Processing: Heat Treatments of Metals Flashcards
What are heat treatments?
Temperature is used to control and alter the microstructure and properties of materials.
When do heat treatment work best?
If the atomic bonds in the material are sufficiently compliant to rearranging at higher temperatures without destroying the material.
Where are heat treatments most common?
Among metals whose metallic bonds provide the required flexibility for rearrangements.
When are heat treatments hardly ever used?
Concrete or other minerals where temperature typically causes damage rather than useful microstructural changes.
What are the limitations of phase diagrams?
They are only true when time is equal to infinity.
What does TTT stand for?
Temperature time transformation diagram of eutectoid steel (0.8% C).
What are non-equilibrium phases?
Bainite and Martensite.
What happens if we cool slowly?
The result is coarse pearlite.
What happens if we cool very rapidly?
The result is fine pearlite.
What is the difference between fine pearlite and coarse pearlite in terms of properties?
Fine pearlite is stronger but more brittle.
What are the properties of bainite?
Straight needles form and are strong but brittle.
What is the strongest phase of steel but also the most brittle?
Martensite.
What are the 3 stable phases?
1) Ferrite
2) Austenite
3) Cementite
How can you alter the microstructure and properties?
1) Reducing internal stresses due to cooling
2) Reducing internal stresses due to plastic deformations (strain hardening).
3) Making grains smaller (more strength, less ductility) or bigger (less strength, more ductility).
Describe the reheating process
Look in notes.
