Creep–fatigue-oxidation interaction in Grade 91 steel weld joints for high temperature applications

The weld joint consisting of a heterogeneous microstructure exhibits a lower fatigue life than that of the base metal. This is due to the presence of soft zone in the heat affected zone (HAZ). At high temperatures and under hold application, strain localization occurs in the soft intercritical HAZ (ICHAZ). Sub-surface creep cavity formation in the soft region and their linkage causes enhanced crack propagation and that translates into lower fatigue life of the weld joint at high temperatures. Occurrence of compression dwell sensitivity in the material is attributed to the presence of surface oxides.