Nickel pig iron (NPI) is a low grade ferronickel invented in China as a cheaper alternative to pure nickel for the production of stainless steel. It is composed of low-grade nickel ore, coking coal, and a mixture of gravel and sand as an aggregate. This mixture is heated in either a blast furnace or an electric arc furnace depending on the desired grade. Impurities are then removed via smelting and sintering processes and the resulting nickel pig iron contains four to 13 percent pure nickel.