Creep and Intergranular Cracking Behavior of Nickel-Chromium-Iron-Carbon Alloys in 360 deg C Water

摘要

Mechanical testing of controlled-purity Ni-x percent Cr-9 percent Fe-y percent C wt at 360 deg C revealed an environmental enhancement in intergranular (IG) cracking and time-dependent deformation high-with (HP) and primary water (PW) over that exhibited argon. Dimples on the IG facets indicated a creep void leaf ton and growth failure mode. IG cracking was located primarily in the interior of the specimen and was not necessarily linked to the environment. Controlled-potential constant extension rate tensile (CERT) experiments showed increases in IG cracking as the applied potential decreased, suggesting that hydrogen was detrimental to the mechanical properties. It was proposed that the environment, through : presence of hydrogen, enhanced IG cracking by enhancing matrix dislocation mobility. This conclusion was on observations that dislocation creep controlled IG cracking of controlled-purity Ni-x percent Cr-9 percent Fe-y percent C in argon at 0 C. Grain-boundary cavitation (GBC) and sliding (GBS) result showed environmental enhancement of the creep rate primarily resulted from an increase in matrix plastic deformation. However, controlled-potential constant load tensile (CLT) experiments did not indicate a change in the creep rate as the applied potential decreased. While this result did not support hydrogen-assisted creep, the material already may have been saturated with hydrogen at these applied potentials, and thus, no effect was realized. Chromium and carbon decreased IG cracking in HP and PW by increasing the creep resistance. The surface film did. not play a significant role in the creep or IG cracking behavior under the conditions investigated.