Microstructural evolution during high temperature dwell-fatigue of austenitic stainless steels

Microstructural evolution related to the mechanical response from isothermal dwell-fatigue testing at 700 degrees C of two austenitic steels, Esshete 1250 and Sanicro 25, is reported. Coherent Cu-precipitates and incoherent Nbcarbides were found to impede dislocation motion, increase hardening and improving the high temperature properties of Sanicro 25. Sparsely placed intergranular Cr- and Nb-carbides made Esshete 1250 susceptible to creep damage and intergranular crack propagation, mainly from interaction of the carbides and fatigue induced slip bands. Dynamic recrystallization of the plastic zone at the crack tip appeared to affect crack propagation of Sanicro 25 by providing an energetically privileged path.

Automated summary

The study found that coherent Cu-precipitates and incoherent Nbcarbides in Sanicro 25 hinder dislocation motion, increase hardening, and improve high temperature properties, while sparsely placed intergranular Cr- and Nb-carbides in Esshete 1250 make it susceptible to creep damage and intergranular crack propagation. Dynamic recrystallization of the plastic zone at the crack tip seemed to affect crack propagation of Sanicro 25 by providing an energetically privileged path.