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Welding different steel grades together?

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Welding different steel grades together?

Old 09-30-22, 12:12 PM
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ezikwa
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Welding different steel grades together?

Hi, I’m looking for info on different steel grade cross compatibility when Tig welding….

I’m building my first emtb and getting to the point where my design is changing as I try and source the materials. Long story short it’s easiest and cheapest for me right now if I bought the seat tube, head tube and bottom bracket in 4130 (mainly as they come in the correct sizes for bikes), and the rest of the tubes in BS4 T45 (and some sheet s515/s14).

Is this going to work?

I like the T45 because I can find it on eBay in the sizes in need, I don’t want to heat treat and apparently the welds will not crack (4130 I have read mixed things re the need for heat treatment?)

Also it’s going to be a long bike for a tall heavy rider, so opting for 35mm-45mm tubes ranging 1mm to 2mm straight walled tube no butting, does that sound right? I’ve seen steel tubes down to .6mm thick on bike specific tubes, so maybe I’m going way too thick?

If these two materials cannot be joined it will have to be a full T45/S514 build and will have to work out the best way to machine tubes inner dimensions to bike specs with the tools available at work….any tips on getting this done without buying special sized reamers etc?

what is the best way to tell if two metals will work well together?

appreciate any help thanks!
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Old 10-01-22, 02:24 AM
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guy153
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I'm pretty sure you can weld T45 to CrMo no problem. They're both high strength low alloy steels. T45 has a bit more Manganese, but so does Reynolds 631, and you can weld that to CrMo just fine. People do all the time. Just use the normal mild steel filler rod (ER70S*) although some people like stainless rods.

As for the thickness, well the triple butted ("dual zone butted") tubes from Reynolds designed for MTBs are 1.1m or 1.2mm at the ends, but drop to 0.6mm in the middle. The alloy on those is a bit stronger than T45. 1mm should be fine unless you're really sending big jumps and things. At 2mm it will feel a bit like you're riding a farm gate. Those diameters probably about right-- I guess you could try 45mm on the DT and 35mm on the TT?

You don't need to heat-treat CrMo unless it's over 3mm thick. In other words, for bike framebuilding purposes, you don't need a heat treatment.
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Old 10-01-22, 06:01 AM
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dsaul
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I don't see any reason why they can't be welded together. I found some info from a manufacturer of T45 tubing that recommends A32 filler wire, which is ER80s2 in the US, for welding it. I would use ER312 stainless filler, as it is designed for welding dissimilar steels like alloyed steel to mild steel or stainless steels. I prefer it for welding anything steel, mostly because it flows nicer that ER70s2, but it is more expensive.
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Old 10-02-22, 10:01 AM
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ezikwa
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Thanks guys very much appreciated!!!
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