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GTAW 304SS to 410SS w/o preheat & w/o PWHT

GTAW 304SS to 410SS w/o preheat & w/o PWHT

GTAW 304SS to 410SS w/o preheat & w/o PWHT

(OP)
I have the unfortunate job of field repairing equipment that involves 302/304 threaded fasteners that were originally GTAW welded to a 410 base plate (the base plate was originally heat treated to HRC35-40). The attached fasteners need to be removed and replaced.

All guidance I have seen so far indicates that I should preheat the 410 and then stress relieve after welding - neither will be practical or possible in my present circumstance.

I am tentatively selecting a 309L filler as my calculations show a resulting FN of ~10, not bad (I think). This is based on WRC-92 and Dr Kotecki calculations with the assumption of 15% dilution with each base material. Same calculation with 310 welding rod shows an FN off the chart so I assume this indicates a fully austenitic weld will result(not good, I think).

There is no governing welding code for this job, so a full blown procedure qualification is not required.

Any advice/comment/criticism from the board is invited please.

Thank you.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

Can you get any pe-heat?
How much cracking can you tolerate?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

PWHT may not be necessary given the size of the fillet weld on the 410 base material. I would try to locally preheat to 500 deg F. No preheat could result in cracking or at most significant hardening in the weld region. How much carbon is in the 410 SS material you are using?

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

(OP)
Hello Metengr & Mr. Stainless,

We might be able to get an acetylene torch up there and get a couple of hundred degrees of preheat, don't know if we can allow 500 though.

The carbon is quite low, our analyzer is indicating only .063%

But now my problem has taken a bit of a twist, and it turns out the fasteners are 303 stainless, not 302/304 as originally told to me. The analyzer reading is telling us we have >.300% sulfur in these fasteners.

I am aware that sometimes problems in welding high sulfur steel can be offset by using a high manganese filler, in this case maybe now I should consider using a 316LMn filler ? The FN calculation drops to about 2. What do you say about that ?

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

tc7;
Send out one of the fasteners for chemical analysis to be sure. I would use a propane or MAPP gas torch, not acetylene. The lower carbon version of 410 ss will help to reduce cracking under minimal to no preheat.

If the fasteners are 303 stainless steel, I would use 310 or 312 stainless steel, NOT 316LMn.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

(OP)
Gee whiz metengr, I thought you would have been proud of me for thinking of the 316LMn !! am I wrong about the benefit of Mn on high sulfur?

You seem very adamant abot NOT using 316LMn, but the 316LMn fits the PWHT exclusion of ASME B31.1 table 132 footnote for the P-No.6 for A numbers A-8 or A-9, does it not ?

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

Why do you believe you cannot get to a 500 degree preheat?

A hand-held oxy-aceteleyne torch can get the area that hot (you need the weld point, plus at least 2-3 inches around the weld to get to full preheat, and the nearby area to be 200-300 deg F to prevent the heat from bleeding off too quickly.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

(OP)
good question racook, I should have explained that. The 410 base plate is embedded in yet another larger base plate that is bolted and sealed with some type of polysulfide material and so the engineers are placing a temperature restriction upon this repair.
Thanks.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

tc7;
I will give you an A for effort. The 316LMn will have a tendency to cause problems with either hot cracking in the weld deposit or dilution with the martensitic stainless steel in the fusion zone. Normally, it is not used for dissimilar metal welding.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

This one should provide for an entertaining read. Please, let us know how this repair goes for you. All I see is one opportunity after another.

Best regards - Al

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

(OP)
Hey Al! don't be bashful, offer your insight to this problem.


In thinking about this overnight, what would anyone think about this approach: welding a butter layer of Inconel 82 (ERNiCr-3)applied to the 410 at 350 deg preheat and hold the 350 for about 15 minutes and slow cool. Then apply a butter layer of the same Inconel 82 to the 303 fastener and fan cool. PT both butter layers and then fit, tack and weld both together with the same 350 deg preheat on the 410 side and slow cool. (Note: using the Inconel didn't pop out of my brilliant mind, I read the mention of using ERNiCr-3 on the web site of a 410 supplier).

Thoughts any one?

