Phase Diagrams Flashcards
What is Gibb’s phase rule?
P+B=C+n
What is the lever rule?
WL x R= Wa x Q
What is a eutectoid?
An invariant point with 3 solids in equilibrium (Bunny ears)
What is an eutectic?
Invariant point with 3 phase in equilibrium
What is peritectoid?
Invariant point with 3 solids in equilibrium ( moustache)
What is Pearlite?
Ferrite + cementite
How do you identify between ferrite and Austenite?
Magnet
What is Hypo?
Left hand side of invariant point
What is hyper?
Right hand side of invariant point
What iron carbide (Fe3C) alloy is less than 2.1wt% carbon
Steel
What is between 2.1 and 6.7wt% carbon?
Cast iron.
How is pearlite formed ?
Slow cooling from austenite region
How is bainite formed?
Moderate cooling from austenite region
How is martensite formed?
Quench from austenite region
How is spherodite formed?
Reheat pearlite or bainite to 700 degrees for 24h then quench
How do you form tempered martensite?
Have to have 100% martensite, the reheat to 500 degrees for a few hours
Describe the difference between tempered and normal martensite?
Martensite: carbon doesn’t have time to diffuse out so very hard but brittle
Tempered martensite: carbon had time to diffuse out when reheated, cementite will form inside a ferrite matrix and austenite will turn into pearlite
How are upper and lower bainite formed?
Upper between 300-500
Lower between 200-300
Cementite rods in ferrite matrix ( thinner rods for lower)
How are coarse and fine pearlite formed?
Coarse: cool down slightly faster
Fine: Cool down in air
Coarse has thicker plates of cementite and ferrite therefore less hard
Effect of tempering and adding carbon
More carbon = harder but less ductile
Tempering: tempering for longer and higher temp decreases hardness but increases ductility
Describe how an IT diagram works
First line is beginning of transformation, second line is 100% transformed
Why can’t bainite be formed on a CC sometimes?
Has to be cooled slowly, by the time it should turn into bainite it has already turned into pearlite q
What is the first curve in a CC?
Minimum cooling rate to form 100% martensite
