Do you know the difference between A706 and A615 bars? - LinkedIn

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Link to Xingtai Steel

Recently, a coworker shared a CRSI (Concrete Reinforcing Steel Institute) document called “Frequently asked questions about reinforcing bars.” (link)

Lots of really good info in there. My favorite one is about A706 bars vs. A615 bars.

We hear it all the time (and see it on the drawings) that for welded rebar and seismic applications, use A706, not A615…, but why?

The CRSI article explains it pretty well (it’s under the section “What is the availability and application of ASTM A706 reinforcing bars?”)

I’ll give you a CliffsNotes version below.

(Estimated reading time: 2 minutes and 18 seconds.)

Tightly Controlled Chemistry

First, the major difference between the two ASTM standards is the chemical make-up of the bars.

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For A706 bars, chemicals are more tightly controlled to enhance weldability. There are maximum limits on carbon, manganese, phosphorus, sulfur, and silicon.

A615, on the other hand, only has a limit on phosphorous.

This is hugely important, which I’ll explain next.

Carbon Equivalent (C.E.) & Preheat Temperatures

AWS (American Welding Society) has an equation for calculating this thing called the “carbon equivalent” (aka C.E.). It is based on the chemical analysis of seven elements:

For A706, the requirement is that the C.E. must be 0.55% or less. (I.e., if you specify A706, you can be sure that the bars you get will have C.E. <= 0.55%)

And since C.E. is linked to the “minimum preheat temperature required for welding,” A706 bars can be welded at much cooler temperatures. (For example, based on the AWS Table below, #3 to #11 A706 bars can be welded at 50 degrees or less.)

So basically, no preheat for A706 in most common cases.

A615, on the other hand, has no C.E. requirements – meaning, the C.E. of any given bar is pretty much unknown.

If you are looking for more details, kindly visit astm a615 rebar.

Because of that, you have to assume the worst case, which could be above 0.75%. So if you want to weld it, the bar must be preheated to 300 to 500 degrees

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