Normalizing is performed after fabrication techniques such as stamping or casting. This is because metals that have been quenched for hardness typically exhibit reduced ductility.
Normalizing transforms your metal’s crystal structure to a ductile state, enhancing toughness and brittleness. Consequently, normalized steels and nickel alloys are easier to machine than their untreated counterparts. Normalizing also prevents failures by relieving residual stress.
Now that you know the purpose of normalizing, it is time we cover key normalizing parameters.
Heating
To perform normalizing, heat your metal to its upper critical temperature. Recovery begins in this stage as defects in the microstructure undergo refinement. This leads to the progressive relief of stresses picked up during other manufacturing processes.
If you are normalizing steels yourself, the big challenge is getting your entire workpiece to heat evenly. Uneven heating produces a metal with inconsistent properties, which later show up as failures in machining or service.
Soaking Time
Once you have heated the steel sufficiently, the next step is to hold it at recrystallization temperature for a predetermined period. During this hold, the mechanical properties change. The longer it is held, the more its properties alter.
As the recrystallization point is reached, bainite and carbides dissipate from the metal. New austenitic grains form, consuming existing dislocations, grain boundaries, and defects. These grains are smaller in size than previous ferritic grains. For more details, you can check the guide on the structure of engineering metals.
Cooling
The last stage of normalizing is the grain growth stage. This growth is controlled by cooling the heated metal in air until it reaches room temperature. Those newly formed grains we just mentioned fully evolve and mature, producing a metal that is strong and ductile.
During cooling, you must carefully monitor the cooling rate. The slower the cooling, the more toughness your metal will exhibit. Likewise, the faster the cooling, the more harndess your metal will exhibit.
