Abstract
When dissimilar welds are heat treated or exposed to in service conditions, long range diffusion of rapidly diffusing elements can be induced by strong gradients in chemical potential across the fusion zone. This diffusion is usually accompanied by precipitation or dissolution of carbides and nitrides. In the present work, six 2·25Cr/9Cr and 2Cr/0·5CrMoV welds in different heat treatment conditions have been characterised by means of optical and electron microscopy. Carbon profiles have been obtained with wavelength dispersive X-ray analysis. A general thermokinetic model for simultaneous precipitation and diffusion, which is implemented in the software MatCalc, has been used to predict the time dependent phase distributions and the carbon profiles based on multicomponent thermodynamic and kinetic data. The calculations and the experimental data show good agreement.
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