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Welding formula question for preheat

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Dinosaur

Dinosaur

Structural
Mar 14, 2002
538
I recently learned that there are more than one carbon equivalent (C.E.) formulas out there. The formulas I am interested in understanding are the AWS and the ASTM versions. If the formula is not met, then welders have to exercise precautions for preheating when welding.

The AWS version includes a term Si/6. The ASTM version includes a term V/5. Can anyone explain the difference? I noticed that ASTM A709 steels contain up to 0.40% Si (some grades even more). The Vanadium content is limited to a much smaller level, typically 0.06% for example. If the silicon content of steel is frequently higher than the limit for Vanadium, then the AWS formula appears more strict.

Is this warranted? If it is, then why would the ASTM folks not think it wise also?
 
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There are several CE formulas’ that are tailored to specific families of carbon and low alloy steels. The reason is response of the metal to welding, based on alloy or micro alloy compositions.

As you can see, the affect of vanadium is greater than that of silicon, which is commonly used to deoxidize (or kill) steel.

Yes, the AWS CE formula is more restrictive and widely used for carbon and some low alloy steels.
 
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Also, you may want to investigate the FAQ below;

faq330-1077
 
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We have a supplier that says most of the steel on the market today for his product (tubular support structures) in the US is recycled steel. He can't get steel that meets the AWS formula but says he can get steel that meets the ASTM formula.

Most of what we do with the AWS is fabrication of A709 Steel and I am assuming by your comment that the AWS formula for C.E. is valid for that family of steel.

I guess the question becomes, which other steels are valid for the C.E. formula in the AWS with the Si/6 term? And, which steels are suitable for the C.E. formula in ASTM?
 
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Keep in mind that CE is a qualitative parameter used for comparison of weldability between materials, and for determining preheat requirements. I don't see where this would be a problem in your situation. If you use recycled steel, and it meets comparable chemical composition and strength requirements for A 709, you can still calculate a CE using the ASTM formula (ignore terms where elements are not reported) and compare with A 709. If the CE is higher or lower, you make adjustments to your preheat requirements.
 
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ASTM A 709 is usually recycled too.

Hg

Eng-Tips policies: faq731-376
 
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