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Up Topic Welding Industry / Technical Discussions / Avoiding Cracks with 312 Stainless?
- - By OBEWAN (***) Date 08-20-2009 16:52
I am trying to cure a cracking problem on 308 and 316 stainless tube fillet welds.

In the past, it is claimed they always cured it here by using a 312 filler.  That is also weldors lore of fame I think.

However, I also have my Text, "The Practical Welding Engineer" by AWS to consider.  I put the hot cracking chemistry equations on page 122 into a spreadsheet to calculate the HCS and UCS hot crack indices.  Guess what?  both 308 and 308L win over 312 according to the "textbook theory".

So that leaves me wondering.  Will I actually gain anything by specifying a 312 over a 308?  Why do we always hear so much about 312 curing cracking problems if 308 is better in theory?  (I am free to use either one for this application since it is only a tack weld used as a locking mechanism on a threaded connector).
Parent - - By waccobird (****) Date 08-20-2009 17:42
You didn't mention if the cracking was in the weld or base metal
Parent - By OBEWAN (***) Date 08-20-2009 17:46
The cracking is down the center of the fillet.

Were are almost certain they are hot cracks.  They are due to weld shrink stress.  We have made them go away in the past by switching from 308 to 312 filler.  I am just looking for a textbook answer that agrees with real world results so we can tell our customer.  I thought of the hot crack indice theory, but it does not agree with the results. LOL.  Actually, I did just redo it and the 312 is 1% better on one indice and way worse on the other.
Parent - - By js55 (*****) Date 08-20-2009 17:49
First of all, what is the cracking problem?
However, 312 is esentially a duplex stainless steel with very high ferrite. It can help prevent hot cracking for the same reason that high ferrite in other 300 series filler do.
Parent - By OBEWAN (***) Date 08-20-2009 17:58
We have a threaded connector that is a tube over a tube at the weld location.  There is actually a small gap under the OD tube that compounds our welding problems.  We have to make 2 tack welds 180 degrees apart to serve as locking mechanisms on the connector.  We specify mandatory filler wire to make fillet welds that bridge the gap.  The leg size on these fillets is around .100".  There is a fair amount of strecthing on the welds as they cool.  If there is any crud in the weld to contribute to a hot crack it is the perfect storm of conditions.  These are manual TIG welds BTW.  The hot cracking theories I am testing were published by Bonomo, Bailey, and Lancaster.  I am referring to the Hot Cracking Susceptibility index and the Units of Cracking Susceptibility index.  They both use drastically different chemistry equations and never seem to agree.
Parent - - By motgar (**) Date 08-20-2009 18:30
OBEWAN,

What are the base materials? 

I understand your post as you are having cracking, in both the 308 and 316 fillet welds.
Parent - - By OBEWAN (***) Date 08-20-2009 18:35 Edited 08-20-2009 19:38
Some tubes are 308 and some tubes are 316.  I think we have the most trouble with the 316.

Some of the details are nickel-plated too, which could really stir the pot.

I don't have any feedback yet as to whether the nickel-plated units have the most cracking occurrences.

We are hoping to establish 312 as the engineering design standard for all 300 series connector welds, but I will need a good textbook answer that agrees with results if the customer asks.  Of course the fall back position is just to cure the problem and not get too deep into theory, but I opened my mouth in a meeting this morning and now they are hoping I can give up a textbook answer.

I am planning to do a weld audit as soon as our ME tells me when they are running in the shop.

Update: I have looked at supplier data sheets on the web.  312 has a ferrite number of FN 50, whereas the 308's have are around FN 10.  I have heard many times about the importance of ferrite content, but if it is so important, why do they not include it in the hot crack probability chemistry equations?  Is there some other scale that would relate crack resistance to ferrite content?  If so I am sure there would be some kind of statistical interaction with all the other major chemical elements. The only way out of this it seems would be for me to do a straight up DOE and just run the different fillers.  I am not sure they want to do that.  They are hoping for a magic bullet. 

