Microstructure and mechanical property assessment of stainless steel-clad plate joint made by hybrid SMAW-GTAW multi-pass welding process

The stainless clad steel plates (SCSPs) are used in several industrial fields such as petroleum and petrochemical industries due to their low cost and good corrosion resistance. In this work, the structural integrity assessment of a welded joint, produced by a hybrid SMAW/GTAW multi-pass welding process of SCSP, was carried out through non-destructive examinations, microstructural observations and mechanical characterization tests. The non-destructive examination showed that the welded zone is free from any sign of defect. The welded joint filled with ER316L revealed the presence of delta-ferrite, which was solidified as skeletal and lathy ferrite under ferritic-austenitic (FA) solidification mode. The microstructure of the weld metal transition zone (WM-TZ) filled with ER309L exhibited the presence of martensitic laths as well as a cellular and columnar structure. It was found that the diffusion of carbon element caused the forming of a decarburized layer in the substrate heat-affected zone (S-HAZ) during the welding process. The observation also revealed the presence of type I and type II boundaries along the fusion line, which are characterized by their martensitic nature. Based on the determination of the WM-TZ dilution percentage, which is equal to 32%, the presence of the martensite was also confirmed by Schaefer diagram. The high micro-hardness values (similar to 429 HV) and the low toughness (similar to 22.9J) measured respectively in vicinity of the WM-TZ also confirm the local hardening zone (LHZ) formed on the welded zone after bending tests.