It is good in increasing toughness, strength and hardness while maintaining ductility. 0.5% of Nickel is good for parts subjected to impact loads at room and very low temperature. Higher amounts of Nickel help enhance the corrosion resistance in presence of Cr like in stainless steel. Ni in steel results in good mechanical properties after annealing and normalizing and thus large castings, forgings and structural parts are made in Nickel-steel.
It is common alloying element in tool steels. Stainless steels, corrosion resistant steel as 4% Cr. This forms carbide and generally enhances harness, wear and oxidation resistance at elevated temperature. This enhances harden-ability of thicker sections.