1. Briefly cite the differences between pearlite, bainite, and spheroidite relative to micro structure and mechanical properties.
2. What is the driving force for the formation of spheroidite?
3. Using the isothermal transformation dia- gram for an iron-carbon alloy of eutectoid composition (Figure 10.22), specify the na- ture of the final microstructure (in terms of microconstituents present and approximate percentages of each) 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 (1400°F) and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure.
(a) Cool rapidly to 350°C (660°F), hold for reciprocal of temperature (in K-1), and 103s, then quench to room temperature. Determine the activation energy for this recrystallization process. (See Section 5.5.)
(c) By extrapolation, estimate the length of time required for 50% recrystallization at room temperature, 20°C (293 K).