Normalizing

Hello Readers, welcome to your own website to understand each and every topic related to the manufacturing process where we transform complex content into simpler ones. In this article, we are focused to cover the meaning of normalizing process, recovery stage, Recrystallization temperature, grain growth stage, advantages, disadvantages, and applications of normalizing process.

MEANING

Normalizing or normalizing annealing is a heat treatment process consisting of austenitizing at temperatures of 30–808 deg C (86–1768 deg F) above the transformation temperature.

Time–temperature regime of normalizing.

Heating.

Holding at austenitizing temperature.

Air cooling.
 
Air or furnace cooling.
 
 
Specially for unalloyed and low-alloy hypoeutectoid steels normalizing process is applied.

Schematic presentation of the influence of austenitizing temperature on the grain size of the structure of a eutectoid steel after normalizing
Fig.1 Schematic presentation of the influence of austenitizing temperature on the grain size of the structure of a eutectoid steel after normalizing

This process is performed only in special cases, for the hypereutectoid steels, and for specially these steels the austenitizing temperature is 30–808 deg C (86–1768 deg F) above the transformation temperature.

On the basis of their carbon content the thermal cycle of a normalizing process is dependent.

The heating rate, the austenitizing temperature, the holding time at austenitizing temperature, and the cooling rate are the the parameters of a normalizing process.

This treatment refines the  grain of a steel which has become coarse-grained because of heating it at a high temperature. eg. forging or welding.

Such grain refinement and 6 Range of austenitizing temperatures for normalizing unalloyed steels depends on their carbon content.

For the purpose of improving the mechanical properties of the workpiece or to obtain much better and more accurate uniform results after hardening, homogenization of the structure by normalizing is usually performed.

For better machinability of low-carbon steels normalizing is applied in some cases.

A specific need for normalizing includes with steel castings due to slow cooling after casting, so a coarse-grained structure develops that usually contains needle like ferrite.

A normalizing treatment at 780–9508 deg C (1436–17428 deg F) depends on the chemical composition which removes the undesirable structure of unalloyed and alloyed steel castings having 0.3–0.6% C.

Structure of DIN 20MnCr5 steel (a) after hot rolling and (b) after normalizing at 880 deg C
Fig. 2 Structure of DIN 20MnCr5 steel (a) after hot rolling and (b) after normalizing at 880 deg C

The structure of steel is usually oriented in the rolling direction after the hot rolling.

Of course, mechanical properties are different between the rolling direction and the direction perpendicular to it.

A normalizing annealing has to be performed to remove the oriented structure and obtain the same mechanical properties in all directions.

After forging at high temperatures, specifically with workpieces that vary widely in cross sectional size, because of the different rates of cooling from the forging temperature, we get the heterogeneous structure made uniform by normalizing.

This treatment can be explained with the metallurgical aspect, the grain refinement and the uniform distribution of the newly formed ferrite–pearlite structure.

Firstly the steel is subjected to ferrite pearlite to austenite transformation, and after the holding time at austenitizing temperature, to a recurring transformation in the normalizing process.

On the basis of austenitization and cooling from the austenitizing temperature, the effect of normalizing is dependent.

The possibly simultaneous formation of ferrite and pearlite is necessary for the desired uniform distribution of ferrite and pearlite after the normalizing.

For the purpose of obtaining a new arrangement of ferrite and pearlite constituents in the structure, not only the carbide dissolution but also the degree of homogenization within the austenite matrix is important after the normalizing.

For creating a microstructure which is relatively ductile for this, the normalizing is very similar to annealing as both involve heating a metal to or above its recrystallization temperature and allowing it to cool slowly.

Structure of steel casting (a) before normalizing and (b) after normalizing
Fig. 3 Structure of steel casting (a) before normalizing and (b) after normalizing

This play much more important role for making the metal more formable, more machinable, and reduces residual stresses in the material that could lead to unexpected failure.

This process allows the material to cool by placing it in a room temperature environment and exposing it to the air in that environment.

Because of lower requirement of furnace time during the cool down process the normalizing is much less expensive as compared to annealing.

There are three main stages of normalizing.

Recovery stage.

Recrystallization stage.

Grain growth stage.

RECOVERY STAGE

To raise the material at a temperature where its internal stresses are relieved, for this a furnace or other type of heating device is used in recovery stage.

RECRYSTALLIZATION TEMPERATURE

The material is heated above its recrystallization temperature, but below its melting temperature while the recrystallization stage is going on.

Because of this new grains without pre existing stresses are formed.

GRAIN GROWTH STAGE

The new grains are fully developed in the grain growth stage.

By allowing the material to cool to room temperature via contact with air this growth can be controlled.

A material with more ductility and reduced hardness is formed after the completion of above three stages.

After that the operations which can further alter mechanical properties are sometimes carried out after the normalizing process.

ADVANTAGES

Greater overall database organization.

Reduction of redundant data.

Data consistency within the database.

A much more flexible database design.

A better handle on database security.

DISADVANTAGES

Since data is not duplicated, table joins are required.

In this the problem are more complicated, and because of this read times are slower.

Because of this joins are required, indexing does not work as efficiently.

Delete anomalies that will cause an error in the systems.

APPLICATIONS

Normalisation is mainly used on carbon and low alloyed steels to normalise the structure after forging, hot rolling or casting.

The hardness obtained after normalising depends on the steel dimension analysis and the cooling speed used (approximately 100-250 HB).

CONCLUSION

We have covered all the important concepts related to normalizing process. Hope you all are crystal clear with all the concepts mentioned here. If you have any questions please use the comments section to get in touch with us. Till then have fun and always keep reading!

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