Chapter 10 Phase Diagrams: The Road Map to Phases and Structures 221 13. During which transformation might stresses cause some austenite to remain untransformed? A. Martensite transformation B. Bainite transformation C. Pearlite transformation D. Ferrite transformation 14. True or False? In tempering cycles, the amount of microstructure change is controlled by the tempering time, not temperature. 15. _____ is the process of forming sheet into deep well or cylinder shapes by pulling it into a die cavity. A. Tempering B. Spheroidizing C. Deep-drawing D. Heat-treating Apply and Analyze 1. Explain how the amount of carbon in an iron- carbon alloy can result in different phases and microstructures. 2. What is the difference between a hypoeutectoid alloy and a hypereutectoid alloy? 3. Describe how different cooling rates affect the cementite structure in G10950 steel. 4. How would a fine pearlite structure be obtained by cooling a small sample of UNS G10800 steel from 1500°F (820°C)? 5. Explain what it means for a metal to “miss the nose” on the IT diagram. 6. What would qualify a sample metal as “brittle”? 7. How does tempering improve the ductility and yield strength of martensite? 8. Why is spheroidized pearlitic steel often used for deep-drawing? Critical Thinking 1. How are knowledge of the iron-carbon phase diagram and isothermal transformation (IT) diagram for an alloy useful when creating parts from that metal? 5. True or False? A phase diagram shows what phases are present at each composition and temperature, and the microstructures that form when the metal is cooled to room temperature. 6. A hypoeutectoid alloy contains structures made of a mixture of ferrite and islands of _____. A. austenite B. bainite C. cementite D. pearlite 7. Which of these UNS steel types is used for making railroad rails? A. G10100 B. G10200 C. G10800 D. G10950 8. When changing the rate of cooling of a metal, _____ is the fastest method of reducing the sample temperature. A. quenching B. soaking C. spheroidizing D. tempering 9. True or False? Fine pearlite has higher strength than coarse pearlite. 10. A(n) _____ is a graphic representation of the transformations forming the microstructures in a steel alloy based on the hold temperature and time. A. eutectoid point B. isothermal transformation (IT) diagram C. microstructure diagram D. phase diagram 11. True or False? An alloy with a bainite structure has a lower yield strength and tensile strength than the same alloy with a pearlite structure. 12. Which of these microstructures requires the quickest cooling time to form? A. Ferrite B. Pearlite C. Bainite D. Martensite Copyright Goodheart-Willcox Co., Inc.