The main reason for adding nickel is to promote an austenitic microstructure. Nickel generally increases ductility and toughness. It also reduces the corrosion rate in the active state and is therefore advantageous in acidic environments. In precipitation hardening steels nickel is also used to form the intermetallic compounds that are used to increase strength. In martensitic grades adding nickel, combined with reducing carbon content, improves weldability.