Pitting Corrosion Resistance Research Articles

Alloy Design Optimization of Stainless Steel's Performance and Environmental Impact Through Taguchi‐Based Grey Relational Analysis

The current work presents an optimization approach for improving stainless steel's performance and environmental impact. A Taguchi‐based grey relational analysis is used to determine the optimal alloy design of six stainless steels (304, 316L, 904L, 2304, 2205, 2507). The alloy design of a multivariable system (C, Mn, Cr, Ni, N, Mo, and Cu) is initially formulated based on the Taguchi orthogonal array. It combines the multiperformances (pitting corrosion resistance, proof strength, tensile strength, and greenhouse gas emissions) to determine a numerical score and suggests the optimal combination of alloy contents. The results are further analyzed using a range analysis to detect the significance of each alloy parameter and its level. The results show that nitrogen plays the most important role in determining the stainless steel's combined performance. Besides, the optimum alloy design consists of a high content of nitrogen, chromium, molybdenum, and copper combined with a low content of nickel. The study has a focus on proposing the systematic approach, Taguchi‐based grey relational analysis, to optimize the stainless steel's different mechanical properties with respect to environmental impact.

Effects of preheating on laser beam–welded NSSC 2120 lean duplex steel

AbstractDuplex stainless steels show sustainable alternative for the conventional austenitic grades, with higher strength, higher resistance against stress corrosion cracking, and lower purchase cost. Thus, duplex stainless steel gains more attention in construction, oil and gas, and chemical industries. Among duplex stainless steels, low nickel and low molybdenum alloyed lean duplex stainless steel are a cost-effective substitution of austenitic grades. However, keeping the balanced ferrite/austenite phase ratio in the weld metal can be challenging, mostly for autogenous and low heat input welding processes. In our research, a newly developed NSSC 2120 lean duplex stainless steel grade was welded autogenously by fiber laser welding process. Different welding parameters and preheating temperatures were used during the experiments. The welds were evaluated by microscopic and metallographic techniques, and also by electrochemical corrosion measurements. The welding parameters and the preheating temperature greatly influenced the weld shape and the austenite content in the weld metal. It was found that the focus point distance from the sheet surface had significant effect on the weld geometry. Changing the focus point distance to + 2 mm, the penetration depth increased from 4.96 to 5.53 mm, and increased the austenite content by 2.6%. Due to the preheating the welds became wider and shallower, e.g., from 4.96 to 4.08 mm penetration depth, while the cross-section are increased from 5.10 to 6.12 mm2 at the same sample. The preheating resulted in more intergranular austenite formation, which meant maximum 4% increase in the weld metal. The increasing austenite content resulted in increasing pitting corrosion resistance in 3.5% NaCl electrolyte, the highest increase was 90 mV.

Elucidating the effect of titanium alloying on the pitting corrosion of ferritic stainless steel

Ferritic stainless steels have been utilized in marine atmosphere and are found to be susceptible to pitting corrosion in our field investigation. Alloying is an important to modify the passive film on the surface and improve the pitting corrosion resistance. Nevertheless, how the addition of titanium modifies the passive film and affects the pitting corrosion resistance of ferritic stainless steels remain controversial. This study has elucidated these topics through microstructure analysis and corrosion properties analysis. The results demonstrate that titanium addition increases the pitting potential almost linearly. Titanium forms TiO2 in the passive film and reduces defect density of the passive film. Moreover, titanium addition induces the precipitation of the Laves phase, which promotes micro-galvanic corrosion. For the titanium-alloyed ferritic stainless steels, pitting corrosion predominantly occurs in the ferrite phase adjacent to the Laves phase. The influence mechanism of titanium on the pitting corrosion of the ferritic stainless steel has been established, which takes micro-galvanic corrosion induced by titanium addition into account.

Porous NiTi Dental Implant Fabricated by a Metal Injection Molding: An in Vivo Biocompatibility Evaluation in an Animal Model.

