The most common types of MIG wire for welding mild steel are ER70S-3 and ER70S-6. These wires are designed to meet minimum tensile strength requirements of 70,000 psi. Choose an ER70S-6 wire for welding on plate that has mill scale or surface contaminants, since this wire incorporates the proper deoxidizer to combat these issues. A deoxidizer absorbs oxygen so that it vaporizes into the arc or forms as scale oxides. ER70S-6 is also better for creating a smooth transition from the weld to the base metal, also known as wash-in or tie-in. Better wash-in may be a requirement in applications subject to fatigue. ER70S-6 wire can provide better wetting at the weld toe when compared to an ER70S-3 wire.