Tensile performance of hybrid steel welded connections subjected to multi-factor accelerated corrosion

This study presents a comprehensive investigation into the corrosion behaviour and tensile performance of hybrid welded connections between carbon steel (Q235) and stainless steel (S30408, EN 1.4301, ASTM 304). A total of sixty welded specimens, representing three material combinations including carbon steel – stainless steel (CS), carbon steel – carbon steel (CC), and stainless steel – stainless steel (SS), were subjected to multi-factor accelerated corrosion tests. Three-dimensional (3D) surface scanning and multifractal analysis were employed to quantitatively characterise the evolution of corrosion morphology. Monotonic tensile tests, combined with digital image correlation (DIC), were carried out to evaluate the post-corrosion mechanical performance of the coupons. It was revealed that the degradation of load-carrying capacity in CS and CC specimens was dominated by the carbon steel base metal, with deterioration rates comparable to those of carbon steel plates alone, indicating that galvanic corrosion had minimal impact on mechanical performance. In contrast, SS coupons exhibited rapid reductions in strength and ductility, primarily due to intergranular corrosion (IGC) induced by sensitisation in the heat-affected zone (HAZ) during welding, as confirmed by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analyses. Notably, IGC was effectively suppressed in CS specimens, where stainless steel was welded to carbon steel, and no significant degradation of the stainless steel was observed. Finally, based on the multifractal characteristics of corroded carbon steel surfaces and an equivalent flat-surface finite element (FE) modelling approach, an efficient and accurate method was proposed for predicting the residual load-carrying capacity of CS/CC welded specimens.