Re: [MW:11997] relation between preheat or post heating to tensile strength

dear all

I'm glad to answer to this question, thought it cannot be explained in single mail.

Answer for 1^st question-By preheating & post heating we have two advantages 1. To avoid hydrogen induced cracking 2. To reduce the cooling rate during solidification of weld metal.

By reducing the cooling rate we can avoid Martensite (hard structure) formation during weld metal solidification

Martensite is hard brittle structure ,where the hardness is high, so tensile strength also will be soo high,

but other required properties like impact strength, ductility are very less and makes the steel not fit for use.

If the interpass temperature goes high than the required , it many leads to coarse grain formation during weld metal solidification due to slow cooling , Generally coarse grain results in low toughness and less tensile strength properties

Answer for 2^nd question-if you increase the bead width or height without preheating the base material , the cooling rate will be less during solidification which results in coarse grain formation , coarse grains will have less tensile and toughness properties.

In case of SAW welding due to Excess Bead width &height may lead to excess dilution due to excess heat input.

Excess bead height may leads to distortion also by excess heat input.

Cooling rate during solidification of weld metal governs the final metallurgical structure of weldmetal,which in turn governs all mechanical properties..!!!

.( I suggest to read "Introduction to Physical Metallurgy by SIDNEY H ANVER " where all the basics metallurgical concepts are clearly explained. )

Regards,

Sudhakar.k

On Sat, Jul 30, 2011 at 11:00 AM, kalyan vvv <vvvkalli@gmail.com> wrote:

Dear experts,

                   Please solve my doubts

                   Could u please explain

                   1) Is their any relation between Preheating/ Post heating/interpass temp to Tensile strength?

                   2) metallurgically what will happen when bead width and bead thickness increases in SAW process? Is this any effect to tensile strength?



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THANKS & REGARDS

KALYAN VVV

WELDING ENGINEER

HYDERABAD
Mob.NO- 09885273257

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