nitrogen strengthened SS

By kam

Date 04-07-2004 12:58

What grade of stainless is this? I dont have chemisrty charts handy. Might help get you more responces.

I'm just guessing but i would probally look at controlling heat input. I have welded austenitc ss but never nitrogen strengthened ss.

kam

By ssbn727 (*****)

Date 04-07-2004 14:44

Hi Chang!
Hmmm, did you preheat and "butter" the carbon steel tube prior to joining it to the nitrogen strengthened austenitic stainless???
I ask this because, the amount of carbon in the tube has to be "mitigated" in order to reduce the amount of dilution into the weld (look at the difference in the CE between the two steels) ...
Also, since the stainless is "nitrided" - you might want to do the same there... One last thing, get rid of the weaving technique (run stringers)when you're welding which will also lower your heat input and reduce the size of the HAZ, so long as you maintain a decent travel speed...
You also may may need to perform PWHT afterwards but then again, all of this also depends on some unlisted variables so, if you would -please give us some more details...

Respectfully,
SSBN727 Run Silent... Run Deep!!!

By Bill A

Date 04-07-2004 16:44

I don't recognize the composition, but nitrogen is a potent austenite stabilizer, as well as a strengthener. (It also imporves pitting resistance, but that effect is greatest when moly is present, too.) Intentional addition of N into the bulk alloy composition is different from "nitriding" that is done either intentionally as a surface treatment or as a result of exposure to certain high temp environments.
I suspect that the combination of 309 and your stainless base metal + carbon steel is producing a 100% austenitic weld deposit that is susceptible to hot cracking upon solidification. If it is a hot cracking problem related to a fully austenitic deposit I'll bet going to Type 312 filler would be an improvement.

By kam

Date 04-07-2004 19:39

Hi Bill
I plotted his materials on the DeLong Diagram and by my calculations he should be in about the 5% ferrite range (thats considering 25% dilution). Didnt try plotting the 312 to see where it puts him. Should help out as you said. Also like the buttering idea as well.

kam

By Bill A

Date 04-07-2004 20:06

KAM, I grabbed a welding book and used the "modified Schaffler diagram" that includes a provision for nitrogen (upon comparison it looks like a clone of the DeLong diagram). Perhaps our difference in results was related to assumed values of the filler metal composition and dilution. I played around with some ranges of things like Si and Mn for the TP309 and dilution rates and did end up with up to a couple percent ferrite with some combinations.

By ssbn727 (*****)

Date 04-08-2004 04:54

Hi Bill!
Sorry for the misuse of the term "nitrided" but, I've seen this done also for certain applications where corrosive and elevated temperature environments were present as a boilermaker working on a few waste incinerator boilers...

So H. Chang, is the stainless a type similar to a 310 grade?
Is the amount of Cb in the grade similar to the japanese version of this type of stainless?

Looking at the chemical compositions of the dissimilar metals to be joined, and since I'm not a metallurgical engineer like yourself, would it be a good idea to "butter" the joints prior to "joining" with a ER309L or even a ER312L if it's available and then weld the joint with a ER 321 (Titanium stabilizers) or a ER347 ("Niobium" otherwise known as Columbium stabilizers) filler in order to minimize the carbon content in the weld and to control the delta ferrite percentage at the same time in order to avoid carbide percipitation? Also, would the addition of nitrogen in the purge or backing gas help maintain some of the strength that may be lost during welding in the stainless?

Would this also destabilize the heat affected zones adjacent to the base metals if heat input is'nt tightly controlled in order to avoid IGA
(intergranular attack due to sensitization of the HAZ) ?

Respectfully,
SSBN727 Run Silent... Run Deep!!!

By Bill A

Date 04-08-2004 16:59

Its been several years since I was involved with welding stainless, but without spending a bunch of time researching the technically correct and defensible answers to your questions I can give you my opinion.

First, I'm assuming corrosion resistance of the weld joint is not a big priority if they are not worried about the corrosion resistance of the mild steel side of the joint.

Buttering is often useful, particularly on the mild steel side of the idssimilar metal joint, but I can't remember ever being involved with a project in which the stainless side of the joint was buttered with a different stainless. Buttering can be done at such a low heat input that it probably would not have a bad effect on the HAZ of the stainless side of the weld joint.

I know that for some time nitrogen was used or proposed for use in shielding gas when making duplex stainless steel welds because the nitrogen had or was thought to have a beneficial effect on maintaining the preferred austenite/ferrite ratio (if I remember correctly) but I don't know if that is the current practice or not. I'm not sure if nitrogen in the gas will add enough to the weld metal deposit to influence the strength of the weld much. I think if strength was a real concern I would consider going to a nickel-based alloy weld metal, but I don't have preferred reference book here so I can't suggest which one might be a good choice.

I'm thinking there may be little or no advantage to a 347 weld deposit to join the buttered surfaces if the operators/designers already made the determination that a steel-to-stainless steel weld is OK in their service environment. If they are worried about sensitization of the weld and HAZ they should be really concerned about what would happen to the mild steel side of the joint.

Delta ferrite is an interesting thing. Too much in high temp environments and you can get emdbrittlement (I can't remember the recommended limit). Too little and you can get solidification cracking.

