An advanced grade of super-austenitic stainless steel with a reduced content of nickel offers a significant economic advantage over nickel-base CRA’s. As the alloy is readily fabricated by conventional techniques, it is an excellent candidate for a variety of applications in the chemical, petrochemical, mining, oil and gas, and refining industries.
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.