Question

 

What is easier: Homogeneous or heterogeneous nucleation? Why?

What does an Isothermal Transformation (IT) Diagram tell us?

How do nucleation rates and diffusion rates influence the shape of the IT Diagram?

What do the letters "A", "F", "P", "B", and "M" mean on these diagrams?

What are the similarities and differences between the following microstructures: Coarse Pearlite; Fine Pearlite; Bainite; Spheroidite; and Tempered Martensite?

How is Martensite (not the tempered kind) formed, and how is it completely different from the other microstructures listed above?

What is the ONLY phase that can transform to into Pearlite, Bainite, or Martensite?

Can you make Tempered Martensite using a single heat treatment, or do you need to use multiple heat treatments?

Answer 1

Heterogeneous nucleation is energetically more favourable because heterogeneous nucleation takes place on already existing surface but for homogeneous nucleation we have to create a new surface.

Isothermal transformation diagrams are temperature vs time diagram on a logarithmic scale.it is useful for understanding the transformation of an alloy steel when it is cooled isothermally.

A- austenite f- ferrite p- pearlite. B- bainite M- martensite

Fine pearlite is harder than coarse pearlite .spherodite is extremely ductile and tough. Bainit is harder and stronger than pearlite. Martensite is hardest strongest and the most brutal of all also they all have different structures at different temperature

austenite can be transformed into pearlite bainite and martensite