Tensile strength of FCAW welds

Date 11-10-2009 03:01

I got some PQR results back that have me concerned.
We ran a 3G test per D1.5 and got these results: yield 83.5 ksi, tensile 94.5 ksi, elongation 25%@ 63% reduction of area.
This was with 0.052 E71T-1 with 100% CO2 @ 40 CFH, at 26V, 230A, 7ipm, Hobart Excel Arc 71. I haven't got CVN results yet. RTs were very clean, and macros, side bends aare good. I'm going from memory on the RSTs but I think the UTS was about 83 ksi with breaks in the base metal. Base metal is A709-50W,

Now I need to run a 1G PQR with the same wire, per the New York State SCM, and there is a limit on tensile results of 95 ksi. We're close to that now so it wouldn't take much to exceed that.

The heat inputs will be about the same because we need to run 5/16" fillets in single passes but amps/volts will be higher as well as travel speed. I haven't measured the parameters on the practice welding yet - that's tomorrow. The wire will be the same lot, test plates will be from the same plates.

What effect will a higher volts, amps, and travel have on the tensile strength?

By 803056

Date 11-10-2009 04:39

Higher heat input results in slower cooling, larger grain size, lower tensile strength, better ductility, lower Charpys. At least that is what I would expect to happen.

Why the higher heat input? I suspect the travel speed will be reduced (from 7 ipm) as you introduce a slight weave to build up the 5/16 inch fillet weld as a single pass weld.

Best regards - Al

By js55

Date 11-10-2009 13:33

Chet,
Might be a good idea to run a telebrinneller to give you a warm and fuzzy and perhaps assist with parameters.
Then do the tensile conversion. It ain't exact of course but it would give some idea.

By HgTX

Date 11-10-2009 17:41

Better ductility and *lower* Charpies? Really?

Hg

By 3.2 Inspector (***)

Date 11-10-2009 18:24

I second that question.

3.2

By CHGuilford (****)

Date 11-11-2009 02:16

I discourage weaving for the 5/16" fillet in the 1F and 2F positions- if the heat input is appropriate, there isn't any need to. Oscillations in the weaving has typically caused small spots along the weld length where the fusion didn't get to the root on 5/16" single pass fillet weld soundness test in that the oscillations. Even the vertical positions show the same problems in my experience.

Actually for the 1G position we should see about 12 ipm for travel speed.

I'm not looking for a higher overall heat input, just higher voltage and amperage but the travel speed will be relatively faster too. That way the arc stays on the leading edge of the puddle so we get decent penetration in 2F. Overall, the heat input will remain roughly the same for a given weld pass size.

Our usual method of attaining slower cooling rates is to allow the interpass temp to go higher. However, with a 1" x 18" x 28" plate, and with 5 strongbacks acting as cooling fins, it's difficult to get the temps up there unless we pack a fire blanket in the back side. 450 deg F is Max but 350 is not easy to get to when using semi-auto FCAW. (I'm not talking 5" long welder qualification plates here).

Being very tired, struggling with hotel internet issues (like characters "magically" appearing some 60 seconds after I type them - boy that's a trip), I had forgotten I asked a similar question before and didn't search on that.
But overall, most responses have been that a slower cooling rate should prevent the tensile value from going too high.

By Metarinka (****)

Date 11-10-2009 15:17

as Al mentioned higher heat input will achieve slow the rate of cooling and increase grain size etc. This can also be achieved by using a preheat and not changing the welding parameters.

BUT I should mention that increasing all three: high voltages, amps AND travel speed won't neccessarily increase heat input. for 2 reasons:

The real formula you are looking for is kiloJoules/inch or another measure of heat input per inch. this formula is found by taking Volts X Amps X 60 / (Travel speed in Inches per minute) It leaves you with a Joules/Inch
Now I mention this because sometimes significantly increasing voltage and amperage means welders will naturally OVER compensate and run faster actually reducing heat input per unit which is normally desired, unless of course you want slower cooling. I included the formula in my welding cost estimator http://www.aws.org/cgi-bin/mwf/topic_show.pl?pid=105308;hl=calculator because all the relevant data was already there. You can play around with it and see what comes up.

The second is a concept of heat conduction theory in that it is exponentially related to the velocity of a moving heat source. In other words a heat source moving twice as fast will have to put in much more than double the energy in order for the material to conduct the same amount of heat away from the source. Conduction is a function of time and if the heat source is only applied momentarily (as it is in welding) the heat affected zone will only grow so wide. This is why you can quickly move your finger through a candle or flame without even feeling it. Most welders will realize this too in welding something like stainless steel that's sensitive to over heating. If you run tiny little stringer beads and go too slow your welds will almost always oxidize too much.

I wish I could remember the formula Stephan or Crisi posted it a year or so ago.

Anyways those 2 concepts work in conjunction. Generally the second one is left out unless we are talking about significant changes in welding speed.

By 803056

Date 11-11-2009 04:07 Edited 11-11-2009 04:18

It will be interesting to see what does happen. Please keep track of the parameters and please keep us in the loop.

I see welders weave FCAW most of the time to produce a full 5/16 inch fillet in one pass. Maybe I shouldn't call it a weave since it involves more than simply swinging the gas nozzle side to side. It is more of a triangular weave the way I do it to ensure fusion to the root and to minimize undercut along the upper toe when welding in the 2F position. I do agree with you that it is very easy to produce slag inclusions and incomplete fusion and overlap along the lower toe in the 2F position if it isn't done properly. I spend a good amount of time showing welders how to do it properly. It's always nice to be able to say, "Hey, I'm only an inspector. If I can do it, an experienced welder should be able to do it."

Best regards - Al