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MATSE 259 - Exam 3 With Complete Solutions
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MATSE 259 - Exam 3 With Complete Solutions
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Solution 2024/2025Pepper
MATSE 259 - Exam 3 With Complete Solutions
Simple Diffusion Dependent Transformations ANS✔✔ No change in number or composition of phases present
Diffusion Dependent Transformations ANS✔✔ Alterations in phase compositions and number of phases present
Diffusionless Transformations ANS✔✔ metastable phase, diffusion is very slow, a new phase
Two Types of Phase Transformation Stages ANS✔✔ Nucleation (small particles) & Growth (increasing the size, parent
phase disappears)
Two Types of Nucleation ANS✔✔ Homogenous (uniform throughout parent phase) & Heterogenous (structural
irregularities, container surfaces and insoluble impurities)
What is the rate of transformation? ANS✔✔ 1/t(0.5)
Phase Transformations ANS✔✔ 1. crossing boundary in phase diagrams
2. during transformation - alloy proceeds to equilibrium
3. but most take time - heat treatment and microstructure
4. in reality we cool rapidly and get intermediate phases
Pearlite ANS✔✔ 1. austenite to alpha + Fe3C
2. Higher temp- coarse pearlite Lower temp- fine pearlite
Bainite ANS✔✔ 1. diffusion is involved
2. appear like plates and needles
3. thickness depends on temp
, Solution 2024/2025
Pepper
4. after nose on diagram
If some portion forms into pearlite or kainite, what must happen before transforming into another microconstutuent?
ANS✔✔ Must reheat back to Austenite
Spheroidite ANS✔✔ 1. heating pearlite or bainite just below eutectoid for long period (24 hr)
2. Fe3C spheres
Martensite ANS✔✔ 1. rapidly cooling to very low temperatures
2. not enough time for diffusion (diffusionless)
3. Cools without passing through transformation curves
4. Body Centered tetragonal (supersaturated, transform into another structure, diffusionless)
5. Appears of sharp plates and needles,
6. Retain Austenite can exist
7. DOES Not appear on phase diagram
Alloy Steels ANS✔✔ 1. Plain Steel - If carbon is only alloying element
2. Alloy Steel - If you add Cr, Ni, Si, or Mn
3. They shift isothermal curve and delay
Continous Cooling Diagrams ANS✔✔ 1. Time is required for reaction to begin and end
2. Isothermal curves are shifted to larger time and lower temps
Critical Cooling Rate ANS✔✔ The minimum rate of quench that produces totally martensite structure
How to Increase Mechanical Behavior? ANS✔✔ 1. Increase carbon content (more Fe3C, stronger, yield and UTS)
Rank the microstructures that can be produced by quenching the eutectoid of Austenite ANS✔✔ Martensite
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