416 stainless is a free-machining variation of martensitic stainless steel with the addition of sulphur or selenium. The material can be hardened by heat treatment to higher strength and hardness levels. It has better machining properties than the austenitic grades, but lower corrosion resistance. 416 Stainless Steels offer the highest machinability of any stainless steel in their sub-critical annealed condition.