• Is a ferro alloy, an alloy of iron and Molybdenum (Molly) with between 60-80% Molybdenum & small amount of carbon. Molly is a potent hardenability agent and is constituent of many heat treatable alloy steels. Molly corrosion improves the corrosion resistance of stainless steels. In iron, Mo is effective in strengthening and hardening causing austenite to transform to fine pearlite or to bainite.