Source: Adapted from The Procedure Handbook of Arc Welding.

The Lincoln Electric Company, 1994.

Although welding stainless steel may not be as difficult as welding aluminum, the metal does have its specific properties that vary from your more common steels.

When MIG welding on stainless, you usually have three choices of transfer depending on your equipment: spray-arc, short-circuiting, or pulsed-arc transfer.

Spray-Arc Transfer

Filler metals for gas metal arc welding stainless steel are specified in AWS – A5.9-93. Click here to view full-size Acrobat .pdf file.

Electrode diameters as great as 1/16-in., but usually 0.045″, 0.035″, and 0.030″, are used with relatively high currents to create the spray-arc transfer. A current of approximately 300-350 amperes is required for a 1/16-in. electrode, depending on the shielding gas and type of stainless wire being used. The degree of spatter is dependent upon the composition and flow rate of the shielding gas, wire-feed speed, and the characteristics of the welding power supply. DCEP (Direct Current Electrode Positive) is used for most stainless-steel welding. A 1or 2% argon-oxygen mixture is recommended for most stainless steel spray arc welding.

On square butt welds, a backup strip should be used to prevent weld-metal drop through. When fitup is poor or copper backing cannot be used, drop-through may be minimized by short-circuit welding the first pass.

Forehand techniques are beneficial when welding with a semiautomatic gun. Although the operator’s hand is exposed to more heat, better visibility is obtained. For welding plate ¼-in. and thicker, the gun should be moved back and forth in the direction of the joint and at the same time moved slightly from side to side. On thinner metal, however, only back and forth motion along the joint is used.

The more economical short-circuiting transfer process for thinner material should be used in the overhead and horizontal position for, at least, the root and first passes. Although some operators use a short digging spray arc to control the puddle, the weld is apt to be unduly porous.

Short-Circuiting Transfer

Power supply units with slope, voltage, and inductance controls are recommended for the welding of stainless steel with short-circuiting transfer. Inductance, in particular, plays an important part in obtaining proper puddle fluidity.

The shielding gas recommended for short-circuiting welding of stainless-steel contains 90% helium, 7.5% argon, and 2.5% carbon dioxide. The gas gives the most desirable bead contour while keeping the CO2 level low enough so that it does not influence the corrosion resistance of the metal. High inductance in the output is beneficial when using this gas mixture.