Creep deformation and local strain distributions in dissimilar metal vvelds betvveen AISI type 316 and 2–25Cr–1 Mo steels made vvith 17Cr–8Ni–2Mo weld metal

Abstract

Austenitic-ferritic steel transition joints made with austenitic weld metal fail prematurely during service, because of the formation of intergranular cracks in the heat-affected zone (HAZ) of the ferritic steel at a distance of ∼ 75–150 Uml;m from the fusion boundary. This characteristic failure mode has been reproduced under uniaxial creep conditions by testing cross-weld specimens at temperatures between 838 and 923 K and at low stresses. Creep tests at high stress result in an entirely different fracture mode, with a more ductile failure occurring well outside the HAZ. The strains associated with these two modes have been examined using a microgrid technique and the failures are shown to be explicable in the terms of the differences in creep properties between the weld HAZ and the 2·25Cr-1 Mo ferritic steel plate.