Before I came here, 5 years ago, they used 312 to solve a similar problem.  Then I heard nothing about this type of weld for 5 years.  Now we are having problems, and it is being blamed on the fact that we have not standardized our designs to 312 filler.  (We have dozens of designs that get away with 308).
Parent - By SWP (**) Date 08-20-2009 19:46
We tried welding a nickel plated joint and had severe cracking problems.  Can't recall the details, but it turned out that nickel plating commonly involves a high phosphorus content which causes hot cracking.  Maybe it was a phosphoric acid pretreatment?  Don't have time to Google it now.
Parent - - By motgar (**) Date 08-20-2009 20:14 Edited 09-11-2009 12:56
OBEWAN,

Here is a link to some literature from Lincoln Electric.  It talks about WRC-1992 Diagram.  Not sure if you have heard of it, or used it before.  Check page 7-8, Section 3.3.2.

http://content.lincolnelectric.com/pdfs/products/literature/c64000.pdf
Parent - By MMyers (**) Date 08-20-2009 20:43
To follow onto this, the WRC 1992 diagram is not going to help you much unless you know the dilution into each side of the joint.  From there, you can use the WRC diagram to determine the primary solidification mode and then that will tell you the susceptibility for cracking.  If you don't know dilution, then you have some assumptions to make which may or may not help you.  Basically to me, it sounds like you don't have enough ferrite in the final joint, of you've got some junk in your 308 wire that's assisting in cracking (high impurity elements).
Parent - - By ssbn727 (*****) Date 08-20-2009 22:43 Edited 08-21-2009 00:31
Hi OBEWAN!

As Motgar also asked this question previously, I have to ask the same below... Also, what is the welding process as well as any other specifications being used to deposit these welds in question???

Do you have tubes - yes!! I mean tubes made of 308 Stainless steel material??? I emphasize the question in that manner not because I want to discredit you, or ridicule you OBEWAN ;) but, 308 is primarily used as filler metal -  the standard for all the lower chromium-Nickel base metals...

The filler material for welding 302 & 304 grade stainless steel... This is the only reason why I ask you for clarification as to whether or not the base metal you are referring to is a 304 base metal as opposed to 308 stainless, and your company is actually working with both 304 as well as 316 grades of stainless steel instead, and why they do not prefer, or opt to switch to an "L" or, low carbon grade of these 2 base metals also.

http://www.ssina.com/publications/welding.html

http://www.ssina.com/view_a_file/weldingbook.pdf

The other question I have to make better sense of your welding problem is, when is the nickel plating applied to the base metal, and can it be applied to the stainless metal after the welding operation is completed instead?

Here's another bunch of links that may or may not assist you further:

http://www.ssina.com/hintsandtips/index.html#4

http://www.ssina.com/publications/ccss.html

http://www.ssina.com/view_a_file/cleaning.pdf

http://www.ssina.com/publications/design.html

http://www.ssina.com/shopfabrication/knowledge.html

Want to learn more about Stainless steels? Here you go:

http://www.ssina.com/training/index.html

Here's an article, or two that may be of interest to you with respect to an alternative to 300 series Austenitic grades of Stainless steels.

http://www.inmotiononline.com.au/articles/1207-Alternative-stainless-steel-grades

http://www.worldstainless.org/NR/rdonlyres/16D7CBB1-1E5F-4338-9A5A-F53504A87667/3265/200seriesstainlesssteel.pdf

http://www.assda.asn.au/index.php?Itemid=89&id=63&option=com_content&task=view

L & H Grades of Stainless Steels with respect to corrosion resistance:

http://www.corrosionist.com/L_H_grades_Stainless_Steels.htm

Here's a nice stainless steel filler metal to base metal chart from Aufhauser:

http://www.brazing.com/products/Weld_Stainless/selection_chart.asp

Here's a useful link to Stainless filler metal selection for various base metals, chemical composition, Flux cored stainless welding wire and shielding gases:

http://www.brazing.com/products/Weld_Stainless/

Stainless steel pipe specifications:

http://www.indpipe.com/images/PDF/stainless_steel_pipe_specification.pdf

Here'sa very thorough site regarding all sorts of Stainless steel info:

http://www.worldstainless.org/About+stainless/

http://www.worldstainless.org/ISSF/Files/ISSF%20Book%20of%20New%20Applications%202009.pdf

http://www.worldstainless.org/About+ISSF/Publications/

http://www.worldstainless.org/SiteMap.htm

Enjoy the reads!!! ;)

