Superior Creep Resistance and Remnant Strength of Novel Tempered Ferritic-Martensitic Steels Designed by Element Addition

The in situ combustion (ISC) technique is promisingly applied in heavy oil recovery, whereas the operation inevitably causes high temperature and high pressure for a long duration in the thermal recovery well. As a critical component, oil casing, traditionally made of plain carbon steel in China, generally suffers from poor creep resistance and degraded remnant strength under such a harsh environment, which leads to frequent casing damage and inferior recovery efficiency. In this study, a strategy was adopted to tackle the issue by adding chromium (Cr) element into the plain carbon steel. We designed two types of novel steel with the respective addition of 1 wt.% and 13 wt.% Cr element into plain carbon steel for oil casing. Surprisingly, the trace addition of Cr element with 1 wt.% effectively lowered the creep rate in a creep test at 600 degrees C and 400 MPa and maintained high remnant tensile strength after creep. More significantly, prior creep history dramatically enhanced remnant strength when Cr element was added up to 13 wt.%. After a long-term creep time of 96 h, the samples were conferred by a stress increment of similar to 92.5 MPa (similar to 11.0%) relative to the creep-free counterparts, whereas the value was reduced by similar to 158.4 MPa (similar to 17.8%) for plain carbon steel under the same deformation conditions. Such superior mechanical performances in the Cr-doped steels are mainly ascribed to precipitation retardation of carbides and sluggish precipitate coarsening, which continuously favors a precipitation-strengthening effect in steel. These findings provide a fundamental understanding of precipitation response and creep behaviors and, more importantly, enable the development of high-performance steels used in the field of unconventional petroleum and gas resources.

Automated summary

In this study, the addition of chromium element in plain carbon steel was found to effectively improve the creep resistance and remnant strength of oil casing under high temperature and high pressure conditions during in situ combustion for heavy oil recovery. The addition of 1 wt.% chromium element reduced the creep rate and maintained high remnant tensile strength, while the addition of 13 wt.% chromium element significantly enhanced the remnant strength after long-term creep. The improved mechanical performance of the chromium-doped steels is attributed to the precipitation retardation of carbides and sluggish precipitate coarsening. These findings contribute to the development of high-performance steels for unconventional petroleum and gas resources.