Some Insights Into the Ratcheting Behavior of P91 Steel at Elevated Temperature

ABSTRACT This article highlights the importance of “opening strain,” which quantifies the amount and direction of net cyclic plastic deformation, in describing the ratcheting behavior of materials. Ratcheting experiments were conducted on P91 steel at 823 K with varying stress amplitude (290–380 MPa) and mean stress (0–120 MPa). Analysis revealed that ratcheting occurs due to unequal cyclic tensile and compressive plastic strains, leading to non‐closure of hysteresis loops, quantified as “opening strain.” The ratcheting behavior of P91 steel exhibited an initial quasi‐stable phase followed by an acceleration phase before failure. Transmission electron microscopic investigation of interrupted test specimens highlighted that dislocation tangles, forests, and networks were associated with minimal strain accumulation in the stable phase. Further investigation of the failed specimens confirmed that the formation of incipient dislocation cells and recrystallized subgrains provided strain‐free paths for dislocation motion and significant strain accumulation in the acceleration phase.