Influence of welding parameters on decarburization in heat affected zone of dissimilar weldments after post weld heat treatment

Purpose: This paper aims to assess an influence of thermal welding parameters on microstructural evolution in the weld adjacent zone of P91 steel, overlayed by austenitic consumables, after post weld heat treatment. Design/methodology/approach: Analysis of the width of decarburized layer on microphotographs of overlayed specimens after tempering 750°C, 7 and 18 hours. Specimens were made by using different heat input and preheating temperature parameters. Findings: It is shown that with increase of the heat input energy, the width of the resulting decarbonized layer decreases linearly; the effect of heating temperature on the layer width is parabolic with a minimum at a temperature of ~195°C. Research limitations/implications: Future research may include comparison of the creep rupture strength of the weldments, made with different welding parameters, to assess the influence of kinetics of decarburization and variation of the parameters on creep rupture strength. Practical implications: Results permit to achieve minimization of rate of carbon diffusion in the weld adjacent zone of the HAZ by means of variation of welded parameters. Originality/value: Experimentally was confirmed a role of high-diffusivity paths (grain boundaries) on carbon diffusion in the HAZ of dissimilar weldments; found correlation between welding parameters and the rate of the diffusion during high temperature exposure.