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Brommers
I have decided to swap to a different filler metal for Tig welding. I used to use stainless filler, er312l. It's a filler that is used widely across the framebuilding world, it's a good option and is very nice to weld with however it is not the "technically" correct choice according to welding handbooks. The technically correct application for 312 (and similar filler 309) is for joining dissimilar metals, mainly stainless and non stainless. A lot of notable framebuilders (44bikes,chumba, btr) use it and I have no doubt it's just fine but I'd like to change.
I've decided to swap to er70s2, which is a more standard filler metal that is used for a very wide range of steels, it is the go to filler metal for chromoly and the technically correct choice for these alloys so I'm going to use it in the future. It's marginally more difficult to weld with and doesn't have as pretty colours because it's not stainless, but it is the better choice in my opinion.
Ultimately er70s2 is a tried and tested filler that has been used with chromoly steel in a range of safety critical applications (aerospace, rollcages etc) for decades. Er312 is well evidenced to be effective but there's no reason to use it over er70s2.