Kinetics and Mechanisms of Hydrogen Attack in 2.25Cr-1Mo Steel.

摘要

It is the purpose of this study to understand the kinetics and mechanisms of the hydrogen attack process in a 2.25Cr-1Mo steel which is a candidate for the pressure vessel material for the coal liquefaction process. An SA387-G22-C2 2.25Cr-1Mo steel together with its heat affected zone and weld sections were used as the material for studying the kinetics and mechanisms of HA. These materials were exposed to 490 to 585/degree/C and 16.2 to 20.7MPa hydrogen pressure for up to 9000 hours. The same materials were exposed to thermal control conditions (490 to 585/degree/C and 0.35MPa helium) so that the difference in volume swelling and mechanical property change is defined as the net effect due to hydrogen alone. Tensile, Charpy impact, and creep/creep rupture properties were evaluated as a function of hydrogen damage. X-ray diffraction and transmission/analytical electron microscopy (TEM/AEM) techniques were used to study the carbide species and their chemical compositions. A two-stage replication/TEM technique was used to study the distribution and growth of methane cavities. Based on the concept of pre-existing cavities and a constrained cavity growth mechanism, a mathematical model is developed and calibrated with experimentally measured parameters. This model is used to predict the material response to temperatures and hydrogen pressures not tested in this study. 125 refs., 74 figs., 36 tabs. (ERA citation 14:003162)