Metallurgical and Electrochemical Properties of Super Duplex Stainless Steel Clads on Low Carbon Steel Substrate produced with Laser Powder Bed Fusion

Abstract

this study aims to improve the corrosion resistance of the low carbon steel by cladding it with super duplex stainless steel using laser powder bed fusion process. critical process parameters such as laser power, laser scan speed, hatch spacing, and powder layer thickness were optimized to achieve the best possible metallurgical bonding between the clad and the substrate. the evaporative losses experienced during the laser melting process resulted in clad layers with lower chromium content (12-25 wt. %) as compared to 26 wt. % of the feedstock powder. A clad thickness of 65.8 µm was achieved after melting ten 50 µm thick powder layers. the higher cooling rates associated with laser powder bed fusion resulted in fine high aspect ratio columnar grain structures with predominantly ferrite grains; however, widmanstätten austenite needles were observed with increasing laser scan speeds. increasing scan speed had a negative impact on the thickness, corrosion resistance, and the pitting potential of the clads exposed to 3.5 wt.% NaCl aqueous solution. Clads produced at the lowest scan speeds showed comparable corrosion resistance to rolled and annealed super duplex stainless steel. Duplex stainless steels (DSS) are a special class of ferrous alloys with a balanced ferrite (δ) and austenite (γ) phase microstructure. This dual-phase structure imparts these steels a high strength, toughness, and increased corrosion resistance in environments containing acids, acid chlorides, seawater, and caustic chemicals. Super duplex stainless steels (SDSS) 1 are a variant of DSS with higher Cr (25-26 wt. %) and Mo (4 wt. %) contents. SDSS typically shows superior pitting and stress corrosion cracking resistance than DSS; therefore, the use of SDSS has been increasing in highly corrosive environments, including oil and gas infrastructure, desalination plants, chemical storage tanks, heat exchangers, and paper/pulp manufacturing facilities 1. Although low carbon steel (LCS) remains to be the most widely used ferrous alloy, its applications are limited because it is highly vulnerable to corrosion in neutral, acidic, or saline environments 2. Corrosion-resistant SDSS alloys possess superior corrosion resistance than the LCS for the aforementioned applications, albeit with a significantly higher material cost. One of the viable means to reduce the component cost without compromising on service life is to manufacture a composite with a low-cost tough and ductile substrate cladded with a wear and corrosion resistant surface, as in the case of SDSS clads on an LCS substrate. These dissimilar metal composites (cladded systems) have been produced in the past using conventional manufacturing techniques such as welding 3-5 , diffusion bonding 6 , powder roll bonding 7 , hot rolling 8 , and reduction bonding 9. However, conventionally manufactured composites are often unfit for field use due to substandard clad-substrate bonding, often leading to clad delamination when subjected to operational stresses in the field. This substandard bond typically ...

Effect of GTAW remelting on the corrosion performance of AISI 316L cladding

“…[ 29 ] For this reason, CPE is quite used as a flexible parameter for fitting the impedance data and is able to provide better fit results. Murkute et al [ 26 ] suggested that n value close to 1 depicted strong passivity of the metal surface, whereas lower n value was typically indicative of a less‐passive or actively corroding system owing to increased nonideality of the metal surface, which was mainly attributed to the increased surface heterogeneity.…”

“…This increase in the nonideality owing to drop in the peak‐negative phase angles is a characteristic of weak and unprotective oxide film formation. [ 26 ]…”

“…This increase in the nonideality owing to drop in the peak-negative phase angles is a characteristic of weak and unprotective oxide film formation. [26] The experimental EIS data presented in the form of Nyquist and Bode plots were further elucidated by fitting the EIS data to an EEC model. As the EIS spectra exhibited a one-time constant feature, so the EEC model shown in Figure 7d, which consisted of Rs, parallel combination of constant phase element (CPE), and resistor (Rp) denoting overall resistance or polarization resistance between electrode/electrolyte interface was used.…”

“…This model has been proposed by several authors for modeling of passivating metal surfaces. [25][26][27] The electrochemical parameters extracted from the fitting of the experimental EIS data to the EEC model are summarized in Table 6. Good fittings were achieved between the experimental and the model data with relatively small χ 2 values of the order of 10 −3 as listed in Table 6.…”

“…[29] For this reason, CPE is quite used as a flexible parameter for fitting the impedance data and is able to provide better fit results. Murkute et al [26] suggested that n value close to 1 depicted strong passivity of the metal surface, whereas lower n value was typically indicative of a less-passive or actively corroding system owing to increased nonideality of the metal surface, which was mainly attributed to the increased surface heterogeneity. On the basis of the data presented in Table 6, it can be inferred that Rs was almost constant for all the clad surfaces, which was also evident from the impedance modulus values at high frequency from the Bode impedance plots.…”