This study assessed the corrosion resistance, intracutaneous reactivity, acute systemic toxicity, and in situ tissue effect of the implantation of porous NiTi fabricated by metal injection molding in animal models. For the intracutaneous reactivity study, five intracutaneous injections were administered per site with and without the tested extract in polar and nonpolar solutions. The extract was also delivered via intravenous and intraperitoneal routes for acute systemic toxicity. TiAl6 V4 (control) and porous NiTi were implanted in rabbit femora for a period of 13 weeks to evaluate the in situ tissue response. Corrosion was evaluated through open and cyclic polarization in PBS, while biocompatibility was investigated by assessing the general conditions, skin irritation score (edema and erythema), and histopathology. No active dissolution or hysteresis loop was observed in the corrosion study. None of the animals exhibited death, moribundity, impending death, severe pain, self-mutilation, or overgrooming. No edema was observed at injection sites. Only the positive control showed an erythematous reaction at 24, 48, and 72 h observations (p < 0.001). Porous NiTi showed a low in situ biological response for inflammation, neovascularization, and fibrosis in comparison to the control implant (p = 0.247, 0.005, and 0.011, respectively). Porous NiTi also demonstrated high pitting corrosion resistance while causing no acute hypersensitivity or acute systemic toxicity. The study concludes that porous NiTi implants were unlikely to cause local sensitization, acute systemic toxicity, or chronic inflammatory reactions in an animal model. Porous NiTi also exhibited osseointegration equivalent to Ti6AI4 V of known biocompatibility.

Studies on the Cooperative Influence of Cr and Mo on the Pitting Corrosion Resistance of Super Austenitic Stainless Steels

The effects of varying Cr and Mo concentrations on the pitting corrosion resistance of super austenitic stainless steels in Cl− solutions were investigated using a combination of immersion experiments, electrochemical measurements, X-ray photoelectron spectroscopy, and first-principles computational simulations. The surface characteristics, impedance, and defect concentration of the passive film were changed, and this eventually resulted in a decrease in the number of pitting pits. Due to a decrease in active sites within the passive film, a delayed beginning of pitting, and the combined effect of MoO42− inhibitors, it was discovered that an increasing Mo concentration slows the rate of pitting extension, resulting in reduced maximum pitting area and depth. Additionally, Mo increased the adsorption energy of nearby atoms, whereas Cr raised the adsorption energy of itself. Interestingly, compared with individual doping, co-doping of Cr and Mo increased work function and adsorption energy, indicating a synergistic impact in enhancing resistance to Cl− corrosion.

Enhanced wear and corrosion resistance of the laser direct metal deposited AISI 316L stainless steel by in-situ interstitial N alloying

To meet the applicability in aggressive environments, the wear and corrosion resistance of additively manufactured 316L stainless steel can be improved by alloying with N. In this work, the in-situ interstitial N alloying of 316L with varying amount of CrxN is first manufactured at ambient environment utilizing the rapid cooling character of laser direct metal deposition (DMD). Combined effects of CrxN addition and DMD processing parameters on the relative density, dissolved N content, microstructure, microhardness, wear performance and corrosion behavior are systematically investigated. The results show that the relative density of the DMD 316L decreases with increasing additive amount of CrxN. A full density 316L sample with a high N content of 0.5 wt% is obtained. The N alloying transforms the solidification mode of DMD 316L from “AF” to “A”, resulting in a fully austenitic phase. The interstitial N promotes the formation of planar dislocations, nano-stacking faults and nano-twins during DMD. As the CrxN addition increases, both the microhardness (278–312 HV) and wear resistance are significantly enhanced owing to the dislocation strengthening and interstitial N solid solution strengthening. Compared with CrxN-free DMD 316L, the DMD 316L with CrxN addition presents superior pitting corrosion resistance. The increasing CrxN addition progressively improves the pitting corrosion resistance due to the positively synergistic effect Cr-N on the stability and repassivation ability of the passive film. This work provides a practical and cost-effective approach for manufacturing advanced 316L with exceptional properties.

Improved heat and corrosion resistance of high electrical conductivity Al-Mg-Si alloys by multi-alloying of Ce, Sc and Y

In order to improve the corrosion and heat resistance of Al-Mg-Si alloy conductor materials, Ce, Sc, Y and Zr were added in Al-Mg-Si alloy to regulate the microstructure. The Al-Mg-Si-Ce-Sc-Y alloy was designed with excellent pitting and intergranular corrosion resistance by obtaining the micron-sized Fe-containing second phase with a lower potential difference to Al matrix, more dispersed grain boundary precipitates with a higher proportion of Si particles, narrower width of PFZ and ideal distribution of intergranular precipitates. The Al-Mg-Si-Ce-Sc-Y alloy also maintained higher hardness, strength and electrical conductivity after overaging and annealing and the corrosion/heat resistance mechanisms were proposed.

