TIG chromoly Q's

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I know some people who build roll cages are on here and I've been vesting interest in welding some chromoly tubing and was curious what type of filler wire are people using? I know some are using ER70s and ER80s but I was having a talk with my welding rep and was telling me if its a structural component ER70s wouldn't do it. It was a tangent topic so I forgot to ask him what he would recommend but I figure it would be better anyhow to see what people who are welding up roll cages are actually using on chromoly... or even those welding it as a structural component for something else. I did a quick search on the web and saw people using ER80s but didn't know if that was adequate for what is considered a "structural" weld or if that was just good enough for a NHRA approved roll cage.Miller Syncrowave 180SDMillermatic 175
Reply:most roll cage tubing is done with er70s-6.  Check out jesse james book "how to weld damn near anything" surprisingly, the section on welding 4130 is pretty good.
Reply:70s-2, 70s-6, and ER80s-d2 are the ones I'm seeing recommended. Some also suggest an ER312 stainless filler wire "can achieve even strength" but as I sit her I'm finicky about using a stainless filler wire for chromoly as in my experience I've only used it in a steel application where I was welding stainless to mild. However my application was not a strength critical one.I've been confusing myself researching filler metals for chromoly so figure it would be best to ask on here. But that Jesse James book sounds interesting. I'll have to call around or just order it off amazon.com.EDIT: I should add this, pretty interesting...AWS articleFiller Metal ChoiceThe main objective was to produce porosity- and crack-free weld deposits. The best filler material to use was a low-carbon alloy, AWS ER70S-2. This welding alloy has a very low carbon content, nominally 0.06, which can handle dilution into the relatively high (in terms of weld metal) 0.30 carbon in the 4130. The resulting diluted weld deposit has a tensile strength of approximately 590 to 620 MPa (85,000 to 90,000 lb/in.2) The actual strength will depend on the amount of dilution with the 4130, weld bead size, and material thickness. This is usually an under match for the 4130 tubing, which could have 760 to 800 MPa (100,000 to 115,000 lb/in.2) tensile strength, depending on how the material was processed. However, if extra joint strength is required, a slightly larger fillet size or gussets can be employed. In addition, this welding wire contains small amounts of aluminum, titanium, and zirconium. Although these elements were initially added to handle welding over mill scale, they also contribute to a less fluid weld pool. The benefit to the welder is easier out-of-position welding. Note: It is recommended all welding on 4130 be performed on ground surfaces free of oil or grease.Several years after making this recommendation, when looking at a catalog from the dragster chassis manufacturer, it was interesting to note it advertising its use of the ER70S-2 filler metal for their 4130 welding. In fact, offering it for sale for those customers purchasing frame parts and doing their own welding!The Internet was searched to see what current recommendations were being made for joining 4130 tubing. Several hundred sites were found that recommend the ER70S-2 welding wire alloy. It was the predominant recommendation. Typical of the Internet, however, there were many improper descriptions of why this alloy should be used and several incorrect recommendations.Go for Higher StrengthIf a higher strength weld is required for perhaps a butt-joint weld that cannot be reinforced, strengthened with a gusset, or put in a less critically stressed area, there are several possible solutions. The use of AWS ER80S-D2, which contains 0.50 moly, will provide a weld deposit with higher strength. When diluted into the 4130 base material, a weld tensile level of 760 to 800 MPa (110,000 to 115,000 lb/in.2) can be achieved. If this higher strength welding wire is employed, a minimum preheat of 65¡C (150¡F) is recommended. It is also possible to use an AWS ER312 stainless steel welding wire. Weld strength can increase to a level slightly higher than with AWS ER80S-D2.Generally, the use of this high chrome stainless alloy is only needed when welding stainless to steel. Do not use an austenitic stainless steel such as an ER308L, which is, unfortunately, sometimes recommended. Diluting this or similar austenitic stainless alloys with 4130 can lead to cracks. Also, consider that providing a higher strength weld deposit cannot compensate for the reduction in strength that will most likely occur in the base metal immediately next to the weld deposit. To achieve the higher strength, the base metal was heat-treated, reducing the weld heat-affected zone area hardness.If the part is heat-treated after welding to achieve very high strength, a matching chemistry filler metal to the 4130 must be employed. Because of the relatively high carbon content, a minimum of 200¡C, (400¡F) preheat and very slow cooling after welding should be used to avoid cracking. After welding, the part can be heated to 870¡C (1600¡F), quenched in oil or water then tempered back to 370¡C (700¡F). This might be considered a complex cycle, but it will result in a tensile strength of approximately 1380 MPa (200,000 lb/in.2). Since the weld is the same chemistry as the base metal, it and the heat-affected zone will have properties similar to the base metal when heat-treated. All critical welds of this type should be inspected for internal soundness to assure they are free from cracks.Closing AdviceWhen welding 4130 chrome moly in the normalized condition, AWS ER70S-2 filler metal, with its low carbon content; is the proper choice. If the part is to be heat-treated after welding, then a filler metal matching the 4130 chemistry should be employed. This requires preheat and special precautions to avoid cracking.
Reply:Originally Posted by KubsI know some people who build roll cages are on here and I've been vesting interest in welding some chromoly tubing and was curious what type of filler wire are people using? I know some are using ER70s and ER80s but I was having a talk with my welding rep and was telling me if its a structural component ER70s wouldn't do it. It was a tangent topic so I forgot to ask him what he would recommend but I figure it would be better anyhow to see what people who are welding up roll cages are actually using on chromoly... or even those welding it as a structural component for something else. I did a quick search on the web and saw people using ER80s but didn't know if that was adequate for what is considered a "structural" weld or if that was just good enough for a NHRA approved roll cage.
Reply:ER70s-2 and a gas lense is all I use, and almost everything i build in my shop is made from chromolly.Tom Rockwell Race Carswww.trracecars.com