Anything I need to do before TIGing stainless to steel?

Metal Shop
#1

I’ll be welding some stainless bolts and nuts to steel for a project I have planned. Anything different to look out for other than same issues with mild steel to mild steel?

#2

I’ve MIG welded the two together before, and don’t remember any issues. I would recommend using either stainless filler, or looking for s filler designed for the combination.

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#3

Back gas is your friend. We don’t have a current setup for backgas though. I’m going to buy my own dual regulator for this. You might be able to get away with fusion welding.

You can MIG it though.

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#4

Does it really need backgas? What if I just lap clean it, prime and paint. Shouldn’t cause any rust issue should it?

#5

I was wondering about filler. I’ll have to look into that. Thx

#6

From Lincoln welding site:

Use 309L (including ER309LSi) when joining mild steel or low alloy steel to stainless steels, for joining dissimilar stainless steels such as 409 to itself or to 304L stainless, as well as for joining 309 base metal. CG-12 is the cast equivalent of 309. Some 308L applications may be substituted with 309L filler metal, but 316L or 316 applications generally require molybdenum and 309L contains no molybdenum.

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#7

I’ve said it before, I have welded stainless Unistrut together with regular MIG wire. It looked good, Very minimal spatter. However it was not going to be exposed to outside weather. It was by accident of course, I didn’t realize it was stainless until I went to put self tapping screws in.

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#8

When welding a bolt head to a flat surface, I don’t think back-gassing will be an issue as there really isn’t any open area for O2. Pretty much the same thing with a nut, the hole is in the center and you’re welding on the outside edge away from the hole - personally I’m not sure how much exposure to O2 there would be. If you put a bolt into the nut and used it to hold nut tight against the base metal, probably wouldn’t much if any air in there. Since welding on outside of nut when cool, bolt should come out.

You could try this on a test piece before you did it on project.

#9

All dissimilar metals that touch are susceptible to galvanic corrosion. Application will dictate if this is acceptable.

Why ss to non-ss?

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#10

When welded together, the regular steel shouldn’t rust any worse than normal. But as rust from the normal steel comes in contact with the stainless, it will also start rusting. More slowly than the normal steel, but still rusting.

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#11

Also, if the metal is heated to high temps, say in a BBQ or fire pit, the heat will accelerate the galvanic action. Stainless won’t be affected as much as will the mild steel where there is contact. If you can use some high temp paint to exclude moisture will help reduce galvanic action quite a bit.

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#12

@LeeCJones might have some good advice on the matter. No pressure on Lee if he doesn’t respond, just figured I’d mention him and his expertise on welding.

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#13

I’ve never witnessed galvanic corrosion beyond the way some guys used to hookup water heaters w/o the special sacrificial couplers…so I cant speak to it.

I’ve got some SS filler rod. I can’t remember if it’s 309 or 316… if you want to try some, let me know, 3/16” I think just can’t remember the cr content.

Painting stainless as I remember does work well.

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#14

It’s 309 filler rod.

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#15

I could use non-ss fasteners, but I want to try ss for a couple of reasons. I’m looking for long term strength on the threads that will have shear forces on them and it will be outside. Secondly, I just want to try it out as I’ve never done it before. Looking to learn.

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#16

Thanks for the offer. I’m going to pick up different fillers based on some research and practice with each prior to fabricating what I’ll be building.

I would take you up on some of your filler, except that I won’t be welding this at DMS but at my shop instead and not sure when I will be able to get there. But I really do appreciate the offer.

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#17

Its been a while since I’ve designed shear connections, but I would think larger diameter bolts would be more effective in shear than stainless compared to conventional zinc coated bolts.

#18

I’m not building a BBQ pit, but your post got me thinking that using SS in certain areas would be perfect for a grill. I’ve built one using flat stock and rollers and then welding it up. Certain portions of the pit start warping and binding after multiple firings. The heat temp paint does work well, but I’ve found it needs to be reapplied after awhile depending on use.

I do want to build a big pit on wheels though. I have a design where the fire box is placed in the the middle of the pit instead of on the end as most use.

#19

It would work, but I just want to try and use ss to see how it performs long term. I’m either using 5/8”or 3/4” nuts and bolts either way.

The other aspect is that I will be insetting the nuts inside the steel tubing. Whereas most welded nuts are placed on the surface. On this application, I will drill holes just larger than the nut &/or bolt head and then weld it flush to the steel tubing face so that I have a flat surface to bolt up a plate to the tubing.

#20

When I worked at UTC Power (Fuel Cells) the large natural gas reformers (high temp catalyst beds cracked methane into Hydrogen and various Nitrogen compounds) we used 310/310S SS. Had great heat corrosion resistance, very restive to Sulfur compounds (S from natural gas), good weldability, etc.

Applications of Grade 310/310S Stainless Steel

Typical Applications Grade 310/310S is used in fluidised bed combustors, kilns, radiant tubes, tube hangers for petroleum refining and steam boilers, coal gasifier internal components, lead pots, thermowells, refractory anchor bolts, burners and combustion chambers, retorts, muffles, annealing covers, saggers, food processing equipment, cryogenic structures.

The reformer was guaranteed for 20 years so probably good for life on the backyard grill.
310 & 310S

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