Stainless teel Welding 6

[nabeel3]

It has been suggested that the weldability of stainless steels can be improved by oxidizing the surface by subjecting it to an elevated temperature in an oxidizing environment. From the penetration point of view, can we agree or disagree, and why?

 

[mfgenggear]

The other was like I said the mixture
Of helium , argon, and on.
If all procedures were not stringent
Porosity would develope.
Aluminum was important to pre heat before
Welding,
Aluminium was always pre etched. For clean.

 

[gtaw]

I take issue with preheating aluminum.

If it is a nonheat treatable, preheat will increase the size of the HAZ. Generally speaking, holding the nonheat treatable aluminum alloys at temperature will reduce the benefits of strain hardening. The amount of damage is dependent on the preheat temperature and the time at temperature while welding.

In the case of the heat treatable aluminum alloys, many can be overaged by holding them at a high temperature (which isn't that high). A single pass weld at high travel speed will be less likely to diminish the mechanical properties significantly, but multipass welds increases the time at temperature and increases the damage caused by overaging the material in and near the HAZ.

Again, generally speaking, even when everything is done properly, one can expect a substantial decrease in tensile strength and yield strength when welding aluminum. This is true with the majority of the aluminum alloys. The reduction in both tensile strength and yield strength are on the order of 40% to 50%. Again, I'm talking in general terms. Consult the code to see what an acceptable test results is for the particular aluminum alloy being welded. Preheatng the material before welding "ain't gonna help matters".

I try to minimize the interpass temperature by cooling the material to room temperature using a fan or even wet rags when making multiple pass welds. It reduces the probability of overaging or reducing the strain hardening strength in the HAZ.

If the welds appear "cold", it is an indication the welder needs to use more current. Perhaps a larger tungsten with higher current carrying capacity is needed.

As for chemical cleaning, we used sodium hydroxide for removing the surface oxide, followed by nitric acid to remove the "smut". Time had to be controlled to minimize pitting the aluminum with the sodium hydroxide. For most application, hand wire brushing is sufficient.

Sorry to digress from the original question.


Best regards - Al

 

[mfgenggear]

@GTAW
quote"I take issue with preheating aluminum."
you are the pro, I now know careful care must be taking of heating any type of material as not to effect material properties.
no worries it was 40-50 years ago, all I know and I saw the results of preventing cracking, aluminum is tough to weld with stringent NDT requirements.
I forgot now what the specification requirement was back then but it was allowed then , it may have changed now, requirements do change. very small indications that were subsurface and surface.
surface indication were easy to rework light grind with flapper wheels, subsurface had to be drilled out and rewelded. PITA in finding the exact location with X-ray films.
if back then if the internal procedure were not followed, radio graphic and flow pen indications doubled, fixing cracked welds was not easy.
and try to salvage parts was not 100% effective. prevention was the key.
I believe the temps were so low it did not effect the tensile requirement, but I don't remember so I bend to your professional knowledge. you are more current.

quote" I try to minimize the interpass temperature by cooling the material to room temperature using a fan or even wet rags when making multiple pass welds. It reduces the probability of overaging or reducing the strain hardening strength in the HAZ. "

Quote "If the welds appear "cold", it is an indication the welder needs to use more current. Perhaps a larger tungsten with higher current carrying capacity is needed."

important information I forgot, thank you so I will take note

"Sorry to digress from the original question."
same here, but I like this type of discussions there is a lot I forgot, that I know just touched the surface.

 

[gtaw]

What keeps my attention with welding is there is more than one way to skin the cat.

With regards to preheating aluminum, I find too many people believe if a little is good, more must be better! They forget, if they ever understood, why we preheat medium carbon, high carbon, and high strength low alloy steels. They apply what they know about steel and figure it is the same for aluminum.

In my welding courses I stress that what works for one base metal may not produce the same result when applied to another. I use high carbon steel as an example. If I heat the high carbon steel to an orange heat and quench it in water, it gets hard at the expense of ductility. If I heat copper to the same color and quench it in water, it is annealed and ductility is increased. The response to heating and cooling are in stark contrast to each other.

There is nothing like a demonstration to drive a point home.

I can picture the welders welding 6061-T6 with GTAW. Along the toes of the completed welds, the dye penetrant test would reveal a multitude of small, fine cracks. For the most part, they are superficial and only a thousandth or two deep. A good scrubbing with a stainless wire brush removes most all of the indications. The Air Force calls it arc erosion. The aluminum oxide is most likely the culprit. It melts and resolidifies with all the tiny cracks. It isn't acceptable if it is detected with the dye penetrant test. Visual examination is unlikely to detect the small cracks. Fun stuff, that aluminum!

Best regards - Al

 

[mfgenggear]

agreed gtaw
aluminum welding is very much under estimated, most of the specification were customer internal propriety, I started out at the floor with high temperature, stainless and aluminum, there were much smarter senior engineers than I was at the time I was in my twenties, very young and naïve. as we progress much learning is required and acquired. it was possibility the lower tensile was permitted. don't remember.
we never had rejections from the customers, and there was work instructions and weld schedules approved by the customer, go figure.

 

[gtaw]

If we were only born with the knowledge and experience we acquire over twenty, thirty, or forty years in the field!

Best regards - Al

 

[mfgenggear]

amen

 

[EdStainless]

With a lot of materials pre-heat may be a misnomer, warming is more like it.
Even with some very heat sensitive SS grades I like them warmed to enough to assure that they are dry before welding.
I have seen so many welds ruined by improper cleaning. There are no insignificant details.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[gtaw]

On the subject of preheat, I can't remember how many times I've been told to "drive the moisture out of the metal before welding."

The less they know ........

Best regards - Al

 

[mfgenggear]

and that may have been the case more of a warm, than a pre-heat

 

[kingnero]

@gtaw
Get them to preheat warm a piece of steel using an oxy-acetylene burner and a heat gun (paint stripper thing) to the same temp and observe the difference of moisture "driven out of the base material".

 

[gtaw]

I like it.

Best regards - Al