Solidification and Transformation Behaviour of a Niobium-Stabilised Austenitic Stainless Steel Weld Metal

摘要

Microstructural examination of an autogeneous 17Cr-12Ni-1Mo-0.2Nb weld has revealed that solidification occurred as both primary ferrite and primary austenite. Compositional profiles in the weld, determined by STEM/EDX analysis, and calculated diffusion distances indicate that the transformation of delta-ferrite to austenite occurred by a diffusional process during cooling. Niobium stabilization appears to restrict M23C6 formation and promote the transformation of retained delta-ferrite to intermetallic phases, including sigma, chi, laves and R-phase, during subsequent elevated temperature ageing of the weld.