In SituScanning Electron Microscopy Analysis of the Interfacial Failure of Oxide Scales on Stainless Steels and Its Effect on Sticking during Hot Rolling

Abstract

Despite various strategies to address sticking failure in stainless steels (STSs), difficulties in understanding its fundamental mechanisms hinder precise solutions during STS fabrication. This study investigated the effect of chromium (Cr) content on the microstructures and failure modes of oxide scales under a tensile load, simulating the hot-rolling process. The dynamic, real-time behavior of crack initiation, propagation, and interfacial delamination in the oxide scales under tension was analyzed using an in situ scanning electron microscopy (SEM) tensile test. With a high Cr content, iron (Fe) oxide and chromium(III) oxide (Cr 2 O 3 ) form a layered structure, which is delaminated along the interfaces between the thin Cr 2 O 3 layer and the bulk after perpendicular cracking. The saturated crack densities obtained from in situ SEM provide interfacial strength, while the elastic modulus and hardness obtained from nanoindentation provide vertical fracture strength. In combination with an ex situ elemental image analysis, the in situ SEM results reveal three different failure modes of the four different STSs. The results confirm that sticking failure is more likely to occur as the Cr content increases.

Statistical in situ scanning electron microscopy investigation on the failure of oxide scales

“…The critical points of yielding and fracture of the film are identified indirectly through features on the force–displacement curve or acoustic emission upon cracking of the film [15–17] . As for multilayered films with multiple phases, in situ microscopic methods that can directly capture the more complex failure processes are desirable [18–20] . However, due to the limited test efficiency, in situ methods so far are often challenged by the lack of statistically reliable analysis on the critical strains and stresses.…”