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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

Nimko M. O., Skulskyi V. Yu.

Journal of Achievements in Materials and Manufacturing Engineering

2023

Vol. 119, nr 1

14--26

Purpose 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. Design/methodology/approach Analysis of the width of decarburised layer on microphotographs of welded or overlayed specimens after tempering at 750°C. Specimens were made by using different welding approaches: single-pass welding, multi-pass welding and overlaying. Findings 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 750°C. 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. Research limitations/implications 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. Practical implications 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. Originality/value 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.

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

Nimko M.O.

Archives of Materials Science and Engineering

2021

Vol. 112, nr 1

23--31

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.