Respectfully,
Henry
Parent - - By OBEWAN (***) Date 08-21-2009 11:44 Edited 08-21-2009 14:09
SSBN: 

1.) The process is manual TIG with 100% Argon with a Miller Dynasty on DCSP.  The weldors control their own amperage with a footpedal, and feed the filler wire by hand.  These welds are only about .100 x .100 in leg size and are about the same in segment length.

2.) Yes, we in most cases use 304 stainless tube.  However, I am pretty sure the tubes we are having trouble with are 316.  I think I got the 308 from some other discussion in the meeting and got confused (or our design engineer was confused).  I checked at matweb.com and they only have specs for 308 sheet, plate, bars, and wire, so your concern is valid (unless it was made from 308 bar.  I think some of these connectors are machined from bar stock due to complex shapes.)  However, our designers are actually looking high and low for 303 stainless tube to "save" money, so anything is possible.  (So far we have only located people who are willing to do a custom mill run for 303 tube, so there is no cost savings LOL.)

3.) It is not possible to plate after welding.  These are lock welds on amphenol connectors for jet engine wiring harnesses that have nylon sheathes and other plastic parts, and they can not be plated after welding.  We could use a dremmel to strip the plating near the welds, or we could check into the process at the supplier to see if they could clean the plating better if some kind of residue is killing us.  I don't think the nickel is the major problem since we make tens of thousands of welds to pure and high nickel alloy parts that are adjacent to most any other stainless alloy.  As one other person said, the phosphorus or other chemicals in the plating process are bad, and hopefully they would be on the outside surface in not in the thickness of the plating itself.

4.) On the L question, we have specd 308L in the past, but corrosion is not really a concern on these.  We also have had better results with 312 vs. 308L.

The reason the info is a bit sketchy and confused is because the design engineer came to see my boss and I with a spreadsheet showing half a dozen different designs with different material conditions and no history on the cracking frequencies.  We are still digging that up, but it may be hard to find since our weld spec allows one free weld repair for any defects that occur in the original process - before it goes to the weld inspector. (We may have to rely on "word of mouth".)

I will check out the links you posted.  Thanks for the info!
Parent - - By OBEWAN (***) Date 08-21-2009 15:00
I don't think there is any hope other than stripping the plating for that concern.

It looks like the phosphorus is part of the plating itself.  The first website I went to warns of poor welding.

http://books.google.com/books?id=eIfcHJtv_kcC&pg=PA282&lpg=PA282&dq=welding+nickel+phosphorus+plating&source=bl&ots=Bqe3mGqofH&sig=0iMMRiV087YwcwSINZtbAxFJPP0&hl=en&ei=xbWOSqPLF42QNoSWzK8K&sa=X&oi=book_result&ct=result&resnum=6#v=onepage&q=welding%20nickel%20phosphorus%20plating&f=false
Parent - By ssbn727 (*****) Date 08-21-2009 16:20
Hi OBEWAN!

I figured that the only way you were working with 308 tube was by boring into bar stock, or if it was welded tubing from sheet... 316 as well as 316L is best welded together using 316L unless it's a high temp application whereby in some situations, a 318 grade is more suitable as the filler should it require filler since this (316) grade as well as most other grades can also be welded autogenously... You know that there are some pretty good lists of SS suppliers in some of those links so, if you were to need the 303 in the future, it may be available in one of those links I posted for your review. ;)

Yep! Sure makes sense to me that the phosphorus in the plating would be the culprit with respect to your cracking issue...
I hope everything turns out for the best! ;)

Respectfully,
Henry
Parent - - By Weldconsultant (*) Date 08-24-2009 09:21
Obewan,

There are two types of Ni plating processes available: Electro-plating and Electroless-plating.  Electro-plating deposits practically 100% Ni while electroless Ni plating deposits Ni with between 3-14% Phosphorous.  This phosphorous is in the plating and not just on the surface.  Presence of Phosphrous causes hot cracking due to formation of Iron-phosphides that have low melting point and weak cohesive strength.

