Influence of the base metal grain size and heat input on decarburization in single pass SAW and multi pass SMAW welded joints of dissimilar ferritic steels

Abstract

This paper aims to assess a separate influence of heat input and base metal grain size on microstructural evolution in the weld adjacent zone of bainitic steels with 1.5…2.0% Cr, welded or overlayed with consumables with 9% Cr after post-weld heat treatment.Analysis of the width of decarburised layer on microphotographs of welded or overlayed specimens after tempering at 750C. Specimens were made by using different welding approaches: single-pass welding, multi-pass welding and overlaying.It is shown that with an increase of the heat input energy, the width of the resulting decarbonised layer decreases linearly; the increase of the base metal grain size leads to a decrease in the layer width after tempering at 750C. The microhardness testing showed the average hardness in the decarburised layer of 15Kh2M2FBS steel was 161 HV0.1 (minimum – 154 HV0.1), while the average hardness in the rest of the heat-affected zone was 192 HV0.1.Future research may include comparing the creep rupture strength of the weldments made with different welding parameters or base metal grain size to assess the influence of these factors on creep rupture strength.Results permit to achieve minimisation of the rate of carbon diffusion in the weld-adjacent area of the heat-affected zone by means of variation of welded parameters and base metal grain size.An influence of high-diffusivity paths (grain boundaries) on carbon diffusion in the heat-affected zone of dissimilar weldments was confirmed experimentally; the correlation between base metal grain size/welding parameters and the rate of the diffusion during high-temperature exposure was found.