A new methodology for investigating the weld joint microstructure and micro-hardness of the austenitic stainless steel clad plate made by SMAW/GTAW multi-pass welding process: part III – clad layer case study

In this study, the influence of repeated thermal cycling during multi-pass welding on the microstructural transformations and mechanical properties of austenitic stainless clad-steel plates (ASCSPs) was investigated, with a particular focus on the clad layer. A novel methodology was employed, involving the complete filling of the groove length and gradually shortening subsequent passes. Microstructural characterization of various zones within the welded joint was conducted using optical microscopy. The results demonstrated that repeated thermal cycles during multi-pass welding caused significant microstructural changes in the weld metal clad layer (WM-CL), including the transformation from columnar to equiaxed grains and the evolution of δ-ferrite morphology from dendritic to skeletal. Additionally, the ferrite number decreased from 8.5 ± 2 in the sixth pass to 2 ± 0.5 in the ninth pass, correlating with increased heat input (HI) from 15.5 kJ/cm to 25.8 kJ/cm and repeated thermal cycling. Furthermore, the heat-affected zone (HAZ) exhibited coarse-grained polygonal austenite near the fusion line, with recrystallization attributed to the high thermal input. Micro-hardness measurements showed a reduction from 320 HV in the sixth pass to 195 HV in the ninth pass, linked to alloying element diffusion and ferrite content reduction. The findings highlight the importance of controlling thermal cycles and HI during multi-pass welding to optimize the microstructural stability and mechanical properties of ASCSP welded joints. These results provide valuable insights for improving the performance of ASCSP in industrial applications.