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

I believe the problem is the HAZ of the 410 stainless. If it is welded without the benefit of preheat, how can one ensure slow cooling? Sounds like wishfull thinking. This material is air hardenable when cooled from elevated temperature. The recommended preheat is 500 degrees F. This sounds like a disaster in the making. I just hope no one is injured as a result of a half hearted attempt at making this repair. I hope someone takes a step back and really thinks about the proper approach. There have been some good suggestions, but there are constraints imposed that run counter to a successful repair.

Best regards - Al

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

(OP)
Just what is the "problem with the HAZ" that you are alluding to Al ? HAZ will always occur, as you well know, so there are only a couple of means at our disposal to offset the effects of the HAZ: preheat and PWHT. ASME acknowledges, as did metengr, that some circumstances permit elimination of PWHT. On the other hand, I stated above that I can apply ~350 deg preheat and can likely let that creep up to 400, which by the way is what B31.1 guidance indicates. Sure, more preheat is better if one has the luxury of no constraints, but where is your recommended 500 deg printed? Nothing "half hearted" is going on here - a problem was posted and request for help was made, contribute with specifics if you want but no need for you to be so critical.

At this point the bigger concern I have is welding to the 303, not the 410.


Incidentally, here is a very interesting report that pertains to repair welding 410 shrouds on steam turbines and trials were done with ERNiCr-3. Oddly, if I'm reading this correctly they chose to use no preheat but then applied a very substantial PWHT. The report is from the "Gruppo Frattura" (?) who I never heard of before but seem to be dedicated to the study of fracture mechanics.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

My point is that the cards are stacked against a successful repair.

AISI 410 belongs to the family of Martensitic stainless steels. They are air hardenable if I remember correctly. The HAZ cooling rate will be accelerated if it is already joined to a heavy plate as you indicated and high preheat is out of the question. PWHT; not possible, so if there is a hardened HAZ there is little chance of mitigating the problem. We haven't broach the need to use low hydrogen welding techniques.

AISI 303 belongs to the family of free machining austenitic stainless steels. High sulfur is a problem which you seemed to be well aware of. What is the sulfur content, around 0.3% or so? That is about 5 times more than the upper limit when good weldability is needed. Manganese will help mitigate the affects of sulfur, but 10 times the sulfur content is recommended when sulfur is on the high side. This isn't on the high side, this is on the very high side.

I don't criticize because one is asking questions, but I think an alternative to welding is encouraged in this case. Reading the scenario painted in this case is like watching a car headed at high speed toward a cliff edge and discovering the brakes are disconnected and the doors are locked.

You've been handed a can of worms. There is very little working in your favor.

The best I can do is say, "Lots of luck, you have my sympathy."

Best regards - Al

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

(OP)
Understood Al, at first you seemed to be belligerent for the sake of being belligerent. Indeed it's a tough situation but there is a solution and it will be attacked in a thoughtful manner so as not to cause death or destruction. I am holding this job up until I am ready to declare a reasonable course of action to my sponsors.

This is how my plan has evolved as of this morning:
1. butter the 303 side with 308L (instead of the original plan to butter with NiCr-3).
2. butter the 410 side with the NiCr-3 using 350-400F local preheat and hold the 350 for a while then taper down in temperature over the course of 15-20 minutes (this is the slow cooling process that you said I was thinking wishfully about - it works, done it before.)
3. PT everything.
4. complete the weld between the 308L buttered 303 and the NiCr-3 buttered 410 with NiCr-3, again holding 350-400F preheat and slow cool by the process described in step 2. We'll also do this in multiple bead fashion, not unlike a temper bead operation.
5. I'll do some trials of this on scrap beforehand and polish some cross sections to examine for cracks. Maybe I can even get a traverse done before the real work begins just to see what we end up with.

FYI - The process will be GTAW with high purity gas, so almost by definition this is a low hydrogen process.

The NiCr-3 filler I intend to use will have 2.5-3.5% Mn which is right at that 10x sulfur ratio we would like to have plus my 308L butter layer should dilute the 303 sulfur down to a considerably much better ratio.


RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

Never say never.
Low heat input, fast cool for the 303, it might work.

