A Novel Approach to Inhibit Intergranular Corrosion in Ferritic Stainless Steel Welds Using High-Speed Laser Cladding

Abstract

Ferritic stainless steels are prone to localized corrosion phenomena such as pitting corrosion or intergranular corrosion, in particular when jointed by fusion welding processes. State-of-the-art techniques to avoid intergranular corrosion mainly consist of alternating alloy concepts or post-weld heat-treatments—all of which are associated with increased production costs. Hence, the present investigation seeks to introduce a novel approach for the inhibition of intergranular corrosion in ferritic stainless steel welds through the use of high-speed laser cladding. Here, vulnerable sites prone to intergranular corrosion along the weld seam area are coated with a chemically resistant alloy, whereby an overlap is achieved. Optical and electron microscopy as well as computer tomography and tensile tests reveal that the detrimental effects of intergranular corrosion in both stabilized and unstabilized ferritic stainless steel are substantially reduced. In addition to that, the effects of varying overlap widths on the identified corrosion phenomena are studied. Moreover, the resulting dilution and precipiation phenomena at the clad–sheet interface are thoroughly characterized by electron backscatter diffraction and energy dispersive X-ray spectroscopy, whereby interrelationships to corrosion resistance can be drawn. As a result of this investigation, the number of techniques for the inhibition of intergranular corrosion is enlarged, and substantial cost-saving potentials in the manufacturing industry are unlocked.

Grain growth and precipitation behaviour of AISI 430 ferritic stainless steel subjected to pulsed laser beam welding using free-form pulse shaping

“…Moreover, the grooves evolving from IGC appear deeper and, thus, more significant. Overall, the temporally resolved mass loss is in good agreement to the evolution of residual mechanical strength of laser-cladded AISI 430 welds which features an approximate exponential decline [33]. In summary, the presented results indicate that the use of comparatively short pulse durations during P-LBW can inhibit chromium carbide precipitation, sensitization and, consequently, IGC within the HAZ due to the inherent thermal gradients and rapid cooling rates, which are obviously amplified in comparison to cw-LBW.…”

“…The use of EBSD-based phase mappings at a high magnification facilitates a robust and prompt means to characterize chromium carbide precipitates at the WM/HAZ boundary [33], whose dimensions following cw-LBW typically lie in the order of tenths to hundreds of nanometres [31]. The crystallographic investigation in Fig.…”

“…In addition, WM grain boundaries occupied by titanium precipitates are prone to dissolution and, thus, the initiation of special forms of IGC which impair the structural integrity of the component [31]. Recent investigations also demonstrate the use of powder-fed laser cladding [32] in order to locally improve the IGC resistance of ferritic stainless steel welds [33].…”

Recent findings on corrosion of ferritic stainless steel weldments: A review

“…In a recent study, Sommer et al [31] investigated the intergranular corrosion of unstabilized AISI 430 FSS weldment produced by laser cladding at high speed. It is observed that the FSS weld joint was prone to intergranular corrosion due to the segregation of the alloy elements within the weld metal zone.…”