High Pitting Resistance Research Articles

Toward High-Pitting Resistance and Low-Cost Austenitic Stainless Steel: The Role of Carbon Alloying

This article investigates the pitting resistance of a newly developed Fe-Cr-Mn-N austenitic stainless steel with 0.14 wt% carbon and its counterpart with 0.02 wt% carbon. By using especially hot-rolled bimetal specimens, we focus on the pitting behavior near the interface between the two alloys and demonstrate that solid solution carbon can significantly improve pitting resistance. The alloyed carbon increases the passive film stability, but the more fundamental reason is that carbon suppresses the active dissolution rate of the matrix, thereby inhibiting the kinetics of pitting growth. These results will highlight the use of carbon alloying in austenitic stainless steel to provide more cost-effective materials with improved corrosion resistance and mechanical strength for the construction industry.

Microstructural, Mechanical, and Electrochemical Characterization of CrMoNbTiZr High-Entropy Alloy for Biomedical Application.

High-entropy alloys (HEA) with superior biocompatibility, high pitting resistance, minimal debris accumulation, and reduced release of metallic ions into surrounding tissues are potential replacements for traditional metallic bio-implants. A novel equiatomic HEA based on biocompatible metals, CrMoNbTiZr, was consolidated by spark plasma sintering (SPS). The relative sintered density of the alloy was about 97% of the theoretical density, indicating the suitability of the SPS technique to produce relatively dense material. The microstructure of the sintered HEA consisted of a BCC matrix and Laves phase, corresponding to the prediction of the thermodynamic CALPHAD simulation. The HEA exhibited a global Vickers microhardness of 531.5 ± 99.7 HV, while the individual BCC and Laves phases had hardness values of 364.6 ± 99.4 and 641.8 ± 63.0 HV, respectively. Its ultimate compressive and compressive yield strengths were 1235.7 ± 42.8 MPa and 1110.8 ± 78.6 MPa, respectively. The elasticity modulus of 34.9 ± 2.9 GPa of the HEA alloy was well within the range of cortical bone and significantly lower than the values reported for commonly used biomaterials made from Ti-based and Cr-Co-based alloys. In addition, the alloy exhibited good resistance to bio-corrosion in PBS and Hanks solutions. The CrMoNbTiZr HEA exhibited an average COF of 0.43 ± 0.06, characterized mainly by abrasive and adhesive wear mechanisms. The CrMoNbTiZr alloy's mechanical, bio-corrosion, and wear resistance properties developed in this study showed a good propensity for application as a biomaterial.

Modification of structural, mechanical, corrosion and biocompatibility properties of Ti40Zr10Cu36Pd14 metallic glass by minor Ga and Sn additions

Ti40Zr10Cu32Pd14Ga4 and Ti40Zr10Cu32Pd14Sn4 (in at%) bulk metallic glasses (BMGs) with different geometries (wedges, rods, ribbons and discs) were prepared by suction casting, melt spinning and splat quenching, respectively. For comparison, the reference Ti40Zr10Cu36Pd14 BMG was cast as a rod with 2 mm diameter and in wedge-shaped form. High-energy X-ray diffraction measurements yielded a critical casting thickness of 2.4, 2.1 and at least 4 mm for the reference, Ga-containing, and Sn-containing BMGs, respectively. The extension of the supercooled liquid region of about 50 K, measured for the glassy rods and ribbons by differential scanning calorimetry, is larger than that of only 20 K found for the splat-quenched discs. As to the alloys’ mechanical properties, the Ti40Zr10Cu36Pd14 glassy rods deform plastically in compression up to a strain of 3.8% and possess a Young’s modulus of 78 GPa. The Sn- and Ga- containing BMG rods reach respectively a plastic strain of 6.1% and 4.7%, and a Young’s modulus of 72 and 63 GPa. Corrosion tests were performed by electrochemical experiments, and the highest pitting resistance was observed for Ti40Zr10Cu32Pd14Sn4 (pitting overpotential ηpit = 446 mV) compared to Ti40Zr10Cu32Pd14Ga4 (379 mV) and Ti40Zr10Cu36Pd14 (183 mV). The results of live/dead assay and cell viability revealed excellent biocompatibility for the Ga-containing BMGs.

