TIG welding: carbon steel & chromoly

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The first thing I have to weld is mild steel to mild steelThe second thing I have to weld is mild steel to chromoly 4130 1/8" wall tubing (as a doubler for new shock mounts)The mild steel in both cases is 1.25 diameter .063" wall tubing.  Its part of a sandrail frame I got used, I would imagine it is A513 Type 5, or similar.I would like some suggestions on the filler wire I should use and anything else that might be helpful Thanks!
Reply:i think er70s wire is commonly used.   youll need to check though on pre and post heating.  I dont know what it is on chromoly.  I just know that its real important.   Good luckIF it Catches...Let it Burn
Reply:Pre and post heating is necessary on chrome moly. I don'r have the specs, but it is the difference between a good weld and a broken weld/brittle part. Don't skip any steps, especially if it is for a shock mount. That'll break off and do some serious damage, especially at high speeds. Just my $.02. If I can find the info, I'll post it.
Reply:I've done thinwall 4130 for years with and without pre-heat and never had a failure on both airplanes and helicopters.This on the Lincoln website might help;TIG WELD 4130!The Lincoln Electric Company, Welding Services. June 2000Yes, you can TIG weld 4130 tubing up to .120" wall thickness easily with the techniques and procedures described in this bulletin. Answered are the top ten most frequently asked questions about TIG welding 4130 Chrome-Moly. These attached procedures apply to typical sporting applications such as experimental airplanes, racing car frames, roll cages, go-carts, bicycles, and motorcycle frames. The suitability of these techniques and procedures must be evaluated for your specific application.Q. Can I weld 4130 using the TIG process?A. Yes, 4130 Chrome-Moly has been TIG welded in the aerospace and aircraft industries for years. As with all welding, proper procedures and techniques must be followed.Q. Do I need to pre-heat?A. Thin wall tubing (< 0.120" wall) applications do not typically require the normal 300ºF to 400ºF pre-heat to obtain acceptable results. However, tubing should be at room temperature (70ºF) or above before welding.Q. What filler material do I use?A. Although there are several good filler materials, ER80S-D2, is one you should consider. This filler material is capable of producing welds that approximate the strength of 4130. ER-70S-2 is an acceptable alternative to ER80S-D2, as is ER70S-6, although the weld strength will be slightly lower.Q. When I use ER70S-2 filler material, do I give up strength for elongation?A. Yes. The filler material, when diluted with the parent material, will typically undermatch the 4130. However, with the proper joint design (such as cluster or gusset, for example), the cross-sectional area and linear inches of weld can compensate for the reduced weld deposit strength.Q. Why is 4130 filler metal not recommended?A. 4130 filler typically is used for applications where the weld will be heat treated. Due to its higher hardness and reduced elongation, it is not recommended for sporting applications such as experimental airplanes, race car frames, roll cages, etc.Q. Can I weld 4130 using any other filler metals?A. Some fabricators prefer to use austenitic stainless steel fillers to weld 4130 tubing. This is acceptable provided 310 or 312 stainless steel fillers are used. Other stainless steel fillers can cause cracking. Stainless filler material is typically more expensive.Q. Do I need to heat treat (stress relieve) 4130 after welding?A. Thin wall tubing normally does not require stress relief. For parts thicker than .120", stress-relieving is recommended and 1,100ºF is the optimum temperature for tubing applications. An Oxy/Acetylene torch with neutral flame can be used. It should be oscillated to avoid hot spots.Q. Do I have to pre-clean 4130 material?A. Remove surface scale and oils with mild abrasives and acetone. Wipe to remove all oils and lubricants. All burrs should be removed with a hand scraper or de-burring tool. Better welding results with clean materials.Q. Do I need to back-purge 4130 material?A. Backpurging is not normally necessary, although some fabricators do. It will not hurt the weld and may improve the root pass of some welds..Q. Should I quench the metal after I finish welding?A. ABSOLUTELY NOT! Rapid quenching of the metal will create problems such as cracking and lamellar tearing. Always allow the weld to slow cool.More Information on TIG Welding Chrome-Moly 4130Find out more about Lincoln Electric's professional line of TIG welders here Or, check out Lincoln cut length TIG welding filler metals here WELDING SPECIFICATION: Aircraft and MotorsportsGENERAL INFORMATION    * Remove all oxides and burrs within 3" of weld area.    * Acetone wipe to remove all cutting oils.    * Assemble and tack weld in joint in a minimum of four (4) places with TIG.    * Tubing should be at minimum temperature of 70ºF (room temperature.    * TIG weld per parameters specified using Lincoln's Precision TIG™: The Power To Perform. 185, 275 or 375. EXAMPLE WELD SCHEDULE INFORMATIONPARENT MATERIAL: 4130MATERIAL CONDITION: Condition (N)MATERIAL THICKNESS: .035" Wall ThicknessFILLER MATERIAL: ER80S-D2 .035" DiameterJOINT TYPE: 90º Tube to Tube.JOINT PREP: Abrasive Clean/Acetone WipeJOINT GAP: .000-.010CURRENT TYPE: D.C.E.N. (DC Electrode Negative)AMPERAGE: 20 - 40 ampsVOLTAGE: 9-12 VoltsTORCH TYPE: LA-9 or LW-20 Magnum TIG TorchCUP SIZE: Gas Lens 7/16" OrificeCUP TYPE: CeramicTUNGSTEN TYPE: 2% ThoriatedTUNGSTEN SIZE: 1/16" DiameterTUNGSTEN SHAPE: PointedTORCH GAS: ArgonFLOW RATE: 15-25 C.F.H.BACK-UP GAS: ArgonFLOW RATE: 5-10 C.F.H.TACKING SEQUENCE: 4-Places (min.)FILLER MATERIAL OPTIONS:Option #1 ER80S-D2Option #2 ER70S-2Option #3 ER70S-6FOOTNOTE: Welding properties change from operator to operator. Techniques such as travel speed, filler type, filler deposition rates, amperage, gas shielding, and arc voltage (distance between tungsten and weld puddle) all have an effect towards heat input, weld strength, and elongation.
Reply:There's really no need to preheat thin wall chromemoly it pretty much preheats its self during welding. If it were mine I would weld with ER80S-D2 Just my 2cents worth. I been welding chrome for past 10 yrs
Reply:wow! that is a great info on Chromoly  I have heard that the ER70S-2 is not to be used on mild steel, but ER70S-6 is ok and according to above it also ok for chromoly.  I will use the ER70S-6 for the mild steel to chromoly joints.Is there a better filler material for the mild steel to mild steel joints other than the ER70S-6?
Reply:Originally Posted by gocirinoI've done thinwall 4130 for years with and without pre-heat and never had a failure on both airplanes and helicopters.
Reply:Cool information. I was told to always pre and post heat. Thanks for the correction guys. I will print out the info and keep it with my welding cart.