Welding Armor plate with stainless wire

By Lawrence (*****)

Date 01-27-2010 00:40

Hey Boss Man,

GMAWP has some advantages with steels when they are thinner than 1/8", especially if the joints are out of position.

As far as using stainless on carbon steel armor plate? ..... I dunno. Is the stainless filler an attempt to avoid pre-heat of the armor plate?

May I ask who's armor plate you are welding that does not have a DOD approved or OEM procedure already in place that includes process and filler?

Is it repair work or original manufacture ??

By ssbn727 (*****)

Date 01-27-2010 00:48

Are you sure that the Stainless steel filler is a 307 grade and not a 309 instead???

Respectfully,
Henry

By MMyers

Date 01-27-2010 13:36

It's an attempt to make a weld that isn't so incredibly hard where it isn't needed. The prime I interned at discussed history of doing this, or maybe they were doing it, or maybe they said it could be done but couldn't do it. It wasn't for critical joints of the hull, more like hangers and other things that hang on the hull.

By brrrrp Date 02-02-2010 21:07

Boss Man,

This practice has its roots in Europe where many of the same steels being used for armor today have been used in abrasion-resistant applications. The manufacturers recommend Type 307 stainless due to its increased Manganese content, which, when cold-worked in some abrasive environment will tend to harden so that the weld metal becomes nearly as hard as the steel base metal. It is also quite ductile as-welded, reducing the tendency for cracking, and the stainless will tend to suck up any stray hydrogen to prevent the occurrence of underbead cracking.

However, for armor applications, the same work-hardening does not occur, so the weld remains undermatched compared to the armor steel. The other grave concern relates to safety and health concerns. During welding, the fumes contain significant levels of hexavalent chromium and manganese, both of which have threshold limit values (TLVs) that have recently been lowered by OSHA. As a result, use of this filler metal will require significant engineering controls to protect the workforce. This could add hundreds of thousands of dollars to a project and cannot be ignored. And that doesn't even speak to the increased cost of this filler metal.

There are numerous high-strength low-alloy steel filler metals available that produce excellent results on all grades of armor steel. If you have the choice, I would certainly recommend choosing some non-stainless solution.

brrrrp

By ssbn727 (*****)

Date 02-03-2010 06:07

Here's a good article from the Welding Research Council/AWS Welding Journal December 2001 article titled: "Interstitial diffusion of Carbon and Nitrogen into Heat Affected Zones of 11 to 12% Chrome Steel Welds. The possibility of introducing austenite stabilizers into the HAZ to restrict grain growth is investigated.

http://files.aws.org/wj/supplement/Meyer12-01.pdf

Here is another interesting article which may, or may not give a clue as to why GMAW-P is being used as opposed to regular GMAW or FCAW with respect to fume generation rates according to the temperatures used to weld the material together, because in the application being used, not only does one need to concern themselves with hexavalent Cr rates, but they also need to concern themselves with the manganese fume generation rates being generated as well...

http://neiljenkins.net/Abstracts/jenkinsTrends05paper.pdf

I personally believe the use of GMAW-P is being used because of excellent out of position weldability, and less overall heat input which would limit the amount of admixture of the base metal within the the weld itself (Dilution) which is very important in this type of application as well as the points being made by "brrrp" which also are very important also... Hot cracking is also a major concern which is why 307 grade is a better choice for this application as opposed to a 309 grade. Charpy impact values are increased with the use of this filler metal also.. Increased ductility and elongation make it ideal for wear resistant steels as well as the increased amount of manganese helps when welding these steels which also contain reasonably high amounts of manganese (Approx 14%) also. Ductility is still good even if higher than desired dilution does occur when welding problem steels, or when subjected to thermal shock or scaling...

Of course realistically, we do not know the composition of the base metal you're welding so, it's a guessing game so to speak as to why exactly this filler choice was made and why GMAW-P was the welding process chosen for the project although, GMAW-P definitely has less dilution than GMAW spray transfer as long as the appropriate shielding gas is also used as well, or FCAW, and if that was one of the conditions that "the powers that be" felt was important enough to avoid then it would make sense to use GMAW-P as the preferred method of transfer for the specific application.

