Solute-dislocation interactions and creep-enhanced Cu precipitation in a novel ferritic-martensitic steel

G115 steel has gained a growing interesting recently for its use in next-generation ultra-supercritical power plant applications. Due to the high densities of dislocations and lath martensite boundaries in G115 steel, interactions between solutes and dislocations result in unique microstructural evolution during creep with the formation of dense Cu-rich precipitates (CRPs) and M(23)C(6 )carbides. Atom-probe tomography reveals that Mn is preferentially associated with CRPs, probably because the Mn atoms reduce the critical energy of nucleation. Solute-dragging and precipitate-pinning effects enhance the formation of dislocation network during earlier creep deformation. Compared with aged G115 steel, long-term creep deformation accelerates the coarsening of CRPs. The fast diffusion of solutes along dislocations, dislocation network walls, and lath boundaries significantly increases the CRP coarsening kinetics. Particle coarsening reduces the pinning strength, causing the dislocation density to decrease and the dislocation network to disappear during long creep stages. Our results enhance our understanding of CRP evolution in G115 steel during creep and provide a guide for the design of novel heat-resistant steels with excellent creep strength. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.