Pitting and General Corrosion Susceptibilities of Materials for High Level Radioactive Waste (HLW) Disposal.

The disposal of high-level radioactive waste (HLW) in deep stable geological formations is accepted at an international level to be the most promising option for its long-term management. The supercontainer concept is currently being considered as the Belgian reference design, wherein the waste will be stored in geological stable clay formations. The outer barrier of the supercontainer is the envelope, which should be made of a corrosion-resistant material as it will be in contact with the aggressive species leaching from the host rock (i.e., chloride) and diffusing through the cementitious barriers of the disposal system. Polarization measurements are carried out to study the pitting susceptibility and the uniform corrosion of possible candidate materials in chloride-rich concrete pore solutions, aerated by high-purity oxygen. The tests are carried out at a deep soil-representative temperature of 60 °C. All materials showed high pitting resistance in aerated concrete pore solutions and can withstand chloride concentrations up to 1 M. Regular 316L and LDX2304 stainless steel also showed good corrosion resistance and can serve as a more economical alternative. The pH of the used pore solutions did affect the measured corrosion rate irrespective of the alloying elements inside the steel grades.

Investigation of acidity on corrosion behavior and surface properties of SS304 in simulated PEMFC cathode environments

This study presents the influence of acidity on the corrosion performance and surface properties of AISI 304 stainless steel (SS304) in the simulated cathode condition of proton exchange membrane fuel cells (PEMFC) with various concentrations of H2SO4. The electrochemical tests indicate that the corrosion resistance of SS304 samples decreases gradually with the solution acidity ascending, but the stable current densities (0.043–0.547 μA cm−2) in the simulated solutions after polarization (0.6 V, 5 h) are all lower than that of the relevant DOE 2025 target (icorr < 1 μA cm−2). Obvious pitting corrosion occur in the solutions with H2SO4 concentration higher than 10−3 M. The surface wettability and interfacial contact resistance (ICR) of the potentiostatically polarized SS304 show an upward trend with the solution acidity increasing, and whether the SS304 samples are polarized or not, their ICR (0.274–1.232 Ω cm2) is far higher than the latest DOE 2025 technical target (<0.01 Ω cm2). The results reveal that surface modification is indispensable for SS304 as bipolar plates, and more attention should be paid to possessing high and stable pitting resistance, hydrophobicity, and interfacial conductivity in an acid environment.

Improving the Mechanical Properties of AISI 2205 Duplex Stainless Steel by Cryogenic Treatment Process

The Duplex stainless steel AISI 2205 is well known for its corrosion resistance, applicable to high pitting and stress resistance. Cryogenic treatment is chosen to boost the mechanical properties of AISI 2205 Stainless Steel. The specimens undergo cryogenic treatment, one of them being treated to the saturated limit. For comparison purpose, one specimen is kept as untreated. Wear test will be conducted at a constant speed and variable load by a pin on disc wear testing apparatus. Wear test is completed to assess the capability of utilizing a specific surface building innovation to diminish wear for a particular application and to research the impact of treatment conditions on the wear execution, so upgraded surface treatment conditions can be figured it out. Eventually, all specimens were undergone with Scanning Electron Microscope analysis.

