Hydrogen Attack of Carbon Steel Produced by an Electrochemical Method at Elevated Temperatures

Abstract

Hydrogen was charged to plain carbon steels at 653-723 K by an electrochemical method using a molten NaOH electrolyte. The catholic potential was kept at-1.7V vs. Air/O^2-(ZrO₂) during the charging, and the current density at this potential was equivalent to the hydrogen pressure of 4-8MPa. Methane bubbles are observed at pearlite/ferrite, cementite/ferrite and non-metallic inclusion (MnS)/ferrite interfaces. The number and radius of methane bubbles increase with increasing of charging temperature and time. The charging steel surface was accompanied with decarbulization. The decarbulization depths showed the Arrehenius relation and they were controlled by the diffusion of carbon in steels.