Property of the phases*

Phase Structure Nature Spheroidite Small Fe3c spheresin   Soft and ductile Coarse pearlite Alternative thick layers of ferrite and cementite Harder & stronger than spheroidite Fine pearlite Alternative thin layers of ferrite and cementite  Harder and stronger than coarse pearlite Bainite Very fine and elongated particles of Fe3c in  Stronger & hander than bainite.  Martensite Body centered tetragonal single phase needle shape. Stronger and harder but ductility is greater than martensite   Tempered martensite Very small Fe3csphere like particlesin

Mechanical properties i.e. strength and plasticity depend on type, number, size and size distribution of phases. For example fine grain size has better properties at room temperature. Coarse grain size improves creep properties.

Failure of metals consists of crack initiation and its growth. Crack can propagate either within the grain or at the grain boundary. Inter-granular failure is always brittle and usually proceeds with particles of the brittle phase being separated out at the boundaries of the grain.