Normalized Steels are obtained through the normalization process, which is a heat treatment that changes the hardenability, mechanical strength and toughness of the steel by heating the material to a temperature just above the austenitizing one (Ac3 + 50-70 °C), maintaining it for about 15 minutes and cooling at room temperature.
This treatment helps reduce internal stresses created by manufacturing processes, such as forging or mechanical processes, thus improving the dimensional stability, the microstructural homogeneity and consequently the response to further heat and thermochemical treatments. In this way, a “thermal memory” is created for subsequent processes that will be carried out at lower temperatures.
What are the benefits of normalization treatment?
An aspect not to be underestimated is that steel, a ductile and very durable material that provides safety and space utilization, gains several benefits from this type of treatment, greatly optimizing its characteristics.
First of all, it allows a much easier processing of the steel itself and provides greater stability. Usually, normalization is performed when a particularly strong steel is required: Normalized steels achieve good mechanical strength and a high impact resistance.
However, it is good to remember that steel plates with different thicknesses give different results, this is because a thinner plate will need less cooling time and will therefore be harder and stronger than a thicker plate.
When to normalize steel
There are several situations where normalized steels are required:
- Plates that require achieving adequate resilient values
- Welded structures where joints altered by electric arc must be brought to a stable metallurgical condition and have perfectly homogeneous hardness values.
- Rings, dished bottoms, calendered plates, and any product obtained from cold or hot plastic deformation. In this case the elongations of the cleavage planes composing the crystalline conglomerate, cause a significant decrease in the ductile properties of the part.
- Cast iron or steel castings with cross-sectional diversity, undercooling phenomena, or repair by welding defective areas. In these artifacts, equilibrium’s loss is caused by heterogeneous structures with widely varying hardnesses even in very confined areas.
- Components already in an acceptable equilibrium condition but requiring preliminary treatment to ensure non-deformability in the final process. Usually, normalization is performed on pre-processed parts that will then need to be cemented, induction hardened, carbonitrided, and in some cases nitrided.
In some cases, a double normalization at different temperatures might be needed, the first at higher temperature to better equalize the grain and the second at lower temperature to refine it.