ANNEALING OF COLD ROLLED STEEL

By | February 20, 2016

Annealing of cold rolled steel is  defined as a process of softening  the material, metal, or an alloy to make it less brittle by heating to a particular temperature ,maintain it at that temperature  for particular duration and ,Cooling it slowly to a particular temperature.

Or

It can be defined as a heating of a material above re crystallization temperature ,maintains at suitable

Temperature and then cooling .

Annealing of cold rolled steel

Cold rolling occurs with the metal below its re crystallization temperature( usually at room temperature).

During  cold rolling process  grain structure is deformed and became closer due to reduction in thickness.

Due to this steel  become hardened and more brittle.

It will reduce the ductility of cold rolled steels and make it useless for end use or forming operation.

Annealing is used for

Softening of  cold rolled steel

Relieving the internal stress developed during cold rolling process

Develop desired mechanical properties suitable for intended applications and Bright Surface Finish .

STAGES OF ANNEALING

Process of relieving internal stresses induced during  cold rolling takes place in  three stages

  • Recovery

Physical and mechanical properties ( Hardness, ductility prop.) which suffered changes during  cold working tend to recover  to their original values. Occurs at the initial phase of annealing at lower temperatures.

In this internal stress are reduced. it will take at temperature 480 deg to 500 deg C.

  • Re crystallization

It is a Process of nucleation of  new strain free crystals  (grains) which replaces all deformed crystals of  the cold worked material. Takes place at a temperature known as re crystallization  temperature .it takes place around 550 deg C .

  • Grain Growth

Increase  in  average  size of  crystals/grains  on  further  annealing  subsequent to the completion  of re crystallization . Grain size has direct effect on the mechanical properties. Hence it is controlled to achieve optimum properties. it will takes place at the time of soaking.

  Annealing  requires

Heating the cold rolled steel to the re crystallization 550 To 700 deg C temperature.

Soaking at this temperature for sufficient time for homogenization and necessary changes to occur.

Cooling at a predetermined rate

Process Variables

Temperature, soaking time , cooling rate depending on  the desired mechanical properties

In order to meet high demand on the cold rolled surface annealing is take place under protective

Gas atmosphere consist of

  • hydrogen

  • nitrogen

Generally low percentage of hydrogen are used because it is quite flammable  and it is considerably

more expensive than nitrogen.

Other types of gases such as methane and the like can be used for annealing process.

 

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