Does 404 SS anneal and become malleable?

[tornitore45]

I need to make a tapered chimney and plan to start with a seamless tube, cut out a triangular slit and coerce the rest into a tapered "round" tube.
I need not to spring back too much.
4" Long Small OD=0.825" Big OD=1.062 Wall=0.04

[Harold_V]

I have not encountered 404 stainless in all my many years in the shop, so I am unable to provide any guidance. However, it is reputed to be easy to fabricate.

You might consider boring a sleeve in which you can drive the piece of tubing, so it will be formed to the desired configuration. Once the wedge is removed, you should be able to push the tube in with a press, or it may even go willingly with a few hammer taps on a block of aluminum placed over the end. Once in place, a tack at each end so it can then be removed for final welding. You also might consider making it a little too long, so you can trim each end.

I'd enjoy reading how you accomplish the task, and I know you will.

H

[Steggy]

Type 404's chemical composition includes a trace amount of carbon and a small amount of nickel, but much less nickel than typically found in 300-series alloys, which sort of makes 404 an austenitic/ferritic hybrid. 404 will not respond to heat treatment, but can be annealed by raising it above its transformation range (~1510° F to ~1600° F), followed by rapid air cooling.

404 finds a lot of use in sheet metal products as a replacement for type 304, which tells me its forming properties are at least as good as the latter, and likely better due to the lower nickel content. So I'd be inclined to think you shouldn't have to anneal the material before you work it.

As stainless alloys go, it's easy to weld via the tungsten-inert-gas (TIG) process, using tri-mix as the shielding gas and a compatible filler. The extremely low carbon content helps to prevent the formation of chromium carbide in the fusion zone, which would otherwise compromise corrosion resistance. In many respects, 404 is similar to 304, but with better mechanical properties.

I've only run into 404 once—years ago, but I was making to guide rods out of 404 round, so I can't comment on how easy or difficult it might be to do what you want. I did have to weld it and found its welding properties were just like 304L.

[GlennW]

As stainless alloys go, it's easy to weld via the tungsten-inert-gas (TIG) process, using tri-mix as the shielding gas and a compatible filler.

Why not Argon?

[tornitore45]

followed by rapid air cooling.

Can you expand on that?
Steel is normally annealed by slow cooling.
Brass can be allowed to cool slowly, speeding up cooling is only for convenience.

All the welding capability I have is silver brazing and flux core which it usually turns out looking like solidified volcanic lava all round the intended spot.
I will braze it including finishing turning rings at the ends.

Until I learn to control the flux wire welding it will be limited to non critical/non cosmetic projects.

[Steggy]

As stainless alloys go, it's easy to weld via the tungsten-inert-gas (TIG) process, using tri-mix as the shielding gas and a compatible filler.

Why not Argon?

Argon is suitable but the weld quality may not be as cosmetically pleasing. In my experience, tri-mix seems to be more forgiving with stainless alloys. It depends a lot on the weldor's skill.

[Steggy]

followed by rapid air cooling.

Can you expand on that?
Steel is normally annealed by slow cooling.

404 is an exception. If you are still in doubt look it up.

All the welding capability I have is silver brazing and flux core which it usually turns out looking like solidified volcanic lava all round the intended spot. I will braze it including finishing turning rings at the ends.

Brazing a stainless alloy is not something I would do. Brazing is a form of hard soldering, a process that doesn't work well with high-chromium-content steels. You really need to weld this material to achieve satisfactory results, TIG being the preferred process (MIG is possible, but won't be very pretty). Spot welding is an alternative if seams overlap. If you can't do it this would be a good case for paying a skilled weldor to do it for you. It all depends on how critical the joint's structural integrity is.

[Harold_V]

I suspect that brazing will border on the impossible. Stainless has a considerable expansion coefficient, so unless the item can be fully restrained while it is brazed, it will open when heat is applied. A difficult process, to be sure.

H

[GlennW]

As stainless alloys go, it's easy to weld via the tungsten-inert-gas (TIG) process, using tri-mix as the shielding gas and a compatible filler.

Why not Argon?

Argon is suitable but the weld quality may not be as cosmetically pleasing. In my experience, tri-mix seems to be more forgiving with stainless alloys. It depends a lot on the weldor's skill.

Can't say that i have ever heard of or seen a reference to using tri mix for TIG welding stainless. MIG, yes.

[whateg0]

I'd add that the cone shaped form to force it into is fine, but just tacking at the ends isn't going to keep the middle from wanting to open up. If I was going to go that route, I'd machine a slot along the seam so it could be tacked in several places along the seam before pulling it out of the form. If I was going to make this part, though, I'd turn a tapered form to place the part over and then hammer form with a nylon hammer.

Dave

[Harold_V]

I'd add that the cone shaped form to force it into is fine, but just tacking at the ends isn't going to keep the middle from wanting to open up.

I agree. With just end tacks, once removed, a center tack would likely work, however, but unless one has access to TIG, this is likely of little use to the OP.

If I was going to go that route, I'd machine a slot along the seam so it could be tacked in several places along the seam before pulling it out of the form.

I'd thought about the idea of simply leaving the formed piece in place, and doing the welding/brazing insitu. Problem is, one would need a form that didn't absorb heat, and provided resistance to soldering the piece in the form. Not much of a challenge, eh?

If I was going to make this part, though, I'd turn a tapered form to place the part over and then hammer form with a nylon hammer.

Having worked on enough stainless to be concerned, that might just be a lot harder than it sounds. Stainless, very unlike copper alloys, doesn't really respond well to that kind of treatment. It likely would work if heated, though, but now the form is also softened. Little chance of heating just the thin material and retaining any substantial heat.

It's going to be interesting to read how this works out in the end. We all stand to gain some knowledge.

H

[Steggy]

Why not Argon?

Argon is suitable but the weld quality may not be as cosmetically pleasing. In my experience, tri-mix seems to be more forgiving with stainless alloys. It depends a lot on the weldor's skill.

Can't say that i have ever heard of or seen a reference to using tri mix for TIG welding stainless. MIG, yes.

Back in my (full-sized) railroad days I regularly TIG-welded stainless with tri-mix, mostly because it was available and tended to make for prettier welds. Technically speaking, tri-mix is "wrong" for stainless, but it does work.

Incidentally, I do all my steel MIG welding with 75/25, and can produce acceptable stainless welds with it. The arc isn't as aggressive as with the more economical CO2, resulting in better weld quality and less spatter. Only thing is 75/25 makes for shallower penetration. That, of course, is a plus when welding sheet metal. I rarely weld sections thicker than 1/4", so 75/25 is practical for me.