Effect of groove configuration on Type-IV creep damages in Gr.122 steel welds

Abstract

Creep strength of high Cr ferritic heat-resistant steel welds decreases more rapidly than base metals due to Type-IV creep damage formed in the heat-affected zone (HAZ) at high temperatures. This paper aims to elucidate the effect of groove configuration of welds on the formation and evolution of Type-IV creep damage. Creep tests using base metal, simulated HAZ and two-types of weld joint; gas tungsten arc and electron beam welds, of the ASME Gr.122 steel were conducted. Decreasing the groove angle and width of HAZ was effective in prolonging the creep life; however, it could not prevent Type-IV failure. Type-IV creep voids were mostly observed in the area about 1.0–3.0 mm below the specimen surfaces, whereas their detailed distributions were dependent on the groove configurations. Both the distribution of the multiaxial stress state and creep strain in HAZ can be considered to influence the formation of Type-IV creep damage. Damage mechanics analysis taking the multiaxial stress state into account can predict fairly well the distribution of Type-IV creep voids and failure times of the weld joints without regard to the groove configurations.