Forged and annealed, magnified r000 diameters, showing pearlite.
This alloy, if allowed to solidify completely before chilling, turns into a uniform solid solution, and at still lower temperatures the solid solution breaks up into a pearlite complex.
Iron and phosphorus unite to form a solid solution which breaks up on cooling into a pearlite.
The difference between softness and hardness in ordinary steel is due to the permanence of a solid solution of carbon in iron if the steel has been chilled or very rapidly cooled, while if the steel is slowly cooled this solid solution breaks up into a minute complex of two substances which is called pearlite.
The pearlite when highly magnified somewhat resembles the lead-tin eutectic of fig.