Correlation Between Rupture and Microstructure of F12 Heat-resistant Steel After Extended Service

Mechanical properties and microstructures of F12 martensite heat-resistant steel samples with different service hours have been analyzed and compared using OM, SEM and XRD method.Results show that with the rise of service time,mechanical properties of above samples degrade severely,due to great variation of the microstructures,such as coarsening of carbides precipitated at original austenite grain boundary,reduction of α-Fe lattice constant in the matrix,complete decomposition of broken and fragmental martensite as well as formation of creep holes in coarsening carbides at grain boundary.Martensite decomposition,carbide corsening and depletion of alloying elements in the matrix are direct reasons leading to the degradation of material properties.