Here's the Avesta Welding manual which is an excellent reference manual on welding with stainless steels, disimilar metals as well as other high & low alloy steels also:

http://www.bohler-uddeholm.cz/czech/files/Prirucka_Avesta_AJ.pdf

Respectfully,
Henry

By 803056

Date 02-03-2010 13:31

Welding hardenable steels with austenitic stainless filler metals has been used for many years as a way to mitigate the affects of hydrogen in the welded joint. Like many things in everyday life, it was discovered that austenitic stainless filler metals successfully welded steels that were otherwise nearly impossible to weld.

To make a long story short, a gentleman, a past president of AWS, told me of his involvement in developing a welding rod to weld armor back in WWII. He discovered that if he coated carbon steel electrodes with the same flux covering used on austenitic stainless steel electrodes (what we classify as E3XX-15), he had success in welding armor plate without cracks. However, if left on the workbench for a couple of days, both the stainless electrode and carbon steel electrode would produce welds that cracked. The secret as we now know is to make sure the electrodes are properly baked before using them.

I took a trip to Aberdeen to check out the welded tank hulls and sure enough, all of the WWII vintage tank hulls were welded with stainless steel electrode.

The use of low hydrogen electrodes was kept under wraps until the middle of the 1950's because it was considered a "military secret" that allowed the US to weld armor without using austenitic stainless steel or nickel electrodes.

We now weld difficult to join steels with low hydrogen electrodes. They work fine on most steels, i.e., hydrogen cracking is minimized by controlling the amount of hydrogen introduced into the weld zone.

However, there are still many who have been taught by the welders that learned to weld in the WWII era that you have to use nickel or high nickel austenitic stainless steel electrodes to weld steels that have high hardness, high carbon, or other difficult to weld properties. I have had very good success welding these steels using "low hydrogen" practices. GMAW is considered a low hydrogen welding process because the electrode is bare wire. However, even bare wire may have drawing lubricants on the surface that can introduce hydrogen into the weld zone. The small amount of hydrogen is not a problem with most steels, but with the high hardenable steels such as armor plate, this can be a problem.

Stainless steel filler metals that are fully austenitic are not as susceptible to hydrogen cracking because they tend to be face centered cubic structures. The unit cell is "empty", i.e., the atoms are positioned at the corners and at the faces so the "box" is empty and can accommodate smaller atoms such as carbon and yes, the tiny itsy bitsy hydrogen atom. The atom of hydrogen is thought to sit peacefully inside the austenitic structure rather than migrating to the hardened heat affected zone where it induces cracking problems.

The mechanism of hydrogen cracking is still being studied. One of the more recent hypotheses is that the hydrogen joins with carbon to form methane, which is much larger than a molecule of hydrogen (H2). The formation of methane seems to better account for the amount of cracking observed than does the formation of H2. It sounds logical to me because when you think about it for a while, where do you typically find an excess of carbon? In the regions where martensite is formed, i.e., in those regions where there is an excess of carbon as a supersaturated solution of carbon and iron. Bang! Right in the HAZ where there is fast cooling and martensite and tempered martensite are most likely to be found. The austenitic structure of the fully austenitic weld is one means of mitigating the hydrogen cracking problem, but there may be other problems that have to be addressed by other means.

Gotta run.

Best regards - Al

By Metarinka (****)

Date 02-04-2010 22:27

correct me if I'm wrong, but due to the FCC structure aren't austenitic stainless steels more easily accepting of all interstitials?

Didn't this lead to infamous 308/309 "Miracle rod" http://www.aws.org/cgi-bin/mwf/topic_show.pl?tid=13901;pg=1 debacle some of you may remember? 309 will hold more interstitials like silica slag in solid solution, so it will will help solve porosity and silica inclusions on carbon steel pipe?

