Four low carbon steels with different Cr and Cu concentrations were prepared to investigate the effect of alloying elements on their corrosion behavior in 3.5% NaCl solution diluted hydrochloric acid and dilute sulphuric acid (pH=1.4-1.5) respectively. Electrochemical measurement and immersion test at room temperature characterized the corrosion behavior and evaluated the corrosion rate.
To investigate the role of Cr and Cu in steels in different solutions, four kinds of low carbon steel with different Cr and Cu concentrations were prepared to investigate the effect of alloying elements on their corrosion behavior. Solutions of 3.5 wt.% NaCl, diluted hydrochloric acid and diluted sulphuric acid (pH=1.4-1.5) were used.
High-Temperature Hydrogen Attack (HTHA) is a phenomenon that involves the formation and accumulation of methane (CH4) in steels operating under conditions where there is hydrogen ingress. To account for the phenomenon, it is necessary to know how the supply of solute carbon atoms occurs. What is discussed here concerns only low-carbon steel within the range 0.08-0.30 wt % carbon that has no intended additions of alloying element such as chromium (Cr) or molybdenum (Mo), and that it is typically delivered in the as-hot worked or normalized condition, resulting in microstructure consisting of pearlite colonies within a matrix of ferrite grains. Carbon steels do not normally contain carbon atoms in solid solution, but most are tied to cementite (Fe3C), except when retained in supersaturated solid solution by rapidly cooling from just below the subcritical temperature Ac1, 727 °C (1340 °F), in which case, the solute carbon atoms do not remain in supersaturated solution for long, they precipitate, but the resulting precipitates are rather unstable and get quickly thermally activated when heated to temperatures that are considered relatively too low to significantly affect the cementite in existing pearlite colonies. Thus, these precipitates may supply solute carbon atoms for HTHA damage to occur at temperatures that would not otherwise occur if there were only cementite in existing pearlite colonies.