Corrosion resistance of weight reduced AlxCrFeMoV high entropy alloys

High entropy alloys with superior hardness and corrosion resistance have proved themselves excellent coating materials. In this study, a pitting corrosion resistance analysis of AlxCrFeMoV alloys (with x = 0, 0.2, 0.6, 1), with outstanding mechanical features, has been conducted. The study was motivated by their exceedingly high pitting resistant equivalent number (PREN) values, in the range of 80–100. Powder metallurgy techniques, including mechanical alloying and spark plasma sintering, were applied to fabricate the designed alloys. To examine the pitting behavior of the alloys, the potentiodynamic and cyclic polarization analysis were performed in 3.5 wt% NaCl solution at 25 °C. The electrochemical impedance spectroscopy has been used to study variations in the surface characteristics of specimens in a saline environment. Also, the comparative chemistry of the passive layers formed in the primary and secondary passivation regions was evaluated by conducting X-ray photoelectron spectroscopy. The examined systems exhibited an exceptionally high pitting resistance, which was attributed to being predominantly caused by the high concentration of PREN elements in the alloys. Contrary to previously reported aluminum (Al) containing high entropy alloys, the addition of Al did not have an adverse effect on the pitting behavior of the current systems. This was due to the absence of Al-rich phases.

Additively manufactured 316L stainless steel with improved corrosion resistance and biological response for biomedical applications

Enhancing the corrosion resistance and improving the biological response to 316 L stainless steel is a long-standing and active area of biomedical research. Here, we analyzed the structure and corrosion tendency of selective laser melted-additively manufactured (AM) 316 L stainless steel (AM 316L SS) and its wrought counterpart. SEM analysis showed a fine (500–800 nm) interconnected sub-granular structure for the AM 316L SS, but a polygonal coarse-grained structure for the wrought sample. Relative to the wrought sample, the AM 316L SS also exhibited a higher charge transfer resistance and higher breakdown potential (˜1000 mV vs. SCE) when tested in biological electrolytes, which included human serum, PBS, and 0.9 M NaCl. A higher pitting resistance (extended passive region) and improved stability of the AM 316L SS was attributed to its dense structure of oxide film and refined microstructure. Finally, material compatibility with pre-osteoblasts was analyzed. Large cytoplasmic extension of osteoblast cells and retention of stiller morphology was observed when cells were cultured on the AM 316L SS as compared to its wrought counterpart, suggesting that the AM 316L SS was a better substrate for cell spreading and differentiation. The differentiation of cultured cells was further validated by western blot for Runx2. Runx2, an anti–proliferative marker indicative of differentiation, was equivalent in cells cultured on either samples, but overall more cells were present on the AM 316L SS. Given its higher corrosion resistance and ability to support osteoblast adherence, spreading and differentiation, the AM 316L SS has potential for use in the biomedical industry.

Spindle speed in friction surfacing of 316L stainless steel – How it affects the microstructure, hardness and pitting corrosion resistance

Using friction surfacing (FS), stainless steel 316L coatings were successfully fabricated on 304 substrates. The spindle speed employed in FS was found to have a more significant effect on the microstructure of the coating surface than that in the cross-section. Compared with the as-received 316L consumable rod, hardness improvement was observed in FSed coatings owing to dynamic recrystallization (DRX) during FS. Moreover, the pitting corrosion resistance of the FSed coatings was enhanced by the severe plastic deformation (SPD), which fragmented the micro-sized MnS inclusions in the consumable rod into inconspicuous size after FS. From the immersion test, pits were gathered in {111} grains of the coatings, and the inferior pitting resistance of the {111} grains could be attributed to their lower stacking fault energy. They sustained considerable elastic strain during FS, and generated a higher residual tensile stress that led to pitting. For the coatings fabricated at a moderate spindle speed (1500 rpm), discontinuous DRX became dominant and the recrystallized random orientated grains weakened the {111} texture, resulting in the highest pitting resistance. However, the pitting corrosion resistance improvement induced by the crystallographic effect of different spindle speeds was less prominent comparing with that caused by MnS inclusion fragmentation. Moreover, the advancing side of the FSed coatings was plastically deformed severely, leading to a stronger {111} texture than in other places, which restricted the pitting corrosion resistance enhancement of entire FSed coating.

Is duplex stainless steel more corrosion resistant than 316L in aqueous acid chloride-containing environments at temperatures higher than 100°C?

