Shielding gas for the stainless steel MIG welding

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    Due to the small thermal conductivity and large linear expansion coefficient, the welding of Austenitic stainless steel is easy to produce deformation, so the welding method with linear energy concentration should be selected as far as possible. MIG welding (Molten inert gas shielded welding) using a molten electrode, with external gas as arc medium, and protect metal droplet, welding pool and welding area of high-temperature metal, is the most commonly used welding method of stainless steel welding. How to choose shielding gas is a primary problem a welder needs to solve.

    Pure argon can only be used for the TIG welding of stainless steel, but not for MIG. Because the surface tension of the stainless steel droplet and the molten pool is large in pure argon gas welding, the liquid metal fluidity of the molten pool is poor, the weld surface cannot be spread and wetting, and the weld pass is poorly formed. Therefore, the following gas mixtures should be selected:

    Ar+1～2% O2 

    The addition of 1-2% O₂ makes the surface tension of the stainless steel droplet and the molten pool decrease, the liquid metal fluidity of the molten pool and the spread wettability of the weld surface is improved. Appropriate weld depth and width, beautiful weld bead forming.

    Ar+2～5% CO₂

    When the 2-5% CO₂ is added, there may be a tendency to carburize. The test shows that CO₂≤5%, weld carbon content ≤0.03%, below in the ultra-low carbon grades. The arc stability is good, the oxidation weakened, the alloying element burns less, has no carburization tendency, is suitable for the stainless steel welding wire short circuit transition, the jet transition and the pulse transition.

    Ar + 25% CO₂

    It is suitable for combination welding of TIG backing welding (pure argon protection, argon filling behind) +MAG filling cover welding, all-position welding, short circuit transition, smooth and beautiful welding seam.

    Ar+5%CO₂+2%O₂

    The arc concentration of ternary mixed gas, good single welding seam and double forming, suitable for stainless steel welding with higher technical requirements.

    Ar+He+CO₂

    The addition of helium gas can increase the welding depth, welding speed and reduce the deformation of weldment.

    Ar+CO₂+ N₂

    This is a new process developed in which the addition of nitrogen can increase the weld depth and weld width.

    Ar + He (25%)

    Suitable for welding nickel alloy solid wire (Nickel 625) MIG welding.