Experiment (4)
Eutectoid, Hypo-eutectoid & Hyper-eutectoid Alloys
Objective
Key Words
Introduction
Procedures
Results/Discussion
References
Objective (write your own version in the report)

1.  Get acquainted with Fe-Fe3C phase diagram.
2.  Study the effect of the eutectoid invariant reaction on steel microstructure.
3.  Differentiate between eutectoid, hypo-eutectoid, and hyper-eutectoid microstructures.

Key Words

Generate your Abstract and line of thought using (some of) the following keywords (use others if possible):
Invariant reactions: eutectoid reaction, Phase diagrams: Fe-Fe3C system, phases, iron alloys types & applications, Microstructure: hyper-, hypo-, eutectoid, pro-eutectoid phases.

Introduction

Discuss the following topics in correct language and organized flow of ideas within your introduction:
1. Definition: Invariant reactions, focusing on the eutectoid reaction
2. Phase transformations in a eutectoid reaction
3. Introducing the Fe-Fe3C system: phases, iron alloys types (steel/cast iron)
4. Bonus: Eutectoid shifts
5. Effect of cooling rate, carbon composition on the phases

Procedures

Include full details: magnification power, etching solution (composition/concentration), heat treatment specifications (temperature/time) if any.

Samples are made out of Fe-Fe3C. Four specimens with different carbon content were investigated as follows:
Specimen 1
Specimen 2,3
Specimen 4
0.35% C
0.8% C with one furnace-cooled and another air-cooled 
1.3% C
Etched for 15 seconds in 2% Nitric acid in alcohol (nital) solution.  Grinding & polishing with diamond paste and finishing with a 1 micron grade, followed by etching with a 2% nitric acid in alcohol solution. 
Similar to 1 

Results/Discussion

Required: A "neat" sketch for the microstructure

Use (ALL) the following questions to build your discussion in a correct language and organized flow of ideas
1. Describe the phase transformation for each specimen from the liquid state to the solid state using the phase diagram, writing the phase transformation eutectoid reaction in its standard format (temperature/composition) for the Fe-Fe3C system.
2. Discuss the effect of the cooling rate on the microstructure.
3. Explain the differences in the microstructure and the existing phases for the four microstructures
4. Compare the expected microstructure to the actual one for all specimens.
5. What is the difference between the eutectoid a (alpha) and the pro-eutectoid a (alpha) in terms of:
        a. Phase region where it is formed
        b. Compositions
        c. Microstructural shape and location, and why! J
Further References/Images

--Use (some of) the following pictures (cite the original reference) and comment on them in your lab report
 
 
[By Moataz Attallah]
 You can use the sketch to the right to trace phase transformation reaction in the Fe-Fe3C (eutectoid reaction). 

 
Fe-Fe3C phase diagram (Celsius scale to the right)
Courtesy of Georgia Tech Phase Diagrams
 
Fe-1.3% C
Fe-0.8% C
 
Pearlite
Austenite
Ferrite
[Courtesy of http://info.lu.farmingdale.edu/depts/met/met205/fe3cdiagram.html]
 
Bonus: Can you figure out what is the name of this phenomenon?
[Reference]
[Courtesy of http://info.lu.farmingdale.edu/depts/met/met205/alloyingeffect.html]
--The following sites and books contain useful information and images for several articles that we have encountered in this experiment. Make sure to check them.

Kalpakjian, Serope. Manufacturing Process for Engineering Materials. Addison Wesley, 3rd Ed., 1997.

Smith, William F. . Principles of Materials Science and Engineering. McGraw Hill, 3rd Ed., 1996. (p. 128-132)

Academic Page for a similar experiment¶¶¶ http://compfab.me.lsu.edu/me3701/experiments/metallography/expt6.htm

Academic Page for a similar experiment¶¶¶ http://compfab.me.lsu.edu/me3701/experiments/metallography/expt7.htm

 
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