Effect of welding polarity on iron dilution, clad chemistry, and interfacial microstructure in multilayer SMAW Inconel 625 overlays on

Abstract

High-strength steels used in the oil and gas industry are susceptible to corrosion in harsh
environments. Although Inconel 625 offers excellent corrosion resistance, its high cost limits
large-scale application. Weld cladding with Inconel 625 provides a cost-effective alternative;
however, excessive dilution with the steel substrate increases iron content and degrades clad
chemistry. This study investigates the effect of welding polarity on iron dilution and clad
chemistry in multilayer SMAW Inconel 625 overlays deposited on SA-387 grade 11 steel.
Three-layer claddings were produced using direct current electrode negative (DCEN) and
direct current electrode positive (DCEP) polarities. Clad chemistry was characterized by
positive material identification (PMI) and scanning electron microscopy with energy-dispersive
X-ray spectroscopy (SEM-EDS). Iron dilution was calculated from measured iron contents.
Under the investigated conditions, the DCEN clad exhibited substantially lower iron content
(3.97 ± 0.12 wt%) compared with the DCEP clad (10.6 wt%). DCEN also permitted a lower
welding current (100–110 A versus 140–150 A for DCEP), resulting in reduced heat input.
These findings demonstrate that DCEN polarity can effectively minimize iron dilution and
produce clad chemistry closer to that of the Inconel 625 filler metal. Corrosion performance
was not directly evaluated in this study and remains a subject for future investigation.

In this study, an SA 387 Gr.11 CL2 steel plate was clad with three layers using the shielded metal arc welding (SMAW) process under two polarity conditions: Direct Current Electrode Negative (DCEN) and Direct Current Electrode Positive (DCEP). Qualitative and quantitative chemical analyses of the clad surface were determined using Positive Material Identification (PMI) alongside Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS). Subsequently, the iron dilution rate was calculated using standard dilution formulas. The results demonstrated that applying the three-layer SMAW process with DCEN polarity reduced the dilution rate from 10% (under DCEP) to approximately 3.9%, indicating lower penetration and a reduced dilution rate compared to DCEP. Furthermore, the use of negative polarity decreased the welding current from 140 A to approximately 110 A, thereby reducing the heat input into the component and mitigating the adverse effects associated with high heat input.