Welding Tips and Tricks

I have been doing some fabrication work and last project all I had was 308L filler rod to use on DOM tubing.
Typically rod choice is 70S2 but can anyone tell me what is the fundamental difference in a joint when the base material is mild steel but the filler rod is 308L instead of 70S2.
Does one produce a much stronger joint than the other, is there a benefit to one over the other or detriment I don't know about?

did this DOM tubing happen to be 4130 Chromoly?

Oscar wrote:did this DOM tubing happen to be 4130 Chromoly?

No it was mild steel, I have seen where when using Chromoly you want to use 310/312 filler rod.
This was the standard mild steel DOM and also some seam welded mild steel as well.

I think you messed up. 308 is for 304 stainless steel, not low carbon steel. You should have used ER70S2.

big gear head wrote:I think you messed up. 308 is for 304 stainless steel, not low carbon steel. You should have used ER70S2.

So what is the possible fall out for using this filler rod on low carbon steel, what happens to the welds?
High failure possibility or ??

I can't say for sure. Maybe someone else will have a better answer, but 309 would have been better. I know people use 309 on low carbon steel sometimes when joining different materials, but I haven't seen a use for 308 on low carbon steel.

This is what I had seen before:

Many people claim that it's fine to weld mild steel with a SS filler, and the truth of the matter is that you will get away with it most of the time.

Having said that, you will never see in code quality welding ( pressure vessels, structural members etc ) where a written welding procedure allows for a
typical austenitic stainless such as 308,309, 316 to be used ( exeption being 312 ) to be used as a filler ( stick, MIG, TIG, Sub Arc ) for welding steel
to itself

Why .....because if there is not enough alloys ( Cr , Ni etc ) in the resultant weld deposit to to control the "hot cracking "
To prevent hot cracking, the you want a microstucture which contains a small amount of ferrite in the austenite structure.
To predict this, you can calculate the ferrite number FN of a weld deposite. All stainless filler metal data sheets will provide the FN of the filler
as this is diluted the FN will drop. The industry minumum "safe zone" is to have a FN of no less than 3

When does the FN drop below this

1. not all fillers are created equal....example, a 308L from one manufacturer will not necessarily have the same FN as another brand

2. dilution due to base metal...welding on stainless to mild steel with a 309 is commonly done...why, because a 309L will generally have the highest
FN of the austenitic ( 308,316) SS. Because there is enough alloys in the stainless base and the filler, the dilution with the mild seel
base is not an issue

3. choice of filler material ER308 and ER316 typically have FN 10 or less. ER309 have FN typcially 13 ..much higher

If you weld on mild steel to mild steel with a stainless filler, the FN can easily drop below 4 or 3. Doesn't guarentee you will "hot crack" , but if you
are welding on lower quality steel ( high Sulfur and phosphorus ) you are asking for trouble

3. Improper use of shielding gas. Stainless steel is sometimes MIG welding using 75Ar/25CO2 because someone told it works. Doing so will drive down the
FN


Bottom line, being aware that over dilution of the stainless can cause hot cracking, you can minimize the
dilution by
- using a relatively large amount of filler ( weld big ) .
- Try not to over penetrate (min current )
- use a filler with a higher FN ( a 309 filler is a MUCH better choice than 316 ...309 has higher Cr and Ni )

It is ok to make a general statement that welding mild steel with stainless filler can be done , but it is incorrect to
say that it is GOOD practice to do so. To say that the only reason people don't use stainless all the time
is nonsense....the cost of labor to put in the weld is much higher than the filler metal cost.

The million dollar question is why would you want to use a stainless filler for welding milds steel

1. the ductility is much higher ( 40-55% elongation ) than mild steel ( about 25-29% ) This can be helfulll
to provide the weld some "give ". Example, a CrMo chassis in a drag racing car that see lots of deformation. Tensile strength is about the same

2. Seems to flow better ??? Mabey, but a proper mild steel filler ER70S-2 flows better ( "flow " is determined by Si content and 70S-2 are higher than SS )

Reason not to ( other than the hot cracking mentioned above )

1. stainless filler have very little cleaning action. Because the process itself ( TIG in DC- ) doesn't offer any cleaning and no flux is generally used
you can only rely on the filler. A ER70S-2 is "triple deoxidized (with Ti, Al, Zr ) to clean the weld. This is why a S-2 mild steel filler is much better
cleaning than a ER70S-6 or stainless. Might not be a problem if you are welding on clean material

2. stainless fillers tends to "stick" in the puddle compared to a ER70S-2 . As a beginner, this can be annoying

Hope his helps and didn't put anyone to sleep

Source: http://www.chaski.org/homemachinist/vie ... php?t=2487

Instead of stainless filler on the DOM you should have matched the base material or use a filler to create the desired weld properties you need (will show a few reasons to dilute base metal). ER70-S2, ER70-S6, ER70S-S3 would all have been a better choice.

DSM8 wrote:
No it was mild steel, I have seen where when using Chromoly you want to use 310/312 filler rod.
This was the standard mild steel DOM and also some seam welded mild steel as well.

