STEEL - Materials for Civil and Construction Engineers - page 93

FIGURE 3.5 Optical pho-
tomicrograph of hot rolled mild
steel plate (magnification: 50x).
FIGURE 3.6 Optical pho-
tomicrograph of hot rolled mild
steel plate (magnification: 400x).
The significance of ferrite, pearlite, and iron carbide formation is that
the properties of the steel are highly dependent on the relative proportions
of ferrite and iron carbide. Ferrite has relatively low strength but is very duc-
tile. Iron carbide has high strength but has virtually no ductility. Combining
these materials in different proportions alters the mechanical properties of
the steel. Increasing the carbon content increases strength and hardness, but
reduces ductility. However, the modulus of elasticity of steel does not
change by altering the carbon content.
All of the preceding reactions are for temperature reduction rates that
allow the material to reach equilibrium. Cooling at more rapid rates greatly