Steel weldability


Given the chemical composition of the steel as determined form specimens cut form existing rebar from an old building, how is the weldability determined?
What is the formula, and what is the criteria for assessing its weldability?
Is the formula for weldability as follows:

%C + %Mn/6 + %Ni/20 +%Cr/10
correct, and if so, what is the acceptance criteria? If this is not the correct formula, what is?

A representative specimen is as follows:

Carbon 0.39?
Manganese 0.66%
Chromium 0.04%
Nickel 0.04%


EN 1011-2 states exactly what you need, it’s a european code so it might not be applicable everywhere. The technical background is (should be) the same everywhere, though…

Above is a snippet.

@kingnero, Could you please expand on this given the codes you work with?

CEv gives an idea about the hardenability of the steel, not the weldability.
Both are however closely linked to eachother.

This has nothing to do with codes, steel doesn’t care whether it is USA, Chinese or European steel.
Besides the chemical composition, weld geometry, heat input, process, … all play a role in whether or not steel is “weldable”. Of course requirements regarding mech. properties are also to be considered.

Please narrow down your question, this might yield better answers…

1 Like

Carbon equivalency

DikCarbon Equivalent01.xls (19 KB)

@kingnero…good to see you back in here. This snippet is from an older Eng-Tips thread that showed up in an internet search in which you provided some input. The purpose of bringing it into SimpliEngineering is to prime discussion on a variety of subjects that might have some universal appeal.

The question of “weldability” often comes up in two subject areas…reinforced concrete (welding rebar) and in structural steel particularly with respect to certain specialized steels or in fatigue issues. Having qualified people in here to answer those questions and help resolve such issues is invaluable to the engineering community at large.

The more corresponding discussion we have on this site with regard to Eng-Tips subjects that may have fallen by the wayside, the better we are able to preserve the legacy of volumes of helpful insight provided by “The House that Dave Built”.

Again, thanks for your input and please keep offering your expertise here on SimpliEngineering.

@dik…nice little spreadsheet…thanks.

Both of these are very different, from a chemical/welding point of view as from a mechanical point of view.

When welding rebar, you want an as little as possible weld nugget in order not to touch the outside diameter of the rebar. The weld capacity isn’t checked in most (standard) cases, but the tensile force each bar can transmit will be checked (and approved if they still have the same properties welded as unwelded). Any undercut will severely punish the result.
Most rebars are also 500 MPa, having a fairly low CEv but are very sensitive to heat treatment (= welding!) as they have undergone severe deformation (cold forming/work hardening) and have reached their high yield/tensile strength that way.

I don’t think I need to explain the welding of structural steels, but the requirements here are very different. For the high strength low alloyed structural steels, the CEv is again of lower importance as those require PWHT anyway, tempering any possible martensite in the base material (in most cases, the filler doesn’t form any martensite).

A lot of people don’t give the welding in a construction much thought, this isn’t a problem in most cases as you can hardly f* up most common steels, but you should consult a welding engineer or similar when you have to weld anything out of the ordinary. I don’t understand why some people take huge risks when a few-hour consult with a specialist will give much more reliable results…