I remember using this much to my advantage in college GTAW courses doing all my fill passes with 308L to lower the chance of inclusions. I also used it for my personal fabrication projects if I was going to be doing multi pass welds. The higher weld quality (at lower effort) made up for the difference in consumables cost. Some 312 rods are marked up just for this very purpose of being "miracle rods" for everything.

By 803056

Date 02-05-2010 04:21

FCC is an empty box ready to be filled.

Al

By ssbn727 (*****)

Date 02-05-2010 05:56

By Superflux (****)

Date 02-05-2010 07:04

Henry,
That is some cool stuff you got there. If only school could have been so much fun. Seemed all my teachers were a cross between the R. Lee Ermy drill seargent character and Sister Octavia.
Thanks
john

By 803056

Date 02-05-2010 14:20

When the subject of interstatials is being discussed I assume we are speaking of small alloying elements such as carbon, hydrogen, etc. that squeeze into the FCC structure. I never considered slag to be on the same scale (size wise) as a single atom that interacts with a FCC base metal to form an interstatial solid solution.

The 309 and 310 alloys are fully austenitic, i.e., FCC, thus they are not tolerant of low melting point constituents and prone to cracking if sufficient ferrite is not present. Type 308 filler metal has more ferrite than either 309 or 310 (if I remember correctly), thus it is more tolerant of LMPC. All the austenitic stainless steel filler metals are more tolerant of hydrogen because it "traps" the hydrogen in the FCC structure.

As to your position that the 308 FM is more tolerant of silica slag and preventing porosity, I'm still sitting here scratching my head.

Poor Scrappy, he took a pounding in that thread. I almost forgot about that one.

Best regards -Al

By ssbn727 (*****)

Date 02-05-2010 16:01 Edited 02-05-2010 16:17

I read you loud and clear Superflux!!! :) :) :)

You said it Al! ;) Scrappy did get a whole lot of heat in that thread mainly because most of the folks who were critizing him didn't fully understand what he was actually doing inside a huge Power boiler which more than likely 90% or more of the responders never even set foot into one of those, and were clueless as to what one would actually encounter in one of those boiler, much lees have an idea of how they are actually designed in such a way that there are indeed inherent redundancies designed and built into these huge power boilers in the first place!!! ;)

I personally worked on just about every type of power boiler design used in both fossil fuels as well as waste to energy (Co-generation) Power plants. So if you were to transport me (Beam me up Scotty!!! :) :) :) ) spontaneously into one of them without any knowledge of where I would end up, or without the aid of engineering drawings, or any type of mapping aid of the plant. I know for a fact that I could find myself around one within 2 minutes maximum and find my way out of one of any size or type within 5 to ten minutes on average... Why do I bother stating this??? Because there are only a handful of folks in here besides myself who can claim the same with some degree of confidence!!! :) :) :)

I say this because I was personally upset at the amount of attacks that were not only lodged at Scrappy (He could have explained himself a whole lot better which didn't help in trying to understand what he was actually attempting to describe in the repair procedure with the so-called "Magic rods"! :( ), but at Boilermakers in general yet for the most part, I refrained from making any comments of my own until very late into the thread...

The type of repairs that are made in these power boilers are only a temporary "band-aid" which is sometimes used as a result of not having enough within the budget for for that particular shut-down to include a permanent type of repair via removal and replacement of such tubes. So the actual permanent repair are then included into the next budget for the following year's annual plant maintenance shut-down...

