Failed weld metal impact test on Cr-Mo-steel

Date 02-04-2011 14:56 Edited 02-04-2011 15:20

Impact performance is a function of heat input into the weld zone, among several other variables. Generally, for a given material less joules per mm gives a higher impact resistance. 1/16" FCAW generally puts a lot of heat into the weld zone. I don't see any figure for GMAW, but I would guess similar sized solid wire would produce low impacts also, although in my experience, GMAW produces slightly higher impacts than FCAW. I'm not really sure what the explanation for that is. Still, 20ft/lbs @ 15F does not seem especially rigorous to me. I'd look around at various wire manufacturers and see what there claimed impacts are for this material and FCAW. If you still can't locate anything, you might try GMAW, metal core. If you go that route, you might call Devasco in Tomball, TX and tell them what your problem is, they custom manufacture specialty wire, if you can order enough. Or you may decide to drop back to 0.052" wire with the FCAW

Edit: Added URL

http://products.esabna.com/EN/home/filler_metals_catalog/filler_metals_product_detail/q/display_id.id4367f2a95c6636.06688505/category_id.822/path.filler_metals_cored_wire_carbon_low_alloy_steel_low_alloy_gasshielded_metal_core_coreweld_w_80cg

By petty4345 (**)

Date 02-04-2011 15:18

Thanks for the reply.
I agree with what you are saying about heat input, and we are paying close attention to that. What we used (27 k/j in.) should have given good results.
The wire manufacturers are telling me that GMAW will produce similar results to what the FCAW did. I have spoken to 3 manufacturers, and they are all saying they do not have a FCAW product that will get the results that I need.
Now, I'm just mostly interested in why it is expected with only this (or now these 2 if you now add GMAW) process(es)?

By jarcher (**)

Date 02-04-2011 15:39

I'll check with people I know hereabouts to see if I can get an answer in terms other than heat input for both processes. There is also a materials section here:

http://www.eng-tips.com/

were you might find a metallurgist that can address the issue. And of course, there are resident degreed welding engineers on this forum that might be able to address why impacts are so problematic with GMAW and FCAW comparatively. There seems to be some thing more than just heat input as an issue.

By petty4345 (**)

Date 02-04-2011 15:33

ESAB tech support is one of the manufacturers that said they had no solid or cored product that would meet our requirements.
I wrote back to ask them about the Coreweld 80-D2.
I'll post what I learn when I here back from them.

By jarcher (**)

Date 02-04-2011 15:50

Their 80Ni wire says their impacts (under properties) would meet your requirements. But they are probably being truthful when they say they can't guarantee impacts, after all, they would make a sale if they could, and my experience with manufacturer's impact claims in the past indicate most of them suffer from inflation slightly (this is industry wide, not just ESAB). If you haven't yet, you still might try Devasco:

http://www.devasco.com/

They have a number of formulations the keep on the shelf; they might have one that would do what you want without you having to buy a whole run of it.

By petty4345 (**)

Date 02-04-2011 16:40 Edited 02-04-2011 18:12

The explaination (which now makes sense) that I got from ESAB on why they did not suggest the 80-D2, is that it does not chemically match the Cr/Mo base metal.
The D2 is Mn/Mo and the B2 is Cr/Mo.
Going along those lines, i guess that's why they did not suggest a Ni electrode either.

I will check out Devasco as you suggested.
Thanks, this all forced me to learn something.

Edit: D2 is Mn/Mo
Table 7 of SFA-5.29 makes all of these designators clear.

By jarcher (**)

Date 02-05-2011 16:19

Actually I cut and pasted the wrong URL, the 80Ni was my intention for the link in the first place, just didn't get the change done before you responded. I'm confident the 80Ni would meet your mechanical requirements. The question then is corrosion resistance, which would have to be tested for to be absolutely sure. My guess is you would find 80Ni to resist corrosion about as well as the B2 for most exposures. But as I said a metallurgical lab would have to run corrosion tests for what ever exposures the finished weld would be exposed to. Maybe somebody will happen by with direct experience using the 80Ni wire with whatever exposures, you would have to specify.

