Phase Diagrams

· At the eutectoid invariant temperature the compositions of the three phases present are:

C_α = Fe: 0.022 wt% C, C_carbide= Fe: 6.67 wt% C , C_γ= Fe: 0.77 wt% C.
· Using these compositions in the lever rule for (723 - ε) C gives:
W_α = (6.67 - 0.77)/(6.67 - 0.02) = 88% by weight,
W_carbide =(0.77 - 0.02)/(6.67 - 0.02) = 12% by weight.

· The weight percent and volume percent of these two materials is about the same. The two-phase pearlite has a lamella structure due to the kinetics of the diffusion processes involved in the phase transition. Ferrite is light in the photograph.

From: Callister, "Materials Science and Engineering," Wiley (1994)