Influence of long-term aging at elevated temperature on welds with carbon migration

Abstract

This study uses 9%Cr parent metal containing boron and2.25%Cr weld metal to study the influence of long-term aging at elevated temperature on the carbon migration between the parent metal and weld metal.The size and number of precipitates in the carbon-enriched zone increase after long-term aging, but the precipitates in the carbon-denuded zone change little, which increases the differences in the mechanical properties between the carbon-enriched and carbon-denuded zones.Finite element analyses indicate that the carbon-denuded zone is damaged first by bearing loads with the damage increasing with long-term aging.Transmission electron microscope(TEM)pictures show that the precipitates at the grain boundaries of the heat affected zone in the9%Cr parent metal change little,but precipitates inside the grains become coarse after long-term aging.Boron is responsible for the changes of the precipitates at grain boundaries and inside the grains,because the boron tends to segregate at the grain boundaries,which slows coarsening of the precipitates by occupying vacancies around the precipitates.