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TIG welding mild steels

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  • TIG welding mild steels

    Q. The other day a friend and I had a conversation about TIG welding mild steels and what filler rod to use. At times porosity occurs during welding and the first thing him & I do is grab a piece of stainless steel filler rod instead of the mild steel filler rod (ER70S3). The weld looks a lot better but is it as strong as if we used the mild steel filler rod? Also can you use S.S. filler on 4130 Chrome-moly? What grades of S.S. are stronger and do you know the tensile strengths of the different grades of S.S. filler rod when welding on mild steels? My friend and I are IHRA Drag Racers and both fabricate and weld a lot of 4130 C.M. (Submitted by: Jim Dadas from Vermilion Ohio)

    A. When you move to a SS filler, it does look nicer, but the welded area is too strong and in the wrong application, gets brittle along the weld and could crack. The reason is because the SS is much harder than the base metal. The correct filler would have similar strength and elongation characteristics. The ER70S-3 or an ER80S-D2 is great for mild steel. You could use a 312 SS filler for your 4130 if you had to. I prefer the ER70S-2 or ER80S-D2 for roll cage applications because of their ability to flex better under a crash yet have great strength too. You might try a TigTectic 680 rod. It has some great coloring that the SS filler has and boasts better elongation percentages too. You might try and weld a few pieces with different fillers and do a bend test. All of the described fillers have adequate tensile strength but really need to be matched to the application as far as elongation or weld bead ductility. For example, you will want your cages to be strong and flexible in case of impact, but you could weld the rear end brackets or spindles with the higher tensile strength fillers.