Please, PLEASE NEVER use stainless filler for 4130 Chromoly. Typically you should always use a filler that matches the base metal or requires dilution of the base metal and filler to create the desired metallurgical properties. 4130 is a great example where you dilute the base metal down with the filler to avoid a brittle weld. When welding 4130 the best filler that experienced and educated welders and engineers use is ER70-S2. The second choice is ER80S-D2. The two fillers create different properties in the weld with ER70-S2 giving more elongation and less martensite in weld. If you notice I did not suggest 4130 filler it is made but requires special treatment after welding and is only needed to be for certain applications. If you use 312 it changes the metallurgic properties and grain structure a lot. 310 stainless itself is used typically in high heat corrosive environments. 312 stainless filler is used to weld castings of similar chemical make up dissimilar metals example stainless to carbon. I will add a few links that better explains welding chromoly then I can do without writing pages upon pages of stuff on forum.

Lot of useful descriptions on these pages
http://netwelding.com/Welding%204130.htm

Explains the metalurgical properties of using ER70-S2 vs. ER80S-d2
http://netwelding.com/4130_Tech_Details.htm

edit had to change my description of 312 filler lumped it with 310 the first time SRY

Now if an engineer tells you to weld with odd ball fillers and they a have WPS for it well you have do what they want and its on them even if they want you to use superglue

Thanks for all the detailed replies.
Since this was a non-structural weld it really wont matter but good to know otherwise.

RE: Chromo welding, I do know only to use the 70S2 when working with that which is exactly what I do anyways.

Was the 308 cheaper or just left over from something else?

Poland308 wrote:Was the 308 cheaper or just left over from something else?

It was what I had on hand ran out of 70S2 in middle of project and had to complete it at that time.

DSM8 wrote:Thanks for all the detailed replies.
Since this was a non-structural weld it really wont matter but good to know otherwise.

RE: Chromo welding, I do know only to use the 70S2 when working with that which is exactly what I do anyways.

Ok you had me concerned when you mentioned using 310 and 312 for it.

dirtmidget33 wrote:Instead of stainless filler on the DOM you should have matched the base material or use a filler to create the desired weld properties you need (will show a few reasons to dilute base metal). ER70-S2, ER70-S6, ER70S-S3 would all have been a better choice.

DSM8 wrote:
No it was mild steel, I have seen where when using Chromoly you want to use 310/312 filler rod.
This was the standard mild steel DOM and also some seam welded mild steel as well.

Please, PLEASE NEVER use stainless filler for 4130 Chromoly. Typically you should always use a filler that matches the base metal or requires dilution of the base metal and filler to create the desired metallurgical properties. 4130 is a great example where you dilute the base metal down with the filler to avoid a brittle weld. When welding 4130 the best filler that experienced and educated welders and engineers use is ER70-S2. The second choice is ER80S-D2. The two fillers create different properties in the weld with ER70-S2 giving more elongation and less martensite in weld. If you notice I did not suggest 4130 filler it is made but requires special treatment after welding and is only needed to be for certain applications. If you use 312 it changes the metallurgic properties and grain structure a lot. 310 stainless itself is used typically in high heat corrosive environments. 312 stainless filler is used to weld castings of similar chemical make up dissimilar metals example stainless to carbon. I will add a few links that better explains welding chromoly then I can do without writing pages upon pages of stuff on forum.

Lot of useful descriptions on these pages
http://netwelding.com/Welding%204130.htm

Explains the metalurgical properties of using ER70-S2 vs. ER80S-d2
http://netwelding.com/4130_Tech_Details.htm

edit had to change my description of 312 filler lumped it with 310 the first time SRY

Good call on not using stainless on chromoly, even though it's not even part of this thread. I've read that people just want to make pretty shiny welds on non-stainless welds and that's why they puposely end up shoving SS filler rod in there, when it's not even close to ideal.

Oscar wrote:
Good call on not using stainless on chromoly, even though it's not even part of this thread. I've read that people just want to make pretty shiny welds on non-stainless welds and that's why they puposely end up shoving SS filler rod in there, when it's not even close to ideal.

I mean, he did mention it in his reply, which is why it was brought up. I was going to reply earlier, but lost track of the post while playing Zombies on Black Ops 3 lol.


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Great reply copy/paste Oscar. The abridged version, it ikey has/will crack even if you can't see it by naked eye. As always use GOOD STANDARD PRACTICES. The post went into really good exploration of WHY not. As already been said, please NEVER weld cromoly tube with 308, you are using that tube for a good reason likey for real safety concerns. 308 vs 309 are VERY different and have VERY different uses although only 1 number apart...no need to try and reinvent the wheel.

Now as Dirtmidget says if that engineer gives you a cockemaimy WPS I would "respectfully" question it, but it's their neck on the line and likely SOME reasoning behind it.

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mild steel, low alloy steel, stainless steel welding need different types of wires and fluxes. welding fluxes for stainless steel contains alloying elements Cr, which gives hardness and resistance to rust. Check American Welding Society guidance, you will get instruction.

http://www.aws.org/
http://www.ylflux.com/

charliehill wrote:mild steel, low alloy steel, stainless steel welding need different types of wires and fluxes. welding fluxes for stainless steel contains alloying elements Cr, which gives hardness and resistance to rust. Check American Welding Society guidance, you will get instruction.

http://www.aws.org/
http://www.ylflux.com/

This is the TIG welding section and he is TIG welding no flux is needed argon is the shielding gas. Only TIG rod I heard of that uses any flux is a stainless TIG rod with a flux core I was told it was developed for putting roots in pipe welds without using a back purge. Never used it or seen it and am not a pipe welder so I don't know if or how well it works. I would think not to well compared to purging, plus never hear anyone using it. Sure if it was as good as purging and cheaper the big industries would use it, so must not be any good.