Read Callister, Chapters 9 and 10. (I know Chapter 9 was part of last week's reading assignment, but it's a long chapter, and I haven't finished discussing it in class yet.) Solve and hand in Problems 10.11, 10.18, 10.35 and 10.38, due date Monday February 9.

Question 10.11

Suppose a steel of eutectoid composition is cooled to 550 C from 760 C in less than 0.5 s and held at this temperature.

  1. How long will it take for the austenite-to-pearlite reaction to go to 50% completion? To 100% completion?
  2. Estimate the hardness of the alloy that has completely transformed to pearlite.

Question 10.18

Make a copy of the isothermal transformation diagram for a 1.13% wt C iron-carbon alloy (Figure 10.28 in 6th edition), then on this diagram sketch and label time-temperature paths to produce the following microstructures:

  1. 6.2% pro-euctectoid cementite and 93.8% coarse pearlite
  2. 50% fine pearlite and 50% bainite
  3. 100% martensite
  4. 100% tempered martensite

Question 10.35

Estimate the Brinell hardnesses for specimens of a 1.13%wt C iron-carbon alloy that have been subjected to the following heat treatments:

  1. Hold at 920 C until everything turns to austenite; then rapidly cool to 250 C, hold for 1000 seconds, quench to room temperature.
  2. Hold at 920 C until everything turns to austenite; rapidly cool to 700 C, hold at this temperature for 100,000 seconds, then quench to room temperature.
  3. Hold at 920 C until everything turns to austenite; rapidly cool to 600C, hold at this temperature for 7 seconds, rapidly cool to 450 C, hold at this temperature for 4 seconds, then quench to room temperature.

Question 10.38

The room temperature tensile strengths of pure copper and pure silver are 209 MPa and 125 MPa respectively.

  1. Make a schematic graph of the room-temperature tensile strength versus composition for all compositions between pure copper and pure silver.
  2. On the same graph schematically plot tensile strength versus composition at 600 C
  3. Explain the shapes of these two curves as well as any differences between them.