Homework 8 Ch10 (ME240 )Spring 2020

San Diego State University

Introduction to Engineering materials (ME 240)

name the two general stages that accompany a phase transformation.

Homework 8 (Chapter 10) Due in Thursday class: 4/23/2020
Chapter 10: Phase Transformations
1. What is more stable, the pearlite or spheroidite microstructure? Why?
2. Cite two major differences between martensitic and pearlitic transformations.
3. 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;
0.60 wt% C with fine pearlite; 0.60 wt% C with coarse pearlite. Justify this ranking.
4. For a eutectoid steel, describe an isothermal heat treatment that would be required to
produce a specimen with 0.68 wt% of carbon to have a hardness of 93 HRB. You may want
to consider the following two data as well as the Fe-C phase diagram (can be found in our
textbook or lecture notes).
5. Name the two general stages that accompany a phase transformation.
6. Consider the following isothermal transformation diagram and the heat treatment designed
by the line segments labeled a-b-c-d. From the list below, choose the
microconstituents/phases that result from this heat treatment: proeutectoid cementite,
tempered martensite, proeutectoid ferrite, spheroidite, martensite, bainite, pearlite.

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