Effect of Nb on the microstructural evolution and microhardness of Super304H austenitic stainless steel weld metals during long-term aging

Abstract

Abstract The microstructural evolution and mechanical properties of Super304H austenitic stainless steel weld metals with Nb-free and 1.0 % Nb-additive were investigated during 650 °C long-term aging. Massive nanoscale M 23C6 particles distributed in the interdendritic regions of the Nb-free weld metal while most of the M 23C6 formed and coarsened on the phase interface between the primary Nb(C, N) phase and matrix in the Nb-bearing weld metal. Nano-sized Cu-rich particles dispersed inside the grains in both weld metals. All of these nano-sized particles gradually coarsened over time. The Cu-rich particles with high distribution density and nanometer size affect the microhardness of both weld metals most during long-term aging. The addition of Nb could increase the microhardness in the relatively short aging time, while the effect of Nb-addition on the microhardness in long-term aging is insignificant.