Medium-Phosphorus Electroless Nickel (Phosphorus Content 5% to 9%) Medium-phosphorus electroless nickel coatings exhibit good corrosion resistance in both alkaline and acidic environments. The coating hardness ranges from 45 to 57 Rc and can be heat-treated to achieve a hardness of 65 to 70 Rc. It also features a fast deposition rate of 18 to 25 µm per hour.