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Steel is annealed by heating the steel to a temperature above the upper critical temperature, holding it there until the temperature is uniform throughout the part, and then slow cooling the part through the transformation range. The heating and cooling rates depend on the composition, shape and size of the part.
Full annealing removes the internal stresses, which build up as a result of cold working and other fabrication processes.
This treatment refines the grain size and enhances the uniformity of the microstructure. In some instances, this treatment will improve machinability.
A previously cold worked part will soften when normalized. An annealed part will harden when normalized.
Normalizing involves heating the steel to about 100°F above its upper critical temperature, generally 1650°F. The component is then held at this temperature until the temperature is uniform throughout the part (generally one hour per inch of thickness), and then cooled in air.
The microstructure produced by normalizing, depending upon the carbon content of the steel, is pearlite (eutectoid), pearlite in a ferrite matrix (hypoeutectoid), or pearlite in a commentate matrix (hypereutectoid). Cooling in air results in a fine pearlite with improved mechanical properties compared to the full annealing process described above.
Normalizing is used to refine the grain structure and to create a more homogeneous structure when a steel is to be reheated for hardening and quenching or full annealing, or to unify the microstructure of the heat effected zone of weldments, segregation in castings and forgings and provide a more uniform structure, and also to provide moderate hardening.
Maximum Load Sizes
