Metallurgical Base

How normalizing different from annealing?

NORMALIZING:

Normalizing is a heat treatment process that is used to make a metal more ductile after it has been subjected to thermal or mechanical hardening processes. Normalizing involves heating a material to an elevated temperature and then allowing it to cool back to room temperature by exposing it to room temperature air after it is heated. This heating and slow cooling alters the microstructure of the metal which in turn reduces its hardness and increases its ductility.  Material is heated to between 750-980°C. The exact heat applied for treatment will vary and is determined based on the amount of carbon content in the metal.

Also read: An introduction about principle of heat treatment of steel

About cooling process: 

After heating material, it is cooled to room temperature. The rate of cooling significantly influences both the amount of pearlite and the size and spacing of the pearlite lamellar. At higher cooling rates, more pearlite forms, and the lamellar are finer and more closely spaced. Both the increased amount of pearlite and the greater fineness of the pearlite result in higher strength and higher hardness. Conversely, lower cooling rates result in softer parts within the metal normalizing process.

Also read: An introduction of metallurgy

ANNEALING:

Annealing is heat treatment that alters the physical and sometimes chemical properties of material to increase its ductility and reduce its hardness making it more workable. It involves heating a material above its recrystallization temperature, maintaining a suitable temperature for a suitable amount of time and then cooling.

Types of annealing process: Here discussing five type of annealing processes.

Process annealing:

Process annealing involves the heating below (20 or 50˚C) the AC1 line. The time is given for recrystallization and re-structuring of the ferrite phase. The steel is then cooled slowly. 

Also read about What is corrosion or deterioration of metal?

Soft annealing:   

Soft annealing perform in high carbon steel, copper alloys and brass alloys. Steel with high carbon content is typically treated with soft annealing process which gives it softer and easier to work structure. Soft annealing process take approx 12 to 48 hours in furnace. Steel heated up to 800˚C (range is 680-800˚C) held at this temperature for 2-4 hours so that the structure fully converts into austenite. Cooling of this steel is performed at a controlled and steady rate of 10 °C (50 °F) per hour until the temperature reaches 690 °C (1274 °F).  

The cooling condition defines the degree of softness attained. The advantage of this process is that a soft and ductile carbon steel is obtained that has a good ability to form.

Stress relief annealing:

Heated up to the temperature of 600 to 650 °C (1112 to 1202 °F) and kept in this condition for hour or more. Then furnace cool till the temperature drops to 426 °C (800 °F) then cooled to ambient temperature slowly in the still air.  

Also read about How chemical elements effect on the steel properties?

Full annealing process:

The long annealing time produces ideal softening. Full annealing is done inside the furnace. After reaching the holding temperature the furnace is turned off, and metal anneals inside the furnace. 

In full annealing the carbon steel is slowly heated to a temperature of 50°C (122°F) above the austenitic temperature (Lies between 750-900°C or 1320-1652°F) also known as “holding temperature,” and then cooled down slowly to the room temperature. The cooling rate recommended is 20°C (68°F) per hour.

Once the metal is reached at 50°C (122°F) it can further be cooled to room temperature using air in environment. The basic heat treatment processes for carbon steel involve conversion of austenite.   

Isothermal Annealing:

In isothermal annealing process, the steel is heated above the upper critical temperature. When the steel is heated above upper critical temperature, it converts rapidly into austenite structure.

After that, the steel is cooled to a temperature below the lower critical temperature 600 to 700°C. The cooling is done by force cooling methods. This temperature is maintained for a specific time period to achieve homogeneous structure in the material. Isothermal Annealing process is mainly applied to low carbon and alloy steel to improve their machinability.

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How normalizing is different from annealing?

After reading above, we come to know that the purpose of both is same to soften the materials and improve machinability.

Steel is gradually cool in air after heat treatment in normalizing but furnace cooling is mandatory in annealing process.

Normalizing has higher yield points ultimate tensile strength and impact strength in comparison to annealing.

Comparatively less soft but annealing more soft and easy to machinable.  Normalized parts are harder, less ductile and less percentage of elongation in comparison to annealed part.

Difference between Normalizing and Annealing

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K Yashdeep

Hye there..! I am Yashdeep Kamal. I completed my Bachelor in Technology(Materials Science and Metallurgical Engineering). Engineer by passion, writer by choice. I have been writing about Composites, Ceramics, polymers, nanotechnology, advance materials and metallurgy etc. You can read about these topics here. Hope it may help you.

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