The Mountain Technology Drive-In Ice Screw is made from nickel chrome molybdenum steel. This steel has ideal properties for the manufacture of ice axe heads.
Most importantly, it has a low transition temperature which means that the metal does not become brittle in the cold. It also has a good resistance to bending and has high impact resistance.
Note that this is not a stainless steel.
This screw is ideal for Scottish winters where pitons are hammered into frozen turf, iced up cracks, etc. It is very robust and strong.