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Best welding rod (tig) for welding 4130 chromoly tubing

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  • #31
    Proper filler material for AISI/SAE 4130 steel

    Wow! there are a lot of posts for this topic, and not being one to be left out, I will add my opinion here also. Although the question is vague as to what the application is, I will attempt to cover all the bases.

    First, the use filler material that closely matches the base metal is not intirely true, as there are many factors that dictate what filler material to choose. FAA AC43.13-1A, section 5, 4-74 (9), states "Use welding rod and electrodes that are compatible with the materials to be welded. Welding rods and electrodes for various applications have special properties suitable for the application intended". Which means that one must carefully choose the correct filler material for the application, and the intended service of the part/structure.

    According to AWS A5.18, the recommended filler for most applications is ER70-S2. The reason for this is that, 4130 is a fairly brittle alloy. Using a more ductile alloy filler material, will of course be fused and "alloyed" with the parent metal, which inturn will allow the joint to be more ductile and reduce the tendancy for tearing and brittleness at the joint.

    Second, the reason that NASCAR and other sanctioning bodies disallow 4130 in favor of 1020 mild steel, is that 4130 doesn't posses the desired properties for energy absorbtion. It's just too darn tough. The low carbon mild steels absorb impact energy far better as they are more ductile. Ironically, early Piper airframes like the J3 Cub, PA-18, PA-20, etc., were all built from 1020 mild steel. Probably not for energy absorbtion in a crash scenario, but probably because of cost factors.

    I have always used ER70-S2 for all of my GTAW joints in both aircraft and racecars, and I have always had either the airframe, or the chassis heat treated, (normalized), for stress relief. If you can't have the entire structure heat treated in an oven in a controlled enviroment, than pre-heat, and post heats should be employed, as well as maintaining correct inter-pass tempatures for critical joints. Most joints in aircraft, and in racing cars, are small and are of thin walled tubing which will dissapate the heat quickly, and spread the induced stresses away from the joint. Field stress relieving will help reduce this built up joint stress, but for complete structures, an oven is best. AISI/SAE 4130 alloy manufactured to MIL-T-6736, is a normalized and annealed seamless tubing possesing a tensil strength of 90,000 psi. This is the desired alloy for aircraft and most race car rules that require 4130 structures.

    Finally, you must determine what your specific application is and what performance you expect from it, before you can choose the best procedure and filler material for it. Also, Tubing joints, and flat sheet cert tests are not comparable criteria, (MIL-SPEC 1595A), for standard bend tests. Again, each application is different.

    I hope this didn't confuse you any further.
    Last edited by AEROWELDER; 09-09-2009, 10:26 PM.

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    • #32
      80S-D2 for ChromeMoly

      80S-D2 is a recognized alternative to 4130. It is even accepted by the vast majority of sanctioning bodies in the racing community. NASCAR, ARCA, NHRA, IHRA, SCCA ok the use of 80S-D2 as filler metal on ChromeMoly.

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      • #33
        Originally posted by WelderMike View Post
        80S-D2 is a recognized alternative to 4130. It is even accepted by the vast majority of sanctioning bodies in the racing community. NASCAR, ARCA, NHRA, IHRA, SCCA ok the use of 80S-D2 as filler metal on ChromeMoly.
        Well,
        With trying to imply no disrespect at all to those groups. I doubt they have ever done testing themselves, and are going off of the recommendation of some frame builder somewhere. Ask them for the test data....I have.

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        • #34
          http://web.a-znet.com/~dave1w/maxim_disaster.htm


          This is a little concerning to me since I have a car from the same builder. I don't know this guy nor do I have any connection to him.
          Reading though this thread jogged my memory on this one and it seemed relevant to the topic. What do you guys think? Quality Control failure? Material failure? Wrong filler?

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          • #35
            Originally posted by Corey74 View Post
            http://web.a-znet.com/~dave1w/maxim_disaster.htm


            This is a little concerning to me since I have a car from the same builder. I don't know this guy nor do I have any connection to him.
            Reading though this thread jogged my memory on this one and it seemed relevant to the topic. What do you guys think? Quality Control failure? Material failure? Wrong filler?

            From the looks of it I would guess it to be a classic embrittlement failure both in the weld fillet and the HAZ. 99% of the time its caused by the welding process, or lack therof. Filler metal has NO INFLUENCE ON THE BASE METAL STRUCTURE IN THE HAZ, despite what the home depot welding book sez. The fillets look small and dainty, too small. Without knowing what filler was used, its only a guess as to if it caused the failures in the weld itself.

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            • #36
              Just quickly looked at those pics, on my screen they look like
              mig welds, can't really tell?
              Gotta agree, I'd be worried about crashing that thing.
              Not enough info to have a conclusion about the why, but
              the bottom line final result is pretty ugly.
              If it was my butt strapped in it I'd be looking at the cage and thinking
              about some gussets. Pictures like that can mess with your confidence.
              Dave P.
              Last edited by FM117; 09-18-2009, 08:42 PM.

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