A company that specializes in manufacturing cutting tools wants to produce highperformance steel cutting tools using a steel with a carbon content of 0.8 wt%. They plan to use a series of heat treatment processes, including austenitizing, quenching, and tempering, to achieve the desired properties. A Time-Temperature-Transformation (TTT) diagram for iron-iron carbide is available in Fig. 2 to help guide the heat treatment process.

Answer the following questions using information contained in both Fig. 1 and Fig. 2.

A.) What is the initial microstructure of the steel before the heat treatment process, and at what temperature should the steel be austenitized? B.) After austenitizing, what cooling rate (rapid or slow) should be applied to obtain a fully martensitic microstructure? Describe how different cooling rates can affect the final microstructure. C.) What factors (i.e., materials properties) should be considered when choosing the tempering temperature and time, and how tempering temperature (low and high) affects these factors?

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Temperature (C) 1600 1538C 1493C 1400 1394C Y+L 1200 y. Austenite 2.14 1000 912C 800a 600 0.76 0.022 a, Ferrite 400 0 1 2 (Fe) 10 Composition (at% C) 15 20 27 25 L 1147C 4.30 a + Fe3C Y+ Fe3C 727C 2500 2000 1500 Cementite (Fe3C). 1000 4 5 6 6.70 Composition (wt% C) Figure 1: Iron-iron carbide phase diagram. Temperature (F) Temperature (C) 1600 1538C 1493C 1400 1394C Y+L 1200 y. Austenite 2.14 1000 912C 800a 600 0.76 0.022 a, Ferrite 400 0 1 2 (Fe) 10 Composition (at% C) 15 20 27 25 L 1147C 4.30 a + Fe3C Y+ Fe3C 727C 2500 2000 1500 Cementite (Fe3C). 1000 4 5 6 6.70 Composition (wt% C) Figure 1: Iron-iron carbide phase diagram. Temperature (F)