Problem Isothermal transformation diagram for an iron-carbon alloy of eutectoid com- position (0.76 wt% C). Assume that the specimen begins at 760°C and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure. 1. Sketch the following treatment on the figure: Rapidly cool to 575°C, hold for 20s, rapidly cool to 350°C, hold for 100s, then quench to room temperature. Specify microcon- tituents with percentage. 2. Sketch the following treatment on the figure: rapidly cool to 600°C, hold 4s, rapidly cool to 450°C, hold for 10s, and rapidly cool to room temperature. Specify microcontituents with percentage. 3. Sketch the following treatment on the figure: rapidly cool to 450°C, hold 10s, rapidly cool to room temperature, heat to 680°C, hold 30hrs, and cool to room temperature. Specify microcontituents with percentage. Temperature (°C) 4. (a) 0.2 wt% C with spheroidite (b) 0.2 wt% C with fine pearlite (e) 0.76 wt% C with fine pearlite (d) 0.76 wt% C with tempered martensite 800 700 600 500 400 300 200 100 10-1 M(start) M(50%) M(90%) Rank from the highest to the lowest hardness: 10 M+A -Eutectoid temperature P 10² Time (s) B 50% 10³ 104 105

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**Problem: Isothermal transformation diagram for an iron–carbon alloy of eutectoid composition (0.76 wt% C).** Assume that the specimen begins at 760°C and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure.

1. **Sketch the following treatment on the figure:** Rapidly cool to 575°C, hold for 20s, rapidly cool to 350°C, hold for 100s, then quench to room temperature. Specify microconstituents with percentage.

2. **Sketch the following treatment on the figure:** Rapidly cool to 600°C, hold 4s, rapidly cool to 450°C, hold for 10s, and rapidly cool to room temperature. Specify microconstituents with percentage.

3. **Sketch the following treatment on the figure:** Rapidly cool to 450°C, hold 10s, rapidly cool to room temperature, heat to 680°C, hold 30hrs, and cool to room temperature. Specify microconstituents with percentage.

4. **Rank from the highest to the lowest hardness:**
   - (a) 0.2 wt% C with spheroidite
   - (b) 0.2 wt% C with fine pearlite
   - (c) 0.76 wt% C with fine pearlite
   - (d) 0.76 wt% C with tempered martensite

**Diagram Explanation:**

- The graph is an isothermal transformation diagram, showing the temperature in degrees Celsius on the vertical axis and the time in seconds on the horizontal axis.
- The diagram includes several curves illustrating the transformation boundaries for different microstructures: austenite (A), pearlite (P), and bainite (B).
- The blue curves represent the start and finish lines for pearlite and bainite transformations.
- Red lines indicate the martensite start (M(start)) and transformation percentages from 50% (M(50%)) to 90% (M(90%)).
- The gray dotted line marks the eutectoid temperature.
- Labels within different zones indicate the phases present in each region, such as A (austenite), P (pearlite), and B (bainite), as well as mixtures like M + A (martensite and austenite).
Transcribed Image Text:**Problem: Isothermal transformation diagram for an iron–carbon alloy of eutectoid composition (0.76 wt% C).** Assume that the specimen begins at 760°C and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure. 1. **Sketch the following treatment on the figure:** Rapidly cool to 575°C, hold for 20s, rapidly cool to 350°C, hold for 100s, then quench to room temperature. Specify microconstituents with percentage. 2. **Sketch the following treatment on the figure:** Rapidly cool to 600°C, hold 4s, rapidly cool to 450°C, hold for 10s, and rapidly cool to room temperature. Specify microconstituents with percentage. 3. **Sketch the following treatment on the figure:** Rapidly cool to 450°C, hold 10s, rapidly cool to room temperature, heat to 680°C, hold 30hrs, and cool to room temperature. Specify microconstituents with percentage. 4. **Rank from the highest to the lowest hardness:** - (a) 0.2 wt% C with spheroidite - (b) 0.2 wt% C with fine pearlite - (c) 0.76 wt% C with fine pearlite - (d) 0.76 wt% C with tempered martensite **Diagram Explanation:** - The graph is an isothermal transformation diagram, showing the temperature in degrees Celsius on the vertical axis and the time in seconds on the horizontal axis. - The diagram includes several curves illustrating the transformation boundaries for different microstructures: austenite (A), pearlite (P), and bainite (B). - The blue curves represent the start and finish lines for pearlite and bainite transformations. - Red lines indicate the martensite start (M(start)) and transformation percentages from 50% (M(50%)) to 90% (M(90%)). - The gray dotted line marks the eutectoid temperature. - Labels within different zones indicate the phases present in each region, such as A (austenite), P (pearlite), and B (bainite), as well as mixtures like M + A (martensite and austenite).
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