Understanding carbide evolution and surface chemistry during deep cryogenic treatment in high-alloyed ferrous alloy.

[Display omitted] • ex-situ and in-situ observations from the microscopic to the nanoscopic level. • SPEM and XPS provide insight into the agglomeration of chemical elements during DCT. • Mo plays a crucial role in DCT through its modification of chemical bonding states. • APT shows preferential formation of Mo-rich M 7 C 3 carbides after DCT. • SANS and SPEM confirm increased formation of M 23 C 6 carbides. The study investigates the effect of deep cryogenic treatment (DCT) on a high-alloyed ferrous alloy (HAFA) and its effectiveness on carbide evolution and chemical shifts of alloying elements. With ex-situ and in-situ observations ranging from the microscopic to the nanoscopic level, we uncover the atomistic mechanism by which DCT affects carbide precipitation, resulting in a 50% increase in carbide volume fraction. Synchrotron-based scanning photoelectron microscopy provides insight into the agglomeration of carbon during exposure to DCT. We find that Mo plays a crucial role in DCT through its modification of chemical bonding states, which is postulated to originate from the loosely-formed primordial Mo 2 C carbides formed during exposure to cryogenic temperatures. These in turn provide energetically favorable nucleation zones that accelerate the formation of M 7 C 3 carbides, which serve as intermediate states for the formation of M 23 C 6 carbides, which most strongly impact the mechanical properties. These results are supported by atom probe tomography, showing the preferential formation of Mo-rich M 7 C 3 carbides in DCT samples, resulting from greater solute mobility. This work clarifies the fundamental mechanisms on how DCT affects HAFA, solving a long-elusive problem. [ABSTRACT FROM AUTHOR]