Nucleation Science

It's phase transformations that make iron and steel so special. Having a transformation from the fcc austenite phase to the bcc ferrite and / or martensite phase, together with the formation of the Fe3C cementite phase, is just another way to say (carbon) "steel".
Whenever a new phase forms "from scratch", it needs to go through the process of nucleation. How and where new phases nucleate is something we can influence - in contrast to the equilibrium ("nirvana") structure.
As it turns out, nucleation is a complex process. Looking at it in some detail needs considerable space, so I will devote several modules to this topic. What you will find in the links is:
  1. Global and local equilibrium for point defects.
    How supersaturated point defects like vacancies start to "precipitate" under simple and ideal circumstances. It's an exercise for finding out how it is not done and why we need to dig deeper.
  2. Homogeneous nucleation.
    The easy way to start a new phase. Unfortunately it is almost impossible and rarely happens.
  3. Heterogeneous nucleation.
    It's dirty business and thus what really happens, just like in real life.
  4. Size and density of precipitates.
    Now that it got started we need to look at what we get, and how that depends on the thermal history.
  5. Precipitation and structures.
    It's about growing up and how that depends on how you were born and raised.

With frame With frame as PDF

go to Glossary

go to 8.4.1 Martensite

go to Science of Alloying

go to TTT Diagrams: 1. The Basic Idea

go to Ostwald Ripening

go to The Al - Cu System

go to 5.3.1 Grain Boundaries

go to Twinning, Shear Deformation and Martensite Formation

go to Size and Density of Precipitates

go to 8.2.2 Tempering and Ostwald Ripening

go to The Story of Self-Interstitials in Silicon

go to 5.3.4 Bulky Things

go to The Second Law

go to Segregation at Room Temperature

go to Global and Local Equilibrium for Point Defects

go to Homogeneous Nucleation

go to Homogeneous Nucleation

go to Precipitation and Structures

go to Dislocation Science - 2. The Reality

go to 8.1.1 Being a Drag

go to Dislocation Science - 3. Specialities

go to 6.3.1 Nirvana once more

© H. Föll (Iron, Steel and Swords script)