Synergistic inhibition of molybdate and phytate on chloride-induced corrosion of carbon steel in simulated concrete pore solutions

Improving the corrosion resistance of reinforcing steel is particularly important to prolong the service life of reinforced concrete (RC) structures. This study proposes a novel mixed corrosion inhibitor of sodium molybdate and sodium phytate to enhance the corrosion resistance of Q235 carbon steel in concrete exposed to aggressive environments. Based on the synergistic inhibition of the mixed corrosion inhibitor with an optimal concentration ratio, the passivation and chloride-induced corrosion of steel in simulated concrete pore solutions were investigated using electrochemical measurements, XPS, AFM, SEM/EDS and ATR-FTIR. The results indicated that the mixed corrosion inhibitor could promote the passivation process of steel by increasing the passive film thickness, despite no significantly improved passivation ability was highlighted for steel. Furthermore, due to the formation of a protective and thick passive film with a specific three-layer structure, the mixed corrosion inhibitor markedly improved the pitting corrosion resistance of steel and exhibited a high inhibition efficiency after 30 days of chloride exposure. Accordingly, the corresponding synergistic inhibition mechanism of the mixed corrosion inhibitor was proposed.

Effect of cutting parameters on pitting corrosion resistance of S32760 duplex stainless steel

AbstractTo improve the performance in service of S32760 duplex stainless steel (DSS) in the marine environment, the influence of cutting parameters of S32760 DSS on the pitting corrosion resistance of the workpiece is studied. Cutting experiments are performed on S32760 DSS by varying the cutting parameters to investigate their effects on the surface morphology. The electrochemical experiments are conducted on the workpiece immersed in the 3.5 wt% sodium chloride solution to investigate how the cutting parameters affect the pitting corrosion resistance of S32760 DSS. The results indicate that the pitting corrosion resistance is influenced by the cutting speed and feed rate, which in turn affects the surface roughness. The cutting depth does not have a significant impact on the surface roughness but significantly affects the pitting resistance. The recommended cutting parameters are as follows: feed rate of 0.1 mm/r, cutting speed of 130 m/min, and cutting depth of 0.4 mm.

Influence of nitrogen content on the pit formation and pit propagation in the welded joints of X5CrNi18‐10 stainless steel

AbstractThe influence of welding current and nitrogen content in argon shielding gas on the resistance of the welded joint (weld metal and heat‐affected zone [HAZ]) of the stainless steel X5CrNi18‐10 to the formation and growth of pits was investigated. Also, the susceptibility of the welded joint to intergranular corrosion was examined. Pitting corrosion resistance indicators were determined based on anodic potentiodynamic polarization measurements in NaCl + Na2SO4 solution, while susceptibility to intergranular corrosion was determined by the potentiokinetic method with a double loop (DL EPR). SEM/EDS was used to analyze the microstructure. It has been shown that higher nitrogen content in shielding gas leads to an increase in the resistance of welded joints (weld metal and HAZ) to the pit formation. However, an improvement in the resistance to the pit formation leads to a decline in the resistance of the welded joint to pit growth. An explanation of this phenomenon is proposed. Also, it was shown that the increase of the welding current increases the susceptibility of the welded joint to intergranular corrosion, while the higher nitrogen content has no effect.

Dissimilar welding of AISI 201 and 202 low nickel stainless steels by GTA and PA welding processes

This paper presents the results of dissimilar joining techniques for AISI 201 and 202 low nickel austenitic stainless steels. These were welded by Gas Tungsten Arc Welding (GTAW) and Plasma Arc Welding (PAW). The tests were performed to examine the weld bead shapes, microstructure, mechanical properties and corrosive behavior of the weld metals with different welding processes. The weld bead shape by GTAW was larger than that performed by PAW. The microstructure of the weld metal produced by GTAW contained more delta ferrite in the austenite matrix than the weld metal produced by PAW. The volume of hardness in welds produced by PAW higher than the GTAW process same with the ultimate tensile strength and percentage elongation welds produced by PAW higher than the GTAW process. According to the potentiodynamic polarization test results, pitting corrosion resistance of the weld produced by PAW was higher than the weld produced by GTAW. Both weld metals showed the pitted area adjacent to the phase boundary between austenite and delta ferrite in the mixed microstructure. Based on the present work, it was concluded that PAW was the more suitable welding procedure for joining dissimilar 201 and 202 austenitic stainless steels.

