Mech 473 Homework Assignment #2 (36 total marks)
1. a) Determine the constants c and n in a sigmoidal equation that describes the rate of
phase transformation in the figure below at 135 oC. b) Determine the activation energy
for the phase transformation from the sigmoidal curves. Hint: the rate of transformation
is the reciprocal of the time required for half of the transformation to occur. Use the
Arrhenius equation. (4 marks)
2. A steel contains 18% cementite and 82% ferrite at room temperature. Estimate the
carbon content of the steel. Is the steel hypoeutectic or hypereutectic? (1 mark)
3. For a Fe – 1.15 %C alloy, determine a) the temperature at which austenite first begins
to transform on cooling, b) the primary microconstituent that forms, c) the amount of
each phase present at 726 oC and e) the composition and amount of each microconstituent
present at 726 oC. (2.5 marks)
4. A steel is heated until 85% austenite forms that has a carbon content of 0.5%. Estimate
the temperature and the overall carbon content of the steel. (1 mark)
5. Compare the interlamellar spacing and the yield strength when a eutectoid steel is
isothermally transformed to pearlite at a) 700 oC and b) 600 oC. (1 mark, ½ each)
6. A steel containing 0.3% C is heated to various temperatures above the eutectoid
temperature, held for one hour and then quenched to room temperature. Determine the
amount, composition and hardness of any martensite that forms when the heating
temperature is 728 oC and 790 oC. (2 marks)
7. A steel microstructure contains 92% martensite and 8% Fe3C where the composition of
the martensite is 1.10%C. Determine the temperature from which the steel was quenched
and the carbon content of the steel. (1 mark)
8. Calculate the amounts of ferrite, cementite, primary microconstituent (primary  and
Fe3C) and pearlite in the following the two steels designated as 1015 and 1095. (4 marks)
9. Estimate the AISI-SAE number for steels having the following microstructures, a) 38%
pearlite – 62% primary ferrite and b) 97% ferrite – 3% cementite. (2 marks)
10. We wish to produce a martensitic stainless steel containing 17% Cr. Recommend a
carbon content and austenizing temperature that would permit us to obtain 100%
martensite during the quench. What microstructure would be produced if the martensite
were then tempered until the equilibrium phases formed? The Fe-Cr-C phase diagram is
provided below for your assistance. (2 marks)
11. You would like to produce a gray cast iron that freezes with no primary austenite or
graphite. If the carbon content in the iron is 3.5%, what percentage of silicon must you
add? (1 mark)
12. What is the primary source of hardening (strengthening) during heat-treating of
steels? (1 mark)
13. What are the unique characteristics of the martensite transformation? Explain the
significance of each characteristic. (2 marks)
14. What are high-speed tool steels and their main applications? What are hot-work tool
steels and their uses? What are cold-work tool steels and their uses? What are waterhardening tool steels and their uses? (4 marks)
15. What are stainless steels and the five different types of stainless steels? (2.5 marks)
16. What is the most significant factor used in the selection of stainless steels, and the
predominant type of stainless steel used in the market? (2 marks)
17. What is meant by stabilization and its significance in regards to stainless steels?
What is another method to reduce the sensitization of stainless steels? (2 marks)
18. What is a quick and easy way to differentiate an austenitic stainless steel from a
ferritic, martensitic or duplex stainless steel? (1 mark)