ABSTRACTThe influences of temperature and chloride content on the corrosion resistance of stainless steels (SS) in acid solution were investigated employing polarisation curves (PC) and electrochemical impedance spectroscopy measurements. Although the duplex SS presented a higher pitting resistance equivalent number than that of 316L SS, the PC for the duplex SS in solution containing 250 ppm chloride ions showed a surprisingly large positive hysteresis loop, suggesting that there was damage to the passive film caused by localised intergranular corrosion at 120oC. In contrast, it was interesting to note that the 316L SS immersed in an acid solution containing 250 ppm chloride did not exhibit pitting corrosion. The oxides naturally formed on both steels at open circuit potential at 120oC had double layer structures and their thicknesses were obtained from constant phase element calculations.

Alloying Behavior and Properties of FeSiBAlNiCox High Entropy Alloys Fabricated by Mechanical Alloying and Spark Plasma Sintering

In this paper, FeSiBAlNiCox (x = 0.2, 0.8) high-entropy alloy (HEA) powders were fabricated by mechanical alloying process, and the powders milled for 140 h were sintered by spark plasma sintering (SPS) technique. The microstructures and properties of as-milled powders and as-sintered samples were investigated. The results reveal that the final milling products (140 h) of both sample powders present the fully amorphous structure. The increased Co contents obviously enhance the glass forming ability and thermal stability of amorphous HEA powders, which are reflected by the shorter formation time of fully amorphous phase and the higher onset crystallization temperature, respectively. According to coercivity, the as-milled FeSiBAlNiCox (x = 0.2, 0.8) powders (140 h) are the semi-hard magnetic materials. FeSiBAlNiCo0.8 HEA powders possess the highest saturation magnetization and largest remanence ratio. The SPS-ed products of both bulk HEAs are composed of body-centered cubic solid solution, and FeSi and FeB intermetallic phases. They possess the high relative density above 97% and excellent microhardness exceeding 1150 HV. The as-sintered bulks undergo the remarkable increase in saturation magnetization compared with the as-milled state. The SPS-ed FeSiBAlNiCo0.8 HEA exhibits the soft magnetic properties. The electrochemical corrosion test is carried out in 3.5% NaCl solution. The SPS-ed FeSiBAlNiCo0.2 HEA reveals the better passivity with low passive current density, and the higher pitting resistance with wide passive region.

Exceptionally high cavitation erosion and corrosion resistance of a high entropy alloy

Cavitation erosion and corrosion of structural materials are serious concerns for marine and offshore industries. Durability and performance of marine components are severely impaired due to degradation from erosion and corrosion. Utilization of advanced structural materials can play a vital role in limiting such degradation. High entropy alloys (HEAs) are a relatively new class of advanced structural materials with exceptional properties. In the present work, we report on the cavitation erosion behavior of Al0.1CoCrFeNi HEA in two different media: distilled water with and without 3.5wt% NaCl. For comparison, conventionally used stainless steel SS316L was also evaluated in identical test conditions. Despite lower hardness and yield strength, the HEA showed significantly longer incubation period and lower erosion-corrosion rate (nearly 1/4th) compared to SS316L steel. Enhanced erosion resistance of HEA was attributed to its high work-hardening behavior and stable passivation film on the surface. The Al0.1CoCrFeNi HEA showed lower corrosion current density, high pitting resistance and protection potential compared to SS316L steel. Further, HEA showed no evidence of intergranular corrosion likely due to the absence of secondary precipitates. Although, the degradation mechanisms (formation of pits and fatigue cracks) were similar for both the materials, the damage severity was found to be much higher for SS316L steel compared to HEA.

