Heat Treatment Flashcards
What is the difference between eutectoid and eutectic?
In a eutectic reaction, a liquid transforms into two solid phases at the same time whereas in a eutectoid reaction, a solid transforms into two other solid phases at the same time
What is Hypoeutectoid?
Less or to the left of the eutectoid point.
What is Hypereutectoid?
More or to the right of the eutectoid point.
What is Proeutectoid?
Proeutectoid is formed before the cooling temperature reaches the eutectoid phase.
What is the purpose of the lever rule and how is it used?
The lever rule determines the proportion of phases present in a mixed-phase sample. To use it, measure the distances from the overall composition point to the phase boundary endpoints on the tie line, and then divide these distances by the total tie line length to find the fractions of each phase.
What are some properties of Bainite?
Formed at intermediate cooling rates, it has an extremely fine structure that is stronger and harder than pearlite and will never be found with pearlite as they are competitive reactions.
What are some properties of Martensite?
Only form at extremely high cooling rates, the hardest and strongest of the steel phases but extremely brittle.
What are some properties of Pearlite?
It is harder and stronger than ferrite, but less ductile and tough.
Why is Martensite hard?
Because martensite is formed through fast cooling the carbon doesn’t have enough time to diffuse out causing the carbon to be trapped in the lattice causing a large amount of strain in the lattice. This reduces the number of slip systems and the carbon hinders dislocation movements.
What does TTT stand for?
Time, Temperature, Transformation
What is the purpose of a TTT curve?
TTT curves are used to predict what phases will be present in a sample due to different cooling regimes.
What is Hardenability?
Hardenability is the ease at which steel will form martensite.
What is the effect of Alloying on Hardenability?
Alloying with particular elements increases the hardenability of steel by shifting the TTT curve to the right.
What is Tempering?
Tempering increases a material’s toughness by heating it to a bit below its melting point and then air-cooling it.
Why is Tempering used for Martensite?
Because martensite is too brittle to be practical we temper it, allowing diffusion to occur leaving us with a material that has nearly the same hardness and strength as martensite but with improved ductility and toughness.