By ssbn727 (*****)

Date 04-08-2004 20:07

Hi Bill A!
Thanks for your input...
After I asked the question about using 321 or 347, I looked up the tensile and yield strengths between them, and with what I think is a 310 grade stainless (the percentages of Cr and Ni are very close) that H. Chang is using and you're correct!!! In fact both the tensile & yield strengths would be lower in the weld when compared to this 310 grade base or parent metal at elevated temps... I could'nt find anything on 312 but, I'll look again... I did however notice that there's Cb in the stainless base metal so, I initially thought that the 347 would be helpful in this situation...
I'm just guessing H. Chang but, Kobelco - a Japanese filler metal & welding products manufacturer may also provide some insight on choosing the optimal filler metal composition for this 310 grade of stainless... The link to their website is on the homepage for the AWS website on the top of the page. Also check out this .pdf from Allegheny Ludlum: http://www.alleghenyludlum.com/ludlum/Documents/309_310.pdf
I did some surfing and I found a very similar composition of this grade of 310 stainless in the British Stainless Steel Association.
The trade name is "HR3C" which is a sulphurizing resistant grade from Sumitomo Metal Industries, sound familiar?
The most impressive site I found was the Sandvik website... they even had Delong, Schaffler and WRC ferrite diagrams for a variety of stainless steel catagories with the formulas for the respective Cr & Ni equivalents!!! Check it out: http://www.steel.sandvik.com/techdata/index.html
http://www.smt.sandvik.com/ When you get there, scroll down on the welding products page where the page shows a ss grades chart w/chem comps... look for for special purpose grades, then look for their (Sandvik) number designations and the AWS ER equivalents.
Compare the chem comps for the 312 (29.9) and the 310 (25.20.C), then scroll down to the special purpose grades and look for grades 25.20.L and right underneath, grade 25.22.2.LMn (310LMo) which has some N in it also... At first, it looks like a match but,wait a minute!!!
In the column to left of the page, click "welding products", then click "wire electrodes and filler wire/rods", then click "properties and applications"... when the chart on the right appears, scroll down to each of the grades that has a dissimilar metals (Austenitic to Carbon stl.) application recommendation... read each one for 309L
(24.13.L & 23 12 L), 24.13.LHF (another 309L),
309Si (24.13.Si & 22 12 H), 309LMo (22.15.3.L & 23 12 2 L) and
312 (29.9)... finally, scroll down to the last grade, Sanicro 72HP (NiCr-3).
The correct choice is in one of those grades that best fits your application!!!

As far as the embrittlement or solidification cracking potential goes,
the delta ferrite limits are between 4 to 10 % generally speaking of course... Hey DGXL! thanks for supporting what I also suggested to H. Chang about the weaving technique!!!

In any event, I appreciate your responses and one thing is for sure, I'm always learning something new from someone in this forum...

Respectfully,
SSBN727 Run Silent... Run deep!!!

By H. Chang (*)

Date 04-09-2004 09:29

Hi, SSBN727
Very much appreciated for your help.
For the tube SUS310J1 welded to itself, ERNiCrMo-3 were used, it is because these joints are in contacted with the flue gas. But for the carbon steel to SUS310J1 joints, they are not in contact with the flue gas, thus ER309L were used.
If the material is other type of 310 without nitrogen added, we will use ER310.
For SUS310J1, I would think Delong diagram is a good reference.
I'll look for the web that you introduce, thanks.
Please check the repair weld conditions and advice.
Kind regards

By H. Chang (*)

Date 04-08-2004 01:53

Many thanks for all of you. The SS material specification is SUS310J1, which is a Japanese material specification(specially assigned by METI, not show in JIS handbook), and it is intended to use as a superheater tube of a city waste incineration boiler, this material is nitrogen strengthened for higher tensile strength at elevated temperature(up to 1472 F), and with good resistance to corrosive flue gas. I would guess that this material is close to SA-213TP310HCbN. The shop welds show acceptable results, But the field welds show that nitrogen cause prosity problem, RT films had proved this, but the double wall/double view RT technique applied to these 1-1/2 in.tube failed to find any image of the tiny cracks on films. I would guess these cracks are much less than 2% sensitivity, since the essential wire of IQI can be seen on those films. I guess it is a hot crack.The same WPS was used.

By DGXL

Date 04-08-2004 17:16

H. Chang:
I've been monitoring this post with interest.

First, the radiographic technique would have to be favorable to locate the types of discontinuities you are experiencing. An elliptical shot (as you noted) may not pick up these indications due to the orientation of the discontinuity vs. the position of the source. If the correct hole/wire is visible in the radiograph, then other factors must be considered.

One item that did catch my eye in your first post is you noted "...weave bead..." My first instinct would be to use stringer beads. This has solved many-a-problem for me with SS. Hot cracking (if that is what is occuring) is typically associated with a weaving technique and also typically ocurs during solidification of the weld metal. Stringers may help to minimize the porosity as well.

You may want to consider a quick and cheap PT examination prior to spending the $$ for the RT.

By H. Chang (*)

Date 04-09-2004 08:40

Hi, DGXL
I agreed that the orientation of the discontiunity could paly an important role at this case. We shoot 10% RT film for quality control purpose, & so did the 100% PT. But this is the first time that I experienced all of the RT films failed to locate the surface cracks that is so easy to pick up by cheap PT.
The repair weld was done with ER309L, preheat to 200F, groove preparation wider than depth, stringer bead, slower travel speed, PT again shown satisfactory result. I would guess that some factors were related to the site conditions, may be it did.
Next time I'll try butter the edge of carbon steel, and test for ER312.
But I just completed the test of using ER NiCrMo-3, which shown satisfactory result. Although I knew that some sources recommended NiCrFe, but I don't have this type welding rod on hand.
Kind regards