Usually this happens because the condition/situation didn't exist, or was overlooked in the previous inspection cycle, and was only discovered after the budget was already allocated, and well into the maintenance shut-down period which made it highly unlikely that any more money from the already allocated budget would be used to perform a permanent repair until the next maintenance cycle... Although the EOR's and the SCWI's don't like to admit it, they do these types of temporary, "Bubble-gum like, Band aid" repairs quite often unfortunately for Scrappy!!! :( :( :(

The point I'm making is that Scrappy did not deserve such a "feeding frenzy" that he experienced in that thread, and I'm really glad that he's preparing himself to take a different track in his career by his desire to become a welding inspector eventually!!! :) :) :)

What really has me scratching my head in this thread is how we got to even include slag in the discussion of the topic in this particular thread when the OP mentioned quite clearly at least to myself that the welding process was a pulsed welding process which could also mean pulsed GTAW since "Boss Man wasn't specific in describing the actual welding process being used... Nonetheless, both Pulsed GTAW and GMAW-P use bare filler wire that have no flux so, I'm just wondering how slag got into the discussion...

Perhaps Joel could explain better to us why by clarifying what he was describing to us in his previous post, because I personally have noticed over time that Joel is a very sharp individual despite his own personal lack of - shall I say "seasoning" that one only gets through tried and true experience, and yet his sponge like desire of wanting to possess more and more knowledge as well as his refreshing honesty in admitting that he doesn't know it all along with not being afraid at all to dive into the work and personally getting his hands dirty which is a very unique quality of a welding engineer, shows me at least that he is most definitely on track into becoming one of the best of the best anywhere IMHO. ;)

Well now that I have stroked your ego a bit Joel, could you please clarify what you were trying to describe to us in your previous post??? ;) :) :)

Respectfully,
Henry

By Metarinka (****)

Date 02-05-2010 19:34

perhaps I should clarify. Obviously yes slag is not an interstitial in and off itself. I was referring to the seeming ability of 308/309 to reduce the likelihood of silica slag formations on the surface of a bead (the black glassy substance all GTAW welders are familiar with) or from becoming slag inclusions. I've personally witnessed and used 308 and 309 filler on carbon steels for this very goal.

I've heard three theories as to why this works. First and the obvious one is that the SS fillers have less silica in them to begin with. I looked up the specifications and found that 308L has 1.0 nominal Si, didn't find any Si %'s for the carbon steels I looked up. The second theory is that the silica is entrained into the grain structure (as an interstitial) and hence never has a chance to form slags. The third and final theory I've heard is that by trapping other interstitial elements in the grain structure their are reduced nucleation elements for silica to grab onto and form slag. Although that last one is a little fuzzy and dubious in my mind. This is what I've heard, and experienced in my own career and training, if this isn't commonly thought to be true perhaps I could do with some reducating?

Now scrappy himself took the heat for mentioning among other things that the magic 309/308 can reduce porosity. I haven't personally witnessed this, but I've never had porosity problems in carbon steels that weren't attributed to something else that was easier to fix. I have heard that the higher oxidation potential of chromium means it will form oxides before the Fe. However I don't see that causing a significant reduction in porosity and if it did would create chromium depleted areas, similar to carbide precipitation. Again as mentioned the FCC has the ability to hold more interstitials, and also IIRC will more readily diffuse gases out of the grain structure at high temperature. A whole portion of low hydrogen control practice is the allowance of hydrogen to diffuse by maintaining a post weld minimum temperature. As I understand it diffusion of hydrogen and other gases is a function of time, temperature, and grain structure.

Therefore my guess would be that oils and other contaminants that form gases at high temperature are both being held in the grain structure and diffusing at a greater rate than carbon steel fillers. Sound reasonable?

By ssbn727 (*****)

Date 02-05-2010 20:31 Edited 02-05-2010 20:35

Sounds reasonable to me Joel! ;) There's also the possibility in Scrappy's case, that there's so much corrosion going on whereby various oxides are coalescing with other substances resulting in very weak, yet not so porous like materials which could theoretically hold together long enough at least until the next maintenance cycle where replacement of the bubble gum like, band-aid repairs will already be a part of the schedule of items to be worked on. ;) Very rarely do these temporary repairs last until the next scheduled maintenance cycle, but one has to work with whatever it is that they are given to work with for the time being. ;)

Respectfully,
Henry

By Boss Man Date 02-05-2010 00:08

Thanks so much for all the info. You guys have been a big help.