lecture 12 and Hw 9 Key Notes

Transformation rate depends on

nucleation and growth rate,

Spherodite

tempered banite/pearlite; hold at 700C for 18+ hours

Tempered Martensite

hold between 250 - 650 C

Hardness and strength increase with

an increase in phase boundaries, as this prevents dislocation movement

phase boundaries and Thermal Conductivity

interfere with electron and phonon movement

Structure for Ferrite is

BCC

Structure for Austenite is

FCC

Pearlite

Alternating bands of ferrite and cementite; more coarse when closer to the eutectoid point

Banite

needle shaped cementite in a ferrite matrix; MUCH FINER than pearlite due to low diffusion rates

Martensite

single phase BCT structure

Eutectoid Composotion changes significantly when

additionall alloying elements are added

Supercooling increases

stable nucleation, but get too low of a temperature and the low diffusion rates will limit it

Increase Temperature =

increase diffusion = larger/fewer crystals

Decrease Temperature =

decrease diffusion = increase in nucleation rates = more smaller crystals

Isothermal transformation diagrams

made from taking data at multiple temperatures

Increase Hardness / Tensile and Yield strength through

increasing impurities = more phase boundries = less dislocation movement

Continuous Cooling Curves

constant rate cooling from eutectoid temp to room temperature; Banite is NOT FORMED

Ranking Hardness

Spherodite < Coarse Pearlite < Fine Pearlite < Banite