Altos Hornos de México, S.A. de C.V. (Monclova, Mexico) Altos Hornos de México S.A. de C.V. (AHMSA) is steel crazy after all these years. The company is Mexico's largest steelmaker, producing more than 3 million tons a year. It makes flat products (plate, hot- and cold-rolled coil, tin-free steel) and long products (heavy and light structural sections, wire rod, wire..