Of course, you might want to use a different process. I used to weld a lot of P5/P11/P22 with impact requirements using SAW, the wire and the flux is out there to do it.

Good luck with this.

By petty4345 (**)

Date 02-07-2011 13:11

We are working with our customer to agree on an exceptable electrode for either GMAW or FCAW.
They understand the impact on use of not being able to use one of these 2 processes.
This is a very large project with many joint configurations, and joint access limitations, so we do need to use SAW, SMAW, GTAW and either GMAW or FCAW (semi-automatic)
Thanks again for your replies/help.

By 803056

Date 02-07-2011 14:47

You may have to use post weld heat treatment to recover some ductility and toughness with the chrome moly steel and matching filler metal.

If you look at foot notes at the end of Table 3.1 in D1.1, the filler metals typically used with the CrMo steels require PWHT or qualification by testing if PWHT is not used.

Best regards - Al

By petty4345 (**)

Date 02-07-2011 15:32

Yes, there is PWHT required. It is an ASME Section VII vessel.
I did not post in the ASME section because I thought this to be more a technical question than a question about the ASME code.
Didn't mean to cause confusion.

By 803056

Date 02-07-2011 15:59

After rereading your post I see you did PWHT the weld.

I didn't have my Section VIII handy, so I looked at B31.3 for the PWHT requirements. B31.3 lists 1300 to 1375 degrees F for 2 hours as the stress relief requirements. It would appear you held a lower temperature for a longer time.

Best regards - Al

By petty4345 (**)

Date 02-07-2011 16:22

The Section VIII temperature requirement is 1,250°F. The reason for the 5 hour at temp. for the PQRs is to allow 2 heat treat cycles for the production part should there be weld repairs after PWHT and testing.
This is maybe playing it too safe in this case, but it's good to know that the welds can tolerate the worst case.
I've seen situations where PWHT had to be repeated for one reason or another and if your PQR is not at temp. for at least 80% of the production part, you need to re-qualify.
Preliminary VT, MT and RT is done before PWHT, but you never know.

By js55

Date 02-07-2011 16:30

The problem with the filler metal and process you are using is twofold.
CrMo fillers have a rather high ductile to brittle transition and 15deg may be below this transition for this filler.
The other thing is the oxides involved with the FCAW process. FCAW in general will realize the worst CVN's of the fusion processes.
Also, keeping heat input low is not always best for CVN's. Keep in mind that sometimes greater heat input will temper and restructure the grains of previous weld beads and actually improve impacts.
Tempering is especially importnat for CrMo's since their microstructure is prediminantly bainite and high toughness microstructural constituents is not in the alloy cards, so to speak as with carbon steels where you can go from polygonal ferrite to acicular ferrite with lower heat input.
If you have to have FCAW and have time I'd run several tests at differing temps and determine where your ductile to brittle is with CVN S curve. You will have an upper shelf and alower shelf. Thelower shelf at lower temps. The transition inbetween will be rapid. The S curve where tell you the limits of your wire.
One other thing. P11 is not intended for colder temp services.

By petty4345 (**)

Date 02-07-2011 18:03

I think it's best that I drop the FCAW/GMAW idea and go to hand held (semi-auto) SAW for some of these joints
Even if I apply every advantage I can come up with, the best i'll probably get is impact properties that just barely meet the 20 ft. lb minimum in a perfect test enviroment, and then have to write a WPS with such tight restrictions on it that it cannot be adheared to on the production floor.
We have to do production impact test plates as we weld the vessel, and if those impacts fail, the vessel welds are rejectable.
my goal is to give the welders the best processes to use to accomplish the work to the requirements, and not give them something that they can easily fail with.
SAW semi-auto is not as easy to use as FCAW, and there will be some complaining but it will be the right thing to do in this situation.