Normalizing is a heat treatment process which is used to make metal, such as steel, more ductile and tough. Thermal and mechanical hardening processes decrease ductility and increase hardness of steel parts. Therefore, normalizing can reform the microstructure into more ductile structures. This reduces the residual stress of the workpiece. Further, normalizing makes the steel more formable and machinable.
In the process of normalizing, the steel gets heated to a specific temperature. This is followed by cooling the metal to room temperature with air. This procedure leads to a new formation of the microstructure of the steel, resulting in reduced hardness and increased ductility.
What are the benefits of normalizing?
Compared to annealing, normalizing is less expensive. Therefore, the procedure is one of the most widely used industrialization process of metals.
Further, normalizing produces harder and stronger metals in contrast to annealing. Thus, it is used for hot-rolled products such as bars, railroad wheels and forged steel products.
How is normalizing different to annealing?
Normalizing and annealing are both heat treatment methods which alter the properties of the treated material. Both processes involve heating steel and other metals to an elevated temperature which is at or above the recrystallization temperature. Then, the metal is allowed to cool down slowly.
The cooling process is the difference between both heat treatment techniques. While the metal gets cooled at a controlled rate in a furnace during the annealing process, normalizing allows to cool the material at room temperature. Typically, this is simply done by exposing the material to air.
Due to the different methods, the metal cools faster in the normalizing process. Normally, this leads to a less ductile and harder material in comparison to annealing. Because of the shortened time in the furnace, normalizing is less expensive than annealing.
The normalizing process
Normalizing consists of the following three main stages:
Stage 1: Recovery
In this stage, the temperature of the material is raised significantly. Typically, a furnace or other heat sources are utilized for this matter. This reduces the internal stresses of the material.
Stage 2: Recrystallization
In the second stage, the metal gets heated to a temperature between the recrystallization and the melting temperature. Thus, new grains form which are not affected by the preexisting stresses.
Stage 3: Grain Growth
In the last stage, the new grains fully develop. The cooling process leads to a material which is less hard on the one hand but more ductile on the other.
Application of normalizing
Normalizing is one of the most extensively used industrial processes. Therefore, it is utilized in a variety of industries. Here are a few examples:
Automotive industry: Typically, ferritic stainless steel stampings are normalized for the use in the automotive industry, in order to reduce the hardness which occurs during the forming process.
Nuclear industry: In the nuclear industry, nickel-based alloys are often normalized due to alterations to the thermal microstructure. These modifications usually occur during the welding process.
Work hardening: Normalizing is used to make carbon steel less brittle after cold- rolling.