Need of Pre-heating and Post heating in welding process:Preheating involves heating the base metal, either in its entirety or just the region surrounding the joint, to a specific desired temperature called as preheat temperature, prior to welding.In this article,I am going to publish about,what is the need of Pre-heating & Post heating in welding process in a detailed manner.
Heating may be continued during the welding process, but frequently the heat from welding is sufficient to maintain the desired temperature without a continuation of the external heat source.
Why Preheat is necessary?
There are four primary reasons to utilize preheat:
(1) It lowers the cooling rate in the weld metal and base metal, producing a more ductile metallurgical structure with greater resistant to cracking.
(2) The slower cooling rate provides an opportunity for any hydrogen that may be present to diffuse out harmlessly without causing cracking.
(3) It reduces the shrinkage stresses in the weld and adjacent base metal, which is especially important in highly restrained joints.
(4) It raises some steels above the temperature at which brittle fracture would occur in fabrication. Additionally, preheat can be used to help ensure specific mechanical properties, such as notch and toughness.
Why Post heating is necessary?
Post heating is done in order to remove further residual stresses present in the weld pool after heat treatment process also.
If post heating is not done,then residual stresses develops as cracks and propogates throughout, resulting in the failure of the material.
Therefore Preheating and Post heating must be done during welding.
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The detailed explanation of need of Pre-heating and Post heating in welding process which was shown below in the form of video.
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