Enhancing the properties of a low carbon steel and SS316L bimetallic interface via mesoscale groove engineering in hybrid wire-arc directed energy deposition

Abstract

In sectors such as marine, chemical processing, construction, and nuclear, bimetallic structures combining low carbon steel (LCS) with stainless steel 316L (SS316L) are widely used for their affordability and superior corrosion resistance. However, joining these dissimilar materials can result in high dilution and un-mixed zones (UMZ), negatively affecting the joint quality. Particularly, high dilution may cause susceptibility to hot cracking in the austenitic zone or low-temperature cracking in the martensitic zone. Additionally, UMZs lead to inconsistent material properties, creating potential weak spots and localized stress concentrations. Both effects not only reduce the mechanical reliability of the joint but also elevate susceptibility to stress corrosion cracking (SCC) under corrosive service conditions. This paper proposes a novel hybrid manufacturing approach that integrates Wire-Arc Directed Energy Deposition (Wire-Arc DED) with precision milling to address these issues at the LCS-SS316L interface when printing three-dimensional bimetallic structures, aiming to minimize dilution and UMZs, thereby enhancing the structural integrity of the bimetallic part. We term this geometry-driven dilution-control strategy “mesoscale groove engineering”, in which a rectangular groove milled in LCS limits base-metal available for melting and thus reduces dilution in the overlying SS316L deposit. Various techniques are employed for microstructure, interfacial, chemical composition, and nano-hardness characterization. It is observed that appropriately sized grooves reduce dilution by 35 % and UMZs by 59.3 %. The reduction in dilution leads to a 26 % reduction in the nano-hardness variance in the largest UMZ. Additionally, slow strain-rate tensile testing (SSRT) in a 3.5 wt% NaCl solution confirms that the groove-engineered interface shows no signs of SCC, while also achieving a 16.4 % increase in ultimate tensile strength without loss in ductility. The proposed approach effectively demonstrates its potential to enhance the interfacial properties of bimetallic structures for specific industrial needs.