ch11 - Chapter 11 Phase Transformations Concept Check 11.1...

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Chapter 11 Phase Transformations Concept Check 11.1 Question: Which is the more stable, the pearlitic or the spheroiditic microstructure? Why? Answer: Spheroiditic microstructures are more stable than pearlitic ones. Since pearlite transforms to spheroidite, the latter is more stable
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Concept Check 11.2 Question: Cite two major differences between martensitic and pearlitic transformations. Answer: Two major differences are: 1) atomic diffusion is necessary for the pearlitic transformation, whereas the martensitic transformation is diffusionless; and 2) relative to transformation rate, the martensitic transformation is virtually instantaneous, while the pearlitic transformation is time-dependent.
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Concept Check 11.3 Question: Make a copy of the isothermal transformation diagram for an iron-carbon alloy of eutectoid composition (Figure 11.23) and then sketch and label on this diagram a time- temperature path that will produce 100% fine pearlite. Answer: Below is shown an isothermal transformation diagram for a eutectoid iron- carbon alloy on which is included a time-temperature path that will produce 100% fine pearlite.
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Concept Check 11.4 Question: Briefly describe the simplest continuous cooling heat treatment procedure that would be used to convert a 4340 steel from (martensite + bainite) to (ferrite + pearlite). Solution: In order to convert from (martensite + bainite) to (ferrite + pearlite) it is necessary to heat above about 720 ° C, allow complete austenitization, then cool to room temperature at a rate equal to or less than 0.006 ° C/s (Figure 11.29).
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Concept Check 11.5 Question: Rank the following iron-carbon alloys and associated microstructures from the highest to the lowest tensile strength: 0.25 wt%C with spheroidite 0.25 wt%C with coarse pearlite 0.6 wt%C with fine pearlite, and
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ch11 - Chapter 11 Phase Transformations Concept Check 11.1...

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