Precipitation and Growth of Ni-Rich Substances in the Oxide Scale of Steel in Mixed C2h5oh-H2o Atmosphere

Abstract

Abstract Nickel is an iconic alloying element in the piercing plug steel. In order to study the formation mechanism of Ni-rich substances in oxide scale of steel under mixed C2H5OH-H2O atmosphere, the high-temperature oxidation experiment was carried out by employing steels with varied Cr and Ni contents, and the oxidation characteristic was explored by using scanning electron spectroscope (SEM), energy dispersive X-ray spectroscopy (EDS), metallographic microscope (OM) and Image-Pro Plus. Under the experimental conditions, it is found that Ni promotes the formation of denser inner oxide scale while Cr inhibits inner oxidation effectively. Congregation of Ni-rich substances is a diffusion process strongly relying on the Ni content of the steel. The total Ni-rich substances dependence of Ni content follows the parabolic law. It is proposed that the Ni-rich substances precipitate once the oxidation of Fe or Cr atoms leaves vacancies for the nearby Ni atoms to fill in to form a substitute Ni-rich crystal structure, and then the Ni-rich substances congregate and grow up as oxidation proceeds. The results are meaningful for the reasonable design of piercing plug steel.