304L/316L WELDING INCLUSIONS?? 1

[MASSEY]

We are welding SS shafts into SS hubs then machinging a smooth large radius where the weld is. We are seeing inclusions or 'pockets' in the weld when machinging it away.
We've tried mig, tig, spray, various gasses, polarities etc.

What is the "best" set-up for having a pure, solid, inclusion-free weld in Stainless Steel?

 

[TVP]

Have you considered using a solid-state process like friction welding rather than arc welding? Inclusions and porosity are eliminated in this process since the workpieces are not melted. I would recomend contacting MTI for more information:

http://www.mtiwelding.com

email: info@mtiwelding.com

 

[pipewelder1999]

Are the hubs cast?
Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[MASSEY]

Hubs not cast, sawn off stock machine bored. The shaft usually extends through two hubs and a pulley.

 

[pipewelder1999]

The only other thing I can think of is contamination from lubricants/cutting fluids. I have repaired/fabricated many shaft/hub assy's for rollers and never encountered any porosity/inclusion problems except when the machinist used anti-sieze comploud for the assembly.

Sorry I can't help more. Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[mcprofusion]

I agree with Pipewelder1999.

Tig is one of the cleanest processes available, if you employ the correct procedure and welding technique. Make sure your parts are clean. Brush clean your joint and use a cleaning solvent to remove any grease.

 

[chiph]

what's your filler metal?

 

[MASSEY]

Wire is: RANDOR - ER308L - .035" with Mix 24 for shield.

Our process is improving, but we are still seeing very small inclusions when the radius is machined in joining the shaft, to the weld, to the hub.

Thanks for your comments & help.

 

[chiph]

try pulsed inverter with er347. this "stirs" things up and the niobium is a great scavenger. just an idea.

 

[boo1]

Agree with the contamination notes above.
Have you tried changing the gas bottles?

 

[MASSEY]

Gas bottles have been changed as well as different types of gas mixes have been tried.

Just came in from the shop floor - getting about one inclusion per weld. The welds I just seen are on a 1" shaft. Perchance the inclusions are at the tacked areas. There are usually 3 tacks welded during assembly then they are welded at a later time.

Currently, we grind out the bad area and re-weld it. Then re-machine it. It we don't get this fixed soon - we won't have to worry about - if you know what I mean.

 

[chiph]

hope you don't mind me asking more questions. how would you classify the dicontinuities? is it a void, or is it filled with something?

 

[pipewelder1999]

If this is a void and not an inclusion, it could be related to the buidup of expanding gas that results from the heating due to welding. When the last part of the weld joins to the rest of the weld, gas is still escaping from the joint. Now if this is a very tight fit, this isnt the problem. Are you tacking with GTAW or are you using SMAW? Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[MASSEY]

The dicontinuities appear to be shallow pockets. These may or may have been filled with something, perhaps the 'something' is removed, relieved, released during the machining process.

Before machining the welds appear to be very 'good'.

I am not welding these joints myself, however, I made a living before and during college as a welder. I've welded for 12 years, I can MIG, TIG, and STICK, I cannot see an error in our process.

Normally these would pass as very good welds, but we are machining that radius in the weld which makes the shaft, the weld, the hub 'look' like one very smooth, solid piece of steel with a transitional curve joining the two different diameters.

We are not tacking with GTAW or SMAW, we are tacking and welding with GMAW.

Thanks for your input, comments & questions.

 

[Vonmagnuson]

I'd almost bet your inclusion is coming from your tack. I think you have contamination forming around the tack and you are including it in the final weld. Is there any way to tack with a tig gun and no filler?

 

[boo1]

I disagree with the tack as the problem source of the problem. The melt through should blend the tacks in. Check the shielding gas flow, then take one parameter at a time and insure it is not introducing contamination. The cleanleness (oil free) is the most common problem

What grade SS are you using?

Cheers

 

[MASSEY]

Grade SS is either 304 or 304L. Some parts are one some are the other.

Thanks for the comments.

 

[mcprofusion]

I pretty sure your problems lies in your tack welds. I assume your tacking with GTAW. Good..Now the parts are SS, which means argon gas shielding is critical, as shielding and backing gas. However, your parts are so tight together i wouldn't think youd be able to use backing. The reason is on SS steel, especially with pipe welding you always need to purge inside to prevent what we call "Sugaring". Surgaring is not good ! You cannot burn over it ..it must be ground out completely and re-welded, to remove the contaminted weld metal.

Note: Whenever using GTAW, any impurities our voids in the underlying weld metal will cause it to grow, and at times blow out at you.

Potential Causes - In your tacking process you are sugaring the other side of the weld metal to a degree, since you have no shielding on the inside. I imagine, that your tacking process could be using a lower current than your GTAW welding procedure, thus making it easy for the final weld to melt thru your tack and mix the good weld metal with the underlying "sugaring/contamination".

Potential Remedies:

(1) Use a higher current in your tacking process, same as your welding procedure.

(2) Make sure your welder uses clean filler rod; this means clipping the end of the filler rod everytime he/she is to lay another tack or weld. Everytime you remove your filler rod from the cup shielding or stop welding, your filler rod is now contaminated. You can see it turn black..if the end is not clipped off, this contamination will enter your weld metal and you will also notice a reduction in puddle wetting and dark oxides floating around and the weld will turn grey. This is extremely important in high purity GTAW welding.

(3) Try Autogenous welding the entire joint before depositing your weld metal.

(4) If the problem still persists, try using an Easy-flo Flux stainless steel grade, to prevent surgaring on the inside. Use a flux since you are unable to use a backing gas.

http://www.matthey.co.za/products_5_home.asp

I hope this helps ..


Marc

MC PRO-FUSION

http://www.mcprofusion.com

 

[mcprofusion]

You might also want try an Argon / Hydrogen shielding mix for your GTAW process.

Argon/Hydrogen mixtures are often used when welding metals such as Inconel and Monel. It can also be used on STainless steels. It is used when no other hsielding gas can prevent porosity. Note it increases the welding heat, helps control the weld bead profile, and gives the puddle better wetting action.

Typical mix is 95-5 Argon-Hydrogen.

 

[quadswift]

Are you machining because you need to, for the process or to provide a 'running' surface, or for'cosmetic' purposes?

Are the defects detrimental to the operation / life of the component? Your engineering group should be able to do the calcs and come up with an acceptance criteria. The requirement for completely defect-free welds is unusual.

The original weld, as welded, is obviously fit for purpose as you appear to be removing a fair amount of it.
You are obviously putting in more weld metal and then removing some of it by machining.If the revelaed defects are associated with the tacks then it would appear that you are removing most of the weld.

Can you leave it in the 'as welded' condition? You could reduce the amount of runs of welding if you can leave it 'as-welded'. Dye pen the final weld and examine to the acceptance criteria provided by your engineering group.

You could set up a test weld and do a dye pen exam of each run to see if you can determine exactly where your defects are occuring.