Unveiling the pitting corrosion mechanism of borated stainless steel in the wet storage environment of spent nuclear fuels

Borated stainless steels (BSSs) with high neutron absorbability are promising alloys for the wet storage of spent nuclear fuel. However, consensus on the underlying mechanisms for the effects of B content in BSS and H3BO3 in wet storage environment on the pitting corrosion resistance of BSSs is still lacking. To determine the mechanisms, we designed three hypoeutectic BSSs containing 0.6, 1.2 and 1.8 wt.% B and systematically investigated their electrochemical behavior in solutions with various Cl−/H3BO3 ratios through experimental and computational studies. Results revealed that the pitting corrosion resistance of BSS was dependent on the synergistic effect of the pit initiation induced by localized Cr depletion and the pit stable growth caused by microgalvanic effect, causing the pitting corrosion preferentially occurred at the (Cr, Fe)2B/matrix interface. A higher B content increased the density and width while reduced the Cr contents of the Cr-depleted regions, enhancing the susceptibility to pitting initiation. Meanwhile, the strengthened micro-galvanic effect between the (Cr, Fe)2B phase and γ matrix further facilitated the stable pit growth. For the H3BO3 effect, the first-principles calculations indicated that the competitive adsorption of B(OH)4− to Cl− inhibited pitting initiation in solutions with lower Cl−/H3BO3 ratios. However, as the Cl−/H3BO3 increased, the inhibition effect of the H3BO3 was weakened, and the acidizing effect became the dominant factor deteriorating the corrosion property. Ultimately, based on the Cr depletion-microgalvanic synergetic mechanism, the corrosion resistance of the BSS was significantly improved by tailoring the size and distribution of the (Cr, Fe)2B phase.

Pit growth kinetics of additively manufactured MoNi over-alloyed type 316L stainless steel

The microstructure and corrosion performance of wrought, laser powder bed fusion (LPBF), and MoNi over-alloyed LPBF type 316L stainless steel is compared. Adding Mo and Ni to LPBF 316L stainless steel resulted in ẟ-ferrite. Potentio-dynamic polarisation was used to rank all microstructures, with LPBF + MoNi has more resistant than LPBF and wrought material. Bipolar electrochemistry was applied, with LPBF samples having the lowest critical pitting potential and highest pit growth kinetics. The best corrosion performance was for LPBF + MoNi stainless steel. Different pitting corrosion resistance as function of process directions were found. The tiny pores negatively impacted the pitting performance.

Study on the Effect of Hydrogen in Argon-Nitrogen Shielding Gas on Pitting Corrosion for Austenitic Stainless Steel by GTA Welding Process

The addition of hydrogen in shielding gas has been found to contribute to increasing the productivity of gas tungsten arc (GTA) welding compared to the processes using argon-nitrogen shielding gas. In this report, the GTA welding joints of AISI 304 stainless steel with Ar-N2 and Ar-N2-H2 addition were fabricated. The microstructure and pitting corrosion resistance were studied in this work. The corrosion characterisation of welds metal was investigated by a potentiodynamic method in NaCl solution. It was found that H2 addition also had effects on delta-ferrite microstructures and corrosion behaviour. Increasing hydrogen in argon-nitrogen shielding gas increased the delta-ferrite content and improved pitting corrosion resistance.

Investigating molybdenum’s sulphur scavenging ability for MoS2 formation in preventing pitting corrosion of stainless steels

The addition of Mo enhances pitting corrosion resistance in 304L stainless steel. However, there is no consensus on the underlying mechanism. One possible explanation is that molybdenum converts sulfide to stable MoS2. This study investigates the effect of MoS2 inclusion on the corrosion of 304L stainless steel by introducing both MnS and MoS2 using spark plasma sintering. The reduction of MoS2 to Mo is observed during the sintering process, contradicting the assumption that the sulfide inclusions can be stabilised by forming MoS2. Therefore, MoS2 formation cannot explain the improved corrosion resistance of 304L stainless steel with the addition of Mo.

Heat-Affected Zone Characterization of X2CrNiN22-2 Lean Duplex Stainless Steel by Metallographic and Electrochemical Techniques

This research aimed to investigate the heat-affected zone of lean duplex stainless steel grade X2CrNiN22-2. Different heat-affected zone microstructures and grain morphologies were developed by Gleeble simulations. The governing microstructures were evaluated by metallographic techniques and electrochemical corrosion measurements. It was found that the 1200-800 °C cooling time significantly affects the microstructure, austenite content, and corrosion properties. The average austenite content in the case of 1 s cooling time is 30.7 ± 1%, which increased with the longer cooling times up to 38.6 ± 0.9%. The rapid cooling times resulted in a more ferritic microstructure, which promoted nitride precipitation in the ferrite grains. The nitride precipitations acted as nucleation sites for pitting initiation in 3.5 wt.% NaCl solution. The lowest pitting potential was measured in the case of the most rapidly cooled sample: 573 ± 31 mV, while the balanced, annealed microstructure had much better pitting corrosion resistance, showing a pitting potential of 1308 ± 62 mV vs. the Ag/AgCl (KCl sat.) reference electrode. The results of this research can be used in designing welding parameters for the welding of the X2CrNiN22-2 lean duplex stainless steel.Graphical