Microstructure, mechanical properties and corrosion resistance of CuZrY/Al, Ti, Hf series high-entropy alloys

A series of high-entropy alloys (HEAs) CuYZrTiHf (Z1), CuYZrAlHf (Z2) and CuYZrAlTi (Z3) were prepared by arc melting. All these HEAs mainly consist of hexagonal close-packed (hcp) dendrites and CuY-type body-centered cubic (bcc) interdendrite phases. The result affirmed that principal elements with hcp structure and suitable atomic size are beneficial to the formation of hcp dendrites. Specially, small content of amorphous phase appears in Z3 HEA, which is related to the increased melt viscosity and principal elements used for preparing bulk metallic glasses. The compressive strength and plastic strain of Z1 are 1340MPa and 13.2%, indicating a plastic fracture. Z2 and Z3 HEAs have higher Vickers hardness and compressive strength but the plasticity is severely depressed. The electrochemical corrosion measurements in the seawater solution were carried on. Z1 and Z2 HEAs possess better corrosion resistance and Z3 has a higher pitting resistance. According to the observation of corrosion morphologies, the interdendritic region containing CuY-type phase is feasible to preferential corrosion.

Effects of Thermal Aging on Microstructure and Corrosion Resistance of AISI 317L Steel Weld Metal in the FSW Process

The AISI 317L grade is an austenitic stainless steel with high Mo content (3.0 wt% min.). Due to the higher pitting resistance, this grade has replaced AISI 316L steel in many applications where the corrosion resistance is a critical property. However, the high Mo can induce phase transformations in high temperature services. In modern oil refinaries and petrochemical industries AISI 317L has been selected for temperatures as high as 550 °C. The goal of this work was to analyze the microstructural evolution and corrosion resistance of base and weld metal of AISI 317L stainless steel. The welded joints were produced by friction stir welding (FSW). The effect of prolonged exposure at 550 °C was investigated in specimens aged for 200h, 300h and 400h. After each aging treatment microstructural characterization was performed by scanning electron microscopy (SEM). Double loop electrochemical polarization reactivation tests (DL-EPR) were performed to evaluate the degree of sensitization of the samples. The results indicated that the increase of the exposure time at 550 °C promotes the formation of intermetallic phases, which causes corrosion decay of the weld metal.

Designing new biocompatible glass-forming Ti75-x Zr10 Nbx Si15 (x = 0, 15) alloys: corrosion, passivity, and apatite formation.

Glass-forming Ti-based alloys are considered as potential new materials for implant applications. Ti75 Zr10 Si15 and Ti60 Zr10 Nb15 Si15 alloys (free of cytotoxic elements) can be produced as melt-spun ribbons with glassy matrix and embedded single β-type nanocrystals. The corrosion and passivation behavior of these alloys in their homogenized melt-spun states have been investigated in Ringer solution at 37°C in comparison to their cast multiphase crystalline counterparts and to cp-Ti and β-type Ti-40Nb. All tested materials showed very low corrosion rates as expressed in corrosion current densities icorr < 50 nA/cm(2). Electrochemical and surface analytical studies revealed a high stability of the new alloys passive states in a wide potential range. This corresponds to low passive current densities ipass = 2 ± 1 µA/cm(2) based on the growth of oxide films with thickness d <10 nm. A homogeneous constituent distribution in the melt-spun alloys is beneficial for stable surface passivity. The addition of Nb does not only improve the glass-forming ability and the mechanical properties but also supports a high pitting resistance even at extreme anodic polarization up to 4V versus SCE were oxide thickness values of d ∼35 nm are reached. With regard to the corrosion properties, the Nb-containing nearly single-phase glassy alloy can compete with the β-type Ti-40Nb alloy. SBF tests confirmed the ability for formation of hydroxyapatite on the melt-spun alloy surfaces. All these properties recommend the new glass-forming alloys for application as wear- and corrosion-resistant coating materials for implants.

Comparing the pitting corrosion behavior of prominent Zr-based bulk metallic glasses

Abstract

Influence of Creq/Nieq on pitting corrosion resistance and mechanical properties of UNS S32304 duplex stainless steel welded joints

Pitting corrosion resistance and mechanical properties of 2304 duplex stainless steel with different Creq/Nieq values after plasma-arc welding and welding thermal simulation were systematically studied. The results showed that the lower the Creq/Nieq value in the experimental range, the better the microstructure after welding or welding thermal cycle. High pitting resistance equivalent number in the chemical composition brought in low weight loss rate and high critical pitting temperature for base metal. Furthermore, as the Creq/Nieq value decreased, the degradation of pitting corrosion resistance after welding thermal cycle reduced.

