water bath at the same temperature. Do you expect that the microstructure of both pieces will be the same or different? Justify your answer. d. note that the time required to initiate the transformation of the austenite phase tends to decrease as the isothermal treatment temperature is reduced for temperatures above approx. 550 C. Why doesn’t the time required for this phase transformation continue to decrease as the temperature is reduced below approximately 550 C? Answer in terms of the two primary
For the isothermal time-temperature-transformation diagram provided (next page) for an Fe-C steel, answer the following (show any work on the diagram):
a. based on the phases depicted, what is the average composition for the Fe-C alloy depicted (be specific). Explain your answer. (Note: you do have the Fe-C phase diagram in your notes and in the text for reference.)
b. in an isothermal heat-treatment of a pure austenite structure at 300 C, how long will it take for austenite to be completely converted to bainite after bainite first begins to form?
c. A standard size, automobile engine block and a 1 mm diameter rod of the same steel composition are taken from a heat-treatment furnace and immersed in a water bath at the same temperature. Do you expect that the microstructure of both pieces will be the same or different? Justify your answer.
d. note that the time required to initiate the transformation of the austenite phase tends to decrease as the isothermal treatment temperature is reduced for temperatures above approx. 550 C. Why doesn’t the time required for this phase transformation continue to decrease as the temperature is reduced below approximately 550 C? Answer in terms of the two primary contributions to phase transformations that we discussed in class.
e. Sketch a thermal treatment curve on the diagram that would produce a tempered martensite microstructure. What is the maximum tempering temperature that you could use?
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