hey have a small job were i would like to mate crom-moly tube to steel tube, can i mig it. thought maybe i could turn it down and work it slow maybe small rout pass and then some cover passes? will the weld puddels of the two different metals blend enough to hold.
No problem. Use e70-s6 wire and 75/25 mixture or pure argon an it will weld good. I weld 4130 on aircraft with s6 and 75/25 gas and have no problems. Do not weld if real cold or in a draft. If you have cold metal preheat before welding.
I have doen this with no problem. I don't remember what the wire was I used but I did use the 75%-25% argon/co2 mix. r
Can you elaborate on cold metal and preheating? Cold metal - you mean if it's fifty deg. outside it's cold? I know it sounds dumb...but I'm serious. Preheating - Bring it up to what? eighty deg? or welding on a hot day is okay? Sounds crazy that such a little fluctuation causes a difference when you're dealing with molten metal.
Welding 4130 c-m cold will cause cracks. Try to weld this inside above 70 deg. If metal is colder pre-heat with a propane torch to 70 to 110 deg then mig. the hot metal will weld better. if in a cold place cover the weld so it will cool slow and if needed use the propane to keed warm---not hot.
If your welding Chrome Moly,and it cools too fast,it gets very brittle. Personally,I try to avoid Chrome Moly. If I had to weld some,I would preheat it to at least 200F,and find a way to cool it slowly. Doug Gore did an excellent atricle on welding Chrome Moly in an old issue of Open Wheel. He experimented with different preheats and filler rod combinations. I might still have it.
Here's something on the topic: -------------------- MIG Welding 4130 Chrome-Moly By Galen White, welding engineer, Miller Electric Mfg. Co. Grade 4130 steel, while containing both chromium and molybdenum as strengthening agents, is considered a heat treatable low alloy (HTLA). Generally referred to as chrome-moly, this HTLA is used largely for aviation, racing and welded tube structure applications. When welding 4130, preheating to 300°F is strongly recommended by the American Welding Society (AWS) to relieve stresses in the metal. When choosing a wire, most people opt for ER80S-D2 or ER70S-2. ER80S-D2 will provide the most weld strength. The ER70S-2 is easier to find and provides a strong weld, but youll be sacrificing some strength by choosing this filler metal over ER80S-D2. When it comes to shielding gas, 75/25 (Ar/CO2) is recommended for most applications and 98/2 (Ar/CO2) for anything over 3/16 in. Cleanliness is critical when welding 4130. Make sure that all mill scale and oils are removed using mild abrasives and/or acetone. When you strike an arc, keep your heat input low to reduce stresses in the metal. Post-weld heat treatment of 4130 varies from one application to another. If ductility and toughness are your goal, post-weld heat treatment is recommended up to 1,200°F. If the material you are welding is thinner than .120 in., stress relief through heat treatment is not as critical. Welding 4130 is a lot like welding mild steel and is easy if you know how. These are just some of the reasons 4130 is considered so flexible and is used on everything from airplane engine mounts to bicycle frames.
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