatments: In each case assume that the specimen begins at 760°C and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenite structure. (a) (a) Rapidly cool to 400°C, hold for 10 seconds, and quench to room temperature. (b) Rapidly cool to 450°C, hold for 103 seconds, and quench to room temperature. In each case (a and b) explain what happens at each stage of the process. A Austenite, B-Bainite, F- Ferrite, M-Martensite, and P Pearlite In your answers include a sketch of the TTT diagram to illustrate the process stages involved and explain clearly the evolution of the microstructural composition. 800 1400 Eutectoid temperature 1200 600 500 800 C 400 A+B 50% 300 M(start) 600 M15096) M19096) ; 200 400 100 200 10 102 103 104 105 106 Time (s) Figure Q5. TTT diagram for an alloy steel (type 4340) (b) Explain how both materials (a and b) produced above in question 5 (a) would behave if exposed to Electrochemical Corrosion. In your answer include: * detailed sketches, . electrochemical equations and * explain a strategy to prevent electrochemical corrosion.

Answer 1

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