"ER70S6 is a mild steel welding wire that contains higher levels of manganese and silicon than other standard grades of MIG wire to produce high quality welds when used on dirty, oily, or rusty steel.  The high silicon content increases the fluidity of the weld pool, thus creating a smoother bead appearance and resulting in minimal post-weld grinding.  This wire is engineered to provide porosity-free, x-ray quality welds at the highest tensile strength (as welded) of all the plain carbon steel wires.  This product requires a shielding gas:  CO2 and/or CO2 mix."

Information found at:   < http://www.weldingmaterialsales.com/Product_pages/er70s6_productpage.htm>