1. Using the iron-Carbon equilibrium phase diagram, please describe the lines of
ID: 2998175 • Letter: 1
Question
1. Using the iron-Carbon equilibrium phase diagram, please describe the lines of transformation to austenite during heating with carbon content < 0.77 wt.%. (Hint: use the transformation starting line (A1) and the transformation finish line (A3)).
2. What is a typical pearlite structure?
3. What is the difference between TTT diagram and CCT diagram? What is the relation between them? How are they used to estimate a quenching hardening process in a heat treat shop?
4. What is the hardenability, and how will the alloy and carbon contents affect it?
5. What are the three phases at the liquid and solid interface during an immersion oil quenching process?
6. Why press quench is used in some quenching hardening process with tremendous cost increase?
7. List five important material properties to understand a steel part
Explanation / Answer
Answer:
From Iron-carbon equilibrium phase diagram, for 0.77 wt% carbon steel on heating from room temperature to A1line, transformation takes place from alpha + ferrite to austenite + ferrite, this formation is diffusion induced where the pearlitic region of the microstructure converts to austenite, still heating above A3, ferrite also coverts to austenite, this is also diffusion induced transformation.
A typical pearlite structure is an alternate layers of ferrite and hard cementite.
The main difference between TTT and CCT diagram is former is a isothermal cooling diagram and later is the continuous cooling diagram, the relation between these two is both shows the time temperature and transformation information, coling from austenitic structure to room temperature. In heat treatment shop the final microstructure is decided based on the cooling curve drawn in the CCT and TTT diagram. In TTT diagram the formation of bainite is shown (it forms on isothermal cooling) but CCT diagram doesn
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