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INTRODUCTION
- Lesson 1
This is the first lesson in a set of images
that I made that demonstrate metallurgical
microstructures of low alloy steels that are in the M.I.T. specimen
collection. These microstructures are
shown to be sensitive
to the processing and environmental history of each macrosopic
specimen. Steel usually consists simply of ferrite and
cementite. The former is ductile and soft, the latter is hard and
brittle. The amount of cementite varies from nearly zero up to as
much as 15% by volume. The cementite can be either the continuous
phase or it can be present as isolated islands. Cementite can
vary in size from a couple of hundred nanometers (10^-9m) to hundreds
of micrometers (10^-6m) ... a range of three orders of magnitude.
The strength (and inversely, the ductility) can vary by about half of
that ... a factor of fifty or so. Even the arrangement of the
cementite can be crucial. Local or macroscopic variations in
carbon and alloy contents cause further purturbations in
properties. |
| Allow plenty of
time to study and to take good notes about each specimen. About
two hours per lesson would be appropriate. You will be expected
to interpret some of these specimens during the final
examination. Feel free to use the Internet to find additional
information about the alloys and applications mentioned here. |
| Whenever the
narrator asks a question, be sure to commit yourself to an answer
before going to the next page. You can backtrack with your
browser's BACK button at any time, of course. Just be sure to click
the FORWARD button to return to the proper page before proceeding so
that you don't get lost. |
| FIRST
SPECIMEN |