Welding annealed 4340 to mild steel

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I need to weld a 1 1/4"  pin made out of 4340 to mild steel. The pin will be protruding through a piece of 2x4x1/4" square tubing. I was planning on using it as a hinge for a tire carrier. Can this be accomplished with a mig welder?
Reply:jj, Are you using ER 70 S6 with gas?You should be ok. 4340 is a good choice for a hinge pin. E70S-6 Solid Carbon-Steel Welding WireSound, porosity-free welds with powerful deoxidizers for your work with shielding gases. Great for construction work, farm implement fabrication, shaft buildup, tanks, truck bodies and general shop applications with poor fit-up or rusty, oily platesSAE 4340 Chemistry Data Carbon 0.38 - 0.43 Chromium 0.7 - 0.9 Iron Balance Manganese 0.6 - 0.8 Molybdenum 0.2 - 0.3 Nickel 1.65 - 2 Phosphorus 0.035 max Silicon 0.15 - 0.3 Sulphur 0.04 max Principal Design Features AISI 4340 is a heat treatable, low alloy steel containing nickel, chromium and molybdenum. It is known for its toughness and capability of developing high strength in the heat treated condition while retaining good fatigue strength. Applications Typical applications are for structural use, such as aircraft landing gear, power transmission gears and shafts and other structural parts. Machinability Machining is best done with this alloy in the annealed or normalized and tempered condition. It can be machined by all conventional methods. However in the high strength conditions of 200 ksi or greater the machinability is only from 25% to 10% that of the alloy in the annealed condition. Forming 4340 has good ductility in the annealed condition and most forming operations are carried out in that condition. It can be bent or formed by spinning or pressing in the annealed state. Bend radii should be 3t or greater. Welding The alloy can be fusion or resistance welded. Preheat and post heat weld procedures should be followed when welding this alloy by established methods.
Reply:Thanks for the reply Jim. I will use ER 70 S6.
Reply:Preheat is very important!  I would give her at least 200 F