to Metals
to Heat treatment technologies
Dr. Dmitri Kopeliovich
Normalizing is a process in which a steel is heated to about 100°F (55°C) above the upper critical temperature, followed by soaking and cooling in still air at room temperature.
Normalizing treatment is similar to the full annealing treatment. The difference is in the cooling method and rate – full annealing involves slow controlled cooling if the furnace or in some medium providing slow cooling rate.
As normalizing requires less time, it is more economically efficient heat treatment method than full annealing.
Normalizing relieves internal stresses caused by cold work while grain growth is limited by the relatively high cooling rate therefore the mechanical properties (strength, hardness) of a normalized steel are better than in an annealed steel.
Since the cooling rate in the normalizing heat treatment is not controlled, the resulting structure is dependent on the thickness of the steel part, therefore the effect of increased mechanical properties is greater in thin parts.
Quality of surface after machining of a normalized part is also better than in an annealed part. This effect is caused by increased ductility of annealed steel favoring formation of tearing on the machined surface.
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