Corrosion of high‐velocity oxy‐fuel (HVOF) sprayed iron‐based amorphous metallic coatings for marine pump in sodium chloride solutions

AbstractFeCrMoMnWBCSi amorphous metallic coatings (AMCs) were deposited onto the 304 stainless steel (base material of pump impeller operated in sand‐containing seawater) by high‐velocity oxygen‐fuel (HVOF) thermal spray. The preparation, microstructural characteristics, and static corrosion behavior of the AMCs were presented. The microstructure and corrosion behavior of the AMCs were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and electrochemical methods. Melt‐spun ribbon and 304 stainless steel were also used for comparison purposes. The results indicated that the AMCs can spontaneously passivate with a wide passive region, and much higher ability to withstand pitting corrosion than that of the 304 stainless steel for the high pitting resistance equivalent value. The passive current density of the AMCs was at least two orders of magnitude higher than the counterpart ribbon, which showed a slightly decreased uniform corrosion resistance of the AMCs due to the incompact structure and porosity. The corrosion resistance of the AMCs increased with the coating thickness and decreased with the concentration of NaCl solution. A stable passivation ability held in the AMCs endowed them suitably used in marine environments.

Stainless steel reinforcing bars – reason for their high pitting corrosion resistance

AbstractIn harsh chloride bearing environments stainless steel reinforcing bars offer excellent corrosion resistance and very long service life for concrete structures, but the high costs limit a more widespread use. Manganese bearing nickel‐free stainless steels could be a cost‐effective alternative. Whereas the corrosion behavior of stainless steels in alkaline solutions, mortar and concrete is quite well established, only little information on the reasons for the high pitting resistance are available. This work reports the results of pitting potential measurements in solutions simulating alkaline and carbonated concrete on black steel, stainless steel DIN 1.4301, duplex steel DIN 1.4462, and nickel‐free stainless steel DIN 1.4456. Duplex and nickel‐free stainless steels are fully resistant even in 4 M NaCl solutions with pH 13 or higher, the lower grade DIN 1.4301 shows a wide scatter between fully resistant and pitting potentials as low as +0.2 V SCE. In carbonated solutions with pH 9 the nickel‐free DIN 1.4456 shows pitting corrosion at chloride concentrations ≥3 M. This ranking of the pitting resistance can be rationalized based on XPS surface analysis results: both the increase of the Cr(III)oxy‐hydroxide and Mo(VI) contents in the passive film and a marked nickel enrichment beneath the film improve the pitting resistance. The duplex DIN 1.4462 shows the highest pitting resistance, which can be attributed to the very high Cr(III)oxy‐hydroxide, to a medium Mo(VI) content in the film and to a nickel enrichment beneath the film. Upon time, the protective properties of the surface film improve. This beneficial effect of ageing (transformation of the passive film to a less Fe2+ containing, more hydrated film) will lead to higher pitting potentials. It can be concluded that short‐term solution experiments give conservative results in terms of resistance to chloride‐induced corrosion in reinforced concrete structures.

Influence of cold work and sigma phase on the pitting corrosion behavior of 25 chromium super duplex stainless steel in 3.5% sodium chloride solution.

AbstractThe effect of cold work (up to 16% strain) and sigma phase precipitation (at 850 °C for 10 and 60 min) on the pitting resistance of 25 chromium super duplex stainless steel were investigated in 3.5% sodium chloride solution at 70 and 90 °C. Anodic polarization scans for cold worked samples revealed immunity to pitting attack at 70 °C even with 16% strain. At 90 °C, the alloy still showed high pitting resistance, pitting occurring at about 600 mV (SCE) for the 16% plastic strain samples. A serious deterioration of the pitting corrosion resistance was found after heating the alloy at 850 °C for 10 min resulting in a clear drop in the pitting potential at 90 °C. After heating for 60 min, the material showed rapid deterioration of pitting corrosion resistance at 70 °C.