The reason why 312 might work better is because 312 (as compared to 308) has greater amount of ferrite which has good solubility for Phosphorous and keeps it out of trouble.

In the abscence of P in the Ni plating, 308 might work better because it has greater amuont of Austenite and may be tougher.

Please check if you can get those electroplated, then you can follow theory and use 308.

Girish
http://www.welding-consultant.com/
Parent - - By OBEWAN (***) Date 08-24-2009 12:03
Yes, thank you for reminding us, but we are also onto the two kinds of plating.  We try to specify electroplating, but sometimes the other one gets through.  Our design engineer is looking into the details regarding plating methods for the units that are cracking.

We have decided to go with the ferrite number theory as far as an explaination goes.
Parent - By 803056 (*****) Date 09-01-2009 10:52
Don't use 303 if you have plans to weld it. 303 is a free machining stainless with Se or S added to give the material free machining characteristics. Both Se and S are low melting point consitituents that will cause the welds to crack along the centerline.

Best regards - Al
Parent - - By Metarinka (****) Date 09-04-2009 18:34
308 was designed specifically for inter welding of austenitic stainless steels (originally was developed for nuclear applications) and thus I usually specify it over any other filler unless there's some over riding concern.

with that in mind 308(L) is the specified filler for 304 to 316 material as it offers a fair balance between over alloying the 304 and under alloying the 316.
I don't have any direct experience with 312 material but it's slightly higher alloy content and it's location on the WRC diagram suggests that you may be getting a higher level of ferrite after welding.

if you are experiencing hot cracking between 304 and 316 my first guess would  be that you are getting low melt point inclusions such as lead, or sulfur. I'm not an expert on plating but that seems like a likely culprit.  specifying 312 would indeed allow for a slightly higher buffer in terms of sulfur or phosphorus, but that's treating the symptoms not the problem, and even then there would be an upper limit for how much "extra" inclusions the 312 filler could take.

My second guess is that you are experiencing rapid cooling due to low heat input, or thermal stress cracking due to uneven cooling of the base material.  without knowing the details of the weld is it a weld between uneven thicknesses of material? or could there possibly be uneven heat input?

my initial reaction though would be to find the source of contamination that is causing the hot cracking as 308 is the standard filler material and there's no reason it shouldn't be able to complete a weld on those materials with acceptable defect rates.
Parent - - By cwi49cwe (*) Date 09-07-2009 00:49
I had to read all the entries before I saw what I considered to be your biggest culpret, there is NO WAY to successfully weld ANY free machining steel or stainless steel due to a "built in " contaminate that is to favor the machining process. Forget about the welding , just think about the machining. I've seen it for 30 years and it's always the welder and welding that is the problem.  S , P , Se  do not lend themselves to welding. There is a commercial fan manufacturer based in MN that learned that the hard way, about $18000 worth and a very upset customer. I tried to tell them but what right did I have to contradict the master welding engineer. When the ultimate in weld strength and integrity is at stake, give WELDING all the considerations, spend a few extra dollars on machining and have a serviceable product. Repair will ALWAYS double the initial cost and than some. The plating process rarely makes welding a favored economical fabication process.
Parent - - By Metarinka (****) Date 09-07-2009 20:52
i agree one hundred percent, in the code books free machining grades are generally considered unweldable.

I'm just confused because I don't think he mentioned using free machining grades only 308, 316 and 312 which are readily weldable
Parent - By ssbn727 (*****) Date 09-07-2009 21:51
Hi Metarinka!

I believe OBEWAN did mention 303 although I think and, lord knows how I don't like ot speculate but, the company he works for was thinking of just CNC machining the entire component by using 303 round bar therefore, eliminating the welding all together. ;) However, they were having a hard time locating a reliable supplier. :)

Respectfully,
Henry
Up Topic Welding Industry / Technical Discussions / Avoiding Cracks with 312 Stainless?

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