Enhance corrosion resistance of 304 stainless steel using nanosecond pulsed laser surface processing

In this study, a novel strategy for nanosecond (ns) laser surface processing was designed to improve the corrosion resistance of commercial 304 stainless steel (304 SS). The influence of different ns-laser parameters on pitting corrosion resistance was systematically investigated. An optimal pitting potential of ∼887 mV, from the origin of 503 mV, was obtained at a laser power of 20 W and a beam size of 116 µm, which was superior to those treated by traditional laser methods. Based on the microstructure observations, it was found that the gradient structured 304 SS was produced by the remelting effect of ns-laser surface processing. Along the direction of laser irradiation, the modified microstructure was composed of ultrafine grains in the topmost surface layer, dislocation accumulations in the sublayer, and coarse grains with nanotwins in the matrix. Additionally, the mechanisms of improved corrosion resistance were also revealed. The experimental results demonstrated that the formation of gradient microstructure containing ultrafine grains was responsible for the exceptional corrosion resistance. It is expected that the advanced ns-laser surface processing will be applied on various metallic materials to meet the practical demands for high corrosion resistance across various industries.

The impressive improvement of CoCrFeMnNi high entropy alloy mechanical properties and pitting corrosion resistance by incorporation of carbon nanotube reinforcement

CoCrFeMnNi high entropy alloy without carbon nanotube (referred to as HEA) and with 0.2 wt% CNT (called HEA + CNT) were successfully synthesized through mechanical alloying and subsequent spark plasma sintering. The samples' phase composition, microstructure, mechanical properties, and corrosion performance were investigated. XRD results showed that the addition of CNT leads to a decrease in crystallite size, reducing it from 209 nm in HEA to 190 nm in HEA + CNT. FESEM results revealed a relatively uniform distribution of smaller carbide phases in the structure of HEA + CNT sample. The addition of CNT increased the ultimate compressive stress (UCS) from 1850 MPa for HEA to 2510 MPa for HEA + CNT. Cyclic polarization results demonstrated higher pitting corrosion resistance in HEA + CNT nanocomposite, where the pitting potentials for HEA and HEA + CNT were equal to 0.127 and 0.201 V vs. SCE, respectively. The CNT addition promoted the repassivation process of the pits in HEA + CNT sample.

Achieving a superior combination of tensile properties and corrosion resistance in AISI420 martensitic stainless steel by low-temperature tempering

The mechanical and electrochemical properties of AISI420 martensitic stainless steels (MSS) tempered at different temperatures (200, 400, and 600 ℃) are systematically investigated. The increased tempering temperature leads to the decreased strength, while the elongation remains relatively stable. Notably, the MSS tempered at 200 ℃ exhibits a superior strength-ductility synergy, featuring a strength of 1.65 GPa, and elongation of 10%. Moreover, increasing tempering temperature reduces the electrochemical properties and pitting corrosion resistance. In the tempered samples, pitting corrosion initiates near the inclusions and carbides, with the Cr-rich carbides and Cr-depleted regions serving as channels that promote the propagation of corrosion.

Joining of additively manufactured fiber-reinforced thermoplastic and metals by ultrasonic energy: Mechanical and corrosion behavior

Ultrasonic joining (U-Joining) is applied to create reinforced hybrid joints between unreinforced or fiber-reinforced polymers and surface-structured metals. While the feasibility of joining additively manufactured (AM) materials was already demonstrated, a detailed description of the process parameters’ effects is still missing. Therefore, this study aims to define the influence of the U-Joining parameters on the mechanical and corrosion properties of AM 20% short-carbon-fiber-reinforced poly-ether-ether-ketone (PEEK-20CF) and 316L stainless steel (316L SS) hybrid joints. Optimal joining parameters were determined via Box-Behnken design of experiments to maximize the joints’ ultimate lap shear forces (ULSF) and displacement at break (DaB), where the results increased from 1.4 ± 0.2 kN to 3.6 ± 0.3 kN (2.6 times) and from 1.2 ± 0.3 mm to 2.4 ± 0.1 mm (2 times), respectively. Microstructural analyses revealed a strong micromechanical interlocking between the parts due to the filling of crevices at the as-built AM metallic part’s rough surface by consolidated PEEK-20CF, which resulted in a mixture of adhesive, cohesive and net tension failure during the lap-shear tests. Finally, the corrosion resistance was also evaluated by potentiodynamic polarization curves, showing that the energy input during the joining cycle slightly reduced the pitting corrosion resistance of the 316L part.