As I said, this should be entertaining as well as educational. I'm never one to say I never make mistakes. That's how I learn. Try it, see what happens, tweak the process and try again.

Make sure you let us know how it works.

Best regards - Al

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

Can you explain why you chose 308L over NiCr-3 for the 303 weld? I can see why you are concerned about welding the 303 fastener, not desirable.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

(OP)
Yes sir, glad you asked -
In my very unscientific way of thinking, the 308L has a ferrite number >10 and the NiCr-3 ferrite number doesn't exist and the 310 which I was originally thinking about has a ferrite number of about zero or less so I thought the 308L would add to crack prevention concerns plus some ferrite would add to greater solubility of sulfur. It also looks like 309L would serve my purposes as well.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

tc7,
In your OP you stated there was no need for a "full blown procedure" as you are not working to any code.
Based on the diversity of replies I would have thought this argument went out the window.
The only way to prove something works is weld it, test it and review the results - the end result is you have a "procedure" that either works or it doesn't.
Cheers,
DD

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

tc7;
I would agree with DD above that you use a mock-up and evaluate the weld region before jumping off of the cliff.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

(OP)
Hi DekDee and metengr-
In the OP I said it is not 'required' in the sense that I am not strictly bound to meet any Code minimums which is semantically different than "not needed". As you may have noticed, I am not marching blindly into this and obviously am giving this much thought and research. It's always my custom to brainstorm these odd ball jobs and conduct trials of some form. In my application I don't think I need tensiles or bends as the construction is fillet welds only. This is likely to be a one time effort and so I'll place my available resources where best served which is, in my own opinion, in macros and traverses of the mock-ups I said I was going to do.

Please stay tuned and please continue to offer any advice that might be useful to me.
Best Regards.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

Good, and use 309L versus 308L for your butter layer.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

(OP)
Can certainly do that metengr,
But what is your reason for urging the 309L ?

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

tc7;
Take a good look at a Schaeffler Delong diagram and you will see that using 308L will result in a dilution zone within the weld deposit that I think will result in cracking concerns from/during solidification. Again, for DMW, you stay away from 308, 316 type electrodes, and go with 309, 310 or even 312 electrodes.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

(OP)
Got it!
Thank you.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

tc7,

Thank you, that makes perfect sense. I can state from experience that sulfur concentration around 0.035 % in base metals is enough to cause centerline segregation and cracking when welding with NiCr-3 filler metal.


metengr,

Would you consider a joint between ductile iron and low alloy steel to be dissimilar metal welding? Fraunhofer Institute in Dresden recommended 308LSi for that application.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

CoryPad;
For the family of ferritic ductile irons I would not for the simple reason it would behave similar to a higher carbon, higher silicon version of low alloy steel in terms of weldability. If you are talking about the family of austenitic ductile irons, this would be a DMW to low alloy steel.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

Can you drill a sample from the base plate an d really check the carbon?
If it is under 0.10% then any small amount of preheat will be good enough.

I like the sound of 309 filler. If you are thinking of buttering it only needs to be done on the 410.
And if the fitting really is 303 throw it away and force them to make a new one. You can't trust the strength (fatigue) of 303 anyway.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

(OP)
Here is an update as promised, if anyone is interested:

We pursued the welding recipe as listed in the 28 Sep post except I chose to follow metengr's urging to use 309L instead of the 308L.
After a few trials, we quickly decided to give up the use of the NiCr-3 (Alloy 82) filler because it was absolutely a nightmare to weld with as it was very sticky and hard to flow deeply into the corner of the root. Outside of the root we had good penetration but our cross sections showed very little penetration into the corner.
So we proceeded to run out a few more mockups with purely 309L and had very good success. We applied the sledge hammer test to a single 303 bar welded to a 410 plate and smashed it into destruction. It took about 15 hits with a 10lb sledge in a variety of directions before the bar separated. Attached pics are testimony to the effort. Other samples were sent to the lab for macros and traverses and I'll post them later for interests sake.

RE: GTAW 304SS to 410SS w/o preheat & w/o PWHT

Did you look at the failure with a magnifying glass?
Was it ductile?
That is the real issue here. Over all it doesn't look bad.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

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