Normalizing

The normalizing of steel is carried out by heating approximately 100 oF above the UCT (Upper Critical Temperature) followed by cooling in air to room temperature. Normalizing can be applied above the UCT for both hypoeutectoid and hypereutectoid steels. Figure 1 shows the normalizing temperatures.

Figure 1. Normalizing temperatures for hypoeutectoid and hypereutectoid steels.

The following is the list of the reasons for normalizing the steel :

To produce a harder and stronger steel than full annealing

To improve the machinability

To modify and refine the grain structure

To obtain a relatively good ductility without reducing the hardness and strength

Figures 2, 3, 4 and 5 show the effect of annealing and normalizing on the ductility, tensile strength, hardness and yield point of steels.

Figure 2. Ductility of annealed and normalized steels.

As indicated in Figure 2, annealing and normalizing do not present a significant difference on the ductility of low carbon steels. As the carbon content increases, annealing maintains the % elongation around 20%. On the other hand, the ductility of the normalized high carbon steels drop to 1 to 2 % level.

Figure 3. Tensile strength of normalized and annealed steels.

Figure 4. Yield point of annealed and normalized steels

Figures 3 and 4 show that the tensile strength and the yield point of the normalized steels are higher than the annealed steels. Normalizing and annealing do not show a significant difference on the tensile strength and yield point of the low carbon steels. However, normalized high carbon steels present much higher tensile strength and yield point than those that are annealed.

Figure 5. Hardness of normalized and annealed steels.

As seen from Figure 5, low and medium carbon steels can maintain similar hardness levels when normalized or annealed. However, when high carbon steels are normalized they maintain higher levels of hardness than those that are annealed.

 

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Last update: October 28, 1999

Prepared by: Serdar Z. Elgun