Re: [MW:11064] thickness

On Mon, May 16, 2011 at 5:50 PM, Matee Toor <matee.toor@gmail.com> wrote:

dears

pleas tell me why preheat treatment is nessesry in welding and also tell

for what composition

what thickness

thands

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Dear Brother

 

      There are four primary reasons to utilize

preheat: (1) It slows the cooling rate in the weld metal and base metal,producing a more

 ductile metallurgical structure with greater resistance to cracking (2) The slower cooling rate

provides an opportunity for hydrogen that may be present to diffuse out harmlessly, reducing

 the potential forcracking  (3) It reduces the shrinkage stresses in the weld and adjacent

base metal, which is especially important in highly restrained joints  and (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

weld metal notch toughness.

Regards

MADHUSOODHANAN NAIR.G

VELOSI(INDIA), 09967901872

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